The Atavism

Sunday, December 9, 2012

Sunday Spinelessness - A Clearwing moth

At last, Dunedin has managed to arrange a proper summer day for a weekend.

The extra heat and sun saw plenty of bugs out and about, and I spotted plenty of familiar critters (native bees,  cicadas, drone flies and magpie moths) for this first time this year.  The real find of the weekend though, was something entirely new to me:

 

You might be a little surprised to learn that you are looking at a moth.

I'm helping design an undergraduate lab on systematics and taxonomy at the moment.  Since the new lab is about insects I've suddenly become very aware of the traits that distinguish various insect groups.  Moths, along with butterflies, make up the order Lepidoptera. You can see a few lepitoperan characters in the above photo: a mouth designed for siphoning nectar from flowers and a body covered in fine scales.

"Lepitoptera" actually mans "scaley wing", and, indeed most butterflies and moths have scales on their wings. This species, though, has got rid of most of it's wing scales (there are plenty of scales on the trialing edge though):




Synanthedon tipuliformis * is member of the "clear wing" moth family Sesiidae. Although I think this one is pretty neat, the family contains some striking species, the most interesting of which are wasp-mimics



Bembecia ichneumoniformis photographed by Lamois and licensed CC3.0



Yes, that's a moth! Sesis apiformis from Flickr user Oldbilluk. Licensed CC2.0




*The species name means, I guess, "looks like a crane fly"... don't see it myself

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Posted by David Winter 10:29 PM | comments(4)| Permalink |

Sunday, December 2, 2012

Sunday Spinelessness - Bark Lice

I should have known that the little challenge I put up last week wouldn't so much as wrinkle the brow of the bug-blogo-sphere's best. The Atavism's two homes means there were two winners. Ted MacRae of Beetles in the Bush chimed in at he blogspot version, correctly identifying the insect as a "bark louse" or psocopteran, and recognizing those stubby white protrusion as yet-to-be expanded wings . Morgan Jackson of Biodiversity in Focus did the same at SciBlogs.



Thanks too to Deborah from Bee of a Certain Age, who hazarded a guess that those white protrusions might be eggs. Certainly a more reasonable guess that my own first thoughts at seeing these bugs crawling over the the Big Tree* in our garden. The plump abdomens and long antennae made me think of the large (but certainly not GIANTspringtails. Ripping up a couple of pieces of bark revealed a whole colony of these odd-looking bugs, and evidence for just how wrong I was. 


The adults have wings, which they hold tent-like over their bodies. Insects are the only invertebrates with wings, so, since spring tails aren't insects, my first guess was horribly inaccurate (glossing over about 400 million years of evolutionary divergence).

As Ted and Morgan worked out, these are "bark lice", members of the order Psocoptera. Although they are related to the "true lice" (Order Phthiraptera), psocopterans are not parasites. Rather, they wander around their trees eating algae, fungi and whatever detritus might be clinging to the bark. The only species that could be considered pests are the "book lice" - small flightless psocopterans that sometimes turn up in old books where they eat the paste that binds pages together. (I have it on good authority that book lice can also destroy botanical collections, so certainly a pest)

A couple of weeks ago I gave Veronika Meduna a tour of our garden and its bugs, and I gather you can hear the result on Radio New Zealand's Our Changing World next week. While I was catching my breath between talking about the mating habits of spiders, and how our native slugs are much more sluggish then their introduced counterparts she asked the obvious question - "why?". Why do I care so much about odd little creatures like bark lice and slugs and spiders? I'm not sure I managed a coherent answer at the time, but I can tell you now, spineless creatures need evangelists because most people have a very skewed view about the way biology works. If your vision of biodiversity is limited to pandas and dolphins and lions and tigers then you are missing out on millions of other ways to be alive.

Take bark lice as an example. I'll admit that I'd never given these creatures a moments thought  before running into them last week. But, in researching this post I found out there are more than four thousand psocopteran species. That is to say, there are almost as many bark lice species as there are mammals - all the lions, tigers, bears, dolphins, whales, marsupials, rodents and bats in the world add up to about 5 400. That matters because species are the fundamental units of biological diversity. Each species represents a distinct evolutionary lineage - free to take up different ecological niches, develop new morphological features or occupy a different geographic range.

To try an illustrate how diverse these unassuming little critters really are, I've put together a "treemap". In the plot below, each of the stained-glass window panels represents the number of species in one psocopteran genus, nested within a family (the heavier lines, with labels ending in -DAE) which in turn is nested within a suborder (the very heaviest lines, labeled -MORPHA). These higher taxonomic ranks are not fundamental units in the way species are. Even so, species placed within a taxonomic group share evolutionary history, and are united by particular morphological characters which they share.  It turns out there are quite a few ways to be a bark louse:




And that's just bark lice!

For me, this chart is the best answer to "why?". How can you know you share the world with all this extraordinary diversity and not want to want to spend your time working out how it got here?


*This is not a botany blog... I really have no idea what the tree is

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Posted by David Winter 6:46 PM | comments(0)| Permalink |

Sunday, November 25, 2012

Sunday Spinelessness - An ID challenge

OK, here's a chance for the bug nerds to show off. A photo of a strange-looking beast I recently ran into:


 

The challenge to readers is to answer the two questions that went through my head when I first uncovered the creature (1) What the hell is that? (2) What's going with those opaque white projections?

Unlike others, I can't often you anything cool as a prize for being right, but surely an electronic record to your entomological know-how will be enough?


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Posted by David Winter 8:09 PM | comments(2)| Permalink |

Sunday, November 18, 2012

Sunday Spinelessness - Shocked from sloth by a beautiful spider

Regular readers will know that I've been pretty slack in posting here in recent weeks. Just the same old boring reason - lots of "real" work to get done and, as much as I enjoy it, blogging necessarily floats to the bottom of TODO lists.

But I was shocked from my sloth this afternoon when I passed that accursed agapanthus and saw a spider I really had to share with the world:


It's an orb-weaving (araneid) spider, a relative of the familiar garden spiders like the very common Eriophora pustulosa that spin orb-shaped webs and catch unlucky flying insects. I can't be sure on the identification of this one, but I reckon (with some support from twitter's resided spider experts, [1], [2]) its a species a species of Novaranea. According to Ray and Lyn Foster's  Big Spider Book New Zealand Novaranea species are most commonly encountered in in grasslands and tussocks, so perhaps this one blew in from the tall grass that covers some the abandoned gardens in our block.

However it made it our garden, I'm very happy to have encountered a such a neat looking spider, and even done a half-decent job capturing some of its beauty:

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Posted by David Winter 3:45 PM | comments(0)| Permalink |

Tuesday, September 25, 2012

All the media!

Oh, hi there. Yeah, it's been a while h'uh? Just been crazy busy lately you know - one thing after another with manuscripts and datasets to analyse, then I got a whole bunch of lab reports to mark. We should totally like, get back to writing/reading about science though. I'll put something up in a bit and...*

So, things have been a little quite here lately. That wasn't a plan to have me an that ridiculous hat up on the front page for a few weeks - just the result of having little spare time. As it turns out, a few things that might be of interest to readers here have been published over that fallow period, here's the links:

I guess to complete the set I'd need to make a TV appearance, though I can't see that happening!


*For people with whom I've had exactly this conversation lately - it's true, I have been busy, I am a terribly friend and we will catch up soon!

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Posted by David Winter 8:07 PM | comments(3)| Permalink |

Tuesday, August 28, 2012

Graduation, nerd blogging and a talk

The most dedicated readers of The Atavism may have noticed a few Sundays have passed without celebration of a spineless creature. Well, you know how blogging is sometimes. A few of the things that have kept me from blogging might be of interest to readers here. This weekend was dedicated to the wearing of silly hats, posing somewhat awkwardly and the conferring of my PhD. It was almost a big enough event to make me wear a tie:


So far I've rested the urge to change the name that appears under these posts to Dr David Winter, we'll see how long that lasts.

I've also been working a little on some more software for evolutionary biology. Since I very much aim this blog at a lay-level, and there is no reason on earth why a lay-person ought to care about the computer programs scientists use to collect and analyse their data, I've decided to set up a dedicated nerd blog. The first post their introduces an R library that can help researchers quickly download data from molecular biology and medical databases.

Finally, I should say their probably won't be a new post here this weekend either, as I'll be at the New Zealand Skeptics Conference, right here in Dunedin. I'll be giving a talk about how the the creation-evolution "debate" as it usually plays out has very little to do with evolutionary biology, and how getting past popular misconceptions about the way evolution works makes most creationist objections to evolution into non-starters. I'll also say why I think good old fashioned creationism is a more respectable position than "intelligent design", so that ought to be fun. If you're in Dunedin you can still register for the whole meeting, my talk is on at 9:50am on Saturday in Archway 3 (the best, and perhaps only, way to find this lecture theatre is to walk into the Archway building and wander around opening doors at random).

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Posted by David Winter 11:35 AM | comments(0)| Permalink |

Thursday, August 9, 2012

Measuring population differentiation in R

ResearchBlogging.org
This is a little bit different than most posts here. I have a paper out today in Molecular Ecology Resources:  "mmod: an R library for the calculation of population differentiation statistics" (doi: 10.1111/j.1755-0998.2012.03174.x). Looking around the web, there aren't many simple expositions of just what a "differentiation statistic" might be, and why the "modern measures of differentiation" my little R package can calculate might improve on the more traditional ones. So,  I thought I'd have a go here. 

Biologists often want to be able to measure the degree to which a population is divided into smaller sub-populations. This can be an important thing to quantify, because sub-populations within highly structured populations are, to some extent, genetically distinct from other sub-populations and therefore have their own evolutionary histories (and perhaps futures).

To illustrate this point I've run some simulations. Imagine if we had 5 subpopulations, each with a thousand individuals. In each population we will follow the fate of a locus with two alleles, R and r that have no effect on survival or reproduction and start with frequencies 0.8 and 0.2 respectively (these numbers motivated by this post). In the absence of gene flow between these populations (Panel 1) the frequency of the r allele bounces around due to genetetic drift (evolutionary change, after all, is inevitable). Crucially though, changes in one population can't effect other populations so we end up with substantial among-population differences in allele frequency. In the next two panels, in each generation a proportion of each population's individuals (0.001 and 0.01 respectively) are drawn from the other populations in the simulation. Now that the populations are sharing genes the lines that represent their allele frequencies pull together  (that is, the among-population variation is reduced). 


 

One way to quantify the among-population variation displayed in these simulations is to look at the number of heterozygotes you expect to observe across the entire population. The final values for P(r) in the first simulation were {0.33, 0.47. 0.88. 0.10. 0.33} with a mean frequency of 0.42 (so the frequency of the R allele would be 0.58). Knowing our Hardy Weinberg, if we had one big population with two alleles, one being at a frequency of 0.42 we'd expect to get 2pq = 2 * 0.42 * 0.58 = 0.40 heterozygotes. We can call that number Hfor expected total heterozygosity. But thats not what we'd actually see in this case. The sub-populations that make up this larger population have their own allele frequencies, when we calculate the expected proportion of heterozygotes for each of these populations by themselves we end up with {0.44, 0.49, 0.21, 0.18, 0.44} for a within-population expected heterozygosity (HS) of 0.35*. This lack of heterozygotes within sub-populations compared with the total population expectation will always arise when genetic drift makes sub-populations distinct from each other.  Masatoshi Nei  used this pattern to propose a statistic to quantify population divergence called GST, which he defined like this:

 GST = (HT HS HT

Nei's motivaton with GST was to generalise Sewall Wright's FST **, which was defined for diploid organisms and two-allele systems, so that it could be used for any genetic data. But there's a problem with this formulation. Because HT  is always larger than H and can't be greater than one, the maximum possible value of  GST  is 1-HS. This dependency on the within-population genetic diversity means comparisons between studies, and even between loci in one study, are difficult (since Hwill likely be different in each case). This is particularly worryingly for highly polymorphic makers like microsatellites, which can give values of HS as high as 0.9, severely constraining the possible values of GST.

Although the problem of  GST's dependence on HS has been known for a while, it's taken some time for new statistics that get around this problem to be developed. Philip Hedrick (doi: 10.1554/05-076.1) along with Patrick Meirmans (doi: 10.1111/j.1755-0998.2010.02927.x) introduced G''ST  - a version of GST that is corrected for the observed value of HS as well as the number of sub-populations being considered. Meirmans used a similar trick to define φ'ST  (doi: 10.1111/j.0014-3820.2006.tb01874.x), another FST analogue that partitions genetic distances into within- and between-population components. Most recently, Lou Joust introduced an entirely separate statistic, D, that  directly measures allelic divergence (doi 10.1111/j.1365-294X.2008.03887.x). 

The statistical programming language R is becoming increasingly popular among biologists. Although there is a strong suite of tools for performing population genetic analyses in R, code to calculate these "new" measures of population divergence have not been available. My package, mmod, fills this gap.  I won't give too many details of the package here, as that's detailed in the paper and the package is will documented. Briefly, mmod has functions to calculate the three statistics described above (and Nei's  GST ), as well as pairwise versions of each statistic for every population in a datastet. It also allows users to perform bootstrap and jacknife re-sampling of datasets, the results of which are returned as user-accessable objects which can be examined with any R function (there is also a helper function to easily apply differentiation statistics to bootstrap sample and summarise the results) . The library is on CRAN, so installation is as easy as typing "install.pacakge("mmod")", the source code is up on github. If want to use the package I'd suggest reading the vignette ("mmod-demo") before you dive in.


I'm keen to hear about bugs or feature requests from users, just email them to david.winter@gmail.com




Reference:

Winter, D.J. (in press). MMOD: an R library for the calculation of population differentiation statisticsMolecular Ecology Resources : dx.doi.org/10.1111/j.1755-0998.2012.03174.x

* mmod actually uses nearly unbiased estimators for these parameters, to deal with the way small population samples can mis-represent the actual allele frequencies in populations.

** I don't want to write an entire history of F-statisitcs here, because it's a big and murky topic, but I did want to make the point that the formulation I gave for GST  is often presented as "Wright's FST " in genetics courses. Wright was certainly aware that his statistic was related to the proportion of heterozygotes you expect to get in a populaiton, but, when he introduced F-statistics in general, and FST  in particular, he was really dealing with correlation among gametes at various levels of population structure. Unfortunately, there are now many many definitions of FST  floating around, and it's probably pointless to argue about a "right one". If you use my package I encourage you to be explicit about, and cite, the particular statistic that you are using. For each of the the FST  analogues that the package calculates the in-line help contains the correct reference. 


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Posted by David Winter 11:00 AM | comments(0)| Permalink |

Sunday, August 5, 2012

Sunday Spinelessness - How snails conquered the land (again and again)

Christie Willcox wrote a nice article this week on how one small group of organisms called "vertebrates" first evolved to live on land. Since you are a vertebrate who lives on land, you should probably go and read Christie's piece. I wouldn't want you, however, to go around thinking those first fish to leave the ocean behind were pioneers making a uniquely difficult transition. By my figuring, onycophorans (velvet worms like peripatus), tardigrades, annelids, nematodes, nemerteans (ribbon worms) and quite a few arthropod lineages have also taken up a terrestrial lifestyle. Many of those lineages were already breathing air before Tiktaalik, Ichthyostega and your other long-lost relatives came along to join them on land. But if you want to talk about transitions from marine to terrestrial lifestyles then you really want to talk about snails. You can find snails living in  almost every habitat between the deep ocean and the desert, and snails have adapted to life on land many different times. In fact, a litre of leaf litter taken from a New Zealand forest can contain snails representing three separate transitions from water to land.

Almost all the land snails I've talked about here at The Atavism are descendants from just one invasion of the land. We call these species the stylommatophorans and you can tell them from other landlubber-snails because they have eyes on stalks (as modeled here by  Thalassohelix igniflua):



These snails are part of a larger group of air-breathing slugs and snails (including species living in fresh water,  estuaries and even the ocean) called pulmonates or "lung snails". As both the common and the scientific names suggest, pulmonates breathe with lungs. Specifically, the mantle cavity, which contains gills in sea snails, is perfused with fine veins that allow oxygen to permeate the snails's blood. In relatively thin-shelled species you can often see this "vasculated" tissue in living animals:




Blacklight photo of Cepaea nemoralis showing 'vascularised' lung. Photo is CC BY-SA via Wikipedian Every1Blowz
The pulmonates can also regulate the amount of air entering their lungs with the help of an organ called the pneumatostome or breathing pore -  an opening to the mantle cavity that the snail can open or close at will:



A leaf-veined slug from my garden - the small opening near the "centre line" of the slug is the pneumatostome. Interestingly, leaf-veined slugs don't have lungs, the pneumatostome opens to a series of blind tubes not unlike an insect's respiratory system

So that, along with a whole load of adaptations that prevent a fundamentally wet animal from drying out, is your basic land snail. But those little leaf-litter snails I've been talking about for the last couple of weeks provide a good reminder that other snail lineages have left the life aquatic. Here's a species you find almost everywhere there is native forest in Otago, Cytora tuarua:

Holotype of Cytora tuarua B. Marshall and Barker, 2007. Photo is from Te Papa Collectons onlne, and provided under a CC BY-NC-ND license
Cytora is from the superfamily Cyclophoroidea, a group of snaisl that have indepedantly adapted to life on (relatively) dry land. (The weirdly un-twisted Opisthostoma is in this post is another cyclophoroid).  Cyclophoroids share some stylommatophoran adaptations to life on land, they've lost their gills and replaced them with a heavily vesculalised mantle cavity. Slightly oddly, cyclophoroids also breathe with their kidneys. Or, at least, the nephridium, an organ which does the same job as a vertebrate kidney, includes "vascular spaces" that the snail can use to collect oxygen from the air. Cyclophoroids don't have an organ equivalent to the breathing pore to control the flow of air into the mantle cavity. Instead the mantle cavity is open and air enters by diffusion, or in larger species, as the result of movements of the animals head. 

For the most part, the respiratory and excretory systems in cyclophoroids are not as well adapted to life on land as those in their stylommatophoran cousins. For this reason, most cyclophoroids are only active in very humid conditions. In my limited experience, Cytora species are usually found deep in moist leaf litter and soil samples, and I've never seen one crawling about. Nevertheless, some species can survive in drier situations, and these are certainly terrestrial snails.

Local leaf litter samples reveal a third move from the water to land. I don't have nice photo of Georissa purchasi, and I can't find anything else on the web either, so you're stuck with a crumby drawing from my notebook:





I did warn you that it was a crumby drawing. In life G. purchasi have an orange-red sort of a hue, and you can often see patches of pigment from the animal through the shell.  Georissa species are from the family Hydrocenidae and are quite closely related to a group of predominantly freshwater snails called nerites. Just like the other lineages discussed, the Hydrocenidae have given up their gills and breathe through a vasculated mantle cavity. Very little is known about the biology of these snails. G. purchasi is sometimes said to be limited to very wet conditions, but I've collected (inactive) specimens form the back of fern fronds well above ground so it can't be completely allergic to dry . 

So, in a handful of leaf litter collected from a Dunedin park you might have cyclophoroids, hydrocenids and  stylommatophorans - descendants from three different moves from sea to land. If we look a little more broadly,  there are are many more examples of this transition.  I've written about the the helicinids before, then there are terrestrial littorines (perwinkle relatives) some of which have both gills and lungs. Plenty of other pulmonate lineages that have also taken up an entirely terrestrial lifestyle. Because some of these groups have adapted to life on land multiple times, there have probably been more than 10 invasions of the land by snails.


Most of the description of Cyclophoroids here is taken from:

Barker, GM (2001) Gastropods on land: phylogeny, diversity and adaptive morphology In Barker (Ed.),  The biology of terrestrial molluscs (pp 1146) CABI Publishing.

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Sunday, July 29, 2012

Sunday Spinelessness - Hairy snails

Here's another of these tiny native snails I talked about last week. Aeschrodomus stipulatus:

 

Not the best photo I'll admit, but it records enough detail to see the two things that set Aeschrodomus apart from most of its relatives in New Zealand. It's tall and hairy. I'm not sure if there is an accepted definition of "hair" when it comes to snail shells, but plenty of different land snails groups have developed processes that extend form the shell. In New Zealand we have the fine bristles of Suteria ide, the filaments of Aeschrodomus and the spoon-shaped processes of Kokopapa (literally "spoon-shell"):

 

K. unispathulata Photo is from David Roscoe / DoC and is under Crown Copyright

I try very hard to avoid the sloppy thinking that presumes there is an adaptive explanation for every biological observaton, but it's hard to see how these hair-like processes would evolve if they didn't serve a purpose. The larger hairs are presumably made from the same calcium carbonate minerals as the rest of shell, and calcium is a precious resource for snails (so much so that empty shells collected from the field often show signs of having been partially eaten by living snails). In those species with finer projections, the hairs are an extension of the "periostracum", a protein layer that covers snail shells.  If we presume that snail hairs come at a cost, in either protein or calcium, what reward are they hairy snails reaping from their investment?

Markus Pfenninger and his colleagues asked just that question by looking at snails from the Northern Hemisphere genus Trochulus (doi: 10.1186/1471-2148-5-59). This genus contains many species that sport very fine and soft hairs. Pfenninger et al.collected ecological data for each species, and used DNA sequences to estimate a the evolutionary relationships between those species. From these data, they were able to infer the common ancestor of modern Trochulus species was probably hairy, and three separate losses of hairyness can explain all the among-species variation in this trait. Moreover, it appears the loss of hairs in Trochulus is associated with a switch for wet to dry habitats. Given this finding, Pfenninger's team hypothesised that, in Trochulus at least, hirsute snails might stick to host plants more effectively than their bald brethren. Indeed, in experiments it took more force to dislodge a hairy shell from a wet leaf than non-hairy one.

Pfenninger's study makes a neat case for the maintenance of hairy shells in Trochulus, but I don't think adherence to leaves can explain all the hairy snails we know about. In New Zealand, most snails with shell processes are limited to leaf litter, a habitat that would seem to make adhering to leaves a positive hindrance to getting around. I don't know if we'll ever have a simple answer as to why some of our snails sport these attachments, but Menno Schilthuizen's work might give us a couple of clues as to why these sorts of shell sculpture arise and stick around. In 2003, Schilthuizen proposed many shell features may arise because those individuals that have them are more likely to procure a mate (or perhaps a desirable mate) (doi: 10.1186/1471-2148-3-13). Although there is quite a lot of evidence for sexual selection in land snails, I don't know of a study testing Schilthuizen's hypothesis on shell sculpture. On the other hand, Schilthuizen's group has found evidence that elebaroate shell sculpture can arise as a response to predation (doi: 10.1111/j.0014-3820.2006.tb00528.x). Opisthostoma land snails from Borneo have extradonary shells, with unwound shapes, ribs and spines:


Opisthostoma mirabile

In Borneo, Opisthostoma species live alongside a predatory slug that attacks these snails by boring a hole into their shells. The unique shape and ornamentation of Opisthostoma shells appears to have evolved to hinder slug attacks. Even more interestingly, geographically distinct populations of slug appear to attack snails in different ways. This local variation in predator behavior could well be a response to local variation in the shell ornamentation - a so called Red Queen process in which each population evolves rapidly while maintaining more or less the same relative fitness

There are certainly plenty of snail-eating animals in New Zealand. Several species of Wainuia land snail appear to specialise in eating micro snails, which they scoop up and carry off using a "prehensile tail" (Efford, 1998 [pdf]). It's entirely possible that the relatively small projections that some our snails sport are preforming the same job that those weirdly distorted Opisthostoma shells serve.


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Sunday, July 22, 2012

Sunday Spinelessness - New Zealand microsnails

When I tell people I study snails for a living I get one of two replies. There's either some version of the "joke" that goes "that must be slow-going" or "sounds action packed", or there's "oh, you mean those giant killer ones we saw when we went tramping?". I guess the joke is funny enough, but I want to make it clear that those giant killer snails from the family Rhytidae, cool as they might be, are not the most interesting land snails in New Zealand.

The local land snail fauna displays a pattern that is quite common for New Zealand animals - we have a very large number of species but those species are drawn from relatively few taxonomic families. Since taxonomic groups reflect the evolutionary history of the species they contain, that pattern most likely arises because New Zealand is (a) quite hard to get to, so few would-be colonists make it here and (b) full of ecological niches and geographic pockets that can drive the formation of new species. In total, there are are probably about 1200 native land snail species in New Zealand - about ten times the number found in Great Britain, which is approximately the same size. That diversity extends to the finest scales - individual sites in native forest might have as many as 60 species sharing the habitat. New Zealand forests probably have the most diverse land snails assemblages in the world (although tropical ecologists, who generally hold that diversity in terrestrial habitats almost invariably increases as you approach the equator, have argued against this conclusion).


You may now be asking why, if this land snail fauna is so diverse, have you never seen a native snail. Well, you've probably walked past thousands of them without noticing. Most of our native land snail species are from the families Punctidae and Charopidae, groups that are sometimes given the common name "dot snails". Meembers of these families are usually smaller than 5 mm across the shell, and are restricted to native forest and in particular to leaf litter. But in native forests, where there's leaf litter there's snails. Grab a handful of leaves, or pull up a log and you're likely to find a few tiny flat-spired snails going about their business. Hell, down here in Dunedin you can even find charopids living under tree-fuschia in a suburban garden.


Like so many native invertebrates, we know very little about our land snails. Lots of people have dedicated substantial parts of their lives to documenting and describing the diversity of these creatures, but even so we don't have a clear understanding of how the native species relate to each other or to their relatives in the rest of the world, or even where one species starts and another ends. Without such a basic understanding, its very hard to ask evolutionary and ecological questions about these species, so for now we remain largely ignorant of the forces that have created the New Zealand land snail fauna.


For the time being I can tell you that a lot of them are really quite beautiful. Since most people don't have handy access to a microscope to see these critters, I thought I would share a few photos from this largely neglected group over the next few weeks. The 2D photographs, with the relatively fine depth of field, don't quite record the beauty of these 3D shells, but I hope it's at least a window into the diversity of these snails.


 Let's start with a snail that is very common in Dunedin parks and forests. This is a species from the genus Cavellia (the strong, sine-shaped ribs being the giveaway) but I won't be able to place it to species until a new review of that genus is published. 




This particular shell is from an immature specimen, and is about 2mm across. When flipped, you can see an open umbilicus that lets you see straight through to the apex of the shell.





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Posted by David Winter 5:30 PM | comments(1)| Permalink |

Wednesday, July 11, 2012

You can't ban redheaded sperm

It's the first week of semester two down here at Otago, which means I will helping with undergraduate labs for the first time this year. I suspect most students end up not liking me all that much, because I find my self teaching in the parts of the genetics program that undergrads like the least. Population genetics, as the name suggests, is the study of the way genes behave in populations, and in many ways its the base from which our understanding of evolution is built. So it's important, but it's also pretty mathsy.


It seems quite a few students have planned their high school and unversity careers in the hope that studying biology meant that could leave maths behind. So, when they are confronted with "p2 + 2pq + q2 = 1" and asked to do something with it, they are unhappy.

That particular formula is for something called the Hardy-Weinberg equilibrium and a significant proportion of students roll their eyes and slump their shoulders when you tell them they are going to need to use it for a problem. They think its arbitrary and irrelevant to anything the least bit important, and what's more it looks a little like it's already solved. So, I'm always looking for ways to convince people that Hardy-Weingberg isn't just simple, but actually intuitive and important. So here's my attempt to explain why knowing a little population genetics is helpful.

You may remember last year  a Danish sperm bank had started turning away would-be donors with red hair, since there is little demand for sperm that might contribute to the creation of a readhead. It turns out, if you know a little bit about population genetics you can see that policy will have little effect on the number of red heads the sperm bank helps to bring into the world.

Hair colour is partially controlled by a gene called MC1R. There are different versions of MC1R floating around in human populations, and one of them has a mutation that stops melanin (a dark pigment)  passing into hairs as they grow. Geneticists call different versions of a gene "alleles", so we'll call this flavour of MC1R the "red hair allele" and give it the symbol r.As I'm sure you know, you have two copies of most of your genes, one inherited from your mother and the other from your father. Red hair is a recessive trait, which means in order to have red hair both of your copies of MC1R need to be the r allele: if you have one or two copies of the "normal" MC1R allele (which we'll call "R") you have some pigment passing into your hair and it will be another colour. We call the total genetic make-up of a person their "genotype", and their physical characteristics their "phenotype", so here's a table showing the genotypes and the phenotypes we're talking about in this post:

Genotype 
r/r
r/R
R/R
Phenotype (hair colour)
Red Hair
Not Red HairNot Red Hair

I know there are a lot of technical terms there (Carl Zimmer will not be happy...), but we do need to be precise when we talk about genetics because, strange as it may seem, there isn't a single definition of the word gene. Once you've got your head around the terms, it's all pretty straight forward: you need two copies of the r allele to have red hair. Think what this means for the Danish sperm bank though. Turning away red headed sperm donors doesn't turn away red headed sperm since there will still be "carriers" with only one copy of r (and, thus, non-red hair) donating sperm and half of those sperm will be "red headed sperm".

How big a problem is this likely to be? First we need to work how common the r allele is, and we can use the frequency of redheads to find that. By long tradition, the frequency of a recessive allele is denoted by "q", so, in a population where one quarter of the alleles are r we'd say q = 0.25. We know that in order to have red hair you need both your copies of the MC1R gene to be the r allele and that you inherit each allele separately. When probabilities are independant we can mutiply them, so the chace someone in this population is a redhead is q x q = q2  = 0.06 .Following the same logic, the frequency of the R/R genotype must be the frequency of R squared (by convention, the frequency of a dominant allele is called "p", so that's p2).

Knowing this relationship, we can work backwards and find the frequency of r if we know the proportion of redheads in a population. In most of Northern Europe, about 4% (0.04) of the populaiton are redheads so  q2 = 0.04 and q = √0.04 = 0.2. As you can see, red hair genes can be a lot more common than redheads:


To understand how the sperm bank's policy will we work, we need to know about those 'carriers' with the mixed genotypes (called "heterozygotes" by genetics geeks). It doesn't matter which order your genes come in, so the probability of being a carrier in the population above will be the chance of getting an R then and r (p x q) plus the chance of getting and r followed by an R (q x p). You can simplify that to 2pq. You might recognize that term, because with it we've rediscovered the one in the first paragraph "p2 + 2pq + q2 = 1". The Hardy-Weinberg equation is just away of moving from allele frequencies to genotype frequencies (or the other way around) and it's based on some very simple observations about the way populations work. We saw that in a population with  4% redheads you get q = 0.2, so p=0.8 and 2pq = 2 x 0.2 x 0.8 = 0.32. Almost a third of the population are carriers, and that's eight times the number of redheads! While the frequency of the red hair allele is low, only a small proportion of the red haired alleles in a population will actually in red haired people:

That's why the sperm banks policy, while prefectly sensible if there really is no demand for sperm from redheads, will do little prevent the creation of red-headed babies.  In the typical case, where 4% of the population are redheads the probability that a donated sperm carries the r allele only moves from 20% to 17% when you exclude red haired donors

It's easy to calculate how the policy would work in populations with more or less redheads:

So, that annoying equation we make the undergrads learn actually tells us something about the world. Obviously, the example I've talked about here is a pretty silly one, but the basic ideas we've discovered above can help us understand some important ideas. Like why genes that cause debilitating diseases aren't completely removed by natural selection, and why inbreeding is a bad idea.

A lot of rare diseases are caused by recessive alleles. They remain rare for the obvious reason that people with such diseases are unlikely to pass on their genes. But they remain present in populations because, as we've found, once recessive alleles get rare the overwhelming majority of them are found in carriers. In this way, rare recessive alleles are seldom exposed to selection so they stick around for a long time.*

Because disease causing genes stick around in populations, there is a pretty good chance that you carry a few alleles that would cause a debilitating disease in someone who had two copies of them. The same applies to anyone you might be hoping to have children with. Thankfully, its very unlikely that your prospective mate with have disease-causing alleles for the same genes that you do. That is, as long as you look beyond the family tree when you look for a mate. If you have a child with someone who is closely related to you, you will have each inherited some of your genes from the same source, which increases the chances you share disease alleles.




*In fact, they often reach a point called "mutation-selection balance" in which the frequency of the allele remains static because new mutations re-create the allele as quickly as selection removes it. JBS Haldane was the first person to notice this, and he used his theory to create a very accurate estimate of the human mutation rate well before we knew what genes were made of!

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Posted by David Winter 12:48 PM | comments(3)| Permalink |

Sunday, July 8, 2012

Sunday Spinelessness - Cuttlefish in drag deceive their rivals

One awesome mollusc deserves another, so let's follow up last weeks octopus post with one on that group's close relatives the cuttlefish.

Cuttlefish are relatively small (the largest grow to 50cm) squid-like cephalopods that present a nice soft and digestible meal to predatory fish and marine mammals. Having lost the shell that most molluscs use to protect themselves cuttlefish have had to develop other defences. Most strikingly, cuttlefish are masters of camouflage

.

The deceptive patterns that cuttlefish put on come from their remarkable skin, and are controlled by a pretty impressive nervous system. The skin is covered in cells called chromatophores which contain granules of pigment. When a cuttlefish decides it's time to disappear it looks around its surroundings and, with the aid of nerves that lead from the brain to the the skin, stretch and twist the chromoatophores  on the skin's surface in such as way as to change the colour of their cells, and ultimately their whole bodies. 

That impressive trick is principally used for camouflage, but cuttlefish and also use their skin as a sort of billboard to signal to other members of their own species, and even put on a strobing light show (possibly used to startle their own prey):


Just this week, researchers have reported evidence for a other trick that cuttlefish can pull off. When males of the Austrian Mourning Cuttlefish (Sepia plangon) see a female they put on a show, producing striped patterns that evidently impress the female. But these animals form male-dominated groups, and rival males often interrupt would-be woo-ers  in mid-display. So, when they spy a receptive female, males want to put on their flamboyant show for her to judge, but also want to make sure they don't attract the attention of rival males that might want to spoil the party. The male Mourning Cuttlefish's answer to this problem? Using only half of his body to put on the female-impressing show, and throwing would-be spoilers off the scent by mimicking a female with the other half.




This gender-splitting  tactic seems to be pretty common. In aquarium experiments about 40% of males would  attempt the deceptive signal when they were displaying in the presence of a rival. Just as the cuttlefish camouflage response requires information from the physical environment, the gender-splitting trick is influenced by what the male can learn of the social environment. If more than one female is available the male will display to both  without bothering to hide his intentions for observers (probably because working out an angle from which he could excite two females while staying under the radar is just not possible). Likewise, if more than one rival male is about that don't bother with the deception - since it wouldn't be possible to maintain the illusion for two rivals viewing from different positions.



Brown, Garwood & Williamson (In press) It pays to cheat: tactical deception in a cephalopod social signalling system. Biology Letters. http://dx.doi.org/10.1098/rsbl.2012.0435w

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Posted by David Winter 9:51 PM | comments(0)| Permalink |

Sunday, July 1, 2012

Sunday Spinelessness - The other mollusc shell

Here's a really cool animal, a female argonaut (sometimes called a paper nautilus):

 

It may not be immediately obvious from the photo, but argonauts are octopuses. Strange octopuses, because the seven species that make up the family Argonautidea are among a handful of octopuses that are capable of swimming through the water column (rather than hanging out on the ocean floor) and they are the only octopuses that fashion themselves a shell. 

The argonaut shell has been a topic of consideration, confusion and conjecture for biologists for a long time. Only females produce the shell. Male argonauts are tiny (about a tenth of the size of the female) and only really serve as sperm donors (in fact, they donate an entire sperm-transferring organ, called the hectocotylus). Once mated, a female argonaut starts producing her shell and lays her eggs in its base. This behaviour has lead some biologists to conclude the shell's primary function is to act as an egg case.  We now know that shell is also used to help the argonaut maintain its position in the water column. By propelling herself to the surface and rocking back and forth an argonaut can introduce an air bubble into her shell. While she's near the surface that air bubble will make her buoyant, but by diving downwards she can reach a point where the increasing water pressure (which compresses the air bubble, decreasing its buoyancy) cancels out the buoyant effect, letter her float in the water colum. At that point she's free to swim about in two dimensions without having to maintain her vertical position.

You can watch this remarkable behaviour  here:




I don't want to talk too much more about the purpose of the argonaut shell, partly because it has already been well covered. Ed Yong wrote a predicably clear and interesting post on the research which uncovered it (which also produced an interesting comments thread) and the lead researcher, Julian Finn from Museum Victoria in Australia, also discussed his work in a really great video.


Instead, I want to talk about the origin of the argonaut shell. Octopuses are molluscs, part of a group of soft-bodied animals that includes clams and mussels and snails. Most molluscs have shells. In fact, despite being arugably the most morphologically diverse of the 35 animal phyla, only a few small groups of molluscs don't contain at least some species that produce shells. The easiest way to explain the presence of shells in so many different molluscan groups is to hypothesize that the last common ancestor of all molluscs had a shell, and most of that ur-mollsuc's descendants have retained this organ. 

In evolutionary biology we call traits that are shared between organisms as a result of their shared evolutionary history "homologies". Homologous traits are often compared with "analgous" ones, parts of organisms that are similar as the result of independent innovations in different evolutionary lineages. We can illustrate the concept using a bat's wing as an example. The forelimbs of bats and whale are made up of the same bones, despite the fact that whales swim and bats fly. That's because bats and whales are both mammals, and they inherited their forelimb bones from a common ancestor before each group radically repurposed their limbs. On the other hand, despite the fact that both bats and stoneflies fly, the insect wing and the bat wing are separate evolutionary inventions and not something the two groups share as a result of shared evolutionary history:

 

The protective shells of snails and clams are homologous to each other, and to the internatilized shells that some squids use to stay afloat. But the argonaut shell is something entirely different. The argonaut shell is made of calcite, where most molluscan shells are argonite. Moreover, the minerals that make up the argonaut shell are extruded from the octopuses tentacles, where other molluscs have an organ called the mantle that they use to produce their shell. 

The fact the argonaut shell is made of different stuff than other molluscan shells, and with the aid of  a different organ, suggests it is a unique evolutionary innovation. So how did shells evolve twice within the molluscs? I can't provide you with a definitive answer, but I do like one (only slightly crazy) speculation. Earth's oceans used to be dominated by another group of shelled molluscs called ammonites. Adolf Naef pointed out that argonaut shells are very similar to some ammonite shells, and suggested the ancestors of ammonites might have laid their eggs in discarded ammonite shells (some modern octopuses certainly spend time hanging out in mollusc shells). Naef suggested ancestral argonauts might then have acquired the ability to repair broken shells (developing the mineral secreting organs on their tenticles) and finally to create their own. 

It's a pretty out-there sort of an idea, and I don't know how you could actually test it. But wouldn't it be cool if the ammonite shell was still being dutifully copied every day, 65 million years after the last ammonite died?




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Posted by David Winter 9:31 PM | comments(6)| Permalink |

Sunday, June 17, 2012

Sunday Spineless - How some snails became red-blooded

Here's something cool that I've meaning to write about for a long time. A native Powelliphanta land snail with an apparently pigment-less foot and head:


That snail (a close relative of speedy carnivore featured here) popped up in Kahurangi National Park at the end of last year. Apart from just being kind of cool, the un-pigmented individual is interesting for a geneticist that studies land snails. For the most part, dark pigmentation in snails results form melanin  (which is perhaps the most common pigment in the animal world). That's true for pigmentation of the shell as well as the animal that caries it around. As you can see, this snail has normal pigmentation on its shell, so clearly its still able to make melanin. The genetic mutation (or developmental defect) that has left this snail white hasn't broken the genes for pigmentation, just the mechanism that moves that pigment around the body wall of the snail.

The ghost Powelliphanta is a pretty cool snail, but there's actually an albino snail that's even more interesting. Every now and again a truly albino individual of the freshwater snail Biomphalaria glabrata pops up. Looking at these mutants we can learn something about the evolutionary history of the these snails:
Photo is CC 2.5 and comes from Lewis FA, Liang Y-s, Raghavan N, Knight M et al in PLoS Tropical Diseases


Free from the pigments that would usually make shell opaque we can see the feature that sets Biomphalaria and other species form the family Planorbidae (ramshorn snails) apart from every other snail. The planorbids are the only red-blooded snails on earth. So why are these snails so different?

As we all know, in order to live animals need to get oxygen from their environment into their bodies. For small animals this doesn't represent a huge problem. Oxygen will flow form areas of high partial pressure (a concept analgous to concentration, but accounting for some of the weird ways gasses behave) to areas in which Oxygen is being used up. So, for instance, most insects pull air directly into their bodies with a set of open tubes (called tracheae). Once the air makes it into those tubes oxygen will passively diffuse into the insect's tissues.

Big animals have a much bigger problem*. Not only do larger animals need much more oxygen to fuel their bodies, they also have to actively transport that Oxygen because the distances it is required to travel can't be achieved by passive diffusion. Lungs and gills are both organs dedicated to pumping more oxygen into animal bodies, and many  animals use blood, and special proteins dissolved in blood, to move oxygen about.

In vertebrates the oxygen-carrying protein is called hemoglobin. Very simply, a hemoglobin molecule is   a cage used to hold iron atoms in such a way that they will bind to an oxygen atom. The iron containing group in the hemoglobin protein (called heme) gives our blood its red colour and its hemoglobin circulating through that snail's body that makes it red.


Heart of Steel is Julian Voss Andreae's sculpture based on the structure of hemoglobin proteins. Pleasingly, the weathering process depicted across  these photos is the result of iron molecules in the steel sculpture binding with oxygen - the very process that underlies the function of hemoglobin. Photo is CC 3.0 care of the artist.

As with every problem life faces, invertebrates have come up with many more interesting ways to move oxygen around than their spined relatives. Annelids (earthworms and their kin), brachiapods and spoon worms have a whole set of iron-containing proteins to do the job. Even more interestingly, molluscs and some arthropods have a protein that uses Copper rather than Iron atoms to co-ordinate an oxygen molecule. This molecule, called hemocyanin, takes on a green-ish blue hue when oxygen binds to it and changes its conformation.

Most snails get through life fine with hemocyanin as the only oxygen-carrying molecule in their blood, so why have Biomphalaria and their cousins become red-blooded? Part of the reasons lies in their lifestyle. Planorbid snails breath with lungs (which only work in air) but live underwater. If you make your living by holding your breath while diving then you really want to have some way of holding on to as much of the oxygen you get form each breath for as long as possible. It seems that Biomphalaria hemoglobin is more efficient at using the oxygen stored  in lungs while diving than any hemocyanin could be.

It's all well talking about why an animal might have evolved a particular trait. But in evolutionary biology it's generally much more intresting to try and work out how. How does an air-breathing snail make its own hemoglobin from scratch? A team lead by Bernhard Lieb asked just that question a few years ago, and found the answer: Biomphalaria hemoglobin was made by cobbling together parts of existing proteins. When Lieb et al (2006, doi: 10.1073/pnas.0601861103) isolated hemoglobin from red-blooded snails they found it was made up of two different components (called peptides), each of which has 13 different sub-components (called domains). When the team compared the sequence of those peptides and their domains to other molluscan proteins they found similarties between the hemoglobin sequences and another iron-containing protein called myoglobin.

Myoglobin is a small molecule that is usually restricted to muscles where is acts as a store of Oxygen (in snails, myoglobin is most commonly found in the muscles that drive the radula, the rasp like organ used to break down food). The Biomphalaria hemoglobin sequences are more closely related to each other than they are to myoglobins from any other species. This pattern suggests the sequences that make up the snail hemoglobin descend from a single common ancestor. Subsequent changes to each of these descendants have allowed the descendants proteins to group together and become "super myoglobins" capable of transporting oxygen through the body.



*The huge number of ways size matters in biology were wonderfully explained by JBS Haldane. I'd reproduce the most famous passage here, but it's probably even better if you discover it by yourself.


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Posted by David Winter 8:28 PM | comments(2)| Permalink |

Sunday, June 3, 2012

Sunday Spinelessness - Nothing to see here

I'm off to the Transit of Venus Forum next week. I'm looking forward to meeting all sorts of clever and interesting people (and escaping the coming snow), but travelling and conferring won't leave much time for a few projects I really need to work on. So, today's blog post is going to have to be squeezed down to its smallest possible form (a queen ant that dropped in to read an early draft of my thesis last spring):



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Posted by David Winter 7:32 PM | comments(0)| Permalink |

Sunday, May 27, 2012

Sunday Spinelessness - Even their eggs are spikey

I really like the leaf vein slugs (Athoracophoridae) that live in our garden and  have featured here in the past. Here's the latest one to pass under my camera:


As much as I like them, I have to admit these guys are actually one of the more boring leaf vein slug species in New Zealand. Some of their relatives are much larger or more colourful and quite a few of them sport large wort-like growths (technically called papillae) that pattern their bodies in various ways. Te Ara and Soil Bugs both have galleries that let you get an idea of their diversity.

A couple of weeks ago I made a little discovery. Some of these slugs also have eggs that are covered in papillae


Not the greatest photo I'll admit. But it's hard work taking photographs in the dense New Zealand bush at the best of times, and I found these eggs in the low-growing cloud forest that covers the Leith Saddle on Mt Cargill. These are certainly slug eggs, so  I did a bit of snooping among Astelia and ferns and other likely looking roosts for these nocturnal animals. I couldn't find any parents-in-waiting, but the ferns were utterly covered in what people that follow mammals might call "sign", so clearly there's a big population in the area. 

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Posted by David Winter 8:05 PM | comments(1)| Permalink |

Friday, May 25, 2012

Selling out to the mainstream media

The other week when I wrote that post about a poorly reported story in Stuff's new science section I emphasised that I really thought it was important that news sites with a large and non-specialist audiences did a good job on science. I was pleased that the people behind the stuff story took the criticism on board, and amended their story.

They also asked me if I'd consider offering my on analysis of science in the news from time to time. Being of the opinion that its always better to do something about a problem rather than simply complain about it, I happily agreed. Here's the first piece to appear, a quick summary of the recent result that coffee isn't killing you and might even be prolonging your life.

I was prepared for a barrage of comments amounting "what does some evolutionary biologist/bug nerd know about medicine", but so far everyone that's taken the time to write something has been very supportive!

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Posted by David Winter 2:41 PM | comments(2)| Permalink |

Sunday, May 20, 2012

Sunday Spinelessness - Lazy Link Blogging Edition

I though I'd do something a little bit different today. Instead of coming up with anything new to say or show you I'm going to steal from give a shout-out to a few New Zealand organisations that highlight  some of the amazing ways that spineless creatures get on with business of living.

Let's start with Landcare Research (Manaaki Whenua), the Crown Research Institute that focuses on bioiversity and environmental issues. As you'd expect, Landcare do lots of work on invertebrates an that's refelected in their public face. Their "What is this bug?" site is a great starting point for anyone trying to put a name to some weird critter that's crawled out from the garden, and topic pages on some of our most interesting creatures (Onychophora, stick insects and our amazingly diverse moth fauna) make for a nice introduction to these groups.

The Landcare site I really want to pull out for special focus is their recently developed guide to freshwater invertebrates. Freshwater invertebrates are often use as "indicator species". Because certain groups of stream invertebrates are very susceptible to pollution or changes to a stream's natural flow, the presence or absence of these groups in particular stretch of water can give us an idea of the health of that water. In order to help community groups or landowner monitor their streams, Landcare has produced some beautiful photographs of stream invertebrates (along with information on how to sample them, and how well each species acts as an indicator). You really should check out the whole site, because some of them are quite beautiful, I'll just give you a taster here:


Left: Kempynus lacewing sporting some impressive 'tusks'. Right: Head shot of the larvae of an Onychohydrus diving beetle. Both images © Landcare Research

The other Crown Research Institute with a special interest in biodiversity is NIWA (the National Institute of Water and Atmosphere, if really wanted to know), who have a particular focus in the strange and wonderful creatures that live in the deep seas. NIWA scientists were part of the team that pulled up those mega-amphipods and I'm really pleased to say they have a great Facebook page dedicated entirely to their invertebrate collection. The NIWA Invertebrate Collection page has recently featured Phronima (one of favourites), Nematodes (perhaps the most under-studied group of animals on earth) an cold-water corals. Again, I encourage you to check out (an follow!) the page, but here are a couple of recent photos to entice you:


Phronima having recently evacuate its salp (© Owen Anderson). Tiny octopus! (photo from Ocean Survey 20/20)


Finally, let's leave the Crown Research Institutes behind and go to Massey University and "Soil Bugs: A guide to New Zealand's soil invertebrates". Soil bugs is run by Dr Maria Minor and contains information and photographs of some of the thousands of species that live in the soil, leaf litter and rotting logs that cover the floors of our forests. Soil invertebrates a hugely important animals, being as they help to release the nutrients locked up in dead wood, but I've gone on about that plenty of times. So let's look a couple of my favourites GIANT Springtails and native land snails:

Left: Holacanthella spinosa Right: Flamulinna zebra. Note, these images are © Massey University, and premission sought be sought to use them elsewhere.


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Posted by David Winter 1:25 PM | comments(0)| Permalink |

Thursday, May 10, 2012

An object lesson in the danger of poor science reporting

As you may have seen, stuff.co.nz, the online portal for the Fairfax conglomerate of papers, has launched a science section. I would like to think one of the largest news websites in the country increasing their focus on science could only be a force for good. I'm afraid the initial offerings have lurched from underwhelming to utterly ridiculous.

The thousands of viewers who found themselves reading the front page of stuff this afternoon would have been met by a giant graphic of a blue sun and a headline claiming

'Solar minimum' could trigger Ice Age



Having been compelled by the click-baiting headline, readers learn that 
The world could be heading for a new 'solar minimum' period, possibly plummeting the planet into an Ice Age, scientists say.
Would it surprise you to lean that scientists said no such thing? In fact, Martin-Puertas et al (2012, doi: 10.1038/ngeo1460) don't have anything to say about ice ages or the future of our sun (which is actually ramping up in activity at the moment). They studied a fossilised lake bed in Germany. Lakes are great recorders of ancient biology and climate as the sediments that settle on their beds create a record of what was going on around them in the past. In this case, researchers were able to show that an historic solar minimum (a period of relatively low solar activity) contributed to a period of cooling in Europe around 3 000 years ago, which lasted for about 200 hundred years. By looking at patterns in the old lake bed that act as a proxies for past changes in windiness* they were able to build a model that explained how changes in solar output might be amplified by other changes in the climate system.

That's a nice result, but how does it relate to "ice ages" (presumably meaning glacial periods that last for tens of thousands of years and cover most of the globe in ice, not the regional pattern lasting 200 years studied here) let alone an imminent one? Even if the sun were to enter a prolonged solar minimum, Martin-Puertas et al. are explicit in their paper, and the press release that got someone at the Fairfax office excited, that the results they report can't be directly used to predict future events.  From the paper:
However, a direct comparison to the Homeric minimum, which was a very deep and persistent minimum with very different orbital parameters when compared with recent solar minima and probably a larger climate response, is not possible
And the press release
Albeit those findings cannot be directly transferred to future projections because the current climate is additionally affected by anthropogenic forcing.
The language in the original version of the article (now edited, but recorded by from the morgue) gives away the motivation of the article's author:
 The period would see a cooling of the planet, refuting predictions of global-warming alarmists.
You can decide if the author of this article is in a place to call anyone else an alarmist.

The comments that followed the article are a perfect illustration of why it's worth getting upset about this sort of reporting. The vast majority of them are from people who don't believe the evidence that recent global warming is the result of our burning of fossil fuels, the rest are from people just generally being confused or disappointed by the lack of clarity on climate change in the media. I've plucked a commentator calling himself James as an example:
Global warming, global cooling, another ice age ? Let's face it, there is "evidence" to support all of these theories. There was also good evidence to support the theory that the world was flat. Science is simply the opinion of a group of intellectuals at any given moment. The mix of the group changes with each new piece of "evidence". Everyone, including the intellectuals should understand that science and their own theories are just that, not indisputable facts.

James is wrong, the evidence that emitting greenhouse gases makes the world warmer is overwhelming and in no way comparable to the idea there will be a new glacial period any time soon. But can we blame him for being wrong when the major sources of news in this country are so willing to publish such rubbish?

As much as I love science blogs and specialist magazines like New Scientist and Scientific American it's important to realise that for that the people that get their science news from these sources are science fans. For most people, mainstream sources like stuff, the Herald  and TV news are going to be the main source of scientific information, and when it's as bad as this article is it any wonder that large sections of our society are left behind by science?



*How amazing is geography - you can reconstruct the windiness of a site 3 000 years ago!


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Posted by David Winter 5:21 PM | comments(5)| Permalink |