I've been going at this Sunday Spinelessness thing for the best part of year now, in that time I've been able to cover a decent amount of the diversity among animals without spines. But up until today there was one clearing omission, so here is The Atavism's first bug:

In day to day speech we use the word 'bug' to describe any creeping, crawling or flying creature that happens to have its skeleton on the outside It would take a taxonomic pedant of the highest order to object to that usage, but 'bug' can also refer to a specific insect order. The Hemiptera are a group of insects with mouthparts specially adapted to sucking. Cicadas, plant hoppers, bed bugs, aphids, scale insects and water striders can all be called "true bugs" as can the star of today's post. It's a member of the shield bugs, or Pentomidae. Both those names refer to the shape of these bugs' bodies:

Like most insects, bugs have two sets of wings. In the shield bugs the base of the forewings is very leathery and sits over top of the much finer and membranous hindwings whcih are used for flying. This particular shield bug didn't seem to the least bit interested in using its wings, I picked it up from the garden path (where I very nearly stood on it) and was quite happy for me to pick it up and drop it off on some plants for a photo shoot.

Labels: bugs, insects, photos, sci-blogs, sunday spinelessness

In sexually reproducing species, the costs of making the next generation often fall unevenly on males and females. Take the rough periwinkle, Littorina saxatilis for an example.

Periwinkles are snails that live in the harsh zone between the sea and the shore on rocky beaches. Life in the inter-tidal means a periwinkle can expect to spent some if its day underwater, some high and dry, and be buffeted by waves the rest of the time. Female L. saxatilis have tweaked the typical marine snail lifecycle in response to their harsh habitats. Instead of laying a lot of eggs which hatch as tiny swimming plankton, L. saxatilis females retain a relatively few eggs within their shells. Safely stowed by their mothers, the young snails can develop to such a size that they are able to look after themselves once they hatch. Which is all well and good, but the maternal care displayed by these periwinkles means males have very different interests than females when it comes to mating. From a male's point of view more is always better, since every mating will increase the number of offspring he will sire. For females it's a different story, they can only retain so many eggs so only need so many matings to maximise the number of offspring they will produce.

In my little sketch of this sexual conflict I've suggested females actually decrease the number of offspring they produce with each mating after some optimal point. That's with good reason, as mating almost always comes at some cost. The examples from species with sexual conflicts can be gruesome; male bedbugs exclusively inseminate females by puncturing their abdomen with a hypodermic penis, some male water striders will attract the attention of predators unitl would-be mates yield to their advances, and ducks, well, Carl Zimmer has said enough about the ducks. There doesn't seem to be anything quite as unsavoury going on with these snails, but Joannesson and colleagues were able to show mating still comes at a cost. Inter-tidal creatures are always at risk of being washed off their rocks. Enough rough periwinkle lives have been lost to the waves that all around the world L. saxatilis populations have evolved into two distinct morphological types, a form with a large muscular foot capable of tightly gripping rocks dominates low on the shore while a less muscular form lives higher on the beach. Since a mating couple presents twice as much surface area to an incoming wave, you might expect mating increases the chance a periwinkle gets swept from the rocks. To test this idea researchers got crafty. Literally. They broke out the hot glue guns and stuck empty shells on to females and saw what happened. They showed that periwinkles sporting an extra shell were more likely to fall off a platform dragged underwater in a laboratory tank and less likely to survive in the wild.

L. saxatilis populations are often very dense (around 200 snails per square metre in this study) so females don't have to go out of their way to provision their eggs with sperm and, given the cost of mating, it's in their interest to dissuade males as much as possible. So how do they do it? In general, snails seek out other snails by following chemical cues in the trail of mucous they leave behind them. Periwinkles males in particular have been shown to follow female trails when they are on the lookout for a mate, so there must be some clue in the mucous that marks it as belonging to a female. To see how L. saxatilis males do at finding females the researchers collected populations of this species, and three other periwinkle species that live in much sparser populations on Swedish beaches. They then filmed these captive snails moving about in the laboratory and totaled up this distance each male covered in following female and male trails. By comparing L. saxatilis males' tracking ability with males from these other species the researchers could isolate the effects of the sexual conflict in L. saxatalis . These other species have sparser populations and different mating systems, which mean females are less likely to achieve the optimal number of matings and sexual conflict is less likely to arise. Here's what they found.

Each point in these charts is the result recorded from one male, the position of the point depends on this distance he covered following male trails (the y- or vertical axis) and the distance covered following female trails (the x- or horizontal axis). So, in the first chart the majority of males spend the majority of their time following female trails and one crawled to the beat of his own drum and followed male trails to the tune of 400 millimetres without showing the slightest interest in females at all. The same overall patter, males following female trails significantly more often than male trails, is repeated in each of the other species (charts 'a' through 'c') but not in L. saxatilis. Male L. saxatilis don't seem to be able to pick male and female trails, even when a different population was subjected to the test (so it's not a local effect in the Swedish snails) and when they were given an hour to get sniffing. So what's going on? Are females deliberately putting pesky males of their scent, or do males in such a densely packed species just not have to bother with tracking females? As the authors point out, the latter seems unlikely since the males' inability to pick female trails leads to an unusually large number of male-male couplings in the wild. Time spent tracking and mounting a male is time that could be spent in search of a female. So, even in a dense population, it's in a males' interest to be able to tell the difference between male and female trails. To put it to the test, the researchers ran one more test. This time the L. saxatilis males were observed among females from another species (the flat periwinkle L . fabalis). In this test, even with the species gap, the L. saxatilis males have no trouble picking out females:

So, given the chance, L. saxatilis males can find female trails but it seems female L. saxatilis aren't giving them the chance. By smelling like males these females reduce the burden of unwanted matings and frequently set males up on accidental male-male couplings

---

Johannesson, K., Saltin, S., Duranovic, I., Havenhand, J., & Jonsson, P. (2010). Indiscriminate Males: Mating Behaviour of a Marine Snail Compromised by a Sexual Conflict? PLoS ONE, 5 (8) DOI: 10.1371/journal.pone.0012005

Labels: evolution, research blogging, sci-blogs, sexual conflict, snails

Spring hasn't quite sprung down here in Dunedin, but it's definitely on it's way. I've just mowen the lawns for the first time in, well, a little while and the garden is full of hints that the days are getting longer and warmer. Two of the traditional Kingdoms ignored by The Atavism are are kicking into reproductive mode:

As you might imagine, I like my harbingers of spring to be a bit more mobile than plants or fungi and a bit more spineless that lambs or swallows. Nothing says spring to me like the low drone of bumblebee queen. Bumblebees can't stand the winter across most of New Zealand, so each bumblebee nest puts it's entire investment in the next flower fulled sumer into a few queens and a few males (bumblebees are like honey bees in that all the workers are female). At the end of one summer the queens fly out, mate, then find a warm dry spot to hibernate through the winter. Right now our garden has two or three big fat queens scoping out every nook and cranny, hoping to find a spot to set up a new nest.

Here's one unfortunate queen who stayed out too late last night, I found her on the lawn drenched by dew and too cold to move.

She's spent about an hour now on a sunny step and has started to walk about and vibrate her wings, I imagine she'll be on her way soon. Obviously, I couldn't resist the opportunity to get some closeups from a model that was unlikely to get away. I had plenty of opportunities to photograph bumblebees last summer, because we had a nest in our garden. I got tonnes of photos of the workers out collecting nectar and pollen:

And moving in and out of the nest (I recorded about one flight in or out every minute in the middle of the day in the middle of summer):

]

Labels: bee, bumblebee, environment and ecology, photos, sci-blogs, spring

I might not have woken up just after 4:30 yesterday morning if it weren't for our squeaky living room swinging slowly open. It had been pushed from its balance by what seemed to me like a long, but not particularly strong earthquake. Of course, it turned out that it was a particularily strong earthquake, 7.1 on the Richter magnitude moment scale, shallow (just 10km below the earth) and close to Christchurch (putting it 400km away from my bedroom). Like everyone else, I woke up to see pictures of the damage in the city's CBD.

I don't have any particular knowledge of geology, but I wanted to find out just what had happened underneath Canterbury to set the earth shaking. Perhaps readers here will be keen to learn too, so here's what I've found out.

Map modified from wiki-commons version of USGS's original

New Zealand's sits right on the boundary of the Pacific and the Australian tectonic plates.This might seem like poor planning, but it's actually the activity at this plate boundary that has kept New Zealand afloat. Some 20 million years ago most of our mini-continent was underwater (in fact, most of our mini-continent is underwater now) and the plate boundary was relatively inert. At about that time the plate switcthed to an active phase, which generated subduction zones either side of the South Island (and resulted in vulcanism of the sort we see today in the North Island's central plateau.) Between the subduction zones the plates collide with each other. It's not a head-on collision, the bulk of the South Island is being moved southward at about 3 cm per year, but the compression that arises from the collision has been enough to send the crust that makes up New Zealand back above the ocean. The most striking result of these collisions is the Southern Alps:

Image from NASA

That line between the snow topped peaks and the coastal plane to the West is the plate boundary.The 450 km long chain of mountains that rise as the Pacific Plate is thrust up against the Australian are synonymous with the rugged beauty of the South Island. But there are risks associated with living a country that is still inventing itself. As you might imagine, mountain building on this scale belies massive forces working under the earth. As the Pacific and the Australian plate slide against each other they carry the crust with them, and that means every now and again something has to give. There hasn't been an earthquake along the alpine fault, which runs along the plate boundary, since Europeans arrived here to record them. It seems displacement between the two plates is more often expressed by quakes in the Marlborough Fault System in the North of the South Island. Yesterday's earthquake was further south than the Marlborough system, along a fault that hadn't previously been mapped. The fact GNS didn't know the fault was there before yesterday doesn't mean it's new, it's only possible to map a fault line from it's surface expression, and it's quite possible for the record of older quakes to be overwritten by fresh geology. Apparently, most of the movement in yeasterday's quake was latteral (rather than up and down), similiar to the eathquakes we would expect from the alpine fault and the Marlborough faults.

We'll learn more about exactly what happened yesterday once GNS scientists have studied their siesmographs and surveyed the area, but we can already summise why the damage varied from suburb to suburb. Part of the reason the CBD was hit hard is that there are more old brick and stone buildings in the central city. Most newer buildings are built to sway in an earthquake, and the vast majority of New Zealand homes are built of wood which can flex and ride out a shake. By contrast, rigid buildings can only move so much before they give way.

The surface on which buildings sit also has a lot to do with how they are effected by earthquakes. This photo from Richard Walker's flickr stream illustrates the cause and the result of a process called liquefaction:

While tectonic plates have been making mountains in the South Island, the elements have been breaking them down. Rivers and glaciers have been scoring away at the alps, bringing rocks down from the mountains to the Canterbury plains in the process. Much of Canterbury sits on layers of gravel and stone delivered to by the braided rivers that characterise the region. Most of the time these gravel beds provide a solid footing, because friction between the stones holds them in place. Something like this

What happens when you shake a structure like that up? The large stones can effectively become suspended in the silt or sand that usually fills up the gaps. In the worst cases (well sorted stones suspended in wet silt) the whole thing can start to behave as a fluid and cause major changes at the surface:

As you can see, i couldn't fit as many stones in my "suspended" version of the gravel bed. All those stones and gravel have to go somewhere and under certain conditions the increase in pressure caused by liquifaction under the surface can form "sand volcanoes" that erupt through the topsoil. Jon Sullivan recored just that phenomenom in a Hoon Hay backyard.

There's plenty more coverage of the earthquake on the net. Geoblogger Chris Rowan has a post with a more thorough run down of the geological setting of the quake and sciblogs has Grant's constantly updated post and some neat maps from Chris McDowall.

Labels: Christchurch, earthquake, geology, sci-blogs, science

Another of Vancouver's pollinators today, and this one's not a bee:

This is another photo form the UBC botanic gardens, and this time it's a beetle in amongst the flowers. More specifically it's Rhagonycha fulva, the common red soldier beetle. A little research tells me these guys are actually native to Europe, but they've become established in much of Canada. I've included these pics under the 'pollinators' heading, even though they aren't principally nectar eaters, soldier beetles are carnivores, in fact the've been used as biological control agens for small pest insects like aphids .Rhagonycha fulva visits flowers, but only to to find other insects living in them:

The flower in question, for those of you wondering, is Astrantia major involucrata. As you might imagine, sticking your head into flowers all day does tend to move a bit of pollen around and Rhagonycha fulva has been shown to be an "incidental" pollinator of a number of plants. That's all you'll get from me today, but there's much better blogging out there for you to read, including photos of the same beetles and the same gardens thank's to the UBC Botanical Gardens own blog.There's a stunning shot of this very beetle in flight here. If that's not enough beetling for your Sunday then Ted MacRae is bound to have something stunning for you to look at, and if you really can't get enough invertebrate blogging then there's a whole mess of it at this moth's Circus of the Spineless hosted by hectocotyli (you should probably look up just what an hectocotylus is too)

Labels: beetle, environment and ecology, photos, sci-blogs, sunday spinelessness, Vancouver