I promised last week that I'd come up with something a bit more cheery than photos of dead flies for the next Sunday Spinelessness post and what could be more uplifting than portraits of motherly devotion? Of course, in this case the mother is a spider. The New Zealand lynx spider Oxyopes gracilipes.

Lynx spiders are a family (Oxopidae) of very active and fast running hunting spiders. The swollen abdomen of the female photographed above is evidence of her gravidity (I was tempted to dedicate this post to Harvest Bird who finds herself in the same condition but I'm not quite sure how someone a little less arachnophilic than I would take that). A few days before I spotted the gravid female I'd taken some pretty poor photos of a male lynx spider on the same plant so we can probably assume he's the father.

She's lost her former globose shape because she's laid her eggs. The silk she's spun around the leave is protective egg sag but lynx spiders take protection very seriously - they won't leave the fate of their eggs to a bit of silk and chance. I checked on the egg sac almost every day for two weeks and never found the lynx spider more than a few centimeters away. Little is known about the behaviour of our lynx spider but their American counterparts have been known to relocate egg sacs when they are threatened by predators or starve to death while standing guard. In the end I had to leave before the spiderlings hatched but in Spiders of New Zealand and their Worldwide Kin Ray and Lyn Forster tell us that the female wanders off shortly before that event.

Labels: arachnophilia, environment and ecology, lynx spiders, might interest someone, Oxopidae, photos, sci-blogs, sunday spinelessness

Hunting around the young shoots you can see spiders and beetles that have met the same fate but it seems it's the true flies of the order Diptera that suffer most and probably the soldier flies that do worst of all:

I realise most people will think taking photographs of dead flies is more than a little macabre but I contend there is something quite beautiful about a crane fly suspended gracefully by its long legs

Or even a predatory robber fly caught, as if in mid-flight.

Ok, I promise I'll find something a bit more uplifting for next week's post!

Labels: Asilidae, diptera, environment and ecology, photos, rhododendron, sci-blogs, Stratiomyidae, sunday spinelessness, Tipulidae

• Fabiana Kubke has heard something strange about Tui and wants your help to check it out. She's not telling us exactly what it is that she's testing just yet but to get involved all you have to do is drop her a line with a few details when you see a Tui. Fabiana described the project and the idea of citizen science to Noelle McCarthy on National Radio so I'll let her provide the details [streaming audio]
• A group of scientists from the Univeristy of Canterbury have been documenting their work on the Chatham Islands with a blog, Life on the Edge of the World.
• The people that brought you Science Creative Quarterly have a sneaky plan: to hijack kids' freakish ability to recall details about hundreds of Pokemon "species"and use it to teach them a few things about real animals. You can read about the phylomon project here - it's brand new and looking for input from graphic artists, photographers, science geeks, gaming geeks and really anyone that's interested.
• Finally, go over and welcome another Otago geneticists to the blogosphere. Tamsin is a PhD student working on the genetics of embryonic development which means she has tonnes of stunning images to blog about.

Labels: citizen science, might interest someone, sci-blogs, science and society, science communication

[Hmm, it seems my clever idea to write up a bunch of Sunday Spinelessness articles and automate their appearance here was scuppered by my inability to actually read a calendar. I guess you can enjoy your spinlessness a day early this week...]

This is a male cabbage tree moth (Epiphryne verriculata) and he's not having a good day.

Usually the cabbage tree moth is one of the nicest examples of cyrpsis, or camouflage, that you'll find. They spend their days sleeping among the dried up leaves on and around cabbage trees. As you can see they are perfectly adapted to that environment - right down to the occasional spot and stripes that extend across the body as well as the wings. For some reason this particular moth alighted, not on the abundant fallen leaves around the base of one of our cabbage tress but on the underside of a nice, bright green Montbretia leaf.

Though, for obvious reasons, you don't see the adult of the cabbage tree moth very often it occurs everywhere the cabbage tree does. The caterpillars, and the half eaten leaves that leave behind, are a good deal more conspicuous. Interestingly, despite their wide range there appears to be a degree of local adaptation in E. verriculata populations. When cabbage trees grown from seeds collected in the North and the South Island are cultivated together in the South Island caterpillars of the cabbage tree moth show a preference for the 'their' southern trees.

Labels: crypsis, environment and ecology, Epiphryne verriculata, fail, moth, photos, sci-blogs, sunday spinelessness

There is something faintly pathetic about the Y-chromosome when its lined up with its peers in a karyotype. Each of the 22 numbered chromosomes pair off with a near identical partner just their size while the Y has to shape up to the X which has more than twice as much DNA and 25 times as many functional genes.

The puny Y-chromosome only looks worse when you realise that mammalian sex chromosomes weren't always so mismatched. 160 million years ago the X and Y were just another pair of chromosomes, albeit the pair that the carried the sex determining gene SRY. Over time the chromosome that went on to become the Y stopped swapping genes with its partner, allowing it to maintain a suite of genes that are beneficial in male bodies but not in females. It's the lack of genetic recombination that sent the Y into its decline. Genes on any other chromosome can be swaped between pairs, meaning over many generations individual gene copies (called alleles) are exposed to natural selection independently of alleles either side of them. The same process doesn't apply to alleles on the Y-chromosome. Since the Y is always passed on as a single unit natural selection acts on the whole thing - a broken gene might make it into the next generation because it is attached to beneficial mutations. The efficiency of natural selection is further reduced in the Y-chromosome because it has a relatively small effective population size (less that one quarter of that for normal chromosomes since only males carry the Y and then in only one copy and even then a larger number of males than females don't contribute to the next generation) which makes genetic drift a strong force.

What we've known about the Y-chromosome's past has has shaped out ideas about what it is now and what it will become. Until quite recently the Y was seen as more or less a derelict chromosome, a few broken remnants of the genes still found on the X and a couple of male-specific genes hanging on the the sex determining gene SRY. People have even go so far as to extrapolate the Y's long slow decline to a future time at which the Y will simply disappear. The first clue that the Y-chromosome might be a little more resilient than that came in 2003. The publication of the complete sequence of the human Y-chromosome revealed more than fossils from the Y's more substantial ancestor. There are plenty of those so called "X-degenerate" segments but most of the active genes in the Y are in large repetitive runs of DNA called the "ampliconic regions". The genes in these regions are mainly made of DNA sequences unique to the Y chromosome and are expressed only in the testes - suggesting the Y has been making its own genes at the same time that its been losing the X-degenerate ones.

Untill this week it has been hard to test the idea of a regenerating Y-chromosome in an evolutionary framework. Those large repeated runs of DNA are very hard to sequence (the standard metaphor is putting together a jigsaw puzzle made entirely of sky) so we haven't had another Y-chromosome sequence to compare ours with. Now, thanks to Jeniffer Hughes and colleagues, we do and the result it stunning. Not only has the Y-chromosome been making genes, it's been making them at an outrageous rate. Thirty percent of our Y-chromosome sequences have no counterpart in the chimpanzee. As the authors say that's the sort of divergence you'd expect to see between humans and chickens, which are separated by 310 million years of evolution not humans and chimps which only split 6 million years ago!

It's evident that, far from being in the tail end of an inexorable decline, the Y-chromosome is evolving a good deal more quickly than the rest of the genome. So, the burning question is what is behind that evolutionary rate? There is probably no single answer to that question but it's safe to assume it results from some of the unique features of the Y-chromosome; a lack of genetic recombination, the presence of those large repetitive sections of DNA and the preponderance of male specific genes.

It's usually a good idea when trying to explain an evolutionary phenomenon to think of explanations that don't invoke natural selection as the main driver as a sort of null hypothesis against which to test other ideas. In this case the increased fixation of new genes on the Y-chromosome might simply reflect an increased rate of production of new genes. Those highly repetitive sections of the Y-chromosome are the perfect substrate for a process called ectopic gene conversion in which a Y-chromosome can recombine with itself and as a result duplicate streches of DNA. We know from human studies that a process like this has made wide scale structural changes in the last 100 000 years and it might be enough to explain the Y's unusual gene production.

I think it's very likely that natural selection also plays a role in the number of of those new genes that become fixed in the human and especially the chimp lineage. Most of the active genes on the Y-chromosome are expressed in the testes and involved in sperm production. Chimpanzees are highly polygynous polygynandrous [Thanks to Harvest Bird for pulling me up on this,], in most cases a female will mate with each of several dominant males in a troop, and a result sperm competition is an important level of selection. Although humans aren't as polygamous as chimps (and likely haven't been in our recent history) it's clear that fertility selection is still an important force and we know for sure that mutations in the Y-chromosome can lead to infertility so, again, the fate of new genes on the Y-chromosome are likely to be driven by selection.

Both the adaptive and non-adaptive explanations above might will be influenced by the lack of recombination in the Y-chromosome. The reduction in the efficiency of natural selection described above will stop very slightly deleterious mutations from being driven to extinction which might mean new genes that would be selected against on any other chromosome become fixed on the Y. This phenomenon can be enhanced when it is coupled with selection producing a 'selective sweep'. If a new beneficial mutation, perhaps associated with sperm competition or fertitily selection, pops up in on a chromosome with a bunch of other mutations that whole thing will be selected for and driven to fixation which has the potential to make for large scale changes quickly.

It is likely that the amazing evolutionary rate of the Y-chromosome is a result of some combination of all these factors but it should be possible to disentangle at least some of their contributions. If sperm competition is a major driver of Y-chromosome evolution then it follows that animals that go in for purely monogamous relationships will have comparatively low rates. Evolution has furnished us a natural experiment to test this idea, all gibbon species form pair bonds and are highly monogamous. We could test the sperm production hypothesis by sequencing the Y-chromosome of two gibbon species and calculating the rate of evolution of a Y-chromosome in a monogamous species. .Although I'm happy to present the test of this idea I'm not going to line up to do it, those repetitive sections of DNA make sequencing Y-chromosome so hard that it took 13 years to do the human one and 8 to finish the chimp one.

Labels: chimpanzee, evolution, genetics, genomics, Human evolution, might interest someone, sci-blogs, science, Y-chromosome

Sunday Spinelessness may have been on hiatus for Christmas and the New Year but the spineless themselves don't observe holidays. During my break in the sunny Wairarapa I've been keeping and eye, and a couple of lenses, on some of the backyard bugs and if I was to say one thing about them it would be that they are hungry

Take the Sidymella crab spiders (previously featured on these pages) hiding in the Christmas Lilies and in particular on dahlia flowers:

I was very pleased when I wandered back to the house to upload the photos from the camera. Not just because I had the answer to my puzzle, but because a tweet from my scibling Brendan let me know I wasn't the only person in the country spending some of Christmas photographing spiders (his impressive jumping spider is here).

Having found at least one of the items on the crab spiders' menu it became clear the fly is pretty common too. It's no surprise that the bright yellow dahlias are one if the flies favourite haunts.

Labels: crab spider, environment and ecology, sci-blogs, Sidymella, sunday spinelessness, Thomisidae