March 31st, 2008


(no subject)

According to a March 30th article from New Scientist, the tuatara, a New Zealand lizard sort of lizard-snake cross LET'S JUST SAY REPTILE, is the fastest-evolving animal known.


When some scientists at the University of Auckland "analysed mitochondrial DNA sequences from 650 to 8000-year-old tuatara remains and compared them with those of living tuatara, they found that the reptile is evolving almost 10 times as fast as the average animal. It is accumulating an average of 1.37 substitutions per base pair every million years compared with an average of 0.2 (Trends in Genetics, DOI: 10.1016/j.tig.2007.12.002)."

Aside from its powers of speedy evolution, the tuatara is also unique in nature in that it has two rows of upper teeth which overlap one row of lower teeth, and has a parietal "third eye", whose specific function scientists are still trying to figure out (it's connected to the brain but covered in opaque scales and appears to have evolved from a working eye -- one possible theory is that it acts as a light sensor and assists in basking). They can hear without having any external ear present, and the males are penis-less. The tuatara also retains a number of unique skeletal characteristics, possibly as a remnant of its evolution from fish.

Probably the only reason they have not yet evolved into our terrifying lizard overlords (besides the fact that they were endangered for many years) is because they reproduce so slowly, taking 15 years to reach sexual maturity, with females producing eggs only every two to four years.

Still, they are badass. The Maori revere the tuatara as a god-form, specifically a messenger of Whiro, the god of death and destruction. Maori women are forbidden to eat them, and the tuatara's presence is said to mark the boundaries between the mundane and the sacred.

All hail the tuatara!

aye aye captain

Rigor Mortis Makes Me Hard

A day after I wrote up about redbacks and their sexual exploits, I learnt of another spider's bizarre bedroom habits. At least these guys don't die to breed. They just pretend to.

Pisaura mirabilis, also known as the Nursery Web Spider, or nuptial gift-giving spider, or a Fishing Spider, or a Raft Spider, is one of a widespread family of wolf-spider-like arachnids well known for their ability to run across water or dive into it after fish and tadpoles, and only build webs for their egg sacs to hatch in once they get tired of lugging them around. And given those eggsacs can be so big the spiders have to run around on tippy-toes to carry them I imagine they get tired quite quickly. (By another odd coincidence, the spider genus Nukuhiva I mentioned in completely unrelated context elsewhere is another Pisaurid.)

But before they have any eggs to care for they have to breed, and to do that the male has to cope with a female potentially more interested in food, rather than pork sword.

Here's a photo of one nervously handing over a gift-wrapped pre-coital bribe.

Others don't get that far. They bring her a gift-wrapped meal alright, then keel over dead as soon as she looks at him anyway, assuming what we shall refer to as the X-P posture. But he's faking it.

Thus, the object of his desire thinks "Hmm, shall I eat him, or hump him.. oh, he's dead. Hey, chocolates gift-wrapped beetle! Tasty!" and picks it up, dragging the male along underneath. Eventually he'll cautiously open one eye, and go for it. Her reaction is presumably something like "What the? You were supposed to be dead! What are you doing with that pedipalp mister... oooooh, that feels nice, carry on"

To quote from one of the papers on the subject

When entering thanatosis, the male would collapse and remain completely motionless while retaining hold of the gift so it was held simultaneously by both mates. When the female initiated consumption of the gift, the male cautiously ‘came to life’ and initiated copulation. Death feigning males were more successful in gaining copulations, but did not have prolonged copulations. We propose that death feigning evolved as an adaptive male mating strategy in conjunction with nuptial gift giving under the risk of being victimized by females.

Actually, Pisaurids don't just play dead to get some, they also play dead to avoid getting killed - see this account for an unfortunate Dolomedes that didn't get away.