Evolution of a polyphenism

Here’s some very cool news: scientists have directly observed the evolution of a complex, polygenic, polyphenic trait by genetic assimilation and accommodation in the laboratory. This is important, because it is simultaneously yet another demonstration of the fact of evolution, and an exploration of mechanisms of evolution—showing that evolution is more sophisticated than changes in the coding sequences of individual genes spreading through a population, but is also a consequence of the accumulation of masked variation, synergistic interactions between different alleles and the environment, and perhaps most importantly, changes in gene regulation.

Unfortunately, it’s also an example of some extremely rarefied terminology that is very precisely used in genetic and developmental labs everywhere, but probably makes most people’s eyes glaze over and wonder what the fuss is all about. I’ll try to give a simple introduction to those peculiar words, and explain why the evolution of a polyphenic pigment pattern in a caterpillar is a fascinating and significant result.

[Read more…]

The real truth about the Sasquatch

As a proud native of the great Pacific Northwest, when an article on one of our noblest creatures was mentioned to me, I had to read it. Here’s the center of the story.

In July 2005, nine residents of Teslin, Yukon,
witnessed through a kitchen window a large bipedal
animal moving through the brush. The next morning, they
collected a tuft of coarse, dark hair and also observed a
footprint measuring 43 cm in length and 11.5 cm in width.

That’s right: physical evidence, a footprint and hair, from…Bigfoot. The Sasquatch. A sample captured in the wild and brought into the lab. Pinned against the wall, trapped and unable to escape the probing appendages of an implacable, intrusive Science.

So they extracted DNA from the hair and amplified conserved mammalian sequences. They sequenced fragments of the DNA and compared them against sequences in the databases, and got a shocking answer. Prepare yourself: here is a diagram of the phylogenetic relationship of Sasquatch to other mammalian species.

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Maximum parsimony tree illustrating the position of the Sasquatch hair sample. Bootstrap support values are given at the nodes. The species and GenBank accession numbers are water buffalo Bubalus bubalis*, yak Bos mutus, cow Bos taurus, wisent Bos bonasus, and
North American bison Bison bison.

The scientists squirm and try to avoid the obvious conclusions of their results, inventing foolish excuses rather than facing reality.

There are several possible explanations for these
results. First, as suggested from molecular analysis of
hair from a suspected Yeti, the Sasquatch might be a
highly elusive ungulate that exhibits surprising morphological convergence with primates. Alternately, the hair
might have originated from a real bison and be unrelated
to the Sasquatch. Parsimony would favor the second
interpretation, in which case, the identity and taxonomy
of this enigmatic and elusive creature remains a mystery.

I wonder what Radical Sasquatch will think of this.

*Wait a minute…the scientific name for the water buffalo is Bubalus bubalis? Bubalus bubalis? No wonder they’re so mean.

Coltman D, Davis C (2006) Molecular cryptozoology meets the Sasquatch . Trends in Ecology and Evolution 21(2):60-61.

Giant octopus attacks!

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Here’s a nifty video (mpg) of an octopus confronting an ROV working off Vancouver Island. The poor thing was just trying to crush and eat an interloper (or perhaps disassemble it for spare parts to use in its high-tech scheme to take over the world), and the ROV operator uses its thrusters to fling debris at it and drive it away.

It’s quite a battle, and the octopus holds on for a surprisingly long time in the face of an extremely obnoxious machine.

Paedocypris

I saw on Muton, and several readers have mentioned it to me, this article about the world’s smallest vertebrate, fish of the genus Paedocypris. It’s a gorgeous translucent cyprinid, so is somewhat related to my favorite fish, Danio rerio. They live in cool, slow moving water in peat swamp forests of Southeast Asia. One female, only 7.9mm long, contained about 50 eggs, so they know it was sexually mature.

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Living Paedocypris progenetica, CMK 18496, (a, b) male, ca 9 mm; (c) female, ca 8.8 mm.

That size isn’t at all shocking—my zebrafish larvae at about that size are active hunters with functioning visual systems, capable of coordinated bouts of swimming, and they’re also very impressive animals…but they don’t have sex. It takes about 6 months for zebrafish to reach sexual maturity, and they are several centimeters long at that point. I would love to know how old these fertile Paedocypris were, but they were captured in the wild and virtually nothing is reported about their behavior or lifecycle. Ah, to have a fish colony that could be raised in a set of beakers, and could produce a couple of generations of crosses in a single semester…

One other clue that these are fully functioning, sexually mature adults are the presence of some pelvic specializations. Males have a hook and flange widget on their pelvic fins, and an odd prepelvic knob. Again, though, without knowing anything about their behavior, we don’t know how these are used in mating and courtship. Wouldn’t it be cool to put a pair under my Wild M3 scope and watch courtship and mating?

i-1a06a4755eb50db864064f6cf9689aa3-paedocypris_pelvis.jpg
(a) Paedocypris micromegethes, paratype male, ZRC 49869, 10.4 mm; pelvic fins, anteroventral view, showing hook and flange on anterior ray. (b) Paedocypris micromegethes, paratype, male, BMNH 2004.11.16.1-40, 10.9 mm, ventrolateral view on hypertrophied pelvic arrector and abductor muscles marked by asterisk symbols. (c) Paedocypris progenetica, paratype male, ZRC 43199, 8.5 mm, scanning electronic micrograph of pelvic region in ventrolateral view, arrow points to keratinized prepelvic knob.

Of course, in addition to not knowing their generation time yet, these fish have another drawback relative to zebrafish: tiny eggs. They extracted a range of sizes from the ovaries, but assuming the smallest are immature, they max out at around 0.3mm diameter. That’s respectable, but Danio eggs are about 1mm in diameter.

Can you tell I’d love to get my hands on a bunch of these little fish? Unfortunately, I’ve heard from fish importers that it is agonizingly expensive and time consuming to bring wild tropical fish into the country, and for good reason: to block invasive species, to prevent the spread of new fish diseases, and also to discourage the plundering of native populations. I may not ever see one of these animals, short of making a trip to Malaysia, and even then I won’t be bringing any home.