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Researchers: Island rule of size evolution does apply to rodents

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Photo op for pig size rodent Capybara, 45 kg, 100 lbs/maradt, Fotolia

This should be a Fri Nite Frite, but only if you live on an island, so…

From Duke U ScienceDaily:

Island rodents take on nightmarish proportions

Rodents of unusual size are 17 times more likely on islands than elsewhere

Whoever wrote that release has a future in frites.

Researchers have analyzed size data for rodents worldwide to distinguish the truly massive mice and giant gerbils from the regular-sized rodents. They found that the furry animals with chisel-like teeth are 17 times more likely to evolve to nightmarish proportions on islands than elsewhere.

The results are in keeping with an idea called the ‘island rule,’ which previous studies claimed didn’t apply to rodents.

More than half of the rodent populations on the 182 islands they looked at weighed in among the top or bottom 2.5 percent for size for their species.

Take Coues’ rice rat, for example, which researchers believe got to the island of Cozumel from nearby Mexico and Guatemala. Some island populations have grown to more than twice the size of their mainland counterparts.

‘Deer mice, too, are nearly twice as big on the Gulf Islands off the coast of Vancouver than on the North American mainland,’ said Durst, who is now a postdoctoral fellow at the University of North Carolina at Chapel Hill.

Thankfully, it isn’t a computer sim; it is apparently a real study, where rodents were sized or dumped onto scales or something.

Scientists don’t know how long ago most rodents arrived on the islands from the mainland territories where they originated, or how long each took to reach peculiar proportions.

For the most part, the researchers discovered that the extreme cases were unusually large, rather than unusually tiny.

File:A small cup of coffee.JPG

Lemme guess: The islands feature few wild cats, foxes, coyotes, or wolves, all known to eat rodents. (Yes, even wolves will eat small rodents if nothing better turns up.)

It may relate in some way to “Researchers say larger size is a genuine pattern in evolution, not neutral drift. One problem with Darwinism dominating evolution thinking is that researchers are looking for “how cows become whales” before we have even mastered simple problems like, Is the island rule general? What drives it?

Desperation breeds defeat.

Note: I’ll shortly be starting a series at Evolution News & Views on the many ways evolution can actually happen. Stay turned.

Here’s the abstract:

he tendency for island populations of mammalian taxa to diverge in body size from their mainland counterparts consistently in particular directions is both impressive for its regularity and, especially among rodents, troublesome for its exceptions. However, previous studies have largely ignored mainland body size variation, treating size differences of any magnitude as equally noteworthy. Here, we use distributions of mainland population body sizes to identify island populations as ‘extremely’ big or small, and we compare traits of extreme populations and their islands with those of island populations more typical in body size. We find that although insular rodents vary in the directions of body size change, ‘extreme’ populations tend towards gigantism. With classification tree methods, we develop a predictive model, which points to resource limitations as major drivers in the few cases of insular dwarfism. Highly successful in classifying our dataset, our model also successfully predicts change in untested cases. (paywall) – P. A. P. Durst, V. L. Roth. Mainland size variation informs predictive models of exceptional insular body size change in rodents. Proceedings of the Royal Society B: Biological Sciences, 2015; 282 (1810): 20150239 DOI: 10.1098/rspb.2015.0239

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2 Replies to “Researchers: Island rule of size evolution does apply to rodents

  1. 1
    Robert Byers says:

    I love the point about not figuring out rodent sixes but saying they got cow/whale thing sown up. AMEN.
    I have noticed indeed how islands had either dwarf or giants of the types on the mainl;and. This is everywhere in the fossil record.
    In fact for this YEC I don’t mind selection allowing size change. Yet it seems to me its not selection but a adaptation to the area. No problem getting bigger if the food is there. No problem getting smaller if the food isn’t.
    Possibly selection on the winners but is it needed.
    Why not restock some island and watch? If it happens quick, which it must, then there is your answer.
    Good subject.

  2. 2
    Brent says:

    Don’t mind the rodents in Okinawa, but the centipedes! Long as my forearm and fat as my thumb and little finger together. Monsters I tell ya!

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