Tuesday, April 04, 2006

Sinister Snails Fox Crabs

Sinister: such a great word, made all the better for being a synonym for left handed. I've never trusted them left handers.

What the devil am I blathering on about? Well mollusc fanciers (or malacologists as I bet they call themselves when trying to impress girls, like saying you're a scientician of any sort helps you pick up chicks (and no, there are no female malacologists, but don't quote me on that)), have discovered that contrary to expectations, back in the Plio-Pleistocene (2.5 MYA to 1.5 MYA) snails with a left handed, or sinistral (we got there eventually) whorl, had a better survival rate than their right handed, or dextral, cousins. The shock of this is that left handed species of cone snails pretty much went extinct 1.8MYA, and whelk dextral and sinistral species have lived side by side, suggesting no advantage and a possible disadvantage to sinistrality. The disadvantage coming about due to sexual selection form the females.

This research (Dietl and Hendricks, Biology Letters, 2006) reads like a forensic investigation, where they studied the number of repaired crab claw scars on paired samples of similar sinistral and dextral shell fossils, with increased scars indicating more survived encounters with hungry crabs. I did similar things back in my osteology/forensic anthropology days, but never on snails. I'm no malacologist. Or osteologist for that matter.
They then watched a crab (a box crab no less) attacking whelks and concluded that it has difficulty opening sinistral snails, although this was in the discussion and they don't present much data to back it up. Maybe they have better things to do?
The analogy of left handed snails and left handed boxers, tennis players and baseballers is then made (baseballers? is that right? hmmm, I'm English so I dunno. They don't mention cricket, but it's true there too, also in Biology Letters, Brooks et al), since the "opponent" knows little about the southpaw. Hmmm, best not take this too far or we'll be likening Matthew Hayden to a whelk soon.
It's an interesting point, but if the advantage of sinistrallity was so much, then why are they so rare? It is an advantage to be sinistral in a right handed world in terms of survival, but sexual selection pulls the other way for the right handers, a point they make, but they also finish the article with "it's not all about sex", nice quip. Malacologists eh? What are they like.
I say however, if everything was sinistral, or if sinistral and dextral were found in equal measures, then the opponent (crab or over hyped British tennis player) would have more experience of cackhandedness, and so the advantage would instantly disappear.
And so ends another overly long, poorly written and ill-informed edition of Big Up Science!

1 comment:

Blue and Brown said...

Thank God it was only molluscs in the Plio-Pleistocene era for whom left-handedness was an advantage. Imagine if those in power were all left-handed. IMAGINE!