Sunday, February 20, 2011
Sunday Spinelessness - Misshapen by love
I'm not finished with photos of spineless life from Vanuatu just yet, but I do have to interrupt that stream of posts again thanks to goings on in our backyard. Ever since I started writing this blog I've wanted to shoehorn a quote from James Thurber, and on Friday I had an encounter that gave me the chance. So here goes:
Surely nothing in the astonishing scheme of life can have nonplussed Nature so much as the fact that none of the females of any of the species she created really cared very much for the male, as such. For the past ten million years Nature has been busily inventing ways to make the male attractive to the female but the whole business of courtship, from the marine annelids up to man, still lumbers heavily along, like a complicated musical comedy. I have been reading the sad and absorbing story in in Volume 6 (Cole to Dama) of the Encyclopædia Britannica. In this volume you can learn all about cricket, cotton, costume designing, crocodiles, crown jewels and Coleridge, but none of these subjects is so interesting as the Courtship of Animals, which recounts the sorrowful lengths to which all males must to go arouse the interest of a lady.
After that memorable introduction, Thurber lists some of the absurd behaviours that males of various species resort to in their attempts to get the attention of females. The fiddler crab's odd little dance, the bowerbird's colourful treasury and the nuptiual gifts providied by some tree crickets are all covered. Thruber restricted himself to the behaviour of animals in his essay, but the pursuit of love has also wrought some very strange body modifications. The peacock flashes his fabulous tail in the hope of winning a peahen's heart, in certain deep-sea fish the male lives only to find a female to which he might attach himself, so he can be subsumed into her body and then there is the creature that ran out from under our recycling bin on Friday:
Those impossibly long and skinny legs mark him out as a harvestman (a group related to spiders) from the sub-order Palpatores. Once I'd prevented his escape, and taken a few more photos I shot an email off to Christopher Taylor who, as well as writing Catalogue of Organisms, just happens to be the brains behind the most recent taxonomic review of these harvestmen in New Zealand. Chris was kind enough to identify him, so I can tell you that you're looking at Pantopsalis albipalpis. Ordinarily an animal that appears to have crawled out of the pages of The War of the Worlds would be more than enough for a post here, but those spindly legs are as nothing when you compare them to the crane-like appendages growing from his head.
Amazingly, those are his jaws, or at least his chelicerae. Arachnids have two sets of limbs associated with their heads, the pedipalps (which spiders use almost like legs, and, in males to deliver sperm if you can imagine such a dual-purpose organ) and the chelicerae which are used to grasp prey and direct it toward the mouth (arachnids don't have chewing mouth-parts like many other arthropods).
Females from Pantopsalis and the related genus Megalopsalis have more or less normal chelicerae which point downwards, let their owners shuffle food towards their mouth and do very little else. As you can see, males are built a little differently. In fact, those massive hinged jaws are so different than the female form that males and females have frequently been mistaken for different species. Even within males, several species have two distinct forms; one with relatively low abd broad chelicerae and another with tall slender chompers.
It's not entirely clear what purpose such massive chilicerae serve, but the fact they are limited to males makes it a pretty sure bet they're just another example of the what Thurber called "the mournful burdens of the male" in the biological world. Perhaps female Pantopsalis just go mad for a giant chelicera, and in each new generation males have to sport ever more rediculous dentition if they want to turn a girls head. The mean spikes and nasty looking claws seem to suggest the giant chelicerae are more of a help to fighters than lovers. A few distantly related harvestman groups have also evovled overgrown jaws, and in those species the males fight with each other for the chance to mate. As with so much of New Zealand's invertebrate fauna, no one has ever studied our harvestmen in a behavioural or ecological sense. It would be fascinating to understand the forces that created this out-sized morphology, and how the distinct male forms are maintained (do they relate to different fighting strategies?) but until someone studies them in detail we just can't know.
However they got their giant jaws, I can't look into the eyes of this last photo without thinking this particular harvestman shares a little of Thurber's opinion on the lengths to which Nature's male have to go:
There are quite a few places you can find better pictures of New Zealand harvestmen around the web. Alan from half-pie has a Megalopsalis, Sciblogs own Brenden Moyle has photos of distantly related harvestmen that have normal sized chelicerae but massive pedipalps and TERRAIN, a forest restoration project in the Taranaki, has some great details of the claws.
The quote at the start is from Thurber's story Courtship Through the Ages which was published in the New Yorker then a collection of short stories. It's really very funny.
Christopher's paper on New Zealand's Pantopsalis is
Taylor, C., 2004. New Zealand harvestmen of the subfamily Megalopsalidinae (Opiliones: Monoscutidae)–the genus Pantopsalis. Tuhinga, 15, pp.53-76.
Labels: harvestman, Opiliones, photos, sci-blogs, sexual selection, sunday spinelessness
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FROM A VERY VERY LONG WAY AWAY!!!
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