A Tiny Arthropod Tells A Tectonic Story

Fascinating piece in the Science Times today concerning Dr. Gonzalo Giribet and a group of Harvard biologists’ research of the tiny mite harvestman and what it tells us about plate tectonics. Although biogeography informing plate tectonics is nothing new and indeed the concept of continental drift originated with German scientist Alfred Wegner’s observation that similar fossils could be found on now distant continents, the mite harvestman tells a more detailed story.

i-16c9e9f994b6775a8abb91561387466a-daddy long legs1.jpg
Steve Gschmeissner/Photo Researcher (left) and Nigel Cattlin/Photo Researchers
(Note: the picture on the right is actually a true spider and not a harvestman. Thanks to Mrs. Tilton for bringing this to our attention and Bug Girl for confirming the grievous error)

A relative of the daddy longlegs, the mite harvestman appears as a mere speck to the human eye. However, the tiny critter has existed in some form or another for hundreds of millions of years and does not disperse well. This means that many different species of harvester mite have remained isolated geographically even when other organisms spread rapidly across and between landmasses “blurring” their histories.

By examining the mite species DNA, the researchers discovered a remarkable correlation between the current pattern of distribution and the makeup of Pangea 255 million years ago. One species of harvester mite found in Florida was not related to other North American species but similar to those found in West Africa. By determining the rate of genetic variation, Dr. Giribet and his team can estimate when landmasses separated from one another providing fascinating detail into an often unclear ancient history.

The New York Times



  1. #1 Stuart Coleman
    August 28, 2007

    Those original ranges look awfully big for a species that can’t move across North America in 255 million years…

    But it’s still pretty convincing and very cool research.

  2. #2 J-Dog
    August 28, 2007

    Excellent! Thanks for the post.

  3. #3 Will
    August 29, 2007

    Very very interesting research, but like Carl Zimmer, you refer to a daddy longlegs, without clarifying what type you’re talking about; it’s variously used to refer to three different arthropods in different parts of the world: a harvestman, a spider and, to me and just about every other Brit, the crane-fly. Obviously, it’s not relevant to research, but it might leave a Brit (who doesn’t know they’re using a colloquialism when they say daddy longlegs) thinking that crane flys and harvestmen are more closely related than they are.

  4. #4 Mrs Tilton
    August 29, 2007

    Hi, love what you’ve done with the place. And the article is fascinating. So it pains me to have to come over all critical, but: surely at least one of those photos is wrong?

    The one on the right — what looks like a close-up EM photo — is, I am practically certain, not an opilione (harvestmen and the like) but a spider. Spiders, like the animal in the picture, have a prosoma (front bit) and opisthoma (back bit) connected by a “wasp-waist” pedicel; opiliones have the same basic body division, but the front and back have such a fat “join” that the animals seem to have but a single segment. Further, all the opiliones that I know have but two eyes, not the eight that this animal, and your typical spider, can boast. Indeed, to judge by the eye pattern and the very small chelicerae, I’d bet it’s not merely a spider, but a member of genus Pholcus — the very spiders that share the nickname “daddy-longlegs” with harvestmen and crane flies!

    Now I don’t know very much about opiliones, and I suppose there could be some wasp-waisted, eight-eyed versions out there. But is it not possible that some copy-editor at the Times fed “daddy longlegs” into Google Image Search (or something similar), and dropped the resulting photo into the article without realising that there’s more than one sort of long-legged daddy?

  5. #5 Andrew Bleiman
    August 29, 2007

    Well I’ll say one thing, the comments have sure changed since joining ScienceBlogs!

    Typical comment prior to SB: “That f%$king bug is SICK yo!”
    Typical comment post SB: (see above)

    Anyway, Mrs. Tilton no apologies necessary. You sound like you are more than a little informed yourself, but I think I know just the team to ask. I will reply or post their response.

    Thanks! – Andrew (the older, wiser, handsomer Bleiman brother)

  6. #6 Mrs Tilton
    August 29, 2007

    Thanks for the kind words, Andrew, but I am a mere amateur. Still, that f%$king bug does look pretty nonopilionish…

    And I have reason for embarrassment myself; that word in my comment above should, of course, be “opisthosoma”.

  7. #7 Andrew Bleiman
    August 29, 2007

    you misspelled opisthosoma?!

    oh the shame…

  8. #8 Andrew Bleiman
    August 29, 2007

    Dear Mrs. Tilton,

    You are most certainly correct. The eight eyes are a dead giveaway. Special thanks to Bug Girl for verifying this for us.

    I think I speak for Zooillogix and our kid sister, the NY Times, when I say we sincerely apologize for the error and any emotional suffering it may have caused.

    Team Zooillogix

  9. #9 Myles na gCopaleen
    August 30, 2007

    Responding to Stuart Coleman’s post a while ago, my guess is that the harvestmen did make it across North America; there are (evidently) 5,000 species of the things, and the map probably only shows the selection of species usefully near tectonic plate borders.

    Excellent article as usual. Many thanks.

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