Getting Along Fine

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The thick legged fiddler crab, Uca crassipes, from Kaledupa

I know updates have slowed down a bit on TGAS, which I did not intend to happen, but I have been working diligently on sorting my photos and putting my arthropod observations into a database. Just last night I celebrated reaching the end of 2011 in my photo backlog. One of the best experiences I had in 2011 was going to the site of the highest recorded sympatric diversity of fiddler crabs (genus Uca) in the world. One of them, Uca cryptica, was first described based on museum specimens that lacked locality information. A later study, from this exact site, determined where they actually came from.

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The formerly cryptic Uca cryptica

In Kaledupa, one of the islands of the Indonesian Wakatobi chain, in a small habitat patch between crowded houses live ten (!) species of fiddler crab together in harmony. I was an undergraduate at the time and I was helping a graduate student with her ecological study that examined what factors allowed such a great diversity of similar organisms with similar lifestyles to be able to coexist happily (well, at least they seemed happy). Hint: it involves some sort of niche partitioning. Also, it didn’t hurt that this variable habitat included both mangrove forest and coral reefs, leading to sediments that I imagine are both calcium rich and high in organic material, and fiddler crabs generally feed on particles in sediment.

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The tetragonal fiddler crab, Uca tetragonon

Along with the fiddler crabs live a distant relative, the sentinel crab (Macropthalmus sp.), a member of the same superfamily (Ocypodoidea) but in a separate family than the fiddler and ghost crabs (Macropthalmidae). These crabs lack the dramatically huge chelipeds that characterize male fiddler crabs, but they are still sexually dimorphic, with males having much larger claws than their female counterparts. For whatever stochastic evolutionary reasons, despite their similar lifestyle the sentinel crabs have not diversified as much or colonized nearly as much of the world’s coasts as fiddler crabs.

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A sentinel crab, Macropthalmus sp.

Although I only got to help with this project for a few days, I really enjoyed it and have very fond memories of it. It’s definitely a spot I would love to return to with my newer, better lenses and my improved photography know-how.

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