September 14, 2008

Busy with Beetles: Collections and Hypotheses

I haven't had much free time since returning from Florida, hence the lack of updates here. My schedule this semester is rather packed. For instance, on Thursdays I have two hours of open time between 10 AM and 9 PM which I will be using to eat. It will all work out, but it will also take a couple of weeks for me to get settled into this new calendar. As it stands right now, though, I haven't even had the chance to edit my photos from the trip.

I have, however, finished identifying the beetle specimens to the extent I've been able without molecular work. It's not a bad collection for under a week's time, and a couple of the species are of particular interest for reasons I'll mention below.

Megalodacne heros is without doubt the most visually spectacular of the bunch. It's one of the largest (if not the largest) of the Erotylidae and quite a colorful insect. I collected four specimens from the pore surface of Ganoderma applanatum, which is not nearly so common in Florida as it is in cooler climates. In Florida, it seems to be replaced by species in the Ganoderma lucidum complex. I didn't find M. heros on any other fungi, including the numerous G. applanatum specimens I saw in the field. That might be chance, of course.

A teneb mimic of M. heros, Platydema ellipticus, was also collected from the pore surface of Phellinus gilvus. While this beetle is substantially smaller than Megalodacne, it has what I suspect is aposematic coloration. That is to say, natural selection has favored individuals with markings similar to the larger and more toxic erotylid in this particular teneb. Five specimens of this insect came back with me.

Platydema nigratum is a close relative of the above. It doesn't have much going for it in terms of coloration, but this is an exciting find for me for two reasons. First, the habitat of this beetle is uncertain. I can say definitively that I collected it from between fruiting bodies of Stereum ostrea, and I watched one specimen chewing on that fungus. I have no doubt at all that it is a fungivore and macrophagous at that. Second, the larva of this species isn't described in the literature. I recovered a specimen of what I believe will turn out to be a larval P. nigratum from within the fleshy base of a relatively large S. ostrea sporophore. Once I've sequenced both adult and larva I should be able to connect the two definitively.

I collected numerous specimens of Neomida bicornis from two fungi. I first found them inside the same G. applanatum sporophores that had Megalodacne on their surface. I found specimens again several days later living in the context of Trametes elegans, a particularly fleshy member of the same genus that contains the ubiquitous turkey tail, T. versicolor. An interesting thing happened when I collected N. bicornis from that fungus that I wish I had noticed in the field. When I first started collecting, I found six specimens and put them in a microtube. Then I noticed additional galleries and collected fourteen more specimens in a second tube. When I brought them all back to the lab, it turned out that all six specimens in the first tube were male and all fourteen in the second were female. The probability of this happening purely by chance is so small that it suggests to me that males and females were segregated for some reason at the moment that I found the insects. I know nothing about the behavior of N. bicornis; I doubt that anyone has really investigated it. Also, it's worth noting that the specimens from Florida are very, very different from what's called N. bicornis in New England, which I've collected from Pycnoporus cinnibarinus at Wachusett. The Floridian specimens have an orange prothorax and males have straight horns. The New England version is dark metallic green and the male's horns are slightly curved. There's a chance, I think, that the two are really two different species and, indeed, I don't find any sequences for Neomida in EntrezGene other than one for a basidiomycete yeast from its gut discovered by Suh and Blackwell. I'm looking forward to pulling sequences from the northern and southern "morphs." If they do turn out to be two different species, I think I get to name one of them. The two insects look so different that I find it hard to believe they could be the same species.

I also found a second Neomida, N. ferruginea, in the context of a second G. applanatum sporophore. I only recovered one specimen of this rather drab little teneb, though. When I eventually do the phylogeny from the genus, I suspect that this beetle will be more closely related to the southern "morph" of N. bicornis than it is to the one from New England. That's just a hunch, of course.

Of course, no teneb hunting expedition would be complete without the recovery of a couple of specimens of Bolitotherus cornutus. I collected specimens of the widely-distributed beetle from both G. applanatum (the same cluster of fruiting bodies above) and G. lucidum on this trip. B. cornutus seems to be the most successful of the larger fungus-dependent tenebs of North America based on my experience. I can hardly help but find the insects whenever I search polypores. The genus, and in fact the whole tribe, is quite small as compared to other teneb tribes, but Bolitotherus seems to be the champ in sheer numbers. Having some specimens from Florida will give me the chance to eventually compare sequences from specimens from three states. Perhaps I'll someday investigate population genetic structure in this insect, which doesn't get around much but seems to be everywhere.

I also have a couple of specimens that I haven't been able to identify beyond family yet, including a few of what are probably Nitidulidae but are potentially Leiodidae, too. I'm hoping for the former, though. Nitidulidae seems to be a family with taxa in transition between feeding on the sap from tree wounds and living on the polypores that grow from those wounds. Most beetle families have hind feet with five segments (tarsomeres). Tenebrionidae, which I've hypothesized to be primitively macrofungivorous, have only four. Nitidulidae still have five, but many species in the family have a markedly decreased fourth tarsomere, so one can imagine a scenario in which the transition from living on the surface of a fungus and eating the hymenium (Erotylidae) leaves the beetles with five tarsomeres, there's a transitional state in which the fourth (or other) tarsomere is reduced as the beetles begin to tunnel into the fungi (Nitidulidae) and, ultimately, the tarsomere is lost entirely over time as a fully fungus-exploiting lifestyle is adopted (Tenebrionidae).

One of the fungi I collected also turned out to be an unusual specimen. A glossy, brown, trametes-like, sessile thing with subdaedaloid pores turned out to be the tropical Nigroporus vinosus. Nobody in my lab has seen it before. One of the ongoing projects in the lab is the exploration of wood-decaying fungi (N. vinosus is a white-rotter) for use in bioremediation. It may be worthwhile to mount another trip to look for unusual species to be cultured in this regard, too. We'll see about that. I'm planning on going back again at some point, anyhow, and perhaps swinging around the Gulf Coast a bit in the future to sample both polypores and beetles from more climes. I've barely scratched the surface here, after all.

Clearly, I've got a ton of work to do, and I haven't even really started yet... hence my absence from the blogosphere of late. Rest assured, though, that situation is only temporary. I have no intention of disappearing just yet!

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