Wednesday, September 11, 2013

The limits of morphology

I was told early on as a graduate student that an insect taxonomist should "kill first, ask questions later" during fieldwork. This was usually said in the context that you might lose a rare specimen if you spend time looking at it, rather than putting in a vial. I am here to tell you that I have deeply regretted following that advice.

Every single time I am working on a taxonomic paper I catch myself having the same wish: "I wish I had seen these specimens alive, just to get a glimpse of how they are using these structures." Morphology can tell us a lot of things but sometimes a dead insect hold its secrets very well.

Exhibit A: In a paper published in 2005, Steve Ashe and I revised the genus Philothalpus. These are striking beetles with questionable taxonomic affinities (at least according to DNA).
Philothalpus brooksi

Abdominal sternum VII

Males in this genus have a perplexing structure (indicted by a white arrow on the figure above) on the ventral side of their abdomen, specifically on the 7th abdominal sternum. Back then we called it a "porose structure". Truth is, we have no idea what it is. A hole on the body with setae around it. Only males have it. But how do they use it? I have no clue. I guess I will be inclined to accept the notion that is used in male/female interactions since it is only present in males but, boy, if only I had seen these guys alive...

The example above came to mind when I recently examined a species (in another genus) with a similar structure:

Exhibit B:

 The structure is present in the same abdominal segment (VII) but it is clearly different than the one above. Are these structures homologous?  Are they used for the same purpose? Morphology cannot answer these questions. Sure, we can do fancy evo-devo here, but that requires live specimens, identifying conserved developmental genes and so on.

What we really need is good old basic natural history observations that can solve these problems. But "kill first, ask questions later" attitudes really do not help. So, next time you are in the field, jot down some observations before you kill those insects.

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