PhD week 19: Dissections

Image of Rhabdoscelus obscurus male genitalia, from Sharp and Muir (1912). Courtesy of the Biodiversity Heritage Library. Licence: CC: BY-SA-NC.

As part of the process of undergoing a taxonomic revision of an insect group, it is important to consider the internal anatomy of the organisms in question. In particular, characteristics of the male genitalia are especially useful for differentiating between species, and for ascertaining relationships between species. For an example of how differences in genitalia can be more obvious than external characters, check out the beautiful leaf beetles Spilopyra sterlingi and S. sumptuosa (compare figures 5 vs 6 and 82 vs 84).

One of the pioneers who investigated insect genitalia in a taxonomic context was David Sharp, who in conjunction with his son-in-law Frederick Muir, published a nearly 200 page monograph that spanned the breadth of beetle diversity. It took several decades for the technique to take hold, but these days, if you have a look at any of the insect taxonomy papers in Zootaxa or Zookeys, it is likely that you will find that these characters have been used in that research. The problem with the technique is that is holds no relevance to readers who are not familiar with the taxon, but for those who are these drawings are frequently the most useful part of the paper.

The process of insect dissection is fairly straightforward—soften the insect, remove the abdomen, open it up to reveal the structures of interest, and then tease them out. Doing it on a creature that is around 3 mm can be a bit challenging. Like everything, the process is fairly intimidating at first but as one becomes more comfortable and skillful at the technique, it quickly becomes a simple routine that is done rapidly and easily. Of course, once the data is collected, it then has to be interpreted! However, that is a story for another time.

References:
Reid CAM, Beatson M. 2010. Revision of the Australo-Papuan genus Spilopyra Baly (Coleoptera: Chrysomelidae: Spilopyrinae). Zootaxa 2692: 1–32
Sharp D, Muir F. 1912. The comparative anatomy of the male genital tube in Coleoptera. Transactions of the Entomological Society of London (3) 477–642

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Read:
   McCulloch D. 2010. A History of Christianity: The First Three Thousand Years London: Penguin
   Psalms 77–80

Websites:
Fitting models to discrete characters
Wikipedia—Vernier scale
Wikipedia—Gloria Patri
Systematics and Biogeography— the blog of David Williams and Malte Ebach

Watched:
Star Trek: Deep Space Nine Season 4