|After doing some
work on asymmetric genitalia in pholcid spiders (papers on Metagonia
mariguitarensis and Kaliana [now Mesabolivar] yuruani), I was
wondering why asymmetric genitalia are so rare in spiders but so
widespread in insects. I was surprised to find that no review on insect
genital asymmetries has been written for over 70 years,
so I spent
several months digging for hundreds of papers on insect gentalia,
mating positions, genital mechanics, and insect relationships. The
story is fairly complex, but it all seems to boil down to one
fundamental difference between insects and spiders: the unpaired versus
paired male copulatory organs.
A short summary has been published in Genetica (2010; PDF).
Dorsal views of genitalia of two closely related species, one symmetric (left: Poecilopsyche pandu, Trichoptera), the other asymmetric (right: P. durdhyodhana); projections of tenth segment in grey (from Schmid, 1968).