One species or two?

Published in Zoologischer Anzeiger 253 (2014), together with D. Dimitrov

When I collected these spiders in Taiwan, I thought I was collecting two different genera, Pholcus (left) and Leptopholcus (right). It was only back home with a good microscope that I realized that the two species were not only the same genus (Pholcus) but that they had almost identical genitalia. This is usually interpreted as a strong indication for conspecificity.

Here we describe these two putative species that differ conspicuously in their microhabitat (rocks vs. leaves), coloration, colour pattern, and body proportions, but have almost indistinguishable genitalia and cytochrome oxidase I (co1) sequences.

We decided to treat the two ‘morphs’ as species for three reasons: (1) they are easily distinguished by several characters; no intermediate specimens were found; (2) subtle yet consistent differences in genital (uncus) shape support the idea of reproductively isolated entities beyond the more conspicuous non-genital differences; (3) each locality provided both types of microhabitat but only one of the two species, arguing against environmental plasticity or polymorphism.

We conclude that probably a very recent expansion into a novel microhabitat has led to speciation and rapid ecological and non-genital differentiation, with insufficient time to accumulate significant genital and genetic differences.