Sexual dimorphisms in pholcid spiders

The extreme sexual size dimorphism of some spiders has long attracted the attention of biologists and triggered countless prominent studies on the phenomenon. This in turn has resulted in a widespread bias in the view of spider sexual dimorphisms, even in reviews on sexual dimorphism that looked beyond size. The present article challenges this view by exemplarily documenting sexual dimorphisms in a single family of spiders, the Pholcidae. It offers a comprehensive overview of sexual dimorphisms in this group, derived from the taxonomic literature. Sexual dimorphisms occur in the prosoma (ocular area, clypeus, sternum), abdomen, chelicerae, legs, sensory organs (setae, tarsal organs), and in coloration. In addition, this review provides a rough and conservative estimate of the number of independent origins of sexual dimorphisms in Pholcidae, based on published morphological and molecular phylogenies and character mapping; more than 120 independent origins are hypothesized. The first general conclusion is that spiders show a wealth of sexual dimorphisms beyond size, even in a family that is virtually absent from the general literature on spider sexual dimorphism. The second conclusion is that the taxonomic literature should be more widely appreciated as a rich source of information, not just as a provider of names. However, much of this information is not easily extracted from taxonomic papers. It is primarily the taxonomists’ responsibility to do that.