Two new species of litter-dwelling Metagonia spiders (Araneae, Pholcidae) document both rapid and slow genital evolution

摘要

The observation that genitalia, rather than other characters, are useful in distinguishing species has resulted in the statement that genitalia evolve relatively rapidly. In this paper we claim that relatively rapid evolution of genitalia may often be restricted to the shapes, numbers, and sizes of individual structures. In contrast, the more basic pattern, including the presence or absence of structures and their interrelationships (the bauplan), does not seem to evolve more rapidly than other (nongenital) aspects of morphology. We document this idea by contrasting two litter-dwelling pholcid species, Metagonia petropolis sp. n. and M. paranapiacaba sp. n., with their mostly leaf-dwelling congeners. Significant differences occur with regard to nongenital aspects of morphology as well as shapes of individual genital structures, but the bauplan of their genitalia is basically the same.