The dark side of an island radiation: systematics and evolution of troglobitic spiders of the genus Dysdera Latreille (Araneae : Dysderidae) in the Canary Islands

Abstract

The spider genus Dysdera Latreille is an excellent model for the study of the evolution of cave life: ten species are known to exist exclusively in the subterranean environment of the Canary Islands, where the genus has undergone local diversification. In the present paper, two new troglobitic species (Dysdera madai, sp. nov. and D. sibyllina, sp. nov.) and the previously unknown sex of five additional species are described and illustrated: the males of D. gollumi Ribera & Arnedo, 1994, D. hernandezi Arnedo & Ribera, 1999 and D. labradaensis Wunderlich, 1991; and the females of D. andamanae Arnedo & Ribera, 1997 and D. gibbifera Wunderlich, 1991. The first direct evidence of troglobitic members of Dysdera in micro- and mesocaverns are reported. The evolution of cave life as hypothesised following a combined morphological and molecular phylogeny is investigated. Troglobitic Canarian Dysdera species have colonised the underground on eight independent occasions. The Dysderidae groundplan represents a preadaptation to cave life and has facilitated the colonisation of caves. Canarian members of Dysdera have a predominantly parapatric mode of speciation, although postspeciation changes in distribution may have obscured allopatric processes. Eye regression and, to a lesser extent, larger body size and appendage elongation characterise troglobitic species. The different levels of troglobiomorphism are interpreted as local adaptations to heterogeneous subterranean conditions. The high levels of sympatry among troglobites are explained by trophic segregation and changes in prey capture strategy were involved in the single identified case of subterranean speciation in the group.