Uncovering overlooked island diversity: colonization and diversification of the medically important spider genus Loxosceles (Arachnida: Sicariidae) on the Canary Islands
Our aim was to assess the evolutionary history of the spider genus Loxosceles on the Canary Islands. We unravelled its present diversity within the archipelago, and investigated its origin, mode and tempo of colonization to and between the islands using a phylogenetic framework.
Canary Islands, Madeira, Iberian Peninsula, North Africa, Mediterranean region, Guinea.
We conducted extensive sampling across the Canary Islands, and examined the phylogenetic relationships among the Canary Island representatives of the genus Loxosceles and with regard to species from western Africa and the Mediterranean Basin. We used an evolutionary criterion (general mixed Yule coalescent) to delimit the evolutionary lineages, and applied fossil and biogeographical calibration points to estimate dates for major cladogenetic events within the Canary Islands using a Bayesian framework.
Phylogenetic analyses revealed the existence of a well-supported clade formed exclusively by Canarian Loxosceles specimens, comprising seven allopatrically distributed evolutionary lineages. Major dispersal events between the islands occurred during the late Miocene. Representatives of the cosmopolitan Loxosceles rufescens were also found on the archipelago.
We have revealed the existence of an overlooked endemic group of medically important spiders. The pattern of diversity of this group fits well with the general dynamic theory of oceanic island biogeography, where maximum diversity is found on islands of intermediate age. The colonization pathway of the group is compatible with a stepping-stone model. Between-islands dispersal was the major driving force for diversification in the group, but a few within-island speciation events were also inferred, such as on Gran Canaria, where the Roque Nublo volcanic event acted as a vicariant agent, promoting the split between the two Gran Canarian lineages. The recently introduced L. rufescens is cohabiting with the endemic lineages.