Evolution of distribution and habitat patterns in endemic millipedes of the genus Dolichoiulus (Diplopoda: Julidae) on the Canary Islands, with notes on distribution patterns of other Canarian species swarms

Abstract

Forty-six species of the genus Dolichoiulus, all endemic, occur on the Canary Islands The highest number of species occur on the largest, highest island (Tenerife); fewest occur on Lanzarote, Fuerteventura (low, xeric), El Hierro and La Palma (small, remote). Most of the Dolichoiulus species live on one island only, as in other endemic Canarian species swarms. The scarcity of pluri-insular Dolichoiulus species, in connection with information on phylogeny, suggests that speciation has mainly taken place within individual islands. Distribution patterns are partly governed by habitat differences between species, but vicariance patterns between species living in the same kind of habitat are evident on La Gomera and Tenerife. Dolichoiulus species occur in all kinds of natural habitats. Laurisilva and cave species are generally paler than other species. In the laurisilva of eastern Tenerife, microhabitat differentiation between species is pronounced. In some, but far from all, cases, species coexisting in the same microhabitat are of different sizes. The ancestral colonizing species of Dolichoiulus is/are hypothesized to have been small and to have lived in coastal habitats. Colonization of higher altitudes was usually accompanied by an increase in body size. Invasion of the laurisilva was usually accompanied by a habitat shift from the ground layer to logs.