Phylogenetic Relationships and Adaptive Shifts among Major Clades of Tetragnatha Spiders (Araneae: Tetragnathidae) in Hawai'i

Abstract

The role of adaptive shifts in species formation has been the subject of considerable controversy for many years. Here we examine the phylogeny of a large radiation of Hawaiian spiders in the genus Tetragnatha to determine the extent to which species splitting is associated with shifts in ecological affinity. We use molecular data from ribosomal 12S and cytochrome oxidase mitochondrial DNA, and allozymes to assess phylogenetic affinity. Ecological associations were recorded for all species under study, and shifts are considered in the context of the phylogeny. Results indicate that there are two major clades of Hawaiian Tetragnatha, one of which has abandoned web building (spiny-leg clade), while the other retains the ancestral condition of web building. Within the spiny-leg clade, the molecular information suggests that the species on anyone island are generally most closely related to each other. Preliminary results for the web-building "complex" of species indicate that there may be groups of web builders that have speciated in a similar manner. Results of the study suggest that, at least within the spiny-leg clade, matching sets of taxa have evolved independently on the different Hawaiian islands. There appears to have been a one-to-one convergence of the same set of "ecomorph" types on each island in a manner similar to that of lizards of the Caribbean.