Phylogeography of the widespread Caribbean spiny orb weaverGasteracantha cancriformis

Abstract

BackgroundModern molecular analyses are often inconsistent with pre-cladistic taxonomic hypotheses, frequently indicating higher richness than morphological taxonomy estimates. Among Caribbean spiders, widespread species are relatively few compared to the prevalence of single island endemics. The taxonomic hypothesisGasteracantha cancriformiscircumscribes a species with profuse variation in size, color and body form. Distributed throughout the Neotropics,G. cancriformisis the only morphological species ofGasteracanthain the New World in this globally distributed genus.MethodsWe inferred phylogenetic relationships across Neotropical populations ofGasteracanthausing three target genes. Within the Caribbean, we estimated genetic diversity, population structure, and gene flow among island populations.ResultsOur findings revealed a single widespread species ofGasteracanthathroughout the Caribbean,G. cancriformis, while suggesting two recently divergent mainland populations that may represent separate species, diverging linages, or geographically isolated demes. The concatenated andCOI(Cytochrome c oxidase subunit 1) phylogeny supported a Caribbean clade nested within the New World. Genetic variability was high between island populations for ourCOIdataset; however, gene flow was also high, especially between large, adjacent islands. We found structured genetic and morphological variation withinG. cancriformisisland populations; however, this variation does not reflect genealogical relationships. Rather, isolation by distance and local morphological adaptation may explain the observed variation.