Phylogeography of the widespread Caribbean spiny orb weaver Gasteracantha cancriformis.

Amanda Crastz-Flores,Ingi Agnarsson,Alma Basco,Lisa Chamberland,Fabian C Salgado-Roa,Greta J Binford

doi:10.7717/peerj.8976

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 hypothesis Gasteracantha cancriformis circumscribes a species with profuse variation in size, color and body form. Distributed throughout the Neotropics, G. cancriformis is the only morphological species of Gasteracantha in the New World in this globally distributed genus.MethodsWe inferred phylogenetic relationships across Neotropical populations of Gasteracantha using 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 of Gasteracantha throughout the Caribbean, G. cancriformis, while suggesting two recently divergent mainland populations that may represent separate species, diverging linages, or geographically isolated demes. The concatenated and COI (Cytochrome c oxidase subunit 1) phylogeny supported a Caribbean clade nested within the New World. Genetic variability was high between island populations for our COI dataset; however, gene flow was also high, especially between large, adjacent islands. We found structured genetic and morphological variation within G. cancriformis island populations; however, this variation does not reflect genealogical relationships. Rather, isolation by distance and local morphological adaptation may explain the observed variation.

Highlights

Tropical island archipelagos are some of the most biodiverse and species-rich ecosystems on the planet (Mittermeier et al, 2011)
Phylogenetic inferences for both the single-gene (COI) and pruned (42 terminals) BEAST concatenated datasets indicated three clades (PP > 0.75) within the New World—two mainland clades and a predominantly island clade that included some individuals from South Eastern United States (SEUS) (Fig. 2; Fig. S1)
We found that G. cancriformis includes a distinctive genetic group that is largely from the Caribbean islands, which suggest that the sea is a geographic barrier that promotes genetic differentiation between islands and mainland

Summary

Introduction

Tropical island archipelagos are some of the most biodiverse and species-rich ecosystems on the planet (Mittermeier et al, 2011). The Caribbean islands are a biodiversity hotspot, rich in endemic species (Mittermeier & Goettsch Mittermeier, 2005; Ricklefs & Bermingham, 2008). Oceanic islands can have both volcanic and sedimentary (e.g., Lesser Antilles, Bermuda) and non-volcanic (e.g., limestone islands of the Bahamas) origins Species compositions on these islands are characterized by long-distance dispersals (LDD) (De Queiroz, 2005; Cowie & Holland, 2006; Gillespie et al, 2012). Results: Our findings revealed a single widespread species of Gasteracantha throughout the Caribbean, G. cancriformis, while suggesting two recently divergent mainland populations that may represent separate species, diverging linages, or geographically isolated demes. Isolation by distance and local morphological adaptation may explain the observed variation

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