Spintharus flavidus in the Caribbean-a 30 million year biogeographical history and radiation of a 'widespread species'

Austin Dziki; Greta J Binford; Jonathan A Coddington; Ingi Agnarsson

doi:10.7717/peerj.1422

Spintharus flavidus in the Caribbean-a 30 million year biogeographical history and radiation of a 'widespread species'

PeerJ. 2015 Nov 19:3:e1422. doi: 10.7717/peerj.1422. eCollection 2015.

Authors

Austin Dziki¹, Greta J Binford², Jonathan A Coddington³, Ingi Agnarsson⁴

Affiliations

¹ Department of Biology, University of Vermont , Burlington, VT , USA.
² Department of Biology, Lewis and Clark College , Portland, OR , USA.
³ Department of Entomology, National Museum of Natural History, Smithsonian Institution , Washington, DC , USA.
⁴ Department of Biology, University of Vermont , Burlington, VT , USA ; Department of Entomology, National Museum of Natural History, Smithsonian Institution , Washington, DC , USA.

Abstract

The Caribbean island biota is characterized by high levels of endemism, the result of an interplay between colonization opportunities on islands and effective oceanic barriers among them. A relatively small percentage of the biota is represented by 'widespread species,' presumably taxa for which oceanic barriers are ineffective. Few studies have explored in detail the genetic structure of widespread Caribbean taxa. The cobweb spider Spintharus flavidus Hentz, 1850 (Theridiidae) is one of two described Spintharus species and is unique in being widely distributed from northern N. America to Brazil and throughout the Caribbean. As a taxonomic hypothesis, Spintharus "flavidus" predicts maintenance of gene flow among Caribbean islands, a prediction that seems contradicted by known S. flavidus biology, which suggests limited dispersal ability. As part of an extensive survey of Caribbean arachnids (project CarBio), we conducted the first molecular phylogenetic analysis of S. flavidus with the primary goal of testing the 'widespread species' hypothesis. Our results, while limited to three molecular loci, reject the hypothesis of a single widespread species. Instead this lineage seems to represent a radiation with at least 16 species in the Caribbean region. Nearly all are short range endemics with several distinct mainland groups and others are single island endemics. While limited taxon sampling, with a single specimen from S. America, constrains what we can infer about the biogeographical history of the lineage, clear patterns still emerge. Consistent with limited overwater dispersal, we find evidence for a single colonization of the Caribbean about 30 million years ago, coinciding with the timing of the GAARLandia landbridge hypothesis. In sum, S. "flavidus" is not a single species capable of frequent overwater dispersal, but rather a 30 my old radiation of single island endemics that provides preliminary support for a complex and contested geological hypothesis.

Keywords: Adaptive radiation; Arachnology; Caribbean; Dispersal; Evolution; GAARLandia; Spintharus; Theridiidae; Zoology.

Grants and funding

Funding for this work comes from National Science Foundation (DEB-1314749 and DEB-1050187-1050253) to I Agnarsson and G Binford and NSF (DBI-1349205) to D Barrington, I Agnarsson and CW Kilpatrick. Additional funds came from the Smithsonian Institution 2013 SI Barcode Network to JA Coddington and I Agnarsson. Development of this project was further supported by a UVM APLE grant to A Dziki. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.