Evidence for Miocene overwater colonization in Caribbean Cyrtognatha spiders

Abstract

Island systems provide excellent arenas to test evolutionary hypotheses pertaining to gene flow and diversification of dispersal-limited organisms. Here we focus on an orbweaver spider genus Cyrtognatha (Tetragnathidae) from the Caribbean, with the aims to reconstruct its evolutionary history, describe its biogeographic history in the archipelago, and to estimate the timing and route of Caribbean colonization. Specifically, we test if Cyrtognatha biogeographic history is consistent with an ancient vicariant scenario (the GAARlandia landbridge hypothesis) or overwater dispersal. We reconstructed a species level phylogeny based on one mitochondrial (CO1) and one nuclear (28S) marker. We then used this topology to constrain a time-calibrated mtDNA phylogeny, for subsequent biogeographical analyses of over 100 originally sampled Cyrtognatha individuals. Our results suggest a monophyletic radiation of Caribbean Cyrtognatha, containing 11 to 14 species that are exclusively single island endemics. Our analyses refute vicariance and instead support an overwater colonization to the Caribbean in mid-Miocene. Having colonized Hispaniola first, Cyrtognatha subsequently dispersed to, and diversified on, the other islands of the Greater, and Lesser Antilles.