Biogeography of Long-Jawed Spiders Reveals Multiple Colonization of the Caribbean

Dispersal ability can affect levels of gene flow thereby shaping species distributions and richness patterns. The intermediate dispersal model of biogeography (IDM) predicts that in island systems, species diversity of those lineages with an intermediate dispersal potential is the highest. Here, we tested this prediction on long-jawed spiders (Tetragnatha) of the Caribbean archipelago using phylogenies from a total of 318 individuals delineated into 54 putative species. Our results support a Tetragnatha monophyly (within our sampling) but reject the monophyly of the Caribbean lineages, where we found low endemism yet high diversity. The reconstructed biogeographic history detects a potential early overwater colonization of the Caribbean, refuting an ancient vicariant origin of the Caribbean Tetragnatha as well as the GAARlandia land-bridge scenario. Instead, the results imply multiple colonization events to and from the Caribbean from the mid-Eocene to late-Miocene. Among arachnids, Tetragnatha uniquely comprises both excellently and poorly dispersing species. A direct test of the IDM would require consideration of three categories of dispersers; however, long-jawed spiders do not fit one of these three a priori definitions, but rather represent a more complex combination of attributes. A taxon such as Tetragnatha, one that readily undergoes evolutionary changes in dispersal propensity, can be referred to as a 'dynamic disperser'.