Biogeography of the Neotropical Exophthalmus genus complex (Entiminae)
The Exophthalmus genus complex (Curculionidae: Entiminae) contains a large radiation (>90 species) in the Caribbean region and about another 50 species on the Neotropical mainland. The Caribbean species show a high degree of single-island endemicity, with more than 90% of the species found from only a single island. This project aims to reconstruct a molecular phylogeny of the Exophthalmus genus complex and investigate the historical biogeography of this group.
The Caribbean is an area with an exceedingly complex geologic history, and has been considered a "natural laboratory of biogeography and evolution" (Ricklefs and Bermingham, 2008). Past studies have focused heavily on vertebrates, owing in part to better knowledge of these groups. In contrast, research on the historical biogeography of Caribbean invertebrates, particularly the arthropods, has remained relatively stagnant, with only a few recent analytical biogeographic studies. My study will contribute to a better understanding of the biogeography of arthropods of the Caribbean.
A recent development added founder event speciation into biogeographic models by introducing the free parameter j (jump) for founder-event jump dispersal, whereby one daughter lineage inherits the ancestral range and another daughter lineage “jumps” to a new area via founder-event speciation. I am interesting in testing this new biogeographic mode in my study.
The patterns of distribution, diversity and endemism in the Exophthalmus genus complex raise numerous questions of broader relevance, as follows. What driving forces have shaped these patterns of distribution and endemism? Do founder-event jump dispersal models provide a best fit for modeling the biogeography history of the complex? How have extant lineages come to occupy both continental and island regions? Which overarching hypothesis of Caribbean biogeography (vicariance, dispersal and GAARLandia) is most closely aligned with this radiation?
Through successive collecting efforts, our lab has assembled a large collection of specimens belonging to the Exophthalmus genus complex from a wide range of localities representing both the Caribbean region and the Neotropical mainland. More than 10 field trips were conducted in eight Caribbean islands and five countries on the mainland. I participated in one such trip to Cuba in 2013.
I have gathered a data set comprising 65 recognized ingroup species of the Exophthalmus genus complex and 26 outgroup terminals. I performed phylogenetic reconstruction and molecular dating based on six genes, using a relaxed clock with fossil calibration points. Biogeographic history reconstructions were inferred with the R package BioGeoBEARS. Likelihood versions of three commonly used biogeographic models (DEC, DIVA and BayArea) were implemented and compared with models adding founder-event jump dispersal and dispersal influenced by prevailing water currents.
Significant results include: (1) model selection strongly favors biogeographic models that included founder-event jump dispersal; (2) the Neotropical mainland was colonized by species from the Caribbean in early Miocene; (3) in situ diversification or range-copying accounts for a majority of the biogeographic events in the Exophthalmus genus complex, whereas inter-island dispersal is relatively infrequent; and (4) when jump dispersal is modeled, the three biogeographic models, DEC, DIVA and BayArea, perform similarly.
A former undergraduate student researcher, Usmaan Basharat, participated in this project. Usmaan was an awardee for the Undergraduate Minority Student Travel Award given by the National Evolutionary Synthesis Center, for attending the 2014 annual Evolution Meeting.
A preprint is available for viewing and commenting at Biorxiv, but also uploaded here (below).