Bribiesca Contreras G., Verbruggen H., Hugall A.F. & O'Hara T.
Plate tectonics shape spatio-temporal patterns of tropical brittle stars
Journal of Biogeography : submitted


Aim: Biogeographic barriers emerged in the tropical oceans as continental masses moved with plate tectonics, and as the tropics contracted to lower latitudes from the late Eocene. These barriers have shaped tropical biodiversity. We characterise large-scale diversity patterns for tropical brittle stars and investigate the effect of biogeographic barriers on these in space and time.
Location: Shallow-water (<200 m) tropical oceans.
Taxon: Tropical shallow-23 water brittle stars.
Methods: We fully integrate phylogenetic and biogeographic model uncertainty to test and quantify the biogeographic structuring across the major ocean basins for five families of brittle stars. These are well sampled in our phylogenies (173 species, 1462 exons, 275 kbp), covering 36-95 percent of the tropical shelf species of each family. We define major bioregions based on patterns of phylogenetic beta diversity.
Results: We find congruence between patterns of shared ancestry of regions and inferred biogeographic histories. Model-averaged biogeographic reconstructions show that faunal patterns reflect the emergence of biogeographic barriers in the tropical world, with evidence of vicariant events driven by the opening of the Atlantic Ocean, the narrowing of the Tethyan Seaway and the rise of the Isthmus of Panama.
Main conclusions: Biogeographic barriers almost completely isolated regional faunas, and the EPB represents an important barrier for dispersal of brittle stars, with only limited, very recent bidirectional dispersal detected through this stretch of open water. Divergence age estimates predate the onset of the different barriers, suggesting that changes associated to the gradual emergence of the different barriers had a stronger effect on the evolutionary history of tropical shallow-water brittle stars.

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