An Interdisciplinary Approach to Studying Incipient Speciation: The Role of Seaways in the Phylogeography of the American Shadow Goby

The tenets of phylogeography include documenting contemporary patterns of biodiversity and discovering the mechanisms underlying those patterns, including processes governing incipient speciation.  A prime region to study such processes is Baja California, where understanding the effects of tectonic changes on the evolution, and possible speciation, of disjunct species is possible.  The contested Viscaíno Seaway hypothesis suggests that a seaway existed 1-2 million years ago in the midpeninsular region of Baja California, connecting the Gulf of California to the Pacific Ocean.  The argument follows that cessation of this seaway subsequently isolated marine and estuarine species in the Gulf, leading to incipient stages of speciation for these taxa.   

The work presented here uses three divergent estuarine fishes (Quietula y-cauda, Gillichthys mirabilis, Sphoeroides annulatus) for a comparative phylogeographic study across the region to evaluate, using recent statistical phylogeographic advances, a priori hypotheses of seaway migration.  To complement this genetic evidence, the geologic record is also being used to reconstruct the paleoenvironment and age of the purported seaway.  Preliminary geologic data reveals a shallow marine environment in the purported region, as evidenced by sedimentological and fossil evidence. Ages, however, have yet to be determined.  Preliminary results from mitochondrial sequence (control region) and microsatellite data from these analyses are consistent with the seaway hypothesis, along with strong evidence for more recent glacially-driven refugia and range expansions in southern California.  Additionally presented are future goals of this work, which involve developing a methodology to enable phylogeographic applications of high-throughput sequencing power to develop multi-locus, informative nuclear loci for taxa-rich studies.