Phylogenetic Relationships of North Pacific Estuarine Gobies and Elevated Endemism in the Gulf of California

North Pacific bay gobies, largely marine temperate and estuarine, have historically been divided into the Chasmichthys and Astrabe groups. Chasmichthys is composed of substrate/surface-dwelling, small gobies with a full complement of fins, scales and pigmentation. The Astrabe group comprises elongate, pale species that are obligate burrow or crevice dwellers. Each distinct morphological/ecological group exists on both sides of the Pacific, suggesting that trans-Pacific migration may have played a role in the evolutionary history of bay gobies. Preliminary phylogenetic results generated from one mitochondrial and four nuclear loci indicate that these groups are not valid, as obligate infaunal forms do not form a monophyletic group. For North American taxa, several species are endemic to the Gulf of California, with their distributions concentrated in the northern part of the Gulf. Moreover, at least two genera (Gillichthys and Quietula) each comprise sister species pairs where one is endemic to the Gulf and the other is distributed both inside and outside of the Gulf. Divergence times for two Gulf endemics (G. seta and Q. guaymasiae) suggest that speciation may have occurred prior to tectonic formation of the Gulf, consistent with a refugium hypothesis. However, the generation of endemic species of bay gobies in the northern Gulf has continued since its formation, as evidenced by results from the genus Gillichthys. A distinct clade within G. mirabilis is restricted to the northern Gulf, and a narrow range of secondary contact with a southern Gulf lineage exists near the vicinity of the Midriff Islands. In addition, the recently resurrected species G. detrusus appears to have diverged from its common ancestor coincident with or shortly after formation of the Gulf, and is found exclusively in the Colorado River Delta. The extremely limited distribution of this endemic species highlights the importance of conservation in the Colorado Delta and upper Gulf, where native biodiversity has been threatened by decades of fresh water diversion, overfishing and coastal development.