The Delta Mudsucker, Gillichthys detrusus, a Valid Species (Teleostei: Gobiidae) Endemic to the Colorado River Delta, Northernmost Gulf of California, Mexico
Substantial genetic and subtle morphological characters document that the Delta Mudsucker or chupalodo delta, Gillichthys detrusus Gilbert and Scofield, 1898, family Gobiidae, is a valid species separate from its widespread sister species, the Longjaw Mudsucker, G. mirabilis Cooper, 1864. This species was erroneously placed in the synonymy of G. mirabilis in 1907 and has since remained unrecognized until this study. The Delta Mudsucker is restricted to a narrow zone of tidally influenced channels of the lowermost Colorado River and adjacent to the mouth of the river within its delta. It is the second fish species endemic to the river's delta in Mexico's Reserva de la Biósfera del Alto Golfo de California y Delta del Río Colorado (Upper Gulf of California and Colorado River Delta Biosphere Reserve). This study underscores the importance of continued reassessment of baseline and cryptic biodiversity, especially in habitats where initial assessment was scant prior to extensive anthropogenic influence.
Southern portion of the Colorado River delta showing the type locality and two recent collection localities of Gillichthys detrusus (modified from http://maps.google.com). Type locality at “Horseshoe Bend” in 1890 (Gilbert and Scofield, 1898) is approximated based on the 1908 USGS map of the region (Steve Nelson, pers. comm.). This locality is no longer part of the river due to eastward channel migration. The two recent collections are from near the former site of the boat landing, “Port Elizabeth,” off the lower main channel of the river, and adjacent to the shrimp farm at Estero Santa Clara on the eastern edge of the delta (geographic coordinates given in Table 1).
Phylogenetic relationships within the genus Gillichthys. Both trees were created in MrBayes (right: first intron of S7 ribosomal protein gene, left: cytochrome b), with posterior probabilities shown above branches and maximum likelihood bootstrap values (100 replicates calculated in GARLI) shown below branches. Specimen locality abbreviations follow Table 1.
Types and recently collected specimens of species of Gillichthys: (A) lectotype of G. detrusus, adult female, USNM 48127, “Horseshoe Bend,” MX; (B) syntype of G. mirabilis, adult male, USNM 5229, San Diego, CA, USA; (C) G. detrusus, adult male, GdeELZ2, “Port Elizabeth,” MX; (D) G. mirabilis, adult male, LACM 56805-1, Devereaux Slough, CA, USA.
Box-plots illustrating difference in mean discriminant scores between Gillichthys detrusus and G. mirabilis.
Contributor Notes
Associate Editor: D. Buth.