Meeting Abstract
Diversion of water from the Colorado River has converted the unique Colorado Delta from variably fresh and brackish environments to marine and hypersaline conditions – paralleling changes due to water extractions around the world. Diversions became extreme subsequent to the construction of Hoover Dam in 1935 and has now dramatically altered the delta environment, potentially impacting the Delta endemic fauna within the biodiverse northern Gulf of California. Here we explore the potential impact of loss of freshwater in the system on a poorly studied Delta endemic silverside, C. hubbsi (Crabtree), relative to its more widely distributed sister species, C. regis (Jenkins and Evermann), in the Gulf endemic genus Colpichthys. Using morphologic, mitochondrial, microsatellite and nuclear sequence data we document hybridization between historically differentiated species. This suggests that the loss of freshwater may have dissolved the ecological factors that once separated these species. However, we do not find strong evidence of a population bottleneck in C. hubbsi. Thus, while there may not be a dramatic impact of population reduction at this time, the species appears to be at risk due to introgression of genes from its sister following loss of ecologic separation. Further work on this system to identify the changing selection regime in genes under selection and to establish the pattern of genetic introgression using high throughput sequencing approaches is merited.
