Geologic and hydrologic concerns about pupfish divergence during the last glacial maximum

Martin et al.'s [1] double-digest, restriction-site-associated DNA sequencing of Death Valley pupfish species (Cyprinodon) and new time-calibrated phylogenetic analysis provide estimated divergence ages for North American pupfish at two scales. On the larger temporal and spatial scale, Martin et al. conclude that the Death Valley pupfish shared common ancestry with: Cyprinodon albivelis Rio Yaqui, Mexico, which drains into the northern Gulf of California, at ca 10 kyr; C. veronicae and C. alvarezi from isolated springs in Nuevo León, Guzmán Basin, northeastern Mexico [2], at ca 17 kyr; and Atlantic coastal pupfish including those from the Yucatan Peninsula, Mexico, and the Bahamas (C. artifrons, C. maya and others) at ca 25 kyr. Martin et al. supported these genetic divergences and temporal estimates in their phylogenetic tree with these statements: ‘these ages are consistent with increased population mixing expected from the formation of large pluvial lakes throughout North America during the most recent glacial period 12–25 thousand years (kya).’ and it ‘is not apparent how low-lying desert populations could have remained isolated within large inland seas … ’ On the smaller scale, Martin et al. also conclude that introgression among pupfish species and subspecies of the 300 km-long Amargosa River of Death Valley occurred in the last 150 years.