Melanism in a High Elevation Population of Gasterosteus aculeatus

Abstract

A population ofGasterosteus aculeatus from Holcomb Creek in the Mojave River drainage occurs at an elevation of 1,960 m in the San Bernardino Mountains, California. This population is unique among California stickleback populations in having some males with melanistic nuptial coloration, a derived character. This population also is characterized by short spines and very low lateral plate counts (mode at zero plates per fish), indicative of a low level of predation by fishes. Possession of this combination of character states probably indicates that the population is native and could have occupied Holcomb Creek since it was on a coastal peneplain that was uplifted without significant erosion during the Pleistocene. Alternatively, the population could have been introduced with trout in the last 100 years, and subsequently evolved melanism or lateral plate and spine length reduction. This is the first report of a melanistic population of G. aculeatus outside of the Pacific Northwest, North America.