Aspects of the Polychromatism in Populations of the Gulf of California Browncheek Blenny, Acanthemblemaria crockeri (Blennioidea: Chaenopsidae)

Abstract

The relationships of the red and melanic color phases of the browncheek blenny, Acanthemblemaria crockeri, are examined. Pure populations of the red phase occur near the heads of the San Lucas and Los Frailes submarine canyons. Introgressive populations of the two phases occur together in a zone of sympatry from Los Frailes to at least Guaymas (central Gulf of California), where the red phase is limited almost completely to females that vary from pure red to intermediate (combination of the red and melanic phases). These red and intermediate females are both less abundant and decreasingly red as one goes north in the zone of sympatry. All males in the zone of sympatry are of the melanic phase and the proportion of melanic phase females increases abruptly in central gulf populations. The distribution pattern suggests: 1) the pure red phase populations of the cape region of Baja California probably developed as an insular population where red can be adaptive in these deeper submarine canyon populations; 2) these pure red phase populations may be homozygous for the red allele; 3) red phase males are not fit north of the cape region either because nonmelanic males cannot attract females (melanic color is important in sexual displays) or because red is obvious and red individuals are removed by predators or a combination of both; and 4) the intermediate phase females are maintained in central gulf populations because of selection for increased sexual dichromatism. Unfortunately, these suggestions do not, at present, adequately explain the odd sex-related distribution of individuals in the zone of sympatry.