LIFE HISTORY STUDIES OF THE LESSER SNOW GOOSE (ANSER CAERULESCENS CAERULESCENS). VI. PLUMAGE POLYMORPHISM,...

The investigated the hypothesis that positive assortative mating for plumage coloration observed in populations of the dichromatic Lesser Snow Goose (Anser caerulescens caerulescens) evolved and persists due to selective advantages accruing to individuals choosing mates phenotypically similar to themselves. We examined potential differences between pure (white × white, blue × blue) and mixed (white × blue, blue × white) pairs for an array of fitness components related to both fecundity and viability. While no differences were detected for most components, mixed pairs consistently enjoyed enhanced nesting success relative to their pure counterparts. In addition, pre-reproductive viability and female offspring recruitment were significantly greater for mixed pairs for some of the cohorts examined. Not only have we failed to find enhanced reproductive success associated with positive assortment, we have provided evidence that there is some advantage associated with negative assortment. In light of our findings, we suggest: 1) that positive assortment results from the use of familial color as one element in species recognition; 2) that the enhanced fitness of mixed pairs, particularly with respect to nesting success, results from complementation of parental behavior; and 3) that while negative assortment will not likely become the rule in this population, the selective advantage of mixed pairs is a potential determinant of pair type frequencies in the La Pérouse Bay population.