Habitat choice by allelic variants in Xiphophorus variatus (Pisces: Poeciliidae) and implications for maintenance of genetic polymorphism

Stream pools in NE Mexico exhibit gradients in dissolved oxygen (DO) concentration with low DO at the upstream ends. These pools contain populations of variable platyfish which are polymorphic at an autosomal locus that affects tailspot pigmentation. Adult males of the cut-crescent morph have a lower metabolic rate than wild type males. Among adult males, all morphs were found in equal proportions at the upstream and downstream ends of the pools, except cut-crescents, which were distributed preferentially toward the upstream ends. The opposite distributional pattern was found among adult females. Habitat choice may contribute to the stability of the tailspot polymorphism, especially because preferences differing between the sexes can lead to disassortative mating -from Author