The Effects of Sex Determining System, Predation and Water Color on Color Pattern Variation

Two behavioral sources of selection that are often found to act in opposition are predation and mate choice: traits that increase an animal's attractiveness to mates may often increase the animal's risk of predation. In guppies, predation has been found to select for cryptically colored males while female mating behavior selects conspicuous males. Conspicuous coloration in guppies is restricted to males through sex-limitation.  In platyfish, however, conspicuous coloration is not restricted to males and, therefore, predation would be directed at both conspicuous females as well as males.  There is intraspecific variation in the mode of sex determination in platyfish: several populations are male heterogametic (XX, XY), like guppies, and others have three sex chromosomes, with three female genotypes (WX, WY, XX) and two male genotypes (YY, XY). Previous studies of these fish have resulted in an excellent understanding of the underlying genetics of 31 color patterns.  Intraspecific variation in sex-determination and the well-established genetics of coloration provide a unique opportunity to investigate the effect of predation and mate choice on the evolution of traits whose genetic basis is known, both when males have a unique sex chromosome and when the sex chromosomes that appear in males are shared with females. I am conducting an on-going field study investigating variation in color pattern allele frequencies in platyfish populations ranging from central Mexico to Belize. This work is directed at evaluating how the sex determination system and differing environmental conditions, including available light, predation levels, water color and sympatric species abundances, affect color pattern variation.

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