Fluctuating asymmetry, spot asymmetry and inbreeding depression in the sexual coloration of male guppy fish

This paper tests the hypothesis that fluctuating asymmetry in exaggerated sexual traits is a sensitive indicator of genetic stress. Inbreeding was used to create genetic stress in two populations of male guppies collected from the Aripo and Paria river basins in Trinidad. Fluctuating asymmetry in the size of carotenoid, melanin and iridescent pigments did not differ between inbred and control males. There was also no difference in spot asymmetry. The lack of response was not caused by inbreeding having no effect on the male phenotype. Inbred Aripo males had less melanin pigment, fewer melanin spots and fewer iridescent subspots, and Paria males had less carotenoid pigment. Our results show that sexual coloration in guppies is sensitive to genetic stress caused by inbreeding, but they provide no support for the hypothesis that genetic stress is reflected particularly well by the degree of fluctuating asymmetry. The different response to inbreeding in the two populations is interesting. There was inbreeding depression in the area of carotenoid pigment in the Paria population, in which this characteristic is known to influence female mate choice, whereas there was no inbreeding depression in the Aripo population, in which females show no detectable preference for carotenoid pigments.