Effect of induced mutations on sexually selected traits in the guppy, Poecilia reticulata

According to the genic capture hypothesis, genetic variance in costly sexual traits is maintained because their expression depends on many genes that affect resource acquisition ability. Hence, such traits should constitute a large mutational target and thus show high sensitivity to deleterious mutations. To test this, we exposed male guppies to a chemical mutagen that induces point mutations, and measured sexual display and ornamental traits in the progeny of the mutagenized fish. For comparison, we measured several life history and morphological traits. Compared with progeny of control males, sons of the mutants took a longer time to mature, and daughters of mutants gave birth to fewer offspring than daughters of control males. No significant effect of mutations on body size, eye size or offspring mortality was detected. Consistent with the genic capture hypothesis, induced mutations negatively affected the courtship display rate. However, the area and spectral characteristics of sexually selected orange spots were not significantly affected. Our results demonstrate that energetically costly courtship display, but not orange coloration, is a reliable indicator of mutation load.