Dr Alessandro Devigili - Sperm tales in guppies: a discovery journey from sexual to artificial selection

In evolutionary biology, some intriguing questions still wait for an exhaustive answer. The maintenance of genetic variability in traits that are under strong directional or stabilizing selection is one of these puzzling questions. Theoretical works suggest that this variability should be rapidly depleted generation after generation, but experimental evidence suggest the contrary. This scenario, coined as the “lek paradox” in mate choice context, perfectly suits to most sexual traits such as male ornaments, which are under strong precopulatory sexual selection in the form of persistent female choice. Other traits that usually face the same situation are those related to ejaculate. When females are sexually promiscuous, male reproductive success depends also on the outcome of sperm competition and cryptic female choice. In natural populations, sperm related traits are strongly selected but, as their precopulatory counterpart, show a high genetic variability. Some alternative non-mutually exclusive hypotheses have been proposed in order to explain these unexpected observations. Here I present results of five experiments aimed at testing these mechanisms using Poecilia reticulata as model species and focusing on postcopulatory traits. I firstly characterized the strength, shape and direction of sexual selection and determined the interplay between pre- and post- copulatory components (exp. 1). I then verified the presence of trade-offs between sexually selected traits (exp. 2) and tested the prediction of the “Genic capture hypothesis” (exp. 3 and 4). Finally, I evaluated the presence of GEIs (genotype-by-environment interactions) in experimentally selected fish lines (exp. 5).