Meccanismi della selezione sessuale postcopulatoria in un guppy (Poecilia reticulata), un pesce teleosteo a fecondazione interna

Given multiple matings from females, sexual selection continues after insemination in the form of postcopulatory sexual selection. This process is formed by two main mechanisms: sperm competition (competition of sperm of two or more males for the fertilization of the eggs of the same female) and cryptic female choice. These act as powerful selective pressures for the evolution of reproductive biology of both males and females. The aim of this thesis is to analyze the relative importance of sperm competition and cryptic female choice in determining a male reproductive success. The study species is the guppy (Poecilia reticulata), a freshwater fish, ovoviviparous with internal fertilization. Using artificial insemination, I studied if females can obtain fecundity benefits from mating with colourful males (as predicted by Sheldon's Phenotype-linked fertility hypothesis), the role of sperm number and sperm quality for sperm competition success, repeatability of a male's fertilization success and the role of MHC genes in non directional cryptic female choice. This technique allows to control for many potential confounding variables, as order of mating, number of sperm inseminated and cryptic female choice. From the experiments, it emerges that directional processes in this species are more important for fertilization success rather than non directional processes, even if a part of variance in fertilization success is explained by a male's similarity for MHC genotype with the female.