" Sexual selection has two components: mate choice and intrasexual competition, both of which can result in differences in mating success. Both components were examined in the mozambique tilapia (Oreochromis mossambicus), a cichlid fish that exhibits a lek-mating system. In lekking animals, a few males are responsible for most matings but the relative importance of female mate choice and competition among males is usually unknown.Field observations of an introduced population made over a three year period in southern Florida revealed that (a) the operational sex ratio is biased towards males and (b) the density of territorial males (those males that defend a spawning pit), male size and spawning pit size are variable. These traits, therefore, may be important for sexual selection.In laboratory experiments examining whether female preferences exist in the absence and in the presence of male-male interactions, females were given a choice between a large and a small male. Females mated randomly with respect to male size when male-male interactions were prevented but preferred large over small males when male-male interactions were permitted. In another experiment, females were presented with a large and a small spawning pit in the absence of male-male interactions. Females preferred large spawning pits. To examine the relationship between male size and spawning pit size, males were permitted to dig spawning pits in large pools. There was no difference in the size of spawning pits dug by large males versus small males either when large and small males were segregated or when they were intermixed. Some males switched spawning pits. Spawning pit size was consequently not a good predictor of male size. Therefore, the ability of a male to defend and retain a spawning pit, not necessarily male size, may be sexually selected.In conclusion, female choice for two traits, male size and spawning pit size, was demonstrated for this lekking species. Large spawning pits were preferred even without male-male interactions. The presence of male-male interactions, however, facilitated female preferences for large males. Both female choice and male-male competition are therefore important in this mating system "
Classificazione: Comportamento, Africa.