All behaviour leading to the fertilization of eggs by sperm. Once fertilization has taken place, there may be further sexual behaviour directed towards further fertilizations, or there may be a switch to parental behaviour. Sexual behaviour may involve copulation, leading to internal or external fertilization, or copulation may be absent. In the three-spined stickleback (Gasterosteus aculeatus), for example, the female swims into the nest, deposits her eggs, and swims out. The male follows the female and fertilizes the eggs.
Every sexually reproducing species must meet a number of criteria. These include mate selection, reproductive timing, coordination during mating, and promotion of viable offspring. Although species vary greatly, each has solved the same basic problems during the course of evolution.
Mate selection is of prime importance in preventing interbreeding between species, and most species have characteristic isolating mechanisms. Different species have different mating systems, but mate selection is always subject to the same evolutionary pressure. The sexual partner should provide the best possible benefit for the offspring, both in terms of genetic contribution and in terms of parental care.
Reproductive timing is largely determined by the habitat, because conditions must be favourable for the extra food requirements of the growing young. Thus, seasonal factors are the main determinants of the sexual cycle that is characteristic of each species. Coordination and cooperation between the sexes is also important when the sexes live apart for part of the season. Finally, promotion of viable offspring is largely a matter of parental care, which is especially well developed in incubation in birds and maternal behaviour in mammals.
Subjects: Zoology and Animal Sciences.