Reproductive behavior

(zoology) The behavior patterns in different types of animals by means of which the sperm is brought to the egg and the parental care of the resulting young insured.

Behavior related to the production of offspring; it includes such patterns as the establishment of mating systems, courtship, sexual behavior, parturition, and the care of young. Successful reproductive efforts require the establishment of a situation favorable for reproduction, often require behavior leading to the union of male and female gametes, and often require behavior that facilitates or ensures the survival and development of the young; the mere union of gametes is not generally sufficient for successful reproduction. For each species, there is a complex set of behavioral adaptations that coordinate the timing and patterning of reproductive activity. Typically, this entails integration of both overt behavioral and internal physiological events in both male and female, all of which are intricately enmeshed in manners adapted to the environment in which the animals live. The behavioral patterns related to reproduction tend to be relatively stereotyped within a species, but diverse among different species—especially distantly related species. The end products of cycles of reproductive activity are viable, fertile offspring which, in turn, will reproduce and thus perpetuate the species.

The relationships between individual males and females and the degree of exclusivity in mating are part of the mating system of a species or population. There are three basic mating system types: monogamy, polygamy, and promiscuity. In monogamy the reproductive unit is generally a single male and a single female, the partners copulate only with each other, there may be shared parental care, and there is some kind of prolonged pair bond. In polygamous mating systems, there is again a prolonged association, but more than two individuals are involved in the relationship. In the promiscuous mating system, there is no prolonged bond formed, and there are multiple matings by members of at least one of the sexes.

Territoriality or dominance occurs in many kinds of mating systems. A territory is an area that is defended against conspecific animals (those of the same species). It may be occupied by a single individual, a bonded male-female pair, or a larger group. The resident of a territory generally has privileged access to the resources on that territory. Where the territory is relatively large, as in many diurnal songbirds, it may include sufficient resources to support a bonded pair and their offspring. By contrast, in many colonially nesting marine birds the territories may encompass little more than a nest site, while food and other resources are collected at a distance. In a special form of territoriality, a lek, males of some species, such as sage grouse, defend small territories that are used only for breeding.

Whereas in a territorial system the outcome of a contest for resources is generally predictable given only the location of the encounter, in a dominance relationship an individual wins regardless of location. In troops of various species of primates, for example, there may be a single dominant male and a hierarchy of males ranking below him. There are many varieties of dominance relationships, with male hierarchies, female hierarchies, mixed-sex hierarchies, and triangular relationships that are departures from linearity. Dominance-related contests may occur seasonally, generally peaking in intensity during the breeding season, and can be of great importance in determining which individuals reproduce.

Mate choice and then courtship are both essential to successful reproduction in animals. The importance of female choice remains controversial. Ultimately, females can benefit by mating with males that are exceptional either in their ability to accrue resources or in the possession of “good genes,” or both. Males forming prolonged pair bonds invest much, and it is not surprising that they may exercise mate choice as well. In a variety of species of invertebrates, for example, males prefer large females to small ones.

Courtship entails a sequence of behavioral patterns that eventually may lead to the completed mating. Patterns of courtship are quite diverse among different species but generally entail reciprocal signaling between male and female. Mate choice is an important function of courtship. Many bouts of courtship break off without going to completed matings, often as a result of choice on the part of one or both partners. Another function of courtship relates to synchronization. The gametes must be shed at a time when sperm are viable, eggs are ripe, male and female are in the appropriate state of readiness, and the environment is supportive of reproductive effort. The progressive interactive sequence of the courtship episode allows for coordinated events to occur at times appropriate for successful reproduction.

Prior to birth or hatching of offspring, parents may engage in behavioral patterns that will aid the young when they arrive. This may entail preparation of a burrow or nest, provision of stored food, or acquisition of other resources. In some species the parent's aid ends with such preparations, but in others parental care may be extensive and prolonged. Parental care, especially maternal care, is highly developed in all species of mammals. By definition, the females of all mammalian species possess mammary glands for the nourishment of young. It is probably for this physiological reason that role reversal is less common among mammals than in other taxa.

Parental investment entails any investment by the parent that increases the ability of the young to survive and reproduce at some cost to the parent. Much parental investment, like milk, cannot be shared; that which is given to one offspring cannot be given to another. Other kinds of parental investment, like defense against predators, is shareable. In addition, the parent making any investment is prevented from engaging in other activities, such as searching for his or her own food or seeking additional mates.

Because they contribute larger gametes and often engage in more extensive parental behavior, the females of most species display a higher level of parental investment than males. Members of the sex investing more (typically females) thus become a limiting resource for the sex investing less (typically males). It is generally agreed that this gives rise to the disparity between female and male reproductive strategies—with males more often competing for access to females and females more choosy than males. See also Animal communication; Behavioral ecology; Ethology; Reproduction (animal).