67 Breeding Behaviour

Key Idea: Behaviours associated with breeding, such as courtship, are adaptations to ensure reproductive success. Many behaviours in animals, including territorial behaviour, are associated with reproduction, reflecting the importance of this event in an individual's life cycle. Most animals breed on an annual basis and show no reproductive behaviour outside the breeding season. When the breeding season occurs, reproductive signals must be given and interpreted correctly, or the chance for successful reproduction may be missed. The short time period that most sexually reproducing animals have in which to breed creates strong selective pressure for behaviour that improves the chances of reproductive success (therefore fitness). Breeding pairs often establish territories to ensure reliable access to resources during breeding, while ritualised courtship behaviours reduce conflict between the sexes so that mating is achieved without injury.

What is courtship?

` Courtship refers to the behaviour of animals just before, during, and just after mating. Courtship is a way for both male and female to evaluate the health, strength, and potential fitness of a possible mate. ` A potential mate may initially be attracted by a call (e.g. male frog calling).

The caller (usually male) may then perform a more intricate display once the responder (usually female) arrives. In other cases the male's call and display may be the same performance. ` Sometimes the male may attract a mate by offering a gift of food. This is relatively common in insects, such as empid flies (right and below).

Sometimes the male himself is unwittingly the "gift of food", such as in praying mantises in which the male is invariably eaten during mating. This behaviour is also common in spiders.

Female empid flies are aggressive hunters, so males have to be careful about how they approach them. Ritualised courtship behaviour by the male helps him to be accepted by the female as a mate. The male's gift of food for the female pacifies her during mating and is a crucial component of mating success.

Do females chose mates?

` Mate choice (or intersexual selection) occurs where members of one biological sex choose mates of the other sex to mate with. Where there is mate choice, one sex competes with same-sex members and the other sex chooses. This competition often involves elaborate rituals, calls, and displays to the choosing sex. ` Females usually have more invested in offspring so their mate choice is important and they are often the choosy sex. Female preference for certain features, e.g. eyes on peacocks tail, is thought to be behind the elaborate structures and displays that have evolved in many species (e.g. peafowl, right).

3D Male

Female

Prey

Onno Zweers cc 3.0

Courtship is a often crucial part of breeding behaviour

FEMALE

Courtship gift

The male gives the female a meal (an insect wrapped up in a cocoon) to keep her occupied while he mates.

Lock and key

The empid flies lock the tips of their abdomens together so that the male's sperm can enter the female. If the sperm were exposed to the air, they would dry out and die.

Male hangs on

The male empid fly grips on to a twig with its front legs during mating. It uses the other four legs to grip on to the female.

MALE

In birds, song is an important mechanism for attracting a mate and proclaiming ownership of a territory. The song also acts as reproductive isolating mechanism, as differences between the songs of two species enables individuals to recognise their own species and mate only with them. Kakapo are a lek species and males attempt to attract a mate to their lek (breeding territory) by producing a low frequency booming sound during the breeding season that can be heard over many kilometres of forest. When a female arrives the male begins a display in which he spreads his wings and rocks side to side. One of the functions of courtship behaviour is to synchronise the behaviours of the male and female so that mating can occur, and to override attack or escape behaviour. Although courtship rituals may be complex, they are very stereotyped and not easily misinterpreted. Males display, usually through exaggerated physical posturing, and the females then select their mates. Courtship displays are species specific and may include ritualised behaviour such as dancing, feeding, and nest-building. Many birds may form life long bonds (e.g. albatross above) and renew these every year by displaying to each other when they arrive at breeding grounds.

1. (a) Why might courtship behaviour be necessary prior to mating?

(b) Why is courtship behaviour is often ritualised, with stereotyped displays?

2. Describe two aspects of mating behaviour in empid flies that help to ensure successful mating:

(a)

(b)

3. (a) Why is choosing the best mate particularly important for females?

(b) Explain how female choice could lead to elaboration of structures and displays in males:

(c) In some species, the female is unable to choose a mate. Elephant seal males fight for the right to mate with a female and defend a harem. Females arriving at the beach often try to avoid the harem, but with males being up to four times heavier this is difficult. How does this system ensure the offspring are likely to have the best genes?