Freitag, 30. März 2018
Duration of courtship effort as a costly signal
R. M. Seymour & P. D. Sozou, 2009
"Where long courtship involves a net cost to the female, this raises the question: why does she not avoid (or reduce) this cost by deciding immediately (or more quickly) whether or not to mate with the male? It may be that a female cannot perfectly assess the male’s quality because of random errors in the signal (Luttbeg, 1996); with more observation time or repeat observations these random errors are reduced. There is, however, another possibility: that the duration of a male’s courtship effort may in itself constitute a useful signal to the female."
"We assume that there is a variable which characterizes the male but which is not known a priori to the female. This can be regarded as the male’s type. In common with Sozou and Seymour (2005), for simplicity we will consider this to be a binary variable. The male’s type is either ‘‘good’’ (G) or ‘‘bad’’ (B). ... We assume that a female gets a positive payoff from mating with a good male, and a negative payoff from mating with a bad male. We assume that a male always gets a positive payoff from mating, but that the ratio of his gain from mating to his cost of courtship is higher for a good male: that is, courtship effort is, relatively speaking, more costly for a bad male. ... The most straightforward interpretation of a male’s type is that it is a measure of his condition: a good male is in good condition; a bad male is in poor condition. A female should prefer to mate with a male in good condition if male condition is positively correlated with genetic quality, or in species with paternal care, a female should prefer to mate with a male in good condition if such a male is a better provider of care. If a male in good condition additionally has a lower cost of producing a strong courtship signal relative to his gain from mating, then the signal can act as an honest indicator of his condition, and a female should prefer to mate with a male producing a strong courtship signal (Parker, 1982; Grafen, 1990a, b). In the model presented here, the duration of a male’s courtship effort constitutes the strength of his signal. An alternative interpretation of male type, proposed by Sozou and Seymour (2005), is modelled on species with facultative postmating paternal care, e.g. humans. It is assumed that the male makes a subjective assessment of the female’s attractiveness, and finds her either attractive, or unattractive. The female does not know for sure her own attractiveness to the male. The female’s attractiveness to the male is a noisy indicator of her quality. The male values the chance of mating with her more highly if she is attractive to him, and in this case he will stay after mating and help raise the offspring. If she is unattractive he will still mate with her if given the opportunity, but will then desert, resulting in a negative payoff to the female. In this interpretation, a male discriminates between females: from his perspective they are not all the same. A female should accordingly discriminate between males on the basis of their intentions towards her (Camerer, 1988)."