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Andrea Pilastro

Sweetness, senses and sexual selection.

I describe a series of experiments on birds in which males possess multiple ornaments in order to win the attention of females. In fact, it is not yet clear why some animals, especially fishes and birds, developed a complex system of multiple ornaments and strategies to attract females.
Until only 20 years ago, Darwin�s idea of female preferences for male ornaments was still controversial, although his theory had received new support from two directions.
First, empirical studies showed that male ornaments are favoured by female choice in several animals. Second, a major problem left open by Darwin, the reasons why females prefer ornamented males, was clarified when genetic models verified the logical coherence of coevolution of male ornaments and female preferences: only most healthy and powerful males can bear the cost of ornaments which become a signal of male genetic quality.
These models, however, do not explain why males of most species evolved multiple ornaments, such as beautiful colours and plumages, courtship songs and displays, instead a single ornament.
It has been suggested that multiple ornaments are adaptive, that is, they are more efficient in conveying information about male quality to the female. A more fascinating explanation suggests that multiple ornaments are the result of the sexual conflict between males and females.
For example, males would exploit female cognitive constraints to increase their mating success with reluctant females by using females propensity to find attractive thosecolours, smells or displays that are shaped by natural preference for food items.
As females become resistant to the seduction of a male�s ornament, the condition promoting an evolutionary arm race is set up and additional ornaments are expected to arise. Alternatively, it has been suggested that multiple ornaments evolve because female choice become more difficult when males differ for several, unrelated ornamental traits (e.g. colour and behavior), instead of a single ornamental trait.
This hypothesis rests on the assumption that females choose their mate by comparing prospecting males instead of on the basis of an absolute scale. An interesting series of experiments on birds and fishes � in which males possess multiple colours aimed at testing these hypotheses.

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Andrea Pilastro

Dept. of Biology, University of Padua
via Ugo Bassi 58/B - 35131 Padova, Italy
T. +39 049 827 6224
F. +39 049 827 6209
e-mail andrea.pilastro@unipd.it
Website: http://www.bio.unipd.it/behavecol/

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