ECOLOGY AND EVOLUTION

The Battle of the Sexes

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Science  08 Sep 2000:
Vol. 289, Issue 5485, pp. 1653
DOI: 10.1126/science.289.5485.1653c

Ritualized displays between the sexes are widespread in animals, especially in monogamous species. Evolutionary explanations have centered on such displays as a means for females to assess male quality, for both sexes to maintain cooperation and mutual stimulation, and/or to coordinate reproductive physiology.

Wachtermeister and Enquist now propose a new explanation in which sexual conflict plays a role. According to this hypothesis, asymmetry between the sexes in their eagerness to mate leads to the evolution of complex rituals as a male tries to lure a female into reproducing earlier than is optimal. They simulate this process using a neural network model, run over 60,000 generations. ‘Male’ signals are fed into the ‘female’ network, which contains internal feedback loops that can react to a sequence of stimuli.

When new male sequences of signals were allowed to evolve, females started to reproduce earlier than optimal, but in response the females then evolved increased resistance to the new displays. This model co-evolutionary process, which entails no female choice or mutual co-operation, appears to operate regardless of the costs of the signal or the quality of the male. — AMS

Behav. Ecol. 11, 405 (2000).

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