Testing multiple hypotheses for the maintenance of male homosexual copulatory behaviour in flour beetles.
Artificial divergent selection for the rate of homosexual copulation (defined as the proportion of homosexual mountings performed by a male in a period of 30 min) has been carried out for 2-3 generations in a population of Tribolium castaneum. A clear response was obtained in each of 4 replicates, corresponding to an overall realized heritability of 0.11 f 0.01. No significant correlated response to selection was observed for the average number of mountings performed by a male during the testing period. Therefore, our results do not agree with evolutionary interpretations of insect homosexual copulation behaviour based on the existence of a negative genetic correlation between the degree of sexual discrimination and sexual activity. On the contrary, they strongly favour the hypothesis of sex recognition being absent in Tribolium casteneum.