Life-history models suggest that`costs of reproduction' can in¯uence the evolution of sexual dimo... more Life-history models suggest that`costs of reproduction' can in¯uence the evolution of sexual dimorphism, but empirical data on this effect are scarce. We tested the idea using`¯ying lizards' (Asian agamids of the genus Draco), because the evolution of`¯ight' (gliding) is likely to have increased the degree to which pregnancy affects maternal locomotor ability (and hence, we infer, has increased the`costs of reproduction'). As predicted, Draco display patterns of sexual dimorphism that are different from those seen in most other lizards. The`wings' (gliding membranes) of female D. melanopogon are signi®cantly larger than those of males of the same body size, a dimorphism that we attribute to natural selection on the ability to glide while encumbered with eggs. Comparisons with non-¯ying lizards suggest that the same selective pressure has also reversed pre-existing patterns of sexual dimorphism in body size and body proportions (relative head size, relative tail length). Measurements of wing-loading, centre of balance and gliding distances of preserved specimens support the hypothesis that a larger body, relatively larger head, and longer tail may improve a female's aerial mobility when she is gravid. Thus, selection for locomotor ability in egg-burdened females (reduction in`costs of reproduction') may have been responsible for a reversal of sexually-selected traits in this lineage.
Sexual selection theory predicts different optima for multiple mating in males and females. We us... more Sexual selection theory predicts different optima for multiple mating in males and females. We used mating experiments and genetic paternity testing to disentangle preand postcopulatory mechanisms of sexual selection and alternate reproductive tactics in the highly promiscuous lizard Eulamprus heatwolei. Both sexes mated multiply: 30-60 % of clutches were sired by two to four fathers, depending on the experiment. Larger males sired more offspring when we allowed male contest competition: 52 % of large males but only 14 % of small males sired at least one offspring. In the absence of male contest competition, females mated promiscuously and there was no large male advantage: 80 % of large males and 90 % of small males sired at least one offspring, and there was no evidence for last-male precedence. Multiple mating did not yield obvious direct or indirect benefits to females. E. heatwolei represents a complex system in which males attempt to improve their fertility success by limiting rivals from access to females and through adopting alternate reproductive tactics. Conversely, females exhibit no obvious precopulatory mate choice but may influence fitness through postcopulatory means by either promoting sperm competition or through cryptic female choice. Our results support the hypothesis that female multiple mating in nonavian reptiles is best explained by the combined effect of mate encounter frequency and high benefits to males but low costs to females.
Life-history models suggest that`costs of reproduction' can in¯uence the evolution of sexual dimo... more Life-history models suggest that`costs of reproduction' can in¯uence the evolution of sexual dimorphism, but empirical data on this effect are scarce. We tested the idea using`¯ying lizards' (Asian agamids of the genus Draco), because the evolution of`¯ight' (gliding) is likely to have increased the degree to which pregnancy affects maternal locomotor ability (and hence, we infer, has increased the`costs of reproduction'). As predicted, Draco display patterns of sexual dimorphism that are different from those seen in most other lizards. The`wings' (gliding membranes) of female D. melanopogon are signi®cantly larger than those of males of the same body size, a dimorphism that we attribute to natural selection on the ability to glide while encumbered with eggs. Comparisons with non-¯ying lizards suggest that the same selective pressure has also reversed pre-existing patterns of sexual dimorphism in body size and body proportions (relative head size, relative tail length). Measurements of wing-loading, centre of balance and gliding distances of preserved specimens support the hypothesis that a larger body, relatively larger head, and longer tail may improve a female's aerial mobility when she is gravid. Thus, selection for locomotor ability in egg-burdened females (reduction in`costs of reproduction') may have been responsible for a reversal of sexually-selected traits in this lineage.
Sexual selection theory predicts different optima for multiple mating in males and females. We us... more Sexual selection theory predicts different optima for multiple mating in males and females. We used mating experiments and genetic paternity testing to disentangle preand postcopulatory mechanisms of sexual selection and alternate reproductive tactics in the highly promiscuous lizard Eulamprus heatwolei. Both sexes mated multiply: 30-60 % of clutches were sired by two to four fathers, depending on the experiment. Larger males sired more offspring when we allowed male contest competition: 52 % of large males but only 14 % of small males sired at least one offspring. In the absence of male contest competition, females mated promiscuously and there was no large male advantage: 80 % of large males and 90 % of small males sired at least one offspring, and there was no evidence for last-male precedence. Multiple mating did not yield obvious direct or indirect benefits to females. E. heatwolei represents a complex system in which males attempt to improve their fertility success by limiting rivals from access to females and through adopting alternate reproductive tactics. Conversely, females exhibit no obvious precopulatory mate choice but may influence fitness through postcopulatory means by either promoting sperm competition or through cryptic female choice. Our results support the hypothesis that female multiple mating in nonavian reptiles is best explained by the combined effect of mate encounter frequency and high benefits to males but low costs to females.
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Papers by Scott Keogh