COSTS OF REPRODUCTION AND THE EVOLUTION OF SEXUAL DIMORPHISM IN A FLYING LIZARD DRACO MELANOPOGON (AGAMIDAE)

Life-history models suggest that 'costs of reproduction' can influence the evolution of sexual dimorphism, but empirical data on this effect are scarce. We tested the idea using 'flying lizards' (Asian agamids of the genus Draco), because the evolution of 'flight' (gliding) is li kely to have increased the degree to which pregnancy affects maternal locomotor ability (and hence, we infer, has increased the 'costs of re production'). As predicted, Draco display patterns of sexual dimorphis m that are different from those seen in most other lizards. The 'wings ' (gliding membranes) of female D. melanopogon are significantly large r than those of males of the same body size, a dimorphism that we attr ibute to natural selection on the ability to glide while encumbered wi th eggs. Comparisons with non-flying lizards suggest that the same sel ective pressure has also reversed pre-existing patterns of sexual dimo rphism in body size and body proportions (relative head size, relative tail length). Measurements of wing-loading, centre of balance and gli ding distances of preserved specimens support the hypothesis that a la rger body, relatively larger head, and longer tail may improve a femal e'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.