Males Become Choosier in Response to Manipulations of Female Wing Ornaments in Dry Season Bicyclus anynana Butterflies

Abstract

Male investment towards reproduction is substantial in some species, and this leads to the evolution of choosy males. Male choice is often directed towards female phenotypes that are good indicators of fecundity such as body size, age, or virgin status, and often acts in the same direction as fecundity selection. In insects, only a few examples exist where male choice is directed towards female ornaments as proxies Butler of female quality. Here, we use dry season males of the sex-role reversed butterfly species Bicyclus anynana to test for differences in male choosiness and investment towards females of varying attractiveness using ornament-manipulations. Male reproductive investment in this species is in the form of a nuptial gift, a spermatophore, given to females upon mating. Males were placed in cages with either wild-type ornamented females or with nonornamented females (center of the dorsal forewing eyespots painted over), and time to mating, duration of mating, and longevity of males and females after a single mating were measured. Ornament manipulations consisted of blocking the UV-reflective scales in the center of the dorsal forewing eyespots of females, a known sexual ornament. Males displayed lower latency to mate and longer mating durations with ornamented females. The longer mating duration did not, however, translate in the transfer of a nuptial gift that increased female longevity or reduced male longevity. Instead, we propose that longer mating durations with ornamented females may represent increased mate guarding behavior or increased sperm transfer.

Keywords: Bicyclus anynana; eyespots; male investment; spermatophore.

Fig. 1.

Female ornament manipulations. (a) Ornamented female (OF). (b) Nonornamented female (NOF). (c and d) M1 eyespots. (e and f) Cu1 eyespots in OF and NOF, respectively. Black paint was applied to the surrounding black scales of the Cu1 eyespot of OF, whereas it completely covered the white central scales of both M1 and Cu1 eyespots of NOF.

Fig. 2.

Mating latency is shorter and mating duration longer with ornamented females. (a) Males took a shorter time to initiate mating with ornamented females (OF) than with nonornamented females (OF). Black line represents median and filled dot denotes mean. (b) Pairs with ornamented females mated for a longer time than pairs with nonornamented females. Error bars represent 95% CI of means. *P < 0.05, **P < 0.01 from independent t-test (two-tailed, α = 0.05).

Fig. 3.

Females live longer than males, but female treatment has no effect on longevity. Longevity (in days) of males mated with ornamented females (Male xOF), of males mated with nonornamented females (Male xNOF), and longevity of the respective females. Black line represents median and filled dot denotes mean. Error bars represent 95% CI of means.