© 1992 International Society for Behavioral Ecology
research-article |
Scramble competition polygyny in the milkweed leaf beetle: combat, mobility, and the importance of being there
Department of Entomology, Cornell University Ithaca, NY 14853, USA
ABSTRACT
I examined the scramble competition mating system of the milkweed leaf beetle, Labidomera clivicollis(Coleoptera: Chrysomelidae), using data on lifetime mating success of two breeding cohorts in Austin, Texas, USA (30° N, 97° W) and one in Bridgeport, New York, USA (43° N, 76° W). Data from six daily censuses were combined with focal animal samples to examine the importance of combat between males and to evaluate the extent to which the characters elytron length, vagility, and emergence date were correlated with male mating success. In both populations, emergence date was the only consistent determinant of the number of mates a male obtained during his lifetime. Males emerging earlier in the season had higher mating success because they were active for more of the breeding season. Male body size (elytron length) was not correlated with mating efficiency or lifetime mating success in either population. Males formed prolonged mating associations with females that lasted for up to 2.5 days and paired males in the New York population had a strong advantage over interlopers attempting to mate with the female. Only 10% of takeover attempts were successful. Selection favored vagile males in New York, where the sex ratio was male biased, but not in Texas, where it was female biased. Males that were more vagile had higher mating efficiencies in New York but did not have higher lifetime mating success because of a trade-off between mating efficiency and survival. Behavioral data demonstrated that lone males spent more time walking and less time feeding than lone females; mating males were unable to feed at all. The survival disadvantage that comes with increased vagility may be due to loss of time spent feeding. The characters examined suggest that the most important thing a male L. clivicollis can do to increase his lifetime mating success is to be present for as much of the breeding season as possible.