The Effect of Behavior and Ecology on Male Mating Success in Overwintering Monarch Butterflies (Danaus plexippus)

Abstract

Monarch butterflies (Danaus plexippus) appear to forego the chemical courtship that is typical of other danaid butterflies, and instead employ a coercive mating system. Females have been described as using resistance behaviors in response to male coercion. Much of our understanding of sexual selection in monarchs is based on observations of mating attempts that occur on the ground, but recent studies report frequent mating attempts in the tree canopy. I compared mating activity on the ground to that in the tree canopy and found that, among heterosexual mating attempts, location did not affect the likelihood of ending in copulation. This suggests that the more easily obtained data on ground attempts may reasonably approximate mating activity in the canopy. The outcome of ground attempts was influenced by vegetation structure and the position of the male relative to the female and the ground at the start of the ground phase of the mating attempt. My observations suggest that butterfly position may be correlated with male search strategy. It remains unclear whether described resistance behaviors represent female or male control. However, the data do demonstrate that attempt outcome is influenced by both behavior and ecology: male search and capture strategies may influence copulatory success, and human-induced changes to the habitat can influence monarch mating activity at overwintering sites.