Reassessment of Sex Role-Reversal Hypothesis in the Tropical Butterfly Acraea encedon (Lepidoptera: Nymphalidae)

Species with extremely female-biased sex ratios are expected to show alteration in the normal sex roles, as a response to male scarcity. The tropical butterfly Acraea encedon is known to be infected with a male-killing bacterium of the genus Wolbachia, which has led to severe sex ratio distortion in some populations where more than 95 % of wild females are infected with the male-killer. Thus, the aggregation of female A. encedon at resource-free landmarks has been interpreted as “female lekking” behaviour, a sex role-reversed form of lekking normally seen in males of many animals. For this paper, sites in Uganda where female-leks have previously been reported (in 1998) were revisited and surveyed for both sex ratio and bacterial prevalence, for 3 years (2005–2007). The hypothesis of sex role-reversal in A. encedon was evaluated in light of the field data obtained. The study concluded that the response of host populations to the gradual spread of the male-killer toward fixation occurs initially at the behavioural level, as sex role-reversal, and finally at the demographic level, by succumbing to extinction.