SEXUAL CONFLICTS AND COPULATION PATTERNS IN POLYANDROUS BRONZE-WINGED JACANAS (METOPIDIUS INDICUS)

Abstract

AbstractSperm competition was intense in polyandrous bronze-winged jacanas because females usually copulated with all their mates before laying a clutch for one of them. Females spent time with each male, but spent more time with the male that received the clutch ('receiver') in the immediate pre-laying and early laying periods, and overall gave more copulations to the receiver than to non-receivers. As receivers provided all the parental care, theory predicts that females should accede to male demands for copulations in order to assure them of their paternity so that they care for the clutch. Receivers may have destroyed clutches in which they gained a low share of the paternity. Conflicts occurred over the pattern of copulations because females were more likely to terminate male- than female-initiated sex events, and vice versa, and the proportion of sex events initiated by an individual and terminated by its mate was high for both males and females. Overall, a higher proportion of male than female initiations resulted in copulations. To test how these conflicts were resolved, I compared polyandrous groups and monogamous pairs. Male-initiated sex events tended to occur at higher rates and peaked later for polyandrous males than monogamous males. Males initiated sex events at higher rates than their mates, and the timing of copulations more closely matched that of male- than female-initiated sex events, suggesting that polyandrous females acceded to male demands for copulations. In monogamous pairs, copulations were less frequent (32 per clutch vs 97 in polyandrous groups). The duration and peak of the pattern of copulations more closely matched the pattern of initiations by females than males. However, both the timing of female-initiated sex events (mainly in the immediate pre-laying and early laying periods) and the high proportion of male initiations to which females responded suggested that copulations in monogamous pairs were also determined more by male preferences. Nonreceivers occasionally facilitated mate changes through tolerating intruder females and by territory adjustments (as described previously in wattled jacana Jacana jacana by Wrege & Emlen, 1998). Polyandrous females may have attempted to retain such males by giving them copulations and hence the opportunity for paternity (the 'sex for influence' hypothesis). Polyandrous females initiated sex events for a longer period than monogamous females, but did not do so at higher rates per male. Female-initiated sex events with non-receivers did not peak in the immediate pre-laying period (unlike those with receivers), and continued after the last egg had been fertilised. Copulations to guard against the loss of non-receiver mates may have been less important than copulations to ensure parental care by receivers, because all polyandrous females initiated sex events at higher rates with receivers and responded to a higher proportion of their initiations.