Mate pairing patterns of monarch butterflies (danaus plexippus L.) at a california overwintering site

We measured parasitism, size, fluctuating asymmetry, and wing condition of mating and nonmating monarch butterflies at a California overwintering site to document mate pairing patterns and to infer from these patterns some of the behavioral processes involved in pair formation. There was no association between parasitism levels of mating pairs, nor did these levels differ in mating and nonmating individuals. There was size-assortative mating early in the mating season i.e., relatively small males tended to couple with relatively small females and larger males coupled with larger females. Mating females were more asymmetric than nonmating females, and there was a positive assortment based on forewing asymmetry. There was also a negative correlation between size and degree of wing damage in mating females. Females that mated in the afternoon were larger than those that mated in the morning and larger size females tended to be mated less frequently than smaller ones at the end of the mating season. We argue that differences in female ability to resist matings affect pairing patterns. Large symmetrical females are probably more attractive to males, but are better able to control their pairing probability by avoiding or resisting some male mating attempts. Males might prefer large females, or large males may simply be more likely to overcome the resistance of large females.