Testing for cryptic female choice in monarch butterflies

Although many studies have examined precopulatory female choice, it is increasingly clear that females may choose paternity after copulation with multiple males. Such cryptic female choice may be more common in species where females have limited precopulatory choice. We tested for cryptic female choice in the monarch butterfly (Danaus plexippus), which has a male-coerced mating dynamic. We used a mating design consisting of female pairs mated to the same 2 males. Using microsatellite markers, we determined P2, the proportion of offspring fathered by the second male. In 3 treatments, we varied the relatedness of females and males and calculated P2 repeatability of the 2 females in a replicate. Assuming cryptic female choice, we predicted more repeatable P2 values for genetically related female pairs than unrelated pairs. Additionally, we predicted that females should favor paternity by unrelated males over brothers to avoid potential inbreeding depression. Our results revealed no P2 repeatability differences between treatments and no differences in paternity of brothers and unrelated males. These results suggest monarchs do not employ cryptic female choice and do not avoid inbreeding postmating. Moreover, we did not find significant sperm precedence; neither first nor second male obtained higher paternity. However, our results suggested that interactions between male and female lineages may slightly affect offspring paternity, suggesting genetic compatibilities may affect sexual selection in this species. We also found a bimodal paternity distribution, confirming that monarchs follow the lepidopteran pattern of paternity, despite precopulatory behavioral differences.