CAREER: The role of local adaptation to reproductive conflict in the distribution of facultatively parthenogenetic reproduction

The most common reproductive mechanism in animals involves males and females but often comes at a cost to females and reduces their rate of reproduction overall. Alternatively, some species can reproduce either with or without male involvement facultatively. This combinatory reproductive mode presents a compelling opportunity for researchers to understand why reproduction that produces males is so widespread. The project will quantify the relationships between density, reproductive behavior, and reproductive mode among populations of a species with just such facultative reproduction in the group Opiliones (harvestman or “daddy-longlegs”). In particular, the work will assess when reproductive mode changes occur, and whether they are in response to male harassment behavior. A novel genetic approach will be employed to identify whether offspring have been produced with or without the involvement of a male. In addition, the project will examine whether female resistance to mating affects the reproductive mode they ultimately use. Students involved in the project will be trained in observational and molecular research approaches as part of a new laboratory course on biodiversity and global applications. This research is being jointly supported by IOS Behavioral Systems and DEB Evolutionary Processes programs. Although facultative parthenogenesis has long interested evolutionary biologists due to the opportunities presented by these systems to examine the evolutionary fitness benefits of alternative reproductive modes, locally adaptive mechanisms for the maintenance of reproductive alternatives, and detailed geographic patterns of reproductive mode have not been explored in natural systems. Additionally, models predicting the maintenance and pattern of multiple reproductive modes that are expressed facultatively commonly assume irreversibility of reproductive mode; an assumption that has not been established empirically. The local adaptation to sexual conflict (LASC) hypothesis was developed to predict when and where females would switch among reproductive modes. LASC predicts that females in habitats with high male density are adapted to frequent male coercion and will resist coercion by males and adopt parthenogenetic reproductive modes, particularly in the early breeding season. Alternatively, females from low-density, female-biased populations will be less likely to exhibit antagonistic behaviors towards males, and/or will be more easily overcome by coercive males. Thus, this study will characterize the geographic landscape of male density, reproductive behavior, and reproductive mode to evaluate this hypothesis. This study and the robust evaluation of the LASC hypothesis will make a valuable contribution to our understanding of the maintenance of reproductive mode variety, particularly in the understudied arachnid order, Opiliones. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.