Behavioral manifestations of sexual conflict: Facultative asexuality, mating phenology, and the loss of nuptial gifts drive reproductive strategies in sclerosomatid Opiliones

Abstract

Sexual conflict is a primary driving force behind how mating behavior evolves. Despite much research on sexual conflict, however, the behavioral manifestations of sexual conflict driven by facultative asexuality, nuptial gifts, and mating phenology are not fully resolved. Leiobunine Opiliones feature all these factors: some species possess nuptial gifts and lack female genital barriers, some species lack precopulatory nuptial gifts and have female genital barriers, and some species are facultatively asexual. Temperate species also have a highly variable reproductive window, with the window of maturation varying greatly both between and within species. All these factors can greatly influence the reproduction of a species and provide mechanisms through which sexual conflict and selection might operate. In this dissertation, I investigated the reproductive behavior of Leiobunum Opiliones to determine how facultative asexuality, nuptial gifts, and mating phenology generate sexual conflict. I first used facultatively asexual Japanese Opiliones to determine whether sex ratio influenced reproductive mode. Female harvesters nearly always reproduced asexually in localities in which males were rare. Surprisingly, however, females in localities with common males also typically reproduced asexually, indicating sexual reproduction with males is likely costly. Following this, I compared sexual conflict behavior between North American sacculate species, in which males give nutritious nuptial gifts, and nonsacculate species, in which males do not. Using machine learning-based tracking, I found significantly higher levels of sexual conflict in nonsacculate species, matching predictions that nuptial gifts were lost in favor of antagonistic male behavior. Interestingly, I detected multiple suites of antagonistic strategies; L. euserratipalpe males favored extended guarding, while L. vittatum males favored extended clasping. In the final study I sought to determine how mating phenology and mating history influenced sexual conflict. I compared behavioral sexual conflict metrics between mated and unmated females and across three consecutive mate encounters. Contrary to theoretical predictions, sexual conflict did not vary with mating history or with encounter number. Throughout my dissertation, I have detected evidence of sexual conflict varying with reproductive mode and nuptial gifts presence and I have established Leiobunum harvesters as excellent species in which to study behavioral sexual conflict.