Sexual selection by the seashore: mate choice and competition in the maritime earwig, Anisolabis maritima

Abstract

Sexual selection involves a complex interplay between intrasexual selection and intersexual selection in which choice and competition converge to maximize reproductive fitness. Our study examines these selective forces in the maritime earwig, Anisolabis maritima, an earwig species in which both females and males possess weaponry. Forceps asymmetry has been noted as a competitive advantage in size-matched small male maritime earwigs and was examined as a factor determining sexual selection along with body size. We examined the roles of these two factors, body size and forceps asymmetry, as it relates to four types of sexual selection; female choice, male choice, male competition, and female competition. We limited the movement of certain earwigs while allowing others to move freely within artificial arenas to examine choice and competition. Our results revealed strong sexual selection for larger sizes through both competition and choice, but there was no preference based on forceps asymmetry. We found significant results in all four trial types, including not only the more traditional male competition and female choice, but also female competition and male choice. However, competition trials yielded our most compelling results. This complex, multidimensional mating system is likely driven by competitive forces and highly influenced by factors determining dominance in intraspecific competition.