Sexual ornamentation and weapons of sexual conflict in cartilaginous fishes

Abstract Sexual selection and sexual conflict often result in the evolution of morphological traits that function to improve reproductive success, often termed sexual weapons and ornaments. Sexual weapons serve to increase the reproductive success of the ardent sex (typically males in dioecious taxa) by force, whereas sexual ornaments are considered ‘desirable’ by the opposite sex, or may exploit pre-existing sensory bias. Cartilaginous fishes (Chondrichthyes: sharks, skates, rays, and chimaeras) exhibit a complex spectrum of reproductive modes and marked variation in the prevalence of genetic polyandry and multiple mating. For these reasons, Chondrichthyes represent an ideal group to study sexual selection, sexual conflict, and their evolutionary consequences. In this review, we summarise existing knowledge regarding the function of several putative ‘weapons of sexual conflict’ (sexual weaponry used to coerce or force females to mate) and ornaments possessed by cartilaginous fishes. Subsequently, we discuss what chondrichthyans and these traits can tell us about sexual selection more broadly, and we highlight major knowledge gaps in the field. A lack of observational data impedes our ability to make robust claims about the function of several traits. However, there is reason to suggest that weaponry resulting from sexually antagonistic selection is abundant in chondrichthyan taxa, whilst only one potential case of sexual ornamentation is known.