Otolith morphology varies between populations, sexes, and male alternative reproductive tactics in a vocal toadfish

Teleost otoliths have been used to discriminate among species, to age individuals, and to extract information about life-history events. However, no study has yet investigated otolith morphology in the context of alternative reproductive tactics. Alternative reproductive tactics are divergent phenotypes within a single sex that vary with respect to how individuals achieve reproduction. In this study, the morphology of sagittal otoliths of the plainfin midshipman fish, Porichthys notatus Girard 1854, was compared between populations, sexes, and male alternative reproductive phenotypes (known as 'type I males or guarders' and 'type II males or sneakers'). Sagitta size increased with fish size and changes in shape were also detected with increasing body size. Plainfin midshipman sagittae begin as simple rounded structures, but then elongate as they grow and take on a more triangular and complex shape with several prominent notches and indentations along the dorsal and caudal edges. Moreover, the sagittae of the two geographically and genetically distinct populations of midshipman fish (northern and southern) differed in shape. Fish from the north possessed taller sagittae with deeper caudal indentations compared to fish from the south. Sagitta shape also differed between females and males of the conventional 'guarder' tactic. Furthermore, guarder males had smaller sagittae for their body size than did sneaker males or females. These differences in sagittal otolith morphology are discussed in relation to ecological and life history differences between the sexes and male tactics of this species. This is the first study to investigate teleost otolith morphology from the perspective of alternative reproductive tactics.