Genetic Basis of Sexual Dimorphism in Anal Fin Morphology of the Fluffy Sculpin Oligocottus snyderi
Author: Andy Quintanilla
Faculty Supervisor: Karen Crow
Department: Biology
Both medial and paired fins/limbs in vertebrates are specified by a shared genetic regulatory network (GRN, Cass et al., 2021; Grandel & Schulte-Merker, 1998). However, medial fins arose before paired fins during vertebrate evolution, indicating that the underlying GRN was first assembled in jawless fishes that lack paired fins (Freitas et al., 2006). Interestingly, most studies have focused on variation in paired fins/limbs and their associated GRN, likely because humans lack medial fins, while relatively few papers have featured modified medial fin morphologies. The dorsal, caudal, and anal fins exhibited by all vertebrate groups, including the jawless, cartilaginous, ray-finned and lobe-finned fishes (but not tetrapods) are collectively referred to as “medial fins.” Medial fins in ray finned fishes exhibit remarkable morphological variation, suggesting that modifications to the fin/limb GRN is common, and a major mechanism for the evolution of vertebrate diversity. For example, variation in anal fin ray morphology in mosquitofish is specified by sonic hedgehog (shh, Ogino et al., 2004), suggesting a role for the 5’ HoxA/D genes (see Freitas et al., 2012; Sakamoto et al., 2009; Zhang et al., 2010). The fluffy sculpin (Oligocottus snyderi) exhibits a modified anal fin ray that is sexually dimorphic, where males exhibit extreme elongation in the first anal fin ray (Morrisi, 1955), that is associated with a unique reproductive strategy called internal gametic association (IGA) that results in copulation and internal insemination, however fertilization is delayed until the clutch is laid in seawater (Ito et al., 2023). This novel and sexually dimorphic trait represent a tractable system for evaluating differences in anal fin gene expression between males and females on the same genetic background.