Sexual and seasonal dimorphisms in the dermal, dental and ampullary structures of the lesser-spotted catshark, Scyliorhinus canicula

Abstract

Sexual dimorphisms in head morphology, integument and dentition of some elasmobranch species have been established. These dimorphisms are reportedly linked to reproductive behaviour, whereby male biting during copulation results in a dimorphism in head dimensions and dentition and, as a result, differences in skin thickness. The findings for Scyliorhinus canicula from the Solent support the findings of other authors, whereby adult males were found to possess longer, narrower mouths and a longer head than adult females. Juvenile male catsharks were found to possess a longer mouth than females. No head, mouth or jaw dimorphisms for hatchling catsharks were found. Adult male catsharks were found to possess unicuspid teeth, with large central cusps, in contrast to the pentacuspid form of female and immature catsharks. A sexual dimorphism was found in the tooth row numbers for hatchling and adult catsharks, with hatchling males possessing a greater number of tooth rows than hatchling females on the lower jaw and adult males possessing a greater number of tooth rows than adult females in the upper jaw. Seasonal comparisons were made to ascertain whether morphological changes occurred that could indicate a mating season for the Solent population of S. canicula. Adult head length, mouth length and mouth width were found to be significantly different. Adult males sampled in all seasons possessed a longer mouth than females sampled in all seasons, whilst the lower jaw length was significantly greater for adult males in all seasons compared to adult females. Juvenile female catsharks were found to possess a thicker epidermis than juvenile male catsharks in all seasons of the year, whilst adult females possessed a thicker epidermal layer than adult males, findings not previously reported in this species. Adult females were found to possess a thicker dermal layer in all seasons compared to adult male catsharks. Adult females also possessed wider and longer dermal denticles on the pectoral fins than adult males. Hatchling catsharks had a greater dermal denticle density on both fins indicating the possession of smaller dermal denticles than hatchling females. A sexual dimorphism was found in the Ampullae of Lorenzini with male catsharks possessing a greater number of alveoli than adult females, possibly both an ecological and reproductive adaptation. The seasonal and sexual dimorphisms found in this study do not directly indicate a specific mating season for this species in the Solent.EThOS - Electronic Theses Online ServiceGBUnited Kingdo