Meeting Abstract
Sexual reproduction in chondricthyans (sharks and rays) takes place through internal fertilization by the insertion of a male’s clasper into a female’s cloaca. Although some chondrichthyans mate in the benthic zone, pelagic animals must accomplish this task while swimming. This presents a challenge for animals to maintain a connection between the clasper and cloaca long enough to ensure the successful transfer of sperm to the female. Denticles, dermal tooth-like structures found on the bodies of most cartilaginous fishes, function to reduce drag along the body of a shark by disrupting the boundary layer; however, it is possible that they also help to establish a roughened surface to increase mating success in pelagic breeding species. We hypothesized that the external genitalia of pelagic breeding animals are covered by dermal denticles to function as anchors for maintaining contact during copulation, while animals that breed near the benthos will be devoid of denticles. We used a combination of scanning electron microscopy (SEM) and paraffin histology to determine whether denticles are present on claspers and/or cloacas from 6 pelagic and 6 benthic mating species. We measured the size, density, spacing, and orientation of denticles when present. Denticles occurred on both female and male reproductive structures for all pelagic breeding species, while denticles were absent in demersal breeding species. The presence of denticles on the external genitalia of pelagic breeding species and absence of denticulation on benthic breeding species, suggests this is likely an adaptation that aids in copulation while swimming.
