Mating Systems of the Bonnethead and Scalloped Hammerhead Sharks in the Southeast United States, as Revealed by Microsatellite DNA Profiling

Just as DNA-profiling has revolutionized our understanding of the reproductive biology of many animal groups, this technology has begun to provide significant new insights into the mating practices and parentage of free-living sharks. Genetic profiling of two shark species (nurse [ Ginglymostoma cirratum ] and lemon [ Negaprion brevirostris ]) have revealed almost ubiquitous multiple paternity of litters within the sampled study populations. In contrast, our recent studies have revealed that female bonnethead sharks ( Sphyrna tiburo ; Family Sphyrnidae [hammerhead sharks]) demonstrate a relatively low frequency of multiple paternity within a given reproductive cycle (p<20% of 22 litters directly tested by microsatellite genotyping). Collectively, these studies indicate diversity in the mating systems of sharks, raising interesting questions as to what factors drive the evolution of female promiscuity and multiple paternity in these ancient fishes. To further explore this issue, we have expanded our analysis of parentage in S. tiburo to include a total of 70 litters (>650 embryos), originating from breeding grounds along the Gulf coast of Florida and South Carolina. Despite an increase in sample size, multiple paternity remained low overall and we tested the hypothesis that it is more common in larger females. We also genotyped 20 litters (>400 embryos) of scalloped hammerheads ( S. lewini ), a larger, ecologically dissimilar congener of S. tiburo . Although we document the first records of multiple paternity in S. lewini , the mating system of this species appears to be more akin to that of S. tiburo than it is to that of N. brevirostris and G. cirratum .