Elasmobranch Reproduction and Mating System Evolution
The collapse of shark populations has resulted from the inability of shark recruitment to keep up with the intense exploitation these animals are experiencing worldwide. Sharks (and elasmobranchs in general) are particularly vulnerable to overexploitation due to their reproductive characteristics (e.g., low fecundity and late age at maturity) which are more similar to that of mammals than teleost fishes. Despite the fact that reproductive capacity is such a pivotal aspect of fisheries management, there is little information available on mating systems, reproductive mechanisms, and genetic basis of parentage in sharks, and elasmobranchs in general. To help increase our understanding of reproduction in elasmobranchs, GHRI scientists are employing both field observational methods and genetic profiling (a type of DNA fingerprinting) to collect basic biological information on reproduction.
Current GHRI research in this area includes studying the genetic basis of mating behavior in the bonnethead shark, Sphyrna tiburo, the scalloped hammerhead, Sphyrna lewini, and the blue shark, Prionace glauca. Because mating behavior of sharks is difficult to observe directly in the wild, it is largely unknown whether the few observed cases of polyandrous mating (i.e., where females mate with multiple males) is the rule or the exception in nature. To answer this question, GHRI researchers are developing and using a type of inherited genetic marker (known as microsatellites) to assess the incidence of multiple paternity in shark litters. Results thus far indicate that multiple paternity is common in some species, but infrequent in others. This type of basic information has direct bearing on both the long-term genetic biodiversity consequences of overfishing one gender, as occurs in some fisheries, as well as on our understanding of the evolution of mating systems in an ancient lineage of vertebrates. GHRI is also studying reproductive parameters and mating behavior in the southern stingray (see Stingray Conservation and Ecology page).
For a description of recent GHRI research on elasmobranch mating see:
Chapman, D.D., M.J. Corcoran, G.M. Harvey, S. Malan and M.S. Shivji. 2003. Mating behavior of southern stingrays, Dasyatis americana(Dasyatidae). Environmental Biology of Fishes 68 (3): 241-245.
Chapman, D.D., P.A. Prodohl, J. Gelsleichter, C.A. Manire and M.S. Shivji. 2004. Predominance of genetic monogamy by females in a hammerhead shark, Sphyrna tiburo: Implications for shark conservation. Molecular Ecology 13: 1965-1974.
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