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Jennifer Schmidt

Associate Professor PhD
UIC Biological Sciences, 4202 MBRB M/C 567
900 South Ashland Ave.
Chicago, IL 60607

Office: (312) 996-5655
Lab: (312) 996-5336
Fax: (312) 413-2691
Email: jvs@uic.edu

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Population and reproductive genetics in the whale shark (Rhincodon typus)

   


The whale shark (Rhincodon typus) is the largest fish in the ocean. These filter-feeding sharks can reach lengths of 18 meters, and can weigh 20 tons. Studies have shown that whale sharks numbers are declining across their range. While these animals are protected in many parts of their range, they are fished legally and illegally in some areas. Whale sharks are slow-growing, they do not breed until they are 25-30 years old, and this makes them particularly slow to recover from overfishing or habitat disruption. Whale sharks are listed as Vulnerable in the IUCN Red List of Threatened Species, and in 2002 the species was placed on CITES Appendix II. The biology and ecology of whale sharks is poorly understood, and more information about the species is badly needed to formulate long-term conservation plans.

Genetic analysis can tell us about whale shark migration and breeding. Microsatellites are repetitive DNA sequences that undergo frequent mutation. As such, microsatellites are very polymorphic, and provide excellent resolution for assessing genetic variability. Baseline biological data are needed to guide effective whale shark conservation. It is not known, for example, whether whale sharks comprise a single worldwide breeding population, or numerous regional populations. We are using genetic analysis to study the genetic relatedness of whale sharks around the world. Our analysis has shown that whale sharks have only low levels of genetic differentiation between geographically distinct populations. These data are indicative of gene flow between populations, supporting migration and interbreeding between groups. As whale sharks cross geographic and political boundaries in their movements, international protection must be sought to ensure the continued survival of this species.

Studying whale shark reproduction and development. Whale sharks reproduction is very poorly studied - their mating behavior has never been reported, they have not been observed giving birth, and we do not know where these activities take place. Until recently it was not even known if whale sharks laid eggs or gave birth to live young. Only a single pregnant female whale shark has ever been reported in the scientific literature. An 11 meter female caught in a Taiwanese fishery in 1995 carried more than 300 live embryos in her uteri. This female demonstrated that the whale shark ovoviviparous, giving birth to live young that hatch from eggs within the uterus. We are using genetic analysis to study the paternity of the remaining embryos from this female. Multiple paternity is common in many shark species, and we can determine genetically whether these embryos were sired by a single or multiple males.