Genetic evidence for regional philopatry of the Bull Shark (Carcharhinus leucas), to nursery areas in estuaries of the Gulf of Mexico and western North Atlantic ocean
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2018 Elsevier B.V. Nursery areas are critical for the reproductive cycle and biological requirements of Bull Sharks (Carcharhinus leucas) as they increase the survival of populations. Females tend to be philopatric to these areas as documented in estuaries from Australia, and inferred in the northern Gulf of Mexico and western North Atlantic Ocean, but not yet confirmed in these region. In coastal waters of the southeastern United States, several sites have been proposed as nurseries for the Bull Shark, but little is known about how adult females utilize these areas during parturition. Philopatry for the Bull Shark was evaluated by comparing sequences of the mitochondrial DNA control-region (mtDNA-CR) and 8 microsatellite loci in juveniles and neonates from four previously reported nursery areas in United States (US) coastal waters; three in the northern Gulf of Mexico (Texas, Louisiana and Charlotte Harbor, Florida) and one in the western North Atlantic Ocean (Indian River Lagoon, Florida). A group of adult individuals from the Gulf of Mexico and Atlantic Ocean off the southeastern US were used to test genetic differences owed to limited gene flow between both regions. The analysis of genetic variation with the mtDNA-CR showed no differences among nurseries within the Gulf but significant differences when comparing the nursery areas of the two regions (Gulf vs Atlantic). In contrast, genetic homogeneity was observed among nursery areas within and between regions with the nuclear microsatellites suggesting male biased dispersal among regions. In addition, adult individuals from each of these two broad regions (Gulf of Mexico and Atlantic Ocean) showed no significant differentiation with any of the markers characterized in this study. These patterns of genetic differences support evidence for philopatry, further relaying the importance of protection and effective management of critical nursery habitats for future conservation of the species.
