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Abstract
Microsatellite DNA analysis was employed to characterize the mating system and population structure of lemon sharks, Negaprion brevirostris (Poey), in the western Atlantic. Microsatellite loci were highly variable (average number of alleles was 23.6) and exhibited high levels of heterozygosity (He ranged from 0.583 to 0.950). Parental genotypes were reconstructed from newborn and juvenile shark genotypes with the aid of two computer programs, Cervus 2.0 and Kinship 1.3. These genotypes were then used to characterize the mating system at our main study site, Bimini, Bahamas. Of 735 young sharks for which we determined year of birth, 708 (96.3%) were assigned to a maternal genotype while 485 (66.0%) were assigned to a paternal genotype. Female sharks generally exhibited philopatry; thirty-two of 45 females returned to Bimini for parturition. Of those 32 philopatric females, 27 of them returned on a biennial cycle. Of 97 litters for which we could determine mating behavior, 84 (86.6%) were the result of polyandry by the female; polyandrous females mated with two to four males per litter. In addition to parentage reconstruction, genetic tagging of the young revealed 12.1% of lemon sharks shed Passive Integrated Transponder (PIT) tags.
Little genetic structure was found across five populations in the western Atlantic. Small, but significant values of estimators of RST and FST were found. Thus, western Atlantic populations likely represent a single stock. If adult females practice philopatry across the Atlantic, male-mediated gene flow, reduces genetic differentiation between populations.
