Population genetic structure of Lemon Sharks in the Western Atlantic: is there evidence of gender-biased dispersal and differences between neutral and adaptive loci?
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Authors
Ashe, Jimiane
Lee
Issue Date
1-Aug-11
Type
Thesis
Language
en_US
Keywords
Alternative Title
Abstract
Sampling difficulties and low genetic diversity
have limited population genetic studies of large, vagile shark species.
Through extensive sampling (580 individuals from 12 locations) and a
multilocus approach involving two mitochondrial DNA loci (control region
and ND2, composite sequence 1,730 bp) and eight microsatellites, I was
able to delineate the population genetic structure of the lemon shark,
Negaprion brevirostris, in the western Atlantic. I articulated two
hypotheses to explain genetic structure in coastal sharks: (1) females
exhibit natal philopatry to parturition sites, resulting in local
population structure and (2) males are dispersive, resulting in high
male-mediated gene flow. I predicted that maternally inherited
mitochondrial genetic markers would be highly structured even on a local
geographic scale, while bi-parentally inherited microsatellite markers
would exhibit little to no genetic structure over the same range.
Significant genetic structure was detected in the mitochondrial
composite sequence of ND2 and control region
(Φ<sub>ST</sub> =0.293, p<0.000001), with at least
seven distinct groups evident in the sampling area (East Peninsular
Florida, West Peninsular Florida/Tiger Beach (Bahamas), Lower Florida
Keys/Bimini (Bahamas)/Belize, Eleuthera (Bahamas), Louisiana, U.S.
Virgin Islands and Brazil). Significant genetic structure was
individually detected in both the coding ND2
(Φ<sub>ST</sub> =0.293, p<0.000001) and the
non-coding control region (Φ<sub>ST</sub> =0.278,
p<0.000001), but the ND2 gene was found to be an inappropriate locus
to test for local adaptation in lemon sharks because all of the
mutations were silent with the exception of a single mutation found in
two sharks. Very weak genetic structure was also detected in nuclear
microsatellites (F<sub>ST</sub> =0.014; p<0.088), but
only between the Brazilian population and all of the others. A Bayesian
analysis of the microsatellite data failed to reject a null hypothesis
that there is one population in the region. Both classes of genetic
marker indicated that geographic distance between sampling areas was
correlated with genetic distance between them. All of these findings are
consistent with my predictions and support the hypotheses of natal
philopatry in females and high male-mediated gene flow. Fine-scale local
genetic structure driven by behavior makes this species and others like
it much more vulnerable to local fishing or habitat destruction than
resource managers currently appreciate. I suggest future work should
sequence larger regions of the mitochondrial genome to fully resolve
population structure in this species and to investigate the possibility
of local genetic adaptation in the coding regions.
Description
Citation
Publisher
The Graduate School, Stony Brook
University: Stony Brook, NY.