Publications (6)17.48 Total impact
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Article: Hybridization between pallid sturgeon Scaphirhynchus albus and shovelnose sturgeon Scaphirhynchus platorynchus.
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ABSTRACT: This study found that introgressive hybridization of the pallid sturgeon Scaphirhynchus albus with the common shovelnose sturgeon Scaphirhynchus platorynchus has probably occurred across the range of S. albus. Bayesian clustering found evidence of hybridization in all management units of S. albus. Some individuals were intermediate at both genetic and morphological characters, and some had discordant results. The results support introgressive hybridization throughout much of the range of S. albus, yet individuals consistent with being pure members of each species were detected in all management units. Simulations demonstrated that it would be very difficult to distinguish introgressed individuals from pure specimens after multiple generations of backcrossing with these microsatellite markers. Using hybrid or backcross fish as broodstock could artificially accelerate the loss of unique genetic variation in S. albus. Additional microsatellite loci or additional genetic markers, along with morphological data may be required to ensure that hybrid or backcross fish are not used. Introgressive hybridization requires at least two generations and generation lengths of S. albus are long, perhaps as long as 30 years. The proportion of individuals consistent with introgressive hybrid origins indicates that hybridization between S. albus and S. platorynchus probably has occurred for several generations and is not a recent phenomenon.Journal of Fish Biology 12/2011; 79(7):1828-50. · 1.68 Impact Factor -
Article: Stock structure of pallid sturgeon analyzed with microsatellite loci
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ABSTRACT: Recovery efforts for the endangered pallid sturgeon (Scaphirhynchus albus) include supplementation of wild stocks with hatchery reared progeny. Identifying the extent of genetic stock structure, which has previously been detected in samples from the range extremes, will help to determine whether stock transfers might be harmful. DNA microsatellite genotypes were screened in pallid sturgeon from the upper Missouri River, lower Missouri River, middle Mississippi River and Atchafalaya River and analyzed using a combination of Bayesian model-based and more traditional F-statistic based methods to characterize genetic differentiation. Scaphirhynchus specimens were collected by researchers active in the recovery effort and genotypes were screened at 16 microsatellite loci. Because there is considerable genetic and morphological overlap between pallid sturgeon, shovelnose sturgeon, and their hybrids, a combination of morphological and genetic techniques were used to eliminate shovelnose and possible hybrids from the sample. Genetic differentiation was detected among samples (overall θ = 0.050, P = 0.001). Pairwise θ, genetic distances, and Bayesian assignment testing reveal that pallid sturgeon from the upper Missouri River are the most distinct group with pairwise comparisons of pallid sturgeon among all the remaining samples exhibiting lower θ values, higher genetic distances, and self assignment scores. Our results indicate that using local broodstock, when available, should be used for pallid sturgeon propagation. If local broodstock are not available, geographically proximate individuals would limit genetic differences between native and stocked individuals.Journal of Applied Ichthyology 07/2007; 23(4):297 - 303. · 0.87 Impact Factor -
Article: Genetic discrimination of middle Mississippi River Scaphirhynchus sturgeon into pallid, shovelnose, and putative hybrids with multiple microsatellite loci
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ABSTRACT: The pallid sturgeon (Scaphirhynchus albus), which is protected under the US endangered species act, and shovelnose sturgeon (S. platorhynchus), which is legally harvested in some locations, are sympatric throughout the range of pallid sturgeon. There is considerable morphological overlap between the species making discrimination problematic. The inability to reliably differentiate between species across all life stages has hampered pallid sturgeon recovery efforts. Furthermore, the two species are believed to hybridize. This study used allele frequency data at multiple microsatellite loci to perform Bayesian and likelihood-based assignment testing and morphological measures and meristics to discriminate pallid, shovelnose, and putative hybrid sturgeons from the middle Mississippi River. Bayesian model-based clustering of the genetic data indicated that two natural genetic units occur in the region. These units correspond to morphologically identified pallid and shovelnose sturgeon. Some individuals were morphologically intermediate and many of these failed to strongly assign genetically as either pallid or shovelnose sturgeon, suggesting they may be hybrids. These data indicate that pallid sturgeon and shovelnose sturgeon are genetically distinct in the middle Mississippi River (F ST=0.036, P<0.0001) and suggest that hybridization between pallid sturgeon and shovelnose sturgeon has occurred in this region with genetic distance estimates indicating the greatest distance is between pallid and shovelnose sturgeon, while hybrid sturgeon are intermediate but closer to shovelnose. This study demonstrates that assignment testing with multiple microsatellite markers can be successful at discriminating pallid sturgeon and shovelnose sturgeon, providing a valuable resource for pallid sturgeon recovery and conservation.Conservation Genetics 01/2007; 8(3):683-693. · 1.61 Impact Factor -
Article: Worldwide phylogeography of the blacktip shark (Carcharhinus limbatus) inferred from mitochondrial DNA reveals isolation of western Atlantic populations coupled with recent Pacific dispersal.
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ABSTRACT: Although many coastal shark species have widespread distributions, the genetic relatedness of worldwide populations has been examined for few species. The blacktip shark, (Carcharhinus limbatus), inhabits tropical and subtropical coastal waters throughout the world. In this study, we examined the genetic relationships of blacktip shark populations (n = 364 sharks) throughout the majority of the species' range using the entire mitochondrial control region (1067-1070 nucleotides). Two geographically distinct maternal lineages (western Atlantic, Gulf of Mexico, and Caribbean Sea clades, and eastern Atlantic, Indian, and Pacific Ocean clades) were identified and shallow population structure was detected throughout their geographic ranges. These findings indicate that a major population subdivision exists across the Atlantic Ocean, but not the Pacific Ocean. The historical dispersal of this widespread, coastal species may have been interrupted by the rise of the Isthmus of Panama. This scenario implies historical dispersal across the Pacific Ocean (supported by the recovery of the same common haplotype from the Philippines, Hawaii, and the Gulf of California reflecting recent/contemporary dispersal abilities) and an oceanic barrier to recent migration across the Atlantic. Genetic structure within the eastern Atlantic/Indo-Pacific (Phi(ST) = 0.612, P < 0.001) supports maternal philopatry throughout this area, expanding previous western Atlantic findings. Eastern Atlantic/Indo-Pacific C. limbatus control region haplotypes were paraphyletic to Carcharhinus tilstoni haplotypes in our maximum-parsimony analysis. The greater divergence of western Atlantic C. limbatus than C. tilstoni from eastern Atlantic/Indo-Pacific C. limbatus reflects the taxonomic uncertainty of western Atlantic C. limbatus.Molecular Ecology 11/2006; 15(12):3669-79. · 5.52 Impact Factor -
Article: Microsatellite and mitochondrial DNA analyses of the genetic structure of blacktip shark (Carcharhinus limbatus) nurseries in the northwestern Atlantic, Gulf of Mexico, and Caribbean Sea.
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ABSTRACT: Abstract We investigated the genetic structure of blacktip shark (Carcharhinus limbatus) continental nurseries in the northwestern Atlantic Ocean, Gulf of Mexico, and Caribbean Sea using mitochondrial DNA control region sequences and eight nuclear microsatellite loci scored in neonate and young-of-the-year sharks. Significant structure was detected with both markers among nine nurseries (mitochondrial PhiST = 0.350, P < 0.001; nuclear PhiST = 0.007, P < 0.001) and sharks from the northwestern Atlantic, eastern Gulf of Mexico, western Gulf of Mexico, northern Yucatan, and Belize possessed significantly different mitochondrial DNA haplotype frequencies. Microsatellite differentiation was limited to comparisons involving northern Yucatan and Belize sharks with nuclear genetic homogeneity throughout the eastern Gulf of Mexico, western Gulf of Mexico, and northwestern Atlantic. Differences in the magnitude of maternal vs. biparental genetic differentiation support female philopatry to northwestern Atlantic, Gulf of Mexico, and Caribbean Sea natal nursery regions with higher levels of male-mediated gene flow. Philopatry has produced multiple reproductive stocks of this commercially important shark species throughout the range of this study.Molecular Ecology 06/2005; 14(7):1911-23. · 5.52 Impact Factor -
Article: Genetic heterogeneity among blacktip shark, Carcharhinus limbatus, continental nurseries along the U.S. Atlantic and Gulf of Mexico
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ABSTRACT: Genetic population structure of the blacktip shark, Carcharhinus limbatus, a commercially and recreationally important species in the southeast U.S. shark fishery, was investigated using mitochondrial DNA control region sequences. Neonate blacktip sharks were sampled from three nurseries, Pine Island Sound, Terra Ceia Bay, and Yankeetown, along the Gulf of Mexico coast of Florida (Gulf) and one nursery, Bulls Bay, on the Atlantic Ocean coast of South Carolina (Atlantic). Sequencing of the complete mitochondrial control region of 169 neonates revealed 10 polymorphic sites and 13 haplotypes. Overall haplotype diversity and percent nucleotide diversity were 0.710 and 0.106%, respectively. Haplotype frequencies were compared among nurseries to determine if the high mobility and seasonal migrations of adult blacktip sharks have maintained genetic homogeneity among nurseries in the Atlantic and Gulf. Chi-square analysis and AMOVA did not detect significant structuring of haplotypes among the three Gulf nurseries, P(2)=0.294, ST=–0.005 to –0.002. All pairwise AMOVA between Gulf nurseries and the Atlantic nursery detected significant partitioning of haplotypes between the Gulf and Atlantic (ST=0.087–0.129, P<0.008), as did comparison between grouped Florida Gulf nurseries and the Atlantic, CT=0.090, P<0.001. Based upon the dispersal abilities and seasonal migrations of blacktip sharks, these results support the presence of philopatry for nursery areas among female blacktip sharks. Our data also support the treatment of Atlantic and Gulf blacktip shark nursery areas as separate management units.Marine Biology 11/2003; 143(6):1039-1046. · 2.28 Impact Factor
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2003–2011
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Southern Illinois University Carbondale
- Department of Zoology
Carbondale, IL, USA
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