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The use of carcasses for the analysis of cetacean population genetic structure: a comparative study in two dolphin species.

Bilgmann K, Möller LM, Harcourt RG, Kemper CM, Beheregaray LB - PLoS ONE (2011)

Bottom Line: This leads to the question of how representative the location of a stranded or entangled animal is with respect to its natural range, and whether similar results would be obtained when comparing carcass samples with samples from free-ranging individuals in studies of population structure.Analyses based on carcass samples alone failed to detect genetic structure in Tursiops sp., a species previously shown to exhibit restricted dispersal and moderate genetic differentiation across a small spatial scale in this region.However, genetic structure was correctly inferred in D. delphis, a species previously shown to have reduced genetic structure over a similar geographic area.

View Article: PubMed Central - PubMed

Affiliation: Marine Mammal Research Group, Graduate School of the Environment, Macquarie University, Sydney, New South Wales, Australia. kerstin.bilgmann@mq.edu.au

ABSTRACT
Advances in molecular techniques have enabled the study of genetic diversity and population structure in many different contexts. Studies that assess the genetic structure of cetacean populations often use biopsy samples from free-ranging individuals and tissue samples from stranded animals or individuals that became entangled in fishery or aquaculture equipment. This leads to the question of how representative the location of a stranded or entangled animal is with respect to its natural range, and whether similar results would be obtained when comparing carcass samples with samples from free-ranging individuals in studies of population structure. Here we use tissue samples from carcasses of dolphins that stranded or died as a result of bycatch in South Australia to investigate spatial population structure in two species: coastal bottlenose (Tursiops sp.) and short-beaked common dolphins (Delphinus delphis). We compare these results with those previously obtained from biopsy sampled free-ranging dolphins in the same area to test whether carcass samples yield similar patterns of genetic variability and population structure. Data from dolphin carcasses were gathered using seven microsatellite markers and a fragment of the mitochondrial DNA control region. Analyses based on carcass samples alone failed to detect genetic structure in Tursiops sp., a species previously shown to exhibit restricted dispersal and moderate genetic differentiation across a small spatial scale in this region. However, genetic structure was correctly inferred in D. delphis, a species previously shown to have reduced genetic structure over a similar geographic area. We propose that in the absence of corroborating data, and when population structure is assessed over relatively small spatial scales, the sole use of carcasses may lead to an underestimate of genetic differentiation. This can lead to a failure in identifying management units for conservation. Therefore, this risk should be carefully assessed when planning population genetic studies of cetaceans.

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Haplotype network for mtDNA control region sequences of bottlenose dolphin carcasses collected from western coastal areas and Spencer Gulf.The size of the ovals is proportional to the number of individuals showing the particular haplotype. Haplotype H1 was considered to be ancestor based on coalescence theory. Each line indicates one mutation between haplotypes, and small circles between connecting lines represent missing or hypothetical haplotypes.
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pone-0020103-g003: Haplotype network for mtDNA control region sequences of bottlenose dolphin carcasses collected from western coastal areas and Spencer Gulf.The size of the ovals is proportional to the number of individuals showing the particular haplotype. Haplotype H1 was considered to be ancestor based on coalescence theory. Each line indicates one mutation between haplotypes, and small circles between connecting lines represent missing or hypothetical haplotypes.

Mentions: We constructed a haplotype network using mtDNA control region sequences for bottlenose dolphin carcasses (Figure 3). The network suggests a shallow scenario of matrilineal diversification for bottlenose dolphins in SA, which was also the case for our free-ranging dataset in [34]. H1 had the highest outgroup probability in both networks, representing the most likely ancestral lineage for the area. Most haplotypes appear to have recently originated from this haplotype. The dataset of dolphin carcasses (n = 51) led to the detection of five haplotypes (Figure 3) compared to 10 haplotypes in the free-ranging dataset (n = 84; [34]). All five haplotypes from dolphin carcasses were also present in the free-ranging dataset [34].


The use of carcasses for the analysis of cetacean population genetic structure: a comparative study in two dolphin species.

Bilgmann K, Möller LM, Harcourt RG, Kemper CM, Beheregaray LB - PLoS ONE (2011)

Haplotype network for mtDNA control region sequences of bottlenose dolphin carcasses collected from western coastal areas and Spencer Gulf.The size of the ovals is proportional to the number of individuals showing the particular haplotype. Haplotype H1 was considered to be ancestor based on coalescence theory. Each line indicates one mutation between haplotypes, and small circles between connecting lines represent missing or hypothetical haplotypes.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3105009&req=5

pone-0020103-g003: Haplotype network for mtDNA control region sequences of bottlenose dolphin carcasses collected from western coastal areas and Spencer Gulf.The size of the ovals is proportional to the number of individuals showing the particular haplotype. Haplotype H1 was considered to be ancestor based on coalescence theory. Each line indicates one mutation between haplotypes, and small circles between connecting lines represent missing or hypothetical haplotypes.
Mentions: We constructed a haplotype network using mtDNA control region sequences for bottlenose dolphin carcasses (Figure 3). The network suggests a shallow scenario of matrilineal diversification for bottlenose dolphins in SA, which was also the case for our free-ranging dataset in [34]. H1 had the highest outgroup probability in both networks, representing the most likely ancestral lineage for the area. Most haplotypes appear to have recently originated from this haplotype. The dataset of dolphin carcasses (n = 51) led to the detection of five haplotypes (Figure 3) compared to 10 haplotypes in the free-ranging dataset (n = 84; [34]). All five haplotypes from dolphin carcasses were also present in the free-ranging dataset [34].

Bottom Line: This leads to the question of how representative the location of a stranded or entangled animal is with respect to its natural range, and whether similar results would be obtained when comparing carcass samples with samples from free-ranging individuals in studies of population structure.Analyses based on carcass samples alone failed to detect genetic structure in Tursiops sp., a species previously shown to exhibit restricted dispersal and moderate genetic differentiation across a small spatial scale in this region.However, genetic structure was correctly inferred in D. delphis, a species previously shown to have reduced genetic structure over a similar geographic area.

View Article: PubMed Central - PubMed

Affiliation: Marine Mammal Research Group, Graduate School of the Environment, Macquarie University, Sydney, New South Wales, Australia. kerstin.bilgmann@mq.edu.au

ABSTRACT
Advances in molecular techniques have enabled the study of genetic diversity and population structure in many different contexts. Studies that assess the genetic structure of cetacean populations often use biopsy samples from free-ranging individuals and tissue samples from stranded animals or individuals that became entangled in fishery or aquaculture equipment. This leads to the question of how representative the location of a stranded or entangled animal is with respect to its natural range, and whether similar results would be obtained when comparing carcass samples with samples from free-ranging individuals in studies of population structure. Here we use tissue samples from carcasses of dolphins that stranded or died as a result of bycatch in South Australia to investigate spatial population structure in two species: coastal bottlenose (Tursiops sp.) and short-beaked common dolphins (Delphinus delphis). We compare these results with those previously obtained from biopsy sampled free-ranging dolphins in the same area to test whether carcass samples yield similar patterns of genetic variability and population structure. Data from dolphin carcasses were gathered using seven microsatellite markers and a fragment of the mitochondrial DNA control region. Analyses based on carcass samples alone failed to detect genetic structure in Tursiops sp., a species previously shown to exhibit restricted dispersal and moderate genetic differentiation across a small spatial scale in this region. However, genetic structure was correctly inferred in D. delphis, a species previously shown to have reduced genetic structure over a similar geographic area. We propose that in the absence of corroborating data, and when population structure is assessed over relatively small spatial scales, the sole use of carcasses may lead to an underestimate of genetic differentiation. This can lead to a failure in identifying management units for conservation. Therefore, this risk should be carefully assessed when planning population genetic studies of cetaceans.

Show MeSH
Related in: MedlinePlus