Limits...
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.

Show MeSH

Related in: MedlinePlus

STRUCTURE results for a) bottlenose dolphin carcasses from Spencer Gulf and western coastal areas, South Australia; and b) combined datasets from bottlenose dolphin carcasses and free-ranging individuals, Spencer Gulf and western coastal areas, South Australia.Each vertical column represents one individual dolphin, and the separation of the column into two colours represents the estimated probability of belonging to one or the other population. F = free-ranging dolphins, C = carcasses. Specific geographic locations where dolphins were found or biopsied: FI = St Francis Isles, WSA = western South Australian coast, CB = Coffin Bay, PL = Port Lincoln, NSG = North Spencer Gulf, SESG = southeast Spencer Gulf. See Figure 1 for geographic locations.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3105009&req=5

pone-0020103-g001: STRUCTURE results for a) bottlenose dolphin carcasses from Spencer Gulf and western coastal areas, South Australia; and b) combined datasets from bottlenose dolphin carcasses and free-ranging individuals, Spencer Gulf and western coastal areas, South Australia.Each vertical column represents one individual dolphin, and the separation of the column into two colours represents the estimated probability of belonging to one or the other population. F = free-ranging dolphins, C = carcasses. Specific geographic locations where dolphins were found or biopsied: FI = St Francis Isles, WSA = western South Australian coast, CB = Coffin Bay, PL = Port Lincoln, NSG = North Spencer Gulf, SESG = southeast Spencer Gulf. See Figure 1 for geographic locations.

Mentions: STRUCTURE did not detect genetic partitioning for bottlenose dolphin between W coastal areas and SG when using carcass samples, which is in contrast to results based on biopsied free-ranging individuals [34], (Figure 1a). For carcasses, we found the probability of P(X/K) to be highest at K = 1 when using either version of the program (standard version 2.0 and version 2.3.3 for weak population structure) and when applying either the independent or the correlated allele frequency model, suggesting the presence of only one population in W coastal areas and SG of SA when using the carcass dataset. Estimates of P(X/K) and the prior α showed consistency among multiple runs, indicating that the burn-in length and the length of the runs were appropriate. Additionally, we ran the STRUCTURE analysis by fixing the number of populations to K = 2 and including population location information to identify potential migrants. Three individuals from SG were identified as potential migrants from W coastal. All three carcasses were relatively fresh. One of the three individuals was found near the population boundary to the W coastal area, and the other two individuals were found far away indicating that they were unlikely to have drifted over the population boundary.


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)

STRUCTURE results for a) bottlenose dolphin carcasses from Spencer Gulf and western coastal areas, South Australia; and b) combined datasets from bottlenose dolphin carcasses and free-ranging individuals, Spencer Gulf and western coastal areas, South Australia.Each vertical column represents one individual dolphin, and the separation of the column into two colours represents the estimated probability of belonging to one or the other population. F = free-ranging dolphins, C = carcasses. Specific geographic locations where dolphins were found or biopsied: FI = St Francis Isles, WSA = western South Australian coast, CB = Coffin Bay, PL = Port Lincoln, NSG = North Spencer Gulf, SESG = southeast Spencer Gulf. See Figure 1 for geographic locations.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0020103-g001: STRUCTURE results for a) bottlenose dolphin carcasses from Spencer Gulf and western coastal areas, South Australia; and b) combined datasets from bottlenose dolphin carcasses and free-ranging individuals, Spencer Gulf and western coastal areas, South Australia.Each vertical column represents one individual dolphin, and the separation of the column into two colours represents the estimated probability of belonging to one or the other population. F = free-ranging dolphins, C = carcasses. Specific geographic locations where dolphins were found or biopsied: FI = St Francis Isles, WSA = western South Australian coast, CB = Coffin Bay, PL = Port Lincoln, NSG = North Spencer Gulf, SESG = southeast Spencer Gulf. See Figure 1 for geographic locations.
Mentions: STRUCTURE did not detect genetic partitioning for bottlenose dolphin between W coastal areas and SG when using carcass samples, which is in contrast to results based on biopsied free-ranging individuals [34], (Figure 1a). For carcasses, we found the probability of P(X/K) to be highest at K = 1 when using either version of the program (standard version 2.0 and version 2.3.3 for weak population structure) and when applying either the independent or the correlated allele frequency model, suggesting the presence of only one population in W coastal areas and SG of SA when using the carcass dataset. Estimates of P(X/K) and the prior α showed consistency among multiple runs, indicating that the burn-in length and the length of the runs were appropriate. Additionally, we ran the STRUCTURE analysis by fixing the number of populations to K = 2 and including population location information to identify potential migrants. Three individuals from SG were identified as potential migrants from W coastal. All three carcasses were relatively fresh. One of the three individuals was found near the population boundary to the W coastal area, and the other two individuals were found far away indicating that they were unlikely to have drifted over the population boundary.

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