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Mixing of porpoise ecotypes in southwestern UK waters revealed by genetic profiling

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ABSTRACT

Contact zones between ecotypes are windows for understanding how species may react to climate changes. Here, we analysed the fine-scale genetic and morphological variation in harbour porpoises (Phocoena phocoena) around the UK by genotyping 591 stranded animals at nine microsatellite loci. The data were integrated with a prior study to map at high resolution the contact zone between two previously identified ecotypes meeting in the northern Bay of Biscay. Clustering and spatial analyses revealed that UK porpoises are derived from two genetic pools with porpoises from the southwestern UK being genetically differentiated, and having larger body sizes compared to those of other UK areas. Southwestern UK porpoises showed admixed ancestry between southern and northern ecotypes with a contact zone extending from the northern Bay of Biscay to the Celtic Sea and Channel. Around the UK, ancestry blends from one genetic group to the other along a southwest--northeast axis, correlating with body size variation, consistent with previously reported morphological differences between the two ecotypes. We also detected isolation by distance among juveniles but not in adults, suggesting that stranded juveniles display reduced intergenerational dispersal. The fine-scale structure of this admixture zone raises the question of how it will respond to future climate change and provides a reference point for further study.

No MeSH data available.


Geographical variation in the residuals from the linear model of the body-length values as a function of age and sex. (a) Residual values are shown on a map and (b) as boxplots per region. (c) The relationship between the individual residuals of body size with individual genetic admixture proportions (%K1) estimated in the Bayesian clustering analysis of structure (Pearson's r = 0.39, p = 8.3 × 10−14).
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RSOS160992F4: Geographical variation in the residuals from the linear model of the body-length values as a function of age and sex. (a) Residual values are shown on a map and (b) as boxplots per region. (c) The relationship between the individual residuals of body size with individual genetic admixture proportions (%K1) estimated in the Bayesian clustering analysis of structure (Pearson's r = 0.39, p = 8.3 × 10−14).

Mentions: As previously reported [14], we found that both age and sex were significant predictors of the body length, explaining about 61% of the total variation (linear model, LM1: F2,334 = 261.1, p < 2.2 × 10−16, n = 336). We inspected the geographical variation in the residuals (figure 4a,b) and observed that porpoises from the southwestern (CWest) area as well as some porpoises from the west area of England displayed significantly larger body size compared to the others (one-way ANOVA, F5 = 15.53, p < 9.9 × 10−14 and p < 0.001 for all Tukey pairwise comparisons involving CWest; electronic supplementary material, table S2). We also observed a strong correlation between individual residuals of body size and individual genetic admixture proportions estimated by STRUCTURE (Pearson's r = 0.39, p = 8.3 × 10−14, figure 4c). Combining the genetic ancestry together with the age and sex in the linear model for predicting the body length increased significantly the total variance explained by the linear model up to 67% (LM2: F3,333 = 225.5, p < 2.2 × 10−16). This model with genetic ancestry offered a significantly better fit to the data compared to a model where it is not included (nested model comparison LM1 versus LM2: ANOVA F1,333 = 60.8, p < 8.2 × 10−14).Figure 4.


Mixing of porpoise ecotypes in southwestern UK waters revealed by genetic profiling
Geographical variation in the residuals from the linear model of the body-length values as a function of age and sex. (a) Residual values are shown on a map and (b) as boxplots per region. (c) The relationship between the individual residuals of body size with individual genetic admixture proportions (%K1) estimated in the Bayesian clustering analysis of structure (Pearson's r = 0.39, p = 8.3 × 10−14).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5383846&req=5

RSOS160992F4: Geographical variation in the residuals from the linear model of the body-length values as a function of age and sex. (a) Residual values are shown on a map and (b) as boxplots per region. (c) The relationship between the individual residuals of body size with individual genetic admixture proportions (%K1) estimated in the Bayesian clustering analysis of structure (Pearson's r = 0.39, p = 8.3 × 10−14).
Mentions: As previously reported [14], we found that both age and sex were significant predictors of the body length, explaining about 61% of the total variation (linear model, LM1: F2,334 = 261.1, p < 2.2 × 10−16, n = 336). We inspected the geographical variation in the residuals (figure 4a,b) and observed that porpoises from the southwestern (CWest) area as well as some porpoises from the west area of England displayed significantly larger body size compared to the others (one-way ANOVA, F5 = 15.53, p < 9.9 × 10−14 and p < 0.001 for all Tukey pairwise comparisons involving CWest; electronic supplementary material, table S2). We also observed a strong correlation between individual residuals of body size and individual genetic admixture proportions estimated by STRUCTURE (Pearson's r = 0.39, p = 8.3 × 10−14, figure 4c). Combining the genetic ancestry together with the age and sex in the linear model for predicting the body length increased significantly the total variance explained by the linear model up to 67% (LM2: F3,333 = 225.5, p < 2.2 × 10−16). This model with genetic ancestry offered a significantly better fit to the data compared to a model where it is not included (nested model comparison LM1 versus LM2: ANOVA F1,333 = 60.8, p < 8.2 × 10−14).Figure 4.

View Article: PubMed Central - PubMed

ABSTRACT

Contact zones between ecotypes are windows for understanding how species may react to climate changes. Here, we analysed the fine-scale genetic and morphological variation in harbour porpoises (Phocoena phocoena) around the UK by genotyping 591 stranded animals at nine microsatellite loci. The data were integrated with a prior study to map at high resolution the contact zone between two previously identified ecotypes meeting in the northern Bay of Biscay. Clustering and spatial analyses revealed that UK porpoises are derived from two genetic pools with porpoises from the southwestern UK being genetically differentiated, and having larger body sizes compared to those of other UK areas. Southwestern UK porpoises showed admixed ancestry between southern and northern ecotypes with a contact zone extending from the northern Bay of Biscay to the Celtic Sea and Channel. Around the UK, ancestry blends from one genetic group to the other along a southwest--northeast axis, correlating with body size variation, consistent with previously reported morphological differences between the two ecotypes. We also detected isolation by distance among juveniles but not in adults, suggesting that stranded juveniles display reduced intergenerational dispersal. The fine-scale structure of this admixture zone raises the question of how it will respond to future climate change and provides a reference point for further study.

No MeSH data available.