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Morphological and genetic divergence in Swedish postglacial stickleback (Pungitius pungitius) populations.

Mobley KB, Lussetti D, Johansson F, Englund G, Bokma F - BMC Evol. Biol. (2011)

Bottom Line: Inland populations from lakes without predators generally have larger body size, and smaller spine length relative to body size, suggesting systematic reduction in spine length.Taken together the results suggest that predation plays a role in shaping morphological variation among isolated inland populations.However, we cannot rule out that a causal relationship between predation versus other genetic and environmental influences on phenotypic variation not measured in this study exists, and this warrants further investigation.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Ecology and Environmental Science, Linnaeus väg 6, Umeå University, 90187 Sweden. mobley@evolbio.mpg.de

ABSTRACT

Background: An important objective of evolutionary biology is to understand the processes that govern phenotypic variation in natural populations. We assessed patterns of morphological and genetic divergence among coastal and inland lake populations of nine-spined stickleback in northern Sweden. Coastal populations are either from the Baltic coast (n = 5) or from nearby coastal lakes (n = 3) that became isolated from the Baltic Sea (< 100 years before present, ybp). Inland populations are from freshwater lakes that became isolated from the Baltic approximately 10,000 ybp; either single species lakes without predators (n = 5), or lakes with a recent history of predation (n = 5) from stocking of salmonid predators (~50 ybp).

Results: Coastal populations showed little variation in 11 morphological traits and had longer spines per unit of body length than inland populations. Inland populations were larger, on average, and showed greater morphological variation than coastal populations. A principal component analysis (PCA) across all populations revealed two major morphological axes related to spine length (PC1, 47.7% variation) and body size (PC2, 32.9% variation). Analysis of PCA scores showed marked similarity in coastal (Baltic coast and coastal lake) populations. PCA scores indicate that inland populations with predators have higher within-group variance in spine length and lower within-group variance in body size than inland populations without predators. Estimates of within-group PST (a proxy for QST) from PCA scores are similar to estimates of FST for coastal lake populations but PST >FST for Baltic coast populations. PST >FST for PC1 and PC2 for inland predator and inland no predator populations, with the exception that PST

Conclusions: Baltic coast and coastal lake populations show little morphological and genetic variation within and between groups suggesting that these populations experience similar ecological conditions and that time since isolation of coastal lakes has been insufficient to demonstrate divergent morphology in coastal lake populations. Inland populations, on the other hand, showed much greater morphological and genetic variation characteristic of long periods of isolation. Inland populations from lakes without predators generally have larger body size, and smaller spine length relative to body size, suggesting systematic reduction in spine length. In contrast, inland populations with predators exhibit a wider range of spine lengths relative to body size suggesting that this trait is responding to local predation pressure differently among these populations. Taken together the results suggest that predation plays a role in shaping morphological variation among isolated inland populations. However, we cannot rule out that a causal relationship between predation versus other genetic and environmental influences on phenotypic variation not measured in this study exists, and this warrants further investigation.

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Within-group PST - FST comparisons for A) PC1 and B) PC2. Global FST are shown as an X. Mean PST estimates (± 95%CI) are shown as symbols.
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Figure 5: Within-group PST - FST comparisons for A) PC1 and B) PC2. Global FST are shown as an X. Mean PST estimates (± 95%CI) are shown as symbols.

Mentions: Within-group estimates of neutral genetic divergence (FST) and phenotypic divergence (PST) in Baltic coast and coastal lake groups demonstrated low estimates for each measure (Table 4, Figure 5). The Baltic coast group had PST >FST with non-overlapping 95% confidence intervals for both PC1 and PC2 suggesting that divergent selection on both spine length and body size is occurring in populations of this group. Coastal lake PST estimates, on the other hand, had overlapping 95% confidence intervals with FST (Table 4, Figure 5) which suggests that within this group, one cannot distinguish between the effects of natural selection and genetic drift on phenotypic appearance. Within the inland no predator group, we found PST <FST for PC1 indicating stabilizing selection on spine length and the opposite trend, namely PST >FST for PC2, suggesting divergent selection in body size in this group (Table 4, Figure 5). Finally, inland populations with predators show PST >FST for PC1 and PC2 suggesting divergent selection on spine length and body size, but estimates of PST are more variable than any other estimate and confidence intervals overlap FST values, making a judgement as to whether natural selection or genetic drift is operating equivocal (Table 4, Figure 5).


Morphological and genetic divergence in Swedish postglacial stickleback (Pungitius pungitius) populations.

Mobley KB, Lussetti D, Johansson F, Englund G, Bokma F - BMC Evol. Biol. (2011)

Within-group PST - FST comparisons for A) PC1 and B) PC2. Global FST are shown as an X. Mean PST estimates (± 95%CI) are shown as symbols.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3198969&req=5

Figure 5: Within-group PST - FST comparisons for A) PC1 and B) PC2. Global FST are shown as an X. Mean PST estimates (± 95%CI) are shown as symbols.
Mentions: Within-group estimates of neutral genetic divergence (FST) and phenotypic divergence (PST) in Baltic coast and coastal lake groups demonstrated low estimates for each measure (Table 4, Figure 5). The Baltic coast group had PST >FST with non-overlapping 95% confidence intervals for both PC1 and PC2 suggesting that divergent selection on both spine length and body size is occurring in populations of this group. Coastal lake PST estimates, on the other hand, had overlapping 95% confidence intervals with FST (Table 4, Figure 5) which suggests that within this group, one cannot distinguish between the effects of natural selection and genetic drift on phenotypic appearance. Within the inland no predator group, we found PST <FST for PC1 indicating stabilizing selection on spine length and the opposite trend, namely PST >FST for PC2, suggesting divergent selection in body size in this group (Table 4, Figure 5). Finally, inland populations with predators show PST >FST for PC1 and PC2 suggesting divergent selection on spine length and body size, but estimates of PST are more variable than any other estimate and confidence intervals overlap FST values, making a judgement as to whether natural selection or genetic drift is operating equivocal (Table 4, Figure 5).

Bottom Line: Inland populations from lakes without predators generally have larger body size, and smaller spine length relative to body size, suggesting systematic reduction in spine length.Taken together the results suggest that predation plays a role in shaping morphological variation among isolated inland populations.However, we cannot rule out that a causal relationship between predation versus other genetic and environmental influences on phenotypic variation not measured in this study exists, and this warrants further investigation.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Ecology and Environmental Science, Linnaeus väg 6, Umeå University, 90187 Sweden. mobley@evolbio.mpg.de

ABSTRACT

Background: An important objective of evolutionary biology is to understand the processes that govern phenotypic variation in natural populations. We assessed patterns of morphological and genetic divergence among coastal and inland lake populations of nine-spined stickleback in northern Sweden. Coastal populations are either from the Baltic coast (n = 5) or from nearby coastal lakes (n = 3) that became isolated from the Baltic Sea (< 100 years before present, ybp). Inland populations are from freshwater lakes that became isolated from the Baltic approximately 10,000 ybp; either single species lakes without predators (n = 5), or lakes with a recent history of predation (n = 5) from stocking of salmonid predators (~50 ybp).

Results: Coastal populations showed little variation in 11 morphological traits and had longer spines per unit of body length than inland populations. Inland populations were larger, on average, and showed greater morphological variation than coastal populations. A principal component analysis (PCA) across all populations revealed two major morphological axes related to spine length (PC1, 47.7% variation) and body size (PC2, 32.9% variation). Analysis of PCA scores showed marked similarity in coastal (Baltic coast and coastal lake) populations. PCA scores indicate that inland populations with predators have higher within-group variance in spine length and lower within-group variance in body size than inland populations without predators. Estimates of within-group PST (a proxy for QST) from PCA scores are similar to estimates of FST for coastal lake populations but PST >FST for Baltic coast populations. PST >FST for PC1 and PC2 for inland predator and inland no predator populations, with the exception that PST

Conclusions: Baltic coast and coastal lake populations show little morphological and genetic variation within and between groups suggesting that these populations experience similar ecological conditions and that time since isolation of coastal lakes has been insufficient to demonstrate divergent morphology in coastal lake populations. Inland populations, on the other hand, showed much greater morphological and genetic variation characteristic of long periods of isolation. Inland populations from lakes without predators generally have larger body size, and smaller spine length relative to body size, suggesting systematic reduction in spine length. In contrast, inland populations with predators exhibit a wider range of spine lengths relative to body size suggesting that this trait is responding to local predation pressure differently among these populations. Taken together the results suggest that predation plays a role in shaping morphological variation among isolated inland populations. However, we cannot rule out that a causal relationship between predation versus other genetic and environmental influences on phenotypic variation not measured in this study exists, and this warrants further investigation.

Show MeSH
Related in: MedlinePlus