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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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Mean (± SE) for 10 morphological measurements and the number of dorsal spines arranged by group. Standard length is reported in mm and relative measurements are in units per standard length. Whole model results of general linear mixed models (GLMM) between groups using population nested within group as a random factor are reported. Groups assigned different letters are significantly different (Tukey-Kramer HSD test). Asterix denote significant differences (α = 0.05)
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Figure 3: Mean (± SE) for 10 morphological measurements and the number of dorsal spines arranged by group. Standard length is reported in mm and relative measurements are in units per standard length. Whole model results of general linear mixed models (GLMM) between groups using population nested within group as a random factor are reported. Groups assigned different letters are significantly different (Tukey-Kramer HSD test). Asterix denote significant differences (α = 0.05)

Mentions: Results of the analyses of the 11 morphological characters are summarized by population in Table 5 (See Methods for complete descriptions of morphological characters). Mean estimates of body length (SL) were highest for the inland populations without predators, but did not differ significantly from the other groups (Figure 3). Relative measures of head depth (per unit of standard length, SL-1) demonstrate that inland populations (with and without predators) have the most divergent morphology while coastal populations (Baltic coast, coastal lakes) show intermediate values for this trait (Figure 3). Relative head-eye length, on the other hand, show Baltic coast and inland lake without predator populations to have the most divergent morphology, with coastal lakes and inland lake - predator populations having intermediate values (Figure 3). Relative estimates of spine length (pelvic, anal, anterior dorsal, middle dorsal, posterior dorsal, girdle length and girdle width) consistently demonstrate significantly longer spines (SL-1) in coastal populations than in inland populations (Figure 3). The one measured meristic character, the number of dorsal spines, was variable in all populations with a mean of 9-10 spines (range 8-11) for all populations except BN, which had a mean of five spines (range 1-10) (Table 5). However, this character was not significantly different between groups (Figure 3).


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)

Mean (± SE) for 10 morphological measurements and the number of dorsal spines arranged by group. Standard length is reported in mm and relative measurements are in units per standard length. Whole model results of general linear mixed models (GLMM) between groups using population nested within group as a random factor are reported. Groups assigned different letters are significantly different (Tukey-Kramer HSD test). Asterix denote significant differences (α = 0.05)
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: Mean (± SE) for 10 morphological measurements and the number of dorsal spines arranged by group. Standard length is reported in mm and relative measurements are in units per standard length. Whole model results of general linear mixed models (GLMM) between groups using population nested within group as a random factor are reported. Groups assigned different letters are significantly different (Tukey-Kramer HSD test). Asterix denote significant differences (α = 0.05)
Mentions: Results of the analyses of the 11 morphological characters are summarized by population in Table 5 (See Methods for complete descriptions of morphological characters). Mean estimates of body length (SL) were highest for the inland populations without predators, but did not differ significantly from the other groups (Figure 3). Relative measures of head depth (per unit of standard length, SL-1) demonstrate that inland populations (with and without predators) have the most divergent morphology while coastal populations (Baltic coast, coastal lakes) show intermediate values for this trait (Figure 3). Relative head-eye length, on the other hand, show Baltic coast and inland lake without predator populations to have the most divergent morphology, with coastal lakes and inland lake - predator populations having intermediate values (Figure 3). Relative estimates of spine length (pelvic, anal, anterior dorsal, middle dorsal, posterior dorsal, girdle length and girdle width) consistently demonstrate significantly longer spines (SL-1) in coastal populations than in inland populations (Figure 3). The one measured meristic character, the number of dorsal spines, was variable in all populations with a mean of 9-10 spines (range 8-11) for all populations except BN, which had a mean of five spines (range 1-10) (Table 5). However, this character was not significantly different between groups (Figure 3).

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