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Opposite environmental and genetic influences on body size in North American Drosophila pseudoobscura.

Taylor ML, Skeats A, Wilson AJ, Price TA, Wedell N - BMC Evol. Biol. (2015)

Bottom Line: However, it is rarely known whether these differences are associated with genetic variation and evolved differences between populations, or are instead simply a plastic response to environmental differences experienced by the populations.However, we also found a genetic signature that was counter to this pattern as flies originating from the northern, cooler population were consistently smaller than conspecifics from more southern, warmer populations when reared under the same laboratory conditions.We conclude that local selection on body size appears to be acting counter to the environmental effect of temperature.

View Article: PubMed Central - PubMed

Affiliation: College of Life and Environmental Sciences, Biosciences, University of Exeter, Penryn Campus, Penryn, Cornwall, TR10 9FE, UK. m.l.taylor@exeter.ac.uk.

ABSTRACT

Background: Populations of a species often differ in key traits. However, it is rarely known whether these differences are associated with genetic variation and evolved differences between populations, or are instead simply a plastic response to environmental differences experienced by the populations. Here we examine the interplay of plasticity and direct genetic control by investigating temperature-size relationships in populations of Drosophila pseudoobscura from North America. We used 27 isolines from three populations and exposed them to four temperature regimes (16°C, 20°C, 23°C, 26°C) to examine environmental, genetic and genotype-by-environment sources of variance in wing size.

Results: By far the largest contribution to variation in wing size came from rearing temperature, with the largest flies emerging from the coolest temperatures. However, we also found a genetic signature that was counter to this pattern as flies originating from the northern, cooler population were consistently smaller than conspecifics from more southern, warmer populations when reared under the same laboratory conditions.

Conclusions: We conclude that local selection on body size appears to be acting counter to the environmental effect of temperature. We find no evidence that local adaptation in phenotypic plasticity can explain this result, and suggest indirect selection on traits closely linked with body size, or patterns of chromosome inversion may instead be driving this relationship.

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Related in: MedlinePlus

Reaction norms for wing sizes (expected values) of each isoline, with temperature as a continuous variable. Lewistown (northern population) = dashed black lines; Show Low (southern population) = solid grey lines; Chiricahua (southernmost population) = dashed grey lines.
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Fig3: Reaction norms for wing sizes (expected values) of each isoline, with temperature as a continuous variable. Lewistown (northern population) = dashed black lines; Show Low (southern population) = solid grey lines; Chiricahua (southernmost population) = dashed grey lines.

Mentions: Where, μ is the mean, Year is a 2-level fixed factor (2008, 2012), T is a linear effect of temperature in °C (mean centred across all observations), Pop is a 3-level fixed factor (Lewistown, Show Low, Chiricahua) and Year.Pop and T.Year.Pop are interaction terms. Our mixed model analysis showed that, after controlling for a small but significant Year effect and a marginally non-significant T.Year interaction effect, there was evidence for plasticity and among-population genetic variance in wing length (Table 2). Average wing length decreases at a rate of 0.201 (0.027) standard deviations units (approximately 0.024 mm) for each degree of temperature rise. However, there was no statistical support for among-population GxEs (represented in our model by the T.pop interaction term). Likelihood ratio tests provided evidence of significant within-population (among isoline) genetic variance (χ21 = 81.2, P < 0.001) and GxE (χ21 = 37.9, P < 0.001). Under the full model (i.e. including GxEs) the (co) variance parameters (SE) were estimated as: VR = 0.153 (0.011), VISO_int = 0.064 (0.022), VISO_slp = 0.026 (0.001) and COVISO_int.slp = −0.007 (0.003), the latter scaling to an intercept-slope correlation rISO_int.slp of −0.571 (0.198). Note that since T was mean centred and the raw data scaled to unit variance, VISO_int can be directly interpreted as the proportion of observed phenotypic variance in wing length attributable to genetic differences among isolines at an average temperature (Figure 3). Overall we conclude that variation in wing sizes is primarily influenced by environmental temperature, with a smaller influence due to genetic variation expressed as significant isoline responses. There were no substantial influences on mean plasticity between populations due to GxE effects, but significant GxE isoline differences.Table 2


Opposite environmental and genetic influences on body size in North American Drosophila pseudoobscura.

Taylor ML, Skeats A, Wilson AJ, Price TA, Wedell N - BMC Evol. Biol. (2015)

Reaction norms for wing sizes (expected values) of each isoline, with temperature as a continuous variable. Lewistown (northern population) = dashed black lines; Show Low (southern population) = solid grey lines; Chiricahua (southernmost population) = dashed grey lines.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4374297&req=5

Fig3: Reaction norms for wing sizes (expected values) of each isoline, with temperature as a continuous variable. Lewistown (northern population) = dashed black lines; Show Low (southern population) = solid grey lines; Chiricahua (southernmost population) = dashed grey lines.
Mentions: Where, μ is the mean, Year is a 2-level fixed factor (2008, 2012), T is a linear effect of temperature in °C (mean centred across all observations), Pop is a 3-level fixed factor (Lewistown, Show Low, Chiricahua) and Year.Pop and T.Year.Pop are interaction terms. Our mixed model analysis showed that, after controlling for a small but significant Year effect and a marginally non-significant T.Year interaction effect, there was evidence for plasticity and among-population genetic variance in wing length (Table 2). Average wing length decreases at a rate of 0.201 (0.027) standard deviations units (approximately 0.024 mm) for each degree of temperature rise. However, there was no statistical support for among-population GxEs (represented in our model by the T.pop interaction term). Likelihood ratio tests provided evidence of significant within-population (among isoline) genetic variance (χ21 = 81.2, P < 0.001) and GxE (χ21 = 37.9, P < 0.001). Under the full model (i.e. including GxEs) the (co) variance parameters (SE) were estimated as: VR = 0.153 (0.011), VISO_int = 0.064 (0.022), VISO_slp = 0.026 (0.001) and COVISO_int.slp = −0.007 (0.003), the latter scaling to an intercept-slope correlation rISO_int.slp of −0.571 (0.198). Note that since T was mean centred and the raw data scaled to unit variance, VISO_int can be directly interpreted as the proportion of observed phenotypic variance in wing length attributable to genetic differences among isolines at an average temperature (Figure 3). Overall we conclude that variation in wing sizes is primarily influenced by environmental temperature, with a smaller influence due to genetic variation expressed as significant isoline responses. There were no substantial influences on mean plasticity between populations due to GxE effects, but significant GxE isoline differences.Table 2

Bottom Line: However, it is rarely known whether these differences are associated with genetic variation and evolved differences between populations, or are instead simply a plastic response to environmental differences experienced by the populations.However, we also found a genetic signature that was counter to this pattern as flies originating from the northern, cooler population were consistently smaller than conspecifics from more southern, warmer populations when reared under the same laboratory conditions.We conclude that local selection on body size appears to be acting counter to the environmental effect of temperature.

View Article: PubMed Central - PubMed

Affiliation: College of Life and Environmental Sciences, Biosciences, University of Exeter, Penryn Campus, Penryn, Cornwall, TR10 9FE, UK. m.l.taylor@exeter.ac.uk.

ABSTRACT

Background: Populations of a species often differ in key traits. However, it is rarely known whether these differences are associated with genetic variation and evolved differences between populations, or are instead simply a plastic response to environmental differences experienced by the populations. Here we examine the interplay of plasticity and direct genetic control by investigating temperature-size relationships in populations of Drosophila pseudoobscura from North America. We used 27 isolines from three populations and exposed them to four temperature regimes (16°C, 20°C, 23°C, 26°C) to examine environmental, genetic and genotype-by-environment sources of variance in wing size.

Results: By far the largest contribution to variation in wing size came from rearing temperature, with the largest flies emerging from the coolest temperatures. However, we also found a genetic signature that was counter to this pattern as flies originating from the northern, cooler population were consistently smaller than conspecifics from more southern, warmer populations when reared under the same laboratory conditions.

Conclusions: We conclude that local selection on body size appears to be acting counter to the environmental effect of temperature. We find no evidence that local adaptation in phenotypic plasticity can explain this result, and suggest indirect selection on traits closely linked with body size, or patterns of chromosome inversion may instead be driving this relationship.

Show MeSH
Related in: MedlinePlus