Abstract
Phenotypic flexibility allows individuals to reversibly modify trait values and theory predicts an individual’s relative degree of flexibility positively correlates with the environmental heterogeneity it experiences. We test this prediction by integrating surveys of population genetic and physiological variation with thermal acclimation experiments and indices of environmental heterogeneity in the Dark-eyed Junco (Junco hyemalis) and its congeners. We combine field measures of thermogenic capacity for 335 individuals, 22,006 single nucleotide polymorphisms genotyped in 181 individuals, and laboratory acclimations replicated on five populations. We show that Junco populations: (1) differ in their thermogenic responses to temperature variation in the field; (2) harbor allelic variation that also correlates with temperature heterogeneity; and (3) exhibit intra-specific variation in thermogenic flexibility in the laboratory that correlates with the heterogeneity of their native thermal environment. These results provide comprehensive support that phenotypic flexibility corresponds with environmental heterogeneity and highlight its importance for coping with environmental change.
Highlights
Phenotypic flexibility allows individuals to reversibly modify trait values and theory predicts an individual’s relative degree of flexibility positively correlates with the environmental heterogeneity it experiences
If flexibility can be locally adapted in this way, empirical evidence for this theory should support three predictions: (1) geographic variation in flexibility corresponds with environmental heterogeneity, (2) genetic variation underlies this phenotypic variation, such that differences in flexibility can be replicated under common garden conditions, and (3) the degree of flexibility should be subjected to natural selection due to its influence on fitness, resulting in a reduction of variability in flexibility for populations occupying more heterogenous environments
We present an acclimation experiment performed in the lab using five Junco populations to test whether the annual thermal regime predicts the degree of flexibility they exhibit under controlled conditions while accounting for genetic relatedness among populations
Summary
Phenotypic flexibility allows individuals to reversibly modify trait values and theory predicts an individual’s relative degree of flexibility positively correlates with the environmental heterogeneity it experiences. We show that Junco populations: (1) differ in their thermogenic responses to temperature variation in the field; (2) harbor allelic variation that correlates with temperature heterogeneity; and (3) exhibit intra-specific variation in thermogenic flexibility in the laboratory that correlates with the heterogeneity of their native thermal environment These results provide comprehensive support that phenotypic flexibility corresponds with environmental heterogeneity and highlight its importance for coping with environmental change. If flexibility can be locally adapted in this way, empirical evidence for this theory should support three predictions: (1) geographic variation in flexibility corresponds with environmental heterogeneity, (2) genetic variation underlies this phenotypic variation, such that differences in flexibility can be replicated under common garden conditions, and (3) the degree of flexibility should be subjected to natural selection due to its influence on fitness, resulting in a reduction of variability in flexibility for populations occupying more heterogenous environments. We expected that there may be variation in thermogenic flexibility among different Junco populations that correlates with the amount of temperature variation they experience
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