The Covariance between Genetic and Environmental Influences across Ecological Gradients

Abstract

Patterns of phenotypic change across environmental gradients (e.g., latitude, altitude) have long captivated the interest of evolutionary ecologists. The pattern and magnitude of phenotypic change is determined by the covariance between genetic and environmental influences across a gradient. Cogradient variation (CoGV) occurs when covariance is positive: that is, genetic and environmental influences on phenotypic expression are aligned and their joint influence accentuates the change in mean trait value across the gradient. Conversely, countergradient variation (CnGV) occurs when covariance is negative: that is, genetic and environmental influences on phenotypes oppose one another, thereby diminishing the change in mean trait expression across the gradient. CnGV has so far been found in at least 60 species, with most examples coming from fishes, amphibians, and insects across latitudinal or altitudinal gradients. Traits that display CnGV most often involve metabolic compensation, that is, the elevation of various physiological rates processes (development, growth, feeding, metabolism, activity) to counteract the dampening effect of reduced temperature, growing season length, or food supply. Far fewer examples of CoGV have been identified (11 species), and these most often involve morphological characters. Increased knowledge of spatial covariance patterns has furthered our understanding of Bergmann size clines, phenotypic plasticity, species range limits, tradeoffs in juvenile growth rate, and the design of conservation strategies for wild species. Moreover, temporal CnGV explains some cases of an apparent lack of phenotypic response to directional selection and provides a framework for predicting evolutionary responses to climate change.

Cold adaptation increases rates of nutrient flow and metabolic plasticity during cold exposure inDrosophila melanogaster

“…However, in natural seasonal environments, nutrient availability declines as cold stress increases with the onset of winter, so natural populations may face resource allocation or acquisition trade-offs that constrain the evolution of energetically expensive cold tolerance strategies [34]. Nonetheless, in nature ectotherms from higher altitudes and latitudes often have higher metabolic rates than similar individuals from lower altitudes and latitudes [35,36]. This pattern is typically attributed to the need for fast growth and development in environments with a short growing season.…”

Long‐term acclimation to reciprocal light conditions suggests depth‐related selection in the marine foundation speciesPosidonia oceanica

“…Patterns of genetic and phenotypic variation of plant and animal populations are closely related to the magnitude of environmental heterogeneity in which they live (Conover, Duffy, & Hice, 2009; Endler, 1977; Hice, Duffy, Munch, & Conover, 2012) and are often independent from geographic distances (Richardson, Urban, Bolnick, & Skelly, 2014). Differential response of distinct populations to local environmental features either can fall within the phenotypic plasticity range of the species (Hall et al., 2007; Pfennig et al., 2010; Schlichting, 1986; Thibert‐Plante & Hendry, 2011) or can be due to evolutionary changes with underlying genetic differentiation among populations (Dowdall et al., 2012; Sanford & Kelly, 2011; Savolainen, Lascoux, & Merilä, 2013).…”

Metapopulation patterns of additive and nonadditive genetic variance in the sea bass (Dicentrarchus labrax)

“…The integration of phenogeography and phylogeography should contribute to better understanding of functional phenotypic evolution, and then fitness performance within and among lineages (Zamudio, Bell, & Mason, 2016). However, phenogeography—with the noticeable exception of counter‐ and cogradient variation studies (Conover, Duffy, & Hice, 2009; Hice, Duffy, Munch, & Conover, 2012) and few Q ST ‐F ST studies (DeFaveri & Merilä, 2013)—remains largely neglected in marine species. Indeed, while studies regarding changes in quantitative phenotypic differences mediated by trait plasticity and/or genetic processes are obviously present in the literature associated to evolutionary ecology of marine species (Conover et al., 2006; Sanford & Kelly, 2011), most studies concentrated at the molecular level (i.e., gene expression studies, population genetics/genomics) rather than on quantitative biological traits aiming to document the causes of variation of an organism phenotype over a large geographic scale, and their impact on fitness.…”