School of the Environment, Yale University, New Haven, Connecticut, USA.
Published: January 2021
AI Article Synopsis
Article Abstract
Countergradient variation has been detected in diverse taxa. In a common manifestation, individuals from colder environments develop faster than conspecifics from warmer environments when placed in a common garden. Where such a pattern exists, it implies a trade-off: Individuals from warmer environments have intrinsic rates of development lower than those demonstrated by other individuals of the same species. We explored a trade-off between development rate and locomotor performance in the wood frog (Rana sylvatica), an amphibian for which countergradient variation has been well documented. We reared wood frogs from 10 populations under two temperature regimes, bracketing the temperatures observed in local natural ponds. Individuals reared under warmer conditions developed more rapidly but exhibited burst speeds 20% lower than individuals reared under colder conditions. The slope of the reaction norm was consistent across the 10 populations and thus, we found no evidence of countergradient variation in performance. Burst speed assays of wild-caught tadpoles from the same populations showed a similar but nonsignificant trend, with greater variability among ponds. Overall, our findings support the existence of a development-performance trade-off that may be of broad importance and which may help explain the widespread occurrence of countergradient variation.
Although we have evidence that many organisms are exhibiting declines in body size in response to climate warming, we have little knowledge of underlying mechanisms or how associated phenotypic suites may coevolve. The better we understand coadaptations among physiology, morphology, and life history, the more accurate our predictions will be of organismal response to changing thermal environments. This is especially salient for ectotherms because they comprise 99% of species worldwide and are key to functioning ecosystems.
Thermoregulatory behaviour determines an organism's body temperature and therefore its physiological condition, and may differ for organisms situated across climate gradients. Species' preferred or selected temperatures may be higher in warmer locations-referred to as coadaptation-or lower in warmer temperatures-countergradient variation. Here, we tested if rainforest amphibians exhibited coadaptation or countergradient thermal selection across an underappreciated spatial climate gradient (vertical height from forest floor to canopy) and separating diel activity (diurnal versus nocturnal behaviour).
Environmental temperatures directly affect physiological rates in ectotherms by constraining the possible body temperatures they can achieve, with physiological processes slowing as temperatures decrease and accelerating as temperatures increase. As environmental constraints increase, as they do northward along the latitudinal thermal gradient, organisms must adapt to compensate for the slower physiological processes or decreased opportunity time. Evolving faster general metabolic rates is one adaptive response posited by the metabolic cold adaptation (MCA) hypothesis.
Gene expression can be highly plastic in response to environmental variation. However, we know little about how expression plasticity is shaped by natural selection and evolves in wild and domesticated species. We used genotypic selection analysis to characterize selection on drought-induced plasticity of over 7,500 leaf transcripts of 118 rice accessions (genotypes) from different environmental conditions grown in a field experiment.
Phenotypic plasticity, the ability of a single genotype to produce different phenotypes under different environmental conditions, plays a profound role in several areas of evolutionary biology. One important role is as an adaptation to a variable environment. While plasticity is extremely well documented in response to many environmental factors, there is controversy over how much of that plasticity is adaptive.
