Temperature heterogeneity correlates with intraspecific variation in physiological flexibility in a small endotherm

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.

Spatial and seasonal variation in thermal sensitivity within North American bird species

“…Thermal breadth, or the range of tolerable conditions, is associated with the level of variability in the local climate, with 'thermal specialists' being found in more stable climates and 'thermal generalists' found in more variable climates (Bozinovic et al, 2011;Stevens, 1989). Given that climatic variability is increasing with climate change (Cai et al, 2022;La Sorte et al, 2021;Pendergrass et al, 2017), these findings highlight the importance of considering population-level variation in thermal breadth (Stager et al, 2021). In seasonal environments, non-migratory organisms must adapt to variable weather across the annual cycle via phenotypic plasticity, often undergoing behavioral and physiological changes (foraging during different times of day, seeking out refugia, gaining fat reserves, etc.)…”

“…These approaches generally ignore adaptive capacity and phenotypic plasticity within species, implicitly assuming that thermal sensitivity, or the influence of temperature on behavior, performance, or fitness, is stationary (static) in both space and time (Jarnevich et al, 2015;Smith et al, 2019). However, emerging physiological evidence suggests that populations of a species may be locally adapted to distinct thermal conditions depending on the climate zones they inhabit, and individuals may dynamically alter their response to seasonal changes in temperature via phenotypic flexibility (Bennett et al, 2019;Louthan et al, 2021;Stager et al, 2021). Approaches assuming constant thermal sensitivity across continental spatial extents and the full annual cycle may thus be inadequate to account for the full spectrum of responses to climate change exhibited by a given species (Sultaire et al, 2022).…”

“…Populations within a species are likely to exhibit non-stationarity in thermal sensitivity across space and time due to physiological mechanisms and constraints (Bennett et al, 2019;Louthan et al, 2021;Stager et al, 2021;Youngflesh et al, 2022;Fig. 1).…”

“…1). Across geographic gradients, populations of wide-ranging species are likely adapted to local climatic conditions (Atkins and Travis, 2010;Stager et al, 2021). Physiological studies have suggested that within species, southern and lowland populations adapted to warm climates demonstrate warmer optimum thermal performance temperatures when compared with northern and high-elevation populations that demonstrate cooler optimums (Richardson et al, 2014;Zillig et al, 2021).…”

Metabolic Profiling and Integration of Metabolomic and Transcriptomic Data From Pectoralis Muscle Reveal Winter-Adaptive Metabolic Responses of Black-Capped Chickadee and American Goldfinch

“…The physiological, biochemical, and molecular mechanisms underlying metabolic flexibility in birds are incompletely understood (Cheviron and Swanson, 2017;Stager et al, 2021). Different bird species can employ or emphasize different mechanisms for generating elevated metabolic rates in cold winter climates (Liknes and Swanson, 2011a,b;Dubois et al, 2016).…”