Abstract
Thermal phenotypic plasticity, otherwise known as acclimation, plays an essential role in how organisms respond to short‐term temperature changes. Plasticity buffers the impact of harmful temperature changes; therefore, understanding variation in plasticity in natural populations is crucial for understanding how species will respond to the changing climate. However, very few studies have examined patterns of phenotypic plasticity among populations, especially among ant populations. Considering that this intraspecies variation can provide insight into adaptive variation in populations, the goal of this study was to quantify the short‐term acclimation ability and thermal tolerance of several populations of the winter ant, Prenolepis imparis. We tested for correlations between thermal plasticity and thermal tolerance, elevation, and body size. We characterized the thermal environment both above and below ground for several populations distributed across different elevations within California, USA. In addition, we measured the short‐term acclimation ability and thermal tolerance of those populations. To measure thermal tolerance, we used chill‐coma recovery time (CCRT) and knockdown time as indicators of cold and heat tolerance, respectively. Short‐term phenotypic plasticity was assessed by calculating acclimation capacity using CCRT and knockdown time after exposure to both high and low temperatures. We found that several populations displayed different chill‐coma recovery times and a few displayed different heat knockdown times, and that the acclimation capacities of cold and heat tolerance differed among most populations. The high‐elevation populations displayed increased tolerance to the cold (faster CCRT) and greater plasticity. For high‐temperature tolerance, we found heat tolerance was not associated with altitude; instead, greater tolerance to the heat was correlated with increased plasticity at higher temperatures. These current findings provide insight into thermal adaptation and factors that contribute to phenotypic diversity by revealing physiological variance among populations.
Highlights
One of the most substantial drivers of biodiversity loss is climate change (Sala et al, 2000)
When novel climatic conditions are physiologically strenuous, species are driven to adapt via genetic change, to migrate, to persist via physiological plasticity, or to succumb to extinction (Fuller et al, 2010)
Intraspecific variation in thermal tolerance has been well-documented in several Drosophila species, including D. buzzatti and D. melanogaster (Sarup, Frydenberg, & Loeschcke, 2009; Sgrò et al, 2010), as well as other organisms (e.g., the common killifish (Fundulus heteroclitus; Fangue, Hofmeister, & Schulte, 2006), Collembola (Bahrndorff, Loeschcke, Pertoldi, Beier, & Holmstrup, 2009), and tsetse fly (Glossina pallidipes; Terblanche, Clusella-Trullas, Deere, & Chown, 2008))
Summary
One of the most substantial drivers of biodiversity loss is climate change (Sala et al, 2000). There are examples of rapid heritable genetic changes in populations in response to climate change (Bradshaw & Holzapfel, 2008), most organisms’ life spans are too long and climate change occurs too rapidly. Within this short time frame, an organism's susceptibility to new environmental conditions (i.e., “tolerance”) can be buffered by plasticity of fitness-related traits (Huey et al, 2012; Seebacher, White, & Franklin, 2015; Somero, 2010). We examined the patterns of thermal tolerance (resistance to both heat and cold stress) and plasticity (variation in tolerance after prior exposure to heat or cold) as our fitness traits
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