Intraspecific variation in thermal acclimation and tolerance between populations of the winter ant, Prenolepis imparis

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.

Transcriptomic signatures of cold adaptation and heat stress in the winter ant (Prenolepis imparis)

“…We collected worker ants from a population on the UC Berkeley campus in Berkeley, California, USA (WGS1984; 122.26317, 37.87281), in June 2014. We chose this site because a previous study showed that P. imparis from this site exhibit phenotypic plasticity in response to both hot and cold temperatures [40]. After the ants were collected, they were immediately placed in one of three separate thermal conditions: (1) an incubator (Fisher Scientific Isotemp Model 650D Large 600 Series Incubator CAT# 11-690-650D) at 35˚C (heat stress), (2) on a roomtemperature bench-top approximately 21˚C, within the temperature range we expect to find their nests (a control), and (3) a walk-in cold room at approximately 5˚C (cold stress).…”

“…A detailed analysis of their nest structure in Florida found that nest chambers were dug 60 cm below ground, at temperatures between 16 and 24˚C [39]. A previous study found populations of P. imparis have different levels of plasticity and thermal tolerance [40] which makes this species an interesting candidate to examine the genetic basis of these traits.…”

“…A previous study found populations of P . imparis have different levels of plasticity and thermal tolerance [ 40 ] which makes this species an interesting candidate to examine the genetic basis of these traits.…”

Indications for rapid evolution of trait means and thermal plasticity in range‐expanding populations of a butterfly

“…We measured two well‐established proxies of cold‐ and heat stress resistance in insects, namely ‘chill‐coma recovery time’ (CCRT) and ‘heat knock‐down time’ (HKDT) (e.g. Bauerfeind & Fischer, 2014; Fischer et al, 2010; Stazione et al, 2020; Tonione et al, 2020). All individuals were tested for CCRT on day 2 of adult life and for HKDT the day after.…”

Evidence for genetic isolation and local adaptation in the field cricket Gryllus campestris

“…The capacity to recover rapidly from cold-induced coma is likely to be particularly relevant in environments where overnight temperatures (or other short-term fluctuations) are cold enough to prevent activity. In the winter ant, Prenolepis impairs, CCRT is faster in high altitude populations: (Tonione et al, 2020). In Drosophila species, CCRT has been related to thermal adaptation as it differentiates between species of tropical and temperate origin (Gibert et al, 2001).…”