Seasonal variation in thermal tolerance of redside dace Clinostomus elongatus

Abstract

Organisms living in environments with oscillating temperatures may rely on plastic traits to sustain thermal tolerance during high temperature periods. Phenotypic plasticity in critical thermal maximum (CT_max) is a powerful thermoregulative strategy that enables organisms to adjust CT_max when ambient temperatures do not match thermal preference. Given that global temperatures are increasing at an unprecedented rate, identifying factors that affect the plastic response in CT_max can help predict how organisms are likely to respond to changes in their thermal landscape. Using an experimental thermal chamber in the field, we investigated the effect of short-term acclimation on the CT_max and thermal safety margin (TSM) of wild-caught redside dace, Clinostomus elongatus, (n = 197) in a northern population in Two Tree River, Ontario. Streamside CT_max trials were used to identify the maximum temperature at which redside dace maintain equilibrium, providing a powerful tool for understanding how thermal stress affects individual performance. CT_max and TSM of redside dace were sensitive to changes in temperature, regardless of season, suggesting that temperature pulses caused by climate change or urban activities can impose negative fitness consequences year round. Interestingly, an individual's recent thermal history was more influential to its thermal tolerance than the current ambient water temperature. While the CT_max of redside dace increased with body size, the effect of body size on TSM remains unclear based on our models. The results provide insight into the thermal performance of redside dace that, to date, has been difficult to assess due to the species' rarity and lack of suitable streamside protocols.

Keywords: Climate change; endangered; long-term acclimation; phenotypic plasticity; short-term acclimation.

Figure 1

Theoretical thermal performance curve showing the final preferendum (T_o), critical thermal minimum (CT_min) and CT_max, adapted from Huey and Kingsolver (1993).

Figure 2

Mean daily ambient water temperature of Two Tree River, Ontario, June 2015–October 2019 (unpublished data from Derek Goertz, Ontario Ministry of Natural Resources and Forestry).

Figure 3

Mean acclimation temperature (T_a, blue) and critical thermal maxima (CT_max, red) of Redside Dace captured in Two Tree River in 2018 (June–October) and 2019 (May, October); data are presented by Julian week to demonstrate seasonal changes in CT_max; standard errors (±SEM) were calculated from variance of monthly means (letters indicate significance between months as calculated by pairwise Wilcox tests).

Figure 4

Mean thermal safety margin (TSM) of Redside Dace captured in Two Tree River in 2018 (June–October) and 2019 (May, October); data are presented by Julian week to demonstrate seasonal changes to TSM; standard errors (±SEM) were calculated from variance of monthly means (letters indicate significance between months as calculated by pairwise Wilcox tests).