Consequences of Thermal Challenge at Extreme Temperatures on Cheirodon interruptus: Possible Response to Global Climate Change
Thermal stress impacts the homeostasis of ectotherms and can affect many characteristics of a species including thermal niche, distribution, feeding, growth, and immune system function. The population of Cheirodon interruptus inhabiting Valcheta Creek is a Neotropical species that has the potential to thrive and survive in a southern environment where individuals are challenged by colder winter temperatures. We studied the response of this population to both high and low extreme temperatures by examining minimum and maximum feeding temperatures, temperature preferences, and biomarkers of the innate immune system. We distributed 72 adult C. interruptus into nine aquaria, equally separated among three treatments: 12.0°C, 21.8°C, and 31.9°C. We determined the extreme temperatures at which 50% of the individuals did not consume food to be 10.7 and 33.3°C. Based on these observations, we adjusted the temperatures by +1.3 and –1.4°C, respectively, to achieve final values of 12.0 and 31.9°C. Following 14 days of acclimation, we conducted preferred temperature assays on individuals, mucus and blood sampling, and morphometric measurements. Our results show that the Valcheta Creek population is a representative example of C. interruptus as a species capable of inhabiting a broad gradient of temperatures, though with a preferred range skewed toward lower temperatures compared to other Neotropical species. The C. interruptus from Valcheta Creek exhibit a temperature preference of 13.5°C, which supports growth and development alongside partial activation of innate immune responses, such as protease activity in mucus and unaltered feeding behavior.
Daily recorded temperatures of aquaria from the arrival of the fish at the laboratory until the end of the experiment. Treatment temperatures were defined based on non-consumption food trials for both cold and hot treatments, resulting in temperatures of 12.0°C (cold treatment), 21.8°C (intermediate treatment), and 31.9°C (hot treatment). Red points indicate the start and the end of each treatment period of 14 days.
Preferred temperature (°C) of individuals of Cheirodon interruptus measured after 14 days acclimated to 12.0°C (cold treatment), 21.8°C (intermediate treatment), and 31.9°C (hot treatment). Preferred temperature values adjusted using a linear regression model based on acclimation temperatures (R2 = 0.829, F = 159.57, P < 0.001). The graph displays 95% confidence bands (violet dotted lines) and 95% prediction bands (black dotted lines). The intersections between the Y = X line and the linear regression model, as indicated by arrows, define the final temperature preferences (FTP).
Biochemical determinations in epidermal mucus of Cheirodon interruptus. Individuals were distributed in three or four aquaria per treatment and acclimated to 12.0°C (cold treatment), 21.8°C (intermediate treatment), and 31.9°C (hot treatment) for 14 days. (A) Protease activity as percentage of trypsin control; (B) Alkaline phosphatase activity expressed as mU g--1 protein. (* P < 0.05; ** P < 0.01).
Hepatosomatic index (HSI; A) and condition factor (B) at the end of the acclimation period for Cheirodon interruptus at three temperatures. Individuals were distributed in three or four aquaria per treatment and acclimated to 12.0°C (cold treatment), 21.8°C (intermediate treatment), and 31.9°C (hot treatment) for 14 days. Data show mean ± standard error. Asterisk indicates significant differences between treatments (* P < 0.05; ** P < 0.01).
Contributor Notes
Associate Editor: C. Bevier.