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.