Seasonal effects on behavior and immunity in a precocial rodent

Abstract

Environmental variation strongly influences individual life histories, behavior, and immunity. For many animals living in non-tropical regions, environmental variation due to season is very important and can be reliably predicted by photoperiod. By manipulating the pre- and post-natal photoperiod for cavies (Cavia aperea), we simulated different birth seasons that go along with predictable differences in life history. Offspring born into simulated spring conditions mature earlier, indicating a fast pace of life compared to offspring born into simulated fall. We investigated the development of two innate (titers of natural antibodies and complement) and one adaptive (immunoglobulin G) immune effectors across multiple life stages. In addition, we tested if three behaviors, indicating risk-taking and stress-coping, differed between seasons. Finally, we tested if behaviors and immune traits correlate with each other as predicted by the pace-of-life syndrome hypothesis. The season of birth influenced average trait expression of both immunity and behavior. Boldness, indicating risk-taking behavior, correlated positively with the titers of natural antibodies, fitting the predictions of the pace-of-life syndrome (POLS). However, fearlessness, indicating how an individual copes with a stressful situation, correlated positively with immunoglobulin G concentrations, against the predictions of the POLS. Together, our results show that behaviors and immune traits react to differences in expected life histories, but do not show the predicted covariation. We conclude that proximate mechanisms and different functions of traits need to be considered to predict the nature of behavior-immune associations. Individual life histories, behavior, and immunity are strongly influenced by the environment individual’s experience during early life. Recent theory predicts correlations between behavior and immunity to arise as a consequence of different life histories. By simulating different birth seasons, we induced different life history expectations as well as a season-dependent development of immunity and behavior. However, correlations between behavior and immunity do not fit theoretical predictions, highlighting the need for more detailed theory.