Distinct effects of two separately applied stressors on behavior in the red flour beetle

Stress is ubiquitous in nature and organisms have evolved mechanisms to cope with it. Stress responses nevertheless vary based on the type of stress, its duration, magnitude, and the organism's physiological status. We studied here the effect of two separately applied stress types, differing also in their duration, on various behavioral responses of the red flour beetle (Tribolium castaneum). The two stress types applied were short-term cold stress and long-term low protein stress. The behavioral response variables were movement activity, preference to move along the test arena edges, latency to emerge from shelter, and preference for dark microhabitat, measured at two stages of the beetles' lives, as young adults after eclosion and one month later. Behavioral responses were stress-specific. Cold-stressed beetles moved over the longest distances but were also the most reluctant to leave an accessible shelter. We interpret this to mean that cold-stressed beetles were the most active under unfavorable conditions and least bold under more favorable, protected conditions. As beetles aged, their movement activity decreased and latency to emerge from shelter increased. Non-stressed beetles were the most consistent in their behavior across all behavioral tests. This finding is similar to those in previous studies and suggests that moderate stress reduces behavioral consistency. While all beetles gained mass during the study period, the two stress types led to different patterns of body mass increase, which was more moderate for cold-stressed than for protein-stressed beetles.