Dimorphic Stress Hormones Figure 7. Corazonin transcript levels decrease during stress. Top: Representative gels from experiments of corazonin and RP49 expression in the w1118 genotype under starvation, osmotic, and oxidative stress. Bottom: Changes in corazonin expression under different stresses for noted times. Data are represented as a % of basal (unstressed) and are normalized to RP49. Starvation and osmotic stress cause a decline in corazonin expression and rises as a function of stress duration. Oxidative stress produces no change in corazonin expression. doi:10.1371/journal.pone.0009141.g007 of the organism from the source of stress. As mentioned previously, there is an inverse relationship between the strength of stress responses and lifespan during homeostatic challenges. For example, mobilization of energy stores to facilitate higher activity levels might lead to enhanced foraging, but also more quickly exhaust energy levels which would lead to a more rapid death in the event food was not found. In general, heightened locomotor activity would facilitate escape behaviors [1]. Corazonin signaling and its impact on activity levels suggests a complex interplay between central signaling and peripheral tissues which determine stress sensitivity. Under non-stressed conditions, our results show a strong influence on the level of corazonin signaling on activity levels in males. In contrast, there is apparently a lack of corazonin dependence in determining normal activity levels in females. However, corazonin signaling does influence the dynamics of stress-induced activity levels in both males and females. In males, the amount of locomotion is inversely related to lifespan duration, and this demonstration is expected as that the increased activity levels lead to rapid decreases in energy reserves, and also lead to abbreviated lifespan [1]. However, in females, enhanced locomo- tor activity is not correlated with lifespan under stress, as the ablation of female corazonin neurons leads to enhanced activity but also lengthened lifespan. Perhaps, part of the difficulties in interpreting these results is that some of the effects of altered corazonin signaling may be manifest as developmental changes of the circuitry that regulates stress behaviors. We are currently attempting to address the contributions of developmental versus acute effects of altered corazonin signaling in Drosophila by employing different strategies to alter corazonin signaling at restricted developmental intervals. The demonstration that corazonin neurons alter both the size of energy stores and at least in females, also alter the utilization of energy suggests that corazonin neurons function in the mechanism of resource allocation. This observation is supported by a recent report that shows differences in the levels of trehalose, a major carbohydrate energy source in insects, in flies lacking corazonin [40]. The impact of altered corazonin neuronal functions on activity levels might also be indicative of a role for corazonin- mediated reallocation of energy during stress. The effects of altered corazonin function on normal locomotion may reflect inherent differences in metabolic capacities which in turn regulate basal activity levels. Throughout the Metazoa, there are inherent differences in how the different sexes respond to stress [e.g., 41]. Specifically, during PLoS ONE | www.plosone.org 11 February 2010 | Volume 5 | Issue 2 | e9141