Meeting Abstract
65.3 Tuesday, Jan. 6 Stress physiology and parasite burden differ during winter and summer breeding in a north-temperate zone temporal opportunist, the red crossbill Loxia curvirostra CORNELIUS, J.M.*; ZYLBERBERG, M.; BREUNER, C.W.; HAHN, T.P.; Univ. of California, Davis; Univ. of California, Davis; Univ. of Montana; Univ. of California, Davis cornelius@ucdavis.edu
Physiological ecologists often explain seasonal patterns in physiology using energetic, behavioral and trade-off hypotheses. However, it is difficult to tease apart and test predictions for these hypotheses because multiple variables change seasonally. For example, changes in physiology that occur during the spring and summer are often related to seasonal breeding behavior, but it is difficult to separate the effects of breeding from other seasonal variables such as temperature or food availability. We collected 6 years of field data from a north-temperate zone opportunist, the red crossbill (Loxia curvirostra), to compare glucocorticoid physiology and parasite load during winter and summer breeding. North-temperate opportunists offer the unique opportunity to make within-species comparisons of breeding physiology under very different thermoregulatory challenges. We found no differences in absolute levels of testosterone, corticosterone binding globulins, or hematocrit in winter versus summer breeders. Winter breeders, however, had higher baseline corticosterone and lower stress-induced corticosterone. The relationships between these and other variables (e.g. breeding condition, body condition, and parasite load) also differ in interesting ways across breeding seasons. For example, Haemoproteus infection is high during summer breeding and absent during winter breeding and degree of infection does not correlate significantly with testosterone, suggesting that the immunocompetance hypothesis cannot fully explain seasonal patterns of parasite burden. We will discuss these and other breeding- stress- immune relationships in this unique comparison of winter and summer breeding physiology.
