Meeting Abstract
S10.2 Tuesday, Jan. 6 Food supplementation experiments: A tool to reveal mechanisms that mediate timing of reproduction SCHOECH, Stephan J; Univ of Memphis, TN sschoech@memphis.edu
Food supplementation studies of free-living animals have been used to address the role of resource availability in timing reproduction. A meta-analysis by Schoech and Hahn (2008) suggests that responsiveness to the supplementary cue of food is lessened at higher latitudes, with the assumption that the brief time during which conditions are appropriate to rear offspring has led to an evolved reliance on photoperiod. Unfortunately, little experimental work has examined potential underlying mechanisms to mediate this differential responsiveness to supplemental food across latitudes. However, considerable research links nutritional state and plasma glucocorticoid levels: both of which can impinge upon the reproductive axis. My labs long-term research on Florida Scrub-Jays shows that suburban birds with access to ad lib supplemental food express early breeding and lessened plasma corticosterone (CORT) levels in comparison to jays in nearby natural habitat. Further, supplementation in natural habitat advances laying, with the effects generally being the greatest in bad years (i. e., years defined by late breeding and poor reproductive output by nonsupplemented controls). Similarly, reproductive output of supplemented jays is greater and exhibits considerably less variance than controls, suggesting fitness benefits of supplementation that are tied to advanced breeding. Generally, CORT levels in early breeding supplemented jays are lower than those of controls. Also, regression analysis suggests that clutch initiation dates of nonsupplemented female breeders are predicted by baseline CORT levels. Although these data are not conclusive and trends can be obscured by year-effects, they suggest a role for corticosterone in timing of breeding. Whether this link might help to explain the above referenced latitudinal trends remains to be seen.
