Meeting Abstract

P2.145  Thursday, Jan. 5  Assessing life history tradeoffs in an opportunistically breeding songbird SCHULTZ, E.M.*; KOCH, R.E.; HAHN, T.P.; Univ. of California, Davis; Univ. of California, Davis; Univ. of California, Davis emschultz@ucdavis.edu

Due to the finite energy budget of an organism, only so much energy can be allocated to somatic physiological processes such as immune function without sacrificing energy to other processes such as reproduction, creating a physiological or life history tradeoff. Life history tradeoffs have been studied extensively in seasonally breeding animals, but little is known about the physiological regulation of these tradeoffs in species with temporally flexible reproductive strategies like the red crossbill Loxia curvirostra. Unlike most songbirds, crossbills are able to reproduce 10 months of the year and can offset the high energetic cost of molt by protracting it over a five-month period, often arresting it for summer breeding. In this study we examined individual variation in allocation to two measures of constitutive innate immune function, a hemolysis-hemagglutination assay and differential white blood cell counts, and compared those results between breeding and non-breeding individuals as well to individuals in varying stages of molt. Preliminary data from a single summer, where the abundance of breeding crossbills was low, lacked any significant trends among these variables, but sample size was small. Data from this current summer and late autumn, where abundance of breeding crossbills was high, will be used to augment these prior data to compare individual variation in reproductive condition and molt stage and will be related to the same measures of immune function. Although most previous research has focused on life history tradeoffs in seasonally breeding animals, these results will provide a novel examination of the relationship among tradeoffs in somatic and reproductive processes in an opportunistic breeder under free-living conditions.