Selection on innate immunity and body condition in Florida scrub-jays throughout an epidemic

Abstract

Opportunities to investigate selection in free-living species during a naturally occurring epidemic are rare; however, we assessed innate immunocompetence in Florida scrub-jays before the population suffered the greatest over-winter mortality in 20 years of study. Propitiously, three months prior to the epidemic, we had sampled a number of male breeders to evaluate a suite of physiological measures that are commonly used to estimate the overall health-state of an individual. There was a significant, positive selection gradient for both Escherichia coli bacterial killing capability and body condition, suggesting that directional selection had occurred upon each of these traits during the disease epidemic.

Figure 1.

(a) Variation in E. coli bacterial killing and (b) body condition (BCI) as a function of survival (0 = dead, 1 = alive), represented as a box (25th and 75th percentiles with median line) and whisker (1.5× interquartile range or max value if less) plot.