OWEN-ASHLEY , N. T.*; WINGFIELD, J. C.; Univ. of Washington, Seattle; Univ. of Washington, Seattle: Seasonal differences in expression of sickness behavior after experimental ‘pseudoinfection’ in free-living song sparrows (Melospiza melodia morphna)
Animals exposed to pathogens initiate an array of adaptive behaviors, such as fever, anorexia, and reduced activity, which jointly divert energy away from normal activities to combat and overcome infection. These behavioral strategies are collectively termed sickness behaviors, and can be triggered experimentally by exposing individuals to lipopolysaccharide (LPS), a component of gram-negative bacteria that mimics the onset of pathogenic infection. Besides energetic costs, expression of sickness behavior may interfere with crucial life-history events, such as territorial defense, mate attraction, and parental care. Male song sparrows of western Washington state (Melospiza melodia morphna) are sedentary and territorial year round, except during molt. Here, we show that acute (1 day) LPS treatment decreased several measures of territorial aggressive behavior in the winter (nonbreeding), but not in the spring (breeding). Males were recaptured immediately following aggression trials. In the winter, LPS-treated males lost more weight than saline-injected controls while breeding males injected with LPS did not lose more weight than controls. Furthermore, LPS treatment did not decrease plasma androgen or luteinizing hormone levels in breeding sparrows after recapture. These data indicate that birds in breeding condition were relatively insensitive to the effects of LPS. On a proximate level, modulation of sickness behavior is likely due to seasonal differences in energy allocation. In support of this hypothesis, wintering sparrows were significantly heavier and had more fat reserves and lower basal corticosterone levels than breeding birds. On an ultimate level, behavioral modification to infection may improve an animal�s ability to cope with seasonal fluctuations in environmental energy demands.
