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Unformatted text preview: Ecology , 87(10), 2006, pp. 24402446 2006 by the Ecological Society of America COSTS OF AN IMMUNE CHALLENGE AND TERMINAL INVESTMENT IN A LONG-LIVED BIRD S VEINN A RE H ANSSEN 1 Biology Department, Faculty of Science, University of Troms , N-9037 Troms , Norway, and Norwegian Institute for Nature Research, Polar Environmental Centre, N-9296 Troms , Norway Abstract. An induced immune challenge can have two counteracting effects on an individuals reproductive investment. (1) The resource demand could increase to fuel the immunologic reaction, which in turn can lead to an adaptive decrease in investment in resource-costly activities, such as reproduction. One the other hand, (2) the individual could assume that the immune activity it experiences is indicative of a serious infection. The latter can lead to an adaptive increase in reproductive investment in response to the reduced prospects of survival and future reproduction, so called terminal investment. To measure such life-history-related consequences of increased immune activity, one group of incubating female Common Eiders ( Somateria mollissima ) was injected with a nonpathogenic antigen (sheep red blood cells, SRBC) while controls were injected with sterile saline. The eider is a long-lived sea-duck. Females, who incubate the eggs and care for young without assistance from the male, engage in facultative anorexia during incubation leading to a large reduction in body mass. Eiders can abandon their young to other females at the cost of reduced young survival. The immune challenge resulted in a larger mass loss, a prolonged incubation period, and reduced return rate, demonstrating both short- and long-term costs of immune challenge. Additionally, in response to what might have been interpreted as reduced survival chances in immune-challenged females, these females more often tended their own brood after hatching, despite having suffered higher costs during incubation. Key words: Common Eider; immunity; immunocompetence; incubation; life history; Somateria mollissima; terminal investment. I NTRODUCTION Infectious organisms are a major contributor to disease and mortality in wild organisms (Barnard and Behnke 1990, Grenfell and Dobson 1995). Thus, the immune defense against pathogenic infections is impor- tant for central fitness traits, such as longevity and reproduction. Life history theory predicts that semelpar- ous organisms allocate their resources optimally between their reproductive attempts so as to maximize lifetime reproduction (Stearns 1992). Thus, when life expectancy is reduced, individuals should allocate resources in favor of current reproduction, i.e., terminal investment (Minchella and LoVerde 1981, Clutton-Brock 1984, Pa rt et al. 1992, Roff 1992, Stearns 1992). Terminal investment is relatively rarely documented, and most of the empirical evidence stems from studies of insects (Roitberg et al. 1992, 1993, Fletcher et al. 1994, Sirot et(Roitberg et al....
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This note was uploaded on 10/14/2010 for the course DDF 1124-445 taught by Professor Gorthermclays during the Spring '10 term at Florida College.
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