Juvenile immune status affects the expression of a sexually selected trait in field crickets


  • Present address: M. W. G. Brinkhof, University of Bern, Department of Social and Preventive Medicine, Division of Epidemiology and Biostatistics, Finkenhubelweg 11, CH-3012 Bern, Switzerland.

A. Jacot, Max Planck Institute for Ornithology, Department of Behavioural Ecology and Evolutionary Genetics, Postfach 1564, D-82305 Starnberg (Seewiesen), Germany.
Tel.: 0049 815 793 2264; fax: 0049 815 93240;
e-mail: jacot@orn.mpg.de


Parasite-mediated sexual selection theory presumes that variation in sexual traits reliably reflects variation in parasite resistance among available mates. One mechanism that may warrant signal honesty involves costs of immune system activation in the case of a parasitic infection. We investigated this hypothesis in male field crickets Gryllus campestris, whose attractiveness to females depends on characteristics of the sound-producing harp that are essentially fixed following adult eclosion. During the nymphal stage, males subjected to one of two feeding regimes were challenged with bacterial lipopolysaccharides (LPS) to investigate condition-dependent effects on harp development as compared to other adult traits. Nymphal nutritional status positively affected adult body size, condition, and harp size. However, nymphal immune status affected harp size only, with LPS-males having smaller harps than control-injected males. In addition, the harps of LPS-males showed a lesser degree of melanization, indicating an enhanced substrate use by the melanin-producing enzyme cascade of the immune system. Thus, past immune status is specifically mirrored in sexual traits, suggesting a key role for deployment costs of immunity in parasite-mediated sexual selection.