Abstract
The immunocompetence handicap hypothesis predicts that male sexual trait expression should be positively correlated with immunocompetence. Here we investigate if immune function in the cricket, Teleogryllus commodus, is related to specific individual components of male sexual signals, as well as to certain multivariate combinations of these components that females most strongly prefer. Male T. commodus produce both advertisement and courtship calls prior to mating. We measured fine-scale structural parameters of both call types and also recorded nightly advertisement calling effort. We then measured two standard indices of immune function: lysozyme-like activity of the haemolymph and haemocyte counts. We found a weak, positive relationship between advertisement calling effort and lysozyme-like activity. There was, however, little evidence that individual structural call components or the net multivariate attractiveness of either call type signalled immune function. The relationships between immunity and sexual signaling did not differ between inbred and outbred males. Our data suggest that it is unlikely that females assess overall male immune function using male calls.
Highlights
Female mate choice based on male sexual ornaments and displays is well documented, but the function of most mating preferences is poorly understood
We did not find any evidence for the overall ability of the five advertisement call characteristics to predict lysozyme activity (F5, 43 = 0.544, P = 0.742) or haemocyte count (F5, 48 = 1.323, P = 0.270), nor for the six characteristics of the courtship call to predict lysozyme activity (F6, 196 = 1.085, P = 0.372) or haemocyte counts (F6, 189 = 2.059, P = 0.060)
In T. commodus calling effort is moderately, positively related to lysozyme-like activity in the haemolymph. There was, no such relationship with haemocyte count, even though haemocyte count is strongly correlated with lysozyme activity (r = 0.56 [49])
Summary
Female mate choice based on male sexual ornaments and displays is well documented, but the function of most mating preferences is poorly understood. Indirect benefits arise if there are paternal effects on a choosy female’s progeny due to inheritance of genes [2] and/or paternal contributions (e.g. increased male care; [3]) that elevate offspring fitness. The mechanisms that allow sexual traits to function as reliable signals of male quality generally require that they are costly to produce or maintain (review: [4]), and that higher quality males pay a smaller marginal cost to increase investment ([5,6] but see [7,8]). A specific case study of the costs of sexual signaling is related to a potential trade-off between sexual trait expression and immune system function. This could be due to genes that directly enhance immune function, or arise indirectly via genes that have a positive effect on body condition [11]
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