Parasites, immunity, and sexual selection

2021 ◽  
pp. 143-158
Author(s):  
Paul Schmid-Hempel
Keyword(s):  
Sexual Selection ◽  
Parasite Load ◽  
Genetic Heterozygosity ◽  
Immune Defences

The sexes (male, female) differ in parasite load and immune defences. In general, males are more frequently infected and often have lower defences. The differences are one consequence of sexual selection, where females invest more in maintenance. Females can choose males based on signs (e.g. ornaments) of higher resistance to parasites. Several theoretical scenarios can explain part of this variation. Advantages also result from genetic heterozygosity. Sex-specific hormones affect immune defences in many ways.

scholarly journals Alternative reproductive strategies in white-throated sparrows are associated with differences in parasite load following experimental infection

2018 ◽  
Vol 14 (7) ◽  
pp. 20180194 ◽  
Author(s):  
R. J. Boyd ◽  
T. R. Kelly ◽  
S. A. MacDougall-Shackleton ◽  
E. A. MacDougall-Shackleton
Keyword(s):  
Sex Differences ◽  
Life History ◽  
Optimal Allocation ◽  
Parasite Load ◽  
Life History Strategies ◽  
Zonotrichia Albicollis ◽  
Load Following ◽  
Infection Susceptibility ◽  
Immune Defences ◽  
Androgen Levels

Immune defences often trade off with other life-history components. Within species, optimal allocation to immunity may differ between the sexes or between alternative life-history strategies. White-throated sparrows ( Zonotrichia albicollis ) are unusual in having two discrete plumage morphs, white-striped and tan-striped. Within each sex, white-striped individuals are more aggressive and provide less parental care than tan-striped individuals. We extended immunocompetence handicap models, which predict sex differences in immunity and parasitism, to hypothesize that infection susceptibility should be greater in white-striped than tan-striped birds. We inoculated birds of both morphs with malarial parasites. Contrary to our prediction, among birds that became infected, parasite loads were higher in tan-striped than white-striped individuals and did not differ between the sexes. Circulating androgen levels did not differ between morphs but were higher in males than females. Our findings are not consistent with androgen-mediated immunosuppression. Instead, morph differences in immunity could reflect social interactions or life-history-related differences in risk of injury, and/or genetic factors. Although plumage and behavioural morphs of white-throated sparrow may differ in disease resistance, these differences do not parallel sex differences that have been reported in animals, and do not appear to be mediated by differences in androgen levels.

The Hamilton and Zuk Hypothesis Revisited: a Meta-Analytical Approach

Behaviour ◽  
1997 ◽  
Vol 134 (3-4) ◽  
pp. 299-320 ◽  
Author(s):  
Robert Poulin ◽  
William J. Hamilton
Keyword(s):  
Sexual Selection ◽  
Meta Analysis ◽  
Analytical Techniques ◽  
Parasite Load ◽  
Data Set ◽  
Fish Morphology ◽  
Negative Effect ◽  
The Subject ◽  
Host Parasite

AbstractThe Hamilton & Zuk (1982) hypothesis of parasite-mediated sexual selection has been the subject of both inter- and intraspecific tests. Past reviews have used vote counting to determine whether this hypothesis is supported by empirical evidence. This study reanalysed 199 separate quantitative assessments of a central prediction of the Hamilton & Zuk hypothesis using meta-analytical techniques. Overall, our meta-analysis showed that there was a significant negative effect of parasites on male showiness as predicted. However the magnitude of this effect varied between host taxa and between endo and ectoparasitic taxa. As a whole intraspecific correlations between parasite load and male showiness provided very little support for the hypothesis with only the effect of parasites on fish morphology matching the Hamilton & Zuk prediction. There was more support for the hypothesis from interspecific studies especially those based upon the original Hamilton & Zuk (1982) data set, although other bird studies provided weaker support. The generality of the Hamilton & Zuk hypothesis in respect to parasite mediated sexual selection across taxa is thrown into doubt by these results. However, in some specific host-parasite systems the role of parasites appears important and future intraspecific tests of parasite-mediated sexual selection should perhaps focus on such systems.

The katydid that was: the tananá, stridulation, Henry Walter Bates and Charles Darwin

2014 ◽  
Vol 41 (1) ◽  
pp. 131-140 ◽  
Author(s):  
Claudio J. Bidau
Keyword(s):  
Sexual Selection ◽  
Charles Darwin ◽  
Bush Cricket

The Amazonian bush-cricket or katydid, Thliboscelus hypericifolius (Orthoptera: Tettigoniidae: Pseudophyllinae), called tananá by the natives was reported to have a song so beautiful that they were kept in cages for the pleasure of listening to the melodious sound. The interchange of letters between Henry Walter Bates and Charles Darwin regarding the tananá and the issue of stridulation in Orthoptera indicates how this mysterious insect, which seems to be very rare, contributed to the theory of sexual selection developed by Darwin.

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