Stabilising selection on immune response in male black grouse Lyrurus tetrix

Abstract

Illnesses caused by a variety of micro- and macro- organisms can negatively affect individuals’ fitness, leading to the expectation that immunity is under positive selection. However, immune responses are costly and individuals must trade-off their immune response with other fitness components (e.g. survival or reproductive success) meaning that individuals with intermediate response may have the greatest overall fitness. Such a process might be particularly acute in species with strong sexual selection because the condition-dependence of male secondary sexual-traits might lead to striking phenotypic differences amongst males of different immune response levels. We tested whether there is selection on immune response by survival and reproduction in yearling and adult male black grouse (Lyrurus tetrix) following an immune challenge with a novel antigen and tested the hypothesis that sexual signals and body mass are honest signals of the immune response. We show that yearling males with highest immune response to these challenges had higher survival, but the reverse was true for adults. Adults with higher responses had highest mass loss and adult males with intermediate immune response had highest mating success. Tail length was related to baseline response in adults and more weakly in yearlings. Our findings reveal the complex fitness consequences of mounting an immune response across age classes. Such major differences in the direction and magnitude of selection in multiple fitness components is an alternative route underpinning the stabilising selection of immune responses with an intermediate immune response being optimal.

Ecological determinants of variation in phenotypic selection on quantitative immune defence traits

“…However, our findings do not align with most empirical studies that report positive directional selection on immune activity (reviewed by Seppälä 2015). In addition to L. stagnalis (Langeloh et al 2017, this study), stabilizing selection on quantitative immune defence traits has been reported in three bird species, blue tit (antibody responsiveness to diphtheria; Råberg and Stjernman 2003), common kestrel (PHA test; Kim et al 2013) and black grouse (antibody responsiveness to tetanus; Soulsbury et al 2018). Furthermore, negative directional selection on antibody responsiveness to tetanus has been detected in specific populations of the common side-blotched lizard that live under low infection risk (i.e.…”

“…the highest trait values lead to the highest fitness; reviewed by Seppälä 2015). Only a few empirical studies show stabilizing selection on such immune parameters (Råberg and Stjernman 2003, Kim et al 2013, Langeloh et al 2017, Soulsbury et al 2018). This discrepancy between theoretical predictions and empirical observations, and the variation in the form of observed selection in empirical studies, highlight the need for examining underlying factors that influence the form and strength of natural selection on immune function.…”

Patterns of environmental variance across environments and traits in domestic cattle

“…Reviews of empirical selection gradients on the mean in natural populations have shown weak directional selection to be common (Blows & Brooks, 2003;Kingsolver, Diamond, Siepielski, & Carlson, 2012;Kingsolver et al, 2001). But many traits with a close connection to fitness are under strong stabilizing selection on the mean (for recent examples, see González Marín, Olave, Avila, Sites, & Morando, 2018;Sanjak, Sidorenko, Robinson, Thornton, & Visscher, 2018;Soulsbury, Siitari, & Lebigre, 2018). When stabilizing selection on the mean is strong and the trait mean approaches the optimum, genotypes increasing V e will be at a disadvantage as they are likely to produce a nonoptimal phenotype (Bull, 1987;Gavrilets & Hastings, 1994;Slatkin & Lande, 1976).…”

Host sex, size, and hemoparasite infection influence the effects of ectoparasitic burdens on free‐ranging iguanas

“…We did, however, find mixed and significant associations of tick burdens with lymphocyte and basophil counts, H:L ratios, and body condition indices. These associations varied by sex, size, and hemoparasite infection rate supporting the supposition that different life stages of animals may invest differently in immune responses (Jackson et al, ; Soulsbury, Siitari, & Lebigre, ), or impacts may be modulated based on size and sex of hosts.…”