Dynamic phenotypic correlates of social status and mating effort in male and female red junglefowl, Gallus gallus

Abstract

Despite widespread evidence that mating and intrasexual competition are costly, relatively little is known about how these costs dynamically change male and female phenotypes. Here, we test multiple hypotheses addressing this question in replicate flocks of red junglefowl (Gallus gallus). First, we test the interrelationships between social status, comb size (a fleshy ornament) and body mass at the onset of a mating trial. While comb size covaried positively with body mass across individuals of both sexes, comb size was positively related to social status in females but not in males. Second, we test for changes within individuals in body mass and comb size throughout the mating trial. Both body mass and comb size declined at the end of a trial in both sexes, suggesting that mating effort and exposure to the opposite sex are generally costly. Males lost more body mass if they (a) were socially subordinate, (b) were chased by other males or (c) mated frequently, indicating that subordinate status and mating are independently costly. Conversely, females lost more body mass if they were exposed to a higher frequency of coerced matings, suggesting costs associated with male sexual harassment and female resistance, although costs of mating per se could not be completely ruled out. Neither competitive nor mating interactions predicted comb size change in either sex. Collectively, these results support the notion that sex-specific costs associated with social status and mating effort result in differential, sex-specific dynamics of phenotypic change.

Keywords: badge of status; comb; condition dependence; cost of mating; sexual coercion; sexual selection; social status.

Figure 1

Schematics of (a) the experimental design outlining how the 20 replicate experimental mating groups of red junglefowl (Gallus gallus) were assembled from unique sets of female and male groups over the course of 3 years, (b) the timeline of the observation trial of each mating group, and (c) comb area measurement, here highlighted in an individual male

Figure 2

Relationship between social status and two condition dependent sexual traits in male and female red junglefowl (Gallus gallus). Relationship between Elo scores (i.e., social status) and (a) male body mass, (b) male comb size, (c) female body mass and (d) female comb size. Data points represent individual birds, with darker regions indicating data point overlaps. Shaded areas around the regression line represent the 95% confidence intervals

Figure 3

Relationship between changes in body mass and multiple sexually selected behaviors in male red junglefowl (Gallus gallus). Adjusted body mass difference was calculated by subtracting the individual's body mass (g) on the day following the mixed‐sex trial from its body mass on the day before the trial, while simultaneously correcting for the regression to the mean effect. Therefore, the adjusted body mass difference does not represent the actual differences in body mass. Adjusted changes in body mass were associated to (a) male social status, (b) male mating success (i.e., number of unique copulation partners), (c) total number of copulations, and (d) the number of times that a male was chased by other males. The removal of outliers does not change qualitatively the results. Data points represent individual males, with darker regions indicating data point overlaps. Shaded areas around the regression line represent the 95% confidence intervals

Figure 4

Relationship between changes in body mass and multiple sexually selected behaviors in female red junglefowl (Gallus gallus). The y‐axes represent adjusted changes in body mass (see Figure 2). Relationship between the adjusted change in female body mass and (a) female social status, (b) female mating success (i.e., number of unique copulation partners), (c) the total number of copulations, and (d) the number of coerced copulations experienced by a female. The removal of outliers does not change qualitatively the results. Data points represent individual females, with darker regions indicating data point overlaps. Shaded areas around the regression line represent the 95% confidence intervals