Effects of social experience, aggressiveness and comb size on contest success in male domestic fowl

Abstract

The ability to dominate conspecifics and thereby gain access to resources depends on a number of traits and skills. Experience of dominance relationships during development is a potential source of learning such skills. We here study the importance of social experience, aggressiveness and morphological traits for competitiveness in social interactions (contest success) in male domestic fowl (Gallus gallus domesticus). We let males grow up either as a single (dominant) male or as an intermediately ranked male in a group of males, and measured their success in duels against different opponents. We found that single-raised males had lower contest success than group-raised males, and that aggression and comb size correlated positively with contest success. This indicates that experience of dominance interactions with other males increases future success in duels. We similarly studied the consequences of growing up as a dominant or subordinate in a pair of males, finding no statistically significant effect of the dominance position on contest success. Finally, we found that males were consistent over time in contest success. We conclude that social experience increases contest success in male domestic fowl, but that certain behavioural and morphological characteristics have an equal or even stronger covariation with contest success.

Keywords: aggression; intra-sexual selection; ontogeny; social dominance; social rank; social status.

Figure 1.

Experimental set-up for the social treatments of focal males. Single, Group and Pair are the social treatments, for testing effects of social rearing on contest success in male domestic fowl. Each box in the figure represents a replicate, containing males and females from the experimental rearings. The bolder male symbols represent the dominant male in the replicate and the dotted circles indicate focal males. The focal males underwent a number of tests, in the form of duels against opponent males from the main population, aggression assays and NA assays (figure 2).

Figure 2.

Time line of social treatments, duels and behavioural assays when testing effects of social rearing on contest success in male domestic fowl. The social treatments (figure 1) started when focal males were three weeks old. Two rounds of duels between focal and opponent males, with 6–7 duels per focal male, were performed six months apart. Aggression was scored one week before and one week after each duel round (A), for both focal and opponent males. Two weeks before the first duel round, an NA assay was performed for the focal males. Exposure to NA was repeated one week later.

Figure 3.

The probability of winning over two rounds of duels between focal and opponent males (see table 1 for statistical analysis). (a,b) Logistic regression curves from a fitted model like the one in table 1, illustrating the importance of aggression (a) and comb size (b), relative to the opponent male, for the probability of the focal male to win, based on focal males from the Single and Group treatments. The inserted histograms show the distributions of the focal–opponent differences in aggressiveness and comb size. (c) The proportion of duels won (mean ± 95% profile confidence intervals from a model like that in table 1) for focal males (n = 16) from the Single and Group treatments, and in lighter grey, the proportion of duels won (mean ± 95% profile confidence intervals from a model like that in table 2) for focal dominant males and focal subordinate males from the Pair treatment (n = 13).

Figure 4.

The proportion of contests won in each of two rounds of duels (autumn and spring) by focal male domestic fowl. The area of the circles is proportional to the number of males with the same proportions of contests won. The dashed line shows a linear regression (F = 24.9, p < 0.001, n_males = 21).