Sexual selection has driven sexual dimorphism in agonistic behaviour in many species. Agonistic behaviour is fundamentally altered by domestication and captivity, but it is unclear whether ancestral sex differences remain. We aimed to evaluate the effect of sex on agonistic behaviour, fighting ability and contest costs. We studied this in domestic pigs (Sus scrofa) where aggression compromises welfare, and sexual dimorphism in aggression has been inconclusively demonstrated. Behaviour and physiology of 827 male and female juvenile pigs were studied during resident-intruder tests and dyadic contests at various ages, while accounting for the relative body weight difference between the opponents. Males won in 79% of contests against females, even when at a large weight disadvantage. The effect of sex increased with age, with males having a 138 times higher likelihood of winning than females when 13 weeks old. In dyadic contests, males invested more time in non-damaging agonistic display behaviour and took longer before escalating into damaging aggression. Males showed ritualized display that included foaming from the mouth and piloerection of the neck hair, which was nearly always absent in females. Contest costs in terms of contest duration, blood lactate and skin lesions where higher for males, especially when fighting another male. Profound sex differences were present for agonistic behaviour, fighting ability and contest costs, and became more pronounced as animals got older. Males invested more in ritualized display before escalating into costly fights, whereas females attacked sooner but also terminated contests more rapidly and with fewer costs. The sexual dimorphism in agonistic behaviour in juvenile domestic pigs is in line with the evolutionary relevance for females’ maternal defence and males’ competition for females.

中文翻译：

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Sus scrofa的仪式化竞争行为，战斗能力和竞争成本的性别二态性

性选择在许多物种的竞争行为中驱动了性别二态性。驯化和圈养从根本上改变了竞争行为，但尚不清楚祖先的性别差异是否仍然存在。我们旨在评估性对竞争行为、战斗能力和比赛成本的影响。我们在攻击性损害福利的家猪（Sus scrofa）中研究了这一点，攻击性的性别二态性尚未得到结论性的证明。研究了 827 头雄性和雌性幼猪的行为和生理，在不同年龄的居民入侵者测试和二元比赛中进行了研究，同时考虑了对手之间的相对体重差异。男性在与女性的比赛中赢得了 79% 的胜利，即使在体重处于很大劣势的情况下也是如此。性别的影响随着年龄的增长而增加，男性在 13 周大时获胜的可能性是女性的 138 倍。在二元比赛中，男性在非破坏性的竞争性展示行为上投入了更多时间，并且在升级为破坏性攻击之前花费了更长的时间。男性表现出仪式化的展示，包括从嘴里冒出泡沫和竖起颈毛，而女性几乎总是不存在这种情况。比赛时间、血乳酸和皮肤损伤方面的比赛成本对男性来说更高，尤其是在与另一名男性战斗时。激烈的行为、战斗能力和比赛成本存在显着的性别差异，并且随着动物年龄的增长而变得更加明显。在升级为代价高昂的战斗之前，雄性在仪式化展示上投入更多，而雌性则更快地攻击，但也更快地结束比赛，成本更低。