Abstract

The ability to win fights is expected to be influenced by the rearing and nutritional conditions experienced by individuals. We hypothesized that crowded rearing conditions would foreshadow intense competition for resources in adult male Gryllus firmus (Scudder) field crickets and thus favour greater investment in mandibular weaponry. In line with prediction, males developed relatively larger weapons in crowded rearing conditions but this investment did not translate into greater success in contests against size-matched males that were reared singly. Rather, we found that low-density males were more likely to defeat high-density males under some experimental conditions, possibly because low-density males are more aggressive. Overall, our strongest observed effect was that males with larger weaponry were more likely to win contests, independent of rearing density. We also manipulated the adult diet of males to test the hypothesis that greater fat loads, and thus potentially greater stamina, would improve success in contests. Contrary to prediction, increased fat load did not increase a male’s probability of winning a contest possibly because fights in field crickets are too short to invoke stamina. Broadly speaking, animals decide whether to give up in a fight by assessing either their own (self-assessment) resource-holding potential (RHP) or by assessing a combination of their own and their opponent’s RHP (mutual assessment). Our study lends some support to the hypothesis that male G. firmus crickets decide to persist in a fight by assessing their own RHP rather than via mutual assessment.

Significance statement

Animals fight each other for access to, and control of, resources that they require for survival and reproduction (e.g. food, shelter, and mates). Although considerable empirical research has shown that individuals having a larger body size or weapons generally possess greater fighting ability—resource-holding potential (RHP)—and are thus typically more successful in combat, the factors contributing to the development of an individual’s RHP have received less attention. One potential environmental factor dictating RHP is population density; however, the effect of density on RHP is difficult to predict. Developing under high density could cause individuals to invest more in RHP-related traits because these conditions might signal intense competition for mates in the near future. However, individuals reared under high density are often less aggressive than their low-density counterparts. The food available to an adult could also be important because the consumption of fat could improve an individual’s stamina, an RHP-related trait important in combat. Our study testing the impact of these two factors on male fighting ability in the sand field cricket (Gryllus firmus) found limited support for the hypothesis that rearing density and diet significantly influence a male’s ability to win a fight against another male. Instead we found stronger support for the notion that, all else being equal, males with larger mandibles, or weapons, than their opponent were more likely to win a fight.

中文翻译：

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饮食和饲养密度对田比赛成绩和沉降的影响

摘要

赢得战斗的能力预计会受到个人所经历的饲养和营养状况的影响。我们假设拥挤的饲养条件将预示成年雄性Gryllus腹中激烈的资源竞争。（Scudder）field，因此倾向于增加对下颌武器的投资。与预测相符，雄性在拥挤的饲养条件下开发了相对较大的武器，但这项投资并未在与单独饲养的大小匹配的雄性比赛中获得更大的成功。相反，我们发现，在某些实验条件下，低密度雄性更可能击败高密度雄性，这可能是因为低密度雄性更具攻击性。总体而言，我们观察到的最强结果是，拥有较大武器的雄鸡更有可能赢得比赛，而与饲养密度无关。我们还操纵了成年男性的饮食习惯，以检验以下假设的假设：更大的脂肪负荷，从而可能更大的耐力，将改善比赛的成功率。与预测相反，增加的脂肪负荷并没有增加男性赢得比赛的可能性，这可能是因为田field的战斗太短而无法引起耐力。从广义上讲，动物通过评估自己的（自我评估）资源持有潜力（RHP）或评估自己与对手的RHP（相互评估）的组合来决定是否放弃战斗。我们的研究为男性这一假设提供了一些支持G. Firmus cket决定通过评估自己的RHP而不是通过相互评估来坚持战斗。

重要性声明

动物为了获得和控制其生存和繁殖所需的资源（例如食物，庇护所和伴侣）而相互争斗。尽管大量的经验研究表明，具有较大身体尺寸或武器的个人通常具有较强的战斗能力-资源持有潜力（RHP）-因此通常在战斗中更为成功，但有助于个人发展RHP的因素已经得到了认可少注意。决定RHP的一种潜在环境因素是人口密度。但是，密度对RHP的影响很难预测。在高密度下发展可能会导致个人对RHP相关性状进行更多投资，因为这些条件可能预示着在不久的将来对伴侣的激烈竞争。然而，在高密度下饲养的个体通常比低密度种群的个体攻击性低。成年人获得的食物也可能很重要，因为脂肪的摄入可以改善个人的耐力，这是与RHP相关的特质，在战斗中很重要。我们的研究测试了这两个因素对沙田板球男性战斗能力的影响（Gryllus firmus）对以下假设的支持有限，该假设是：饲养密度和饮食会显着影响男性赢得与另一雄性战斗的能力。取而代之的是，我们发现以下观点得到了更强有力的支持：在所有其他条件相同的情况下，下颌骨或武器更大的男性比其对手更有可能赢得战斗。