Data from: Partner switching can favor cooperation in a biological market

Intraspecific cooperation and interspecific mutualisms can be promoted by mechanisms that reduce the frequency with which cooperative organisms are exploited by unhelpful partners. One such mechanism consists of changing partners after interacting with an uncooperative individual. I used McNamara et al.'s (Nature, 451, 2008, 189) partner switching model as a framework to examine whether this mechanism can select for increased cooperative investment by house sparrows (Passer domesticus) collaborating to rear offspring; previous research on this species has shown that substantial cooperative investments by both pair members are required to achieve high pay-offs from collaborating. I found that the poorer the outcome of a breeding attempt relative to the number of eggs the female invested, the greater the likelihood of partner switching. The incidence of partner switching changed seasonally, with peak switching coinciding with an increase in the number of alternative partners available to females. After females switched partners, their breeding outcomes rose to match those of females that remained with the same partner; this was not the case for males that switched partners. Consistent with the model's prediction, males in stable partnerships achieved over 25% higher than average reproductive success, which was attributable to both persistently good breeding outcomes and their older partners' high fecundity. These results provide empirical support for the hypothesis that partner switching favours increased cooperative investment levels, and they demonstrate that variation in the relative value of by-product benefits can enhance that process.种内合作与种间互利共生可通过降低合作生物被无益合作者剥削频率的机制得以促进。其中一种典型机制为：在与不合作个体互动后更换合作伙伴。本研究以McNamara等人（《自然》，451卷，2008年，第189页）提出的伙伴更换模型为框架，探究该机制是否能推动合作抚育后代的家雀（Passer domesticus）提升合作投入水平；此前针对该物种的研究显示，配对双方均需投入足量合作行为，才能从合作中获得高额收益。研究发现，繁殖尝试的结果相较于雌性投入的卵数越差，雌性更换伙伴的概率便越高。伙伴更换的发生率随季节动态变化，更换峰值与雌性可获取的替代伙伴数量增加的时段相吻合。雌性更换伙伴后，其繁殖成果提升至与留存原配对伙伴的雌性相当的水平；但雄性更换伙伴后并未出现这一情况。与模型预测相符，维持稳定配对的雄性个体的繁殖成功率较平均值高出25%以上，这一结果可归因于两方面：一是持续良好的繁殖表现，二是其年长配偶具备较高的繁殖力。本研究结果为「伙伴更换可促进合作投入水平提升」这一假说提供了实证支撑，同时表明副产品收益的相对价值差异能够强化这一合作调控过程。