Data from: Does the risk of sperm competition help explain cooperation between reproductive competitors? A study in the ocellated wrasse (Symphodus ocellatus)

Although cooperating individuals may gain benefits, they risk being cheated by their allies. Therefore, to understand the persistence of cooperation by mutual benefits, it is important to document both the potential benefits of cooperation and the risks of cheating. We experimentally examined evidence of cooperation in the ocellated wrasse (Symphodus ocellatus), a fish species with males that exercise three reproductive strategies: satellite and sneaker males attempt to parasitically spawn in the nests of nesting males. Nesting males have been hypothesized to tolerate satellites as a result of satellite aid in defense against sneaker males and help in courting females. Here, we provide evidence that cooperation between reproductive competitors may arise in response to sperm competition from other males. After we experimentally removed satellites, nesting males had more sneakers at their nest and experienced a higher rate of sneaking when they spawned (increased sperm competition risk). When we experimentally distracted nesting males to prevent their acting aggressively toward satellites, satellites spawned with females and ate eggs in the nest. Our results suggest that nesting males and satellites gain fitness benefits of reduced direct reproductive and sperm competition through cooperation. However, nesting males risk losing paternity, while satellites experience increased aggression and must invest in aggression themselves (i.e., they act aggressively toward sneakers).

尽管合作的个体可从中获益，却也面临被盟友欺骗的风险。因此，若要理解基于互惠的合作何以持续，同时记录合作的潜在收益与欺骗风险便至关重要。我们针对眼斑隆头鱼（Symphodus ocellatus）的合作行为开展了实验探究。该物种的雄性个体存在三种繁殖策略：卫星雄鱼（satellite males）与寄生雄鱼（sneaker males）会寄生在筑巢雄鱼（nesting males）的巢穴中进行产卵。此前已有假说提出，筑巢雄鱼之所以容忍卫星雄鱼，是因为后者可协助其抵御寄生雄鱼，并帮助其向雌鱼求偶。在此，我们的研究证实，繁殖竞争者之间的合作或许是为了应对其他雄性带来的精子竞争。当我们通过实验移除卫星雄鱼后，筑巢雄鱼的巢穴周围会出现更多寄生雄鱼，且其产卵时遭遇寄生产卵的概率更高，即精子竞争风险上升。当我们通过实验干扰筑巢雄鱼，使其无法对卫星雄鱼发起攻击时，卫星雄鱼会与雌鱼一同产卵，并取食巢穴内的鱼卵。我们的研究结果表明，筑巢雄鱼与卫星雄鱼可通过合作，减少直接繁殖竞争与精子竞争，从而获得适合度收益。但与此同时，筑巢雄鱼也面临丧失父权的风险，而卫星雄鱼则会遭遇更多攻击，且自身也需投入攻击行为，即对寄生雄鱼发起攻击。