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).

尽管合作个体可从合作中获益，但也面临被同盟者欺骗的风险。因此，为阐明基于互惠收益的合作行为如何得以持续维持，同时完整记录合作的潜在收益与欺骗风险均至关重要。我们以眼斑濑鱼（ocellated wrasse，*Symphodus ocellatus*）为实验对象，探究其合作行为的相关证据；该物种的雄性存在三种繁殖策略：卫星雄鱼与偷配雄鱼会寄生在筑巢雄鱼的巢穴中进行寄生产卵。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偷配雄鱼，同时帮助吸引雌性。本研究证实，繁殖竞争者之间的合作或可演化自对其他雄性精子竞争（sperm competition）的应对：当我们通过实验移除卫星雄鱼后，筑巢雄鱼的巢穴周边出现了更多偷配雄鱼，且在其产卵时遭遇偷配的概率显著升高，即精子竞争风险加剧；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，卫星雄鱼会与雌性一同产卵并取食巢穴内的鱼卵。研究结果表明，筑巢雄鱼与卫星雄鱼均可通过合作，获得直接繁殖竞争与精子竞争程度降低的适合度（fitness）收益；然而，筑巢雄鱼也面临父权（paternity）丧失的风险，而卫星雄鱼则会遭遇更多攻击，且自身也需投入攻击性行为，即对偷配雄鱼发起攻击。