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).