LAUSR

Reciprocity is one of the evolutionary mechanisms explaining cooperation between individuals and explains behaviors where individuals follow the rules “help who helped you before” (direct reciprocity) or “help anyone if helped by someone” (generalized reciprocity). In direct reciprocity, decisions require individual recognition and the ability to remember the outcome of past interactions with individual partners. In contrast, in generalized reciprocity, decisions only require that individuals remember if they received help in previous interactions, irrespective of partner identity. Some species of outcrossing, simultaneous hermaphrodites trade eggs as predicted by a reciprocity mechanism, that is one individual offers its eggs to the partner conditionally upon receiving eggs from the partner before. As a first step toward understanding the decision rules used by egg‐traders, we tested whether they discriminate between familiar, previously cooperative partners and unfamiliar partners. We asked this question in the marine annelid worm Ophryotrocha diadema , where monogamous partners engage in egg trading by exchanging eggs every 4 days. By switching partners between pairs (thus exposing them to unfamiliar partners), we show that worms did not delay egg donations nor diminish clutch size compared to control (sham switched) pairs, where worms were kept with the same (familiar) partners. These results suggest that worms do not discriminate between familiar and unfamiliar partners and reciprocate eggs irrespective of partner identity.