Peña Jorge, Nöldeke Georg, Puebla Oscar
Am Nat. 2020 Mar;195(3):524-533. doi: 10.1086/707016. Epub 2020 Jan 9.
Egg trading-whereby simultaneous hermaphrodites exchange each other's eggs for fertilization-constitutes one of the few rigorously documented and most widely cited examples of direct reciprocity among unrelated individuals. Yet how egg trading may initially invade a population of nontrading simultaneous hermaphrodites is still unresolved. Here, we address this question with an analytical model that considers mate encounter rates and costs of egg production in a population that may include traders (who provide eggs for fertilization only if their partners also have eggs to reciprocate), providers (who provide eggs regardless of whether their partners have eggs to reciprocate), and withholders (cheaters who mate only in the male role and just use their eggs to elicit egg release from traders). Our results indicate that a combination of intermediate mate encounter rates, sufficiently high costs of egg production, and a sufficiently high probability that traders detect withholders (in which case eggs are not provided) is conducive to the evolution of egg trading. Under these conditions, traders can invade-and resist invasion from-providers and withholders alike. The prediction that egg trading evolves only under these specific conditions is consistent with the rare occurrence of this mating system among simultaneous hermaphrodites.
卵子交易——即雌雄同体同时交换彼此的卵子以实现受精——是为数不多的有严格记录且被广泛引用的非亲属个体间直接互惠的例子之一。然而，卵子交易最初是如何侵入一个非交易型雌雄同体种群的，这一问题仍未得到解决。在此，我们通过一个分析模型来解决这个问题，该模型考虑了在一个可能包括交易者（只有当他们的伴侣也有卵子进行回报时才提供卵子用于受精）、提供者（无论其伴侣是否有卵子进行回报都会提供卵子）和扣留者（只以雄性角色交配并仅用自己的卵子促使交易者释放卵子的欺骗者）的种群中的配偶相遇率和卵子生产成本。我们的结果表明，中等的配偶相遇率、足够高的卵子生产成本以及交易者发现扣留者的概率足够高（在这种情况下不提供卵子）这三者的结合有利于卵子交易的进化。在这些条件下，交易者能够侵入并抵御来自提供者和扣留者的入侵。卵子交易仅在这些特定条件下进化的预测与这种交配系统在雌雄同体中罕见出现的情况相符。
