Courtship behavior as a war of attrition in a simultaneous hermaphrodite: Supplementary material

In outcrossing
hermaphrodites with unilateral mating, where for each mating interaction one
individual assumes
the female role and the other the male role,
each individual must take a sexual role opposite to that of its partner. In the
polychaete worm Ophryotrocha diadema,
the decision on sexual role is likely at stake during the day-long courtship.
Here we describe, for the first time, courtship and pseudocopulation in this
species, quantify their pre-copulatory behavior, and search for behavioral
traits predicting the prospective sexual role (i.e., behavioral sexual
dimorphism), by analyzing the courtship behavior of pairs of worms during the day
preceding a mating event. We did not find any behavioral cue predicting the
sexual role worms were to play; partners’ pre-copulatory behaviors were
qualitatively and quantitatively symmetrical. We interpret this as the outcome
of a war of attrition where partners share the preference for the same sexual role,
and both hide their ‘willingness’ to play the less preferred one, until one individual
reaches its cost threshold and accepts the less preferred sexual role.

在异交型单侧交配的雌雄同体中，每对交配互动中，一方扮演雌性角色，另一方扮演雄性角色，每个个体必须承担与其伴侣相反的性角色。在多毛纲环节动物 Ophryotrocha diadema 中，性角色的决定可能在为期一天的求偶过程中至关重要。本研究首次描述了该物种的求偶和拟交配行为，量化了其交配前的行为，并通过分析交配事件前一天成对环节动物的求偶行为，探寻预测未来性角色的行为特征（即行为性二型性）。我们未发现任何预示环节动物将扮演的性角色的行为线索；伴侣的交配前行为在质和量上均呈对称性。我们将此解释为一场消耗战的结果，双方共享对相同性角色的偏好，并且都隐藏了自己对扮演不受欢迎性角色的‘意愿’，直到某一方的成本阈值达到并接受扮演不受欢迎的性角色。