Data from: Age, experience and sex – do female bulb mites prefer young mating partners?

In species where advancing sire age is associated with decreased progeny fitness, female resistance to mating with old partners can be expected to evolve. In polyandrous species, such resistance may be contingent on female mating experience: virgins should be relatively indiscriminate to ensure egg fertility, whereas non-virgins can be expected to base their re-mating decisions on the age of their previous versus potential new partners, and ‘trade up’ if previously mated with old males. Here, we tested these predictions using a promiscuous and relatively long-living bulb mite (Rhizoglyphus robini), in which old sire age is associated with decreased fecundity of daughters. In a fully factorial design, we applied two male treatments: young and old, and three female treatments: virgin, previously mated to an old male and previously mated to a young male. Consistent with earlier studies, we observed a reduced mating success of old males. However, we found no support for attributing this result to female discrimination, as female behaviour in response to male mounting attempts was not affected by the age of the suitor, or by its interaction with the age of the female’s previous mate. Interestingly, females were passive during 93% of male mounting attempts observed, suggesting that once they are located by a male, they exert little control over copulation. Old males had lower mate searching activity and were less efficient in obtaining matings (lower success rate per mounting attempt), suggesting a decreased mate securing ability due to aging. Overall, our results suggest that in bulb mites, male ability to secure mates declines with age, whereas they do not support the prediction that females actively discriminate against old partners.

在父本年龄增加与后代适合度下降相关联的物种中，雌性对与年长配偶交配的抗性理应会演化形成。在多雄交配物种中，这类抗性可能取决于雌性的交配经历：未交配雌性通常不会过度挑剔，以保障卵的受精率；而已交配雌性则会基于其此前配偶与潜在新配偶的年龄做出再次交配的决策，若此前与年长雄性交配，则会选择更优质的配偶。在此，我们以混杂交配且寿命相对较长的罗宾根螨（Rhizoglyphus robini）为研究对象验证了上述预测，该物种中父本年龄较高会导致雌性后代的繁殖力下降。本研究采用完全因子实验设计，设置两组雄性处理：年轻雄性与年长雄性；三组雌性处理：未交配雌性、曾与年长雄性交配的雌性、曾与年轻雄性交配的雌性。与此前的研究结果一致，我们观察到年长雄性的交配成功率更低。然而，我们并未发现该结果可归因于雌性的配偶识别偏好，因为雌性对雄性爬跨尝试的行为反应，既不受求偶雄性年龄的影响，也不受其与雌性此前配偶年龄的交互效应影响。值得注意的是，在观测到的93%的雄性爬跨尝试中，雌性均处于被动状态，这表明一旦被雄性定位，雌性几乎无法控制交配过程。年长雄性的配偶搜寻行为更少，且在获取交配机会时效率更差（单次爬跨尝试的成功率更低），这表明衰老会导致雄性的配偶获取能力下降。总体而言，我们的研究结果表明，在罗宾根螨中，雄性获取配偶的能力随年龄增长而下降，但并不支持雌性会主动排斥年长配偶的预测。