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.在父本年龄增长与后代适合度降低相关的物种中，雌性对与年长配偶交配的抵抗性有望演化产生。在一妻多夫制物种中，这类抵抗性可能取决于雌性的交配经历：处女雌性通常会相对无差别地交配以保证卵的受精率，而非处女雌性则会基于其既往配偶与潜在新配偶的年龄来做出再次交配的决策，若此前曾与年长雄性交配，则可能会「择偶升级」。本研究以混交且寿命相对较长的罗宾根螨（Rhizoglyphus robini）为实验对象，检验上述预测，该物种中父本年龄增大会导致雌性后代的繁殖力降低。本研究采用完全析因设计，设置两组雄性处理（年轻雄性与年长雄性）以及三组雌性处理（处女雌性、此前与年长雄性交配过的雌性、此前与年轻雄性交配过的雌性）。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择偶识别，因为雌性对雄性攀爬行为的响应并未受求偶雄性的年龄影响，也未受其与雌性既往配偶年龄的交互作用影响。有趣的是，在观测到的93%的雄性攀爬行为中，雌性均处于被动状态，这表明一旦被雄性定位，雌性对交配过程几乎没有控制权。年长雄性的配偶搜寻活性更低，且获取交配的效率也更低（每次攀爬尝试的成功率更低），这表明衰老会导致雄性的配偶获得能力下降。总体而言，本研究结果表明，罗宾根螨中雄性的配偶获得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。