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.

在雄性亲本年龄增长与后代适合度降低相关的物种中，雌性对与年长雄性配偶交配的抗性预计会演化形成。在实行一妻多夫制（polyandrous）的物种中，这类抗性可能取决于雌性的交配经历：未交配雌性通常会相对不加选择，以保障卵的受精率；而已交配雌性则会基于先前配偶与潜在新配偶的年龄来做出再次交配决策，若此前曾与年长雄性交配，则会择偶升级（trade up）。本研究以一种具有混交行为且寿命较长的球根螨（Rhizoglyphus robini，罗宾根螨）为实验对象，验证了上述预测——该物种中雄性亲本年龄增长与雌性后代的繁殖力下降相关。本研究采用完全析因设计，设置两类雄性处理组（年轻雄性、年长雄性）与三类雌性处理组：未交配雌性、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歧视：雌性对雄性攀附尝试的行为反应，并未受求偶雄性的年龄影响，也未受其与雌性先前配偶年龄的交互效应影响。有趣的是，在观测到的93%的雄性攀附尝试中，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无法施加控制。年长雄性的觅偶活动能力更低，且获得交配的效率也更差（单次攀附尝试的交配成功率更低），这表明雄性因衰老导致获得配偶的能力下降。总体而言，本研究结果表明，在罗宾根螨中，雄性获得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雄性配偶的预测。