Data from: No evidence for size-assortative mating in the wild despite mutual mate choice in sex-role-reversed pipefishes

Size-assortative mating is a nonrandom association of body size between members of mating pairs and is expected to be common in species with mutual preferences for body size. In this study, we investigated whether there is direct evidence for size-assortative mating in two species of pipefishes, Syngnathus floridae and S. typhle, that share the characteristics of male pregnancy, sex-role reversal, and a polygynandrous mating system. We take advantage of microsatellite-based “genetic-capture” techniques to match wild-caught females with female genotypes reconstructed from broods of pregnant males and use these data to explore patterns of size-assortative mating in these species. We also develop a simulation model to explore how positive, negative, and antagonistic preferences of each sex for body size affect size-assortative mating. Contrary to expectations, we were unable to find any evidence of size-assortative mating in either species at different geographic locations or at different sampling times. Furthermore, two traits that potentially confer a fitness advantage in terms of reproductive success, female mating order and number of eggs transferred per female, do not affect pairing patterns in the wild. Results from model simulations demonstrate that strong mating preferences are unlikely to explain the observed patterns of mating in the studied populations. Our study shows that individual mating preferences, as ascertained by laboratory-based mating trials, can be decoupled from realized patterns of mating in the wild, and therefore, field studies are also necessary to determine actual patterns of mate choice in nature. We conclude that this disconnect between preferences and assortative mating is likely due to ecological constraints and multiple mating that may limit mate choice in natural populations.体型选型交配（size-assortative mating）指交配配对个体间的体型非随机关联，预计在存在相互体型偏好的物种中较为常见。本研究针对两种兼具雄性妊娠、性角色反转及多夫多妻交配系统特征的海龙——佛罗里达海龙（Syngnathus floridae）与尖海龙（S. typhle），探究其是否存在体型选型交配的直接证据。我们借助基于微卫星的“遗传捕获”技术，将野生捕获的雌性个体与从怀孕雄性育幼囊中重构得到的雌性基因型进行匹配，并利用这些数据分析这两个物种的体型选型交配模式。此外，我们构建了模拟模型，用以探索雌雄两性对体型的正向、负向及拮抗偏好如何影响体型选型交配。研究结果与预期相悖：我们未在不同地理区域或不同采样时段的两个物种中，发现任何体型选型交配的证据。进一步分析显示，两项可能为繁殖成功率带来适合度优势的性状——雌性交配顺序及单雌性转移卵数，并未对野外种群的配对模式产生影响。模型模拟结果表明，强烈的交配偏好难以解释研究种群中观测到的交配模式。本研究证实，通过实验室交配试验确定的个体交配偏好，可能与野外实际的交配模式相脱节，因此，野外研究对于明确自然界中真实的配偶选择模式同样不可或缺。我们最终推断，偏好与选型交配之间的这种脱节，大概率源于生态限制与多次交配行为——后者可能会限制自然种群中的配偶选择机会。