Data from: Pipefish embryo oxygenation, survival and development: egg size, male size and temperature effects

In animals with uniparental care, the quality of care provided by one sex can deeply impact the reproductive success of both sexes. Studying variation in parental care quality within a species and which factors may affect it can therefore shed important light on patterns of mate choice and other reproductive decisions observed in nature. Using Syngnathus typhle, a pipefish species with extensive uniparental male care, with embryos developing inside a brood pouch during a lengthy pregnancy, we assessed how egg size (which correlates positively with female size), male size and water temperature affect brooding traits that relate to male care quality, all measured on day 18, approximately 1/3, of the brooding period. We found that larger males brooded eggs at lower densities, and their embryos were heavier than those of small males independent of initial egg size. However, large males had lower embryo survival relative to small males. We found no effect of egg size or of paternal size on within-pouch oxygen levels, but oxygen levels were significantly higher in the bottom than the middle section of the pouch. Males that brooded at higher temperatures had lower pouch oxygen levels presumably because of higher embryo developmental rates, as more developed embryos consume more oxygen. Together, our results suggest that small and large males follow distinct paternal strategies: large males positively affect embryo size while small males favour embryo survival. As females prefer large mates, offspring size at independence may be more important to female fitness than offspring survival during development.

在存在单亲抚育（uniparental care）的动物类群中，某一性别所提供的抚育质量可深刻影响两性的繁殖成功率。因此，研究同一物种内抚育质量的变异及其影响因素，可为阐明自然界中观察到的配偶选择模式与其他繁殖决策提供重要见解。本研究以粗吻海龙（Syngnathus typhle）为对象，该物种具有全面的雄性单亲抚育行为，胚胎会在漫长孕期内于育幼袋（brood pouch）中发育，本研究评估了卵大小（与雌性体型呈正相关）、雄性体型及水温如何影响与雄性抚育质量相关的育幼性状，所有性状均在育幼期的第18天——约为总育幼时长的1/3——进行测定。研究发现，体型更大的雄性所承载的卵密度更低，且其胚胎重量显著高于小型雄性的胚胎，这一差异不受初始卵大小的影响。但相较于小型雄性，大型雄性的胚胎存活率更低。本研究未发现卵大小或父本体型对育幼袋内氧气水平存在显著影响，但育幼袋底部的氧气水平显著高于中部区域。在更高水温下抚育后代的雄性，其育幼袋内氧气水平更低，这可能是由于胚胎发育速率更快——发育程度更高的胚胎耗氧量更大。综合以上结果，本研究表明大型与小型雄性采取了截然不同的抚育策略：大型雄性可提升胚胎的最终大小，而小型雄性则更倾向于保障胚胎存活率。由于雌性偏好体型较大的配偶，独立后代的体型对于雌性的适合度（fitness）可能比发育阶段的后代存活率更为重要。