Data from: Replicated origin of female biased adult sex ratio in introduced populations of the Trinidadian guppy (Poecilia reticulata).

There are many theoretical and empirical studies explaining variation in offspring sex ratio but relatively few that explain variation in adult sex ratio. Adult sex ratios are important because biased sex ratios can be a driver of sexual selection and will reduce effective population size which affects population persistence and shapes how populations respond to natural selection. Previous work on guppies (Poecilia reticulata) gives mixed results, usually showing a female-biased adult sex ratio. However a detailed analysis showed that this bias varied dramatically throughout a year and with no consistent sex-bias. We used a mark-recapture approach to examine the origin and consistency of female-biased sex ratio in four replicated introductions. We show that female-biased sex ratio arises predictably and is a consequence of higher male mortality and longer female lifespans with little effect of offspring sex ratio. Inconsistencies with previous studies are likely due to sampling methods and sampling design which should be less of an issue with mark-recapture techniques. Together with other long-term mark-recapture studies, our study suggests that bias in offspring sex ratio rarely contributes to adult sex ratio in vertebrates. Rather, sex differences in adult survival rates and longevity determine vertebrate adult sex ratio.

已有大量理论与实证研究阐释了子代性比（offspring sex ratio）的变异规律，但针对成体性比（adult sex ratio）变异的相关研究则相对匮乏。成体性比具有重要研究价值：失衡的性比可成为性选择（sexual selection）的驱动因素，同时会降低有效种群大小（effective population size），进而影响种群存续（population persistence），并塑造种群对自然选择（natural selection）的响应模式。过往针对孔雀鱼（Poecilia reticulata）的相关研究结果存在分歧，多数报道显示其成体性比偏向雌性。然而一项细致分析表明，该性比偏差在全年内存在显著波动，且无稳定的偏性特征。本研究采用标记重捕法（mark-recapture），对4个重复引入的孔雀鱼种群开展了雌性偏性成体性比的起源与稳定性分析。研究结果显示，雌性偏性的成体性比可被稳定预测，其成因源于雄性更高的死亡率与雌性更长的寿命，而子代性比对此几乎无影响。过往研究结果的不一致性，大概率源于抽样方法与抽样设计的局限，而标记重捕技术则可有效规避此类问题。结合其他长期标记重捕研究成果，本研究表明，在脊椎动物（vertebrate）类群中，子代性比极少对成体性比产生贡献。相反，成体存活率（adult survival rates）与寿命的性别差异才是决定脊椎动物成体性比的核心因素。