Variance components of sex determination in the copepod Tigriopus californicus estimated from a pedigree analysis

Extensive theory exists regarding population sex ratio evolution that predicts equal sex ratio (when parental investment is equal). In most animals, sex chromosomes determine the sex of offspring, and this fixed genotype for sex has made theory difficult to test since genotypic variance for the trait (sex) is lacking. It has long been argued that the genotype has become fixed in most animals due to the strong selection for equal sex ratios. The marine copepod Tigriopus californicus has no sex chromosomes, multiple genes affecting female brood sex ratio and a brood sex ratio that responds to selection. The species thus provides an opportune system in which to test established sex ratio theory. In this paper, we further our exploration of polygenic sex determination in T. californicus using an incomplete diallel crossing design for analysis of the variance components of sex determination in the species. Our data confirm the presence of extra-binomial variance for sex, further confirming t..., Tigriopus californicus are tidal pool copepods with unusual variance in brood sex ratio. Field-caught individuals were used to create two artificial selection lines using truncation selection to select for highly male-biased broods in one line and highly female-biased broods in another line. After six generations, these lines were used to do a diallel cross of families within and between lines, generating an F1 generation, followed by backcrosses to the parental lines. Crosses were done using eight families from each parental line in two blocks of crosses between four families for F1 generation. The sex of all individuals from each brood in the crosses was observed and a pedigree used to an \"Animal Model\" analysis to estimate the quantitative genetic variance in sex of individuals in a generalized linear model using Bayesian analysis. Sex in this model was treated as a threshold trait - a binary phenotype driven by an underlying (unobservable) continuous 'liability' phenotype of many ge..., Data are provided in comma-delimited text files.
Analysis code are provided for use with R.

现有大量关于种群性比演化的理论，其预测当亲本投资（parental investment）相等时，种群性比将趋于均等。在绝大多数动物中，性染色体决定子代性别，由于该性状（性别）缺乏基因型变异（genotypic variance），这种固定的性别基因型使得相关理论难以得到验证。长期以来学界普遍认为，由于对均等性比的强烈选择压力，绝大多数动物的性别基因型已趋于固定。
海洋桡足类加州虎猛水蚤（Tigriopus californicus）不具备性染色体，存在多个影响雌性子代窝性比的基因，且其窝性比可对选择作出响应。因此该物种为验证已有的性比理论提供了绝佳的实验体系。
本研究采用不完全双列杂交设计（incomplete diallel crossing design），对该物种性别决定的方差组分进行分析，以此进一步探究加州虎猛水蚤的多基因性别决定机制。本研究数据证实了性别存在超二项分布方差（extra-binomial variance），进一步验证了t……，加州虎猛水蚤是潮间带池沼桡足类，其窝性比存在异常变异。
研究人员以野外捕获的个体为材料，通过截断选择法（truncation selection）构建了两个人工选择系（artificial selection lines）：一个选择系针对高度偏雄性的子代窝进行选育，另一个则针对高度偏雌性的子代窝进行选育。历经6代选育后，利用这两个选择系开展系内及系间家系双列杂交，获得F1代，随后进行回交（backcross）至亲本系的实验。F1代杂交分为两个组块，每组使用每个亲本系的8个家系，以4个家系为单位开展杂交。
对所有杂交子代窝的全部个体进行性别观测，并结合系谱（pedigree）信息采用动物模型（Animal Model）分析，通过贝叶斯分析（Bayesian analysis）框架下的广义线性模型（generalized linear model），估算个体性别的数量遗传方差（quantitative genetic variance）。该模型将性别视为阈值性状（threshold trait）——一种由潜在（不可观测）的连续‘责任性状（liability phenotype）’驱动的二元表型，该责任性状由众多ge……。
数据集以逗号分隔的文本文件形式提供。
配套分析代码适用于R语言环境。