Morphological and molecular traits associated with the passive dispersal of rotifer diapausing eggs

Diapausing eggs are a critical life-history stage in rotifers, serving as dispersal units and enabling population persistence under adverse conditions. Despite their ecological significance, the factors shaping their phenotypic variation and the genetic basis of this variation remain largely unexplored. This study pursues the phenotypic characterization of traits potentially related to dispersal in diapausing eggs of two cryptic rotifer species, Brachionus plicatilis and Brachionus rotundiformis. We also examined intraspecific variation in these traits by comparing clones of B. plicatilis derived from floating and sinking diapausing eggs, which may reflect different dispersal strategies. Specifically, we quantified traits related to egg and embryo size, shape, internal structure, weight and lipid content. Additionally, we performed a genome-wide association study (GWAS) in B. plicatilis to identify genetic variants associated with key dispersal-related traits. Significant differences in the phenotypic characterization of the diapausing eggs were found between the two rotifer species: B. plicatilis produced larger and heavier diapausing eggs, while B. rotundiformis exhibited higher lipid content. Broad-sense heritability indicated stronger genetic control of most traits in B. plicatilis, whereas lipid area showed higher heritability in B. rotundiformis. Differences between floating and sinking diapausing eggs in B. plicatilis were linked to lipid content. Floating eggs displayed significantly higher lipid reserves. Genomic analyses identified SNPs significantly associated with embryo area, egg weight, and lipid content, located near genes involved in morphogenesis, embryo development and a protein family that forms gap junctions. This study represents one of the first GWAS applications targeting diapausing egg traits in aquatic microinvertebrates and provides insights into the genetic architecture governing dispersal strategies in rotifers.滞育卵（diapausing eggs）是轮虫生活史中的关键阶段，既可作为扩散载体，也能帮助种群在逆境条件下存续。尽管其生态意义重大，但调控滞育卵表型变异的因素以及该变异的遗传基础仍未得到充分探索。本研究针对两种隐存轮虫物种——褶皱臂尾轮虫（Brachionus plicatilis）与圆形臂尾轮虫（Brachionus rotundiformis）的滞育卵，开展与扩散相关性状的表型表征工作。同时，我们通过比较源自漂浮型与沉降型滞育卵的褶皱臂尾轮虫克隆株，分析该物种内的性状变异，以此反映不同的扩散策略。具体而言，我们量化了与卵及胚胎尺寸、形态、内部结构、重量以及脂质含量相关的各项性状。此外，我们在褶皱臂尾轮虫中开展全基因组关联研究（genome-wide association study, GWAS），以鉴定与关键扩散相关性状相关的遗传变异。研究发现两种轮虫的滞育卵表型存在显著差异：褶皱臂尾轮虫所产的滞育卵体积更大、重量更高，而圆形臂尾轮虫的滞育卵脂质含量更高。广义遗传力分析显示，褶皱臂尾轮虫的多数性状受更强的遗传调控，而圆形臂尾轮虫的脂质面积性状具有更高的遗传力。褶皱臂尾轮虫中漂浮型与沉降型滞育卵之间的性状差异与脂质含量相关，漂浮型卵的脂质储备显著更高。基因组分析鉴定出与胚胎面积、卵重及脂质含量显著相关的单核苷酸多态性（single nucleotide polymorphisms, SNPs），这些位点位于参与形态发生、胚胎发育以及构成间隙连接的蛋白质家族的相关基因附近。本研究是首批针对水生微型无脊椎动物滞育卵性状开展全基因组关联研究的案例之一，为解析轮虫扩散策略的遗传结构提供了重要见解。