Data from: Sex-determining chromosomes and sexual dimorphism: insights from genetic mapping of sex expression in a natural hybrid Fragaria × ananassa subsp. cuneifolia

We studied the natural hybrid (Fragaria × ananassa subsp. cuneifolia) between two sexually dimorphic octoploid strawberry species (Fragaria virginiana and Fragaria chiloensis) to gain insight into the dynamics of sex chromosomes and the genesis of sexual dimorphism. Male sterility is dominant in both the parental species and thus will be inherited maternally, but the chromosome that houses the sex-determining region differs. Thus, we asked whether (1) the cytotypic composition of hybrid populations represents one or both maternal species, (2) the sex-determining chromosome of the hybrid reflects the location of male sterility within the maternal donor species and (3) crosses from the hybrid species show less sexual dimorphism than the parental species. We found that F. × ananassa subsp. cuneifolia populations consisted of both parental cytotypes but one predominated within each population. Genetic linkage mapping of two crosses showed dominance of male sterility similar to the parental species, however, the map location of male sterility reflected the maternal donor in one cross, but not the other. Moreover, female function mapped to a single region in the first cross, but to two regions in the second cross. Aside from components of female function (fruit set and seed set), other traits that have been found to be significantly sexually dimorphic in the pure species were either not dimorphic or were dimorphic in the opposite direction to the parental species. These results suggest that hybrids experience some disruption of dimorphism in secondary sexual traits, as well as novel location and number of quantitative trait locus (QTL) affecting sex function.

本研究以两个具性别二态性（sexual dimorphism）的八倍体草莓物种（Fragaria virginiana与Fragaria chiloensis）之间的天然杂交种（Fragaria × ananassa subsp. cuneifolia）为研究材料，旨在阐明性染色体的动力学特征及性别二态性的起源机制。雄性不育在两个亲本物种中均为显性性状，因此将通过母系遗传，但二者携带性别决定区域的染色体并不相同。基于上述背景，本研究提出三个核心科学问题：（1）杂交种群的细胞型组成是否涵盖一个或两个亲本物种？（2）杂交种的性别决定染色体是否匹配雄性不育在母本供体物种中的位置？（3）杂交种的杂交后代是否较亲本物种呈现出更弱的性别二态性？研究结果显示，Fragaria × ananassa subsp. cuneifolia种群同时包含两种亲本细胞型，但每个种群内仅有一种细胞型占据主导地位。对两个杂交组合开展遗传连锁作图后发现，雄性不育的显性遗传特性与亲本物种一致；然而，雄性不育的图谱定位仅在一个杂交组合中对应母本供体的染色体，另一组合则未呈现这一对应关系。此外，雌性功能相关的数量性状位点（quantitative trait locus, QTL）在首个杂交组合中仅定位于单个区域，而在第二个杂交组合中则定位于两个独立区域。除雌性功能相关性状（坐果率与结籽率）外，在纯种中被证实存在显著性别二态性的其余性状，要么未表现出性别二态性，要么其二态性方向与亲本物种完全相反。上述结果表明，杂交种在次级性性状的二态性上存在一定程度的紊乱，同时影响生殖功能的数量性状位点（QTL）的位置与数量也出现了新的变异模式。