Zoology and Evolutionary Biology, Department of Biology, University of Konstanz, 78457 Konstanz, Germany.
Unidad Ejecutora Lillo (CONICET), Fundación Miguel Lillo, Tucumán, Argentina.
Proc Biol Sci. 2020 Jul 8;287(1930):20200969. doi: 10.1098/rspb.2020.0969.
Animal genitalia vary considerably across taxa, with divergence in many morphological traits, including striking departures from symmetry. Different mechanisms have been proposed to explain this diversity, mostly assuming that at least some of the phenotypic variation is heritable. However, heritability of the direction of genital asymmetry has been rarely determined. Anablepidae are internally fertilizing fish where the anal fin of males has been modified into an intromittent organ that transfers sperm into the gonopore of females. Males of anablepid fishes exhibit asymmetric genitalia, and both left- and right-sided individuals are commonly found at similar proportions within populations (i.e. antisymmetry). Although this polymorphism was described over a century ago, there have been no attempts to determine if genital asymmetry has a genetic basis and whether the different morphs are accumulating genetic differences, as might be expected since in some species females have also asymmetric gonopores and thereby can only be fertilized by compatible asymmetric males. We address this issue by combining breeding experiments with genome-wide data (ddRAD markers) in representative species of the two anablepid genera with asymmetric genitalia: and . Breeding experiments showed that all offspring were asymmetric, but their morphotype (i.e. right- or left-sided) was independent of parental morphotype, implying that the direction of asymmetry does not have a strong genetic component. Consistent with this conclusion, association analyses based on approximately 25 000 SNPs did not identify markers significantly associated with the direction of genital asymmetry and there was no evidence of population structure between left- and right-sided individuals. These results suggest that the direction of genital asymmetry in anablepid fishes might be stochastic, a commonly observed pattern in species with antisymmetry in morphological traits.
动物生殖器在分类群之间差异很大，具有许多形态特征的差异，包括明显的不对称性。已经提出了许多不同的机制来解释这种多样性，大多数假设至少有一些表型变异是可遗传的。然而，生殖器不对称的方向的遗传力很少被确定。Anablepidae 是内部受精的鱼类，雄性的臀鳍已被修改为一个交接器官，将精子转移到雌性的生殖孔中。Anablepidae 鱼类的雄性具有不对称的生殖器，并且在种群中以相似的比例常见到左侧和右侧个体（即反对称）。尽管这种多态性在一个多世纪前就已被描述，但尚未尝试确定生殖器不对称是否具有遗传基础，以及不同的形态是否积累了遗传差异，因为在某些物种中，雌性的生殖孔也不对称，因此只能由相容的不对称雄性受精。我们通过在具有不对称生殖器的两个 Anablepidae 属的代表性物种中结合繁殖实验和全基因组数据（ddRAD 标记）来解决这个问题： 和 。繁殖实验表明，所有后代都是不对称的，但它们的形态（即左侧或右侧）与亲代形态无关，这意味着不对称的方向没有强烈的遗传成分。与这一结论一致，基于大约 25000 个 SNPs 的关联分析没有鉴定出与生殖器不对称方向显著相关的标记，并且在左侧和右侧个体之间没有种群结构的证据。这些结果表明，Anablepidae 鱼类生殖器不对称的方向可能是随机的，这是形态特征反对称物种中常见的模式。
