Department of Ecology, Faculty of Science, Charles University, Prague, Czechia.
Institute of Animal Physiology and Genetics, The Czech Academy of Sciences, Liběchov, Czechia.
Sex Dev. 2021;15(4):272-281. doi: 10.1159/000514195. Epub 2021 Mar 23.
Transitions from environmental sex determination (ESD) to genotypic sex determination (GSD) require an intermediate step of sex reversal, i.e., the production of individuals with a mismatch between the ancestral genotypic and the phenotypic sex. Among amniotes, the sole well-documented transition in this direction was shown in the laboratory in the central bearded dragon, Pogona vitticeps, where very high incubation temperatures led to the production of females with the male-typical (ZZ) genotype. These sex-reversed females then produced offspring whose sex depended on the incubation temperature. Sex-reversed animals identified by molecular and cytogenetic markers were also reported in the field, and their increasing incidence was speculated as a climate warming-driven transition in sex determination. We show that the molecular and cytogenetic markers normally sex-linked in P. vitticeps are also sex-linked in P. henrylawsoni and P. minor, which points to quite ancient sex chromosomes in this lineage. Nevertheless, we demonstrate, based on a crossing experiment with a male bearded dragon who possesses a mismatch between phenotypic sex and genotype, that the used cytogenetic and molecular markers might not be reliable for the identification of sex reversal. Sex reversal should not be considered as the only mechanism causing a mismatch between genetic sex-linked markers and phenotypic sex, which can emerge also by other processes, here most likely by a rare recombination between regions of sex chromosomes which are normally sex-linked. We warn that sex-linked, even apparently for a long evolutionary time, and sex-specific molecular and cytogenetic markers are not a reliable tool for the identification of sex-reversed individuals in a population and that sex reversal has to be verified by other approaches, particularly by observation of the sex ratio of the progeny.
从环境性别决定（ESD）到基因型性别决定（GSD）的转变需要一个性别反转的中间步骤，即产生与祖先基因型和表型性别不匹配的个体。在羊膜动物中，这种方向的唯一有充分记录的转变是在中央鬃狮蜥（Pogona vitticeps）的实验室中显示的，那里非常高的孵化温度导致产生具有典型雄性（ZZ）基因型的雌性。这些性别反转的雌性随后产生的后代的性别取决于孵化温度。在野外也报道了通过分子和细胞遗传学标记识别的性别反转动物，并且推测其发病率的增加是性别决定的气候变暖驱动的转变。我们表明，在 Pogona vitticeps 中通常与性别连锁的分子和细胞遗传学标记也与 Pogona henrylawsoni 和 Pogona minor 连锁，这表明在该谱系中存在相当古老的性染色体。然而，我们基于与具有表型性别和基因型不匹配的雄性鬃狮蜥的杂交实验表明，所使用的细胞遗传学和分子标记可能不可靠用于识别性别反转。性别反转不应被视为导致遗传性别连锁标记与表型性别不匹配的唯一机制，这种不匹配也可能通过其他过程产生，这里最可能是通过正常性连锁的性染色体区域之间的罕见重组。我们警告说，性连锁的，即使显然在很长的进化时间内，以及性别特异性的分子和细胞遗传学标记，不是识别群体中性别反转个体的可靠工具，性别反转必须通过其他方法验证，特别是通过观察后代的性别比例。
