Data from: Cryptic recombination in the ever-young sex chromosomes of Hylid frogs

Sex chromosomes are expected to evolve suppressed recombination, which leads to degeneration of the Y and heteromorphism between the X and Y. Some sex chromosomes remain homomorphic, however, and the factors that prevent degeneration of the Y in these cases are not understood. The homomorphic sex chromosomes of the European tree frogs (Hyla spp.) present an interesting paradox. Recombination in males has never been observed in crossing experiments, but molecular data are suggestive of occasional recombination between the X and Y. The hypothesis that these sex chromosomes recombine has not been tested statistically, however, nor has the XY recombination rate been estimated. Here we use Approximate Bayesian Computation coupled with coalescent simulations of sex chromosomes to quantify X-Y recombination rate from existent data. We find that microsatellite data from H. arborea, H. intermedia, and H. molleri support a recombination rate between X and Y that is significantly different from zero. We estimate that rate to be approximately 105 times smaller than that between X chromosomes. Our findings support the notion that very low recombination rate may be sufficient to maintain homomorphism in sex chromosomes.

性染色体（sex chromosomes）通常会进化出重组抑制现象，这会引发Y染色体退化，并导致X与Y染色体间出现异型性。然而，部分性染色体仍保持同型性，此类案例中阻止Y染色体退化的相关机制尚不明确。欧洲树蛙属（Hyla spp.）的同型性染色体便是一个颇具研究价值的悖论：杂交实验从未观测到雄性个体发生重组，但分子数据却暗示X与Y染色体间偶尔存在重组事件。然而，关于这类性染色体发生重组的假说尚未经过统计学检验，XY染色体间的重组率也未得到估算。本研究结合近似贝叶斯计算（Approximate Bayesian Computation）与性染色体溯祖模拟（coalescent simulations），基于现有数据对X-Y染色体间的重组率进行定量分析。研究结果显示，取自林氏树蛙（Hyla arborea）、中间树蛙（Hyla intermedia）以及莫勒尔树蛙（Hyla molleri）的微卫星（microsatellite）数据，支持X与Y染色体间存在显著非零的重组率。经估算，该重组率约比X染色体间的重组率低105倍。本研究结果支持“极低的重组率或足以维持性染色体的同型性”这一观点。