Arntzen Jan W, Jehle Robert, Bardakci Fevzi, Burke Terry, Wallis Graham P
National Museum of Natural History, Research Department, Leiden, The Netherlands.
Evolution. 2009 May;63(5):1191-202. doi: 10.1111/j.1558-5646.2009.00611.x. Epub 2009 Jan 14.
Hybridization between divergent lineages often results in reduced hybrid viability. Here we report findings from a series of independent molecular analyses over several seasons on four life stages of F1 hybrids between the newts Triturus cristatus and T. marmoratus. These two species form a bimodal hybrid zone of broad overlap in France, with F1 hybrids making up about 4% of the adult population. We demonstrate strong asymmetry in the direction of the cross, with one class (cristatus-mothered) making up about 90% of F1 hybrids. By analyzing embryos and hatchlings, we show that this asymmetry is not due to prezygotic effects, as both classes of hybrid embryos are present at similar frequencies, implicating differential selection on the two hybrid classes after hatching. Adult F1 hybrids show a weak Haldane effect overall, with a 72% excess of females. The rarer marmoratus-mothered class, however, consists entirely of males. The absence of females from this class of adult F1 hybrids is best explained by an incompatibility between the cristatus X chromosome and marmoratus cytoplasm. It is thus important to distinguish the two classes of reciprocal-cross hybrids before making general statements about whether Haldane's rule is observed.
不同谱系之间的杂交往往会导致杂种活力降低。在此，我们报告了在几个季节里对蝾螈Triturus cristatus和T. marmoratus的F1杂种四个生活阶段进行的一系列独立分子分析的结果。这两个物种在法国形成了一个广泛重叠的双峰杂交区，F1杂种约占成年种群的4%。我们证明了杂交方向上存在强烈的不对称性，其中一类（以cristatus为母本）占F1杂种的约90%。通过分析胚胎和幼体，我们表明这种不对称性并非由于合子前效应所致，因为两类杂交胚胎的出现频率相似，这意味着孵化后对这两类杂种存在差异选择。成年F1杂种总体上表现出较弱的霍尔丹效应，雌性个体多出72%。然而，较罕见的以marmoratus为母本的那一类完全由雄性组成。这类成年F1杂种中没有雌性个体，最合理的解释是cristatus的X染色体与marmoratus的细胞质不相容。因此，在对是否观察到霍尔丹法则做出一般性陈述之前，区分这两类正反交杂种很重要。
