Echelle Anthony A, Dowling Thomas E, Moritz Craig C, Brown Wesley M
Zoology Department, Oklahoma State University, Stillwater, OK, 74078.
Museum of Zoology and Department of Biology, University of Michigan, Ann Arbor, MI, 48109.
Evolution. 1989 Aug;43(5):984-993. doi: 10.1111/j.1558-5646.1989.tb02544.x.
Restriction-endonuclease analysis of mitochondrial DNA (mtDNA) of the unisexual M. clarkhubbsi complex and close sexual relatives indicated that the unisexual complex arose through multiple, nonreciprocal hybridizations involving females of M. peninsulae. High-resolution analyses using restriction endonucleases that cleave at 4-bp sites revealed mtDNA sequence diversity that was low among unisexuals but high among individuals of M. peninsulae. The identification of M. peninsulae as a parent of the unisexuals conflicts with some details of previous allozyme comparisons. One possibility is that the unisexuals were derived from hybridization involving M. beryllina and a recently extinct form of M. peninsulae. In contrast to the unisexuals, contemporary hybrids of M. peninsulae and M. beryllina are formed by reciprocal matings. The origins of extant unisexual lineages from nonreciprocal hybridizations, together with their low mtDNA diversity relative to the maternal ancestor, implies strong constraints on origins of unisexuality via hybridization. Data on reproduction by contemporary F hybrids reveal one form of genetic/developmental constraint: M. peninsulae and M. beryllina may now have diverged beyond the point where the hybrid origin of new unisexual lineages is possible.
对单性的克拉克哈布斯美洲鳉复合体及其近缘有性繁殖亲属的线粒体DNA（mtDNA）进行限制性内切酶分析表明，该单性复合体是通过涉及半岛美洲鳉雌鱼的多次非相互杂交产生的。使用在4碱基位点切割的限制性内切酶进行的高分辨率分析显示，单性个体的mtDNA序列多样性较低，而半岛美洲鳉个体的mtDNA序列多样性较高。将半岛美洲鳉鉴定为单性个体的亲本与之前同工酶比较的一些细节相冲突。一种可能性是，单性个体源自涉及贝氏美洲鳉和一种最近灭绝的半岛美洲鳉的杂交。与单性个体不同，半岛美洲鳉和贝氏美洲鳉的当代杂种是通过相互交配形成的。现存单性谱系源自非相互杂交，以及它们相对于母本祖先较低的mtDNA多样性，这意味着通过杂交产生单性的起源受到强烈限制。当代F杂种繁殖的数据揭示了一种遗传/发育限制形式：半岛美洲鳉和贝氏美洲鳉现在可能已经分化到新的单性谱系无法通过杂交起源的程度。
