Johnson Steven G, Bragg Eric
Department of Biological Sciences, University of New Orleans, New Orleans, Louisiana, 70148.
Evolution. 1999 Dec;53(6):1769-1781. doi: 10.1111/j.1558-5646.1999.tb04561.x.
We used mtDNA sequence variation to assess the origin, age, and spatial patterns of sequence divergence of triploid hybrid and diploid spontaneous parthenogens from southeastern United States populations of the freshwater snail Campeloma. There was strong support for multiple origins of both parthenogens using likelihood-ratio tests, and we argue that parthenogens are recently derived from sexuals. Atlantic coastal populations of C. limum or C. floridense were the maternal ancestors of Gulf Coast triploid hybrids in the Florida Panhandle. Sequence divergence within monophyletic groups of both parthenogens is similar to within-population divergence found in sympatric sexuals, and monophyletic clades of hybrid and spontaneous parthenogens are geographically widespread throughout the Atlantic and Gulf Coast rivers. These patterns are consistent with higher dispersal rates and recent range expansion of parthenogens, which should reduce the effects of mutation accumulation or parasitism. Range expansion may have occurred through interdrainage transfer during Pleistocene glacial periods.
我们利用线粒体DNA序列变异来评估来自美国东南部淡水蜗牛坎氏螺种群的三倍体杂交体和二倍体自发孤雌生殖体的起源、年代以及序列分歧的空间模式。通过似然比检验，有力支持了这两种孤雌生殖体具有多个起源，并且我们认为孤雌生殖体是最近从有性生殖体衍生而来的。佛罗里达狭长地带墨西哥湾沿岸三倍体杂交体的母系祖先为大西洋沿岸的滨海坎氏螺或佛罗里达坎氏螺种群。两种孤雌生殖体单系群内的序列分歧与同域有性生殖体中发现的种群内分歧相似，并且杂交体和自发孤雌生殖体的单系分支在地理上广泛分布于整个大西洋和墨西哥湾沿岸河流。这些模式与孤雌生殖体更高的扩散率和近期的范围扩张相一致，这应该会减少突变积累或寄生的影响。范围扩张可能是在更新世冰川期通过水系间转移发生的。
