Shapiro Leo H
Department of Ecology and Evolution, State University of New York at Stony Brook, Stony Brook, New York, 11794-5245.
Evolution. 1998 Jun;52(3):784-796. doi: 10.1111/j.1558-5646.1998.tb03702.x.
In this study, previously unrecognized hybridization was documented between two meadow katydids in each of two disjunct contact zones, in the southeastern United States and along the Potomac River near Washington, DC. These two zones have very different histories and dynamics of interaction between the two taxa. Orchelimum nigripes and O. pulchellum (Tettigoniidae: Conocephalinae) are distributed west and east, respectively, of the Appalachian Mountains, from the Great Lakes to the Gulf Coast and along the Atlantic Coastal Plain from New York to the Florida Keys, but are not found in the Appalachians themselves. In addition, during this century O. nigripes has become established in a small area east of the Appalachians, in the Potomac River basin, where it has completely replaced O. pulchellum along the river corridor above Washington, DC. I sampled katydids from 40 sites across both hybrid zones and mapped geographic patterns of genetic variation (allele frequencies at two diagnostic loci) and variation in a morphometric index for males. Although the two taxa are quite distinct over most of their extensive distributions, there is clear evidence of introgression in both contact zones. In the Deep South, samples from a transect along the Gulf Coast define a broad hybrid zone of about 50-100 km, while samples from a transect 200 km to the north define a zone of about 150-250 km in width. Only one Deep South population shows a deviation from Hardy-Weinberg equilibrium at either locus, and there is no evidence of linkage disequilibrium in any Deep South population. In the Potomac region, there is a narrow upstream-downstream hybrid zone along the river. Within the Potomac River floodplains downriver from Washington, DC, as well as outside the floodplains throughout the region, O. pulchellum is present in abundance, but O. nigripes markers are virtually absent. Within the floodplains upriver from Washington, DC, O. nigripes is abundant, but O. pulch***ellum markers are virtually absent. All four mixed ancestry Potomac populations sampled show strong and highly significant linkage disequilibrium, although only one clearly deviates from single-locus Hardy-Weinberg equilibrium. The position of the Deep South hybrid zone is generally consistent with interspecific and intraspecific phylogeographic patterns previously reported for numerous taxa from the southeastern United States. The observed genetic and morphometric clines appear to be the result of neutral introgression over thousands of years. In the much younger Potomac hybrid zone, O. nigripes appears to be spreading downriver, interbreeding with O. pulchellum, and replacing it. The mechanism for this replacement remains uncertain, but may be clarified by ongoing behavioral, genetic, and breeding studies.
在本研究中，记录到在美国东南部以及华盛顿特区附近波托马克河沿岸两个不连续接触区域内，两种草甸螽斯之间发生了此前未被认识到的杂交现象。这两个区域中两个分类单元之间的相互作用历史和动态差异很大。黑足奥蟋（Orchelimum nigripes）和秀色奥蟋（O. pulchellum）（螽斯科：锥头螽斯亚科）分别分布在阿巴拉契亚山脉以西和以东，从五大湖到墨西哥湾沿岸，以及沿大西洋海岸平原从纽约到佛罗里达群岛，但在阿巴拉契亚山脉本身并未发现。此外，在本世纪，黑足奥蟋已在阿巴拉契亚山脉以东的一小片区域即波托马克河流域定居，在华盛顿特区上游的河流走廊沿线它已完全取代了秀色奥蟋。我从两个杂交区域的40个地点采集螽斯样本，并绘制了遗传变异（两个诊断位点的等位基因频率）的地理模式以及雄性形态测量指数的变异情况。尽管这两个分类单元在其大部分广泛分布区域内差异明显，但在两个接触区域都有明显的基因渗入证据。在深南地区，沿着墨西哥湾沿岸的一个样带的样本界定了一个约50 - 100公里宽的广泛杂交区域，而向北200公里处一个样带的样本界定了一个宽度约为150 - 250公里的区域。深南地区只有一个种群在任何一个位点偏离了哈迪 - 温伯格平衡，并且在任何深南种群中都没有连锁不平衡的证据。在波托马克地区，沿着河流有一个狭窄的上下游杂交区域。在华盛顿特区下游的波托马克河漫滩内以及整个区域的漫滩外，秀色奥蟋大量存在，但几乎没有黑足奥蟋的标记。在华盛顿特区上游的漫滩内，黑足奥蟋数量众多，但秀色奥蟋的标记几乎没有。所采集的波托马克河四个混合血统种群都显示出强烈且高度显著的连锁不平衡，尽管只有一个明显偏离单一位点的哈迪 - 温伯格平衡。深南杂交区域的位置总体上与之前报道的来自美国东南部众多分类单元的种间和种内系统地理学模式一致。观察到的遗传和形态测量渐变似乎是数千年来中性基因渗入的结果。在年轻得多的波托马克杂交区域，黑足奥蟋似乎正在向下游扩散，与秀色奥蟋杂交并取代它。这种取代的机制仍然不确定，但正在进行的行为、遗传和繁殖研究可能会阐明这一点。
