Howard Daniel J, Waring Gwendolyn L
Department of Biology, New Mexico State University, Las Cruces, NM, 88003, USA.
Department of Biology, Museum of Northern Arizona, Flagstaff, AZ, 86001, USA.
Evolution. 1991 Aug;45(5):1120-1135. doi: 10.1111/j.1558-5646.1991.tb04379.x.
Two closely related species of ground crickets, Allonemobius fasciatus and A. socius, overlap and hybridize in a contact zone in the eastern United States. In earlier work, Howard (1986) described geographic variation in the width of the zone and in the strength of reproductive isolation between the two ground crickets. The zone was wider in the hills and mountains of southeastern Ohio and West Virginia than along the eastern coastal plain, and reproductive isolation appeared to be stronger where the zone was wider. Howard attributed the greater width in the mountains to the wide intermingling and patchy distribution of habitats appropriate for a species adapted to a northern climate and for a species adapted to a southern climate. He also pointed out that the mosaicism and the increased breadth of the zone in the mountains enhanced the probability of occurrence of reinforcement. We tested three predictions that emerged from Howard's hypothesized links among topographic diversity, zone width, and the strength of reproductive isolation. The first two predictions were fulfilled. The northern cricket, A. fasciatus, occurred in the high mountains south of its previously known distributional limit; and the zone narrowed considerably in Illinois, an area of low topographic diversity. These results provide further evidence for the importance of the environment in determining the structure of the zone. The third prediction was falsified. Contrary to the prediction, the strength of reproductive isolation between the two species was as strong in Illinois as in the Appalachian Mountains. This result suggests that if reinforcement has occurred in the zone, the width of the zone has not been a major factor in the process.
两种亲缘关系密切的地蟋，即条纹异距蟋（Allonemobius fasciatus）和社交异距蟋（A. socius），在美国东部的一个接触区域重叠并杂交。在早期的研究中，霍华德（1986年）描述了该区域宽度以及这两种地蟋之间生殖隔离强度的地理变异情况。该区域在俄亥俄州东南部和西弗吉尼亚州的山区比在东部沿海平原更宽，而且在区域较宽的地方生殖隔离似乎更强。霍华德将山区更宽的区域归因于适合适应北方气候的物种和适应南方气候的物种的栖息地广泛混合和斑块状分布。他还指出，山区区域的镶嵌性和更宽的宽度增加了强化现象发生的可能性。我们检验了从霍华德关于地形多样性、区域宽度和生殖隔离强度之间的假设联系中得出的三个预测。前两个预测得到了证实。北方的条纹异距蟋出现在其先前已知分布范围以南的高山地区；而且在地形多样性较低的伊利诺伊州，该区域大幅变窄。这些结果为环境在决定该区域结构方面的重要性提供了进一步的证据。第三个预测被证伪。与预测相反，这两个物种之间的生殖隔离强度在伊利诺伊州和阿巴拉契亚山脉一样强。这一结果表明，如果该区域发生了强化现象，那么区域宽度在这个过程中并非主要因素。
