Mandel M J, Ross C L, Harrison R G
Department of Ecology and Evolutionary Biology, Corson Hall, Cornell University, Ithaca, NY 14853, USA.
Mol Ecol. 2001 Mar;10(3):703-9. doi: 10.1046/j.1365-294x.2001.01213.x.
Two closely related field crickets, Gryllus firmus and G. pennsylvanicus, hybridize along an extensive north-south zone in the eastern United States. Crosses between G. firmus males and G. pennsylvanicus females produce viable and fertile F1, but the reciprocal cross consistently fails to produce offspring. Wolbachia, a bacterial parasite of arthropods that causes unidirectional incompatibilities in a variety of insect species, has been suggested as the cause of the observed incompatibility between G. pennsylvanicus and G. firmus. We examine the presence/absence of Wolbachia strains, defined by sequencing the ftsZ gene, in four cricket populations from the north-eastern United States. Most G. firmus individuals are infected (100% in Guilford, Connecticut; 65% in Seaside Park, New Jersey) and > 95% of those infected harbour a single strain of Wolbachia. All individuals in G. pennsylvanicus populations (Ithaca, New York; Sharon, Connecticut) are infected; the majority of individuals carry a second strain of Wolbachia, but a significant fraction carry the same strain found commonly in G. firmus. The presence of an apparently identical Wolbachia strain in crickets of both species means that some crosses between G. pennsylvanicus males and G. firmus females should be compatible. We have no evidence of such compatibility. Furthermore, if Wolbachia infections are responsible for the observed incompatibility between species, then incompatibilities must also exist within G. pennsylvanicus, because this species harbours both Wolbachia strains. Although some single pair crosses within G. pennsylvanicus do fail to produce offspring, the proportion is lower than expected if Wolbachia were responsible. Therefore, Wolbachia is unlikely to be involved in reproductive isolation between the two cricket species.
两种亲缘关系密切的田野蟋蟀，即坚强弓背蚁蟋（Gryllus firmus）和宾夕法尼亚弓背蚁蟋（G. pennsylvanicus），在美国东部沿着一条广阔的南北区域杂交。坚强弓背蚁蟋雄性与宾夕法尼亚弓背蚁蟋雌性杂交产生的F1代可存活且可育，但反交始终无法产生后代。沃尔巴克氏体（Wolbachia）是一种节肢动物的细菌寄生虫，在多种昆虫物种中会导致单向不相容性，有人认为它是观察到的宾夕法尼亚弓背蚁蟋和坚强弓背蚁蟋之间不相容性的原因。我们检测了美国东北部四个蟋蟀种群中通过ftsZ基因测序定义的沃尔巴克氏体菌株的有无。大多数坚强弓背蚁蟋个体受到感染（康涅狄格州吉尔福德的感染率为100%；新泽西州海滨公园的感染率为65%），且超过95%的受感染个体携带单一菌株的沃尔巴克氏体。宾夕法尼亚弓背蚁蟋种群（纽约州伊萨卡；康涅狄格州沙龙）的所有个体均受感染；大多数个体携带第二种沃尔巴克氏体菌株，但有相当一部分个体携带与坚强弓背蚁蟋中常见的相同菌株。两种蟋蟀中都存在明显相同的沃尔巴克氏体菌株，这意味着宾夕法尼亚弓背蚁蟋雄性与坚强弓背蚁蟋雌性之间的一些杂交应该是相容的。但我们没有这种相容性的证据。此外，如果沃尔巴克氏体感染是导致观察到的物种间不相容性的原因，那么在宾夕法尼亚弓背蚁蟋内部也必然存在不相容性，因为该物种同时携带两种沃尔巴克氏体菌株。尽管宾夕法尼亚弓背蚁蟋内部的一些单对杂交确实无法产生后代，但如果是沃尔巴克氏体导致的，这个比例会低于预期。因此，沃尔巴克氏体不太可能参与这两种蟋蟀之间的生殖隔离。
