mechanisms of sympatric speciation in monophagous sawflies

1.研究了蕨类相关锯蝇属的同域物种形成与寄主转移。(1)日本血吸虫复合体的同域物种形成主要发生在日本34°N附近的狭窄区域。(2)日本血吸虫和sasayamensis是由同域种形成分离的兄弟种，几乎在它们的分布范围内都表现出时间隔离。(3)在同域种形成之后，两种兄弟种——H.athrii和H.takeuchii在地理上完全隔离。通过比较547个线粒体coii基因序列，分析了日本血吸虫复合体和sasayamensis在当地种群间的系统发育关系。它们的分子系统发育树显示，日本血吸虫复合体的寄主种和sasayamensis的本地种群形成了不同的集群，尽管这两个兄弟姐妹在形态上没有分离。日本血吸虫复合体遗传变异与同域物种形成过程的关系尚不清楚。马尾锯蝇（Loderus genucinctus）在单倍体组中有3个种内核型变异：n=9、n=10和n=11，这是由Robertsonian重排引起的。除了近畿和中部地区分布着衍生型n=10和n=11外，日本广泛分布着推测为祖先型n=9。这种异父性核型分布可能是由于同域条件下杂合子的适合度低于纯合子。全北松锯蝇的性信息素具有明显的地理差异，这可能导致种群间的生殖隔离现象。

1.Sympatric speciation with host shift was investigated in the fern associated sawfly genus Hemitaxonus. (1) In H.japonicus complex, sympatric speciation is occurring in the narrow region around 34° N in Japan. (2) H.japonicus and H.sasayamensis, sibling species separated by sympatric speciation, show temporal isolation almost over their distributional ranges. (3) Two sibling species, H.athrii and H.takeuchii, are completely isolated geographically after sympatric speciation.2.Phylogenetic relationships among the local populations of H.japonicus complex and H.sasayamensis were analyzed by comparing 547 nucleotide sequences of the mitochondrial gene coding CO II.Their molecular phylogenetic trees revealed that the host races of H.japonicus complex and local populations of H.sasayamensis formed distinct clusters, though these two siblings were not separated morphologically. The relationship between genetic variation and the process of sympatric speciation in H.japonicus complex was not clear.3.The horsetail sawfly Loderus genucinctus had three intraspecific karyotype variation in a haploid set : n=9, n=10 and n=11, due to Robertsonian rearrangement. A presumably ancestral type n=9 is widely distributed in Japan except for Kinki and Chubu districts, where the derived types n=10 and n=11 are distributed. Such parapatric distribution of karyotypes may be due to the lower fitness of heterozygotes than homozygotes under the sympatric condition.4.Holearctic pine sawfly Neodiprion sertifer showed considerable geographical variation of sex pheromone, which may cause the development of reproductive isolation among local population.