Mechanisms of sympatric speciation in monophagous sawflies

在日本西南部34 ° N附近约10 km宽的狭窄区域内，日本半轴螨Hemitaxonus japoicus complex的新寄主种Polyblepharum正由原种Tripteron种形成。每个寄主种族的成年雌性在自己的寄主植物上产卵。F_1雌虫先将耳蕨交配到多眼耳蕨上产卵。宿主选择可能是破坏性的，由一个基因控制。两个小种利用相似但不同的挥发性化学物质作为产卵刺激物，其沸点分别在100和150 ℃/1 mmHg之间。新蜂种的幼虫失去了在旧寄主植物上生存的能力，这是由于成年雌性继续在新寄主植物上产卵。两个小种之间的不对称交配是一种重要的交配后生殖隔离机制，可以阻止基因从旧宿主小种流向新宿主小种。两个寄主小种的染色体和等位酶多态性没有明显差异，但在pYS家族串联重复DNA序列的miner条带上存在20 bp的差异，可能明确了寄主小种形成与遗传变异的关系。姐妹种H.sasayamensis可能是由寄主转移的H.sasayamensis同域分化而来，在分布区的大部分地区是暂时隔离的。

Mechanisms of sympatric speciation were investigated for Hemitaxonus japoicus comples, of which the new host race, polyblepharum race is being formed from the original race, tripteron race, in the narrow zone of about 10 km wide around 34ﾟN in the south-western part of Japan without geographical isolation. Adult females of each host race lay eggs on their own host plant. F1 females prefere Polystichum tripteron to P.polyblepharum for oviposition. Host selection may be disruptive, controlled by one gene. Two races use similar but distinct volatile chemichal substants for oviposition stimulants, of which the boiling points are between 100 and 150ﾟC/1mmHg, respectively. The newhost race larvae lose the ability to survive on the old host plant, caused by conditioning that the adult females continue to lay eggs on the new host plant. Asymmetrical mating developing between two racesis an importat post-mating reproductive isolating mechanism to preventthe gene flow from the old host race to the new. There is no remarkable differentiation in chromosome and allozyme polymorphisms between two host races, but the difference of 20 bp in the miner band of pYS family of tandemly repetitive DNA sequences between them may clear the relationship between host race formation and genetic variation. The sibling species H.sasayamensis is supposed to have speciated sympatrically from H.japonicus with host shift and to have been temporall isolated on the most parts of distribution.