Genetic and chemoecological studies on sympatric host shift and host race formation in monophagous sawflies

研究了日本血吸虫复合体田间种群共域寄主迁移和寄主小种形成的机制。主要研究结果如下：1.在日本西南部34ﾟN附近约10公里宽的区域内，新的寄主小种多眼小种正在形成，没有地理隔离。2.两个小种的成虫寄主选择可能受一个多态基因控制。它们的产卵刺激剂是相似但不同的化学物质，如棕榈酸甲基。3.两个寄主小种在等位酶多态性和高度重复的DNA序列上表现出很小的差异。这表明该叶蝉的共域寄主小种的形成速度很快。4.寄主植物上的种类交配、不对称交配、条件化幼虫死亡等隔离因素对共域寄主小种的形成起重要作用。这种不对称的交配阻止了基因从最初的寄主种群流向新的寄主种群，在新的寄主种群中，性信息素是相关的，但尚未被识别。5.我们试图在实验室里创造一个新的寄主种族。将Tripteron小种雌性与多眼小种雄性杂交，再将F1雌性与多眼小种雄性交配。我们成功地获得了F2代雌蜂只在多眼皮上产卵。

Mechanisms of the sympatric host shift and host race formation in the field populations of Hemitaxonus japonicus complex were investigated. Main results are as follows:1. The new host race, polyblepharum race is being formed from the original one, tripteron race, in the area of about 10 km wide around 34ﾟ N in the south-western part of Japan without geographical isolation. 2. The adult host selection of two races may be controlled by a polymorphic gene. Their oviposition stimulants are similar but distinct chemical substants, like palmitic acid methyl. 3. Two host races show the very small diferentiation in allozyme polymorphisms and highly repeated DNA sequences. This suggests that the rate of sympatric host race formation is very fast in this sawfly. 4. Some isolating factors such as assortative mating on host plants, asymmetrical mating, larval mortality due to conditioning play important roles for sympatric host race formation. The asymmetrical mating prevents the gene flow from the original host race population to the new one, where the sex pheromones are concerned but not identified yet. 5. We tried to make a new host race in the laboratory. The tripteron race females were crossed to the polyblepharum race males, and the F1 females were mated again with the polyblepharum race males. We have succeeded to get F2 females ovipositing only on Polysticum polyblepharum.