| Co-Investigator(Kenkyū-buntansha) |
NISHIDA Ritsuo Fac. Agric., Kyoto Univ., Asso. Pro., 農学部, 助教授 (30135545)
NAKAMURA Koji Grad. School of Natural Sci., Kanazawa Univ., Prof., 理学部, 教授 (70111755)
AOTSUKA Tadashi Fac. Sci., Tokyo Metropolitan Univ., Asso. Pro., 理学部, 助教授 (40106604)
KADOTA Yuichi National Science Museum, Principal Researcher, 植物研究部, 主任研究官 (30124184)
KIMURA Masahito Grad. School of Environmental Earth Sci., Hokkaido Univ., Pro., 大学院・地球環境科学研究科, 教授 (30091440)
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| Research Abstract |
1. Coevolutionary relationships between the phytophagous ladybird beetles of the Epilachna vigintioctomaculata complex and their host plants were investigated. Analyses of allozymes and mtDNA of the ladybird beetles suggested that (1) host shift in the ladybird beetles occurred during a very short evolutionary time, from solanaceous plants to plants of other families (Asteraceae, Papaveraceae, Berberidaceae, etc.) now utilized by certain members; (2) genetic difference between conspecific allopatric populations was resulted from the "isolation by distance": and (3) host specificity functions as a crucial reproductive barrier between coexisting sympatric members of the E. vigintioctomaculata complex.
2. Molecular, morphometric, and phenological analyses of thistles (Cirsium), one of the major host plants of the E. viglntioctomaculata complex, distributed in the southern part of Hokkaido revealed that they are genetically very similar to each other in spite of their distinct morphological
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and ecological differences, suggesting that an ancestral Cirsium species underwent rapid phyletic radiation in Hokkaido and surrounding areas, perhaps during the glacial period. Although not all thistles are suitable as the host plants of the ladybird beetles, thistle species utilized by the ladybird beetles did not constitute a monophyletic cluster.
3. The substance contained in Cirsium kagamontanum, that act as a feeding deterrent against infestation by a thistle feeding E. niponica, was identified as pectolinarin. But this flavonoid did not induce feeding rejection by another thistle feeding species E. pustulosa.
4. Genetic background of growth performance on different host plants was studied and compared between different populations of E. vigintioctolmaculata with different geographic origins and host plants.
5. These results suggests that the shift of host plants in various members of the E. vigintioctomaculata complex proceeded very rapidly, as adaptation to local food environments. Low vagility of the ladybird beetles may have enhanced this process . Less
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