| Budget Amount *help |
¥1,800,000 (Direct Cost: ¥1,800,000)
Fiscal Year 1991: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1990: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1989: ¥1,000,000 (Direct Cost: ¥1,000,000)
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| Research Abstract |
Cuckoo parasitism of the Azure-winged Magpie (Cyanopica cyana) started about 20 years ago in central Japan and spread rapidly throughout the breeding areas of the magpie. This quick spread is because the magpie had no counter-adaptations to cuckoo parasitism. The magpie, however, has developed counter-adaptaions (rejection of cuckoo eggs, aggressiveness to cuckoos, etc.) to cuckoo parasitism within 10 years. Thus the cuckoo parasitism of the magpie is no longer as successful as it was at the beginning stages. Throughout this change, breeding success rates, numbers of cuckoos and magpies, and parasitism frequency all changed dynamically. The Siberian Meadow Bunting (Emberize cioides) was one of the major hosts in central Japan more than 60 years ago. The bunting is, however, a rare host at present in this region and has the strongest egg discrimination ability. Besides this case, there are some changes of local hosts usage recently and local differences of parasitism relations between c
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uckoo and it's host are known in Japan. Both the Great Reed Warbler (Acrocephalus arundinaceus) population at Lake Biwa and the magpie population at Higashi-matsuyama in Kanto plain had a high rate of egg rejection in spite of their total or nearly total lack of cuckoo parasitism.
The most likely explanation for this fact is that these populations were parasitized by the cuckoo in the past and have kept the counter-adaptaions which were developed in that period. From the comparisons of egg markings between cuckoos and their hosts, it was expected that cuckoo eggs have a trend of non-specialist and cuckoo gentes are not always so concrete.
From these facts and expectations, I concluded that there are two alternative pathways in co-evolution between the cuckoo and its host. One is the adaptation towards non-specialized host usage by which the cuckoos always change their hosts or populations through adaptation and counter-adaptation. Another is adaptation in the direction of host specialization, which will develop egg mimicry and stable relation for a long time. Less
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