日本の農地に優占するフトミミズ科4 種の高温乾燥耐性

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  • Effects of high temperature and drought conditions on four Megascolecidae earthworms dominant in agricultural fields in Japan

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Because earthworms are vulnerable to high temperatures and dry conditions, their response to high temperatures is useful for understanding the seasonal dynamics of earthworm densities and environmental change impacts induced by agricultural activity on earthworms. However, there is little information on the high temperature tolerance of the Megascolecidae species. The family is dominant in Asia, with some species becoming invasive in other continents, where they may cause problems by changing ecosystem structure. This study's objective was to determine the high temperature tolerance of four Megascolecidae species (Metaphire hilgendorfi, M. agrestis, Amynthas corticis, and A. micronarius). Two experiments were conducted. In the first experiment, incubation temperatures were set to five levels (15, 20, 25, 30, and 35°C) under soilless conditions. The 50% lethal temperature was determined after 2 days of incubation; the lethal temperatures for M. hilgendorfi, M. agrestis, A. corticis, and A. micronarius were 22.5, 21.3, 31.9, and 25.5°C, respectively. In the second experiment, four moisture levels, 30, 40, 50, and 60% of water holding capacity (WHC), were set, and the temperature increased weekly from 15 to 35˚C. Survival rate and weight were measured weekly. Metaphire agrestis was removed from the analysis because the culture conditions of the experiment were not suitable for this species. At the lowest moisture condition (WHC30%), almost all individuals died, within one week. Dry conditions thus have a severe effect on earthworms. The 50% lethal temperature increased with increasing moisture level, with drastic weight loss occurring just before onset of the lethal temperature. Tolerance to higher temperature of epigeic species was lower than that of endogeic species.

収録刊行物

  • Edaphologia

    Edaphologia 112 (0), 1-8, 2023-01-05

    日本土壌動物学会

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