ヒメネズミの繁殖活動

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タイトル別名
  • Reproductive activity in <I>Apodemus argenteus</I> TEMMINCK
  • ヒメネズミ ノ ハンショク カツドウ

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説明

A study of reproductive activity in the Japanese long-tailed field mouse, Apodemus argenteus, was carried out from March 1960 through November 1961 at the deciduous forest in Moiwa-yama, Sapporo. During the study, 527 field mice were trapped and grouped into overwintered or current year's individuals by degree of tooth wear.<BR>In the population studied, reproductively active males (with tubular epididymus and swollen seminal vesicles) and females (with turgid uteri or embryos) were found at the same time from April to September in 1960 and from March to August in 1961. The majority of reproductively active mice were overwintered ones through the breeding season. Although a small part of young adults with an estimated age of over 2 months after birth was capable of reproducing during their first summer of life, a lower level of reproductive activity was found in the young adults than overwintered ones. Average litter size for the overwintered females was 4.1, while that for the current year's ones was 3.2.<BR>Young mice appeared first in the population during May or June and comprised a low percentage of the population until July or August. In later part of the breeding season, the percentage of immature individuals increased so that the percentage of reproductively active individuals in the population showed a rapid decrease. There were no significant monthly changes in sex ratio, although there was a bias toward males in the overwintered population in 1960.<BR>The average body weight for overwintered mice was about 13 g in the spring and rose abruptly to about 17 g by the summer. Young mice born at the beginning of the breeding season reached sexual maturity and approached weight of overwintered ones, while young born in the second half of this period weighed an average of about 10g through the summer.

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