| Abstract: | The large Japanese field mouse, Apodemus speciosus, is a
potential indicator of environmental stress, but this function has not been confirmed by
histological studies. Since environmental stress affects the reproductive function of
mice, we determined the reproductive characteristics of this species at two locations:
Toyama (36°35ʹN, 137°24ʹE) and Aomori (40°35ʹN, 140°57ʹE). Mice were captured during
May–November (n=119) and July–November (n=146) at these locations, respectively. We
classified the breeding season from the numbers of pregnant females and young, in addition
to the spermatogenic cycle and seasonal changes in seminiferous tubule morphology of
males. Testicular weight was measured, and seminiferous tubule morphology was examined
histologically. Fourteen stages were found in the seminiferous epithelium cycle based on
acrosome formation and spermatid head morphology. At both locations, the breeding season
peaked from late summer to early autumn and possibly in spring. Spermatogenic activity was
classified into 4 periods from June to November: resting around June and October–November;
resumptive around July; active around August; and degenerative around September. During
the resting period, the seminiferous tubules consisted of Sertoli cells, spermatogonia and
spermatocytes. Spermatogenesis began during the resumptive period, and spermatids were
observed. During the active period, active spermatogenesis and a broad lumen were
observed. During the degenerative period, spermatogenesis ended, and Sertoli cells,
spermatogonia, spermatocytes and degenerating exfoliated round spermatids were observed.
This study provides scientific information about the testicular histopathological
evaluations of the large Japanese field mouse for its use as an index species of
environmental pollution. |
