Duration of spermatogenesis in the vole (Microtus agrestis) and bank vole (Clethrionomys glareolus)

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Abstract
In the laboratory colonies puberty in M. agrestis occurred at about 6 wk of age but in the bank vole (C. glareolus) it was 5-6 wk later. The duration of the seminiferous epithelial cycle was estimated in C. glareolus to determine whether this dissimilarity was associated with a difference in the duration of the cycle of the seminiferous epithelium. Sexually mature males were used and kept in a photoperiod of 16 h light/day. Each was injected s.c. with 25 .mu.Ci [3H]thymidine. M. agresitis were subjected to different day-night cycles and testes were significantly heavier in animals from 16L:8D than those from 6L:18D. In Clethrionamys, the cycle length was 6.7 .+-. 0.2 days, and the total duration of spermatogenesis 31.0 .+-. 0.7 days, both significantly shorter than in M. agrestis (P < 0.002). Although there was some selection for high fertility within the colony of M. agrestis, which had been genetically closed for 13 yr, there was no difference in the duration of spermatogenesis between laboratory and wild M. agrestis. The cycle was significantly shorter in C. glareolus indicating that the difference in age at puberty between these 2 spp. may be associated with later initiation of spermatogenesis in C. glareolus than in M. agrestis.