Fig. 4

Testicular morphological differentiation of testes in Brandt’s voles that experienced long-term long and short photoperiodic exposure, including changes in testis volume from PNW10 to PNW19 (a), correlations between testicular volume and mass (b), testis mass (c) and diameters of seminiferous tubules (d) between the photo-responsive and photorefractory subgroups. Data were analysed using independent-sample t test. Asterisks (*) indicate significant differences; *: P < 0.05, **: P < 0.01, ***: P < 0.001. LP, long photoperiod; SP, short photoperiod; LP-R, males responding to long photoperiod with large testes; LP-PR, photorefractory males in long photoperiod with small testes; SP-PR, photorefractory males in short photoperiod with large testes; SP-R, males responding to short photoperiod with small testes