In seasonally breeding subtropical mammal, the Indian pelm squirrel (Funambulus pennanti), reproductive recrudescence is initiated before the winter solstice followed by sexually active condition which extends until t...In seasonally breeding subtropical mammal, the Indian pelm squirrel (Funambulus pennanti), reproductive recrudescence is initiated before the winter solstice followed by sexually active condition which extends until the end of summer season. Onset of seasonal regression coincides with the annual decrease in daily photoperiod and the increased level of relative humidity resulting from the arrival of monsoon at this latitude. To test the photoperiodic responses, the groupe of squirrels were exposed to natural day length (NDL), long day length (LD15:9), and Short day length (LD 6: 18) over a period of one year beginning from March. Squirrels of all these groupe were exposed to similar ambient temperature and humidity conditions.Initially, the rate of testicular development was similar in control and long day squirrels attaining peak values in May (0.67 cm3) and June (0.7 cm3) respectively. Thereafter, while the gonads of controls regressed, the latter maintained a plateau. On the other hand, the gonads of short day squirrels regressed sharply until June (0.21 cm3)followed by spontaneous recrudescence and finally a plateau (0.55 cm3). These results indicate that initially squirrels are photosensitive (as long days are gonadostimulatory and short days are inhibitory) in the first half of summer season but eventually become refractory to the inhibitory effect of short days. Obvinusly, an acyclic condition is developed under constant long as well short day conditions maintaining the neurocndocrine-gonadal-axis in a continuously active state. We suggest that in nature although gonadal growth of this species does not synchronize with the increase in daily photoperiod, it is partially regulated by an interplay of annual photocycle and humidity conditions. Present study also indicates that this species has developed a strong photoperiodic mechanism which may surposs the reproductive effect of other environmental factors when maintained in constant conditions of day length.展开更多
文摘In seasonally breeding subtropical mammal, the Indian pelm squirrel (Funambulus pennanti), reproductive recrudescence is initiated before the winter solstice followed by sexually active condition which extends until the end of summer season. Onset of seasonal regression coincides with the annual decrease in daily photoperiod and the increased level of relative humidity resulting from the arrival of monsoon at this latitude. To test the photoperiodic responses, the groupe of squirrels were exposed to natural day length (NDL), long day length (LD15:9), and Short day length (LD 6: 18) over a period of one year beginning from March. Squirrels of all these groupe were exposed to similar ambient temperature and humidity conditions.Initially, the rate of testicular development was similar in control and long day squirrels attaining peak values in May (0.67 cm3) and June (0.7 cm3) respectively. Thereafter, while the gonads of controls regressed, the latter maintained a plateau. On the other hand, the gonads of short day squirrels regressed sharply until June (0.21 cm3)followed by spontaneous recrudescence and finally a plateau (0.55 cm3). These results indicate that initially squirrels are photosensitive (as long days are gonadostimulatory and short days are inhibitory) in the first half of summer season but eventually become refractory to the inhibitory effect of short days. Obvinusly, an acyclic condition is developed under constant long as well short day conditions maintaining the neurocndocrine-gonadal-axis in a continuously active state. We suggest that in nature although gonadal growth of this species does not synchronize with the increase in daily photoperiod, it is partially regulated by an interplay of annual photocycle and humidity conditions. Present study also indicates that this species has developed a strong photoperiodic mechanism which may surposs the reproductive effect of other environmental factors when maintained in constant conditions of day length.
