Effect of photoperiod in the regulation of the annual testicular cycle of a subtropical mammal, the Indian palm squirrel, Funambulus pennanti.

Amar Bahadur Singh, C. M. Chaturvedi

Research output: Contribution to journalArticle

Abstract

In seasonally breeding subtropical mammal, the Indian palm 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, three groups of squirrels were exposed to natural day length (NDL), long day length (LD 15:9), and short day length (LD 6:18) over a period of one year beginning from March. Squirrels of all these groups 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. Obviously, an acyclic condition is developed under constant long as well short day conditions maintaining the neuroendocrine-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.(ABSTRACT TRUNCATED AT 250 WORDS)

Original languageEnglish (US)
Pages (from-to)65-73
Number of pages9
JournalBiomedical and environmental sciences : BES
Volume8
Issue number1
StatePublished - Jan 1 1995

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Sciuridae
day length
Mammals
Photoperiod
photoperiod
annual cycle
mammal
humidity
Humidity
plateau
Atmospheric humidity
Gonads
summer
relative humidity
monsoon
breeding
Recurrence
winter
Refractory materials
Breeding

ASJC Scopus subject areas

  • Public Health, Environmental and Occupational Health
  • Health, Toxicology and Mutagenesis

Cite this

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title = "Effect of photoperiod in the regulation of the annual testicular cycle of a subtropical mammal, the Indian palm squirrel, Funambulus pennanti.",
abstract = "In seasonally breeding subtropical mammal, the Indian palm 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, three groups of squirrels were exposed to natural day length (NDL), long day length (LD 15:9), and short day length (LD 6:18) over a period of one year beginning from March. Squirrels of all these groups 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. Obviously, an acyclic condition is developed under constant long as well short day conditions maintaining the neuroendocrine-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.(ABSTRACT TRUNCATED AT 250 WORDS)",
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AU - Chaturvedi, C. M.

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N2 - In seasonally breeding subtropical mammal, the Indian palm 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, three groups of squirrels were exposed to natural day length (NDL), long day length (LD 15:9), and short day length (LD 6:18) over a period of one year beginning from March. Squirrels of all these groups 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. Obviously, an acyclic condition is developed under constant long as well short day conditions maintaining the neuroendocrine-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.(ABSTRACT TRUNCATED AT 250 WORDS)

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