Submitted on July 18, 2007
Accepted on September 20, 2007
Photoperiodic and hormonal influences on fur density and regrowth in two hamster species
Matthew J. Paul1*, Nicole T. George2, Irving Zucker3, and Matthew P Butler2
1 Psychology, University of California, Berkeley, California, United States
2 Integrative Biology, University of California, Berkeley, California, United States
3 Psychology, University of California, Berkeley, California, United States; Integrative Biology, University of California, Berkeley, California, United States
* To whom correspondence should be addressed. E-mail: matthew.paul{at}umassmed.edu.
Temperate and boreal mammals undergo seasonal changes in pelage that facilitate thermoregulation in winter and summer. We investigated photoperiodic influences on pelage characteristics of male Siberian and Syrian hamsters. Fur density (mg fur/cm2 skin) was measured by weighing the shavings of fur patches removed from the dorsal and ventral surfaces of hamsters maintained in long days (LDs) or transferred to short days (SDs). Patches were re-shaved 3 weeks later to assess fur regrowth (mg re-grown fur/cm2 skin). Fur density was greater in SD than LD Siberian hamsters after 11 weeks of differential phototreatment. The onset of increased fur density in SDs was accompanied by a transient increase in fur regrowth (dorsal surface: weeks 11-14; ventral surface: weeks 7-10 and 11-14), suggestive of a seasonal molting process. Fur density, body mass, and pelage color of Siberian hamsters returned to values characteristic of LD males after a similar duration of prolonged SD treatment (>27 weeks) and appear to be regulated by a similar or common interval timing mechanism. In Syrian hamsters, dorsal fur density, fur regrowth, and hair lengths were all greater in SD than LD males. Castration increased and testosterone (T) treatment decreased both dorsal and ventral fur regrowth in LD and SD hamsters, but the effects of T manipulations on fur density were limited to decreased dorsal fur density after T treatment. Decreased circulating T in SDs likely contributes to the seasonal molt of male hamsters by increasing the rate of fur growth during the transition to the winter pelage.
