Photoperiod and population density interact to affect reproductive,
adrenal, and immune function in male prairie voles (microtus
ochrogaster).
Nelson, Randy J., Joshua B. Fine, Gregory E. Demas, and Christopher A.
Moffatt.
Department of Psychology, Behavioral Neuroendocrinology Group, and
Department of Population Dynamics, Reproductive Biology Division, The
Johns Hopkins University, Baltimore, MD 21218-2686 USA
APStracts 2:0263R, 1995.
Seasonal breeding of rodents is often associated with changes in
adrenal function; altered adrenal function could account, in part,
for seasonal changes in immune function, and ultimately, influence
seasonal fluctuations in survival. Animals commonly monitor the
annual change in photoperiod to ascertain the time of year, and to
make appropriate seasonal adjustments in physiology and behavior.
Several extrinsic factors affect reproductive responsiveness to
photoperiod. The interaction between population density and
reproductive and adrenal responsiveness to photoperiod was assessed
in the present experiment. Adult male prairie voles (Microtus
ochrogaster) were maintained individually for 10 weeks in long (LD
16:8) or short (LD 8:16) photoperiods in rooms with either high
(10.96 animals/m3) or low (0.18 animals/m3) population densities.
Regardless of population density, short-day voles regressed the size
of their reproductive organs; reproductive organ masses were higher
in long-day voles housed in high density as compared to low density
rooms. Paired adrenal masses were reduced in short-day voles, but
were unaffected by population density; serum corticosterone
concentrations were significantly elevated in short-day as compared
to long-day animals. In both photoperiods, basal blood corticosterone
levels were higher in voles from low density, as compared to high
density rooms. Splenic masses were unaffected by day length, but were
elevated among high density animals. Similarly, serum IgG levels were
elevated among high density animals. These results suggest that
population density per se, in the absence of behavioral interactions,
can affect reproductive size, and possibly function, in long day
conditions, and that prairie voles, which are highly social, exhibit
higher corticosterone and lower IgG levels in low as compared to high
densities. These results may be important in understanding arvicoline
population fluctuations, as well as improving animal husbandry
practices in the lab.
Received 1 February 1995; accepted in final form 12 September
1995.
APS Manuscript Number R85-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 31 October 95