Fh. Bronson et Mc. Kerbeshian, REACTIONS OF REPRODUCTIVELY PHOTORESPONSIVE VERSUS UNRESPONSIVE MEADOW VOLES TO SIMULATED WINTER CONDITIONS, Canadian journal of zoology, 73(8), 1995, pp. 1479-1488
At least some populations of meadow voles (Microtus pennsylvanicus) co
mprise individuals that vary greatly in the degree to which their repr
oduction can be controlled by day length. Some individuals respond to
the short days of winter with complete gonadal inhibition, others are
insensitive to this cue and thus have the capacity to reproduce opport
unistically during the winter, and still others are intermediate in th
eir responsiveness. The relative costs and benefits associated with so
me of the nonreproductive dimensions of these different strategies are
explored. The two extreme phenotypes, reproductively photoresponsive
and unresponsive individuals, were exposed in the laboratory to winter
versus summer conditions, as defined by photoperiod, temperature, and
quality of diet. This was done in cages that required the voles to le
ave their nests and subject themselves to ambient conditions in order
to feed. The winter condition exerted a potent influence on body mass,
body fat, food intake, nest building, pelage depth,and the amount and
temporal pattern of feeding, as well as reproductive potential. The r
esults suggest that the major nonreproductive advantage enjoyed by the
photoregulated phenotype is a decrease in body mass and hence a decre
ase in required foraging time that anticipates harsh winter conditions
. The opportunists also may lose mass in response to harsh conditions,
but this is a direct and immediate response for which they may be poo
rly prepared.