Testing the heat limitation hypothesis: Do lactating females make use of
wind to increase their energy intake and reproductive performance under
hot summer conditions?
Abstract
1. Global warming is rapidly emerging as a universal threat that could
alter the distribution of many animal species and change their
morphology, physiology, behavior and life history. The heat dissipation
limitation (HDL) hypothesis proposes that females’ reproductive
performance is limited by their capacity to dissipate heat. Although
exposure to wind is known to increase heat exchange, its effect on
reproductive performance is unknown. 2. In this study, the effect of
simulated wind on the energy budget and milk energy output of female
striped hamsters (Cricetulus barabensis) was measured under cool (21°C)
and hot (32.5°C) ambient temperatures and the preference of hamsters for
windy conditions in lactating females was tested both in the laboratory
and the wild. 3. Females lactating at 32.5°C significantly decreased
their energy intake and milk output, and raised lighter offspring than
those lactating at 21°C. Exposure to wind significantly increased both
energy intake during lactation and heat loss at both temperatures.
Females lactating at 32.5°C considerably increased their reproductive
output when exposed to wind. Moreover, females kept at an ambient
temperature of 21°C preferred sheltered conditions whereas those kept at
32.5°C preferred exposure to simulated wind. We captured significantly
more lactating female hamsters on windy days in summer and on calm days
in spring. Wrapping a glass vessel in the fresh pelt of a striped
hamster significantly reduced the rate of both water loss and cooling.
4. These findings support the HDL hypothesis; high ambient temperatures
do appear to limit the energy intake and reproductive output of
lactating hamsters. Small mammals lactating under hot conditions may be
able to utilize the cooling properties of wind to increase their energy
intake and milk production, and thereby their reproductive output and
fitness.