Experiment 1
BODY MASS
The body mass of the four treatment groups was not significantly different on day 5 prior to the commencement of the temperature and wind treatments (temperature, F 1,50=0.01,P >0.05; wind, F 1,50=1.27,P >0.05, Figure 1A). The body mass of females kept at an ambient temperature of 32.5°C subsequently became significantly lower than that of those kept at 21°C for the remainder of the experiment (day 6, F 1,50=13.37, P <0.01). On the final day of the experiment (day 16), the body mass of hamsters kept at 32.5°C was 17.8% lower, on average, than that of those kept at 21°C (day 15, F 1,50=35.26, P <0.01). Body mass was not, however, significantly affected by the simulated wind treatment (day 6, F 1,50=0.38,P >0.05, day 15, F 1,50=0.27,P >0.05).
FOOD INTAKE
Food intake did not differ significantly among the four treatment groups prior to commencement of the temperature and wind treatments (day 5, temperature, F 1,50=0.25,P >0.05; wind, F 1,50=0.10,P >0.05, Figure 1B). Females kept at an ambient temperature of 32.5°C subsequently consumed significantly less food than their counterparts kept at 21°C (day 6,F 1,50=64.79, P <0.01). The food intake of females kept at 32.5°C was 51.1% lower, on average on day 14, than that of females kept at 21°C (F 1,50=69.67,P <0.01). Wind also had a significant effect on food intake; females exposed to simulated wind consumed significantly more food at both 21°C and 32.5°C than those that were not (day 6,F 1,50=12.84, P <0.05). The food intake of females exposed to simulated wind was 11.7% higher at 21°C, and 29.9% higher at 32.5°C, than that of females that were not exposed to simulated wind (day 14, F 1,50, =3.82,P <0.05). Asymptotic food intake was significantly affected by both temperature (F 1,50=128.87,P <0.01) and simulated wind (F 1,50=8.84, P <0.01, Figure 2A). The asymptotic food intake of females kept at 32.5°C was 51.2% lower, on average (post hoc , P <0.05) than that of those kept at 21°C. Exposure to simulated wind elevated asymptotic food intake by 17.1% at 21°C, and by 25.4% at 32.5°C (post hoc ,P <0.05). Asymptotic food intake was also positively correlated with body mass (Figure 3A).
ENER INTAKE AND DIGESTIBILITY
The GEI and DEI of females kept at an ambient temperature of 32.5°C was, on average, 54.9% and 55.2% lower, respectively, that that of females kept at 21°C (GEI, F 1,50=354.02,P <0.01, Figure 2B; DEI,F 1,50=371.12, P <0.01, Figure 2C). Maintaining females at an ambient temperature of 32.5°C also significantly affected GEF, and females kept at this temperature produced considerably less feces than those kept at 21°C (F 1,50=371.12, P <0.01, Figure 2D). The GEI of females that were exposed to simulated wind, on average, 21.7% higher at 21°C and 28.8% higher at 32.5°C than that of females that were not exposed to simulated wind (F 1,50=28.30, P <0.01). Irrespective of temperature, females exposed to simulated wind also had significantly higher DEI and produced more feces than those that were not exposed to simulated wind (DEI, F 1,50=28.85,P <0.01; GEF, F 1,50=10.77,P <0.01). Neither temperature or or exposure to simulated wind, significantly affected digestibility (temperature,F 1,50=1.83, P >0.05; wind,F 1,50=0.01, P >0.05, Figure 2E).
MEO
MEO was considerably affected by temperature; females kept at an ambient temperature of 32.5°C produced 58.1% less milk than those kept at 21°C (F 1,50=13.78, P <0.01, Figure 2F). Although MEO was not significantly affected by exposure to simulated wind (F 1,50=0.01,P >0.05), it was significantly affected by an interaction between temperature and simulated wind (F 1,50=9.42, P <0.01). Furthermore, females exposed to simulated wind produced 25.6% less milk at an ambient temperature of 21°C (post hoc ,P <0.05) but 64.2% more milk at 32.5°C (post hoc , P <0.05). There was a significant correlation between MEO and asymptotic food intake; females that produced more milk seemed to consume more food (Figure 3B). MEO was also positively correlated with body mass (Figure 4A).
LITTER SIZE AND LITTER MASS
Litter size did not differ among the four treatment groups before treatments began (day 5, temperature, F 1,50=0.23,P >0.05; wind, F 1,50=0.37,P >0.05, Figure 5A). The litter size of females kept at an ambient temperature of 21°C did not change significantly during the experiment, whereas that of females kept at 32.5°C became significantly smaller from day 11 than that of females kept at 21°C (day 11, F 1,50, =4.68, P <0.05). By the end of the experiment (day 16), the females kept at an ambient temperature of 32.5°C had raised, on average, 29.5% less pups than those kept at 21°C (day 15, F 1,50=9.72,P <0.05). Litter size was also significantly affected by wind after day 13 (day 13, F 1,50=4.88,P <0.05). On day 15, females that were exposed to wind raised 7.3% more pups at 21°C, and 56.0% more pups at 32.5°C (F 1,50=4.19, P <0.05) than those that had not been exposed to wind (Figure 5A). There was a significant correlation between litter size and asymptotic food intake; females that raised more pups seemed to consume more food towards the end of the experiment at ambient temperatures of both 21°C and 32.5°C (Figure 3C). Litter size was also positively correlated with MEO; the more pups that females raised, the more milk they produced (Figure 4B).
Litter mass was not significantly different among the four treatment groups before the treatments began (day 5, temperature,F 1,50=0.02, P >0.05; wind,F 1,50=0.11, P >0.05, Figure 5B). The litter mass of females kept at an ambient temperature of 21°C was significantly higher than that of those kept at 32.5°C. From day 8 onwards, the litter mass of females kept at 32.5°C was significantly lower than that of those kept at 21°C (day 8,F 1,50=5.45, P <0.01), and by the end of the experiment (day 16) the litter mass of females kept at 32.5°C was 38.6% lower, on average, than that of those kept at 21°C (day 15,F 1,50=20.51, P <0.01). Although litter mass was not significantly affected by exposure simulated wind, it was by the interaction between temperature and simulated wind on day 14 and 15 (day 14, F 1,50=4.93,P <0.05). At an ambient temperature of 21°C, the litter mass of females exposed to simulated wind was 12.6% lower than that of those that had not been exposed to simulated wind, whereas at 32.5°C the litter mass of females exposed to simulated wind was 47.7% higher than that of those which had not been exposed to simulated wind (post hoc , P <0.05). Litter mass was positively correlated with asymptotic food intake; females that raised heavier offspring tended to consume more food in the second week of lactation at both 21°C and 32.5°C (Figure 3D). Litter mass was also positively correlated with MEO; females with heavier pups seemed to produce more milk at both 21°C and 32.5°C (Figure 4C).
Pup growth was significantly attenuated by temperature; the mean pup mass of females kept at an ambient temperature of 32.5°C was significantly lower from day 7 than that of those kept at 21°C (day 7,F 1,50=5.30, P <0.01, Figure 5C). At the end of the experiment, the pups of females that had been kept at 32.5°C were 30.8% lighter, on average, than those that had been kept at 21°C (day 15, F 1,50=13.84,P <0.01). Pup mass was not significantly affected by exposure to simulated wind (day 15, F 1,50=0.01,P> 0.05), but was by the interaction between temperature and simulated wind from day 7 to day 15 (day 7,F 1,50=4.91, P <0.05). Pups raised by females that had been exposed to simulated wind were 18.8% lighter at 21°C, and 35.3% heavier at 32.5°C, than those raised by females that had not been exposed to simulated wind (day 15,F 1,50=5.46, P <0.05, Figure 5C).