Divergent selection for heat loss in mice: II. Correlated responses in feed intake, body mass, body composition, and number born through fifteen generations.

Abstract

ABSTRACT:Divergent selection for heat loss (kcal·kg −.75 ·d −1 ) , measured in 9-to 11-wk-old male mice, was conducted for 15 generations. Selection for high (MH) and low (ML) heat loss and unselected control (MC) occurred in each of three replicates for a total of nine unique lines. Feed intake in males was measured during Generations 9 through 15. Body mass at commencement of mating in females and at time of measurement of heat loss in males was recorded. Body fat percentage at 12 wk for animals of Generations 6, 10, and 14 was predicted as a function of electrical conductivity and body mass. Litter size was recorded for all generations, and components of litter size were evaluated at Generation 11 in one replicate and Generation 12 in the other two replicates. Feed intake changed in the same direction as heat loss for the MH and ML selections; at Generation 15, the difference between MH and ML ( P < .002) was 20.6% of the MC mean. Body mass did not change with selection for heat loss. Differences in body fat percentage were not significant in earlier generations, but at Generation 14, MH and ML were significantly ( P < .01) different with MH mice having the lowest fat percentage; MC was intermediate. Selection had a significant (MH vs ML; P < .01) effect on litter size, causing an increase in MH and a decrease in ML. This difference was explained by a difference ( P < .01) in ovulation rate. There was no asymmetry of response in feed intake, fatness, litter size, or number of ovulations.

Correlated responses in maternal performance following divergent selection for heat loss in mice1

“…The test for selection response (MH vs. ML) tended toward significance (P < 0.11), and there was no evidence for asymmetry of selection response (P = 0.54). These results are similar to those observed by Nielsen et al (1997a), except that the difference between the MH and ML was greater and more significant after generation 15 than in the more recent generations used in the current study. As in the earlier report, MH dams produced more pups than ML dams, and MC dams were intermediate for litter size born.…”

“…As in the earlier report, MH dams produced more pups than ML dams, and MC dams were intermediate for litter size born. Nielsen et al (1997a) demonstrated that differences in litter size among the lines were due to differences in ovulation rate. Estimates of milk production per collection period for MH and ML dams averaged across all 3 replicates are shown in Table 3.…”

“…Thus, asymmetry of selection response could not be tested in these latter characteristics. We have made the assumption that the significant correlated responses (milk production, dam feed intake, and efficiency) were symmetric because other measures of significant correlated responses that we have studied and reported in which the MC line was included (feed intake of 8-to 11-wk males, body fatness, and locomotor activity; Nielsen et al, 1997a andMousel et al, 2001) have all been symmetric. Our assumption is straightforward for dam feed intake and efficiency based on our other data in these lines of mice.…”

Genetic variance and covariance patterns for body weight and energy balance characters in an advanced intercross population of mice

“…Feed intake (FI) showed a heritability of 0.27, and this is within the range (0.20 to 0.30) used by Nielsen et al [42] to calculate genetic correlations for this character with heat loss in the original selection study with the MH and ML lines. The magnitude of the heritability of feed intake conventionally has been expected to be similar to that for heat loss [41].…”

“…All characters were measured in over 2000 mice from an advanced intercross population derived from a cross of lines originally selected for low (ML) and high (MH) heat loss [41,42]. This population was developed for an eventual fine mapping analysis of QTL, and it was useful to first estimate heritabilities and genetic correlations to serve as a basis for comparison with the QTL results.…”