Individual Variation in Metabolism and Reproduction of Mus: Are Energetics and Life History Linked?

Abstract

The possibility of functional relationships between energetics and life-history characteristics has been of considerable interest to evolutionary ecologists. Among species of mammals, life-history variables generally are not correlated with mass-independent basal metabolic rate, with the possible exceptions of maximal intrinsic rate of increase, litter size and reproductive effort during lactation. Whether this is generally true at the level of variation among individuals within a population (individual variation) is unclear. Therefore, we tested whether basal or maximal metabolic rates of random-bred female mice (Mus domesticus) were correlated with the size of their litters, litter mass, or mean offspring mass. The effects of variation in maternal mass, maternal age, experimental block and duration of fasting (for basal metabolic rate) were removed by calculating residuals from multiple regression equations. Basal and maximal metabolic rate were not significantly correlated with any of the life-history variables we studied. Thus, our results are generally consistent with those from interspecific comparisons of mammals: little evidence suggests necessary associations between metabolic rates and life history.

Associations between basal metabolic rate and reproductive performance in C57BL/6J mice

“…Additional work measuring BMR at multiple points throughout the reproductive process might be necessary to ultimately test the hypothesis. Nevertheless, our data provide substantial support to the body of previous work that has suggested that individual variations in BMR in nonreproductive individuals do not provide an enabling mechanism for greater sustained metabolic rates leading to enhanced litter sizes or litter masses at either birth or weaning (Derting and McClure, 1989;Hayes et al, 1992b;Johnson et al, 2001b;Krol et al, 2003;Speakman and Krol, 2005).…”

“…In all cases excepting the indirect measure of resorption, when we statistically removed the effect of M b on BMR, the significant associations to the reproductive performance measures disappeared. Similar patterns of association between M b , BMR and reproductive performance were observed in laboratory mice by Hayes and coworkers (Hayes et al, 1992b) utilising the BMR measured prior to rather than after reproduction. This indicates that measuring BMR after reproduction made no difference to the nature of the associations between these traits.…”

“…The absence of an association between variations in BMR and morphology is consistent with the large number of studies that have failed to establish the expected links between individual variations in BMR and markers of reproductive output (Derting and McClure, 1989;Earle and Lavigne, 1990;Hayes et al, 1992b;Johnson et al, 2001b;Stephenson and Racey, 1993a;Stephenson and Racey, 1993b). One possible reason for this failure is that previous studies have tended to measure BMR in pre-reproductive animals.…”

“…By measuring BMR in the period following rather than preceding reproduction we hoped to reveal associations between BMR and reproductive performance that have eluded previous attempts to establish such associations (Derting and McClure, 1989;Earle and Lavigne, 1990;Hayes et al, 1992b;Johnson et al, 2001b;Krol et al, 2003;Stephenson and Racey, 1993a). Despite this different protocol, the relationships between BMR and the parameters of reproductive output commonly used (birth litter size, weaning litter size and weaning litter mass) were all exceedingly weak and involved BMR explaining considerably less than 20% of the observed variance in any particular trait.…”

Maximal sprint speeds and muscle fiber composition of wild and laboratory house mice

“…As compared with house mice captured in the wild (usually living commensally), lab strains typically exhibit many differences, including less responsiveness to environmental cues affecting reproduction, higher growth rates, and much more docile temperaments (6,34,38). As part of a larger research program using house mice as a model system for quantitative genetic analyses (10) of questions derived from evolutionary physiology (13,15,21) have compared a randombred strain of laboratory house mice (Hsd:ICR) with wild mice captured from a commensal Wisconsin population. In this comparison, we also found many differences, such as the lab mice being larger at all ages postweaning and displaying less voluntary activity on running wheels (11,35).…”