Basal metabolic rate is positively correlated with parental investment in laboratory mice

Abstract

The assimilation capacity (AC) hypothesis for the evolution of endothermy predicts that the maternal basal metabolic rate (BMR) should be positively correlated with the capacity for parental investment. In this study, we provide a unique test of the AC model based on mice from a long-term selection experiment designed to produce divergent levels of BMR. By constructing experimental families with cross-fostered litters, we were able to control for the effect of the mother as well as the type of pup based on the selected lines. We found that mothers with genetically determined high levels of BMR were characterized by higher parental investment capacity, measured as the offspring growth rate. We also found higher food consumption and heavier visceral organs in the females with high BMR. These findings suggested that the high-BMR females have higher energy acquisition abilities. When the effect of the line type of a foster mother was controlled, the pup line type significantly affected the growth rate only in the first week of life, with young from the high-BMR line type growing more rapidly. Our results support the predictions of the AC model.

Limits to sustained energy intake. XXII. Reproductive performance of two selected mouse lines with different thermal conductance

“…Moreover, given the strain differences discussed above, this seems an unlikely explanation for the data presented here. However, the positive correlation between RMRt and thermal conductance observed in the M strain mice (Selman et al, 2001b) suggests a potential alternative explanation for the observations on mice selected for high and low BMR (Sadowska et al, 2013). It is potentially the case that the mice with higher BMR also had higher thermal conductance, and were hence able to dissipate more heat, and this was the primary factor regulating the level of their reproductive performance, with the observed changes in the alimentary tract in that study a secondary response.…”

“…The thermal conductance of these mice was measured by Gębczyński (Gębczyński, 2005) at generation 19, and no significant differences were noted. The relevance of these measurements to the mice studied by Sadowska et al (Sadowska et al, 2013) is however uncertain because they are separated by 8 years (and 13 generations) of continued selection, hence there has been ample time for a difference in thermal conductance as a correlated trait to develop between these two studies. Note that although a similar time elapsed between the characterisation of thermal conductance of the lines studied here and the present study of their reproductive performance a reduction in the difference in thermal conductance between the lines over this interval seems unlikely.…”

“…It is potentially the case that the mice with higher BMR also had higher thermal conductance, and were hence able to dissipate more heat, and this was the primary factor regulating the level of their reproductive performance, with the observed changes in the alimentary tract in that study a secondary response. Unfortunately, thermal conductance differences between the strains were not measured in this previous study (Sadowska et al, 2013). The thermal conductance of these mice was measured by Gębczyński (Gębczyński, 2005) at generation 19, and no significant differences were noted.…”

“…Consequently, although it seems unlikely that a central limit imposed by gut capacity was responsible for the line difference, it remains feasible that the individual differences within lines could be attributed to such an effect. Sadowska et al (Sadowska et al, 2013) studied the reproductive performance of mice that had been selected for high and low basal metabolic rate (BMR) and found that those with high BMR had greater reproductive performance. They attributed this difference to differences in the assimilation capacity of the alimentary tract, and hence concluded their data were consistent with the central limitation hypothesis.…”

“…Four different ideas have emerged to explain why intake and expenditure might be limited (reviewed in Speakman and Król, 2005a;Piersma and van Gils, 2010;Speakman and Król, 2011). The 'central limitation hypothesis' (Weiner, 1989;Weiner, 1992;Peterson et al, 1990;Sadowska et al, 2013) suggests that limits are imposed by the uptake capacity of the alimentary tract. The 'peripheral limitation hypothesis' (Hammond et al, 1996) posits the limit resides in the capacities of the tissues where the energy is expended.…”