Energy Allocation in Mammalian Reproduction

SYNOPSIS. On behavioral, hormonal, and physiological grounds, mammalian reproduction can be compartmentalized into the following continuous sequence of events: mating (courtship, estrous), gestation, parturition, lactation, post-lactational parental care, and maternal recovery. We point out that comparing the relative allocation of energy for these events across mammals is difficult because of life history variability (e.g., litter size, birth weight), allometry, phylogeny, and individual variation. We review the empirical and theoretical literature on each of these events with respect to: different methodologies in measuring energy use;broad patterns of energy consumption across diverse mammalian taxa; and, identification of particular reproductive characteristics (e.g., birthing, parental care) which may be costly but have yet to receive energetic measurements. Although most studies have consideredgestation and lactation the critical reproductive events for energy expenditure, variation in these events is substantial and almost certainly is a function of relative allocation of time togestation vs. lactation as well as the presumed energetic costs of mating, birthing and parental care. In addition, repeated observations show that behavioral compensation is an extremely important strategy for minimizing energy requirements during reproduction. From this review, we argue that more complete analyses will come from (1) incorporating energetic measurements in studies of mammalian behavior and (2) including mechanisms of behavioral compensation into physiological studies.