Bone loss is a physiological cost of reproduction in white-footed mice (Peromyscus leucopus)

The effects of parity and litter size on bone metabolic activity in pregnant and lactating sows

During gestation and lactation, female mammals often mobilize endogenous nutrient reserves to meet the resource demands of offspring production. These mobilized stores include calcium, phosphorous and other minerals that are resorbed from maternal bone to facilitate rapid mineralization of offspring bones. The extent to which bone mineral is resorbed is governed by the total amount of mineral taken in from the diet, but also by the competing demands of offspring and the minimum level of bone density that a female must sustain to support self-maintenance. The maximum amount of bone that a female may mobilize is undoubtedly dependent a variety of maternal traits, including age and reproductive experience (i.e., parity). We evaluated changes in serum concentrations of biomarkers of metabolic activity (total deoxypyridinoline [tDPD] and osteocalcin [OC]) of maternal bone and its relationship to reproductive output and parity throughout pregnancy and lactation in Yorkshire sows. Litter size did not affect bone metabolism; however, serum concentrations of both tDPD and OC were significantly higher in sows with little or no reproductive experience when compared to sows that had produced at least 3 litters prior to the current reproductive bout. This suggests a shift in ability or physiological strategy to meet offspring mineral demands that is acquired or associated with reproductive experience.

Changes in bone turnover and calcium homeostasis during pregnancy and lactation in mammals: a meta-analysis

Large amounts of calcium are required during pregnancy and lactation to support fetal and neonatal bone growth and calcification. An inadequate supply of calcium during these stages can lead to unsuccessful reproduction or impaired offspring fitness. During reproduction, female mammals undergo numerous physiological changes, including adaptations to allow an adequate supply of calcium. The lack of quantitative studies analysing these physiological changes from a comparative perspective limits our ability to explain and understand these adaptations. Herein, we present our meta-analysis of studies reporting changes in bone turnover and calcium homeostasis during pregnancy and lactation in 14 species of mammals. Our meta-analysis of 60 studies showed that all species have a similar pattern of physiological changes during pregnancy and lactation, which include: (1) decreased serum calcium concentrations; (2) bone tissue loss; (3) decreased serum calcitonin and parathyroid hormone concentrations; and (4) increased serum calcitriol concentration, regardless of changes in parathyroid hormone concentrations. In addition, we found a negative relationship between: (1) serum calcium concentrations and the number of teats; and (2) serum parathyroid hormone concentrations and litter mass.

Female White-Footed Mice (Peromyscus leucopus) Trade Off Offspring Skeletal Quality for Self-Maintenance When Dietary Calcium Intake is Low

During gestation and lactation in mammals, calcium and other minerals are transferred from female to offspring to support skeletal ossification. To meet mineral requirements, females commonly mobilize mineral from their own skeleton to augment dietary intake. Because the fitness costs of bone loss are expected to limit the amount of endogenous mineral that females transfer to their young, the amount of mineral allocated to offspring is predicted to be influenced by the availability of mineral in the female's diet. Calcium is the most abundant element in bone, and exogenous calcium appears to be limiting for many species. Thus, we expected that females would adjust mineral allocation to offspring relative to calcium abundance in the diet. We provided breeding female white-footed mice (Peromyscus leucopus) with a low-calcium (0.1% Ca) or a standard diet (0.85% Ca) for approximately 1 year. Body mass and skeletal size of pups did not differ between diets. Relative to pups from females on the standard diet, pups from females on the low-calcium diet had less calcium and phosphorus in their femurs and humeri, less body calcium content, reduced mass of their femurs and humeri, and had femurs with a reduced width. Reproducing white-footed mice mobilize more bone when calcium intake is low; however, our results suggest that this does not completely compensate for a reduction in calcium intake. Thus, it appears that when calcium availability is low, female white-footed mice reduce the quantity of mineral allocated per offspring as a means of maintaining their own skeletal condition.

Peromyscus as a model system for understanding the regulation of maternal behavior

The genus Peromyscus has been used as a model system for understanding maternal behavior because of the diversity of reproductive strategies within this genus. This review will describe the ecological factors that determine litter size and litter quality in polygynous species such as Peromyscus leucopus and Peromyscus maniculatus. We will also outline the physiological and social factors regulating maternal care in Peromyscus californicus, a monogamous and biparental species. Because biparental care is relatively rare in mammals, most research in P. californicus has focused on understanding the biology of paternal care while less research has focused on understanding maternal care. As a result, the social, sensory, and hormonal cues used to coordinate parental care between male and female P. californicus have been relatively well-studied. However, less is known about the physiology of maternal care in P. californicus and in other Peromyscus species. The diversity of the genus Peromyscus provides the potential for future research to continue to examine how variation in social systems has shaped the mechanisms that underlie maternal care.