Date Published: March 28, 2019
Publisher: Public Library of Science
Author(s): Diego A. Torres, Mariella B. Freitas, Sérgio L. P. da Matta, Rômulo D. Novaes, Reggiani Vilela Gonçalves, Daniel Becker.
During mammalian pregnancy and lactation, the maternal demand for calcium is increased to satisfy fetus and newborn skeletal growth. In addition to the dietary intake, females use the calcium contained in their bones to supply this increased demand, leading to a decrease in maternal bone mineral content. In reproductive insectivorous female bats, bone loss has been described as a physiological cost of reproduction, due to the reported increased risk of bone fracture. This physiological cost may be the mechanism underlying the conflict between increasing litter size and maintaining wing skeletal integrity, which would help to explain the small litter size of most bat species. If bone loss is a linking cost between reproduction and survival in bats, and most bat species have small litter sizes, one would expect to find a loss of bone and an increasing probability of bone fracture during pregnancy and lactation in other non-insectivorous bats. In this study, we tested for the existence of this cost in the Great-fruit eating bat, Artibeus lituratus. We analyzed trabecular structure, bone strength and bone mineral content for the humerus bone, hypothesizing that bone loss during reproduction in females would increase the risk of fracture. Our results showed a decrease of 22–31% in bone trabecular area in lactating females, rapidly compensated following weaning. Bone strength did not differ among reproductive and non-reproductive groups and seems to be more influenced by bone organic components rather than mineral contents. Since we observed bone loss during reproduction yet the humerus strength seems to be unaffected, we suggest that bone loss may not represent a physiological cost during reproduction for this frugivorous bat.
Size at birth, age at maturity or growth patterns are life-history traits that contribute to the strategy of an organism to successfully achieve survival and reproduction . However, it has been proven that these traits cannot be selected simultaneously to increase fitness’ components [2,3], therefore organisms must trade-off between different traits (e.g. number of offspring vs. size of offspring ).
Body weight of pregnant females was higher than in non-pregnant and lactating females, but not significantly different from post-lactating females (Table 1). Considering the macroscopic and microstructural parameters analyzed, post-lactating bats showed increased values for bone dry weight as compared to all other groups, including the non-pregnant group (Table 1). Bone trabecular area was higher in pregnancy and post-lactation groups compared to lactating bats, indicating reduced bone mass in lactating bats (Table 1). All other parameters showed similar values among reproductive groups (Table 1).
This study reports, for the first time, bone loss during lactation in a fruit-eating bat. Bone loss was confirmed by decreased trabecular area in the epiphysis of the humerus. Although confirmed, this loss seems to be marginal due to the lack of changes in other parameters, such as trabecular width and trabecular separation. The hypothesis that reproduction is a period of high risk of bone fracture in female bats was not supported for this species, since bone strength parameters were not decreased in pregnant or lactating females. In addition, our findings suggest that the strength of the humerus in A. lituratus may be more influenced by other bone components rather than calcium or phosphorus. Connective tissue components such as collagen and elastin can influence force production during maximal effort, act on stability, responsiveness and also help maintaining bone strength .