Is bone loss a physiological cost of reproduction in the Great fruit-eating bat Artibeus lituratus?

Abstract

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.

Fig 1. Correlations of body weight with bone characteristics in Artibeus lituratus females.

Correlation between body weight and bone length (top) and between body weight and dry bone weight (bottom). Black lines represent regression line and dotted lines respresent lower and upper confidence limit (95%).

Fig 2. Correlations between bone characteristics in Artibeus lituratus females.

Correlation between bone calcium, bone phosphorus and dry bone weight with bone strength parameters in Artibeus lituratus females. Black lines represent regression line and dotted lines represent 95% confidence limit.

Fig 3. Bone histology of Artibeus lituratus females.

Representive areas of trabecular bone in Non-pregnant (A), pregnant (B), lactating (C) and post-lactating (D) female Artibeus lituratus. Note that trabeculae are thinner in lactating female. Tr = trabecula, Ma = bone marrow. Sections were stained with hematoxylin and eosin.