Histologic Analysis of Bone Development of the Florida manatee, Trichechus manatus latirostris

Abstract

The amount of bone tissue present in an organism does not remain constant throughout a lifetime. Aquatic mammals generally have more dense bones than their terrestrial counterparts and there is little to no information on aquatic mammal bone development. The Florida manatee is a fully aquatic mammal which represents a good example of dense, amedullary bones. The abundance of prominent bone tissue histological features such as osteocytes, mesenchyme, and trabeculae provide a mechanism to determine how bone tissue of the same species differs due to age. The goal of this study was to evaluate key histological differences between bone samples, from manatees of various ages, in order to approximate the age using characteristics of the bone tissue. Nasal tissue including bone from manatees in the perinatal, calf, juvenile, and adult stages of development was embedded in paraffin, sectioned and stained using trichrome. The number of osteocytes was counted at 40X and 100X total magnifications. Analysis of the osteocyte quantity using a chi square test for goodness of fit shows a significant trend (p<2.2*10-16) directly corresponding to the age of manatee. As the age of manatee increased, greater amounts of osteocytes were counted. Further observations indicate trabeculae are more abundant and prominent in early developmental stages (perinatal and calf) compared to the latter stages (juvenile and adult) in which mature or secondary bone is predominant. Using visual approximation, adult bone contained the largest bone volume, but showed minor signs of degradation and degeneration by osteoclast activity. These results are in agreement with the available information regarding intramembranous bone development, and successfully show a proportional relationship between age and osteocyte number. More specific data, such as the exact age of manatee and computer calculated bone volume/osteocyte lacunae count, would allow us to further model this determined correlation between bone volume and age.