Developmental horizons in quadrupedal and leaping primates

Abstract

Recent work on development of primates indicates the body develops in a highly modular manner; that is, different systems (e.g., neural versus muscular) have different rates of growth and may be influenced by independent selective pressures. Here, we investigate age‐related changes in limb muscle mass, limb bone length, as well as the relative status of skeletal ossification and tooth mineralization at birth in two species of primates. Cheirogaleus medius, an arboreal quadruped, and Galago moholi, a vertical clinger/leaper, were studied. Both neonatal and adult primates were dissected from both species and analyzed for potential similarities and differences in developmental schedules. Limb muscle mass and limb bone lengths were measured in all specimens. Cranial and dental development of neonates was assessed using computed tomographic reconstructions and histology. In hindlimb (thigh vs. leg) muscle mass distribution, Galago had a drastic change from neonate to adult via differentially more growth in the thigh (increasing from 57 to 83 % of total hindlimb muscle mass). Alternatively, muscle mass distribution in the forelimb remains stable across age in both species postnatally. More tarsals (3) and ankle epiphyses (1 to 3) have commenced ossification in newborn Galago compared to Cheirogaleus (2 tarsals, 0 epiphyses), but the lack of ossification in carpals and wrist epiphyses is similar. Intermembral index (IMI) ‐ (Humerus+Radius)*100/(Femur+Tibia) ‐ decreases postnatally in both species. Limb muscle mass index (forelimb muscle mass*100/hindlimb muscle mass) decreases postnatally in both species, more drastically than IMI; the overall index is much lower in Galago compared to Cheirogaleus already at birth. Neonatal Galago is relatively more advanced in cranial ossification. For example, the nasal capsule is more ossified (e.g., mesethmoid center has appeared at birth). The mineralization of deciduous teeth reached similar levels at birth in the two species. However, Cheirogaleus has more mineralized replacement teeth as a neonate than Galago. Results support the hypothesis of highly modular development across age in primates, and suggest that muscular, skeletal, and dental structures can respond differentially to selection pressures. In addition, though both primates are initially nest‐bound, advanced hindlimb development in Galago suggests that adaptations for an upright lifestyle (vertical clinging and leaping) are apparent in development well before infants can locomote independently.Support or Funding InformationBCS‐0959438, BCS‐1231350, BCS‐1231717, BCS‐1728263, BCS‐1830894, and BCS‐1830919.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.