Postnatal development of the largest subterranean mammal (Bathyergus suillus): Morphology, osteogenesis, and modularity of the appendicular skeleton

Abstract

Background Subterranean mammals show a suite of musculoskeletal adaptations that enables efficient digging. However, little is known about their development. We assessed ontogenetic changes in functionally relevant skeletal traits, and ossification patterns (periosteal and endochondral bone modules) in a truly subterranean scratch‐digging rodent, Bathyergus. We studied 52 individuals (202 long bones) from a wild population by using a multiscale approach involving internal and external morphology. Results Multivariate analysis showed significant morphological changes during ontogeny. A specialized phenotype is expressed perinatally (eg, greater external robustness and developed olecranon, teres major, and deltoid processes), whereas adults presented slender bones with significantly thicker cross‐sections. Ossification modules scaled mostly isometrically with body size parameters. Periosteal modules showed high variability and tended to grow faster than endochondral modules. Conclusions Scratch‐digging adaptations appear at perinatal age and then specialize in subadults. Early development of agonistic and digging behaviors and onset of sexual maturation seems to contribute to its development, although genetic factors also seem to play an important role. Ontogenetic differences are probably a trade‐off to counteract weaker cortical bone properties and poor muscle development in juveniles, whereas slender but thicker cortical bones maximize bone resistance during burrow construction without compromising locomotor performance in adults.

Hind foot drumming: Morphofunctional analysis of the hind limb osteology in three species of African mole‐rats (Bathyergidae)

“…Many studies have used osteological indices to analyze the long bones of rodent species for adaptations to locomotory behavior (Echeverria et al, ; Elissamburu & Vizcaino, ; Montoya‐Sanhueza et al, ; Salton & Sargis, ; Samuels & Van Valkenburgh, ; Sargis, ). These indices provide insight into various parameters of osteology including indications of function.…”

“…However, these studies grouped several species together and no individual species comparisons were performed (Chen & Wilson, ; Samuels & Van Valkenburgh, ; Wilson & Geiger, ). More recently Montoya‐Sanhueza, Wilson, and Chinsamy () used similar methods to analyze the long bones of B. suillus at different ages to determine how these morphofunctional indices change with the age of the animal. The purpose of the present study was to determine if adaptations for a specialized behavior such as hind foot drumming can be detected using previously established osteological indices of the pelvis, femur, tibia, and third metatarsal, in three species of African mole‐rats.…”

Evo‐devo explores the endless forms most beautiful, from extreme traits to subtle diversities

“…In this issue, authors investigate a variety of fascinating anatomical and life‐history adaptations from niches below the earth's surface to the night sky. Montoya‐Sanhueza et al explore the post‐natal development of the highly specialized limbs of the Cape dune mole rat, a fully‐subterranean mammal that is endemic to the Western Cape Province of South Africa. By analyzing bones on a detailed micro‐anatomical level and relating developmental changes to the external anatomy, limb function and changes in animal behavior as maturation commences, Montoya‐Sanhueza et al reveal how a combination of both genetic and behavioral factors related to digging likely impact the process of mole rat limb maturation.…”

“…Montoya‐Sanhueza et al explore the post‐natal development of the highly specialized limbs of the Cape dune mole rat, a fully‐subterranean mammal that is endemic to the Western Cape Province of South Africa. By analyzing bones on a detailed micro‐anatomical level and relating developmental changes to the external anatomy, limb function and changes in animal behavior as maturation commences, Montoya‐Sanhueza et al reveal how a combination of both genetic and behavioral factors related to digging likely impact the process of mole rat limb maturation. Similarly, Camacho et al use 3D geometric morphometrics to interrogate skull diversity amongst phyllostomid bats, which are adapted to suit a variety of nocturnal dietary habits.…”

“…In this issue, authors investigate a variety of fascinating anatomical and life-history adaptations from niches below the earth's surface to the night sky. Montoya-Sanhueza et al 1 showing that hemipenis-like structures persist in this allfemale species throughout embryonic development. In addition, μCT scans provide exquisite detail of brain development.…”