Development of epiphyseal structure and function inDidelphis virginiana (Marsupiala, Didelphidae)

Abstract

This study addressed the question of how the epiphyses of growing mammals change their external shape and internal architecture during postnatal development. Ontogenetic transformations in the external form and internal structure of the fore‐ and hindlimb epiphyses were examined in a mixed cross‐sectional sample of Didelphis virginiana using two methods: morphometric analysis of linear epiphyseal dimensions and histological staining of serially sectioned epiphyses. Metric data indicate that Virginia opossums are born with relatively short hindlimbs and long forelimbs, but by the time they are weaned their hindlimbs are longer than their forelimbs. Functional integration of the locomotor system in D. virginiana involves a decoupling of fore‐ and hindlimb growth rates so that between birth and weaning, femoral length, diaphyseal cross‐sectional area, and articular surface area increase at a significantly faster rate than the corresponding humeral dimensions. Histological results demonstrate that these differences in growth rate are reflected in morphology of the humeral and femoral growth plate and epiphyseal cartilages. The humeral cartilages exhibit a level of cellular organization characteristic of more mature limb elements at earlier developmental stages compared to the femoral cartilages, which assume this anisotropic structure relatively later in postnatal development. Results presented here also reveal that the formation of articular cartilage and the initiation of epiphyseal ossification in D. virginiana are both correlated with the development of independent positional behaviors prior to weaning. These histological data, therefore, suggest that mechanical loading associated with the postnatal onset of locomotor and postural development may provide an important stimulus for the progression of ossification and the formation of articular cartilage in the epiphyses of growing mammals. J. Morphol. 239:283–296, 1999. © 1999 Wiley‐Liss, Inc.

Evolution of the patella and patelloid in marsupial mammals

“…Repeated evolutionary losses and regains of an ossified patella are thus very plausible for marsupials, perhaps through evolutionary 'maintenance' of a transitional structure like the patelloid. Marsupials are known to have apomorphically delayed hindlimb development (Hamrick, 1999;Sánchez-Villagra, 2002;Garland et al, 2007;Sears, 2009) compared with other mammals, so we speculate that this heterochronic shift might have also impacted patellar development and its evolution. New data on patellar development in marsupials are urgently needed, especially in light of novel recent insights into the tissue origins and molecular controls of patellar development in mammals (Eyal et al, 2015;Eyal et al, 2019;Márquez-Flórez et al, 2018;Samuels & Campeau, 2019).…”

“…A hallmark of marsupials is their developmental strategy: marsupials have relatively short gestation periods, after which the newborn crawls to the teat for a prolonged lactation phase, typically within a pouch ( Aplin & Archer, 1987 ). As a result, the embryo has delayed hindlimb development, and accelerated forelimb and cranial development ( Hamrick, 1999 ; Sánchez-Villagra, 2002 ; Garland et al, 2017 ; Sears, 2009 ). Despite the constraints imposed by such as strategy ( Garland et al, 2017 ), and geographical limitation to Australasia and South America today, the over 350 extant species of marsupials exhibit great diversity in their size, lifestyle, behaviour and anatomy ( Walton & Richardson, 1989 ; Burgin et al, 2018 ; Mammal Diversity Database, 2020 ).…”