Abstract
Osteocytes are mature versions of osteoblasts, bone-forming cells that develop in two ways: via 'static' osteogenesis, differentiating and ossifying tissue in situ to form a scaffold upon which other bone can form, or 'dynamic' osteogenesis, migrating to infill or lay down bone around neurovasculature. A previous study regressed the volume of osteocyte lacunae derived from dynamic osteogenesis (DO) of a broad sample of extant bird species against body mass, the growth rate constant ( k), mass-specific metabolic rate, genome size, and erythrocyte size. There were significant relationships with body mass, growth rate, metabolic rate, and genome size, with the latter being the strongest. Using the same avian histological dataset, we measured over 3800 osteocyte lacunar axes derived from static osteogenesis (SO) in order to look for differences in the strength of form-function relationships inferred for DO-derived lacunae at the cellular and tissue levels. The relationship between osteocyte lacunar volume and body mass was stronger when measuring SO lacunae, whereas relationships between osteocyte lacunar volume versus growth rate and basal metabolic rate disappeared. The relationship between osteocyte lacuna volume and genome size remained significant and moderately strong when measuring SO lacunae, whereas osteocyte lacuna volume was still unrelated to erythrocyte size. Our results indicate that growth and metabolic rate signals are contained in avian DO but not SO osteocyte lacunae, suggesting that the former should be used in estimating these parameters in extinct animals.
Highlights
Osteocytes derived from static osteogenesis (SO-derived osteocytes) differentiate in situ from mesenchyme, form early in bone growth and act as the scaffolding for subsequent bone formation by those derived from dynamic osteogenesis (DO-derived osteocytes)
The significant and moderate relationships between avian SO-derived osteocyte lacunar volume and genome size or body mass that were found with DO-derived osteocyte lacunae are maintained, they are both slightly weaker
Our results indicate that for the purposes of estimating avian genome size or body mass from osteocyte lacunar volume, there is no significant difference between DOderived and SO-derived osteocytes
Summary
Osteocytes derived from static osteogenesis (SO-derived osteocytes) differentiate in situ from mesenchyme, form early in bone growth and act as the scaffolding for subsequent bone formation by those derived from dynamic osteogenesis (DO-derived osteocytes). Osteocyte lacunae conform to their dimensions during osteogenesis and their shape is linked to their function [1,2]. Osteocyte lacunae are usually well preserved in fossil bone, offering a rich dataset for addressing palaeobiological questions surrounding extinct animals [3]. One such question is how the size of the genome has changed in various clades over evolutionary history. There have been many studies done to investigate the possible link between cell size and genome size, and if histological evidence can offer enough of a signal to estimate genome size for extinct animals [7,8].
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