Biology subjects

Heveran, C. M.

Publications and source records attributed to Heveran, C. M..

5 recordsLinked to original sources

bioRxiv2021

Experimental Studies of Carpenter Bee (Xylocopa: Apidae) Thorax Mechanics During Defensive Buzzing

Approximately 10% of flowering plant species conceal their pollen within tube-like poricidal anthers. Bees extract pollen from poricidal anthers via floral buzzing, a behavior during which they apply cyclic forces by biting the anther and rapidly contracting their flight muscles. The success of pollen extraction during floral buzzing relies on the direction and magnitude of the forces applied by the bees, yet these forces and forcing directions have not been previously quantified. In this work, we developed an experiment to simultaneously measure the directional forces and thorax kinematics produced by carpenter bees (Xylocopa californica) during defensive buzzing, a behavior regulated by similar physiological mechanisms as floral buzzing. We found that the buzzing frequencies averaged about 130 Hz and were highly variable within individuals. Force amplitudes were on average 170 mN, but at times reached nearly 500 mN. These forces were 30 - 80 times greater than the weight of the bees tested. The two largest forces occurred within a plane formed by the bees flight muscles. Force amplitudes were moderately correlated with thorax displacement, velocity and acceleration amplitudes but only weakly correlated with buzzing frequency. Linear models developed through this work provide a mechanism to estimate forces produced during non-flight behaviors based on thorax kinematic measurements in carpenter bees. Based on the buzzing frequencies, individual bees capacity to vary buzz frequency and predominant forcing directions, we hypothesize that carpenter bees leverage vibration amplification to increase the deformation of poricidal anthers, and hence the amount of pollen ejected.

biophysics↗

bioRxiv2021

Perilacunar bone tissue exhibits sub-micrometer modulus gradation which depends on the recency of osteocyte bone formation

Osteocytes are capable of resorbing and replacing bone local to the lacunar-canalicular system (LCS remodeling). However, the impacts of these processes on perilacunar bone quality are not understood. It is well established that aging is associated with reduced whole-bone fracture resistance, reduced osteocyte viability, and truncated LCS geometries, but it remains unclear if aging changes perilacunar bone quality. In this study, we employed atomic force microscopy (AFM) to quantify sub-micrometer gradations from 2D maps surrounding osteocyte lacunae in young (5 mo) and aged (22 mo) female mice. AFM-mapped lacunae were also imaged with confocal laser scanning microscopy to determine which osteocytes had recently deposited bone as determined by the presence of fluorochrome labels. These assays allowed us to quantify gradations in nanoscale mechanical properties of bone-forming/non-bone-forming osteocytes in young and aged mice. This study reports for the first time that there are sub-micrometer gradations in modulus surrounding lacunae and that these gradations are dependent upon recent osteocyte bone formation. Perilacunar bone adjacent to bone-forming osteocytes demonstrated lower peak and bulk modulus values when compared to bone near non-bone-forming osteocytes from the same mouse. Bone-forming osteocytes also showed increased perilacunar modulus variability. Age reduced lacunar size but did not significant effect modulus gradation or variability. In general, lacunar morphology was not a strong predictor of modulus gradation patterns. These findings support the idea that lacunar-canalicular remodeling activity changes the material properties of surrounding bone tissue on a sub-micrometer scale. Therefore, conditions that affect osteocyte health have the potential to impact bone quality. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=62 SRC="FIGDIR/small/461298v1_ufig1.gif" ALT="Figure 1"> View larger version (29K): org.highwire.dtl.DTLVardef@1fe5a68org.highwire.dtl.DTLVardef@1e17e90org.highwire.dtl.DTLVardef@13c2e3corg.highwire.dtl.DTLVardef@1ff9f38_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗

bioRxiv2021

The mouse bone metabolome is sexually dimorphic and is associated with whole bone strength

Cortical bone quality, which is sexually dimorphic, depends on bone turnover and therefore the activities of remodeling bone cells. However, sex differences in cortical bone metabolism are not yet defined. Adding to the uncertainty about cortical bone metabolism, the metabolomes of whole bone, isolated cortical bone without marrow, and bone marrow have not been compared. We hypothesized that the metabolome of isolated cortical bone would be distinct from that of bone marrow and would reveal sex differences. Metabolite profiles from LC-MS of whole bone, isolated cortical bone, and bone marrow were generated from humeri from 20-week-old female C57Bl/6J mice. The cortical bone metabolomes were then compared for 20-week-old female and male C57Bl/6J mice. Femurs from male and female mice were evaluated for flexural material properties and were then categorized into bone strength groups. The metabolome of isolated cortical bone was distinct from both whole bone and bone marrow. We also found sex differences in the isolated cortical bone metabolome. Based on metabolite pathway analysis, females had higher lipid metabolism, and males had higher amino acid metabolism. High-strength bones, regardless of sex, had greater tryptophan and purine metabolism. For males, high strength bones had upregulated nucleotide metabolism, whereas lower strength bones had greater pentose phosphate pathway metabolism. Since the higher strength groups (females compared with males, high strength males compared with lower strength males) had higher serum CTX1/P1NP, we estimate that the metabolomic signature of bone strength in our study at least partially reflects differences in bone turnover. These data provide novel insight into bone bioenergetics and the sexual dimorphic nature of bone material properties in C57Bl/6 mice.

cell biology↗

bioRxiv2021

The flying insect thoracic cuticle is heterogenous in structure and in thickness-dependent modulus gradation

The thorax is a specialized structure central to an insects ability to fly. In the thorax, flight muscles are surrounded by a thin layer of cuticle. The structure, composition, and material properties of this chitinous structure may influence the efficiency of the thorax in flight. However, these properties, as well as their variation throughout anatomical regions of the thorax or between insect taxa, are not known. In this work, we provide a multi-faceted assessment of thorax cuticle for fliers with asynchronous (honey bee; Apis mellifera) and synchronous (hawkmoth; Manduca sexta) muscles. We investigated cuticle structure using histology, material composition through confocal laser scanning microscopy, and modulus gradation with nanoindentation. Our results suggest that cuticle properties of the thorax are highly dependent on anatomical region and species. Modulus gradation, but not mean modulus, differed between the two types of fliers. In some regions, A. mellifera had a positive linear modulus gradient from cuticle interior to exterior of about 2 GPa. In M. sexta, the modulus gradients were variable and were not well represented by linear fits with respect to cuticle thickness. We utilized finite element modeling to assess how measured modulus gradients influenced maximum stress in cuticle. Stress was reduced when cuticle with a linear gradient was compressed from the high modulus side. These results support the protective role of the A. mellifera thorax cuticle. Our multi-faceted assessment advances our understanding of thorax cuticle structural and material heterogeneity and the potential benefit of material gradation to flying insects. Graphical Abstract O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY Statement of SignificanceThe insect thorax is essential for efficient flight but questions remain about the contribution of exoskeletal cuticle. We assessed the thorax cuticle using a high resolution multi-faceted approach to determine how cuticle properties vary within thorax anatomical regions and between fliers with asynchronous (honey bee; Apis mellifera) and synchronous (hawkmoth; Manduca sexta) muscles. We examined structure using histological staining, modulus using nanoindentation, and material composition using confocal scanning light microscopy. We further utilized finite element modeling to understand the effect of the modulus gradations observed experimentally on stress accumulation. Cuticle properties vary through cuticle thickness, by thorax region, and between flight lineages.

biophysics↗

bioRxiv2020

Development and analytical validation of a finite element model of fluid transport through osteochondral tissue

Fluid transport between cartilage and bone is critical to joint health. The objective of this study was to develop and analytically validate a finite element model of osteochondral tissue capable of modeling cartilage-bone fluid transport. A biphasic viscoelastic model using an ellipsoidal fiber distribution was created with three distinct layers of cartilage (superficial zone, middle zone, and deep zone) along with a layer of subchondral bone. For stress-relaxation in unconfined compression, our results for compressive stress, radial stress, effective fluid pressure, and elastic recoil were compared with established biphasic analytical solutions. Our model also shows the development of fluid pressure gradients at the cartilage-bone interface during loading. Fluid pressure gradients developed at the cartilage-bone interface with consistently higher pressures in cartilage following initial loading to 10% strain, followed by convergence towards equal pressures in cartilage and bone during the 400s relaxation period. These results provide additional evidence that fluid is transported between cartilage and bone during loading and improves upon estimates of the magnitude of this effect through incorporating a realistic distribution and estimate of the collagen ultrastructure. Understanding fluid transport between cartilage and bone may be key to new insights about the mechanical and biological environment of both tissues in health and disease.

bioengineering↗