Biology subjects

Buchmann, S.

Publications and source records attributed to Buchmann, S..

4 recordsLinked to original sources

bioRxiv2024

Widespread evolution of poricidal flowers: A striking example of morphological convergence across flowering plants

The evolution of tube-like floral morphologies that control pollen release via small openings (functionally poricidal flowers) represents a taxonomically and geographically widespread instance of repeated and independent evolution of a functionally similar morphology. Poricidal flowers are also often closely associated with buzz pollination by bees. Yet we lack an updated angiosperm-wide survey of their phylogenetic distribution. We identify all known angiosperm genera containing poricidal flowers via a literature survey. We determined their phylogenetic distribution and minimum number of independent gains and losses via a species-level angiosperm-wide phylogeny. We estimated if evolution of poricidal flowers is associated with changes in speciation/extinction via diversification rate analyses. Poricidal flowers occur across 87 angiosperm families and 639 genera containing >28,000 species. At the species level, an average of 205 independent gains and 215 losses of poricidal flowers occurred. Angiosperm-wide analyses suggest an early burst in poricidal evolution, but no differences in net diversification (origination-extinction) between non-poricidal and poricidal taxa. Analyses for two focal families however indicate strong context-dependent effects of poricidal flowers on diversification. Poricidal evolution thus represents a large-scale example of convergent evolution in floral form, but effects on diversification appear to be strongly contingent on phylogenetic and ecological background.

evolutionary biology↗

bioRxiv2022

Astrocyte 3D Culture and Bioprinting using Peptide Functionalized Hyaluronan Hydrogels

The often-forgotten astrocytes play an important role in the central nervous system, contributing to the development of and maintenance of synapses, recycling of neurotransmitters, and the pathophysiology of various neurodegenerative diseases. Hydrogels can provide improved support and attachment for the culture of astrocytes in 3D models, which could further be used to advance clinical in vivo like tissue models of numerous diseases. For full applicability, these gels must be of scalable and defined origin and with stable attachment elements, such as peptides. In this study, the generation of a functional 3D astrocyte model is presented using a hyaluronan-based hydrogel system conjugated with the peptide sequences cyclic RGD (cRGD) and IKVAV, known promoters of cell attachment. Encapsulation of the neuroblastoma cell line SH-SY5Y and glioblastoma cell line U87 is successfully demonstrated over a 6-day culture period. The presence of the peptides cRGD and IKVAV does not change the cells viability. Human fetal primary astrocytes (FPA) are further tested for the 3D culture in these materials, similarly, showing that the peptides have no effect on the viability over a 6-day culture period. mRNA expression analysis reveals no biologically significant changes in the 3D cultures FPA or the U87 cells. Morphological analysis, on the other hand, revealed that FPA have a higher degree of interactions with the hyaluronan-based gels compared to the cell lines. This interaction is enhanced by peptide conjugation, in particular cRGD. Finally, we demonstrated that the peptide conjugated hydrogels could be used for bioprinting of FPA, opening up for defined neural astrocytic co-culture.

bioengineering↗

bioRxiv2021

Structural Dynamics of Real and Modeled Solanum Stamens: Implications for Pollen Ejection by Buzzing Bees

An estimated 10% of flowering plant species conceal their pollen within tube-like anthers that dehisce through small apical pores (poricidal anthers). Bees extract pollen from poricidal anthers through a complex motor routine called floral buzzing, whereby the bee applies vibratory forces to the flower stamen by rapidly contracting its flight muscles. The resulting deformation depend on the stamens natural frequencies and vibration mode shapes, yet for most poricidal species these properties have not been sufficiently characterized. We performed experimental modal analysis on Solanum elaeagnifolium stamens to quantify their natural frequencies and vibration modes. Based on morphometric and dynamic measurements, we developed a finite element model of the stamen to identify how variable material properties, geometry and bee weight could affect its dynamics. In general, stamen natural frequencies fell outside the reported floral buzzing range, and variations in stamen geometry and material properties were unlikely to bring natural frequencies within this range. However, inclusion of bee mass reduced natural frequencies to within the floral buzzing frequency range and gave rise to an axial-bending vibration mode. We hypothesize that floral buzzing bees exploit the large vibration amplification factor of this mode to increase anther deformation, which may facilitate pollen ejection.

biophysics↗

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↗