Asymmetric drop coalescence launches fungal ballistospores with directionality

Abstract

Thousands of fungal species use surface energy to power the launch of their ballistospores. The surface energy is released when a spherical Buller's drop at the spore's hilar appendix merges with a flattened drop on the adaxial side of the spore. The launching mechanism is primarily understood in terms of energetic models, and crucial features such as launching directionality are unexplained. Integrating experiments and simulations, we advance a mechanistic model based on the capillary-inertial coalescence between the Buller's drop and the adaxial drop, a pair that is asymmetric in size, shape and relative position. The asymmetric coalescence is surprisingly effective and robust, producing a launching momentum governed by the Buller's drop and a launching direction along the adaxial plane of the spore. These key functions of momentum generation and directional control are elucidated by numerical simulations, demonstrated on spore-mimicking particles, and corroborated by published ballistospore kinematics. Our work places the morphological and kinematic diversity of ballistospores into a general mechanical framework, and points to a generic catapulting mechanism of colloidal particles with implications for both biology and engineering.

Timing of fungal spore release dictates survival during atmospheric transport

“…The ascomycetes, an enormously large and diverse phylum, fire sexual spores from a pressurized cell finely tuned to minimize dissipation (43)(44)(45)(46)(47). The basidiomycetes, a similarly diverse phylum, eject spores using a surface tension catapult and achieve precise control of spore range immediately after discharge (71)(72)(73)(74)(75)(76)(77). These adaptations suggest spore dispersal is under considerable selective pressure.…”

Beyond power amplification: latch-mediated spring actuation is an emerging framework for the study of diverse elastic systems

“…If these direct measurements are still not feasible, computational or analytical approaches can pinpoint the spatial distribution and dynamics of elastic energy storage that can be later validated in the actual organism (e.g. Deegan, 2012;Liu et al, 2017;Rosario and Patek, 2015).…”

“…With a contact latch, the shape and removal speed of the latch strongly influence system output (Ilton et al, 2018;Bolmin et al, 2019); however, tribological analyses of contact latches are still needed. Parameters such as droplet surface separation or rupture force are relevant for fluidic latches (Noblin et al, 2009;Liu et al, 2017), whereas linkage lengths and mechanical advantage are important for geometric latches (Koh et al, 2013;Longo et al, 2018;Olberding et al, 2019). It is as yet unknown which geometries, materials or dynamic features characterize effective latches and their roles across different situations.…”

“…A brief look at the diversity of these systems points towards the many open questions of how their outputs relate to performance. For example, microscopic fungal ballistospores and stylets of jellyfish nematocysts are launched with high acceleration and low velocity using LaMSA; these mechanisms allow tiny structures in a viscous environment (low Reynolds number) to move a short distance (Nüchter et al, 2006;Liu et al, 2017;Roper and Seminara, 2019). Systems used for puncture (Anderson, 2018) are likely operating under different performance demands from those used for seed or pollen ejection (Sakes et al, 2016).…”

“…Instead, springs and latches (see Glossary) enable the enhanced power output of jumping insects. In the 50 years since the inception of this field, a great diversity of organisms have been discovered that use elastic mechanisms and latches to generate fast movements in small systems, including many that do not have muscles, such as plants and fungi (Edwards et al, 2005;Forterre et al, 2005;Noblin et al, 2009;Singh et al, 2011;Vincent et al, 2011;Deegan, 2012;Marmottant et al, 2013;Sakes et al, 2016;Liu et al, 2017;Poppinga et al, 2017;Roper and Seminara, 2019).…”