Measuring and analysing animal closing forces: a mobile setup and new R package

Abstract

Animal closing forces such as bite and pinch forces may determine access to food and mates and are therefore important performance metrics related to fitness. However, despite the diversity and ecological importance of smaller animals such as many crustaceans and insects, knowledge on the predictors and evolution of closing forces in these taxa is extremely scarce. Here we present a mobile and light-weight closing force measurement setup that is tailored to measure closing forces of a wide range of animals, especially smaller taxa, and an R package for analysing the measurements. During a measurement, in vivo closing forces are converted to an electrical signal by a highly sensitive piezoelectric force transducer. The transducer is housed in a setup that can be manufactured with a 3D printer and generic parts, and the electric signal is amplified by a custom charge amplifier. The R package automatically extracts maximum force values and individual force curves for further curve shape analyses. The shape of these curves may yield information on the underlying biomechanics, physiology, and behaviour during biting/pinching, and has only rarely been studied. We think that the new measurement setup, its ease of use, reproducible components, and fast assembly will enable rapid force measurements in the field and in the lab. In combination with the R package, it will facilitate research on the micro- and macroevolution of animal closing forces in a wide range of taxa, especially in smaller vertebrates and the megadiverse arthropods.