Biological reality complicates universal theory: A decade of work on puncture across organisms

Puncture, using sharpened tools to penetrate a target, is widespread in living systems, with examples found across phyla spanning several orders of magnitude in size, speed and a variety of functions. For the past decade, researchers have explored the fundamental mechanics that underly these systems with the goal of developing morphological and mathematical models for the energetics of puncture applicable to any biological system. However, this focus on universality can often ignore the diversity of biological reality. Numerous studies have shown that biological puncture systems are incredibly complex, composed of multiple interacting variables, defying the search for a one-size-fits-all model. Here, I review our current understanding of biological puncture mechanics in terms of both the baseline energetics of these systems as well as how the complex relationships between tool shape, target structure and puncture dynamics drive their performance. I then offer a new framework for examining biological, puncture systems based on the flow of energy during the puncture event. The energy flowchart is a framework for examining puncture systems rooted in mechanical principles that still accounts for biological diversity. I apply this energy flowchart method to a series of case studies for organisms that use puncture for injection, prey capture, defense and reproduction. These energy flowcharts combine common physical principles with biological complexity to give a more holistic understanding of biological puncture.