Complex fluids in animal survival strategies.

Patrick A Rühs,Peter Fischer,Jotam Bergfreund,Stefan J Gstöhl,Pascal Bertsch

doi:10.1039/d1sm00142f

Patrick A Rühs, Peter Fischer + Show 3 more

Open Access

https://doi.org/10.1039/d1sm00142f

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Abstract

Animals have evolved distinctive survival strategies in response to constant selective pressure. In this review, we highlight how animals exploit flow phenomena by manipulating their habitat (exogenous) or by secreting (endogenous) complex fluids. Ubiquitous endogenous complex fluids such as mucus demonstrate rheological versatility and are therefore involved in many animal behavioral traits ranging from sexual reproduction to protection against predators. Exogenous complex fluids such as sand can be used either for movement or for predation. In all cases, time-dependent rheological properties of complex fluids are decisive for the fate of the biological behavior and vice versa. To exploit these rheological properties, it is essential that the animal is able to sense the rheology of their surrounding complex fluids in a timely fashion. As timing is key in nature, such rheological materials often have clearly defined action windows matching the time frame of their direct biological behavior. As many rheological properties of these biological materials remain poorly studied, we demonstrate with this review that rheology and material science might provide an interesting quantitative approach to study these biological materials in particular in context towards ethology and bio-mimicking material design.

Highlights

Animals are under constant selective pressure to adapt themselves to their surrounding environment
From penguin species climate-adapted size differences[2] to the food-adapted Darwin finches,[3] an overwhelming array of examples suggests that selective pressure continues to drive natural selection and, if successful, results in well-adapted animals that integrate into an ever-changing environment.[4]
In the following we reviewed how animals passively and actively utilize the rheological properties of exogenous or endogenous, biotic or abiotic complex fluids toward a competitive advantage for movement, prey, defense, and reproduction (Fig. 2)

Summary

Introduction

Animals are under constant selective pressure to adapt themselves to their surrounding environment. Complex fluids like sand or mucus exhibit strain and time dependent flow behavior and we show how gastropods secrete their endogenous viscoelastic locomotion aid and lizards exploit granular rheology to ‘‘swim’’ in sand (Fig. 3). Terrestrial gastropods, such as slugs and snails, crawl with a single foot by a mechanism called adhesive locomotion.

Discussion and perspectives

Findings

Conflicts of interest