Dogs lap using acceleration-driven open pumping

Abstract

Dogs lap because they have incomplete cheeks and cannot suck. When lapping, a dog's tongue pulls a liquid column from the bath, suggesting that the hydrodynamics of column formation are critical to understanding how dogs drink. We measured lapping in 19 dogs and used the results to generate a physical model of the tongue's interaction with the air-fluid interface. These experiments help to explain how dogs exploit the fluid dynamics of the generated column. The results demonstrate that effects of acceleration govern lapping frequency, which suggests that dogs curl the tongue to create a larger liquid column. Comparing lapping in dogs and cats reveals that, despite similar morphology, these carnivores lap in different physical regimes: an unsteady inertial regime for dogs and steady inertial regime for cats.A nimals that interact with an air-fluid interface have evolved highly specialized behaviors to deal with the physical challenge of crossing fluidic regimes. Archerfish adjust for index of refraction when shooting water jets through the interface to catch prey (1, 2), some marine copepods leap into the air to avoid predation (3-6), and lizards and frogs run or skip across the water surface to escape predators (7-9). However, almost all terrestrial animals interact regularly with the air-water interface when they drink or feed (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22). These animals use a wide array of mechanisms to breach the interface and transport fluid into their bodies, including viscous dipping, capillary suction, viscous suction, licking, and lapping (17). For mammalian carnivores, their mechanisms for drinking are constrained by the anatomy of the oral apparatus: with incomplete cheeks, they cannot form a seal to suck fluids into the mouth, and instead use the tongue to lap up fluids (17,(19)(20)(21)(22). Lapping is a behavior that is familiar to most pet owners worldwide, but its physical mechanism is only understood in felines (21), and the underlying physics of drinking by dogs remains unexplained.When a dog laps, the tongue first extends, and is curled backward (ventrally) into a "ladle" shape. The curled tongue impacts the liquid surface, inducing a splash. The tongue then retracts into the mouth, and the cycle is completed when the jaws snap shut. During tongue retraction, fluid adheres to the dorsal side of the tongue and is pulled upward toward the mouth, forming a water column that extends from the bath (21, 22). Informal observations from previous studies (17, 21) have suggested that dogs scoop water with the ventral side of the tongue in the ladle, but recent X-ray imaging has shown that most of the scooped liquid falls off the tongue, and only liquid that sticks to the dorsal side of the tongue is transported to the throat (22). Based on the lack of the use of the curled tongue as a ladle, and general anatomical similarity, Crompton and Musinsky (22) concluded that dogs and cats share the same basic mechanism of drinking. However, the kinematics and the hydrodynamics of lapping by...

Jaw Kinematics and Tongue Protraction-Retraction during Chewing and Drinking in the Pig

“…When the jaw begins opening, the tongue protrudes to collect the food particles before retracting to reposition the bolus on the occlusal surface (Crompton 1989;Hiiemae et al, 1978). During lapping, the tongue also protrudes during early opening and then retracts later during opening, trapping the aliquot prior to the next cycle (Hiiemae et al, 1978;Thexton and McGarrick 1988;Crompton 1989;Thexton and Crompton 1989;Reis et al, 2010;Crompton and Musinsky 2011;Gart et al 2015). During drinking in pigs, the tongue extends into the liquid with the snout immersed, suggesting that the tongue may assist sucking to bring the liquid into the oral cavity (Thexton et al, 1998;German and Crompton 2000), and may potentially be the primary driver of liquid transport (German and Crompton 2000).…”

Cats use hollow papillae to wick saliva into fur

“…Surface tension is exploited by animals to drink, walk, climb, and jump (10)(11)(12). Cats use surface tension to pull up water during lapping (13), while dogs use their tongues like ladles to drink (14).…”

A new microfluidic method enabling the generation of multi-layered tissues-on-chips using skin cells as a proof of concept

“…The main novelty of our work is the development of a method based on parallel flow to compartmentalize in different and homogeneous layers a three-dimensional structure, thus enabling the modelling of complex tissues, in particular epithelia, which are characteristically composed of a lower stromal and an upper epithelial component. This method differs from previously published methods 30 , 31 , 35 – 38 , 40 , 59 , which mainly model epithelial tissues as simple monolayers lacking a stroma. Therefore, our method allows better modelling of epithelial real structure and, consequently, the physiology and tumorigenesis of these tissues.…”

“…For instance, in general, tissues are not generated in hollow microchannels, and frequently, they are seeded from the top instead of being microfluidically loaded 27 . Microfluidic tissues-on-chips (TOCs) have thus far modelled simple epithelia, such as lung, gut and liver, or stratified epithelia, such as cornea, as 2D single-cell layers 28 – 38 , or in the case of skin, as 2D epithelial and dermal cell layers separated by a porous membrane 30 , 39 , 40 . Although TOCs represent an important leap towards the generation of improved in vitro epithelial models, challenges such as downscaling preserving tissue function or the lack of a biologically meaningful stromal component still await solution 23 .…”