Hydration affects the physical and mechanical properties of baleen tissue.

Alexander J Werth,Michael V Rosario,Robert W Harriss,Todd L Sformo,J Craig George

doi:10.1098/rsos.160591

Alexander J Werth, Michael V Rosario + Show 3 more

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https://doi.org/10.1098/rsos.160591

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Abstract

Baleen, an anisotropic oral filtering tissue found only in the mouth of mysticete whales and made solely of alpha-keratin, exhibits markedly differing physical and mechanical properties between dried or (as in life) hydrated states. On average baleen is 32.35% water by weight in North Atlantic right whales (Eubalaena glacialis) and 34.37% in bowhead whales (Balaena mysticetus). Baleen's wettability measured by water droplet contact angles shows that dried baleen is hydrophobic whereas hydrated baleen is highly hydrophilic. Three-point flexural bending tests of mechanical strength reveal that baleen is strong yet ductile. Dried baleen is brittle and shatters at about 20–30 N mm−2 but hydrated baleen is less stiff; it bends with little force and absorbed water is squeezed out when force is applied. Maximum recorded stress was 4× higher in dried (mean 14.29 N mm−2) versus hydrated (mean 3.69 N mm−2) baleen, and the flexural stiffness was >10× higher in dried (mean 633N mm−2) versus hydrated (mean 58 N mm−2) baleen. In addition to documenting hydration's powerful effects on baleen, this study indicates that baleen is far more pliant and malleable than commonly supposed, with implications for studies of baleen's structure and function as well as its susceptibility to oil or other hydrophobic pollutants.

Highlights

Baleen is a uniquely specialized oral tissue with no functional analogue or evolutionary homologue
Baleen is made entirely of dead, cornified cells and fibres. It is wholly composed of alpha-keratin, a fibrous protein creating intermediate filaments [8,9] found in many mammalian integumentary structures including hair, horn, nails, claws and hooves [10,11], yet baleen grows throughout life from living keratinocyte cells in the gums, in the same manner and speed as other keratinous integumentary structures [12]
Tests of alternate drying and hydration indicate that right whale baleen is nearly one-third water by weight

Summary

Introduction

Baleen is a uniquely specialized oral tissue with no functional analogue or evolutionary homologue It hangs in sheets (called plates or laminae) from the palate of whales, where it filters aggregations of small planktonic or nektonic prey from seawater. Baleen is made entirely of dead, cornified cells and fibres It is wholly composed of alpha-keratin, a fibrous protein creating intermediate filaments [8,9] found in many mammalian integumentary structures including hair, horn, nails, claws and hooves [10,11], yet baleen grows throughout life from living keratinocyte cells in the gums, in the same manner and speed as other keratinous integumentary structures [12]. The plates and fringes together alter water flow around and within the mouth to trap aggregations of prey [5,16,17,18]

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