Deadly hairs, lethal feathers – convergent evolution of poisonous integument in mammals and birds

Abstract

Hairs and feathers are textbook examples of the convergent evolution of the follicular appendage structure between mammals and birds. While broadly recognized for their convergent thermoregulatory, camouflage and sexual display functions, hairs and feathers are rarely thought of as deadly defence tools. Several recent studies, however, show that in some species of mammals and birds, the integument can, in fact, be a de facto lethal weapon. One mammalian example is provided by African crested rats, which seek for and chew on the bark of plants containing the highly potent toxin, ouabain. These rats then coat their fur with ouabain-containing saliva. For efficient toxin retention, the rodents have evolved highly specialized fenestrated and mostly hollow hair shafts that soak up liquids, which essentially function as wicks. On the avian side of the vertebrate integumental variety spectrum, several species of birds of New Guinea have evolved resistance to highly potent batrachotoxins, which they acquire from their insect diet. While the mechanism of bird toxicity remains obscure, in a recently published issue of the journal, Dumbacher and Menon explore the intriguing idea that to achieve efficient storage of batrachotoxins in their skin, some birds exploit the basic permeability barrier function of their epidermis. Batrachotoxins become preferentially sequestered in their epidermis and are then transferred to feathers, likely through the exploitation of specialized avian lipid-storing multigranular body organelles. Here, we discuss wider implications of this intriguing concept.

Gene loss in keratinization programs accompanies adaptation of cetacean skin to aquatic lifestyle

“…The general ability of cetaceans to form vibrissae suggests that their lack of body hair is likely caused by the suppression of hair patterning rather than a defect in the hair follicle morphogenesis program per se . Preservation of the follicle‐forming program in dolphins for the sake of developing sensory pits highlights the overall importance of the tactile perception of skin appendages, a feature that also co‐evolved in birds in form of filoplumes, sensory vibrissa‐like feathers .…”

How chemotherapy and radiotherapy damage the tissue: Comparative biology lessons from feather and hair models

“…Similar to the hair follicles, the feather follicles are formed through reciprocal interactions between the epithelium and mesenchyme. [21][22][23][24][25][26] Such epithelial-mesenchymal interactions continue to regulate post-natal follicle function. [21,[27][28][29][30] In their adult life, both form a follicular structure and have a dermal papilla in the proximal end that controls their cyclic growth and regeneration.…”

“…Feather and hair are epithelial organs from convergent evolution. Similar to the hair follicles, the feather follicles are formed through reciprocal interactions between the epithelium and mesenchyme . Such epithelial‐mesenchymal interactions continue to regulate post‐natal follicle function .…”

Understanding skin morphogenesis across developmental, regenerative and evolutionary levels

“…As animals evolved, more and more complex integument organs evolved to adapt to the ever‐changing environment. Particularly notable in this respect are the diverse follicle and follicle‐like ectodermal appendages that endow animal skin with its many functions, including thermoregulation, camouflage, defense and mechano‐sensing to name a few . Several articles in this issue examine evolutionary aspects of hair follicle neogenesis after wounding and hair and feather follicle repair after genotoxic damage .…”

“…Particularly notable in this respect are the diverse follicle and follicle-like ectodermal appendages that endow animal skin with its many functions, including thermoregulation, camouflage, defense and mechano-sensing to name a few. [43,63] Several articles in this issue examine evolutionary aspects of hair follicle neogenesis after wounding [19,20] and hair and feather follicle repair after genotoxic damage. [54] Mallarino and Barsh discuss the evolution and the mechanisms for periodic pigmentation pattern specification and implementation, focusing on stripe-like patterns that evolved in a number of rodents.…”