Adaptive functions of vertebrate molting cycles

Abstract

SYNOPSIS Cyclic epidermal cellular prohfeiation,with or without keratinization is a vertebrate characteristic Such activity probably obeys an autonomous rhythm which is legulated through neuro humoral S)stcms in response to envnonmental (piox imate)stimuli and related to adaptive (ultimate) factors In seeking cause and effect lelationships, however, it becomes apparent that the same environmental parameter may be both an ultimate and a pioximate factor, the latter also regulating the rate of lesponse With regard to molting in homoio'heims, tempeiatuie acts in such a capacity in many species. Peiiodic shedding of the outer epidermis in fish amphibians and reptiles does not appear to be coirelated with seasonal factors to the extent that avian and mammalian molts are. The evolution of vertebrate molting cycles has amounted to the entraining of inherent epidermal C)cles with seasonal demands by the organism itself and the environment,these demands act as regulating mechanisms Pieadapted structures such as feathers and hairs function collectively as plumage and pelage in their various roles but separately in their growth and leplacement cycles which, however, are coordinated for maximum functional efficiency Molting is also synchionized with the seasonal cycle according to the availability of energy resources and time to complete the essential functions (in addition to molting) The evolved molting systems as manifested in the gieat variety of patterns and types in the vertebrates, may thus be legarded as almost individual responses to selective piessures acting on a umveisil vertebrate chaiacter. The basic regulatoiy system involves the neuro hvpophyseal complex which contiols target endocrines affecting various functions which themselves influence epidermal mitosis and, ultimately, molting 1 he mechanism in its simplest form controls the animals metabolism through the thyroid acting independently in a permissive capacity or synergistically with the adrenal and gonadal hormones which are regulated directly and/or indirectly through negative feedback. © 1972 by the American Society of Zoologists.