Continuous light and physiology of arctic birds and mammals

Abstract

Many investigations of pineal function have been conducted on animals experiencing artificial laboratory environments. The use of species that naturally experience extreme conditions, such as constant light or darkness, is suggested as a possible way to clarify some of the confusion that exists in the pineal literature at the present time. Arctic species are adapted to an environment in which conditions of constant light are naturally replaced with periods of alternating light. Other conditions of the arctic also vary, including temperature, wind, precipitation, available food, and inter- and intra-species interactions. Arctic species must be highly attuned to their harsh environment. Four species of arctic homeotherms have particular promise as models for the study of pineal function: Snowy owls (Nyctea scandiaca ) and short-eared owls (Asio flammeus ), in contrast with most other owls, must annually switch from being day-active to being at least partially night active. The Arctic fox (Alopex lagopus ) shows regular circannual variations in several parameters alleged to be under the influence of the pineal in other species, including reproduction, activity levels, and seasonal molts. Lemmings (Lemmus trimucronatus ) have two periods of reproductive activity per year, one at the height of the constant light season, and a less intense period that coincides with minimal light. Hormonal activity and possibly pineal activity in lemmings is also implicated in periodic, large scale population fluctuations.