Environmental Endocrinology: Insights into the Diversity of Regulatory Mechanisms in Life Cycles.

All organisms must time their life cycles appropriately and organize life history stages into temporal sequences that enhance fitness in a changing environment. The endocrine system plays a major regulatory role in transducing information from the environment into morphological, physiological, and behavioral responses appropriate for the time of year. The perception, transduction, response pathways via neural and endocrine mechanisms are beginning to be explored and underscore the critical regulatory roles they play. Whereas many conserved mechanisms (evolutionary constraints hypothesis) are emerging, there is a growing realization that there may be alternate pathways unique to populations and individuals (evolutionary flexibility hypothesis). Field investigations (field endocrinology) over the past 45 years have revealed patterns of hormonal responses to environmental changes, physical and social, that could not have been anticipated from laboratory investigations alone. These patterns include differences at population and individual levels that have enabled new insights into acclimation and adaptation to environmental transitions. The number of species studied under natural conditions has grown exponentially in recent years to include all vertebrate classes and some invertebrates as well. These data are now driving evolutionary perspectives and with the advent of comparative genomics a new and exciting era of evolutionary/ecological endocrinology is developing. This article gives a brief overview of where the field stands now and where it is likely to go in the future especially in relation to the networks of regulatory pathways and how they can be modulated to enable acclimation of individuals as well as populations. One illustrative example, mechanisms underlying modulation of the adrenocortical responses to environmental stress, is the focus of this communication. These "coping" mechanisms will be key for acclimation and adaptation to global change.