Centre for Biological Diversity

Thyroid hormones and life-histories – an avian perspective

Suvi Ruuskanen, Department of Biology, University of Turku, FIN

The diverse life histories in the animal kingdom constitute a major part of biodiversity, where species vary in e.g. reproductive rates and longevity. Several physiological parameters have been proposed to be “mediators” to life-history variation. Potential, but rather neglect mediators are the thyroid hormones (TH). However, thyroid hormones (THs) have often been seen as purely metabolic hormones, and they have gained relatively little attention in eco-evolutionary context. Yet, individuals are exposed to THs starting prenatally, and THs likely contribute to life-history variation among and within species. THs have key pleiotropic functions both in development and coordinating transitions across life-history stages, such as initiation of breeding, moult and migration. I provide an overview on the role of THs on coordinating life-history events, and their associations with life-history strategies, focusing on birds. For example, we show, using a comparative analysis, that THs are associated with life-history strategies across species: altricial-precocial continuum and migratory vs resident species. I also summarize our recent results using experimental manipulations revealed that prenatal THs can have programming effects, influencing hatching, growth and biological markers of aging, and potentially also on initiation of reproduction and moult. Thus, THs certainly are key hormones widely affecting individual phenotype and performance, and we call for more research effort in an eco-evolutionary setting.