The role of IGF-1 in reproductive life history

The ultimate purpose of most organisms is the production of gametes and the start of a new generation. To achieve this goal, individuals have to cope with countless environmental challenges. This has led to the evolution of a seemingly endless variety of reproductive strategies, which life history theory attempts to place in an evolutionary framework. Although the approach has been very successful, the proximate mechanisms shaping its evolution are not yet well understood. Only recently have the physiological underpinnings of life history decisions become a major focus in evolutionary biology, with hormones receiving particular attention. Because of their pleiotropic effects, hormones function as organism-wide integrators of molecular networks to orchestrate the necessary physiological and behavioral modifications at different life stages. Insulin-like growth factor 1 (IGF-1) has been suggested to function as a major physiological mediator of life history decisions. It is an evolutionarily highly conserved regulatory hormone in all animals and is involved in almost all major life stages including development, growth, reproduction and aging. However, our understanding of its role may be biased by a few model organisms that have been mostly studied in the lab. The next important challenge is to combine the strengths of field ecology and endocrinology to investigate the hormonal regulation of behavior and the physiology of organisms in their natural environment. I propose to combine recently established techniques in physiology with traditional methods in behavioral ecology to gain insights into the effects of IGF-1 in a free-living European passerine, the bearded reedling (Panurus biarmicus). This novel line of research will benefit from and build upon my existing collaborations with the University of Debrecen and the Konrad Lorenz Institute of Ethology in Vienna. The complementary facilities, skills and expertise of the two groups will provide me with a unique framework to combine fieldwork with extended semi-natural aviary experiments that are unfeasible in the field. I will study the effects of IGF-1 on reproductive decisions by measuring its natural variation over the breeding cycle, and will manipulate IGF-1 levels within this range to investigate the effects on processes that have never been addressed in natural conditions, including the onset of the reproductive period and parental investment. I will investigate the role of IGF-1 in sexual maturation and ornament expression, which is important in determining individual life history in wild passerines. To integrate the proximate mechanisms into an ultimate evolutionary framework, I will evaluate the adaptive significance of IGF-1 by testing the newly acquired plumage ornaments in mate choice experiments. The proposed approach will help shed comprehensive new light on the mechanisms behind individual reproductive decisions and life history.

The ultimate purpose of most organisms is the production of gametes to start a new generation. However, to achieve this goal, individuals have to cope with countless environmental challenges. This has led to the evolution of an endless variety of reproductive strategies, which life history theory attempts to place in an evolutionary framework. Although this approach has been very successful, the proximate mechanisms shaping its evolution are not well understood. Only recently, the physiological underpinnings of life history decisions became a major focus in evolutionary biology, with hormones receiving particular attention. Because of their pleiotropic effects, they function as organism-wide integrators of molecular networks to orchestrate the necessary physiological and behavioral modifications at different life-history stages. Insulin-like growth factor 1 (IGF-1) has been suggested to function as a major physiological mediator of life history decisions. It is an evolutionarily highly conserved regulatory hormone and is involved in almost all major life stages including pre- and postnatal development, growth, reproduction and aging. However, our understanding of its role may be biased by studies on a few artificially bred organisms. The next important challenge is to combine the strengths of field ecology and endocrinology to investigate the hormonal regulation of behavior and the physiology of organisms in their natural environment. In collaboration with Dr. dm Lendvai (University of Debrecen) and Dr. Herbert Hoi (Konrad Lorenz Institute of Ethology, Vienna), I investigated the role of IGF-1 in the development and expression of reproductive strategies in the bearded reedling (Panurus biarmicus). The complementary facilities, skills and expertise of the two groups provided me with a unique framework to combine fieldwork in the Hortobgyi National Park with extended semi-natural aviary experiments that are unfeasible in the field. First, I recorded the natural fluctuation of IGF-1 plasma levels of free-living animals during the breeding season and investigated its effects on behaviour and breeding success. Based on these data, I manipulated IGF-1 levels within the natural range using a new injection technique and observed its impact on mate choice and courtship behavior. Another aspect of my research focused in the role of IGF-1 in molting and the expression of plumage ornaments. The collected data reveal a positive relationship between IGF-1 and plumage growth and quality. Since mate choice and reproductive success are tightly linked to certain plumage characteristics, these findings may reflect the long-term effects of IGF-1 on reproductive strategies of bearded reedlings. The knowledge gained in this project sheds comprehensive new light on the mechanisms behind individual reproductive decisions and life history. Considering that IGF-1 is a phylogenetically ancient hormone, this newly gained information is also relevant for other species.