Evolution of vertebrate brain size: an experimental approach

Why is the human brain so different from that of any other animal species? What are the evolutionary events in vertebrates that have led to the human brain? These questions have fascinated evolutionary biologists for centuries and continue to be key issues in modern evolutionary biology. A massive research effort in this area over the last decade has produced considerable evidence about the selective pressures that have shaped the evolution of the enormous variation in brain size among vertebrates. Comparative studies relating both within- and between species variation in brain size to a variety of ecological and behavioural traits have uncovered some of the evolutionary pathways by which contemporary species have adapted to their physical and social environment. But while comparative studies are an essential first step in understanding the evolutionary events leading towards the human brain, these studies lack the conclusive evidence only acquired by proper experimental testing. The project outlined here aims at filling this gap by experimentally testing the key issues in the study of brain size evolution. Specifically the project will make use of the small- and large-brained guppy lines (Poecilia reticulata; brain weight selected lines - BWS lines), that I recently developed in Niclas Kolm`s group at the EBC at Uppsala University to investigate the potential costs and benefits of having small or large brains. I first want to concentrate on the behavioural consequences of large and small brains and compare cognitive ability between the lines. With this unique system I then aim to investigate the consequences of differential investment into brain development. Since the brain is among the most costly organs to build and maintain, a selection on relative brain size will inevitably reveal trade-offs with other body parts. I will examine differences in secondary sexual characters in males (costly ornaments like carotenoid spots and fin- and gonopodium size and behaviours like competitiveness and courtship vigour) and life-history traits in females (fecundity, offspring size, time to maturation) and directly linked to these questions I will test courtship success by genotyping sperm donated in females and offspring from mixed groups in large semi-natural tanks. Further trade-offs suggested by theory and comparative studies, which I am eager to test, include longevity, gut size and aspects of physiology such as metabolic rate. But I will also investigate how brain morphology changes in response to a strong selection on brain size and therefore examine whether some brain structures respond more to selection and whether it is neuron size or neuron number that changes to produce brain size differences. Finally I will use quantitative genetic tools to explore the variance and covariance between brain size, body size and life history in the existing pedigree of approximately 2000 breeder individuals spanning five generations. To tackle these questions I will collaborate with numerous leading scientists, supervise three masters students and hope to transfer the acquired know-how to Austria when moving back to Vienna.

No additional funding sources recorded.