Evolutionary Changes in Early Brain Development

University Of California-Irvine, Irvine CA

Investigators

Abstract

The forebrain is proportionately larger in humans than in other mammals. Similarly, the forebrain is proportionately larger in parrots and songbirds than in other birds. These species differences in adult brain proportions have been well described and are thought to account for species differences in behavioral complexity and intelligence. Almost completely unknown, however, are the developmental mechanisms that generate such species differences. Previous work from the Striedter laboratory has shown that forebrain enlargement in parrots and songbirds occurs because the forebrain's precursor cells in these species proliferate for a longer period of time, thereby generating a larger forebrain precursor pool. Although this is a powerful mechansim for enlarging a brain region, other species may enlarge a brain region by other mechanisms, such as changing the spatial patterns of gene expression in young embryos or changing the rates at which precursor cells divide. The proposed research explores these alternative mechanisms by comparing brain region sizes, patterns of gene expression, and rates of cell division across young embryos of different bird species, including parakeets, quail, chickens, and ducks. If one or more of these parameters differs between the examined species, then evolution is free to vary brain proportions through several different developmental mechanisms, rather than constrained to utilize just one. More generally, the findings will clarify some of the rules that govern brain evolution. An important long-term goal is to manipulate brain development in ways that follow these rules and, thus, mimic the natural evolutionary changes. Such experiments are exciting because they will allow for the testing of evolutionary hypotheses. Overall, the proposed work will motivate and train at least one graduate student and several undergraduates performing independent research. It will also excite and educate the general public, who will be exposed to it through public lectures and outreach to student groups.