The Genetic Regulation of size Variation in the Transcriptome of the Cerebrum in the Chicken and its role in domestication and brain size evolution

Abstract

Background: Large difference in cerebrum size exist between avian species and populations of the same species and is believed to reflect differences in processing power. During domestication chickens developed a larger cerebrum compared to their wild progeny, the Red Jungle fowl. The underlying mechanisms that control cerebrum size and the extent to which genetic regulation is similar across brain regions is not well understood. In this study, we combine measurement of cerebrum size with genome-wide genetical genomics analysis to identify the genetic architecture of the cerebrum, as well as compare the regulation of gene expression in this brain region with gene-expression in other regions of the brain (the hypothalamus) and somatic tissue (liver). Results: We identify one candidate gene that putatively regulates cerebrum size ( MTF2 ) as well as identified a large number of eQTL that regulate the transcriptome in cerebrum tissue, with the majority of these eQTL being trans-acting. The overall regulation of gene expression variation in the cerebrum was markedly different to the hypothalamus, with relatively few eQTL in common. In comparison, the cerebrum tissue shared more eQTL with a distant tissue (liver) than with a neighboring tissue (hypothalamus). Conclusion: The candidate gene for cerebrum size ( MTF2 ) has previously been linked to brain development making it a good candidate for further investigation as a regulator of inter-population variation in cerebrum size. The lack of shared eQTL between the two brain regions implies that genetic regulation of gene expression appears to be relatively independent between the two brain regions and suggest that co-evolution between these two brain regions might be more functionally driven than developmental. These findings have relevance for current brain size evolution theories.

The Effects of Domestication on the Brain and Behavior of the Chicken in the Light of Evolution

“…Phenomena like this are seldom found, but have led to an intensive discussion of the allometric method in comparative neurobiology (Clutton-Brock and Harvey [1980], Harvey [1988], and Stephan et al [1988]). Recent studies suggest that, at least in the chicken, the gene loci controlling variations in brain and body mass during domestication have separate genetic architectures and are therefore not directly constrained [Henriksen et al, 2016;Höglund et al, 2020]. This means that it is not necessarily better to rely on relative than absolute brain sizes in correlative studies.…”