The domesticated brain: genetics of brain mass and brain structure in an avian species.

R Henriksen,D Wright,L Andersson,M Johnsson,P Jensen

doi:10.1038/srep34031

Abstract

As brain size usually increases with body size it has been assumed that the two are tightly constrained and evolutionary studies have therefore often been based on relative brain size (i.e. brain size proportional to body size) rather than absolute brain size. The process of domestication offers an excellent opportunity to disentangle the linkage between body and brain mass due to the extreme selection for increased body mass that has occurred. By breeding an intercross between domestic chicken and their wild progenitor, we address this relationship by simultaneously mapping the genes that control inter-population variation in brain mass and body mass. Loci controlling variation in brain mass and body mass have separate genetic architectures and are therefore not directly constrained. Genetic mapping of brain regions indicates that domestication has led to a larger body mass and to a lesser extent a larger absolute brain mass in chickens, mainly due to enlargement of the cerebellum. Domestication has traditionally been linked to brain mass regression, based on measurements of relative brain mass, which confounds the large body mass augmentation due to domestication. Our results refute this concept in the chicken.

Highlights

Brain size variation across vertebrate species continues to fascinate evolutionary biologists, due to the cognitive and behavioral phenotypes it is thought to underlie
These results indicate that loci affecting cerebellum and total brain mass may have been directly selected upon during domestication, or that these loci are closely linked with other genes targeted by domestication selection
Domesticated chickens (WL) have a larger brain mass and body mass than their wild progenitor, but whereas body mass has increased by ~85% during domestication, brain mass has only increased by ~15%

Summary

Introduction

Brain size variation across vertebrate species continues to fascinate evolutionary biologists, due to the cognitive and behavioral phenotypes it is thought to underlie. Most studies on brain size differences suggest some kind of trade-off between the costs of developing and maintaining 7 energetically expensive brains and certain physiological variables (such as body size 1, 8 metabolic rate 2, development time 3) or lifestyle variables (e.g. foraging ecology 4 and social 9 environment 5). One physiological variable that correlates notably with brain size is body size 1. Researchers have often relied on relative rather than absolute brain size in correlative studies. The relationship between body size and brain size is, poorly understood and the use of allometry in brain size evolution 14 studies has been criticized 8-10. Understanding the genetics of brain size evolution is extremely pertinent to determine the relationship between brain size and body size. To what degree there is overlap (and potential pleiotropy) between the genes responsible for both

Methods

Results

Conclusion