Selection for Reduced Fear of Humans Changes Brain and Cerebellum Size in Red Junglefowl in Line with Effects of Chicken Domestication

Abstract

A central part of the domestication syndrome is a reduction in relative brain size. In chickens, it has previously been shown that domesticated birds have smaller relative brain mass, but larger relative mass of cerebellum, compared to their ancestors, the Red Junglefowl. It has been suggested that tameness may drive the domestication syndrome, so we examined the relationship between brain characteristics and tameness in 31 Red Junglefowl from lines divergently selected during ten generations for tameness. Our focus was on the whole brain, cerebellum, and the remainder of the brain. We used the isotropic fractionator technique to estimate the total number of cells in the cerebellum and differentiate between neurons and non-neuronal cells. We stained the cell nuclei with DAPI and performed cell counting using a fluorescence microscope. NeuN immunostaining was used to identify neurons. The absolute and relative masses of the brains and their regions were determined through weighing. Our analysis revealed that birds selected for low fear of humans (LF) had larger absolute brain mass, but smaller relative brain mass, compared to those selected for high fear of humans (HF). Sex had a significant impact only on the absolute size of the cerebellum, not its relative size. These findings support the notion that selection for increased tameness leads to an enlargement of the relative size of cerebellum in chickens consistent with comparisons of domesticated and ancestral chickens. Surprisingly, the HF birds had a higher density of neurons in the cerebellum compared to the LF line, despite having a smaller cerebellum overall. These findings highlight the intricate relationship between brain structure and behavior in the context of domestication.

Feeding flaxseed to chicken hens changes the size and fatty acid composition of their chicks’ brains

“…The current study adds to the scarce fundamental knowledge about n-3 FAs and chicken brain development. To date, research on relative brain size has focused on the effects of domestication or the effect of selection for tameness ( Agnvall et al, 2017 ; Gjøen et al, 2023 ) and tends to not assess the effect of maternal nutrition. Feeding flaxseed to breeders increases broiler offspring brain size and alters the FA composition of layer offspring.…”

Correction: Gjøen et al. Selection for Reduced Fear of Humans Changes Brain and Cerebellum Size in Red Junglefowl in Line with Effects of Chicken Domestication. Brain Sci. 2023, 13, 988

“…There were errors in the original publication [1]: 1. In the Abstract, the following sentence is wrong: "Our analysis revealed that birds selected for low fear of humans (LF) had larger absolute brain mass, but smaller relative brain mass, compared to those selected for high fear of humans (HF)".…”