The genetic regulation of size variation in the transcriptome of the cerebrum in the chicken and its role in domestication and brain size evolution

Selection for Tameness in Red Junglefowl Recapitulates Genetic Loci Associated With Domestication-Related Brain Composition

Domestication involves huge phenotypic shifts via strong directional selection. The resulting changes, often termed the Domestication Syndrome, typically encompass numerous traits; however, the most universal of these are changes in reduced fear of humans (tameness) and brain composition. To assess how early domestication selection may have focused on tameness and its interaction with brain composition, a Red Junglefowl (Gallus gallus) population (the wild progenitor of the domestic chicken) was used to create two lines bidirectionally selected for fear of humans over eight generations of selection. These selection lines were then used to make an intercross population. Using a combination of genome-wide mapping in the intercross and between-line analysis of the selection lines, we show that the genetic loci for tameness co-localise with genetic loci for brain composition and anxiety behaviour. Furthermore, the detected loci for brain composition also co-localise with brain composition loci identified in a separate wild × domestic intercross. These results indicate that tameness and brain composition are either pleiotropic or genetically linked, and that tameness selection appears to recapitulate the same loci that have been selected by domestication itself. Therefore, selection for increased tameness could be the initial selection pressure driving the core of the domestication syndrome.

Comparative Transcriptome Analysis of Hens' Livers in Conventional Cage vs. Cage-Free Egg Production Systems

Different conditions of production systems including stocking density, thermal conditions, and behavior restriction can have a significant detrimental effect on the health and performance of laying hens. The conventional cage system is one of the systems that have been reported to cause stress problems in birds, due to social and behavioral stress. Emerging technologies have facilitated a deeper understanding of animal responses to various scenarios and can be an additional tool to conventional ones to assess animal welfare, where transcriptomic analysis has the potential to show the genetic changes that occur in response to stress. According to this, the aim of this work was to characterize the liver transcriptome of hens housed under two egg production systems (conventional cage and cage-free). Liver tissue from Hy-Line Brown hens housed in conventional cage (n = 3) and cage-free (n = 3) production systems at week 80 of age was processed using the Illumina platform to identify differentially expressed genes with a padj < 0.05. Regarding the differentially expressed genes, 138 genes were found, of which 81 were upregulated and 57 downregulated. Some of the genes of interest were TENM2, GRIN2C, and ACACB, which would indicate greater fat synthesis in the liver of caged hens. The enriched KEGG pathways were DNA replication and the cell cycle. In conclusion, it was identified that the cage production system may influence DNA replication and the cell cycle since the genes related to these terms were found suppressed, which would indicate cellular instability.

Age-dependent genetic architectures of chicken body weight explored by multidimensional GWAS and molQTL analyses

Chicken body weight (BW) is a critical trait in breeding. Although genetic variants associated with BW have been investigated by genome-wide association studies (GWAS), the contributions of causal variants and their molecular mechanisms remain largely unclear in chickens. In this study, we construct a comprehensive genetic atlas of chicken BW by integrative analysis of 30 age points and 5 quantitative trait loci (QTL) across 27 tissues. We find that chicken growth is a cumulative non-linear process, which can be divided into three distinct stages. Our GWAS analysis reveals that BW-related genetic variations show ordered patterns in these three stages. Genetic variations in chromosome 1 may regulate the overall growth process, likely by modulating the hypothalamus-specific expression of SLC25A30 and retina-specific expression of NEK3. Moreover, genetic variations in chromosome 4 and chromosome 27 may play dominant roles in regulating BW during Stage 2 (8-22 weeks) and Stage 3 (23-72 weeks), respectively. In summary, our study presents a comprehensive genetic atlas regulating developmental stage-specific changes in chicken BW, thus providing important resources for genomic selection in breeding programs.

Brain shapes of large-bodied, flightless ratites (Aves: Palaeognathae) emerge through distinct developmental allometries

Comparative neuroanatomical studies have long debated the role of development in the evolution of novel and disparate brain morphologies. Historically, these studies have emphasized whether evolutionary shifts along conserved or distinct developmental allometric trends cause changes in brain morphologies. However, the degree to which interspecific differences between variably sized taxa originate through modifying developmental allometry remains largely untested. Taxa with disparate brain shapes and sizes thus allow for investigation into how developmental trends contribute to neuroanatomical diversification. Here, we examine a developmental series of large-bodied ratite birds (approx. 60-140 kg). We use three-dimensional geometric morphometrics on cephalic endocasts of common ostriches, emus and southern cassowaries and compare their developmental trajectories with those of the more modestly sized domestic chicken, previously shown to be in the same allometric grade as ratites. The results suggest that ratites and chickens exhibit disparate endocranial shapes not simply accounted for by their size differences. When shape and age are examined, chickens partly exhibit more accelerated and mature brain shapes than ratites of similar size and age. Taken together, our study indicates that disparate brain shapes between these differently sized taxa have emerged from the evolution of distinct developmental allometries, rather than simply following conserved scaling trends.

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

The avian class is characterized by particularly strong variability in their domesticated species. With more than 250 breeds and highly efficient commercial lines, domestic chickens represent the outcome of a really long period of artificial selection. One characteristic of domestication is the alterations in brain size and brain composition. The influence of domestication on brain morphology has been reviewed in the past, but mostly with a focus on mammals. Studies on avian species have seldom been taken into account. In this review, we would like to give an overview about the changes and variations in (brain) morphology and behavior in the domestic chicken, taking into consideration the constraints of evolutionary theory and the sense or nonsense of excessive artificial selection.