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The CYP8B1 gene is known to catalyse reactions that determine the ratio of primary bile salts 2 and the loss of this gene has recently been linked to lack of cholic acid in the bile of naked-2 mole rats, elephants and manatees using forward genomics approaches. We screened the 2 CYP8B1 gene sequence of more than 200 species and test for relaxation of selection along 3 each terminal branch. The need for retaining a functional copy of the CYP8B1 gene is 3 established by the presence of a conserved open reading frame across most species screened 3 in this study. Interestingly, the dietary switch from bovid to cetacean species is accompanied 3 by an exceptional ten amino-acid extension at the C-terminal end through a single base 3 frame-shift deletion. We also verify that the coding frame disrupting mutations previously 3 reported in the elephant are correct, are shared by extinct Elephantimorpha species and 3 coincide with the dietary switch to herbivory. Relaxation of selection in the CYP8B1 gene of 3 the wombat (Vombatus ursinus) also corresponds to drastic change in diet. In summary, our 3 forward genomics based screen of bird and mammal species identifies recurrent changes in 3 the selection landscape of the CYP8B1 gene concomitant with a change in dietary lipid 4 content.

3 1 established by the presence of a conserved open reading frame across most species screened 3 2 in this study. Interestingly, the dietary switch from bovid to cetacean species is accompanied 3 3by an exceptional ten amino-acid extension at the C-terminal end through a single base 3 4 frame-shift deletion. We also verify that the coding frame disrupting mutations previously 3 5 reported in the elephant are correct, are shared by extinct Elephantimorpha species and 3 6 coincide with the dietary switch to herbivory. Relaxation of selection in the CYP8B1 gene of 3 7 the wombat (Vombatus ursinus) also corresponds to drastic change in diet. In summary, our 3 8 forward genomics based screen of bird and mammal species identifies recurrent changes in 3 9 the selection landscape of the CYP8B1 gene concomitant with a change in dietary lipid 4 0 content. 4 1

Black-bone chicken (BBC) meat is popular for its distinctive taste and texture. A complex chromosomal rearrangement at the fibromelanosis (Fm) locus on the 20th chromosome results in increased endothelin-3 (EDN3) gene expression and is responsible for melanin hyperpigmentation in BBC. We use public long-read sequencing data of the Silkie breed to resolve high-confidence haplotypes at the Fm locus spanning both Dup1 and Dup2 regions and establish that the Fm_2 scenario is correct of the three possible scenarios of the complex chromosomal rearrangement. The relationship between Chinese and Korean BBC breeds with Kadaknath native to India is underexplored. Our data from whole-genome re-sequencing establish that all BBC breeds, including Kadaknath, share the complex chromosomal rearrangement junctions at the fibromelanosis (Fm) locus. We also identify two Fm locus proximal regions (∼70 Kb and ∼300 Kb) with signatures of selection unique to Kadaknath. These regions harbor several genes with protein-coding changes, with the bactericidal/permeability-increasing-protein-like gene having two Kadaknath-specific changes within protein domains. Our results indicate that protein-coding changes in the bactericidal/permeability-increasing-protein-like gene hitchhiked with the Fm locus in Kadaknath due to close physical linkage. Identifying this Fm locus proximal selective sweep sheds light on the genetic distinctiveness of Kadaknath compared to other BBC.

Skeletal muscle fibers rely upon either oxidative phosphorylation or the glycolytic pathway with much less reliance on oxidative phosphorylation to achieve muscular contractions that power mechanical movements. Species with energy-intensive adaptive traits that require sudden bursts of energy have a greater dependency on glycolytic fibers. Glycolytic fibers have decreased reliance on OXPHOS and lower mitochondrial content compared to oxidative fibers. Hence, we hypothesized that gene loss might have occurred within the OXPHOS pathway in lineages that largely depend on glycolytic fibers. The protein encoded by the COA1/MITRAC15 gene with conserved orthologs found in budding yeast to humans promotes mitochondrial translation. We show that gene disrupting mutations have accumulated within the COA1 gene in the cheetah, several species of galliform birds, and rodents. The genomic region containing COA1 is a well-established evolutionary breakpoint region in mammals. Careful inspection of genome assemblies of closely related species of rodents and marsupials suggests two independent COA1 gene loss events co-occurring with chromosomal rearrangements. Besides recurrent gene loss events, we document changes in COA1 exon structure in primates and felids. The detailed evolutionary history presented in this study reveals the intricate link between skeletal muscle fiber composition and the occasional dispensability of the chaperone-like role of the COA1 gene.

Small and midsize deletions and insertions (InDels) are major events that play a crucial role in the evolution of genome size and contribute to the genetic and phenotypic diversity of species. In recent years, considerable attention has been given to studying small indels associated with various developmental, growth, and production traits in domestic chicken breeds. Additionally, small and midsize indels have been studied between chicken and phylogenetically more distant species such as duck, turkey, rock pigeon, and other passerine birds. However, the investigation of small and midsize deletions in the wild relatives of chickens has been relatively overlooked until now. To address this gap, our study aimed to identify the presence and distribution of midsize deletions (> 1 Kb) in the wild relatives of chickens. We conducted a comparative genomic analysis using high-quality genomic data from four species belonging to the Gallus genus. Our analysis revealed the existence of more than 125 midsize deletions in the three other species compared to Gallus gallus (red junglefowl). These midsize deletions were found to be distributed in intergenic regions and within introns of various protein-coding genes but not in the exonic regions of protein-coding genes. Furthermore, we observed a trend between the number of midsize deletions and the phylogenetic distance in the phylogeny of the Gallus genus. The most ancestral species, Gallus varius (green junglefowl), exhibited the highest deletions, followed by Gallus lafayettii (Ceylon junglefowl) and Gallus sonneratii (grey junglefowl). Some protein-coding genes harboring deletions in their introns and upstream regions were associated with body development, production, growth traits, abdominal fat deposition, behavioral patterns such as stress, fear, anxiety, plumage color, and adaptation to extreme climatic conditions. Our study finds that the midsize deletions identified in wild relatives of red junglefowl contribute less than 1% of DNA loss with a rate of 8-44 Kb/My during the evolution of the Gallus genus.

Black-bone-chicken (BBC) breeds are famous for their distinctive meat texture and taste. However, the relationship between BBC breeds, especially the Kadaknath breed native to India, is poorly understood. Here, we establish that all BBC breeds, including Kadaknath, share a common complex chromosomal rearrangement at the FM locus on the 20th chromosome, which is responsible for the melanin hyperpigmentation throughout the body. While we find breed-specific gene flow between BBC and commercial breeds, the shared ancestry of all BBC breeds and pattern of isolation by distance suggest Kadaknath is closely related to Tibetan BBC. Interestingly, two FM locus proximal regions (~70Kb and ~300 Kb) have signatures of selection unique to Kadaknath. These regions harbor several genes with protein-coding changes, with the Bactericidal/permeability-increasing-protein-like (BPIL) gene having two Kadaknath-specific changes within the protein domains. The absence of these changes in other BBC breeds suggests this variation arose after the separation of these breeds. Our results indicate that the rearrangement at the FM locus and protein-coding changes in the BPIL gene were selected simultaneously in Kadaknath due to close physical linkage. The identification of this FM locus proximal selective sweep sheds light on the distinctiveness of Kadaknath compared to other BBC.