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International Journal of Molecular Zoology 2025, Vol.15, No.1 http://animalscipublisher.com/index.php/ijmz © 2025 AnimalSci Publisher, registered at the publishing platform that is operated by Sophia Publishing Group, founded in British Columbia of Canada. All Rights Reserved. Publisher AnimalSci Publisher Editedby Editorial Team of International Journal of Molecular Zoology Email: edit@ijmz.animalscipublisher.com Website: http://animalscipublisher.com/index.php/ijmz Address: 11388 Stevenston Hwy, PO Box 96016, Richmond, V7A 5J5, British Columbia Canada International Journal of Molecular Zoology (ISSN 1927-534X) is an open access, peer reviewed journal published online by AnimalSci Publisher. The journal is publishing all the latest and outstanding research articles, letters and reviews in all aspects of molecular zoology, containing behavior, structure, evolution, classification, habits and distribution of animals, also including the relative fields on embryology, developmental biology, systematics, genetics and genomics, ecology, physiology, as well as biochemistry. Meanwhile we also publish the articles related to basic research, such as anatomy, morphology and taxonomy, which are fundamental to molecular technique’s innovation and development. AnimalSci Publisher is an international Open Access publisher specializing in animal molecular breeding, including molecular zoology and relative fields registered at the publishing platform that is operated by Sophia Publishing Group (SPG), founded in British Columbia of Canada. All the articles published in International Journal of Molecular Zoology are Open Access, and are distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. AnimalSci Publisher uses CrossCheck service to identify academic plagiarism through the world’s leading plagiarism prevention tool, iParadigms, and to protect the original authors’ copyrights.
International Journal of Molecular Zoology (online), 2025, Vol. 15, No.1 ISSN 1927-534X http://animalscipublisher.com/index.php/ijmz © 2025 AnimalSci Publisher, registered at the publishing platform that is operated by Sophia Publishing Group, founded in British Columbia of Canada. All Rights Reserved. Latest Content The Hidden Complexity of Capra Evolution: A Multi-Layered Phylogenomic Reconstruction Using Chromosome-Level Assemblies Xiaofang Lin, Xuming Lü International Journal of Molecular Zoology, 2025, Vol. 15, No. 1, 1-9 Transcriptomic and Metabolomic Analysis of Feed Efficiency in Chickens Xinghao Li, Jia Xuan International Journal of Molecular Zoology, 2025, Vol. 15, No. 1, 10-19 Advances in the Genetic Regulation of Feather Coloration in Domestic Geese: From Candidate Genes to Functional Genomics Jingya Li, Mengyue Chen International Journal of Molecular Zoology, 2025, Vol. 15, No. 1, 20-28 Advances in Artificial Breeding and Genomic Selection of Channa spp. Yue Zhu, Jinni Wu International Journal of Molecular Zoology, 2025, Vol. 15, No. 1, 29-37 Genetic Regulation of Fast Growth Traits and Genomic Selection for Breeding in Groupers Chengmin Sun, Rudi Mai International Journal of Molecular Zoology, 2025, Vol. 15, No. 1, 38-47
International Journal of Molecular Zoology, 2025, Vol.15, No.1, 1-9 http://animalscipublisher.com/index.php/ijmz 1 Research Insights Open Access The Hidden Complexity of Capra Evolution: A Multi-Layered Phylogenomic Reconstruction Using Chromosome-Level Assemblies Xiaofang Lin 1 , XumingLü2 1 Tropical Animal Medicine Research Center, Hainan Institute of Tropical Agricultural Resources, Sanya, 572025, Hainan, China 2 Institute of Life Science, Jiyang College of Zhejiang A&F University, Zhuji, 311800, Zhejiang, China Corresponding author: xiaofang.lin@hitar.org International Journal of Molecular Zoology, 2025, Vol.15, No.1 doi: 10.5376/ijmz.2025.15.0001 Received: 24 Nov., 2024 Accepted: 30 Dec., 2024 Published: 10 Jan., 2025 Copyright © 2025 Lin and Lü, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Lin X.F., and Lü X.M.., 2025, The hidden complexity of capra evolution: a multi-layered phylogenomic reconstruction using chromosome-level assemblies, International Journal of Molecular Zoology, 15(1): 1-9 (doi: 10.5376/ijmz.2025.15.0001) Abstract Capra species vary extensively in body shape, habitat, and chromosome structure. Yet, their evolutionary histories have been hard to establish. This study uses high-quality chromosome-level genome data of some of the most important Capra species to investigate their evolutionary history. The study combines multiple sources of information. It involves phylogenetic analysis, comparison between gene trees and species trees, testing for gene flow between species, and analysis of chromosome structural changes. The results show that gene trees are not concordant with the species tree in general. It is likely to be a result of incomplete lineage sorting and hybridization among species in the past. Genes transferred between Capra lineages were also found in the research. Several chromosome rearrangements were discovered, as well as gene family changes implicated in basic biological processes. These changes could have been central to the mechanisms by which new species arose. The scientists also compared the formation of key biological pathways-like those for immunity and metabolism—in both species based on multi-omics data. In all, the research more clearly describes the interrelationship among Capra species and introduces new ideas of chromosome evolution and new mammal species emergence. Keywords Genus Capra; Phylogeny; Chromosomal rearrangement; Gene introgression; Chromosome-level genome assembly 1 Introduction The genus Capra includes mountainous animals in the Bovidae family and Caprinae subfamily. It contains wild and domesticated animals. They are known for their survival in harsh environments, different horn shapes in males and females, and well-developed ruminant digestive systems. Because of their success in harsh, low-resource environments, Capra species are ideal examples from which to learn about animal adaptation to mountains, the domestication process, and new species formation. It contains nine or more known species, including the Alpine ibex (Capra ibex), the wild goat (Capra aegagrus), the markhor (Capra falconeri), and the domestic goat (Capra hircus). They are found in parts of Europe, North Africa, the Middle East, and across Asia (Zhou et al., 2019). The wild species have limited, fragmented populations due to geography and specialized habitat needs. At the same time, domestic goats—originating from C. aegagrus-exist almost everywhere now because of human spread. These ecological and geographical differences together render it interesting and complicated to look into how all these species are related (Gippoliti and Robovský, 2018). Previous studies to investigate the evolution of Capra were not straightforward. They were largely based on fragmented genetic data, tiny samples, and mostly mitochondrial or low-resolution nuclear DNA. As such, the resulting evolutionary trees naturally tended to disagree with each other. These disagreements were then further exacerbated by events including past hybridization, incomplete lineage sorting, and gene flow between species. Their interbreeding has also gone on unabated with the wild goats, thereby obliterating species lines and also complicating their evolutionary history (Lin et al., 2023; Wang et al., 2023). To address these concerns, the current research employs well-constructed assembled chromosome-level genomes of different Capra species. Whole genomes account for a better understanding of how the species had evolved.
International Journal of Molecular Zoology, 2025, Vol.15, No.1, 1-9 http://animalscipublisher.com/index.php/ijmz 2 The study analyzes genome structure diversity, gene flow in the past between the species, and chromosomal rearrangements that may have resulted in their divergence. The study reveals the complex interaction of the genus Capra and presents new ideas about the genetic alterations that are accountable for their fast evolution and adaptation. 2 Chromosome-Level Genome Assembly and Analytical Methods Next-generation sequencing technologies and bioinformatics tools now make it possible to produce high-quality chromosome-level genome assemblies. Such a complete genome is required in order to study the evolutionary process and genetic variation within the genus Capra. 2.1 Sample selection and sequencing strategies Good-quality assemblies of the genome must be created using good-quality samples and proper sequencing technologies. Long-read sequencing technologies like PacBio and Oxford Nanopore are widely used because they possess the ability to resolve complicated parts of the Capra genome (Shirasawa et al., 2021; Sperling et al., 2024). Short-read information is typically combined with the long reads such that errors are complemented and assembly quality is improved. In addition, Hi-C sequencing is useful in the capture of the 3D genome architecture. It uncovers the interaction mode of different parts of DNA, thus assisting in the bridging of breaks and improving assembly overall (Ghurye et al., 2018). 2.2 Assembly workflow and quality evaluation of chromosome-level genomes Genome assembly is a sequence of several significant steps: assembling contigs into chromosomes and correcting errors. Many of these processes are done automatically using software like AutoHiC and Chrom-pro. They utilize Hi-C reads and deep learning to enhance continuity in the genome and reduce error (Jiang et al., 2023; Jiang et al., 2024). Genome integrity is also verified at the conclusion of assembly by such methods as BUSCO scores evaluating the percentage of predicted genes and reference genome comparison as a quality control to ensure structural accuracy. 2.3 Identification of orthologous genes and construction of phylogenomic datasets To study the relationship between Capra species, researchers look for orthologous genes-genes with a common ancestor. For that, they compare genomes of different species and detect homologous gene sequences (Kolmogorov et al., 2016; Kolmogorov et al., 2018). Researchers, having discovered those common genes, utilize them to build phylogenomic datasets. These datasets are used to reconstruct the evolutionary history of the Capra genus (Shirasawa et al., 2021). 2.4 Genome alignment and detection of chromosomal rearrangements Genome alignment is an indispensable task for identifying the chromosomal rearrangements, which is vital in understanding the evolutionary mechanisms of the Capra genome. Reference-assisted assemblers such as Ragout2 can be utilized to align the reference genome with the target genome and therefore identify large-scale chromosomal structural rearrangement events (Kolmogorov et al., 2016; Kolmogorov et al., 2018). Hi-C data also assists in confirming these rearranged events and provides more comprehensive structural information. Detection of such structural variation is of tremendous value to reveal the complex mechanisms in Capragenome evolution. 2.5 Gene tree-species tree reconciliation and introgression detection approaches Gene tree-species tree reconciliation helps in the resolution of gene tree-species tree conflict. Such conflicts often arise due to events like gene duplications or gene losses. By aligning and comparing such trees, researchers can build more accurate phylogenies. Detection of introgression is another important method that is used to identify evidence of gene flow among species. When genes move between species, they can make it harder to see obvious evolutionary relationships. These techniques are especially important to use to study Capra, whose gene transfers in the past have made its evolutionary history difficult. All together, these methods help show howCapra species are related and how their genomes came to be over time (Yang, 2024).
International Journal of Molecular Zoology, 2025, Vol.15, No.1, 1-9 http://animalscipublisher.com/index.php/ijmz 3 3 Phylogenetic Reconstruction and Evolutionary Patterns inCapra The phylogenetic past of Capra is one that involves solving gene tree conflict using advanced methods that account for ILS and introgression. These processes cause the reticulate evolutionary patterns observed in Capra, hence the necessity of using comprehensive phylogenomic analysis to untangle its complex evolutionary history. 3.1 Phylogenetic tree construction using multiple methods For the construction of phylogenetic trees for Capra species, scientists prefer to utilize combinations of methods such as maximum likelihood (ML), Bayesian inference, and coalescent methods. These allow for full depiction of the relationships of the species through the consideration of more than a single source of information as well as variability. ML and Bayesian methods can deal with large-scale genomics and also produce large-resolution trees. Coalescent methods come in handy in such cases of ILS cases and gene tree-mismatching scenarios-scenarios common in rapidly evolving lineages (Figure 1) (Morales‐Briones et al., 2020; Meleshko et al., 2021; Wang et al., 2023; Herrig et al., 2024). Figure 1 Phylogenetic tree of Capra(Adopted from Wang et al., 2023) Image caption: The colored circles (A-E) correspond to the evolutionary branches A-E in the phylogenetic tree (Adopted from Wang et al., 2023) 3.2 Gene tree discordance and analysis of incomplete lineage sorting (ILS) Gene tree discordance is a common scenario in systematic genomics inference, primarily induced by factors like incomplete lineage sorting (ILS) and hybridization. In the genus Capra, ILS has the potential to cause divergent genomic regions bearing contradictory phylogenetic signals and making it challenging to reconstruct truthful germline trees. This has been through the development of software such as Phytop to measure and visualize the amount of ILS hybridization to facilitate identification of phylogenetic uncertainty as well as elucidation of the evolutionary history of complicated lineages (Morales‐Briones et al., 2020; Shang et al., 2024). A profound understanding of the impact of ILS is the remedy for addressing gene tree conflict and the improvement of phylogenetic inference accuracy (Hibbins et al., 2020). 3.3 Genome-wide evidence of introgression and historical hybridization Wen et al. (2016) found that historical infiltration and hybridization played a pivotal role in evolutionary history within the genus Capra. Genome-wide phylogenetic comparison reveals that infiltration can lead to the loss of the species' phylogenetic boundary, and the phenomenon also often occurs in oak tree and mosquito clades. On the one hand, they facilitate the accumulation of genetic diversity, and on the other hand, they are a reticular complex
International Journal of Molecular Zoology, 2025, Vol.15, No.1, 1-9 http://animalscipublisher.com/index.php/ijmz 4 pattern of evolution that is most accurately described by a phylogenetic network model taking into account both ILS and infiltration (Tomasco et al., 2022; Herrig et al., 2024). 3.4 Signals of reticulate evolution and lineage divergence withinCapra Reticular evolution is an impressive feature of Capra evolution. Its typical manifestations include hybridization and invasion and species lineages branching away from the traditional dityping branch system. Phylogenetic network analysis is able to better characterize such a multi-faceted evolutionary process by taking into account multiple hybridization events as well as gene flows among lineages (Wen et al., 2016; McLay et al., 2023). Such work is of particular interest for the recognition of complex evolutionary processes in the Capra genus as well as for studies of the ancient phylogenetic history concealed by gene tree discordance and hybridization (McLay et al., 2023; Herrig et al., 2024). 4 Chromosomal Structural Variation and Its Role in Lineage Divergence 4.1 Detection and classification of chromosomal rearrangement events Chromosomal rearrangements-translocations, inversions, fusions, and fissions-would have been significant contributors over the time span to the evolution of Capra species and reshaping their genomes. Scientists in this study compared chromosome-level genomes of different Capra species (C. hircus, C. aegagrus, C. ibex, and C. falconeri) by whole-genome alignment. They also utilized Hi-C data and tools like Ragout2 and SyRI for ordering and detecting a collection of chromosomal rearrangements (Meyer et al., 2024). It was noted from the results that different rearrangements were found to take place in only a few species. C. ibex, for example, had inversions that can facilitate it to be adapted to mountain high life. Such structural rearrangements can divide areas of the genome where gene order is usually alike and can also affect gene regulation in the form of gene switching on and off. They can also inhibit recombination, which ties together helpful combinations of genes—a factor that would result in local adaptation. Finally, chromosomal rearrangements need to have been a key role in the generation of new Capra species and their colonization into new habitats. These results inform us about the ways in which evolutionary innovations are generated by structural rearrangements of genomes in very rapidly evolving species (Watson et al., 2021). 4.2 Effects of chromosomal structural variation on gene expression and adaptation Chromosomal structural variations (SVs) are among the primary factors that enable animals like Capra to evolve and evolve. Such types of change-whether inversions, translocations, or other rearrangements-can affect the function of genes by rearranging 3D genome architecture and disrupting needed control regions (Ruggieri et al., 2022). SVs, for example, can change a gene's number of copies or affect the compactness of DNA. This can turn some of the genes on and off in various ways, allowing animals to survive in other environments. Inversions are a form of SV that repress recombination in regions of the genome. This does not allow good combinations of genes to be disrupted, which allows local adaptation. By preserving good traits, these alterations allow species to adapt faster to their environment. SVs also impact gene function across the whole genome, not a small place. These extreme changes can produce new traits and help in the creation of new species by introducing diversity and flexibility. Generally, SVs significantly impact gene function and are one of the main reasons that have contributed to the great development of Capraspecies (Xuan, 2024). 4.3 The role of chromosomal evolution in speciation processes Chromosomal evolution is one of the major mechanisms that bring about new species development. It does so by helping to form reproductive barriers. An example of this happening includes in Raphicerus antelope, where X chromosomal differentiation, through differentiation of certain regions of the DNA, has the potential to form sterile hybrid females. This is contrary to prior hypotheses such as Haldane's rule (Robinson et al., 2021). In yet another example, the long-snouted seahorse shows how chromosome inversions can isolate certain sets of genes from one another. This is so that they do not interbreed and new species emerge (Meyer et al., 2024). These examples show how chromosome changes isolate genes from flowing and are some of the principal drivers of speciation.
International Journal of Molecular Zoology, 2025, Vol.15, No.1, 1-9 http://animalscipublisher.com/index.php/ijmz 5 4.4 Cross-species synteny and evolutionary relationships Cross-species synteny analysis is a great tool for genome evolution and studying relationships between Capra species. The authors of this paper compared chromosome-level genomes in some key species-Capra hircus, C. aegagrus, C. ibex, and C. falconeri. The researchers identified most parts of the genome to be in the same place between the species, i.e., syntenic blocks. Special structural adaptations were, however, made for some special species. Capra hircus and its relative C. aegagrus had nearly identical genomes, reflecting how closely they are related. While C. ibex and C. falconeri also had more changes, like inversions and chromosome fusion. These kinds of changes may be responsible for particular adaptation to environment or to reproductive isolation. These structural differences were most of them found near sites where new species diverged, and what this implies is that they most likely contributed to the formation of new lineages of Capra. Synteny maps created in this study not only help track in which direction the Capra species evolved, but also detect emergent genome characteristics that arose because of their rapid growth (Tigano et al., 2021). 5 Multi-Omics Integration Reveals Functional Genetic Shifts in Evolution 5.1 Comparative genomics to identify key genes involved in evolutionary processes Comparative genomics is a powerful way to determine significant genes that contribute to evolution. By comparing the genomes of different species, scientists are able to identify functional genome elements and discover new genes or pathways that emerged during evolution. The mechanism works by analyzing genes conserved among species and looking at how they stayed the same or evolved. It helps researchers understand the ways species have adapted to the world around them. When genomic data is put together with other data from biology-such as from proteomics or metabolomics-it becomes easier to spot genes that have experienced positive selection. Such genes may have core roles in helping species survive and develop (Slodkowicz and Goldman, 2020). 5.2 Proteomics and metabolomics revealing mechanisms of adaptive evolution Proteomics and metabolomics are also important to unravel species adaptation over time. Proteins are the link between genes and traits and indicate how cells respond to genetic or environmental change (Zhang and Kuster, 2019). Combining proteomics with other data assets, scientists can build a more intricate understanding of how life systems function and provide new insights into how adaptation arises (Zhang and Kuster, 2019). Metabolomics, which examines small molecules in cells, can be important in portraying what metabolic pathways and gene alleles are required for specific adaptations in any species (Watanabe and Tohge, 2023). Together, these technologies show that metabolites and proteins play central roles in species transformation and evolution (Wörheide et al., 2021; Sanches et al., 2024). 5.3 Gene family expansion/contraction and their species-specific functions Gene family expansion and contraction are the natural process of how species gain distinguishing features. When some gene families expand or contract, it could be developing new functions to set the species up for adaptation. In plant biology, it has been seen that the sets of metabolic genes, i.e., sequentially duplicated ones (tandem duplicates), are linked with metabolic divergence and special features (Watanabe and Tohge, 2023). These gene alterations have a tendency to produce functions found in a particular species but not in others. This shows the plasticity and responsiveness of genomes to the forces of evolution. By employing the integration of several types of information-such as genomics, proteomics, and metabolomics-scientists can gain enhanced knowledge about how these gene alterations affect evolution (Yang et al., 2021). 5.4 Analysis of positively selected genes and ecological adaptation Gene analysis positive selection is extremely crucial to species ecological adaptability studies. Following the determination of some loci that underwent forward selection evolution, authors in Slodkowicz and Goldman et al. (2020) are able to relate genetic changes with phenotypic adaptation. Positive selection sites tend to be localized within functionally important regions of proteins, reflecting their significant role in adaptive evolution (Slodkowicz and Goldman, 2020). Integrated evolutionary and structural analysis helps reveal how species evolve
International Journal of Molecular Zoology, 2025, Vol.15, No.1, 1-9 http://animalscipublisher.com/index.php/ijmz 6 genetically against environmental stresses such as pathogens and heterogeneous substances (Slodkowicz and Goldman, 2020). Such approaches improve our understanding of the mechanisms of niche adaptation of species through genetic changes. 6 Emerging Technologies and Methodological Innovations inCapra Evolutionary Studies 6.1 Applications of RNA-seq and single-cell omics in immunity and development RNA sequencing, especially the application of single-cell RNA sequencing (scRNA-seq), has completely revolutionized the investigation of gene expression at the single-cell level, in an effort to deeply investigate the heterogeneity and developmental process of cells. Single-cell omics technology like scRNA-seq can profile expression divergence between single cells and is extremely crucial in understanding the immune system and developmental biology of the Capra species (Linnarsson and Teichmann, 2016; Yip et al., 2019). Joining scRNA-seq with additional omics strategies such as proteomics and epigenetics is capable of an end-to-end analysis of cellular function and condition and, as a result, an end-to-end investigation into developmental processes and immune responses (Stuart and Satija, 2019; Ahmed et al., 2022) (Figure 2). Similarly, such technology is feasible to identify the genes that have highly varying and extreme values among varied cells and consequently better understanding of Capra’s intricate processes (Yip et al., 2019). Figure 2 RNA sequencing and proteomics scatter plot (Adopted from Sanches et al., 2024) Image caption: A: High correlation between transcriptomics and proteomics data; B, C: Discrepancies between gene expression changes and protein level changes for certain genes/proteins. The 45-degree line in red dashed represents the theoretical correspondence, where changes in gene expression at the RNA-Seq level will on average reflect changes at the protein level (Adopted from Sanches et al., 2024) 6.2 Role of ancient dna techniques in reconstructing extinct Capralineages Ancient DNA (aDNA) techniques are also at the forefront of unraveling the evolutionary history of extinct Capra species. aDNA techniques enable researchers to recover and analyze DNA from fossilized bones and ancient skeletons, and with this, reconstruct past genetic diversity and dynamics for the species. Since there is overlap with other developing technologies like high-throughput sequencing, scientists can now recreate evolutionary pasts of extinct Capra species. They can also ascertain genetic characteristics that enabled certain species to survive—or why others went extinct (Yu et al., 2023). This not only increases our understanding of Capra evolution, but also helps us in finding good genetic markers which can be used for the protection of the current species that is present today. 6.3 High-throughput structural variation analysis and 3D genome technologies Sophisticated structural variation analysis and 3D genome techniques are now the main tools with which researchers investigate Capra evolution. The techniques enable researchers to see how the DNA is packed and organized within the nucleus. They also show how genomic structure variations influence how genes work and physical characteristics develop (Liu et al., 2023). Technologies in the process of development, like HiRES (which is a fusion of Hi-C and RNA sequencing), allow researchers to investigate at the same time the connection
International Journal of Molecular Zoology, 2025, Vol.15, No.1, 1-9 http://animalscipublisher.com/index.php/ijmz 7 between gene expression and DNA. Such data reveal how the genome evolves throughout development and the life of the animal (Liu et al., 2023). By linking genome structure with gene function, such technologies determine how structural variation is utilized to evolve Capra species. They assist in describing how such adaptations can create outstanding evolutionary characteristics. 7 Concluding Remarks The phylogeny of the history of the evolution of the Capragenus has been contentious for a long time, mainly due to the fact that different genetic markers provide different results. Current studies show huge difference between trees built from mitochondrial DNA (mtDNA) and trees built from Y-chromosome data. As an example, phylogenetic studies using Y-chromosome genes like AMELY and ZFY revealed two clades within Capra. One of the groups includes the domestic goat (Capra hircus), the wild goat (Capra aegagrus), and the markhor (C. falconeri), and this would mean that domestic goats could have originated from these wild ones. However, mtDNA analysis shows two groups as well, but the species in each group are not the same. This difference could be because of mtDNA introgression-where there was a transfer of mitochondrial genes between species many years ago. Chromosome-scale assemblies of genomes have turned out to be extremely useful for deconstructing the complex evolution of Capra species. Such high-quality genomes give exact details about DNA changes at the level of the entire chromosome. This enables scientists to build more accurate evolutionary trees. This accuracy becomes helpful when multiple genetic markers-e.g., mtDNA and Y-chromosome information-deliver conflicting data. Chromosome-scale assemblies can also detect gene flow and introgression between species, which can make evolutionary patterns more challenging to identify and track. Overall, these genome assemblies give scientists more powerful tools with which to study the history of relationship among Capraspecies and their evolution. Further studies into Capra evolution will need to move beyond the frontiers of constructing species trees and into the field of investigating gene interaction networks. This will also explain how genetic change comes into play to affect adaptation and evolution. By using chromosome-level genome assemblies and functional genomics data sets, researchers can map complex gene networks that direct evolution. These experiments have the capacity to illustrate how particular genetic changes make up phenotypic variety and enable Capra species to persist under varied habitats. Such an integrated process will provide a comprehensive idea about adaptation and speciation mechanisms within the genus Capra. Acknowledgments We thank the Animal Research team for support and assistance in data acquisition and data collection. Conflict of Interest Disclosure The authors affirm that this research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest. References Ahmed R., Zaman T., Chowdhury F., Mraiche F., Tariq M., Ahmad I., and Hasan A., 2022, Single-cell RNA sequencing with spatial transcriptomics of cancer tissues, International Journal of Molecular Sciences, 23(6): 3042. https://doi.org/10.3390/ijms23063042 Ghurye J., Rhie A., Walenz B., Schmitt A., Selvaraj S., Pop M., Phillippy A., and Koren S., 2018, Integrating Hi-C links with assembly graphs for chromosome-scale assembly, PLoS Computational Biology, 15(8): e1007273. https://doi.org/10.1371/journal.pcbi.1007273 Gippoliti S., and Robovský J., 2018, Lorenzo Camerano (1856-1917) and his contribution to large mammal phylogeny and taxonomy, with particular reference to the genera Capra, Rupicapra and Rangifer, Rendiconti Lincei. Scienze Fisiche e Naturali, 29: 443-451. https://doi.org/10.1007/s12210-018-0686-7 Herrig D.K., Ridenbaugh R.D., Vertacnik K.L., Everson K.M., Sim S.B., Geib S.M., Weisrock D.W., and Linnen C.R., 2024, Whole genomes reveal evolutionary relationships and mechanisms underlying gene-tree discordance in Neodiprion sawflies, Systematic Biology, 73(5): 839-860. https://doi.org/10.1093/sysbio/syae036
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International Journal of Molecular Zoology, 2025, Vol.15, No.1, 10-19 http://animalscipublisher.com/index.php/ijmz 10 Research Report Open Access Transcriptomic and Metabolomic Analysis of Feed Efficiency in Chickens Xinghao Li, Jia Xuan Institute of Life Sciences, Jiyang Colloge of Zhejiang A&F University, Zhuji, 311800, Zhejiang, China Corresponding author: jia.xuan@jicat.org International Journal of Molecular Zoology, 2025, Vol.15, No.1 doi: 10.5376/ijmz.2025.15.0002 Received: 10 Dec., 2024 Accepted: 14 Jan., 2025 Published: 24 Jan., 2025 Copyright © 2025 Li and Xuan, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Li X.H., and Xuan J., 2025, Transcriptomic and metabolomic analysis of feed efficiency in chickens, International Journal of Molecular Zoology, 15(1): 10-19 (doi: 10.5376/ijmz.2025.15.0002) Abstract Feed efficiency is an important trait in poultry breeding and farming. It is related to the utilization of resources and can also help farmers reduce costs. This study summarizes the application of transcriptomics and metabolomics in the research of chicken feed efficiency in recent years, and introduces the methods of multi-omics integration. These methods can help identify candidate genes and screen molecular markers, which are of great reference value for improving the feed conversion rate of poultry in the future, conducting molecular breeding and nutritional regulation. The results show that feed efficiency is influenced by many factors. In high-efficiency and low-efficiency chickens, the gene expression and metabolic products in the liver and intestines are different. Changes in fat and sugar metabolism, as well as the immune system, may be important ways to affect feed efficiency. This study aims to provide a reference framework for molecular improvement and nutritional intervention to enhance the conversion efficiency of poultry feed in the future. Keywords Feed efficiency; Transcriptomics; Metabolomics; Non-coding RNA; Multi-omics integration 1 Introduction Feed efficiency (FE) is a crucial trait in poultry production, which directly affects the profit of breeding. Because in some chicken breeds, feed costs can account for more than 70% of the total cost (Patience et al., 2015; Ye et al., 2024). Improving feed efficiency not only makes breeding more profitable, but also reduces the waste of resources and the discharge of manure, and is more environmentally friendly. Whether it is large-scale commercial breeding or small-scale breeding, improving feed efficiency has always been an important goal in breeding (Yi et al., 2015; Sinpru et al., 2021; Ruban and Danshyn, 2024). The genetic structure of feed efficiency is complex and the heritability is moderate. It is relatively difficult to improve this trait by traditional methods (Xiao et al., 2021; Ye et al., 2024). Feed efficiency is affected by many physiological processes, such as metabolism and immune response, etc. These processes involve many genes and interact with environmental factors, making the situation rather complex (Yang et al., 2020; Sinpru et al., 2021). Yi et al. (2015) and Ye et al. (2024) found that traditional breeding methods had low accuracy in discovering and utilizing these specific genes related to feed efficiency, which also slowed down the speed of genetic improvement. This study explored how the feed efficiency of chickens is regulated by genes through the integration of transcriptomics and metabolomics analysis, expounded the gene expression and metabolic pathways of high-efficiency and low-efficiency chickens, identified some key genes, regulatory RNAs, and important metabolic processes related to high feed efficiency. This study aims to establish a relatively complete molecular framework to facilitate more precise breeding plans in the future and also promote the genetic improvement of poultry feed efficiency. 2 Feed Efficiency Traits and Their Biological Complexity 2.1 Definitions and measurement approaches Poultry feed efficiency (FE) is mainly measured by two indicators: feed conversion rate (FCR) and residual feed intake (RFI). FCR refers to how much feed a chicken needs to consume for each additional kilogram of body
International Journal of Molecular Zoology, 2025, Vol.15, No.1, 10-19 http://animalscipublisher.com/index.php/ijmz 11 weight. This indicator reflects the efficiency of a chicken in converting feed into body weight. RFI is the difference between the actual feed consumed and the predicted feed needed. This indicator has little relation to growth rate and yield and is independent (Prakash et al., 2020). Both of these traits have certain heritability. The heritability of FCR is between 0.31 and 0.49, and that of RFI is between 0.42 and 0.52. This indicates that FE can be improved through selection and breeding. To measure these indicators, it is necessary to record the feed intake, weight changes, or egg production of each chicken over a period of time, and then calculate the values of these traits and the relationships among them using genetic and statistical models (Aggrey et al., 2010; Marchesi et al., 2021; Zhou et al., 2022). 2.2 Factors affecting FE in chickens Feed efficiency is influenced by factors such as genetics, physiology and nutrition, and the interaction among these factors is very complex. The genetic factors of the host play a significant role in the differences in feed efficiency, but the intestinal microbiota, especially the flora in the cecum, cannot be ignored either. Wen et al. (2021) and Zhou et al. (2022) found that the composition of cecal microbiota could explain up to 28% of the differences in RFI. The research by Wu et al. (2019) and Zampiga et al. (2021) indicates that the composition of the diet, such as energy and nutrient density, as well as the addition of additives like amino acids and minerals, can directly affect the absorption and utilization of feed, thereby enhancing feed efficiency. Dao et al. 's research in 2023 indicates that environmental factors, such as chicken coop conditions, management methods, and the use of kitchen waste as alternative feed, can also affect feed intake, digestibility, and health, thereby influencing feed efficiency. The interaction between genetics and diet can also regulate the intestinal flora and further affect feed efficiency (Wen et al., 2021; Bernard et al., 2024). 2.3 Physiological and molecular basis of FE variability Physiologically, factors such as digestive efficiency, nutrient absorption, metabolic level, and body composition (such as protein deposition and fat accumulation) all affect the feed efficiency of chickens (Aggrey et al., 2010; Tallentire et al., 2016). At the molecular level, genome-wide association studies (GWAS) identified many candidate genes and gene regions related to feed efficiency, such as ATRNL1, PIK3C2A, and SORCS3, which are involved in metabolic regulatory pathways (Figure 1) (Marchesi et al., 2021). The microbiota in the intestinal tract, especially some bacteria in the cecum and duodenum, can also affect energy acquisition, short-chain fatty acid production and nutrient absorption, thereby influencing feed efficiency (Wen et al., 2021; Zhou et al., 2022; Bernard et al., 2024). The research results of Wen et al. (2021) and Zhou et al. (2022) indicate that although the interaction between host genes and microorganisms is not strong, some specific bacterial classifications remain stable in chicken flocks with high feed efficiency, suggesting that they may have potential for utilization in breeding and microbial management. 3 Transcriptomic Approaches to Study Feed Efficiency 3.1 RNA-seq and gene expression profiling Zhou et al. (2015), Yang et al. (2020), and Xiao et al. (2021) conducted transcriptome comparisons in the mammary muscle, liver, duodenum, and adipose tissue of chickens with high and low feed efficiency, and discovered hundreds and thousands of differentially expressed genes (DEGs) related to feed efficiency. Yi et al. (2015) and Ye et al. (2024) found that quantitative RT-PCR was often used in these studies to verify the expression differences of some key genes to ensure the reliability of RNA-seq data. Some new sequencing techniques, such as 3’UTR-seq, have also discovered regulatory features like intron retention, which is helpful for understanding the transcriptional regulatory mechanisms related to feed efficiency (Wang et al., 2022). 3.2 Key biological pathways identified The genes related to mitochondrial function, oxidative phosphorylation and tricarboxylic acid cycle (TCA) in high-efficiency chickens are often upregulated, indicating that their energy metabolism capacity is stronger (Xiao et al., 2021; Yuan et al., 2024); but, the immune and inflammatory response pathways of low-efficiency chickens are often more active, which may imply that high immune system activity consumes energy and thereby affects
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