Genome-wide analysis sheds light on the high-altitude adaptation of the buff-throated partridge (Tetraophasis szechenyii).

The buff-throated partridge (Tetraophasis szechenyii) is a hypoxia-tolerant bird living in an extremely inhospitable high-altitude environment, which has high ultraviolet (UV) radiation as well as a low oxygen supply when compared with low-altitude areas. To further understand the molecular genetic mechanisms of the high-altitude adaptation of the buff-throated partridges, we de novo assembled the complete genome of the buff-throated partridge. Comparative genomics revealed that positively selected hypoxia-related genes in the buff-throated partridge were distributed in the HIF-1 signaling pathway (map04066), response to hypoxia (GO:0001666), response to oxygen-containing compound (GO:1901700), ATP binding (GO:0005524), and angiogenesis (GO:0001525). Of these positively selected hypoxia-related genes, one positively selected gene (LONP1) had one buff-throated partridge-specific missense mutation which was classified as deleterious by PolyPhen-2. Moreover, positively selected genes in the buff-throated partridge were enriched in cellular response to DNA damage stimulus (corrected P value: 0.028006) and DNA repair (corrected P value: 0.044549), which was related to the increased exposure of the buff-throated partridge to UV radiation. Compared with other avian genomes, the buff-throated partridge showed expansion in genes associated with steroid hormone receptor activity and contractions in genes related to immune and olfactory perception. Furthermore, comparisons between the buff-throated partridge genome and red junglefowl genome revealed a conserved genome structure and provided strong evidence of the sibling relationship between Tetraophasis and Lophophorus. Our data and analysis contributed to the study of Phasianidae evolutionary history and provided new insights into the potential adaptation mechanisms to the high altitude employed by the buff-throated partridge.

Genomic evidence sheds light on the genetic mechanisms of musk secretion in muskrats.

Adult male muskrat (Ondatra zibethicus) has a pair of scent glands which secret musk to attract females during the breeding stage. The goal of the present study was to investigate the genetic mechanisms of musk secretion of muskrats at the whole genome level. Comparative genomics illustrated obvious expansion in 809 gene families, of which nine gene families played pivotal roles in steroid biosynthesis, possibly related to muskrat musk secretion. We identified 1112 positively selected genes (PSGs) in the muskrat, including estrogen receptor 1 (ER1), an important influencing factor to the weight and size of the scented glands of muskrats. HSD17B3, HSD17B4, CYP7B1 and CYP17B1, crucial to steroid hormone biosynthesis, were under strong positive selection in the muskrat, and phylogenetic analysis of HSD and CYP450 classes revealed high gene diversity. Functional enrichment revealed many pathways associated with musk secretion and/or growth and degeneration of scented gland significantly, such as peroxisome, PI3K-Akt signaling pathway, apoptosis, and prostate cancer. Two muskrat-specific missense mutations (Pro237Thr and Ser297Ile) were detected in LIPC, which were reported to be involved cholesterol metabolic process. More importantly, the missense mutations discovered in LIPC were classified as deleterious by PolyPhen-2, possibly affecting the musk secretion of muskrats.

Comparative genomics sheds light on the predatory lifestyle of accipitrids and owls.

Raptors are carnivorous birds including accipitrids (Accipitridae, Accipitriformes) and owls (Strigiformes), which are diurnal and nocturnal, respectively. To examine the evolutionary basis of adaptations to different light cycles and hunting behavior between accipitrids and owls, we de novo assembled besra (Accipiter virgatus, Accipitridae, Accipitriformes) and oriental scops owl (Otus sunia, Strigidae, Strigiformes) draft genomes. Comparative genomics demonstrated four PSGs (positively selected genes) (XRCC5, PRIMPOL, MDM2, and SIRT1) related to the response to ultraviolet (UV) radiation in accipitrids, and one PSG (ALCAM) associated with retina development in owls, which was consistent with their respective diurnal/nocturnal predatory lifestyles. We identified five accipitrid-specific and two owl-specific missense mutations and most of which were predicted to affect the protein function by PolyPhen-2. Genome comparison showed the diversification of raptor olfactory receptor repertoires, which may reflect an important role of olfaction in their predatory lifestyle. Comparison of TAS2R gene (i.e. linked to tasting bitterness) number in birds with different dietary lifestyles suggested that dietary toxins were a major selective force shaping the diversity of TAS2R repertoires. Fewer TAS2R genes in raptors reflected their carnivorous diet, since animal tissues are less likely to contain toxins than plant material. Our data and findings provide valuable genomic resources for studying the genetic mechanisms of raptors' environmental adaptation, particularly olfaction, nocturnality and response to UV radiation.

Comparative Genomics Reveals the Genetic Mechanisms of Musk Secretion and Adaptive Immunity in Chinese Forest Musk Deer.

The Chinese forest musk deer (Moschus berezovskii; FMD) is an artiodactyl mammal and is both economically valuable and highly endangered. To investigate the genetic mechanisms of musk secretion and adaptive immunity in FMD, we compared its genome to nine other artiodactyl genomes. Comparative genomics demonstrated that eight positively selected genes (PSGs) in FMD were annotated in three KEGG pathways that were related to metabolic and synthetic activity of musk, similar to previous transcriptome studies. Functional enrichment analysis indicated that many PSGs were involved in the regulation of immune system processes, implying important reorganization of the immune system in FMD. FMD-specific missense mutations were found in two PSGs (MHC class II antigen DRA and ADA) that were classified as deleterious by PolyPhen-2, possibly contributing to immune adaptation to infectious diseases. Functional assessment showed that the FMD-specific mutation enhanced the ADA activity, which was likely to strengthen the immune defense against pathogenic invasion. Single nucleotide polymorphism-based inference showed the recent demographic trajectory for FMD. Our data and findings provide valuable genomic resources not only for studying the genetic mechanisms of musk secretion and adaptive immunity, but also for facilitating more effective management of the captive breeding programs for this endangered species.