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Sika deer are known to prefer oak leaves, which are rich in tannins and toxic to most mammals; however, the genetic mechanisms underlying their unique ability to adapt to living in the jungle are still unclear. In identifying the mechanism responsible for the tolerance of a highly toxic diet, we have made a major advancement by explaining the genome of sika deer. We generated the first high-quality, chromosome-level genome assembly of sika deer and measured the correlation between tannin intake and RNA expression in 15 tissues through 180 experiments. Comparative genome analyses showed that the UGT and CYP gene families are functionally involved in the adaptation of sika deer to high-tannin food, especially the expansion of the UGT family 2 subfamily B of UGT genes. The first chromosome-level assembly and genetic characterization of the tolerance to a highly toxic diet suggest that the sika deer genome may serve as an essential resource for understanding evolutionary events and tannin adaptation. Our study provides a paradigm of comparative expressive genomics that can be applied to the study of unique biological features in non-model animals.

Abstract Background Previous investigations of phylogeny in Cervus recovered many clades without whole genomic support. Methods In this study, the genetic diversity and phylogeny of 5 species (21 subspecies/populations from C. unicolor, C. albirostris, C. nippon, C. elaphus and C. eldii) in the genus Cervus were analyzed using reduced-representation genome sequencing. Results A total of 197,543 SNPs were identified with an average sequencing depth of 16 x. A total of 21 SNP matrices for each subspecies/population and 1 matrix for individual analysis were constructed, respectively. Nucleotide diversity and heterozygosity analysis showed that all 21 subspecies/populations had different degrees of genetic diversity. C. eldii, C. unicolor and C. albirostris showed relatively high expected and observed heterozygosity, while observed heterozygosity in C. nippon was the lowest, indicating there was a certain degree of inbreeding rate in these subspecies/populations. Phylogenetic ML tree of all Cervus based on the 21 SNP matrices showed 5 robustly supported clades that clearly separate C. eldii, C. unicolor, C. albirostris, C. elaphus and C. nippon. Within C. elaphus clade, 4 subclades were well differentiated and statistically highly supported: C. elaphus (New Zealand), C. e. yarkandensis, C. c. canadensis and the other grouping the rest of C. canadensis from China. In the C. nippon clade, 2 well-distinct subclades corresponding to C. n. aplodontus and other C. nippon populations were separated. Phylogenetic reconstruction indicated that the first evolutionary event of the genus Cervus occurred approximately 7.4 millions of years ago. The split between C. elaphus and C. nippon could be estimated at around 3.6 millions of years ago. Phylogenetic ML tree of all samples based on individual SNP matrices, together with geographic distribution, have shown that there were 3 major subclades of C. elaphus and C. canadensis in China, namely C. e. yarkandensis (distributed in Tarim Basin), C. c. macneilli/C. c. kansuensis/C. c. alashanicus (distributed in middle west of China), and C. c. songaricus/C. c. sibiricus (distributed in northwest of China). Among them, C. e. yarkandensis was molecularly the most primitive subclade, with a differentiation dating back to 0.8–2.2 Myr ago. D statistical analysis showed that there was high probability of interspecific gene exchange between C. albirostris and C. eldii, C. albirostris and C. unicolor, C. nippon and C. unicolor, and there might be 2 migration events among 5 species in the genus Cervus. Conclusions Our results provided new insight to the genetic diversity and phylogeny of Cervus deer. In view of the current status of these populations, their conservation category will need to be reassessed.

The present study examined the effects of dietary vitamin A (VA) on antioxidant functions, immune functions and production performance in farmed sika deer. Forty healthy male sika deer (initial body weight (BW): 47.07 ± 4.75 kg; 8 months of age) were randomly assigned to four treatments on the basis of BW. The dietary treatments included a basal diet (containing 330 U/kg VA) supplemented with 0 (control), 2500, 5000 or 10,000 U/kg retinol acetate (500,000 U/g, Rovimix A500, Roche, Basel, Switzerland). The results showed that deer fed a diet supplemented with 5000 U/kg VA had higher (p