Abstract
Simple SummaryThe reindeer (Rangifer tarandus) is a unique ruminant that lives in arctic areas characterized by severe living conditions. Low temperatures and a scarce diet containing a high proportion of hard-to-digest components have contributed to the development of several adaptations that allow reindeer to have a successful existence in the Far North region. These adaptations include the microbiome of the rumen—a digestive organ in ruminants that is responsible for crude fiber digestion through the enzymatic activity of microorganisms. In this study, research was conducted on the ruminal microbiome of reindeer of the Nenets breed living in various climatic zones of the Russian Arctic (in the Yamalo-Nenetski Autonomous District and Nenetski Autonomous District. The impacts of the habitat, season of the year, sex, and age factors on the rumen microbiome were investigated. As a result, it was found that significant differences in the reindeer ruminal microbiome composition are associated with the region of habitat and change of seasons that the reindeer are exposed to. The distinctions mainly come down to different ratios of bacteria involved in the metabolism of volatile fatty acids and cellulose decomposition in the rumen, which is apparently a reflection of the different plant components in the diet in different regions and seasons.The reindeer (Rangifer tarandus L.) is a unique animal inhabitant of arctic regions. Low ambient temperatures and scant diets (primarily, lichens) have resulted in different evolutional adaptations, including the composition of the ruminal microbiota. In the study presented here, the effects of seasonal and regional aspects of the composition of the ruminal microbiota in reindeer (Nenets breed, 38 animals) were studied (wooded tundra from the Yamalo-Nenetski Autonomous District (YNAD) vs. from the Nenetski Autonomous District (NAD)). The ruminal content of calves (n = 12) and adult animals (n = 26, 15 males and 11 females) was sampled in the summer (n = 16) and winter seasons (n = 22). The composition of the ruminal microbial population was determined by the V3–V4 16S rRNA gene region sequencing. It was found that the population was dominated by Bacteroidetes and Firmicutes phyla, followed by Spirochaetes and Verrucomicrobia. An analysis of the community using non-metric multidimensional scaling and Bray–Curtis similarity metrics provided evidence that the most influential factors affecting the composition of ruminal microbiota are the region (p = 0.001) and season (p = 0.001); heat map analysis revealed several communities that are strongly affected by these two factors. In the summer season, the following communities were significantly larger compared to in the winter season: Coriobactriaceae, Erysipelothrihaceae, and Mycoplasmataceae. The following communities were significantly larger in the winter season compared to in summer: Paraprevotellaceae, Butyrivibrio spp., Succiniclasticum spp., Coprococcus spp., Ruminococcus spp., and Pseudobutyrivibrio spp. In NAD (tundra), the following communities were significantly larger in comparison to YNAD (wooded tundra): Verrucomicrobia (Verruco-5), Anaerolinaceae, PeHg47 Planctomycetes, cellulolytic Lachnospiraceae, and Succiniclasticum spp. The following bacterial groups were significantly larger in YNAD in comparison to NAD: cellulolytic Ruminococaceae, Dehalobacteriaceae, Veillionelaceae, and Oscilospira spp. The significant differences in the ruminal microbial population were primarily related to the ingredients of diets, affected by region and season. The summer-related increases in the communities of certain pathogens (Mycoplasmataceae, Fusobacterium spp., Porphyromonas endodentalis) were found. Regional differences were primarily related to the ratio of the species involved in ruminal cellulose degradation and ruminal fatty acids metabolism; these differences reflect the regional dissimilarities in botanical diet ingredients.
Highlights
The reindeer (Rangifer tarandus L.) is a unique ruminant that inhabits climatically severe arctic regions
The ruminal content of calves (4–8 months of age, n = 12) and adult (2–8 years of age, n = 26, 15 males and 11 females) reindeer (Nenets breed, total 38 animals) in the summer–autumn (n = 16) and winter–spring seasons (n = 22) of 2017–2018 was collected. This included 18 animals from the Yamalo-Nenetski Autonomous District (YNAD), including 6 samples collected in summer and 12 in winter, and 20 from the Nenetski Autonomous District (NAD), including 10 samples collected in summer and 10 in the winter season (Figure 1, Supplementary Table S1)
The sequencing of the 16S rRNA gene in the collected samples resulted in 1,058,032 sequences of acceptable quality, an average of 25,687 reads per sample
Summary
The reindeer (Rangifer tarandus L.) is a unique ruminant that inhabits climatically severe arctic regions. The geographic isolation of reindeer from other Cervidae ruminants, in combination with the specific environmental conditions present, has resulted in certain morphologic and functional adaptations in the digestive system [4,5,6], including the specific microbial population of the rumen. The rumen is a digestive organ in ruminants where the major degradation of complex polysaccharides from botanical diet ingredients occurs through enzymatic systems of the symbiotic microbial population [7,8,9]. The composition of the ruminal microbiota can be affected by different biotic and/or abiotic factors. Biotic factors include the diet composition, feed additives, genetics, and physiological status of the host organism (age, health).
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