Topographic barriers drive the pronounced genetic subdivision of a range-limited fossorial rodent

Due to their limited dispersal ability, fossorial species with predominantly belowground activity usually show increased levels of population subdivision across relatively small spatial scales. This may be exacerbated in harsh mountain ecosystems, where landscape geomorphology limits species' dispersal ability and leads to small effective population sizes, making species relatively vulnerable to environmental change. To better understand the environmental drivers of species' population subdivision in remote mountain ecosystems, particularly in understudied high-elevation systems in Africa, we studied the giant root-rat (Tachyoryctes macrocephalus), a fossorial rodent confined to the afro-alpine ecosystem of the Bale Mountains in Ethiopia. Using mitochondrial and low-coverage nuclear genomes, we investigated 77 giant root-rat individuals sampled from nine localities across its entire ~1000 km2 range. Our data revealed a distinct division into a northern and southern group, with no signs of gene flow, and higher nuclear genetic diversity in the south. Landscape genetic analyses of the mitochondrial and nuclear genomes indicated that population subdivision was driven by slope and elevation differences of up to 500 m across escarpments separating the north and south, potentially reinforced by glaciation of the south during the Late Pleistocene (~42,000-16,000 years ago). Despite this landscape-scale subdivision between the north and south, weak geographic structuring of sampling localities within regions indicated gene flow across distances of at least 16 km at the local scale, suggesting high, aboveground mobility for relatively long distances. Our study highlights that despite the potential for local-scale gene flow in fossorial species, topographic barriers can result in pronounced genetic subdivision. These factors can reduce genetic variability, which should be considered when developing conservation strategies.

A Comparative Study on the Distribution Pattern of Endocrine Cells in the Gastrointestinal Tract of Two Small Alpine Mammals, Plateau Zokor (Eospalax baileyi) and Plateau Pika (Ochotona curzoniae)

Endocrine cells can secrete a variety of gastrointestinal hormones that regulate gastrointestinal digestion and absorption, which, in turn, play an important role in animal growth, metabolism, and acclimation. The small alpine mammals, plateau zokor (Eospalax baileyi) and plateau pika (Ochotona curzoniae), live in a unique ecotope with cold, hypoxic environments and short plant-growing seasons, resulting in differential adaptive digestive strategies for foods. Studying the distribution pattern of endocrine cells in the gastrointestinal tract (GIT) of these two animals can lead to a better understanding of the survival strategies of animals in an alpine environment. In this study, we used histochemical and immunohistochemical methods to compare the distribution pattern of argyrophilic cells and the expression of 5-HT cells, Gas cells, and Glu cells in the GIT of the plateau zokor with those of the plateau pika. The results showed that these endocrine cells we studied were widely distributed in the gastrointestinal organs of both these small mammals, and their morphology and distribution location in the GIT were almost the same. However, there were significant differences in the distribution density of argyrophilic cells between different organs in the GIT. The distribution density of argyrophilic cells in the duodenum, jejunum, ileum, and rectum of plateau zokor was significantly lower than that of plateau pika (p < 0.05) and, in the cecum of plateau zokor, was significantly higher than that of plateau pika (p < 0.001). The positive expression of 5-HT cells in the corpus I, corpus II, and pylorus of the stomach, duodenum, ileum, and rectum of plateau zokor was significantly higher than that of plateau pika (p < 0.01). In addition, the positive expression of Glu cells in the cecum was significantly higher (p < 0.01) and in the duodenum and colon was significantly lower (p < 0.05) in the plateau zokor than in the plateau pika. We conclude that the distribution pattern of endocrine cells in the GIT is consistent with the respective animals' diets, with the plateau zokor feeding on high-fiber roots and plateau pika preferring to intake the aboveground parts of plants with lower fibers.

The Complex and Well-Developed Morphological and Histological Structures of the Gastrointestinal Tract of the Plateau Zokor Improve Its Digestive Adaptability to High-Fiber Foods

The morphological and histological traits of the gastrointestinal tract (GIT) enable the animal to perform some specific functions that enhance the species’ adaptability to environments. The plateau zokor (Eospalax baileyi) is a subterranean rodent that mainly forages on plant roots in the Qinghai-Tibet Plateau, but little is known about the mechanism by which the plateau zokor digests roots that have high fiber contents. In this study, we used comparative anatomy methods to compare the morphological and histological traits of the GIT of both the plateau zokor and the plateau pika (Ochotona curzoniae), a small, fossorial lagomorph that forages aboveground plant parts, in order to clarify the traits of the plateau zokor’s GIT and to understand its adaptations to high-fiber foods. The results showed that the foods which plateau zokors eat have a higher fiber content than those which the plateau pikas eat. The plateau zokor has a double-chambered and hemi-glandular stomach (the tubular glands are only in the gastric corpus II, and the gastric fundus is keratinized), whereas the plateau pika has a simple, wholly glandular stomach. The gross morphological indicators (organ index and relative length) of the GIT were significantly lower in the plateau zokor than they were in the plateau pika (p < 0.001). However, the thickness of the gastric corpus II mucosal layer and the gastric fundus muscle layer are significantly higher in the plateau zokor than they are in the plateau pika (p < 0.001), and the thickness of each layer of intestinal tissue is higher in the plateau zokor than it is in the plateau pika. Additionally, the small intestinal villi also are higher and wider in the plateau zokor than they are in the plateau pika. Our results suggest that instead of adapting to digest the high-fiber diet by expanding the size of the GIT, the plateau zokor has evolved a complex stomach and a well-developed gastrointestinal histological structure, and that these specialized GIT structures are consistent with an optimal energy-economy evolutionary adaptation strategy.

DNA metabarcoding uncovers the diet of subterranean rodents in China

OBJECTIVE

A type of rodent called a zokor causes great harm to agriculture and forestry production due to its large and sophisticated diet. As this rodent lives subterrane for most of its life, researchers know little about its dietary habits. Further understanding of its diet is important for developing green and sustainable control strategies for the zokor.

METHODS

Chloroplast trnL gene and internal transcription spacer 1 primers were selected for high-throughput sequencing of stomach contents of captured zokor by DNA metabarcoding.

RESULTS

A total of 25 zokors were selected, the food list of 32 families, 80 genera, and 154 species was obtained. At the family level, it was found that zokors mainly fed on Asteraceae, Poaceae, Rosaceae, Pinaceae, Brassicaceae, and Apiaceae. At the genus level, zokors mainly fed on Echinops, Littledalea, Artemisia, Picea, Cirsium, and Elymus. The diet alpha diversity of Eospalax cansus was slightly higher than that of Eospalax cansus (P>0.05). The zokor's diet is highly phconsistent with the resources of its habitat. Most food choices tend to be the same between the two zokors. They fed primarily on Calamagrostis, Cirsium, Echinops, Medicago, Sanguisorba, and Taraxacum. Zokors mainly fed on the roots of perennial herbs, which are important source of energy.

CONCLUSION

High-throughput sequencing-based DNA metabarcoding technology has effectively revealed the diet of zokors and indicated that zokors are food generalists.