The colonization and divergence patterns of Brandt's vole (Lasiopodomys brandtii) populations reveal evidence of genetic surfing

Antioxidant response to severe hypoxia in Brandt's vole Lasiopodomys brandtii

The antioxidant defense system is essential for animals to cope with homeostasis disruption and overcome oxidative stress caused by adverse environmental conditions such as hypoxia. However, our understanding of how this system works in subterranean rodents remains limited. In this study, Brandt's vole Lasiopodomys brandtii was exposed to normoxia (21% O₂ ) or hypoxia (mild or severe hypoxia: 10% or 5% O₂ ) for 6 h. Changes in key enzymes of the classic enzymatic antioxidant system at both mRNA and enzyme activity levels, and tissue antioxidant levels of the low-molecular-weight antioxidant system were determined in brain, liver, and kidney. Transcript levels of the upstream regulator NF-E2-related factor 2 (Nrf2) were also measured. We found that the mRNA expression of Nrf2 and its downstream antioxidant enzyme genes in L. brandtii were relatively conserved in response to hypoxia in most tissues and genes tested, except in the liver. Hepatic Nrf2, Cu/Zn SOD, GPx1, and GPx3 levels were significantly upregulated in response to mild hypoxia, whereas Mn SOD level decreased significantly in severe hypoxia. Unmatched with changes at the RNA level, constitutively high and relatively stable antioxidant enzyme activities were maintained throughout. For the low-molecular-weight antioxidant system, an abrupt increase of cerebral ascorbic acid (AA) levels in hypoxia indicated a tissue-specific antioxidant response. Although hypoxia did not cause significant oxidative damage in most tissues tested, the significant decrease in antioxidant enzyme activities (GPX and GR) and increase in lipid peroxidation in the kidney suggest that prolonged hypoxia may pose a critical threat to this species.

Diverse energy metabolism patterns in females in Neodon fuscus, Lasiopodomys brandtii, and Mus musculus revealed by comparative transcriptomics under hypoxic conditions

The effects of global warming and anthropogenic disturbance force animals to migrate from lower to higher elevations to find suitable new habitats. As such migrations increase hypoxic stress on the animals, it is important to understand how plateau- and plain-dwelling animals respond to low-oxygen environments. We used comparative transcriptomics to explore the response of Neodon fuscus, Lasiopodomys brandtii, and Mus musculus skeletal muscle tissues to hypoxic conditions. Results indicate that these species have adopted different oxygen transport and energy metabolism strategies for dealing with a hypoxic environment. N. fuscus promotes oxygen transport by increasing hemoglobin synthesis and reduces the risk of thrombosis through cooperative regulation of genes, including Fga, Fgb, Alb, and Ttr; genes such as Acs16, Gpat4, and Ndufb7 are involved in regulating lipid synthesis, fatty acid β-oxidation, hemoglobin synthesis, and electron-linked transmission, thereby maintaining a normal energy supply in hypoxic conditions. In contrast, the oxygen-carrying capacity and angiogenesis of red blood cells in L. brandtii are promoted by genes in the CYP and COL families; this species maintains its bodily energy supply by enhancing the pentose phosphate pathway and mitochondrial fatty acid synthesis pathway. However, under hypoxia, M. musculus cannot effectively transport additional oxygen; thus, its cell cycle, proliferation, and migration are somewhat affected. Given its lack of hypoxic tolerance experience, M. musculus also shows significantly reduced oxidative phosphorylation levels under hypoxic conditions. Our results suggest that the glucose capacity of M. musculus skeletal muscle does not provide sufficient energy during hypoxia; thus, we hypothesize that it supplements its bodily energy by synthesizing ketone bodies. For the first time, we describe the energy metabolism pathways of N. fuscus and L. brandtii skeletal muscle tissues under hypoxic conditions. Our findings, therefore, improve our understanding of how vertebrates thrive in high altitude and plain habitats when faced with hypoxic conditions.

Phylogeny and evolution of Lasiopodomys in subfamily Arvivolinae based on mitochondrial genomics

The species of Lasiopodomys Lataste 1887 with their related genera remains undetermined owing to inconsistent morphological characteristics and molecular phylogeny. To investigate the phylogenetic relationship and speciation among species of the genus Lasiopodomys, we sequenced and annotated the whole mitochondrial genomes of three individual species, namely Lasiopodomys brandtii Radde 1861, L. mandarinus Milne-Edwards 1871, and Neodon (Lasiopodomys) fuscus Büchner 1889. The nucleotide sequences of the circular mitogenomes were identical for each individual species of L. brandtii, L. mandarinus, and N. fuscus. Each species contained 13 protein-coding genes (PCGs), 22 transfer RNAs, and 2 ribosomal RNAs, with mitochondrial genome lengths of 16,557 bp, 16,562 bp, and 16,324 bp, respectively. The mitogenomes and PCGs showed positive AT skew and negative GC skew. Mitogenomic phylogenetic analyses suggested that L. brandtii, L. mandarinus, and L. gregalis Pallas 1779 belong to the genus Lasiopodomys, whereas N. fuscus belongs to the genus Neodon grouped with N. irene. Lasiopodomys showed the closest relationship with Microtus fortis Büchner 1889 and M. kikuchii Kuroda 1920, which are considered as the paraphyletic species of genera Microtus. T_MRCA and niche model analysis revealed that Lasiopodomys may have first appeared during the early Pleistocene epoch. Further, L. gregalis separated from others over 1.53 million years ago (Ma) and then diverged into L. brandtii and L. mandarinus 0.76 Ma. The relative contribution of climatic fluctuations to speciation and selection in this group requires further research.

The reproductive inhibitory effects of levonorgestrel, quinestrol, and EP-1 in Brandt's vole (Lasiopodomys brandtii)

Background

Rodent pests can inflict devastating impacts on agriculture and the environment, leading to significant economic damage associated with their high species diversity, reproductive rates and adaptability. Fertility control methods could indirectly control rodent pest populations as well as limit ecological consequences and environmental concerns caused by lethal chemical poisons. Brandt’s voles, which are common rodent pests found in the grasslands of middle-eastern Inner Mongolia, eastern regions of Mongolia, and some regions of southern Russia, were assessed in the present study.

Methods

We evaluated the effects of a 2-mg/kg dose of levonorgestrel and quinestrol and a 1:1 mixture of the two (EP-1) on reproductive behavior as well as changes in the reproductive system, reproductive hormone levels, and toxicity in Brandt’s voles.

Results

Our results revealed that all three fertility control agents can cause reproductive inhibition at a dosage of 2 mg/kg. However, quinestrol caused a greater degree of toxicity, as determined by visible liver damage and reduced expression of the detoxifying molecule CYP1A2. Of the remaining two fertility control agents, EP-1 was superior to levonorgestrel in inhibiting the secretion of follicle-stimulating hormone and causing reproductive inhibition. We believe that these findings could help promote the use of these fertility control agents and, in turn, reduce the use of chemical poisons and limit their detrimental ecological and environmental impacts.

Complete mitochondrial genomes confirm the generic placement of the plateau vole, Neodon fuscus

The plateau vole, Neodon fuscus is endemic to China and is distributed mainly in Qinghai Province. It is of public health interest, as it is, a potential reservoir of Toxoplasma gondii and the intermediate host of Echinococcus multilocularis. However, genetic data of this species are lacking, and its name and taxonomy are still a controversy. In the present study, we determined the nucleotide sequence of the entire mitochondrial (mt) genome of N. fuscus and analyzed its evolutionary relationship. The mitogenome was 16328 bp in length and contained 13 protein-coding genes, 22 genes for transfer RNAs (tRNA), two ribosomal RNA genes and two major noncoding regions (O_L region and D-loop region). Most genes were located on the heavy strand. All tRNA genes had typical cloverleaf structures except for tRNA^{Ser (GCU)}. The mt genome of N. fuscus was rich in A+T (58.45%). Maximum likelihood (ML) and Bayesian methods yielded phylogenetic trees from 33 mt genomes of Arvicolinae, in which N. fuscus formed a sister group with Neodon irene and Neodon sikimensis to the exclusion of species of Microtus and other members of the Arvicolinae. Further phylogenetic analyses (ML only) based on the cytb gene sequences also demonstrated that N. fuscus had a close relationship with N. irene. The complete mitochondrial genome was successfully assembled and annotated, providing the necessary information for the phylogenetic analyses. Although the name Lasiopodomys fuscus was used in the book ‘Wilson & Reeder’s Mammal Species of the World’, we have confirmed here that its appropriate name is N. fuscus through an analysis of the evolutionary relationships.