Subterranean Rodent Species Research Articles

Patterns of Genetic Diversity and Gene Flow Associated With an Aridity Gradient in Populations of Common Mole-rats, Cryptomys hottentotus hottentotus.

Genetic adaptation is the change of a population toward a phenotype that best fits the present ecological conditions of the environment it inhabits. As environmental conditions change, allele frequencies shift, resulting in different populations of the same species possessing genetic variation and divergent phenotypes. Cooperatively breeding common mole-rats (Cryptomys hottentotus hottentotus) inhabit environments along an aridity gradient in South Africa, which provides an opportunity for local genetic adaptations to occur. Using one mitochondrial gene (cytochrome b) and 3,540 SNP loci across the whole genome, we determined the phylogenetic relationship, population structure and genetic diversity of five populations of C. h. hottentotus located along an aridity gradient. Mitochondrial data identified population-specific clades that were less distinct in the two mesic populations, potentially indicating historical or recent gene flow, or the retention of ancestral haplotypes. Arid and semi-arid populations formed a distinct cluster from the non-arid populations. Genetic diversity and gene flow were higher in arid-dwelling individuals, suggesting greater connectivity and interactions between colonies in arid regions in comparison to mesic ones. Using an Aridity Index, we determined that isolation by environment, rather than isolation by geographical distance, best explains the genetic distance between the populations. Further analyses using target loci may determine if there are differing underlying genetic adaptations among populations of C. h. hottentotus. These analyses could help unravel population differences in response to environmental factors within a subspecies of bathyergid mole-rat and determine the adaptive capacity of this small nonmigratory subterranean rodent species in response to aridification in the face of climate change.

Same scenario, different scripts: Landscape genetics in two codistributed subterranean rodents of the genus Ctenomys

AbstractSubterranean rodents of the genus Ctenomys typically occupy fragmented habitats, many currently altered by anthropogenic development. These changes affect functional connectivity among individuals, reducing gene flow levels. This study assessed the functional connectivity of two sympatric species of subterranean rodents, Ctenomys australis and Ctenomys talarum, examining the impact of landscape changes on their population genetic structure at a fine spatial scale. We conducted a spatially continuous sampling over 12 km of coastline in Southeastern Buenos Aires Province, Argentina, genotyping 91 and 106 individuals of C. australis and C. talarum, respectively, using 10–12 microsatellite loci. We applied various spatial layers characterizing both species' habitats to evaluate the landscape configuration's effect on individual gene flow. We employed Bayesian genetic clustering methods to infer population structure levels. Ctenomys talarum showed greater structure than C. australis. NDVI temporal variation was the main factor influencing C. australis' genetic structure, whereas suitable habitat, linked to the current landscape configuration, was the most significant factor in shaping C. talarum's genetic structure. Differences in dispersal capacity and habitat specificity appear to have influenced the population genetic structures of these species. The results indicated varying sensitivities to landscape changes; temporal landscape variations primarily impacted C. australis' genetic connectivity, whereas for C. talarum, the current landscape configuration was more influential.

Human activities modulate reciprocal effects of a subterranean ecological engineer rodent, Tachyoryctes macrocephalus, on Afroalpine vegetation cover.

Human activities, directly and indirectly, impact ecological engineering activities of subterranean rodents. As engineering activities of burrowing rodents are affected by, and reciprocally affect vegetation cover via feeding, burrowing and mound building, human influence such as settlements and livestock grazing, could have cascading effects on biodiversity and ecosystem processes such as bioturbation. However, there is limited understanding of the relationship between human activities and burrowing rodents. The aim of this study was therefore to understand how human activities influence the ecological engineering activity of the giant root-rat (Tachyoryctes macrocephalus), a subterranean rodent species endemic to the Afroalpine ecosystem of the Bale Mountains of Ethiopia. We collected data on human impact, burrowing activity and vegetation during February and March of 2021. Using path analysis, we tested (1) direct effects of human settlement on the patterns of livestock grazing intensity, (2) direct and indirect impacts of humans and livestock grazing intensity on the root-rat burrow density and (3) whether human settlement and livestock grazing influence the effects of giant root-rat burrow density on vegetation and vice versa. We found lower levels of livestock grazing intensity further from human settlement than in its proximity. We also found a significantly increased giant root-rat burrow density with increasing livestock grazing intensity. Seasonal settlement and livestock grazing intensity had an indirect negative and positive effect on giant root-rat burrow density, respectively, both via vegetation cover. Analysing the reciprocal effects of giant root-rat on vegetation, we found a significantly decreased vegetation cover with increasing density of giant root-rat burrows, and indirectly with increasing livestock grazing intensity via giant root-rat burrow density. Our results demonstrate that giant root-rats play a synanthropic engineering role that affects vegetation structure and ecosystem processes.

Burrow systems of modern subterranean rodents (Ctenomyidae): key neoichnologic features and recognition of fossil examples

This study is aimed to identify the distinctive ichnologic features of burrow systems of two ctenomyid species of extant solitary and subterranean rodents (Ctenomys azarae and C. talarum occidentalis) from La Pampa Province (Argentina). A total of 12 active burrows from different biogeographic provinces were cast with polyurethane foam, then excavated and the entire system was mapped. Ctenomyid burrow systems are shallow (average depth 0.30 m), branched, and subhorizontal with several plugged entrances, having a main tunnel and secondary ones arranged in a single level. Curved length, tortuosity, fractal dimension branching angles, and the scarcity or absence of chambers are similar in both species. The average horizontal diameter is 66 mm, the burrow cross-section is subcircular to vertical elliptical, and entrance ramps slope at an average of 22°. Surface ornamentation in the form of sets of three curved claw traces composing a chevron pattern is dominant. Ctenomys azarae is distinguished from C. talarum occidentalis by the presence of food caches and wider sets of claw traces. Ctenomyidae burrows are easily distinguished from those of Octodontidae and Caviidae using the relative diameter index. The outlined criteria are applied to identify fossil examples of Late Miocene-Holocene ctenomyid burrows.

Active Nrf2 signaling flexibly regulates HO-1 and NQO-1 in hypoxic Gansu Zokor (Eospalax cansus).

Gansu zokor (Eospalax cansus) is a typical subterranean rodent species with resistance to ambient hypoxia. The nuclear factor erythroid 2-related factor 2 (Nrf2) signaling plays a key role in regulating redox homeostasis. However, little is known about the regulation of Nrf2 signaling in Gansu zokor. We exposed Gansu zokors and SD rats to chronic hypoxia (44h at 10.5% O2) or acute hypoxia (6h at 6.5% O2) andmeasured the activities of heme oxygenase-1 (HO-1) and NAD(P)H quinone oxidoreductase-1 (NQO-1)，gene expression of HO-1, NQO-1, Nrf2, Kelch-like ECH-associated protein-1 (KEAP1), and β-transducin repeat-containing protein (β-TRCP) in the brain and liver. We found that Gansu zokor increased the NQO-1 protein content and activity, HO-1 protein content in the brain, and increased HO-1 activity and mRNA level, NQO-1 activity and protein content in the liver by up regulating Nrf2 gene expression under chronic hypoxia. Although acute hypoxia enhanced the expression of Nrf2 gene, only the level of HO-1 mRNA in the liver increased. Besides, the HO-1 and NQO-1 genes in the brain, HO-1 genes and NQO-1 mRNA in the Gansu zokor liver were significantly higher than those in SD rats under normoxia. Negative regulators of Nrf2 signaling were tissue specific: KEAP1 protein decreased in the brain, and β-TRCP decreased in the liver. The Nrf2 signaling and expression of downstream antioxidant enzymes were different under different oxygen concentrations, reflecting the flexible characteristics of Gansu zokor to deal with the hypoxic environment.

Seismic Signaling for Detection of Empty Tunnels in the Plateau Zokor, Eospalax baileyi.

There are considerable challenges involved in studying the behavior of subterranean rodents owing to the underground nature of their ecotope. Seismic communication plays a crucial role in the behavior of subterranean rodents, particularly solitary ones. The plateau zokor (Eospalax baileyi), a solitary subterranean rodent species endemic to the Qinghai-Tibet Plateau, will usually occupy empty neighboring tunnels in order to extend their territory. Little is known, however, about the process of territorial occupation or the function of animal communication when occupation is taking place. Based on previous studies of subterranean rodent communication, we hypothesized that plateau zokors use seismic signals to detect neighboring tunnels and then occupy them when it was found their neighbors were absent. To test this, we placed artificial tunnels close to active original zokor tunnels to simulate the availability of an empty neighboring tunnel, and then the seismic signals when a zokor chose to occupy the empty artificial tunnel were recorded. The results showed that the frequency of zokors occupying artificial empty tunnels within 48 h was 7/8, In all of these instances, the zokors generated seismic signals before and after occupation of the empty artificial tunnel. The number of seismic signals generated by the zokors increased significantly (p = 0.024) when they detected and occupied the artificial tunnels, compared to those generated in their original tunnels without the presence of an artificial tunnel alongside. Inside the original tunnels, the inter-pulse time interval of the seismic signals was significantly higher (p < 0.001), the peak frequency of these signals was significantly higher (p < 0.01), and the energy of the signals was significantly lower (p = 0.006), compared with those when an artificial tunnel was positioned next to the original. The results of this study suggest that plateau zokors first generate seismic signals to detect empty neighboring tunnels and that they are empty. In the absence of neighbor plateau zokors, they occupy the empty tunnels to extend their own territory.

Microsatellite DNA variation in Spalacopus cyanus, a social subterranean rodent endemic to Chile (Rodentia: Octodontidae)

We used five polymorphic microsatellite loci to examine patterns of genetic variation within and among colonies of coruros (Spalacopus cyanus) at three localities in central Chile. Detailed comparisons of genetic variation at two locations, Los Maitenes in the northern portion of the species’ range and El Alamo in the south, displayed very different patterns of variation. Overall variation (alleles per locus and heterozygosity) within and among colonies at Los Maitenes was several times higher than observed at El Alamo, with the latter showing patterns of variation more consistent with a social species of subterranean rodent. Comparisons among Los Maitenes, El Alamo, and Los Vilos, another northern population, revealed a distinct genetic subdivision between northern and southern localities, indicating little evidence of genetic exchange between these two regions. We discuss these patterns of variation in relation to previous genetic research on Spalacopus and other subterranean rodents.

Digestive Tract Morphology and Gut Microbiota Jointly Determine an Efficient Digestive Strategy in Subterranean Rodents: Plateau Zokor

Simple SummaryInvestigation of mechanistic insights of digestive strategies in rodents can be difficult, but it is important to understand how rodents adapt to different environments. Applying physiological analyses to compare the differences between digestive tracts in plateau zokor and laboratory rats, we found that the length and weight of the digestive tract of the plateau zokor was significantly greater than the laboratory rat. Particularly, the weight and length of the large intestine and cecum in plateau zokor is three times that of the laboratory rat. Our gut microbiota analysis results showed that bacteria associated with cellulose degradation were significantly enriched in laboratory rats, when compared to plateau zokor. However, both plateau zokor and laboratory rats were predicted to share the same functions in carbohydrate metabolism and energy metabolism. Our findings suggest that both the morphology of the digestive tract and gut microbiota are vital to the digestion in wild rodents.Rodents’ lifestyles vary in different environments, and to adapt to various lifestyles specific digestion strategies have been developed. Among these strategies, the morphology of the digestive tracts and the gut microbiota are considered to play the most important roles in such adaptations. However, how subterranean rodents adapt to extreme environments through regulating gut microbial diversity and morphology of the digestive tract has yet to be fully studied. Here, we conducted the comparisons of the gastrointestinal morphology, food intake, food assimilation, food digestibility and gut microbiota of plateau zokor Eospalax baileyi in Qinghai-Tibet Plateau and laboratory rats Rattus norvegicus to further understand the survival strategy in a typical subterranean rodent species endemic to the Qinghai-Tibet Plateau. Our results revealed that plateau zokor evolved an efficient foraging strategy with low food intake, high food digestibility, and ultimately achieved a similar amount of food assimilation to laboratory rats. The length and weight of the digestive tract of the plateau zokor was significantly higher than the laboratory rat. Particularly, the weight and length of the large intestine and cecum in plateau zokor is three times greater than that of the laboratory rat. Microbiome analysis showed that genus (i.e., Prevotella, Oscillospira, CF231, Ruminococcus and Bacteroides), which are usually associated with cellulose degradation, were significantly enriched in laboratory rats, compared to plateau zokor. However, prediction of metagenomic function revealed that both plateau zokor and laboratory rats shared the same functions in carbohydrate metabolism and energy metabolism. The higher digestibility of crude fiber in plateau zokor was mainly driven by the sizes of cecum and cecum tract, as well as those gut microbiota which associated with cellulose degradation. Altogether, our results highlight that both gut microbiota and the morphology of the digestive tract are vital to the digestion in wild rodents.

Examining sex disparities in risk/reward trade-offs in Smith's zokors, Eospalax smithii

Risk taking is imperative for the survival and fitness of animals since they are constantly facing innumerable threats from various sources. Indeed, the ability of the individual to balance the costs and benefits of various options and adopt a wise decision is critical for the animal well-being. We modified several traditionally used anxiety tests [The modified light-dark box (mLDB), the modified open field test (mOFT) and the modified defensive withdrawal apparatus (mDWA)] by adding a palatable food reward within the anxiogenic zone which granted us to assess the sex differences in risk-taking behavior in Smith's zokors (Eospalax smithii), a typical subterranean rodent species endemic to the Qinghai-Tibetan Plateau. Concomitant with our working hypothesis, female zokors showed strong aversion and avoidance behavioral responses when tested in the mOFT and mDWA while there were no apparent sexually dimorphic behavioral changes when they were tested in the mLDB (Except for the percentage of food consumed and the latency till start feeding). Furthermore, comparison between the three behavioral paradigms revealed that both sexes showed different behavioral responses toward the different behavioral tests. Sex differences in repeatable behaviors were more profound in females than males. This might reflect different degrees of risk perception and emotionality that may differ considerably between the different models of anxiety. Our results highlighted the functional significance of a trade-off between risk and incentives in natural environment that both male and female zokors differ in the processing of risk assessment in the presence of a food reward.

Carbohydrate and Lipid Metabolism Characteristics of Hypoxia Tolerance in Gastrocnemius of the Gansu zokor, Eospalax cansus

Gansu zokor (Eospalax cansus) is a typical subterranean rodent species, and the balance between energy production and consumption has critical function for this creature to adapt to its hypoxia environment. However, little is known about the energy metabolism of gastrocnemius in Gansu zokor. Thus, we exposed Gansu zokors and similar-sized Sprague-Dawley rats (SD rats) to normoxia (21% O2), hypoxia I (6h at 6.5% O2), hypoxia II (44h at 10.5% O2) or hypoxia III ( 10d at 10.5% O2). We fi rst compared the plasma glucose and plasma lipid levels in Gansu zokor with those in SD rats; and we found that Gansu zokor had a higher overall plasma lipid levels than those in SD rats, interestingly, compared with SD rats, the plasma glucose level in Gansu zokor was no higher in all groups and even signifi cantly lower in the normoxia and hypoxia III. Furthermore, transcriptomic analysis of gastrocnemius in Gansu zokor (6.5% O2 VS 21% O2) indicated its carbohydrate and lipid metabolic alterations after exposed to hypoxia, suggesting that the change in metabolism was linked to the hypoxia environment. Hence, we then measured the transcriptional and translational levels of carbohydrate and lipid metabolism-related genes, glucose and fructose levels in gastrocnemius. We found that unlike rat, Gansu zokor gastrocnemius enhanced fructose-driven metabolism through increased the fructose transporter (GLUT5) expression in all hypoxia groups, and Gansu zokor also could enhanced lipid metabolism by increasing the expression of acetyl-Coenzyme A acyltransferase 2 (ACAA2) and stearoyl-CoA desaturase 1 (SCD1) after exposure to long-term hypoxia condition (10d at 10.5% O2). Overall, these fi ndings indicate that Gansu zokor could increase energy supply by enhancing fructose-driven metabolism and lipid metabolism to cope with hypoxia environment, which playing an important role in hypoxia tolerance.

Supermole-rat to the rescue: Does the naked mole-rat offer a panacea for all that ails us?

Over the previous several decades, many non-traditional research models have offered new avenues of exploration for biomedical research. The promise of these animals is primarily derived from adaptations to unique or challenging environments that share key factors with a disease or pathology of interest (e.g., hypoxemia or hypercarbia are clinically relevant and are also in vivo consequences of environmental hypoxia and hypercapnia, respectively). Animals adapted to such environments allow us to ask the question: how has nature solved a particular problem and what can we learn to inform novel translational research into the treatment of related diseases and pathologies? One of the most promising mammalian models that have garnered increasing attention from researchers and the public are naked mole-rats (NMRs). The NMR is a small and eusocial subterranean rodent species that live in a putatively hypoxic and hypercapnic burrow environment. Intriguingly, whereas most non-traditional biomedical models offer insight into one or only a few diseases related to a common physiological stress, NMRs in contrast have proven to be resistant to a very wide range of ailments, including aging, cancer, and hypoxia- and hypercapnia-related disorders, among many others. In the present commentary, we discuss progress made in understanding how NMRs overcome these challenges and speculate on the origins of their remarkable abilities.

Evoked auditory potentials from African mole-rats and coruros reveal disparity in subterranean rodent hearing.

Hearing in subterranean rodents exhibits numerous peculiarities, including low sensitivity and restriction to a narrow range of comparatively low frequencies. Past studies provided two conflicting hypotheses explaining how these derived traits evolved: structural degeneration and adaptive specialization. To further elucidate this issue, we recorded auditory brainstem responses from three species of social subterranean rodents that differ in the degree of specialization to the underground habitat: the naked mole-rat (Heterocephalus glaber) and the Mashona mole-rat (Fukomys darlingi), which represent the ancient lineage of African mole-rats (Bathyergidae), and the coruro (Spalacopus cyanus), a South American rodent (Octodontidae) that adopted a subterranean lifestyle in more recent geological time. Additionally, we measured call amplitudes of social vocalizations to study auditory vocal coupling. We found elevated auditory thresholds and severe hearing range restrictions in the African mole-rats, with hearing in naked mole-rats tending to be more sensitive than in Mashona mole-rats, in which hearing notably deteriorated with increasing age. In contrast, hearing in coruros was similar to that of epigeic rodents, with its range extending into ultrasonic frequencies. However, as in the mole-rats, the coruros' region of best hearing was located at low frequencies close to 1 kHz. We argue that the auditory sensitivity of African mole-rats, although remarkably poor, has been underestimated by recent studies, whereas data on coruros conform to previous results. Considering the available evidence, we propose to be open to both degenerative and adaptive interpretations of hearing physiology in subterranean mammals, as each may provide convincing explanations for specific auditory traits observed.

The joint effect of micro- and macro-climate on the thermoregulation and heat dissipation of two African mole-rat (Bathyergidae) sub-species, Cryptomys hottentotus mahali and C. h. pretoriae.

The effect of the macro- and microclimate on small mammal thermoregulation in the past has been studied independently instead of investigating the dual effect of both the components. This study addresses this dearth in knowledge by exploring the dual effect of both micro- and macro-climate on the thermoregulatory responses of two subterranean rodent species belonging to the family Bathyergidae, namely the more arid dwelling Mahali mole-rat (Cryptomys hottentotus mahali) and less arid dwelling Highveld mole-rat (C. h. pretoriae). Open flow through respirometry was used to quantify resting metabolic rates (RMR), evaporative water loss (EWL), core body temperature (Tb), the ratio between the evaporative heat loss and metabolic heat production (EHL/MHP: evaporative cooling capacity) and conductance (Cdry) over a range of increasing ambient temperatures (Ta; 20-42°C). Furthermore, RMR, EWL, Tb, EHL/MHP and Cdry were measured at the mole-rat's thermal maxima (43°C). At cooler temperatures, the arid-dwelling C. h. mahali possesses a broader thermoneutral zone (~5°C; 27.2-32.1°C), while C. h. pretoriae possess a single thermoneutral point (33.6°C). This is in response to the greater selection pressure to conserve energy in the more arid regions inhabited by C. h. mahali. Contrastingly, at hotter temperatures, there were no significant thermoregulatory differences in EWL, EHL/MHP or Cdry responses between the two sub-species, as expected due to the limitations bestowed by the buffered microclimates (burrow systems). Thus, neither macro-climate, nor micro-climate singularly moulds the thermoregulatory adaptations, but rather, it appears to be a combined effect from both climates. Other small endotherms may share this dual response, and therefore, it is crucial to incorporate the effect of both macro- and microclimates into future climate models when determining the ecological capabilities and persistence of a species.

Potential distribution models from two highly endemic species of subterranean rodents of Argentina: which environmental variables have better performance in highly specialized species?

Potential distribution models from two highly endemic species of subterranean rodents of Argentina: which environmental variables have better performance in highly specialized species?

Interspecific skull variation at a small scale: The genus Eospalax exhibits functional morphological variations related to the exploitation of ecological niche

Ecology influences the process of speciation. The interspecific differences in mammalian skull morphology, induced by environmental factors, are important when investigating speciation. In the Qinghai–Tibetan Plateau, the genus Eospalax consists of six species of subterranean rodents, each with its unique niche, making it an ideal model for studying the relationship between biological evolution and the environment. Here, the interspecific differences in five of the six extant species (E. cansus, E. baileyi, E. rufescens, E. smithii, and E. fontanierii) were evaluated at the morphometric and ecological levels using geometric morphometrics, a powerful tool for studying morphological variation. The multivariate analysis of variance showed significant differences in skull morphology on the dorsal and ventral sides in all species. The thin-plate splines showed that the variations in skull morphology were primarily in the infraorbital foramen, frontal bone, zygomatic arch, occipital bone, incisors, incisive foramen, and tooth row. The multivariate regression analysis showed a significant positive correlation between skull morphological variations and ecological factors; precipitation accounted for the more variations than altitude and temperature. Species inhabiting regions with the highest altitude, minimum precipitation, and temperature (E. baileyi) had the largest infraorbital foramen and zygomatic arch, shortest occipital bone and widest frontal bone, smallest angle formed by two incisors, and longest incisive foramen. Our study elucidates the relationship between skull morphological differentiation and environmental factors in Eospalax, while the biological response to the environment detected warrants further investigation. Our results can provide references for speciation at local environmental scale.

The mTORC1/eIF4E/HIF-1α Pathway Mediates Glycolysis to Support Brain Hypoxia Resistance in the Gansu Zokor, Eospalax cansus.

The Gansu zokor (Eospalax cansus) is a subterranean rodent species that is unique to China. These creatures inhabit underground burrows with a hypoxia environment. Metabolic energy patterns in subterranean rodents have become a recent focus of research; however, little is known about brain energy metabolism under conditions of hypoxia in this species. The mammalian (mechanistic) target of rapamycin complex 1 (mTORC1) coordinates eukaryotic cell growth and metabolism, and its downstream targets regulate hypoxia inducible factor-1α (HIF-1α) under conditions of hypoxia to induce glycolysis. In this study, we compared the metabolic characteristics of hypoxia-tolerant subterranean Gansu zokors under hypoxic conditions with those of hypoxia-intolerant Sprague-Dawley rats with a similar-sized surface area. We exposed Gansu zokors and rats to hypoxia I (44 h at 10.5% O2) or hypoxia II (6 h at 6.5% O2) and then measured the transcriptional levels of mTORC1 downstream targets, the transcriptional and translational levels of glycolysis-related genes, glucose and fructose levels in plasma and brain, and the activity of key glycolysis-associated enzymes. Under hypoxia, we found that hif-1α transcription was upregulated via the mTORC1/eIF4E pathway to drive glycolysis. Furthermore, Gansu zokor brain exhibited enhanced fructose-driven glycolysis under hypoxia through increased expression of the GLUT5 fructose transporter and ketohexokinase (KHK), in addition to increased KHK enzymatic activity, and utilization of fructose; these changes did not occur in rat. However, glucose-driven glycolysis was enhanced in both Gansu zokor and rat under hypoxia II of 6.5% O2 for 6 h. Overall, our results indicate that on the basis of glucose as the main metabolic substrate, fructose is used to accelerate the supply of energy in Gansu zokor, which mirrors the metabolic responses to hypoxia in this species.

Exposure to eagle owl feces induces anti-predator behavior, physiology, and hypothalamic gene responses in a subterranean rodent, the plateau zokor (Eospalax baileyi)

Predator odors are natural stressors that induce anti-predator defensive responses, which have developed under evolutionary pressures to maximize the fitness of an individual to avoid dangerous confrontations. In this study, we analyzed the defensive responses of a subterranean rodent species, the plateau zokor (Eospalax baileyi), to predation threat, and examined the trade-offs between defensive responses and foraging. Plateau zokors were exposed to 1, 3, and 6 g of eagle owl (Bubo bubo) feces, and the anti-predator behavioral, hormonal, and hypothalamic corticotropin-releasing factor and c-fos mRNA expression responses were analyzed and compared with the control (distilled water). Exposure of the animals to owl feces led to significant reductions in both duration of feeding and amount of food consumed, while some defensive behavioral responses (e.g., freezing and rearing) were more significant in the exposed animals than in the control. Serum levels of adrenocorticotropic hormone and corticosterone in plateau zokors exposed to owl feces were significantly higher compared with the control. The hypothalamic corticotropin-releasing factor and c-fos mRNA expression levels of plateau zokors exposed to 1, 3, and 6 g owl feces increased significantly, concomitant with the amount of eagle owl feces presented. Owl feces induced various behavioral, hormonal, and hypothalamic gene expression changes in plateau zokors exposed to them. Some behavioral and gene expression (but not hormonal) responses appeared to be threshold dependent. Predator odors supersede other signals and can provide comprehensive information to prey during life-threatening events. The plateau zokor is a typical subterranean rodent living in dark and enclosed subterranean habitats. Owing to this special habitat, zokors may be able to recognize ground predator odors and respond defensively. We investigated changes in behavior, hormones, and the hypothalamic corticotropin-releasing factor and c-fos mRNA expression levels of the plateau zokor when exposed to different amounts of eagle owl feces. We believe that our study makes a significant contribution to the literature because our results support the predation risk allocation hypothesis, showing that eagle owl feces inhibit foraging and induce various anti-predatory behavioral and neuroendocrine responses in plateau zokors.

Characteristics of the mitochondrial genome of Qinling zokor (Eospalax rufescens)

We report the complete mitochondrial genome for the Eospalax rufescens, a typical subterranean rodent species and endemic in China. The resulting E. rufescens mitogenome is 16,355 bases in size, containing 13 protein-coding genes (PCGs), 2 ribosomal RNA (rRNA) genes, 22 transfer RNA (tRNA) genes, and 1 noncoding control region (D-loop). The base compositions present highly biased toward A + T nucleotides. Moreover, twelve of all 13 PCGs initiated with ATN start codon, whereas ND1 began with GTG start codon. Stop codons in 13 PCGs were all typical types except incomplete stop codon T for ND4. We further provide a Maximum Likelihood phylogenetic tree showing relationships among E. rufescens and other common subterranean rodents in family Spalacidae.

Evolution of Hemoglobin Genes in a Subterranean Rodent Species (Lasiopodomys mandarinus).

The Mandarin vole (Lasiopodomys mandarinus), a typical subterranean rodent, has undergone hematological adaptations to tolerate the hypoxic/hypercapnic underground environment. Hemoglobin (Hb) genes encode respiratory proteins functioning principally in oxygen binding and transport to various tissues and organs. To investigate the evolution of α- and β-hemoglobin (Hb) in subterranean rodent species, we sequenced Hb genes of the Mandarin vole and the related aboveground Brandt’s vole (L. brandtii). Sequencing showed that in both voles, α-globin was encoded by a cluster of five functional genes in the following linkage order: HBZ, HBA-T1, HBQ-T1, HBA-T2, and HBQ-T2; among these, HBQ-T2 is a pseudogene in both voles. The β-globin gene cluster in both voles also included five functional genes in the following linkage order: HBE, HBE/HBG, HBG, HBB-T1, and HBB-T2. Phylogenetic analysis revealed that the Mandarin vole underwent convergent evolution with its related aboveground species (Brandt’s vole) but not with other subterranean rodent species. Selection pressure analyses revealed that α- and β-globin genes are under strong purifying selection (ω < 1), and branch-site analyses identified positive selection sites on HBAT-T1 and HBB-T1 in different subterranean rodent species. This suggests that the adaptive evolution of these genes enhanced the ability of Hb to store and transport oxygen in subterranean rodent species. Our findings highlight the critical roles of Hb genes in the evolution of hypoxia tolerance in subterranean rodent species.

Hybridization between subterranean tuco-tucos (Rodentia, Ctenomyidae) with contrasting phylogenetic positions

Reproductive compatibility usually decreases according to increasing genetic difference and the time of divergence between species. However, the amount of modification required to influence hybridization may vary in different species. Thus, it is extremely important to conduct studies that seek to understand what and how variables influence the reproductive isolation of species. We have explored a system involving two species of subterranean rodents that present morphological, karyotypic, and evolutionary history differences and are capable of generating hybrids. To gain insight into the karyotype organization of genus Ctenomys, we examined the chromosome evolution by classical and molecular cytogenetics of both parental species and hybrids. Furthermore, we have used different approaches to analyze the differences between the parental species and the hybrids, and determined the origin of the hybrids. The results of our work demonstrate unequivocally that some species that present extensive differences in chromosome organization, phenotype, evolutionary history, sperm morphology and genetic, which are usually associated with reproductive isolation, can generate natural hybrids. The results also demonstrate that females of both species are able to generate hybrids with males of the other species. In addition, the chromosome-specific probes prepared from Ctenomys flamarioni provide an invaluable tool for comparative cytogenetics in closely related species.