Subterranean Rodent Research Articles

Sociality does not drive the evolution of large brains in eusocial African mole-rats

The social brain hypothesis (SBH) posits that the demands imposed on individuals by living in cohesive social groups exert a selection pressure favouring the evolution of large brains and complex cognitive abilities. Using volumetry and the isotropic fractionator to determine the size of and numbers of neurons in specific brain regions, here we test this hypothesis in African mole-rats (Bathyergidae). These subterranean rodents exhibit a broad spectrum of social complexity, ranging from strictly solitary through to eusocial cooperative breeders, but feature similar ecologies and life history traits. We found no positive association between sociality and neuroanatomical correlates of information-processing capacity. Solitary species are larger, tend to have greater absolute brain size and have more neurons in the forebrain than social species. The neocortex ratio and neuronal counts correlate negatively with social group size. These results are clearly inconsistent with the SBH and show that the challenges coupled with sociality in this group of rodents do not require brain enlargement or fundamental reorganization. These findings suggest that group living or pair bonding per se does not select strongly for brain enlargement unless coupled with Machiavellian interactions affecting individual fitness.

Prenatal predatory stress in a wild species of subterranean rodent: Do ecological stressors always have a negative effect on the offspring?

In pregnant females, a failed predatory event not only induces individual responses but also represents a significant change in the developmental environment of the offspring, which may lead to modifications in their phenotype that may persist at different stages of life. We evaluate whether prenatal exposure to predatory cues affects anxiety behavior, behavioral response to predator cues, stress response to immobilization, and immune response to sheep red blood cells (SRBC) and phytohemagglutinin (PHA) in juveniles of the subterranean rodent Ctenomys talarum. We found that prenatal predator stress (PPS) (1) increased juvenile anxiety-like behaviors and the appearance of antipredator behaviors, (2) did not affect the response of offspring to predatory stressors, and (3) did not influence the physiological response of juveniles to stressors (immobilization) nor the immunological responses to SRBC and PHA challenges. This work shows the influence of PPS on the development of behavioral responses in the offspring, whom displayed a state of anxiety and behavioral changes associated with decreased locomotor activity and avoidance behaviors. Thus, these individuals prenatally exposed to predatory cues show behavioral adaptations that may contribute to avoid predators in the adult life.

Changes in selection intensity on the mitogenome of subterranean and fossorial rodents respective to aboveground species

Several rodent lineages independently acquired the ability to dig complex networks of tunnels where fossorial and subterranean species spend part or their whole life, respectively. Their underground lifestyles imposed harsh physiological demands, presumably triggering strong selective pressures on genes involved in energy metabolism like those coding for mitochondrial proteins. Moreover, underground lifestyles must have increased inbreeding and susceptibility to population bottlenecks as well as restricted migration, leading to small effective population size (Ne) that, in turn, must have reduced the effectiveness of selection. These stringent environmental conditions and small Ne might be still operating as antagonist factors of selection efficacy in these rodents. In this report, we tested, in a phylogenetic framework, how the intensity of selection on protein-coding mitochondrial genes (mt-genes) fluctuated along the evolution of fossorial and subterranean rodents respective to aboveground lineages. Our findings showed significant selection relaxation in most mt-genes of subterranean hystricomorphs (African mole-rats, tuco-tucos, and coruro), while only in three mt-genes of fossorial hystricomorphs (degus, red vizcacha rat, and fossorial spiny rats) selection efficacy was strongly reduced, probably due to demographic constraints. Conversely, selection intensification was found to have occurred in three mt-genes in fossorial sciuromorphs (ground squirrels, chipmunks, marmot, and allies). Our findings indicated that evolution of mitogenomes in fossorial and, mainly, in subterranean rodents was a complex output of a balance between intense ecological and physiological pressures, together with demographic constraints leading to genetic drift that, in turn, might have resulted in relaxed selection in hystricomorphs.

Different regulation of cortisol and corticosterone in the subterranean rodent Ctenomys talarum: Responses to dexamethasone, angiotensin II, potassium, and diet

When harmful environmental stimuli occur, glucocorticoids (GCs), cortisol and corticosterone are currently used to evaluate stress status in vertebrates, since their secretions are primarily associated to an increased activity of the hypothalamic-pituitaryadrenal (HPA) axis. To advance in our comprehension about GCs regulation, we evaluated the subterranean rodent Ctenomys talarum to assess cortisol and corticosterone response to (1) the negative feedback of the HPA axis using the dexamethasone (DEX) suppression test, (2) angiotensin II (Ang II), (3) potassium (K+) intake, and (4) different diets (vegetables, grasses, acute fasting). Concomitantly, several indicators of individual condition (body mass, neutrophil to lymphocyte ratio, blood glucose, triglycerides and hematocrit) were measured for diet treatments. Results confirm the effect of DEX on cortisol and corticosterone in recently captured animals in the field but not on corticosterone in captive animals. Data suggest that Ang II is capable of stimulating corticosterone, but not cortisol, secretion. Neither cortisol nor corticosterone were responsive to K+ intake. Cortisol levels increased in animals fed with grasses in comparison to those fed with vegetables while corticosterone levels were unaffected by diet type. Moreover, only cortisol responded to fasting. Overall, these results confirm that cortisol and corticosterone are not interchangeable hormones in C. talarum.

Noninvasive age estimation in rodents by measuring incisors width, with the Zaisan mole vole (Ellobius tancrei) as an example

Abstract Non-invasive age estimation is critically important for many field studies but often it represents a significant challenge. In rodents, upper incisors represent a part of a cranium which can be readily measured in an alive animal. We propose an age estimation method based on the measurements of both upper incisors’ width (IW) for a subterranean rodent, Ellobius tancrei. The IW measurements for 77 laboratory-born females and 81 males were fitted, separately for the sexes, by sigmoidal Gompertz growth functions to obtain the asymptotic values. Based on the data set encompassing pre-asymptotic ages, we then derived a polynomial regression model with log-transformed age as а predictor. The analysis revealed no statistically significant sex difference in growth patterns. Derived model explained 91% of IW variation and was used to obtain predicted values of age and their 95% prediction intervals through inverse calculations. We conclude that IW is a potentially useful age indicator for mole voles and possibly other rodents in cases when invasive or time-consuming methods are non-appropriate.

Function-related Drivers of Skull Morphometric Variation and Sexual Size Dimorphism in a Subterranean Rodent, Plateau Zokor (Eospalax baileyi).

Sexual dimorphism is prevalent in most living organisms. The difference in size between sexes of a given species is generally known as sexual size dimorphism (SSD). The magnitude of the SSD is determined by Rensch's rule where size dimorphism increases with increasing body size when the male is the larger sex and decreases with increasing average body size when the female is the larger sex. The unique underground environment that zokors (Eospalax baileyi) live under in the severe habitat of the Qinghai‐Tibetan Plateau (QTP) could create SSD selection pressures that may or may not be supported by Rensch's rule, making this scientific question worthy of investigation. In this study, we investigated the individual variation between sexes in body size and SSD of plateau zokors using measurements of 19 morphological traits. We also investigated the evolutionary mechanisms underlying SSD in plateau zokors. Moreover, we applied Rensch's rule to all extant zokor species. Our results showed male‐biased SSD in plateau zokors: The body‐ and head‐related measurements were greater in males than in females. Linear regression analysis between body length, body weight, and carcass weight showed significant relationships with some traits such as skull length, lower incisor length, and tympanic bulla width, which might support our prediction that males have faster growth rates than females. Further, the SSD pattern corroborated the assumption of Rensch's rule in plateau zokors but not in the other zokor species. Our findings suggest that the natural underground habitat and behavioral differences between sexes can generate selection pressures on male traits and contribute to the evolution of SSD in plateau zokors.

Retinal S-opsin dominance in Ansell\u2019s mole-rats (Fukomys anselli) is a consequence of naturally low serum thyroxine

Mammals usually possess a majority of medium-wavelength sensitive (M-) and a minority of short-wavelength sensitive (S-) opsins in the retina, enabling dichromatic vision. Unexpectedly, subterranean rodents from the genus Fukomys exhibit an S-opsin majority, which is exceptional among mammals, albeit with no apparent adaptive value. Because thyroid hormones (THs) are pivotal for M-opsin expression and metabolic rate regulation, we have, for the first time, manipulated TH levels in the Ansell’s mole-rat (Fukomys anselli) using osmotic pumps. In Ansell’s mole-rats, the TH thyroxine (T4) is naturally low, likely as an adaptation to the harsh subterranean ecological conditions by keeping resting metabolic rate (RMR) low. We measured gene expression levels in the eye, RMR, and body mass (BM) in TH-treated animals. T4 treatment increased both, S- and M-opsin expression, albeit M-opsin expression at a higher degree. However, this plasticity was only given in animals up to approximately 2.5 years. Mass-specific RMR was not affected following T4 treatment, although BM decreased. Furthermore, the T4 inactivation rate is naturally higher in F. anselli compared to laboratory rodents. This is the first experimental evidence that the S-opsin majority in Ansell’s mole-rats is a side effect of low T4, which is downregulated to keep RMR low.

Spatial and temporal divergence of the torquatus species group of the subterranean rodent Ctenomys

Subterranean rodents of the genus Ctenomys have experienced an explosive radiation and rapidly colonized the southern cone of South America. The torquatus group, one of the main groups of the genus, comprises several species and species complexes which inhabit the eastern part of the distribution of Ctenomys including southern Brazil, northern and central Uruguay and north-eastern Argentina. This group has undergone a high chromosomal diversification with diploid numbers varying from 41 to 70. The aim of this study was to investigate the origins of the torquatus group as well as its diversification patterns in relation to geography and cladogenesis. Based on mitochondrial cytochrome b nucleotide sequences we conducted a Bayesian multi-calibrated relaxed clock analysis to estimate the ages of the torquatus group and its main lineages. Using the estimated evolutionary rate we performed a continuous phylogeographic analysis, using a relaxed random walk model to reconstruct the geographic diffusion of the torquatus group in a temporal frame. The torquatus group originated during the early Pleistocene between 1.25 and 2.32 million years from the present in a region that includes the northwest of Uruguay and the southeast of the Brazilian state of Río Grande do Sul. Most lineages have dispersed early towards their present distribution areas going through subsequent range expansions in the last 800,000 – 700,000 years. Ctenomys torquatus went through a rapid range expansion for the last 200,000 years, becoming the most widespread species of the group. The colonization of the Corrientes and Entre Ríos Argentinean provinces supposes at least two crossing events across the Uruguay River between 1.0 and 0.5 million years before the present, in the context of a cold and dry paleoenvironment. The resulting temporal and geographic frame enables the comprehension of the incidence of both, the amplitude of distribution areas and divergence times into the patterns of chromosomal diversification found in the group.

Individual condition and inflammatory response to PHA in the subterranean rodent Ctenomys talarum (Talas tuco-tuco): A multivariate approach

Several components of individual condition can modulate immune function in vertebrates. One of the most common techniques used by ecologists to estimate immune responsiveness in wild populations is the phytohemagglutinin (PHA)-skin test, which is usually considered a proxy of cell- mediated activity. To determine the influence of individual condition on the magnitude of this immune index we assessed the variability in the inflammatory response to PHA in the subterranean solitary rodent, Ctenomys talarum (Talas tuco-tucos), including 18 variables associated with different aspects of individual condition that are indicative of physical, physiological, parasitological and immunological state. A partial least square (PLS) regression analysis was performed on the condition and the response variables to identify those having greater contribution to overall variation in the response. The first two components explained together 77.5% of the maximum achievable explained variance in the inflammatory response to PHA (60% of total variance). Abundance of eggs of Trichuris pampeana, eosinophil, monocyte and neutrophil counts, together with reproductive condition were identified as the most important variables affecting the inflammatory response. The first component negatively associated the inflammatory response to PHA with the abundance of the nematode T. pampeana, and with counts of eosinophils and monocytes. The second component negatively associated the inflammatory response to PHA with reproductive condition, neutrophils and eosinophils. We discuss the general negative effect of infection on the immune responsiveness of wild animals and highlight the usefulness of the multivariate approaches in providing information on physiology, parasitology and health relationships to assess patterns of variation in immune responses.

An allometric analysis of sexual dimorphism in Ctenomys australis: integrating classic morphometry and functional performance in vivo

The South American rodents of the genus Ctenomys (Rodentia, Hystricognathi), which use both forelimbs and incisors to dig, show strong, specialized morphological adaptations to living in the underground niche. In these rodents, the effectiveness of a bite − in this case the potential to inflict physical damage − mostly depends on the strength of the incisors (e.g. bending and torsion stresses) and the power of the masseteric muscle of the jaw. Ctenomys australis (the sand dune tuco-tuco) is a highly territorial subterranean rodent that builds large and exclusive burrow systems in coastal sand dunes found continuously along the Atlantic coast of the Buenos Aires province, Argentina. Incisors in this species are used both in agonistic encounters among congeners (i.e. reproductive or territorial intentions) as well as to dig and increase the size of their burrows daily (e.g. acquisition of plant material as food resources). We first characterized sexual dimorphism in cranial traits involved in aggressive interactions between males, analyzing ontogenetic trajectories of both sexes. We also analyzed some remarkable attributes of sexual dimorphism in subadult and adult individuals, the bending and torsion stresses and the bite performance in vivo, hypothesizing that males are able to apply comparatively stronger bite forces at their incisor tips than females, concordant with a broader mandible for the insertion of a powerful adductor musculature. Bite forces were measured in vivo in wild animals of both sexes using a strain gauge load cell force transducer. These individuals were also used to estimate the incisor area (CA), the 2nd moment of inertia of the incisors (I, or the bending strength to external forces), and the torsional strength of the incisor (J), all traits involved in the production of the force that can be withstood at the incisor tips. Ontogeny explained some sexual differences in the cranial traits of adults, expressed as (i) morphological changes related to body size variation, and (ii) morphological changes associated with differences in the slope of ontogenetic trajectories (regardless of body size variation). Recordings of in vivo bite forces were significantly higher in adult males than in females. These differences in bite forces were not associated with the sex itself, but the sexual dimorphism in body size. Although males did not show significantly higher allometric coefficients for I, J and CA than females, males still showed a strong sexual dimorphism in these traits due to body size variation. On the other hand, measurements of mandibular width – an estimator of the relative size of masseteric muscles – in vivo showed strong differences between sexes, suggesting higher force performance at the incisor tips for males. Overall, we observed that many attributes related to bite performance might have been molded by sexual selection, which implies differences in allometric coefficients from some morphological traits throughout ontogeny.

Ontogeny of long-range vocalizations in a Neotropical fossorial rodent: the Anillaco Tuco-Tuco (Ctenomys sp.).

Tuco-tucos (Ctenomys spp.) are subterranean rodents that produce territorial, high intensity long-range vocalizations (LRVs) of broadband and low frequency that are essential for long-distance communication between individuals in different tunnel systems. Despite their importance, the development of LRVs remains poorly understood. In adult Anillaco Tuco-Tucos (Ctenomys sp.) the LRV is composed by two types of syllables (series and individual notes) that are repeated a variable number of times. We studied the development of the LRVs in eight juveniles of the Anillaco Tuco-Tuco ranging from 14–28 to 104–118 days after birth. We (1) tested whether the syllables followed any of three alternative developmental modes (retention of juvenile vocalizations, modification of juvenile precursors or de novo appearance in adults), (2) evaluated the development of structural and acoustic features of syllables, and (3) tested the prediction that juveniles should produce a greater proportion of atypical series in precursors of the LRV than adults, due to lack maturation and/or precise coupling of neuromuscular and anatomical structures. The LRV of the Anillaco Tuco-Tuco exhibited a mixed developmental mode: while series developed from juvenile precursors whose acoustic features gradually approached those of adults, individual notes appeared later in the ontogeny and de novo with acoustic features indistinguishable from those of adults. The number of series per vocalization increased through development and varied from one to 25 in juvenile males and from one to six in juvenile females. The structure of the most common series type (triad) did not exhibit ontogenetic changes and was present as such at the onset of the emission of vocalizations. On the contrary, acoustic features of juvenile triad notes changed with age in both sexes (duration 90% increased through development, while bandwidth 90% and peak frequency decreased). Furthermore, juveniles emitted a higher proportion of atypical series than adults (7.4% vs. 0.3%), as expected in the development of any complex behavior that requires practice to be mastered. The maturation of the LRV occurred well before the sexual maturation, presumably due to the protracted time needed to acquire or build a burrow system long before mating is possible. We propose that protracted vocal development is another component in the slow developmental strategy of Ctenomys and subterranean rodents in general.

P53 gene cloning and response to hypoxia in the plateau zokor, Myospalax baileyi

Abstract The plateau zokor (Myospalax baileyi) is a specialized subterranean rodent that lives on the Qinghai-Tibet Plateau. The species has evolved a series of strategies to adapt to its hypoxic environment and hypercapnia. p53 is a tumour suppressor gene that plays a crucial role in the cellular response to hypoxia by inducing cell cycle arrest, cell apoptosis, DNA damage repair and angiogenesis. To investigate the sequence characteristics of p53 and the response to hypoxia in plateau zokor, we cloned the p53 coding DNA sequence, analysed it, and measured the expression level of p53 at different altitudes in plateau zokor and rats. Our results show that the coding DNA sequence is 1179 bp, consisting of 392 amino acid residues. Compared to human p53, the subterranean rodents have two mutation sites in common with the human hotspots in the DNA-binding domain. Compared to subterranean rodents, plateau zokor have a mutation at residue 309. In addition, subterranean rodents have two convergent sites at residues 78 and 84. The expression levels of p53 in plateau zokor tissues increase significantly from 2260 m to 3300 m, but there was no significant difference in rats at those altitudes. Our results suggest that subterranean rodents have two mutation sites in common with the human hotspots in the DNA-binding domain, the mutation of Gly309Asp is a unique mutation site of plateau zokor p53, and there are two convergent sites enhancing subterranean rodent adaptation to hypoxic conditions. In addition, p53 is sensitive to the oxygen concentration in plateau zokor, and hypoxia upregulates the levels of p53. Generally, plateau zokor use this strategy to adapt to a hypoxic environment.

祁连山东段高原鼢鼠(Eospalax baileyi)土丘空间分布格局及其与环境因子的空间关联性

PDF HTML阅读 XML下载 导出引用 引用提醒 祁连山东段高原鼢鼠(Eospalax baileyi)土丘空间分布格局及其与环境因子的空间关联性 DOI: 10.5846/stxb201612292705 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然基金项目（31460635）；甘肃省国际科技合作项目（2013GS06893）；农业部公益性行业科研项目（201203041） Relationship between the spatial distribution of the mounds of plateau zokor (Eospalax baileyi) and environmental factors in eastern Qilian Mountain Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:高原鼢鼠推土造丘行为对高寒草地生态系统的生产和生态功能有重要影响，研究高原鼢鼠土丘空间分布格局及其与环境因子的关系，可以揭示高原鼢鼠栖息地利用和选择规律，为合理控制鼠害及保护草地生物多样性提供科学依据。于2014年8月在祁连山东段选取面积为140m×100m的高原鼢鼠栖息地，消除景观尺度取样带来的气候、地形和土壤的异质性，利用地统计学方法，分析高原鼢鼠土丘的空间分布格局、并揭示其与环境因子中土壤容重、土壤水分、植物地上、地下生物量、根系营养物质含量（可溶性糖、粗蛋白、粗脂肪）以及各功能群丰富度（禾本科、莎草科、杂类草）的空间关系。半方差函数及普通克里格插值表明，高原鼢鼠土丘存在中等程度的空间变异且呈现聚集分布，各环境因子均存在不同程度的空间异质性。交方差函数分析表明，高原鼢鼠分布虽与各环境因子在多种尺度下表现出复杂的空间关联性（正的或负的），但mantel检验发现土壤容重、莎草科丰富度与高原鼢鼠土丘分布呈现显著的负空间关联性，杂类草丰富度和根系粗脂肪含量与高原鼢鼠土丘分布存在显著正空间关联性。综上所述，高原鼢鼠主要栖息利用在土壤疏松、莎草科丰富度较低、杂类草较多和根系粗脂肪含量较高的地方。 Abstract:Plateau zokor (Eospalax baileyi) is a subterranean rodent endemic to the Tibetan Plateau, and it plays an important role in the alpine rangeland system because of the ecosystem function in terms of substance circulation and energy exchanges. However, at high population density, zokors are regarded as pests aggravating the degradation of rangelands. As zokors live underground, they dig tunnels in the soil for foraging or mating. In digging tunnels, the soil is pushed out on the ground as mounds, which reduce the grazing area and cover the forages. However, the mounds made by zokors create environmental heterogeneity, which increases the species diversity and nutrient recycling in soil. Therefore, the mounds have an important impact on the alpine rangeland ecosystem. Studying the spatial distribution of plateau zokor mounds and its correlation with environmental factors can reveal its role in habitat use and selection, which is the basis for controlling zokor damage and protecting biodiversity in the place. The variables of traditional statistics must be random variables, and the traditional statistics can not clarify the relationship between the variables and geographic location. As a result, the traditional statistics can not explain the reasons that influence the spatial distribution patterns in population studies. Currently, the geostatistical analysis methods are often used to study population spatial distribution patterns. In our study, we selected the small habitat of plateau zokor (140m×100m) in eastern Qilian Mountain because a small habitat can eliminate the heterogeneity of climate and geography. We used the semivariogram and ordinary kriging of geostatistical analysis methods to analyze the spatial heterogeneity of zokor mounds and the environmental factors that influence the distribution of mounds. The purpose of this study was to determine the relation between the distribution of zokor mounds and environmental factors, including soil bulk density, soil moisture, aboveground biomass, underground biomass, root's water-soluble sugar, crude protein, crude fat, richness of grass, and richness of forbs and sedges. The results of semivariogram and ordinary kriging indicated that the mounds of plateau zokor presented clumped distribution with medium variation level, and all environmental factors had spatial heterogeneity in the studying site. The results of a crossvariogram analysis showed that the distribution of zokor mounds had a positive spatial correlation with soil moisture and aboveground as well as underground biomass at the same studying scale (10.74-71.85m). The distribution of zokor mounds had a positive spatial correlation with forage nutrients, such as root's crude protein and water-soluble sugar at the studying scale (10.74-30.82m), as well as root's crude fat at the studying scale (10.74-44.01m). Besides, the distribution of zokor mounds had a positive spatial correlation with forbs at all studying scales. The mantel test indicated that the distribution of zokor mounds had a significant negative spatial correlation with soil bulk density and richness of sedge and a significant positive spatial correlation with richness of forbs and the contents of root's fat. In conclusion, the plateau zokors prefer to select the alpine meadows with softer soil, more forbs as well as plants with higher root's fat in this studying site. 参考文献 相似文献 引证文献

Contrasts in body size and growth suggest that high population density results in faster pace of life in Damaraland mole-rats (Fukomys damarensis)

We studied the correlates of population density and body size, growth rates, litter size, and group size in Damaraland mole-rats (Fukomys damarensis (Ogilby, 1838)) at two study sites with contrasting population densities. Group size, litter size, and the probability of recapture were independent of study site. However, body size differed between the two study sites, suggesting that population density may affect life-history traits in social mole-rats. At the low-density site (0.13 groups/ha), individuals were significantly larger and subordinate males showed higher growth rates than at the high-density site (0.41 groups/ha), which may indicate that high population density in subterranean rodents enhances pace of life. The larger size of nonreproductive individuals at the low-density site could adapt individuals at lower population densities to larger dispersal distances.

Skull shape and size variation within and between mendocinus and torquatus groups in the genus Ctenomys (Rodentia: Ctenomyidae) in chromosomal polymorphism context.

We tested the association between chromosomal polymorphism and skull shape and size variation in two groups of the subterranean rodent Ctenomys. The hypothesis is based on the premise that chromosomal rearrangements in small populations, as it occurs in Ctenomys, produce reproductive isolation and allow the independent diversification of populations. The mendocinus group has species with low chromosomal diploid number variation (2n=46-48), while species from the torquatus group have a higher karyotype variation (2n=42-70). We analyzed the shape and size variation of skull and mandible by a geometric morphometric approach, with univariate and multivariate statistical analysis in 12 species from mendocinus and torquatus groups of the genus Ctenomys. We used 763 adult skulls in dorsal, ventral, and lateral views, and 515 mandibles in lateral view and 93 landmarks in four views. Although we expected more phenotypic variation in the torquatus than the mendocinus group, our results rejected the hypothesis of an association between chromosomal polymorphism and skull shape and size variation. Moreover, the torquatus group did not show more variation than mendocinus. Habitat heterogeneity associated to biomechanical constraints and other factors like geography, phylogeny, and demography, may affect skull morphological evolution in Ctenomys.

Environmental factors could constrain the use of long-range vocal signals in solitary tuco-tucos (Ctenomys; Rodentia, Ctenomyidae) reproduction

Ctenomys are mainly solitary subterranean rodents. Life underground has advantages (protection against predators, environmental control and reduced competition) but also implies disadvantages (digging costs, coping with hypercapnia, physiological and sensory changes, and communication problems) that can affect the social structure. Reproduction is a critical moment in the use of the signal repertoire, because individuals should locate in space, travel to, contact and copulate with a suitable partner. Energy expenditure involved in digging (connecting) tunnels makes difficult to attain a partner burrow system, but predation risk involved in moving above ground can counterbalance it and coupled with the spatial structure of the population, can determine the best communicative strategy to contact and locate a potential partner. Vocalisations allow to communicate over longer distances an with a reduced risk, while chemical signals, mostly aimed at vomerolfaction involve proximity or direct contact with the sample odour thus making information gathering more risky. As Ctenomys can use different signal types to gather different types of information leading to copulation, we propose that the use of these signals would be flexible, depending mostly on population spatial structure and type of predators living in the zone. This is because differences among species and/or populations in the use and characteristics of long-range vocalisations could be induced by environmental and/or social factors. This variation could be considered as a case of phenotypic plasticity, determining communication strategies variability in reproductive context, mostly dependent on long-range communication signals and the behaviour of males.

Can Niche Modeling and Geometric Morphometrics Document Competitive Exclusion in a Pair of Subterranean Rodents (Genus Ctenomys) with Tiny Parapatric Distributions?

Species with similar ecological requirements coexisting in the same geographic region are prone to competitively exclude each other. Alternatively, they may coexist if character displacement acts to change the niche requirements of one or both species. We used two methodological approaches (ecological niche modeling [ENM] and geometric morphometrics) to test two hypotheses: given their behavioral, morphological, and ecological similarities, one species competitively excludes the other; and, character displacement enables their coexistence at two sites in which the species are known to occur in sympatry. The results from the ENM-based approach did not provide evidence for competitive exclusion; however, the morphometric analyses documented displacement in size of C. minutus. This result, suggests that C. minutus might exclude C. flamarioni from areas with softer soils and higher food availability. We stress the importance of using multiple methodological approaches when testing prediction of competitive exclusion. However, both methods had limited explanatory power given that the focal species possess truly peculiar distributions, being largely parapatric and restricted to narrow, small geographic areas with a strange distribution and there is a need to search for additional methods. We discuss the idiosyncrasy of the ENM-based approach when applied to organisms with subterranean habits.

Evolution of the CLOCK and BMAL1 genes in a subterranean rodent species (Lasiopodomys mandarinus)

Lasiopodomys mandarinus, a subterranean rodent, spends its entire life underground. To test whether the CLOCK and BMAL1 genes of L. mandarinus have undergone adaptive evolution to underground darkness, we cloned and analyzed their complete cDNA sequences, using Lasiopodomys brandtii as a control. The phylogenetic trees of the CLOCK and BMAL1 genes were similar to the trees of the conserved Cyt b gene，further, L. mandarinus clustered with L. brandtii and Microtus ochrogaster in the phylogenetic tree. The Q-rich region of the CLOCK gene in L. mandarinus was different from that of other subterranean rodents. Using phylogenetic analysis maximum likelihood (PAML), the ω value (ω<1) in different lineages showed that both genes have undergone purifying selection. The M8 model identified some positive selection sites in the CLOCK gene, most of which were located in the trans-transcription activation domain (TAD). In conclusion, CLOCK and BMAL1 genes did not exhibit convergent molecular evolution in subterranean rodents. Moreover, our study highlights the important functionality of the TAD, which is putatively of functional relevance to CLOCK protein activity. The present findings provide novel insights into adaptation to underground darkness, at the gene level, in subterranean rodents.

Examining object recognition and object-in-Place memory in plateau zokors, Eospalax baileyi

Recognition memory is important for the survival and fitness of subterranean rodents due to the barren underground conditions that require avoiding the burden of higher energy costs or possible conflict with conspecifics. Our study aims to examine the object and object/place recognition memories in plateau zokors (Eospalax baileyi) and test whether their underground life exerts sex-specific differences in memory functions using Novel Object Recognition (NOR) and Object-in-Place (OiP) paradigms. Animals were tested in the NOR with short (10min) and long-term (24h) inter-trial intervals (ITI) and in the OiP for a 30-min ITI between the familiarization and testing sessions. Plateau zokors showed a strong preference for novel objects manifested by a longer exploration time for the novel object after 10min ITI but failed to remember the familiar object when tested after 24h, suggesting a lack of long-term memory. In the OiP test, zokors effectively formed an association between the objects and the place where they were formerly encountered, resulting in a higher duration of exploration to the switched objects. However, both sexes showed equivalent results in exploration time during the NOR and OiP tests, which eliminates the possibility of discovering sex-specific variations in memory performance. Taken together, our study illustrates robust novelty preference and an effective short-term recognition memory without marked sex-specific differences, which might elucidate the dynamics of recognition memory formation and retrieval in plateau zokors.

Interspecific interactions may not influence home range size in subterranean rodents: a case study of two tuco-tuco species (Rodentia: Ctenomyidae)

Coexistence between species with similar niche requirements is often facilitated by displacement of morphological, behavioral, or physiological characteristics. Experiments comparing treatments with and without the presence of potential competitors are ideal for testing hypotheses of interspecific competition. Here, we investigate a fundamental aspect in the natural history of a species: the home range. We determined whether co-occurrence can influence the home range size of 2 subterranean rodent species, Ctenomys flamarioni and C. minutus. We evaluated home range size in populations of both species in allopatry and sympatry along the coastal plain of southern Brazil. Animals were radiotracked, and the home range size of each individual was estimated using grid cells and minimum convex polygon methods. We found no significant differences in home range size between sites or species, and the interaction was nonsignificant. We also found no relationship between home range size and body mass or sex. Our results suggest that co-occurrence may not influence home range size in these species, perhaps due to environmental adaptations that facilitate coexistence (e.g., microhabitat segregation and dietary modifications). Further, the characteristics of the sandy dune habitat may act as environmental filters, favoring similar home range sizes for both species. A coexistência entre espécies com requerimento similares de nicho é normalmente facilitada por deslocamento de caractere morfológico, comportamental ou fisiológico. Experimentos comparando tratamentos com e sem a presença de competidores potenciais são ideais para testar hipóteses sobre competição interespecífica. Neste estudo nós investigamos um aspecto fundamental da história natural de uma espécie: a área de vida. Nós determinamos se a co-ocorrência pode influenciar no tamanho da área de vida de dois roedores subterrâneos, C. flamarioni e C. minutus. Para isso foi avaliado o tamanho da área de vida em populações das duas espécies em locais onde se distribuem de forma alopátrica e simpátrica, ao longo da planície costeira do extremo sul do Brasil. O tamanho da área de vida de cada animal foi estimado utilizando os métodos de grid de células e mínimo polígono convexo, por meio da utilização de rádios colares fixados em cada indivíduo. Os resultados não apontaram nenhuma diferença significativa no tamanho da área de vida entre os sítios ou espécies, e as interações entre eles também não foi significativa. Além disso, não foi encontrado relação entre tamanho da área de vida com massa corporal ou sexo. Nossos resultados sugerem que a co-ocorrência pode não influenciar o tamanho da área de vida das espécies, isto pode se dá devido a adaptações ambientais que facilitam a coexistência (por exemplo, segregação de microhabitat e modificações na dieta). Além disso, as características do habitat de dunas arenosas podem atuar como filtro ambiental, favorecendo tamanhos semelhantes de área de vida em ambas as espécies.