Subterranean Rodent Research Articles

Habitat and Burrow System Characteristics of the Blind Mole Rat Spalax galili in an Area of Supposed Sympatric Speciation.

A costly search for food in subterranean rodents resulted in various adaptations improving their foraging success under given ecological conditions. In Spalax ehrenbergi superspecies, adaptations to local ecological conditions can promote speciation, which was recently supposed to occur even in sympatry at sites where two soil types of contrasting characteristics abut each other. Quantitative description of ecological conditions in such a site has been, nevertheless, missing. We measured characteristics of food supply and soil within 16 home ranges of blind mole rats Spalax galili in an area subdivided into two parts formed by basaltic soil and pale rendzina. We also mapped nine complete mole rat burrow systems to compare burrowing patterns between the soil types. Basaltic soil had a higher food supply and was harder than rendzina even under higher moisture content and lower bulk density. Population density of mole rats was five-times lower in rendzina, possibly due to the lower food supply and higher cover of Sarcopoterium shrubs which seem to be avoided by mole rats. A combination of food supply and soil parameters probably influences burrowing patterns resulting in shorter and more complex burrow systems in basaltic soil.

Sharing the space: distribution, habitat segregation and delimitation of a new sympatric area of subterranean rodents.

Subterranean rodents of the genus Ctenomys usually present an allopatric or parapatric distribution. Currently, two cases of sympatry have been recognized for the genus in the coastal dunes of southern Argentina and southern Brazil. In this context, they are ideal models to test hypotheses about the factors that delimit the patterns of space use and to understand interspecific interactions in small mammals. We investigated the vegetation structure, plant biomass and soil hardness selected by two species of subterranean rodents (Ctenomys flamarioni and C. minutus) when distributed in sympatry and allopatry from nine different areas along the line of coastal dunes in southern Brazil. In addition, our work presents a new record of a third area of sympatry for the genus Ctenomys. Ctenomys flamarioni and C. minutus show habitat segregation in the area where they occur in sympatry. These species show segregation in their selection of microhabitats, differing in relation to soil hardness, plant biomass, and plant cover. Ctenomys flamarioni showed a distinction in habitat selection when occurring in allopatry and sympatry, whereas C. minutus selected the same habitat characteristics under both conditions. A possible explanation to the observed pattern is that these species have acquired different adaptations over time which allows them the ability to exploit different resources and thus avoid competitive interactions all together.

Morphological Constraints in the Craniomandibular Complex of Chisel‐tooth Digging Mole‐rats

African mole-rats are subterranean rodents from the family Bathyergidae, which consists of six genera, five of which (Cryptomys, Fukomys, Georychus, Heliophobius and Heterocephalus) are chisel-toot...

Solitary Ethiopian wolves increase predation success on rodents when among grazing gelada monkey herds

Mixed-species associations generally form to increase foraging success or to aid in the detection and deterrence of predators. While mixed-species associations are common among mammals, those involving carnivorous predators and potential prey species are seldom reported. On the Guassa Plateau, in the Ethiopian highlands, we observed solitary Ethiopian wolves (Canis simensis) foraging for rodents among grazing gelada monkey (Theropithecus gelada) herds. The tolerant and sometimes prolonged (> 1h) associations contrasted with the defensive behaviors exhibited by geladas toward other potential predators. Ethiopian wolves spent a higher proportion of time foraging and preyed more successfully on rodents when among geladas than when alone, providing evidence that gelada herds increase the vulnerability of subterranean rodents to predation. Ethiopian wolves appear to habituate gelada herds to their presence through nonthreatening behavior, thereby foregoing opportunistic foraging opportunities upon vulnerable juvenile geladas in order to feed more effectively on rodents. For Ethiopian wolves, establishing proximity to geladas as foraging commensals could be an adaptive strategy to elevate foraging success. The novel dynamics documented here shed light on the ecological circumstances that contribute to the stability of mixed groups of predators and potential prey.

DNA metabarcoding diet analysis for species with parapatric vs sympatric distribution: a case study on subterranean rodents.

Closely related sympatric species commonly develop different ecological strategies to avoid competition. Ctenomys minutus and C. flamarioni are subterranean rodents parapatrically distributed in the southern Brazilian coastal plain, showing a narrow sympatric zone. To gain understanding on food preferences and possible competition for food resources, we evaluated their diet composition performing DNA metabarcoding analyzes of 67 C. minutus and 100 C. flamarioni scat samples, collected along the species geographical ranges. Thirteen plant families, mainly represented by Poaceae, Araliaceae, Asteraceae and Fabaceae, were identified in the diet of C. minutus. For C. flamarioni, 10 families were recovered, with a predominance of Poaceae, Araliaceae and Asteraceae. A significant correlation between diet composition and geographical distance was detected in C. minutus, whereas the diet of C. flamarioni was quite homogeneous throughout its geographical distribution. No significant differences were observed between males and females of each species. However, differences in diet composition between species were evident according to multivariate analysis. Our results suggest some level of diet partitioning between C. flamarioni and C. minutus in the sympatric region. While the first species is more specialized on few plant items, the second showed a more varied and heterogeneous diet pattern among individuals. These differences might have been developed to avoid competition in the region of co-occurrence. Resource availability in the environment also seems to influence food choices. Our data indicate that C. minutus and C. flamarioni are generalist species, but that some preference for Poaceae, Asteraceae and Araliaceae families can be suggested for both rodents.

Burrow architecture and burrowing dynamics of Ctenomys in foredunes and paleoenvironmental implications

Ctenomys sp., also known as tuco-tuco, is a solitary subterranean small rodent that inhabits sandy soils in South America. We studied burrow system architecture of Ctenomys flamarioni communities from the foredunes of the Southern Brazil Coastal Plain by inserting plaster of Paris and excavating the tunnels. The structure of the burrow system is complex with interlinked tunnels, one occasionally open entrance, multiple chambers and turnarounds, blind laterals, varying slopes, T-junctions, bifurcations, and two different levels. A specific isolated chamber is used as a latrine, while another is used as a nest. The burrow entrance is open only when the rodent is taking out sand or feeding. The tunnels have an average depth of 35cm (deepest at 55cm and the most superficial at 15cm near the entrance). The average burrow length ranges from 190 to 500cm. The tunnels have different heights and widths varying from 5.5–9.3cm wide to 6–11cm high. The entrance is inclined ~28°. The central part of the burrow system has a steeper slope, with an inclination of ~38°. The plaster molds preserve claw marks of four digits of up to 4mm in depth. Collapsed burrows are rapidly sealed to avoid the entrance of predators. Ctenomys sp. burrows provide a suitable microhabitat, which is used by the animals as protection from adverse environmental conditions, particularly during the winter when wind impacts the coastal area. The extensive interlinking tunnels provide underground routes to escape from predators. Ctenomys burrows in coastal dune environments are appreciably more complex than those excavated in arid environments, which are shallower with no chambers and a slope of up to 20°. Such difference in the architecture of the burrows can be used as a criterion to reconstruct the paleoenvironment of burrow systems in the rock record.

Retraction: “Do cortisol and corticosterone play the same role in coping with stressors? Measuring glucocorticoid serum in free‐ranging guanacos (Lama guanicoe)”, by R. Ovejero, A. Novillo, M. Soto‐Gamboa, M.E. Mosca‐Torres, P. Cuello, P. Gregório, G. Jahn and P. Carmanchahi

Journal of Experimental Zoology Part A: Ecological Genetics and PhysiologyVolume 323, Issue 2 p. 73-73 RetractionFree Access Retraction: “Do cortisol and corticosterone play the same role in coping with stressors? Measuring glucocorticoid serum in free-ranging guanacos (Lama guanicoe)”, by R. Ovejero, A. Novillo, M. Soto-Gamboa, M.E. Mosca-Torres, P. Cuello, P. Gregório, G. Jahn and P. Carmanchahi This article retracts the following: Differential Responses of Cortisol and Corticosterone to Adrenocorticotropic Hormone (ACTH) in a Subterranean Rodent (Ctenomys talarum) FEDERICO VERA, ROXANA RITA ZENUTO, CARLOS DANIEL ANTENUCCI, Volume 317Issue 3Journal of Experimental Zoology Part A: Ecological Genetics and Physiology pages: 173-184 First Published online: April 18, 2012 First published: 11 February 2015 https://doi.org/10.1002/jez.1918Citations: 1AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat The above article, published online on 30 September, 2013 in Wiley Online Library (wileyonlinelibrary.com), has been retracted by agreement between the journal Editor-in-Chief, David Crews, and Wiley Periodicals Inc. The retraction is due to substantial overlap with two other papers, one published in General and Comparative Endocrinology (Vera, Antenucci & Zenuto, 2011) and the other published in Journal of Experimental Zoology Part A (Vera, Zenuto & Antenucci, 2012). References Ovejero R, Novillo A, Soto-Gamboa M, Mosca-Torres ME, Cuello P, Gregório P, Jahn G, Carmanchahi P. 2013. Do cortisol and corticosterone play the same role in coping with stressors? Measuring glucocorticoid serum in free-ranging guanacos (Lama guanicoe). J. Exp. Zool. 319A: 539– 547. doi: 10.1002/jez.1918 Wiley Online LibraryCASWeb of Science®Google Scholar Vera F, Antenucci CD, Zenuto RR. 2011. Cortisol and corticosterone exhibit different seasonal variation and responses to acute stress and captivity in tuco-tucos (Ctenomys talarum). Gen. Comp. Endocrinol. 170: 550– 557. doi: 10.1002/jez.1711 Wiley Online LibraryCASPubMedWeb of Science®Google Scholar Vera F, Zenuto RR, Antenucci CD. 2012. Differential responses of cortisol and corticosterone to adrenocorticotropic hormone (ACTH) in a subterranean rodent (Ctenomys talarum). J. Exp. Zool. 317: 173– 184. doi: 10.1016/j.ygcen.2010.11.012 Wiley Online LibraryCASWeb of Science®Google Scholar Volume323, Issue2February 2015Pages 73-73 ReferencesRelatedInformation

Aerosol deposition in nasal passages of burrowing and ground rodents when breathing dust-laden air

The adaptation of subterranean rodents, which dig passages with their front teeth, to underground life presumes the formation of protection mechanisms against inhaling dust particles of different size when digging. One such mechanism can be a specific pattern of air-flow organization in the nasal cavity. To verify this assumption, we conducted a comparative study of the geometry and aerodynamics of nasal passages of a typical representative of subterranean rodents, the mole vole, and a representative of ground rodents, the house mouse. Numerical modeling of air flows and the deposition of micro- and nanoparticle aerosols indicate that sedimentation of model particles over the whole surface of the nasal cavity is higher in the mole vole than in the house mouse, while, on the contrary, particle deposition on the surface of the olfactory epithelium is much less in the burrowing rodent as compared to the ground rodent. The adaptive significance of the latter was substantiated by an experimental study on the inflow of hydrated manganese oxide MnO · (H2O)x and Mn ion nanoparticles from the nasal cavity into brain. It has been shown with use of magnetic resonance tomography (MRT) that there is no difference between the studied species with respect to the inflow of particles or ions by the olfactory bulb when they are introduced intranasally. Meanwhile, when inhaling a nanoparticle aerosol of MnCl2, the Mn deposition in the house mouse’s olfactory bulbs significantly exceeds that in the mole vole’s bulbs. Thus, the morphology of nasal passages as a factor determining the aerodynamics of upper respiratory tract ensures more efficient protection of both the lungs and brain against inhaled aerosols for burrowing rodents than for ground ones.

A re-assessment of Rensch's rule in tuco-tucos (Rodentia: Ctenomyidae: Ctenomys) using a phylogenetic approach

Sexual size dimorphism (SSD) is affected by a large number of factors, mating system being one of the most relevant. Almost 70 species of subterranean rodents of the genus Ctenomys are considered highly polygynic, and polygyny jointly with absence of paternal care of the young, favours high SSD. In this respect, Rensch's rule predicts that SSD scales with body size so that when males are larger than females SSD tends to increase with body size. We studied SSD and Rensch's rule in 28 taxa of Ctenomys using a phylogenetic approach employing the method of phylogenetic reduced major axis (pRMA) to perform reduced major axis (RMA) model II regression in the form of log10(male mass) on log10(female mass). The RMA regression slope (β) was statistically tested to accept or reject the null hypothesis that βpRMA=1.0. A slope significantly >1.0 would signal concordance with Rensch's rule. Our results showed that despite a high degree of male-biased SSD as expected from polygynic species, Rensch's rule is not verified in this rodent group. The causes of the non-concordance with Rensch's rule as well as its taxonomic level of application are discussed in terms of current models of SSD.

Immune challenge but not dietary restriction affects spatial learning in the wild subterranean rodent Ctenomys talarum

Several lines of evidence suggest that learning and triggering an immune response are both metabolically expensive and thus likely to be subject to nutritional trade-offs between them and other competing demands. Therefore, we evaluated if an immune challenge with a novel antigen affects spatial learning in the subterranean rodent Ctenomys talarum under two different dietary conditions. The results showed that immune-challenged animals were affected in their spatial learning capabilities, increasing the number of errors and marginally the time required to reach the goal of a complex labyrinth. No effect of the dietary restriction nor interaction between factors were observed. This work provides support for the existence of a trade-off between the costs of the immune defense and learning abilities, indicating that when investment is required to fight infection, fewer resources are available for learning. The absence of effect of nutritional condition on this trade-off suggests that other physiological processes, besides cognition, may be limited by the energetic resources necessary to the more immediately critical immune response.

Surprisingly low risk of overheating during digging in two subterranean rodents

Capacities for and constraints of heat dissipation are considered to be important factors governing maximum intensity and duration of physical activity. Subterranean mammals are endurance diggers, but because of lack of air currents in their burrows, high relative humidity and other physical constraints, the capacity of common mammalian cooling mechanisms underground is very limited. We analyzed surface and body core temperature changes after digging in soft and hard substrates in two species of African mole-rats (Bathyergidae, Rodentia); the social giant mole-rat Fukomys mechowii and the solitary silvery mole-rat Heliophobius argenteocinereus. As expected, we observed an increase of body core temperature in both species after digging in both substrates. Surprisingly, and contrary to our expectations, we observed remarkable decrease of mole-rats' surface temperature immediately after the end of the digging trials. This decrease was greater in soft and moister soil than that in hard and drier soil. Our results suggest that mole-rats may effectively avoid overheating in burrows by effective cooling while digging, especially in wet soil. This indicates that burrowing in soils moistened by rains could be easier than previously thought contributing thus to mole-rats success in challenging environment of subterranean burrows.

Adaptations to a Subterranean Environment and Longevity Revealed by the Analysis of Mole Rat Genomes

Subterranean mammals spend their lives in dark, unventilated environments that are rich in carbon dioxide and ammonia and low in oxygen. Many of these animals are also long-lived and exhibit reduced aging-associated diseases, such as neurodegenerative disorders and cancer. We sequenced the genome of the Damaraland mole rat (DMR, Fukomys damarensis) and improved the genome assembly of the naked mole rat (NMR, Heterocephalus glaber). Comparative genome analyses, along with the transcriptomes of related subterranean rodents, revealed candidate molecular adaptations for subterranean life and longevity, including a divergent insulin peptide, expression of oxygen-carrying globins in the brain, prevention of high CO2-induced pain perception, and enhanced ammonia detoxification. Juxtaposition of the genomes of DMR and other more conventional animals with the genome of NMR revealed several truly exceptional NMR features: unusual thermogenesis, an aberrant melatonin system, pain insensitivity, and unique processing of 28S rRNA. Together, these genomes and transcriptomes extend our understanding of subterranean adaptations, stress resistance, and longevity.

Interpopulation differences in parasite load and variable selective pressures on MHC genes inCtenomys talarum

We explore potential geographic variation in the pathogen-mediated selective pressures acting on major histocompatibility complex (MHC) loci in the subterranean rodent Ctenomys talarum, evaluating the impact of differences in parasite load between 2 populations (Mar de Cobo [MdC] and Necochea [NC]) on immunogenetic variation and selection on MHC genes in this species. Because Ctenomys from NC face lower parasite load and presumably weaker pathogen-mediated selection on MHC, we expected to find a weaker correlation between MHC variation and parasite load or immunocompetence, or both, in this population compared to that at MdC. MHC-associated cues are used in other species of rodents as kinship markers to avoid inbreeding, and because kinship structure is less pronounced in NC, we predicted that use of MHC-associated cues in mate choice would be less apparent in this population. We characterized MHC variation in NC as a function of parasite load and immunocompetence and compared our results with previous findings for MdC. The 2 populations were sampled across different, but consecutive, years. Using coinertia analyses, we found a significant positive association between a specific DRB allele and intensity of infection by fleas in NC. We explored the use of MHC-associated cues in mate choice in NC and found support for both the “good-genes” and the “genetic compatibility” hypotheses. As expected, associations between MHC and parasite load or immunocompetence were weaker in NC. Evidence indicated that females in NC selected for males with lower MHC diversity. This suggests that parasite-driven selection acting directly on MHC genes seems to be greater for the population facing higher parasite load. However, parasite-driven selection mediated by mate choice may not only be influenced by levels of parasite diversity in the population but also by characteristics of the mating system.

Novel microsatellite markers obtained from Gansu zokor (Eospalax cansus) and cross-species amplification in Plateau zokor (Eospalax baileyi)

Zokor (Mysopalacinae) is a group of subterranean rodents. Although they are regarded as important components in the ecosystems they belong to, due to their underground lifestyle, very little is known about their ecology and behavior. Development of microsatellite markers can potentially assist in addressing behavioral and ecological questions such as dispersal, mating and social systems. Here we report the development of 11 polymorphic microsatellite loci from the genome of Eospalax cansus using 454 shot-gun sequencing. Genetic diversity was assessed using DNA samples of 47 individuals of E. cansus from a single location. Cross-amplification in Eospalax baileyi was also tested, with five polymorphic markers being amplified successfully. These markers are the first published microsatellites loci from E. cansus and will be invaluable for studies addressing ecological and behavioral questions involving E. cansus and E. baileyi, and potentially other species in Mysopalacinae.

Inflammation in response to phytohemagglutinin injection in the Talas tuco-tuco (Ctenomystalarum): implications for the estimation of immunocompetence in natural populations of wild rodents

The immunological variation in wild populations and its relation to life-history traits has recently become a central topic in the field of evolutionary biology, considering the critical contribution of immunity to an individual’s fitness. A common technique used by ecologists to estimate immunocompetence in wild populations is the phytohemagglutinin (PHA) – skin test. In this test, the degree of local swelling triggered by PHA is usually considered an estimate of T-lymphocyte activity, although there is an ongoing debate regarding this interpretation. Here, we coupled the PHA–skin test with a histological analysis to examine the temporal development of the cell-mediated response in the subterranean rodent Talas tuco-tuco (Ctenomys talarum Thomas, 1898). The inflammation response involved lymphocytes, neutrophils, eosinophils, and macrophages at the site of injection, achieving an increase of total leukocytes from 12 to 48 h after injection. However, the abundance of any of the leukocytes observed did not correlate with the degree of swelling at any time studied, suggesting that caution should be taken when interpreting the results of the PHA-induced swelling response. Particularly, the magnitude of macroscopic swelling should not be considered a priori as indicative of T-lymphocyte activity in wild-caught rodents. Our results highlight the importance of avoiding oversimplified approaches to measuring immunocompetence.

Molecular identification of Taenia mustelae cysts in subterranean rodent plateau zokors (Eospalax baileyi).

Cestode larvae spend one phase of their two-phase life cycle in the viscera of rodents, but cases of cestodes infecting subterranean rodents have only been rarely observed. To experimentally gain some insight into this phenomenon, we captured approximately 300 plateau zokors (Eospalax baileyi), a typical subterranean rodent inhabiting the Qinghai-Tibet Plateau, and examined their livers for the presence of cysts. Totally, we collected five cysts, and using a mitochondrial gene (cox1) and two nuclear genes (pepck and pold) as genetic markers, we were able to analyze the taxonomy of the cysts. Both the maximum likelihood and Bayesian methods showed that the cysts share a monophyly with Taenia mustelae, while Kimura 2-parameter distances and number of different sites between our sequences and T. mustelae were far less than those found between the examined sequences and other Taeniidae species. These results, alongside supporting paraffin section histology, imply that the cysts found in plateau zokors can be regarded as larvae of T. mustelae, illustrating that zokors are a newly discovered intermediate host record of this parasite.

Digital dissection of the masticatory muscles of the naked mole-rat, Heterocephalus glaber (Mammalia, Rodentia).

The naked mole-rat, Heterocephalus glaber, of the family Bathyergidae is a subterranean rodent that feeds on underground roots and tubers and digs extensive tunnel systems with its incisors. It is a highly unusual mammal with regard to its social structure, longevity, pain insensitivity and cancer resistance, all of which have made it the subject of a great deal of research in recent years. Yet, much of the basic anatomy of this species remains undocumented. In this paper, we describe the morphology of the jaw-closing musculature of the naked mole-rat, as revealed by contrast-enhanced micro-computed tomography. This technique uses an iodine stain to enable the imaging of soft tissues with microCT. The iodine-enhanced scans were used to create 3D reconstructions of the naked mole-rat masticatory muscles from which muscle masses were calculated. The jaw-closing musculature of Heterocephalus glaber is relatively very large compared to other rodents and is dominated by the superficial masseter, the deep masseter and the temporalis. The temporalis in particular is large for a rodent, covering the entirety of the braincase and much of the rear part of the orbit. The morphology of the masseter complex described here differs from two other published descriptions of bathyergid masticatory muscles, but is more similar to the arrangement seen in other rodent families. The zygomaticomandibularis (ZM) muscle does not protrude through the infraorbital foramen on to the rostrum and thus the naked mole-rat should be considered protrogomorphous rather than hystricomorphous, and the morphology is consistent with secondarily lost hystricomorphy as has been previously suggested for Bathyergidae. Overall, the morphology of the masticatory musculature indicates a species with a high bite force and a wide gape–both important adaptations for a life dominated by digging with the incisors.

Chromosome synapsis and recombination in simple and complex chromosomal heterozygotes of tuco-tuco (Ctenomys talarum: Rodentia: Ctenomyidae)

The chromosomal speciation hypothesis suggests that irregularities in synapsis, recombination, and segregation in heterozygotes for chromosome rearrangements may restrict gene flow between karyotypically distinct populations and promote speciation. Ctenomys talarum is a South American subterranean rodent inhabiting the coastal regions of Argentina, whose populations polymorphic for Robertsonian and tandem translocations seem to have a very restricted gene flow. To test if chromosomal differences are involved in isolation among its populations, we examined chromosome pairing, recombination, and meiotic silencing of unsynapsed chromatin in male meiosis of simple and complex translocation heterozygotes using immunolocalization of the MLH1 marking mature recombination nodules and phosphorylated histone γH2A.X marking unrepaired double-strand breaks. We observed small asynaptic areas labeled by γH2A.X in pericentromeric regions of the chromosomes involved in the trivalents and quadrivalents. We also observed a decrease of recombination frequency and a distalization of the crossover distribution in the heterozygotes and metacentric homozygotes compared to acrocentric homozygotes. We suggest that the asynapsis of the pericentromeric regions are unlikely to induce germ cell death and decrease fertility of the heterozygotes; however, suppressed recombination in pericentromeric areas of the multivalents may reduce gene flow between chromosomally different populations of the Talas tuco-tuco.

PHA-induced inflammation is not energetically costly in the subterranean rodent Ctenomys talarum (tuco-tucos)

Immune activity has been proposed to be associated with substantial costs, due to trade-offs with other functions or activities that share common resources and contribute to an animal's fitness. However, direct estimates of the cost of mounting an immune response are few and have been performed mainly in birds. Thus, further work is needed to clarify the relative costs of different components of the immune system and the role of environmental and life-history traits in modulating the costs of resistance. Within the components of immunity, inflammation is considered to be associated with a larger energetic expenditure. Here, we evaluated the energetic cost of the inflammatory response to phytohemagglutinin (PHA) in a wild population of a subterranean rodent, Ctenomys talarum, and the trade-offs between immune activity and reproduction. C. talarum develops an inflammatory response to PHA, but contrary to our predictions, this response was not associated with an increase in oxygen consumption regardless of reproductive status or sex. Our study shows that an immune challenge may not always result in a detectable energetic cost. We discuss the possibility that other currencies could be underlying the cost, such as micro-or macronutrients requirements, autoimmunity or oxidative stress.

Social and Environmental Influences on Daily Activity Pattern in Free-Living Subterranean Rodents: The Case of a Eusocial Bathyergid.

Predictable daily activity patterns have been detected repeatedly even in mammals living in stable environments, as is the case for subterranean rodents. Whereas studies on activity of these rodents under laboratory conditions almost exclusively have concerned themselves with the influence of light, many field studies have revealed signs of an association between the activity pattern and daily fluctuations of temperature under the ground. This would assume that behavioral thermoregulation is probably involved. The only exceptions to the relationship between temperature and activity are 2 eusocial mole-rats of the genus Fukomys (Bathyergidae, Rodentia), which indicates that activity patterns could be affected also by social cues. To better understand how social and environmental factors influence the activity pattern in a eusocial mole-rat, we monitored the outside-nest activity in another species of this genus, the Ansell's mole-rat (Fukomys anselli), which has a relatively small body mass, high conductance, and more superficially situated burrows. Its daily activity had 1 prominent peak (around 1400 h), and it was tightly correlated with the temperature measured at depth of foraging burrows. Since F. anselli has high thermoregulatory requirements to maintain stable body temperature below the lower critical temperature, we conclude that the observed pattern is probably the result of minimizing the cost of thermoregulation. There were no significant differences in the daily activity patterns of breeding males and females and nonbreeders. Members of the same family group tended to have more similar activity patterns, but consistent activity synchronization between individuals was not proven. From the comparison of available data on all subterranean rodents, we assume that social cues in communally nesting mole-rats may disrupt (mask) temperature-related daily activity rhythms but probably only if the additional cost of thermoregulation is not too high, as it likely is in the Ansell's mole-rat.