Non-shivering thermogenesis in four species of African mole-rats differing in their sociality

Many mammalian species are adapted to living in burrows for most of their lives. Inhabiting such thermally stable environments may influence the variation on the species thermogenic capacity, particularly non-shivering thermogenesis (NST). African mole-rats (Bathyergidae) are subterranean rodents occurring in fynbos, grassland and wooded savannas across sub-Saharan Africa that vary in the complexity of their social systems, ranging from strictly solitary to highly social species. The presence and magnitude of NST are well known in social bathyergids, but no such data exist for their solitary counterparts. In this study, we quantified NST in three solitary mole-rat species represented by three distinct genera together with one social species. Our results showed that NST in all species is functional. Maximum metabolic rate after norepinephrine injection was equivalent to 269% of resting values in the social giant mole-rat Fukomys mechowii and 166%, 282% and 157% in the three solitary species: the silvery mole-rat Heliophobius argenteocinereus, the Cape mole-rat Georychus capensis and the Cape dune mole-rat Bathyergus suillus, respectively. To test our prediction that NST capacity is higher in solitary bathyergids, we combined our data with those available for other members of this family. In contrast to our prediction, NST did not differ between social and solitary bathyergids. Body mass, as the main factor, and minimum air temperature (Tmin), accounts for more than 80% of NST variation in bathyergid mole-rats.Fil: Luna, Facundo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Okrouhlík, J.. University of South Bohemia; República ChecaFil: McKechnie, A. E.. University of Pretoria; SudáfricaFil: Bennett, N. C.. University of Pretoria; SudáfricaFil: Sumbera, Radim. University of South Bohemia; República Chec

Functional anatomy and disparity of the postcranial skeleton of African mole-rats (Bathyergidae)

DATA AVAILABILITY STATEMENT : The original contributions presented in this study are included in the article/Supplementary material, further inquiries can be directed to the corresponding author.The burrowing adaptations of the appendicular system of African mole-rats (Bathyergidae) have been comparatively less investigated than their cranial adaptations. Because bathyergids exhibit different digging modes (scratchdigging and chisel-tooth digging) and social systems (from solitary to highly social), they are a unique group to assess the effects of distinct biomechanical regimes and social organization on morphology. We investigated the morphological diversity and intraspecific variation of the appendicular system of a large dataset of mole-rats (n = 244) including seven species and all six bathyergid genera. Seventeen morpho-functional indices from stylopodial (femur, humerus) and zeugopodial (ulna, tibia-fibula) elements were analyzed with multivariate analysis. We hypothesized that scratchdiggers (i.e., Bathyergus) would exhibit a more specialized skeletal phenotype favoring powerful forelimb digging as compared to the chisel-tooth diggers, and that among chisel-tooth diggers, the social taxa will exhibit decreased limb bone specializations as compared to solitary taxa due to colony members sharing the costs of digging. Our results show that most bathyergids have highly specialized fossorial traits, although such specializations were not more developed in Bathyergus (or solitary species), as predicted. Most chisel tooth-diggers are equally, or more specialized than scratch-diggers. Heterocephalus glaber contrasted significantly from other bathyergids, presenting a surprisingly less specialized fossorial morphology. Our data suggests that despite our expectations, chisel-tooth diggers have a suite of appendicular adaptations that have allowed them to maximize different aspects of burrowing, including shoulder and neck support for forward force production, transport and removal of soils out of the burrow, and bidirectional locomotion. It is probably that both postcranial and cranial adaptations in bathyergids have played an important role in the successful colonization of a wide range of habitats and soil conditions within their present distribution.The Becas Chile, Government of Chile, the National Research Foundation, the SARChI Chair of Mammalian Behavioral Ecology and Physiology and Czech Science Foundation Project GACR.http://frontiersin.org/Ecology_and_Evolutionam2023Mammal Research InstituteZoology and Entomolog

Fossorial adaptations in African mole-rats (Bathyergidae) and the unique appendicular phenotype of naked mole-rats

DATA AVAILABILITY: All the data generated and analysed in this study are included in this published article and its supplementary information files.CODE AVAILABILITY: The code for all analyses is available at: https://github.com/gabrielsaffa/african_mole_rats.Life underground has constrained the evolution of subterranean mammals to maximize digging performance. However, the mechanisms modulating morphological change and development of fossorial adaptations in such taxa are still poorly known. We assessed the morpho-functional diversity and early postnatal development of fossorial adaptations (bone superstructures) in the appendicular system of the African mole-rats (Bathyergidae), a highly specialized subterranean rodent family. Although bathyergids can use claws or incisors for digging, all genera presented highly specialized bone superstructures associated with scratch-digging behavior. Surprisingly, Heterocephalus glaber differed substantially from other bathyergids, and from fossorial mammals by possessing a less specialized humerus, tibia and fibula. Our data suggest strong functional and developmental constraints driving the selection of limb specializations in most bathyergids, but more relaxed pressures acting on the limbs of H. glaber. A combination of historical, developmental and ecological factors in Heterocephalus are hypothesized to have played important roles in shaping its appendicular phenotype.Financial support for the research trip to Kenya of J.U.M.J. was provided by The National Geographic Society, whereas funding support for the maintenance of the original NMR colonies was provided by the University of Cape Town and the South African National Research Foundation (NRF). DST-NRF is acknowledged for the financial support to establish the MIXRAD micro-focus X-ray tomography facility at Necsa.https://www.nature.com/commsbioam2023Mammal Research InstituteZoology and Entomolog

Phylogeography of a widespread sub-Saharan murid rodent Aethomys chrysophilus: the role of geographic barriers and paleoclimate in the Zambezian bioregion

Murid rodents of the genus Aethomys are one of the most common rodents in drier habitats in sub-Saharan Africa. Among them, the red veld rat Aethomys chrysophilus is the most widespread species with the core distribution located in the Zambezian bioregion. In this study, we describe phylogeographic structure of the species and estimate its age from a time-calibrated phylogeny of the genus. Seven parapatric clades were identified in the mitochondrial cytochrome b phylogeny, where some of the distributions of these clades have been separated by previously described biogeographical divides (Zambezi-Kafue river system, Rukwa Rift and the Eastern Arc Mountains). One internal clade corresponded to populations previously described as a distinct species, Aethomys ineptus. The whole A. chrysophilus complex was estimated to be 1.3 (0.5–2.4) Mya old, with A. ineptus originating 0.7 (0.1–1.4) Mya before present. The internal position of A. ineptus was also recovered in phylogenetic reconstruction based on two nuclear genes and thus it is not a consequence of mitochondrial introgression. In addition, we analyzed skull form variation across the species’ distributional range and found no significant difference between A. ineptus and the rest of A. chrysophilus complex

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.The Czech Science Foundation (14–2758 S, to P.N.), Grant Agency of Charles University (325515, to K.K.) and the European Social Fund and the state budget of the Czech Republic (CZ.1.07/2.3.00/30.0022, to S.O.).http://www.nature.com/srepam2018Mammal Research InstituteZoology and Entomolog

Spatial and temporal activity patterns of the free-living giant mole-rat (Fukomys mechowii), the largest social bathyergid.

Despite the considerable attention devoted to the biology of social species of African mole-rats (Bathyergidae, Rodentia), knowledge is lacking about their behaviour under natural conditions. We studied activity of the largest social bathyergid, the giant mole-rat Fukomys mechowii, in its natural habitat in Zambia using radio-telemetry. We radio-tracked six individuals during three continuous 72-h sessions. Five of these individuals, including a breeding male, belonged to a single family group; the remaining female was probably a solitary disperser. The non-breeders of the family were active (i.e. outside the nest) 5.8 hours per 24h-day with the activity split into 6.5 short bouts. The activity was more concentrated in the night hours, when the animals also travelled longer distances from the nest. The breeding male spent only 3.2 hours per day outside the nest, utilizing less than 20% of the whole family home range. The dispersing female displayed a much different activity pattern than the family members. Her 8.0 hours of outside-nest activity per day were split into 4.6 bouts which were twice as long as in the family non-breeders. Her activity peak in the late afternoon coincided with the temperature maximum in the depth of 10 cm (roughly the depth of the foraging tunnels). Our results suggest that the breeding individuals (at least males) contribute very little to the work of the family group. Nevertheless, the amount of an individual's activity and its daily pattern are probably flexible in this species and can be modified in response to actual environmental and social conditions

Bite force in the strictly subterranean rodent family of African mole-rats (Bathyergidae) : the role of digging mode, social organization and ecology

DATA AVAILABILITY STATEMENT : The data are deposited in the Dryad Digital Repository https://datadryad.org/stash/dataset/doi:10.5061/dryad.ksn02v772 (Kraus et al., 2022).Bite force is an ecologically relevant performance trait that has been measured to better understand the adaptations to diet and habitat use. Moreover, bite force is relevant in understanding reproductive success, as well as inter- and intraspecific competition. African mole-rats (Bathyergidae, Rodentia) are a unique clade of mammals that use different digging strategies, show different types of social organization and occur in ecologically diverse savanna habitats in sub-Saharan Africa. Whereas previous studies have suggested these animals have exceptionally high bite forces, the ecological and other proximate and ultimate drivers of variation in bite force in the group remain unstudied. In the present study we measured in vivo bite force of 394 adult specimens from 10 African mole-rat species including all genera within the family. Our results show that in African mole-rats digging mode is a major driver of variation in bite force, with chisel-tooth diggers being stronger biters than scratch diggers. Moreover, species living in habitats characterized by low and irregular precipitation patterns and in soils with a high content of coarse particles have a higher bite force than species occupying habitats with a regular rainfall pattern and fine soil types. This suggests that bite force in bathyergids has evolved in concert with rainfall and soil characteristics of different savanna habitats, which have contributed to the successful radiation of these subterranean mammals across sub-Saharan Africa.Czech Science Foundation.http://www.wileyonlinelibrary.com/journal/fec2023-07-02hj2023Mammal Research InstituteZoology and Entomolog