Muscle architecture and muscle fibre type composition in the forelimb of two African mole-rat species, Bathyergus suillus and Heterocephalus glaber.

The scratch-digging Cape dune mole-rat (Bathyergus suillus), and the chisel-toothed digging naked mole-rat (Heterocephalus glaber) are African mole-rats that differ in their digging strategy. The aim of this study was to determine if these behavioural differences are reflected in the muscle architecture and fibre-type composition of the forelimb muscles. Muscle architecture parameters of 39 forelimb muscles in both species were compared. Furthermore, muscle fibre type composition of 21 forelimb muscles were analysed using multiple staining protocols. In B. suillus, muscles involved with the power stroke of digging (limb retractors and scapula elevators), showed higher muscle mass percentage, force output and shortening capacity compared to those in H. glaber. Additionally, significantly higher percentages of glycolytic fibres were observed in the scapular elevators and digital flexors of B. suillus compared to H. glaber, suggesting that the forelimb muscles involved in digging in B. suillus provide fast, powerful motions for effective burrowing. In contrast, the m. sternohyoideus a head and neck flexor, had significantly more oxidative fibres in H. glaber compared to B. suillus. In addition, significantly greater physiological cross-sectional area and fascicle length values were seen in the neck flexor, m. sternocleidomastoideus, in H. glaber compared to B. suillus, which indicates a possible adaptation for chisel-tooth digging. While functional demands may play a significant role in muscle morphology, the phylogenetic differences between the two species may play an additional role which needs further study.

The Curious Case of the Naked Mole-Rat: How Extreme Social and Reproductive Adaptations Might Influence Sex Differences in the Brain.

Research in the neurobiology of sex differences is inherently influenced by the study species that are used. Some traditional animal research models, such as rats and mice, show certain sex differences in the brain that have been foundational to neurobiological research. However, subsequent work has demonstrated that these differences are not always generalizable, especially to species with different social structures and sex-associated roles or behaviors. One such example is the naked mole-rat (Heterocephalus glaber), which has an unusual social structure among mammals. Naked mole-rats live in large groups where reproduction is restricted to a dominant female, called the "queen," and often only one breeding male. All other animals in the group, the "subordinates," are socially suppressed from reproduction and remain in a prepubescent state as adults, unless they are removed from the presence of the queen. These subordinates show little to no sex differences in external morphology, neural morphology, or behavior. However, there are a suite of neurobiological differences between subordinate and breeding naked mole-rats. After naked mole-rats attain breeding status, many of the classically sexually differentiated brain regions increase in volume (paraventricular nucleus, medial amygdala, bed nucleus of the stria terminalis). There are additionally social status differences in sex hormone receptor expression in the brain, as well as other changes in gene expression, some of which also show sex differences - though not always in the predicted direction based on other rodent studies. Data from naked mole-rats show that it is critical to consider the evolved social structure of a species when studying sex differences in the brain.

Immune competence and spleen size scale with colony status in the naked mole-rat.

Naked mole-rats (NM-R; Heterocephalus glaber) live in multi-generational colonies with a social hierarchy, and show low cancer incidence and long life-spans. Here we asked if an immune component might underlie such extreme physiology. The largest lymphoid organ is the spleen, which plays an essential role in responding to immunological insults and may participate in combating cancer and slowing ageing. We investigated the anatomy, molecular composition and function of the NM-R spleen using RNA-sequencing and histological analysis in healthy NM-Rs. Spleen size in healthy NM-Rs showed considerable inter-individual variability, with some animals displaying enlarged spleens. In all healthy NM-Rs, the spleen is a major site of adult haematopoiesis under normal physiological conditions. However, myeloid-to-lymphoid cell ratio is increased and splenic marginal zone showed markedly altered morphology when compared to other rodents. Healthy NM-Rs with enlarged spleens showed potentially better anti-microbial profiles and were much more likely to have a high rank within the colony. We propose that the anatomical plasticity of the spleen might be regulated by social interaction and gives immunological advantage to increase the lifespan of higher-ranked animals.

Comparative forelimb morphology of scratch-digging and chisel-tooth digging African mole-rat species.

Bathyergus suillus (Cape dune mole-rat) and Heterocephalus glaber (naked mole-rat) are two species of subterranean burrowing rodents. Bathyergus suillus occurs in soft sandy soils and is regarded as a scratch-digger, while H. glaber is found in hard, compact soils and is a chisel-tooth digging species. The present study aimed to determine musculoskeletal differences in the forelimb of these two species. The muscles of the forelimb, back and neck were dissected to the points of origin and insertion in the left and right forelimbs, B. suillus (n = 7) and H. glaber (n = 5). Dissected muscles were photographed before maceration to demonstrate muscle attachments. The scapular spine, acromion process and clavicle were relatively straight in B. suillus. In comparison a curved scapular spine, acromion process and clavicle were observed in H. glaber. In both species, the clavicle rested on the greater tuberosity of the humerus. In B. suillus, the deltoid tuberosity was prominent and situated more distally on the humeral shaft compared to the indistinct, more proximally situated deltoid tuberosity in H. glaber. A prominent bony structure underlying the thenar pad as well as a cartilaginous protrusion beneath the hypothenar pad were observed on the palmar surface of the manus in B. suillus. Prominent claws were observed in B. suillus. A robust m. sternohyoideus was observed in H. glaber while mm. tensor fasciae antebrachii and coracobrachialis were absent. The flexors of the antebrachium of B. suillus had additional and enlarged attachment sites. The forelimb of B. suillus may be morphologically adapted for scratch-digging with relatively large and additional forelimb muscles and robust bones. In comparison, H. glaber had a reduction in the relative size, amount of muscles as well as number of attachment sites in the forelimb muscles, while the well-developed ventral neck muscles may facilitate neck and head stabilisation during chisel-tooth digging.

Comparative morphometric analysis of lungs of the semifossorial giant pouched rat (Cricetomys gambianus) and the subterranean Nigerian mole rat (Cryptomys foxi).

Lungs of the rodent species, the African giant pouched rat (Cricetomys gambianus) and the Nigerian mole rat (Cryptomys foxi) were investigated. Significant morphometric differences exist between the two species. The volume of the lung per unit body mass was 2.7 times larger; the respiratory surface area 3.4 times greater; the volume of the pulmonary capillary blood 2 times more; the harmonic mean thickness of the blood-gas (tissue) barrier (τht) ~29% thinner and; the total pulmonary morphometric diffusing capacity (DLo2) for O2 2.3 times more in C. foxi. C. gambianus occupies open burrows that are ventilated with air while C. foxi lives in closed burrows. The less morphometrically specialized lungs of C. gambianus may be attributed to its much larger body mass (~6 times more) and possibly lower metabolic rate and its semifossorial life whereas the 'superior' lungs of C. foxi may largely be ascribed to the subterranean hypoxic and hypercapnic environment it occupies. Compared to other rodents species that have been investigated hitherto, the τht was mostly smaller in the lungs of the subterranean species and C. foxi has the highest mass-specific DLo2. The fossorial- and the subterranean rodents have acquired various pulmonary structural specializations that relate to habitats occupied.

Hind foot drumming: Morphofunctional analysis of the hind limb osteology in three species of African mole-rats (Bathyergidae).

Hind foot drumming is a form of seismic signaling that plays a vital role in the communication of several Bathyergidae species. Hind foot drumming is initiated by the rapid movement of the whole hind limb by flexion and extension of the hip and knee. This study aimed to determine if morphological adaptations of the hind limb osteology were measurable using established morphometric analyses in two drumming (Bathyergus suillus and Georychus capensis) and one non-drumming (Cryptomys hottentotus natalensis) African mole-rat species. Forty-three linear measurements of the hind limb were taken in 48 limbs (n = 16 limbs per species) and 32 indices were calculated. Mixed model analysis of variance was used to compare the three species and sexes within a species. Thirteen indices had significant differences between species. Eleven indices had significant differences between sexes within a species. Significant differences between the drumming (B. suillus and G. capensis) and the non-drumming species were observed in three indices. The femoral greater trochanter was relatively shorter in the drumming species compared to the non-drumming species, which is proposed to allow for increased hip joint mobility, thereby permitting drummers to move their limbs at the rapid speed required to generate seismic signals. Furthermore, the small in-lever (shorter greater trochanter) may increase the velocity of limb motion. The robust tibias in the drumming species, as indicated by the tibial robustness index, are likely to counter the additional biomechanical load caused by the muscles involved in hind foot drumming. The relatively small hind feet seen in the drumming species allows for reduced limb weight needed for the rapid extension and flexion motion required during hind foot drumming. The significant differences reflected in the hind limb osteological indices between B. suillus and G. capensis and the non-drumming species are indicative of adaptations for hind foot drumming.

Is the Mole Rat Vomeronasal Organ Functional?

The colonial naked mole rat Heterocephalus glaber is a subterranean, eusocial rodent. The H. glaber vomeronasal organ neuroepithelium (VNE) displays little postnatal growth. However, the VNE remains neuronal in contrast to some mammals that possess nonfunctional vomeronasal organ remnants, for example, catarrhine primates and some bats. Here, we describe the vomeronasal organ (VNO) microanatomy in the naked mole rat and we make preliminary observations to determine if H. glaber shares its minimal postnatal VNE growth with other African mole rats. We also determine the immunoreactivity to the mitotic marker Ki67, growth-associated protein 43 (GAP43), and olfactory marker protein (OMP) in six adult and three subadult H. glaber individuals. VNE volume measurements on a small sample of Cryptomys hottentotus and Fukomys damarensis indicate that the VNE of those African mole rat species are also likely to be growth-deficient. Ki67(+) cells show that the sensory epithelium is mitotically active. GAP43 labelling indicates neurogenesis and OMP(+) cells are present though less numerous compared to GAP43(+) cells. In this respect, the VNO of H. glaber does not appear vestigial. The African mole rat VNE may be unusually variable, perhaps reflecting reduced selection pressure on the vomeronasal system. If so, African mole rats may provide a useful genetic model for understanding the morphological variability observed in the mammalian VNO. Anat Rec, 2019. © 2019 Wiley Periodicals, Inc. Anat Rec, 303:318-329, 2020. © 2019 American Association for Anatomy.

Naked Mole-Rats: Blind, Naked, and Feeling No Pain.

Around the world and across taxa, subterranean mammals show remarkable convergent evolution in morphology (e.g., reduced external ears, small eyes, shortened limbs and tails). This is true of sensory systems as well (e.g., loss of object vision and high frequency hearing). The naked mole-rat (Heterocephalus glaber) displays these typical subterranean features, but also has unusual characteristics even among subterranean mammals. Naked mole-rats are cold-blooded, completely furless, very long-lived (> 30 years), and eusocial (like termites). They also live in large colonies, which is very unusual for subterraneans. Their cortical organization has reduced area for visual processing, utilizing 30% more cortex for tactile processing. They are extremely tolerant to oxygen deprivation, and can recover from 18 min of anoxia. Their pain pathway is reduced and they feel no pain from acidosis. They are the only rodent tested to date whose pheromone-detecting vomeronasal organ shows no postnatal growth. These features may be a result of this species' "extreme subterranean lifestyle" that combines living underground and living in large colonies. Many respiring animals cramped together in unventilated burrows elevates CO2 levels, high enough to cause acidosis pain, and depletes O2 concentrations low enough to kill other mammals. The naked mole-rat may be an extreme model of adaptation to subterranean life and provides insights into the complex interplay of evolutionary adaptations to the constraints of subterranean living. Anat Rec, 2018. © 2018 American Association for Anatomy.

Unique features of the skin barrier in naked mole rats reflect adaptations to their fossorial habitat.

The stratum corneum (SC), the top layer of the epidermis, is the functional site of the skin barrier and serves to maintain hydration of the body by preventing water loss and thwarting the entrance of pathogens. The naked mole rat (NMR) (Heterocephalus glaber) is a rodent that resides in hypoxic underground tunnels in arid Africa. NMRs are not only hairless; their skin is devoid of glands and pain sensation. To understand how the skin barrier of the NMR is uniquely adapted to this environment, skin samples from the dorsum and ventral abdomen in one adult and one neonate were examined by transmission electron microscopy using both reduced osmium tetroxide to assess overall structure and ruthenium tetroxide post-fixation to assess lipid organization. These findings were compared with that of hairless mice-a well-defined model for skin barrier studies. The plasticity of the skin was evaluated on 10 NMRs from a colony at the Philadelphia Zoo in humid and dry conditions by measuring cutaneous hydration, transepidermal water loss (TEWL), and pH. The epidermal ultrastructure of the NMR differed from hairless mice by having the following features: decreased content of lamellar bodies (LBs), higher LB pleomorphism, periodic presence of abnormal lipid bilayers, and an unusually thick SC. The NMRs developed significant TEWL and a trend toward decreased hydration when subjected to dry conditions. While these features illustrate an imperfect skin barrier in terrestrial mammals, they likely represent adaptations of the poikilothermic NMRs to their unique natural fossorial climate. Prolonged exposure to decreased humidity could possibly lead to adverse health effects in this species.

Superficial, suprahyoid, and infrahyoid neck musculature in naked mole-rats (Heterocephalus glaber): Relative size and potential contributions to independent movement of the lower incisors.

Naked mole-rats (Heterocephalus glaber) are fossorial, eusocial rodents that exhibit the unusual capability of moving their lower incisors independently in lateral and rostroventral directions. The evolution of this trait would presumably also involve concurrent alterations in neck musculature to support and control movements of the lower incisors. In order to assess morphological adaptations that might facilitate these movements, we performed detailed dissections of the neck musculature of adult naked mole-rats. In addition to characterizing attachment sites of superficial, suprahyoid, and infrahyoid musculature, we also quantified muscle mass and mandibular features thought to be associated with gape (condyle height, condyle length, and jaw length). Based on muscle attachment sites, the platysma myoides may contribute to lateral movement of the lower incisor and hemi-mandible in naked mole-rats. The large digastric muscle is likely to be a main contributor to rostroventral movement of each lower incisor. The geniohyoid and mylohyoid muscles also likely contribute to rostroventral movements of the lower incisors, and the mylohyoid may also produce lateral spreading of the hemi-mandibles. The transverse mandibular (intermandibularis) muscle likely serves to reposition the lower incisors back to a midline orientation following a movement.

Brain atlas of the African mole-rat Fukomys anselli.

African mole-rats are subterranean rodents that spend their whole life in underground burrow systems. They show a range of morphological and physiological adaptations to their ecotope, for instance severely reduced eyes and specialized somatosensory, olfactory, and auditory systems. These adaptations are also reflected in the accessory sensory pathways in the brain that process the input coming from the sensory organs. So far, a brain atlas was available only for the naked mole-rat (Heterocephalus glaber). The Ansell's mole-rat (Fukomys anselli) has been the subject of many investigations in various disciplines (ethology, sensory physiology, and anatomy) including magnetic orientation. It is therefore surprising that an atlas of the brain of this species was not available so far. Here, we present a comprehensive atlas of the Ansell's mole-rat brain based on Nissl and Klüver-Barrera stained sections. We identify and label 375 brain regions and discuss selected differences from the brain of the closely related naked mole-rat as well as from epigeic mammals (rat), with a particular focus on the auditory brainstem. This atlas can serve as a reference for future neuroanatomical investigations of subterranean mammals.

Normal physiological functions in two animal species with highly different vitamin d status compared to that of humans / Funciones fisiológicas normales en dos especies animales con estatus de vitamina d muy diferentes del actual en seres humanos

Mole rats live in permanent darkness, in networks of underground tunnels (which extend up to 1 km in the subsoil), excavated with their incisors, in warm and semi-arid areas of South Africa. Mole rats have an unusually impoverished vitamin D3 status with undetectable and low plasma concentrations of 25- hydroxyvitamin D3 and 1α,25-dihydroxyvitamin D3, respectively. They express 25-hydroxylase in the liver and 1-hydroxylase and 24-hydroxylase in their kidneys. The presence of specific receptors (VDR) was confirmed in the intestine, kidney, Harderʼs glands and skin. In spite of their poor vitamin D3 status, the apparent fractional intestinal absorption of calcium, magnesium and phosphate was high, always greater than 90%. Oral supplementation with cholecalciferol to mole rats did not improve the efficiency of gastrointestinal absorption of these minerals. Mole ratsdo not display the typical lesion of rickets: hypertrophic and radiolucent growth cartilages. Histological studies reported normal parameters of trabecular and cortical bone quality. Marmosets (monkeys of the New World) are not hypercalcaemic, eventhough they exhibit much higher levels of 25-hydroxyvitamin D3, 1α,25-dihydroxyvitamin D3 and parathyroid hormonethan that of rhesus monkeys and humans. Fed a high vitamin D3 intake (110 IU/day/100 g of body weight), a fraction of the experimental group was found to display osteomalacic changes in their bones: distinct increases in osteoid surface, relative osteoid volume, and active osteoclastic bone resorption. These findings suggest that some marmosets appears to suffer vitamin D-dependent rickets, type II. The maximum binding capacity of the VDR or the dissociation constant of VDR1α,25(OH)2D3 complex of mole rats and New World monkeys are distinctly different of VDR isolated from human cells. Health status of those species appears to be adaptations to the mutations of their VDR. Though rare, as mutations may occur at any time in any patient, the overall message of this review to clinicians may be: recent clinical studies strongly suggests that the normality of physiological functions might be a better indicator of the health status than the serum levels of vitamin D metabolites. (AU)

Las ratas topo viven en la oscuridad permanente, en redes de túneles subterráneos excavadas con sus incisivos (que se extienden hasta 1 km en el subsuelo), en áreas cálidas y semiáridas de Sudáfrica. Las ratas topo tienen un estatus de vitamina D3 inusualmente empobrecido con concentraciones plasmáticas indetectables de 25-hidroxivitamina D3 y bajas de 1α, 25-dihidroxivitamina D3. Poseen 25-hidroxilasa en el hígado y 1-hidroxilasa y 24-hidroxilasa en sus riñones. La presencia de receptores específicos (VDR) ha sido confirmada en el intestino, el riñón, las glándulas de Harder y la piel. A pesar de su pobre estatus de vitamina D3,la absorción fraccional intestinal aparente de calcio, magnesio y fosfato fue alta, siempre superior al 90%. La suplementación oral con colecalciferol a las ratas topo no mejoró la eficacia de la absorción gastrointestinal de estos minerales. No muestran la lesión típica del raquitismo: cartílagos de crecimiento hipertróficos y radiolúcidos. Varios estudios histológicos confirman los hallazgos radiológicos y se informan parámetros normales de la calidad ósea trabecular y cortical. Los titíes (monos del Nuevo Mundo) exhiben calcemias normales con niveles más elevados de 25-hidroxivitamina D3, 1α,25-dihidroxivitamina D3 y hormona paratiroidea que los monos rhesus y los seres humanos. Un tercio de un grupo de titíes alimentados con una alta ingesta de vitamina D3 (110 I/día/100 g de peso corporal) exhibió cambios osteomalácicos en sus huesos: aumento en la superficie osteoide, volumen osteoide y activa reabsorción osteoclástica. Estos hallazgos sugieren que una fracción de la población de titíes padece raquitismo dependiente de vitamina D, tipo II. Debido a mutaciones ocurridas hace millones de años, las máximas capacidades de ligamiento del VDR o los valores de la constante de disociación del complejo VDR-1α,25(OH)2D3 de las ratas topo o monos del Nuevo Mundo son muy diferentes de los verificables en receptores aislados de células humanas actuales. El mensaje de esta revisión a los médicos clínicos podría ser: varios estudios clínicos recientes indican que la normalidad de las funciones fisiológicas de un paciente es un mejor indicador de su salud que los niveles séricos de los metabolitos de la vitamina D. (AU)

Reproduction triggers adaptive increases in body size in female mole-rats.

In social mole-rats, breeding females are larger and more elongated than non-breeding female helpers. This status-related morphological divergence is thought to arise from modifications of skeletal growth following the death or removal of the previous breeder and the transition of their successors from a non-breeding to a breeding role. However, it is not clear what changes in growth are involved, whether they are stimulated by the relaxation of reproductive suppression or by changes in breeding status, or whether they are associated with fecundity increases. Here, we show that, in captive Damaraland mole-rats (Fukomys damarensis), where breeding was experimentally controlled in age-matched siblings, individuals changed in size and shape through a lengthening of the lumbar vertebrae when they began breeding. This skeletal remodelling results from changes in breeding status because (i) females removed from a group setting and placed solitarily showed no increases in growth and (ii) females dispersing from natural groups that have not yet bred do not differ in size and shape from helpers in established groups. Growth patterns consequently resemble other social vertebrates where contrasts in size and shape follow the acquisition of the breeding role. Our results also suggest that the increases in female body size provide fecundity benefits. Similar forms of socially responsive growth might be more prevalent in vertebrates than is currently recognized, but the extent to which this is the case, and the implications for the structuring of mammalian dominance hierarchies, are as yet poorly understood.

Kinematics of chisel-tooth digging by African mole-rats.

Mole-rats are known to use their protruding, chisel-like incisors to dig underground networks of tunnels, but it remains unknown how these incisors are used to break and displace the soil. Theoretically, different excavation strategies can be used. Mole-rats could either use their head depressor muscles to power scooping motions of the upper incisors (by nose-down head rotations) or the lower incisors (by nose-up head rotations), or their jaw adductors to grab and break the soil after penetrating both sets of incisors into the ground, or a combination of these mechanisms. To identify how chisel-tooth digging works, a kinematic analysis of this behaviour was performed based on high-speed videos of 19 individuals from the African mole-rat species Fukomys micklemi placed inside transparent tubes in a laboratory setting. Our analysis showed that the soil is penetrated by both the upper and lower incisors at a relatively high gape angle, generally with the head rotated nose-up. Initially, the upper incisors remain approximately stationary to function as an anchor to allow an upward movement of the lower incisors to grab the soil. Next, a quick, nose-down rotation of the head further detaches the soil and drops the soil below the head. Consequently, both jaw adduction and head depression are jointly used to power tooth-digging in F. micklemi The same mechanism, but with longer digging cycles, and soil being thrown down at smaller gape sizes, was used when digging in harder soil.

Functional Morphology of the Olfactory Mucosa and Olfactory Bulb in Fossorial Rodents: The East African Root Rat (Tachyoryctes splendens) and the Naked Mole Rat (Heterocephalus glaber).

Optimal functioning of the olfactory system is critical for survival of fossorial rodents in their subterranean lifestyle. This study examines the structure of the olfactory mucosa and olfactory bulb of two fossorial rodents exhibiting distinct social behaviors, the East African root rat and the naked mole rat. The social naked mole rat displayed simpler ethmoturbinates consisting of dorsomedial and broad discoid/flaplike parts that projected rostrally from the ethmoid bone. In the solitary root rat however, the ethmoturbinates were highly complex and exhibited elaborate branching which greatly increased the olfactory surface area. In addition, when correlated with the whole brain, the volume of the olfactory bulbs was greater in the root rat (4.24×10-2) than in the naked mole rat (3.92×10-2). Results of this study suggest that the olfactory system of the root rat is better specialized than that of the naked mole rat indicating a higher level of dependence on this system since it leads a solitary life. The naked mole rat to the contrary may have compensated for its relatively inferior olfactory system by living in groups in a social system. These findings demonstrate that structure of the olfactory system of fossorial mammals is dictated by both behavior and habitat.

Comparative gastrointestinal morphology of Tachyoryctes splendens (Rüppell, 1835) and Heliophobius emini, (Noack, 1894) two species of East African mole-rats.

Tachyoryctes splendens (Northeast African mole-rat) and Heliophobius emini (Emin's mole-rat) are two African mole-rats that represent separate allopatric rodent families namely Spalacidae and Bathyergidae respectively. While these species consume a similar diet of underground plant storage organs such as roots and tubers, T. splendens has been reported to additionally consume small amounts of aerial foliage. This study aims to provide detailed gross morphological and histological morphometric analyses of the gastrointestinal tract (GIT) of these two subterranean species. The formalin fixed gastrointestinal tracts of T. splendens (n = 9) and H. emini (n = 6) were photographed, weighed and measured. The length and basal surface areas were calculated for each anatomically distinct region. Representative histological samples were prepared and stained using Hematoxylin and Eosin. Microscopic luminal measurements were used to calculate a surface enlargement factor and the luminal surface area of each region. Tachyoryctes splendens had a large double chambered hemi-glandular stomach with a macroscopically visible transition from keratinized stratified squamous epithelium to glandular epithelium. The cecum was large and the luminal surface revealed a single spiral fold. The ascending colon of T. splendens was arranged in a spiral, with two centripetal and two centrifugal windings. The descending colon was arranged in a single parallel loop, similar to H. emini. A narrow colonic groove was accompanied by V-shaped folds on either side. Heliophobius emini had a simple glandular stomach, a large, haustrated cecum that displayed a cecal appendix and the descending colon was arranged in a single parallel loop. The internal aspect of the colon revealed a wide colonic groove extending from the ceco-colic junction to distal colon. As both species originate from a similar geographical region and ingest very similar diets, it is likely that the differences in the GIT morphology are attributed to phylogeny as the species represent two different families of mole-rats.

A Macro-Anatomical Investigation of the Some Skull Bones of Nehring's Blind Mole Rats (Spalacidae: Nannospalax nehringi).

This study was aimed to demonstrate the specific anatomical features of the skull bones of Nehring's blind mole rats. Eight skulls, belonging to animals of both sexes, were used. The occipital squama contributed to the formation of the caudal portion of the skull roof. The foramen magnum was quite large. The external occipital crest was present only in the males. The parietal bones formed the middle portion of the skull roof together with the well-developed inter-parietal bones. The zygomatic process of the temporal bone formed the zygomatic arch by extending to the temporal process of the zygomatic bone. The zygomatic process of the frontal bone and the frontal process of the zygomatic bone laterally bordered the orbit. There was a single septal process of the nasal bone. Each ramus of the mandibula had four processes. The mandibular ramus had an angular process on its caudal rim, which extended dorsolaterally. The dorsal free end of the mandibular ramus possessed a coronoid process. In the back, there were two other processes, situated medially and laterally. The medially situated process was referred to as a condylar process, and the laterally situated process was referred to as an alveolar process. The alveolar process detected on the mandibular ramus has not been reported in any rodent species, other than those of the family Spalacidae. Blind mole rats can be a real eye-opener for evolutionary science. The burrowing rodents are key to answering a controversial question about how new species arise.

Long bone histology of the subterranean rodent Bathyergus suillus (Bathyergidae): ontogenetic pattern of cortical bone thickening.

Patterns of bone development in mammals are best known from terrestrial and cursorial groups, but there is a considerable gap in our understanding of how specializations for life underground affect bone growth and development. Likewise, studies of bone microstructure in wild populations are still scarce, and they often include few individuals and tend to be focused on adults. For these reasons, the processes generating bone microstructural variation at intra- and interspecific levels are not fully understood. This study comprehensively examines the bone microstructure of an extant population of Cape dune molerats, Bathyergus suillus (Bathyergidae), the largest subterranean mammal endemic to the Western Cape of South Africa. The aim of this study is to investigate the postnatal bone growth of B. suillus using undecalcified histological sections (n = 197) of the femur, humerus, tibia-fibula, ulna and radius, including males and females belonging to different ontogenetic and reproductive stages (n = 42). Qualitative histological features demonstrate a wide histodiversity with thickening of the cortex mainly resulting from endosteal and periosteal bone depositions, whilst there is scarce endosteal resorption and remodeling throughout ontogeny. This imbalanced bone modeling allows the tissues deposited during ontogeny to remain relatively intact, thus preserving an excellent record of growth. The distribution of the different bone tissues observed in the cortex depends on ontogenetic status, anatomical features (e.g. muscle attachment structures) and location on the bone (e.g. anterior or lateral). The type of bone microstructure and modeling is discussed in relation to digging behavior, reproduction and physiology of this species. This study is the first histological assessment describing the process of cortical thickening in long bones of a fossorial mammal.

[Morphological diversity in the postnatal skull development in representatives of two families of rodents (Spalacidae, Castoridae, Rodentia)].

This is the first study to describe the results of measurement of three information parameters of morphological diversity (entropy, the measure of organization, and the Kullback-Leibler divergence) in the course of postnatal development of the skull in the populations of two rodent species (greater mole rat (Spalax microphthalmus Guld.) and Eurasian beaver (Castor fiber (L.)). The terms "morphosystem" and "morphological space" and its structure are introduced. Within the framework of the developed approach, "morphological diversity" is considered as a variable associated with the morphological space structure. Testing the hypothesis of the dominance of self-organization processes and an increase in the organization of the morphological diversity of the skull in the course ofontogeny showed its inconsistency. The morphosystem of the skull of the studied species undergoes transitions between more organized and less organized states, periodically approaching and departing from the "steady state." Such dynamics characterizes the morphosystem of the skull as a dynamic and nonlinear system.

Intra-sexual selection in cooperative mammals and birds: why are females not bigger and better armed?

In cooperatively breeding mammals and birds, intra-sexual reproductive competition among females may often render variance in reproductive success higher among females than males, leading to the prediction that intra-sexual selection in such species may have yielded the differential exaggeration of competitive traits among females. However, evidence to date suggests that female-biased reproductive variance in such species is rarely accompanied by female-biased sexual dimorphisms. We illustrate the problem with data from wild Damaraland mole-rat, Fukomys damarensis, societies: the variance in lifetime reproductive success among females appears to be higher than that among males, yet males grow faster, are much heavier as adults and sport larger skulls and incisors (the weapons used for fighting) for their body lengths than females, suggesting that intra-sexual selection has nevertheless acted more strongly on the competitive traits of males. We then consider potentially general mechanisms that could explain these disparities by tempering the relative intensity of selection for competitive trait exaggeration among females in cooperative breeders. Key among these may be interactions with kin selection that could nevertheless render the variance in inclusive fitness lower among females than males, and fundamental aspects of the reproductive biology of females that may leave reproductive conflict among females more readily resolved without overt physical contests.