Lauren Sahd

Vertebral bodies are composed of two types of metameric elements, centra and arches, each of which is considered as a developmental module. Most parts of the teleost vertebral column have a one‐to‐one relationship between centra and arches, although, in all teleosts, this one‐to‐one relationship is lost in the caudal fin endoskeleton. Deviation from the one‐to‐one relationship occurs in most vertebrates, related to changes in the number of vertebral centra or to a change in the number of arches. In zebrafish, deviations also occur predominantly in the caudal region of the vertebral column. In‐depth phenotypic analysis of wild‐type zebrafish was performed using whole‐mount stained samples, histological analyses and synchrotron radiation X‐ray tomographic microscopy 3D reconstructions. Three deviant centra phenotypes were observed: (i) fusion of two vertebral centra, (ii) wedge‐shaped hemivertebrae and (iii) centra with reduced length. Neural and haemal arches and their spines displayed bilateral and unilateral variations that resemble vertebral column phenotypes of stem‐ward actinopterygians or other gnathostomes as well as pathological conditions in extant species. Whether it is possible to distinguish variations from pathological alterations and whether alterations resemble ancestral conditions is discussed in the context of centra and arch variations in other vertebrate groups and basal actinopterygian species.

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.

Several species of African mole-rats use seismic signalling by means of hind foot drumming for communication. The present study aimed to create three-dimensional reconstructions and compare volumetric measurements of 27 muscles of the hind limb of two drumming (Georychus capensis and Bathyergus suillus) and one non-drumming (Cryptomys hottentotus natalensis) species of African mole-rats. Diffusible iodine contrast-enhanced micro-computed tomography (diceCT) scans were performed on six specimens per species. Manual segmentation of the scans using VGMAX Studio imaging software allowed for individual muscles to be separated while automatically determining the volume of each muscle. The volume of the individual muscles was expressed as a percentage of the total hind limb volume and statistically compared between species. Subsequently, three-dimensional reconstructions of these muscles were created. Musculus gracilis anticus had a significantly larger percentage of the total hind limb muscle volume in both drumming species compared to the non-drumming C. h. natalensis. Furthermore, several hip and knee extensors, namely mm. gluteus superficialis, semimembranosus, gluteofemoralis, rectus femoris and vastus lateralis, had significantly larger muscle volume percentages in the two drumming species (G. capensis and B. suillus) compared to the non-drumming species. While not statistically significant, G. capensis had larger muscle volume percentages in several key hip and knee extensors compared to B. suillus. Additionally, G capensis had the largest summed percentage of the total hind limb volume in the hip flexor, hip extensor, knee extensor and ankle plantar flexor muscle groups in all the three species. This could be indicative of whole muscle hypertrophy in these muscles due to fast eccentric contractions that occur during hind foot drumming. However, significantly larger muscle volume percentages were observed in the scratch digging B. suillus compared to the other two chisel tooth digging species. Moreover, while not statistically significant, B. suillus had larger muscle volume percentages in several hip extensor and knee flexor muscles compared to G. capensis (except for m. vastus lateralis). These differences could be due to the large relative size of this species but could also be influenced by the scratch digging strategy employed by B. suillus. Therefore, while the action of hind foot drumming seems to influence certain key muscle volumes, digging strategy and body size may also play a role.

Hind foot drumming as a form of seismic signaling plays a pivotal role in the communication of various mammalian species including Bathyergidae (African mole‐rats). The aim of the present study was to histologically determine if the action of hind foot drumming would influence the number of type II fibers present in the hind limb muscles of two drumming (Georychus capensis and Bathyergus suillus) and one non‐drumming (Cryptomys hottentotus natalensis) bathyergid species. Twenty‐one frozen muscles of each species were selected for the purpose of mid‐belly cryostat sections. These sections were immunohistochemically labeled for myosin heavy chain slow muscle fibers (MHCs). In addition, oxidative capacity was determined by means of histochemical staining. A high percentage of fast type II muscle fibers was found in all the functional muscle groups, although there were no statistical differences between the drumming and non‐drumming species. Bathyergus suillus had significantly fewer type II fibers in mm. semitendinosus, gluteofemoralis, tibialis cranialis, plantaris, and the medial head of m. gastrocnemius compared to the other two species. In all three species, the majority of the muscle fibers in all functional muscle groups demonstrated low oxidative capacity which correlated with the expression of type II muscle fibers. It therefore seems likely that the number of type II muscle fibers in the hind limb muscles of the Bathyergidae species studied here is more influenced by either body size or digging strategy rather than being an adaptation for hind foot drumming.

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.

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.

Seismic signalling in the form of hind foot drumming plays an integral role in the communication of several species of African mole‐rats (Bathyergidae). To produce these vibrational signals, alternating hind limbs strike the ground repetitively at high speeds by flexion and extension of the hip and knee. This descriptive study aimed to determine whether anatomical differences in hind limb osteology and/or musculature between drumming and non‐drumming species of three Bathyergidae species could be detected. Formalin‐fixed left and right hind limbs of 24 animals (N = 48) consisting of three species (n = 16 each) of two drumming species, Georychus capensis and Bathyergus suillus, and one non‐drumming species, Cryptomys hottentotus natalensis, were dissected to determine the origins and insertions of individual muscles. After dissection, all soft tissue was removed by maceration. Hind limb bones, including the pelvis, were photographed, and the exact muscle origin and insertion points were electronically mapped onto the images using imaging software. On lateral view, the acetabular position was parallel to the sacrum in G. capensis, while being more ventral in position in the other two species. The shape of the femur head was spherical and the neck defined in all species. The distal shaft of the femur was gracile and the epicondyles were robust and prominent in the non‐drumming C. h. natalensis compared with the drumming species. Shallow and relatively wide patellar grooves were observed in all three species. In the two drumming species, m. gracilis was single, whereas it was double in C. h. natalensis. In all three species, m. tensor fasciae latae was absent. The more dorsal positioning of the acetabulum in G. capensis may be needed to increase the stability of the spine and allow for more force to be exerted on the pelvis during drumming. It is unlikely that m. gracilis plays a role in drumming, as the singularity or doubling thereof is variable among rodents. It is additionally postulated that m. gluteus superficialis has taken the hip rotator role of m. tensor fasciae latae as it partially inserted onto the lateral fascia of the thigh. The more robust ilia, femoral shafts and tibiae observed in the two drumming species studied here are possible adaptations for hind foot drumming, as robust bones are able to withstand the additional biomechanical loading during drumming.

Golden moles are small, fossorial, and primarily insectivorous mammals mostly endemic to South Africa. They belong to an ancient African clade of placental mammals (Afrotheria) that likely radiated from an herbivorous ancestor. Nearly half of the 21 golden mole species are listed as threatened; but remarkably little is known about their basic biology and gastrointestinal tract (GIT) morphology. This study provides a morphometric and histochemical analysis of the GIT of seven chrysochloridae species, including three threatened taxa. Macroscopically, all species examined had simple GITs with simple, wholly glandular stomachs and no cecum. Histologically, the pylorus was dominated by parietal cells. Neutral mucin cells were found on the luminal surface and in the gastric pits, while mixed acid and neutral mucin cells were found in the proximal parts of the gastric glands. The proximal intestine had typical small intestinal histological features such as villi. Typical colonic mucosal features were absent as villi were present throughout the intestinal tract. Goblet cells were abundant and increased toward the distal intestine. These intestinal goblet cells contained mostly mixed mucins. Stomach and intestinal content analysis confirmed the presence of arthropod exoskeleton material and possible small vertebrate remnants, commensurate with a low‐fibre, protein‐rich diet. This may account for their simple GIT morphology, as seen convergently in other unrelated insectivorous mammals. This study provides better representation of variation in GIT morphology among chrysochloridae and within the enigmatic Afrotheria clade. Additionally, it provides a better understanding of the mucin distribution in relation to diet and phylogeny of golden moles.

Several muroid rodent species are distributed throughout southern Africa. Some species are reportedly classified as opportunistic omnivorous rodents consuming plant, seed, and insect material. This study aims to provide a detailed morphometric analysis of the gastrointestinal tract (GIT) of four such omnivorous species, including stomach content analysis. Fixed GIT specimens (n = 5 of each) of Rhabdomys dilectus (Mesic four‐striped grass mouse), Rhabdomys pumilio (Xeric four‐striped grass mouse), Aethomys chrysophilus (Red rock rat), and Lemniscomys rosalia (Single‐striped grass mouse) were weighed. Length and circumference measurements of each anatomically distinct GIT region were determined to calculate the basal surface area (BSA). Histological sections from each GIT region were used to calculate a surface enlargement factor (SEF). The BSA and SEF were multiplied to calculate the luminal surface area (LSA) of each GIT region. Stomach content was analyzed both macroscopically and histologically. All species had a similar GIT morphology, namely a unilocular, hemiglandular stomach with a clear limiting ridge, which indicated the transition from stratified squamous epithelium to glandular epithelium. A large loosely spiralled cecum was present in all species. A narrowing of the cecal apex accompanied by lymph aggregates, confirmed histologically in both Rhabdomys species, indicated a cecal appendix. A single short colonic loop with a unique folding pattern for each species was present in the proximal colon. The colonic mucosal surface presented with proximal V‐shaped, and distal longitudinal folds. Intermediate transitional S‐shaped folds were present in three species (R. dilectus, R. pumilio, and L. rosalia). Colonic mucosal folds indicated hindgut specialization similar to other muroid rodents. The hindgut specialization was further supported by morphometric analysis, which indicated large BSA and LSA measurements in the cecum and colon. These adaptations are consistent with herbivory, despite stomach content analysis revealing omnivorous tendencies.