Rhabdomys Pumilio Research Articles

Prevalence and genetic diversity of Bartonella spp. in wild small mammals from South Africa.

Bartonella spp. are intracellular bacteria associated with several re-emerging human diseases. Small mammals play a significant role in the maintenance and spread of Bartonella spp. Despite the high small mammal biodiversity in South Africa, there is limited epidemiological information regarding Bartonella spp. in these mammals. The main aim of this study was to determine the prevalence and genetic diversity of Bartonella spp. from wild small mammals from 15 localities in 8 provinces of South Africa. Small mammals (n = 183) were trapped in the Eastern Cape, Free State, Gauteng, Limpopo, Mpumalanga, Northern Cape, North West, and Western Cape provinces of South Africa between 2010 and 2018. Heart, kidney, liver, lung, and spleen were harvested for Bartonella DNA screening, and prevalence was determined based on the PCR amplification of partial fragments of the 16S-23S rRNA intergenic spacer (ITS) region, gltA, and rpoB genes. Bartonella DNA was detected in Aethomys chrysophilus, Aethomys ineptus, Gerbillurus spp., Lemniscomys rosalia, Mastomys coucha, Micaelamys namaquensis, Rhabdomys pumilio, and Thallomys paedulcus. An overall prevalence of 16.9% (31/183, 95% CI: 12.2%-23%) was observed. Bartonella elizabethae, Bartonella grahamii, and Bartonella tribocorum were the zoonotic species identified, while the remaining sequences were aligned to uncultured Bartonella spp. with unknown zoonotic potential. Phylogenetic analyses confirmed five distinct Bartonella lineages (I-V), with lineage IV displaying strong M. coucha host specificity. Our results confirm that South African wild small mammals are natural reservoirs of a diverse assemblage of Bartonella spp., including some zoonotic species with high genetic diversity, although prevalence was relatively low.IMPORTANCESmall mammals play a significant role in the maintenance and spread of zoonotic pathogens such as Bartonella spp. Despite the high small mammal biodiversity in southern Africa including South Africa, there is limited epidemiological information regarding Bartonella spp. in these mammals across the country. Results from our study showed the liver and spleen had the highest positive cases for Bartonella spp. DNA among the tested organs. Bartonella elizabethae, B. grahamii, and B. tribocorum were the three zoonotic species identified and five distinct Bartonella lineages (I-V) were confirmed through phylogenetic analyses. To the best of our knowledge, this study presents the first extensive nuclear diversity investigation of Bartonella spp. in South African small mammals in South Africa.

Reconfiguration of the visual code and retinal cell type complement in closely related diurnal and nocturnal mice.

How does evolution act on neuronal populations to match computational characteristics to functional demands? We address this problem by comparing visual code and retinal cell composition in closely related murid species with different behaviours. Rhabdomys pumilio are diurnal and have substantially thicker inner retina and larger visual thalamus than nocturnal Mus musculus. High-density electrophysiological recordings of visual response features in the dorsal lateral geniculate nucleus (dLGN) reveals that Rhabdomys attains higher spatiotemporal acuity both by denser coverage of the visual scene and a selective expansion of elements of the code characterised by non-linear spatiotemporal summation. Comparative analysis of single cell transcriptomic cell atlases reveals that realignment of the visual code is associated with increased relative abundance of bipolar and ganglion cell types supporting OFF and ON-OFF responses. These findings demonstrate how changes in retinal cell complement can reconfigure the coding of visual information to match changes in visual needs.

Densities of a perennial invasive tree, Acacia cyclops, decline in the 20 years since inception of biological control with two seed-reducing agents, a flower-galling midge and a seed-feeding weevil

Two biological control agents, a flower-galling midge (Dasineura rubiformis, Cecidomyiidae), and a seed-feeding weevil (Melanterius maculatus, Curculionidae), are consistently and substantially reducing the seeding capacity of Acacia cyclops in South Africa. Simultaneously there has been a conspicuous decline in the density of the weed in some areas over the past 20 years. Besides the two biological control agents, indigenous granivores, especially striped field mice (Rhabdomys pumilio), destroy a considerable proportion of the seeds that are produced. Fire is another key factor driving the population dynamics of A. cyclops. Most wildfires kill all the existing trees in areas that burn and nearly all (ca. 90 %) of the seeds in the soil are scorched and destroyed during fires. Dormancy is broken in the surviving seeds, of which nearly all (88 %) germinate during the first winter-rainfall season, the rest doing so during the following winter so that two years after fire no seeds remain in the soil. Approximately 13 % of all the seedlings which germinate following fire events survive through their first hot, dry summer and become established to form the next cohort of plants. Historically, the surviving recruits were abundant enough to form a closed canopy within 3–4 years. This pattern was sustained because A. cyclops plants produced an abundance of seeds each year which accumulated in the soil, typically reaching numbers of 1000–4000 seeds m−2 within a few years of the preceding fire. Since the establishment of biological control, the numbers of seeds in the soil under existing trees has dropped with time, but a pool of dormant seeds persists which usually produces enough seedlings to allow the weed to still form a closed canopy after a first fire event. Since the inception of biological control, the cohorts of new plants that grow up after a first fire only yield a small fraction of their potential seed production, resulting in few if any seeds accumulating in the soil under these plants. When these areas under biological control burn a second time there are insufficient seedlings to replace the plants killed by the fire and densities in the new cohort of plants are regularly at least 95 % lower than the densities in the thickets before the two fires. While the process relies on spontaneous outbreaks of wildfires, the interaction of biological control, indigenous granivores and fire is bringing A. cyclops under excellent control.

African striped mice have relatively smaller brains in the food deprived dry season than in the wet season

The ability to alter the mass of energetically consumptive organs in response to seasonal variation in nutritional access has been demonstrated in several species from temperate climates, but less so from other climate zones. We predicted that adult striped mice (Rhabdomys pumilio) from the Succulent Karoo semi-desert in South Africa have lower organ masses during the hot summer dry season with low food availability (n = 28) when compared to the food-rich wet season (n = 25) as a possible adaptation to reduced energy expenditure. Food availability in the wet season was more than twice than that of the dry season. Body mass was positively correlated with most organ masses considered, except for the spleen. Mandible length, as a non-plastic measure of body size, was positively correlated with the mass of heart and stomach. Relative to body mass and to mandible length, kidneys and the small intestine were heavier in the wet season than during the dry season in both sexes. Liver masses were greater in females (but smaller in males) during the wet season, possibly due to increased female reproductive investment during this season. Both sexes had relatively heavier brains (by 9.6% on average) during the wet season than during the dry season, which is the first indication of the Dehnel phenomenon in a rodent, in a subtropical climate, and in the southern hemisphere. Future studies will have to test whether this change in brain size is reversible. Having relatively smaller brains during the dry season could be a mechanism to reduce energy consumption. In conclusion, our study indicates that striped mice may save energy during the food restricted dry season by reducing energetically expensive organ masses, including brain mass.

A multifunctional Wnt regulator underlies the evolution of rodent stripe patterns.

Animal pigment patterns are excellent models to elucidate mechanisms of biological organization. Although theoretical simulations, such as Turing reaction-diffusion systems, recapitulate many animal patterns, they are insufficient to account for those showing a high degree of spatial organization and reproducibility. Here, we study the coat of the African striped mouse (Rhabdomys pumilio) to uncover how periodic stripes form. Combining transcriptomics, mathematical modelling and mouse transgenics, we show that the Wnt modulator Sfrp2 regulates the distribution of hair follicles and establishes an embryonic prepattern that foreshadows pigment stripes. Moreover, by developing in vivo gene editing in striped mice, we find that Sfrp2 knockout is sufficient to alter the stripe pattern. Strikingly, mutants exhibited changes in pigmentation, revealing that Sfrp2 also regulates hair colour. Lastly, through evolutionary analyses, we find that striped mice have evolved lineage-specific changes in regulatory elements surrounding Sfrp2, many of which may be implicated in modulating the expression of this gene. Altogether, our results show that a single factor controls coat pattern formation by acting both as an orienting signalling mechanism and a modulator of pigmentation. More broadly, our work provides insights into how spatial patterns are established in developing embryos and the mechanisms by which phenotypic novelty originates.

TIGER: Single-step in vivo genome editing in a non-traditional rodent

Rodents are taxonomically diverse and have evolved a variety of traits. A mechanistic understanding of such traits has remained elusive, however, largely because genome editing in non-traditional model species remains challenging. Here, using the African striped mouse (Rhabdomys pumilio), we describe TIGER (targeted invivo genome editing in rodents), a method that relies on a simple intraoviductal injecting technique and uses recombinant adeno-associated viruses (rAAVs) as the sole vehicle to deliver reagents into pregnant females. We demonstrate that TIGER generates knockout and knockin (up to 3 kb) lines with high efficiency. Moreover, we engineer a double-cleaving repair rAAV template and find that it significantly increases knockin frequency and germline transmission rates. Lastly, we show that an oversized double-cleaving rAAV template leads to an insertion of 3.8 kb. Thus, TIGER constitutes an attractive alternative to traditional exvivo genome-editing methods and has the potential to be extended to a broad range of species.

The genomic basis of temporal niche evolution in a diurnal rodent

Patterns of diel activity-how animals allocate their activity throughout the 24-h daily cycle-play key roles in shaping the internal physiology of an animal and its relationship with the external environment.1,2,3,4,5 Although shifts in diel activity patterns have occurred numerous times over the course of vertebrate evolution,6 the genomic correlates of such transitions remain unknown. Here, we use the African striped mouse (Rhabdomys pumilio), a species that transitioned from the ancestrally nocturnal diel niche of its close relatives to a diurnal one,7,8,9,10,11 to define patterns of naturally occurring molecular variation in diel niche traits. First, to facilitate genomic analyses, we generate a chromosome-level genome assembly of the striped mouse. Next, using transcriptomics, we show that the switch to daytime activity in this species is associated with a realignment of daily rhythms in peripheral tissues with respect to the light:dark cycle and the central circadian clock. To uncover selection pressures associated with this temporal niche shift, we perform comparative genomic analyses with closely related rodent species and find evidence of relaxation of purifying selection on striped mouse genes in the rod phototransduction pathway. In agreement with this, electroretinogram measurements demonstrate that striped mice have functional differences in dim-light visual responses compared with nocturnal rodents. Taken together, our results show that striped mice have undergone a drastic change in circadian organization and provide evidence that the visual system has been a major target of selection as this species transitioned to a novel temporal niche.

Mammal diversity of an urbanised environment in an arid zone of south-west Africa

Thorough investigation of the entire mammalian assemblages has not been hitherto conducted in any African city. Most studies were limited to single species causing problems to citizens or to small mammals causing health hazard. In 2011–2020, 81 mammal species were recorded in Windhoek, the capital of Namibia, although only 34 (42.0%) species occurred in the inner zone of the city (50 sq. km). The most speciose (25 species) order were rodents. Within this order the most speciose was the family Muridae (n = 13 species), while the most common rodent species were: Rhabdomys pumilio, Mastomys coucha, Gerbilliscus leucogaster, and Gerbillurus paeba. The second most speciose group of mammals were Chiroptera represented by 14 (17.3%) species in the outer zone (650 sq. km) and 8 species (23.5%) in the inner zone. Ungulates, although mostly rare or uncommon, were in the outer zone represented by eight (9.9%) species. None was, however, recorded in the inner zone. Nineteen Carnivora species (23.5%) were recorded in the outer zone, but only two of them in the inner zone. Other species recorded in Windhoek were representatives of seven other orders: Eulipotyphla (n = 4 spp.), Macroscelidea (n = 3), Lagomorpha (n = 3), Hyracoidea (n = 1), Primates (n=2), Tubulidentata (n = 1), and Pholidota (n = 1). Two species, Cynictis penicillata and Geosciurus inauris, were found to be relatively common in the inner zone. They have reached a population density (5.6 and >2.0 individuals per 100 ha, respectively) higher than in any other cities in Namibia, and probably in southern Africa at large. Despite intense searching in the inner zone, Hystrix africeaustralis and Procavia capensis were only recorded in a shrubby hill. The Procavia capensis population was estimated at 40–70 individuals. A few troops of Papio ursinus are resident only in the outer zone. The following species recorded in Windhoek are in the IUCN Red List of Threatened Species: Acinonx jubatus, Panthera pardus, Felis nigripes, Hyaena brunnea, and Smutia temminckii. Noteworthy is the absence of any alien mammal species in the inner zone, and the presence of only Mus musculus in the outer zone of the city. The protection of mammals in Windhoek, especially in the outer zone, may act as a catalyst to move the municipality governance towards a more effective biodiversity conservation.

Cognitive performance is linked to survival in free-living African striped mice.

Cognition is shaped by evolution and is predicted to increase fitness. However, the link between cognition and fitness in free-living animals is unresolved. We studied the correlates of cognition and survival in a free-living rodent inhabiting an arid environment. We tested 143 striped mice (Rhabdomys pumilio) using a battery of cognitive tests, including: (i) an attention task, (ii) two problem-solving tasks, (iii) a learning and reversal learning task, and (iv) an inhibitory control task. We related cognitive performance with days of survival. Better problem-solving and inhibitory control performance were significant correlates of survival. Surviving males showed greater reversal learning which may be related to sex-specific behavioural and life-history characteristics. Specific cognitive traits and not a composite measure of general intelligence underpins fitness in this free-living rodent population, enhancing our understanding of the evolution of cognition in non-human animals.

Description and comparison of brain distribution of oxytocin receptors in Rhabdomys pumillio and Rhabdomys dilectus

Oxytocin receptor (OXTR) distribution in the brain has been associated with different reproductive and social strategies of species. Rhabdomys pumilio (R. pumilio) and Rhabdomys dilectus (R. dilectus) are two sister rodent species that live in large/medium (but flexible) or small (mostly solitary) social groups respectively. In this study, we describe and compare the distribution of OXTR in these two species. OXTR binding in the brain of R. pumilio (8 females and 5 males) and R. dilectus (8 females and 5 males) adults was determined using autoradiography. Our results revealed significant differences in the nucleus accumbens, diagonal band, medial preoptic area, lateral habenula, superior colliculus, periaqueductal area and anterior paraventricular nucleus (higher in R. dilectus), and the dorsal lateral septum and anterior bed nucleus of the stria terminalis (higher in R. pumilio). OXTR density in other brain regions, such as the amygdala nuclei and hippocampus, did not differ between the two species. Sex differences were found in the medial preoptic area and ventral region of the lateral septum in R. pumilio (OXTR density higher in males) and in the anterior paraventricular thalamic nucleus, ventromedial nucleus of the hypothalamus and basolateral amygdala of R. dilectus (OXTR density higher in females). A sex difference in the density of OXTR was also found in the posterior region of the bed nucleus of the stria terminalis, where it was higher in males than in females of both species. This study shows species-specific brain distribution of OXTR in R. pumilio and R. dilectus that are unique, but with similarities with other polygynous or promiscuous rodent species that live in variable size groups, such as R. norvergicus, C. sociabilis, S. teguina and M. musculus.

Influence of vegetation structure, seasonality, and soil properties on rodent diversi community assemblages in west Mount Kilimanjaro, Tanzania.

Rodent diversity and community assemblages are affected by several biotic and abiotic factors such as vegetation structure and seasonality. Vegetation structure particularly ground cover influences rodent diversity and community assemblages through provision of food resources and protection from predators. Such information is important for understanding species–habitat relationships for management and conservation. This study was conducted to determine the influence of vegetation structure, seasonality, and soil properties on species richness, abundance, community assemblages, and habitat association of rodents in west Mt Kilimanjaro. Rodent trapping was conducted using removal and capture–mark–recapture (CMR) methods with medium‐sized Sherman's live traps, snap, and Havarhart traps. Rodents were trapped during wet and dry seasons for three consecutive nights at 4 weeks intervals from April 2020 to March 2021. Environmental variables including vegetation structure, soil physical properties, and disturbance levels were recorded for each habitat type. Fourteen species of rodents were trapped in 25,956 trap nights. Rhabdomys pumilio, Praomys delectorum, and Lophuromys verhageni were the most dominant species across all habitats and seasons. L.verhageni occurred in all habitats while R.pumilio was restricted from occurring in montane forests. Moreover, species richness and abundance were influenced by habitat types, seasonality, soil type, and ground cover. Generally, both species richness and abundance were higher in fallows and montane forests and significantly lower in plantation forest and agricultural fields. In addition, rodent diversity was highest in fallows, followed by montane forests, and lowest in agricultural fields. Furthermore, rodents were associated with habitat types and vegetation structure forming two major community assemblages that significantly differed between habitats. Our study conclude that, community assemblages of rodents on Mt. Kilimanjaro were affected by functional spatial heterogeneity of the habitats occupied. Therefore, use of different habitats by rodents may be indicative of the landscape integrity and ecosystem changes based on species assemblages.

Phylogeography of the mesic-adapted striped mouse, Rhabdomys dilectus chakae (Rodentia: Muridae) in forest margins of the Eastern Cape and southern KwaZulu-Natal provinces of South Africa

Abstract Rhabdomys is a genus that occupies a variety of habitats, including forest margins. Among the Rhabdomys taxa, Rhabdomys dilectus chakae has a distribution that covers the eastern seaboard of South Africa, with a poorly defined divergence date from its sister taxon Rhabdomys dilectus dilectus. Here, we study three mitochondrial markers (cytochrome b, cytochrome c oxidase I and partial control region) of R. d. chakae across the Eastern Cape and KwaZulu-Natal forests of South Africa, aiming to determine the cladogenesis (molecular dating) and effective population size of this subspecies through time, in addition to its cladogenesis in relationship to other species within the genus. A phylogenetic analysis revealed six clades within Rhabdomys, confirming that our study area is occupied solely by R. d. chakae, to the exclusion of other recognized sibling species. A fossil-calibrated Bayesian relaxed molecular clock estimated a recent split between R. d. chakae and R. d. dilectus ~1.4 ± 0.35 Mya and between two Rhabdomys pumilio groups, coastal A and B, at 1.16 ± 0.44 Mya. Coalescent Bayesian skyline plots revealed a stable population of R. d. chakae in the study area that was in slow decline until 2500 years ago, when there was an expansion in the late Holocene. Radiation within Rhabdomys dates as far back as 4.27 Mya, and subsequent demographic fluctuations primarily reflect palaeoclimatic changes.

Inhibitory responses to retinohypothalamic tract stimulation in the circadian clock of the diurnal rodent Rhabdomys pumilio.

In both diurnal and nocturnal mammals, the timing of activity is regulated by the central circadian clock of the suprachiasmatic nucleus (SCN). The SCN is synchronized to the external light cycle via the retinohypothalamic tract (RHT). To investigate potential differences in light processing between nocturnal mice and the diurnal rodent Rhabdomys pumilio, we mimicked retinal input by stimulation of the RHT ex vivo. Using Ca2+ imaging, we observed excitations as well as inhibitions of SCN neurons in response to electrical RHT stimulation. In mice, the vast majority of responses were excitatory (85%), whereas in Rhabdomys, the proportion of excitatory and inhibitory responses was similar (51% excitatory, 49% inhibitory). Glutamate blockers AP5 and CNQX blocked the excitatory responses to RHT stimulation but did not abolish the inhibitory responses in mice or Rhabdomys, indicating that the inhibitions were monosynaptically transmitted via the RHT. Simultaneous application of glutamate blockers with the GABAA antagonist gabazine blocked all inhibitory responses in mice, but not in Rhabdomys. Collectively, our results indicate that in Rhabdomys, considerably more inhibitory responses to light are present and that these responses are driven directly by the RHT. We propose that this increased proportion of inhibitory input could reflect a difference in the entrainment mechanism employed by diurnal rodents.

Obligatory homeothermy of mesic habitat-adapted African striped mice, Rhabdomys pumilio, is governed by seasonal basal metabolism and year-round 'thermogenic readiness' of brown adipose tissue.

Small mammals undergo thermoregulatory adjustments in response to changing environmental conditions. Whereas small heterothermic mammals can employ torpor to save energy in the cold, homeothermic species must increase heat production to defend normothermia through the recruitment of brown adipose tissue (BAT). Here, we studied thermoregulatory adaptation in an obligate homeotherm, the African striped mouse (Rhabdomys pumilio), captured from a subpopulation living in a mesic, temperate climate with marked seasonal differences. Basal metabolic rate (BMR), non-shivering thermogenesis (NST) and summit metabolic rate (Msum) increased from summer to winter, with NST and Msum already reaching maximal rates in autumn, suggesting seasonal preparation for the cold. Typical of rodents, cold-induced metabolic rates were positively correlated with BAT mass. Analysis of cytochrome c oxidase (COX) activity and UCP1 content, however, demonstrated that thermogenic capacity declined with BAT mass. This resulted in seasonal differences in NST being driven by changes in BMR. The increase in BMR was supported by a comprehensive anatomical analysis of metabolically active organs, revealing increased mass proportions in the cold season. The thermoregulatory response of R. pumilio was associated with the maintenance of body mass throughout the year (48.3±1.4 g), contrasting large summer-winter mass reductions often observed in Holarctic rodents. Collectively, bioenergetic adaptation of this Afrotropical rodent involves seasonal organ adjustments influencing BMR, combined with a constant thermogenic capacity dictated by trade-offs in the thermogenic properties of BAT. Arguably, this high degree of plasticity was a response to unpredictable cold spells throughout the year. Consequently, the reliance on such a resource-intensive thermoregulatory strategy may expose more energetic vulnerability in changing environments of food scarcity and extreme weather conditions due to climate change, with major ramifications for survival of the species.

Well-fed African striped mice are prepped for cold spells

Being too cold or getting overheated is a strain for creatures that maintain a stable body temperature; some just go with the flow, allowing their body temperature to fluctuate to conserve energy. In contrast, creatures that maintain a constant body temperature must continually fuel their furnaces to remain warm during cold spells, and small rodents are particularly vulnerable as their tiny frames haemorrhage heat. So how do they manage to remain warm during colder times of year? Shaun Welman and Nomakwezi Mzilikazi from Nelson Mandela University, South Africa, teamed up with Martin Jastroch from Stockholm University, Sweden, to find out how tiny African striped mice (Rhabdomys pumilio) keep warm through the seasons.Heading out to collect the mini rodents near Gqeberha (formerly Port Elizabeth), South Africa, during winter, summer, autumn and spring, Welman and Mzilikazi measured the rodents’ metabolic rates as they rested overnight by recording how much oxygen the animals consumed. The pair then kickstarted the animals’ internal heaters by injecting them with noradrenaline, and remeasured their oxygen consumption to find out how much energy they were putting into generating warmth. A day later, the researchers chilled the mice by replacing the air in their surroundings with heliox (79% helium and 21% oxygen), which carries heat away from the animals’ bodies to cool them rapidly, while recording their oxygen consumption to find out how much energy they were using to try to remain warm when conditions were really cold. So how did the animals from different seasons fare? Surprisingly, all of the animals maintained a stable body mass of ∼48 g, even though African striped mice from another region of South Africa – where the climate is predictable, but food is unreliable – gained mass to survive winter. In addition, the Gqeberha animals’ metabolic rates doubled when resting in winter. The mice also turned up their brown fat heaters – which produce warmth without shivering – in autumn, consuming more oxygen than they had in the summer. And, when Welman and Mzilikazi chilled the mice with heliox, the summer mice had the lowest metabolic rate when they became hypothermic, while the winter, spring and autumn mice had metabolic rates that were about 50% higher. In short, the winter Gqeberha mice were consuming more energy than they did in summer.So, which of the mice's tissues were using the most energy to maintain their body temperature? Welman and Jastroch checked the animals’ brown fat, but found that even though the winter mice carried more of the tissue, the key proteins responsible for brown fat heat production fell by 25%. Brown fat could not be responsible for the winter metabolic rise. Instead, the mice were building up other organs, including the liver and intestines, to increase their metabolic rate to keep warm during the cold season.But why have the Gqeberha African striped mice opted for a profligate lifestyle during winter when other rodents conserve energy? Welman suspects that the temperate region's bountiful food supply allows the mice to maintain their high-octane way of life across the seasons. But why they do so is more baffling.Mzilikazi thinks it has something to do with the unpredictable cold snaps that strike Gqeberha. ‘We argue that sporadic cold spells at the study site pressurised African striped mice to maintain a high level of heat production throughout the year’, she says. So, the mice keep their brown fat on standby, in case of sudden cold periods between autumn and spring. But keeping their heaters prepared for spontaneous action could place them at risk if their plentiful food supply dries up thanks to climate change.

Characteristics influencing local enhancement in free-living striped mice

Social learning is widespread across species; however, we still know little about the impact of individual differences in behaviour on social transmission. We aimed to investigate factors influencing social learning in free-living Rhabdomys pumilio, a group-living, arid-adapted mouse. We studied 52 mice in a lid opening task in a field laboratory. We created observer-demonstrator dyads with demonstrators either opening lids or not. We measured success of observers to open lids, their attention and latency to open and time spent interacting with the device. We also considered influences of observer age, sex, group size and personality traits. Demonstrator success did not influence observer success, although attention towards the demonstrator did impact the observers’ time spent with the device. Males were more successful than females and more active/explorative observers interacted with the device faster and for a longer time compared to less active/explorative counterparts. We found no influence of age and group size on mouse success. Striped mice appeared to use cues from other individuals to learn how to solve the task and it was influenced by sex and personality. Striped mice in this studied population may use local enhancement to acquire information socially.

Variation in brain volume in nine populations and three taxa of the African striped mouse Rhabdomys.

Brain size can vary between populations in different environments because of different selection pressures on behaviours, such as learning and memory, related to spatial, social and environmental differences. We investigated the variation in total and broad-scale regional brain size in the murid rodent genus Rhabdomys from different environments. We assessed taxon-, population- and sex-level differences in total and regional brain volume in three populations each of three taxa (arid-occurring Rhabdomys pumilio and mesic-occurring Rhabdomys dilectus chakae and R. d. dilectus) originating across southern Africa. We μCT-scanned crania obtained from museums in South Africa and used digital software to create endocasts and extract total endocranium and regional volumes: olfactory bulb, anterior cerebrum, posterior cerebrum, cerebellum volume and petrosal volume. Total endocranial volume scaled with basal skull length and all-region volumes scaled with total endocranial volume. We found taxon-, and population-level differences in total endocranial volume. Relative anterior and posterior cerebrum volume did not differ significantly between taxa or populations, but relative cerebellum volume was larger in arid populations than mesic populations. Relative olfactory bulb volume was larger in mesic R. dilectus than in the R. pumilio, but petrosal lobule volume was larger in R. pumilio populations than in R. dilectus. Males had larger total endocranial volumes than females. Drivers of larger total endocranial volumes in R. pumilio are not immediately clear from our results. Environmental seasonality of food availability, cognitive buffering and locomotion may all correlate with total endocranial volume size, whereas the influence of sociality cannot be excluded. The environment and degree of semi-arboreality are likely driving variation in cerebellum, olfactory bulb and petrosal lobule volumes.

Generalist indigenous herbivores resist alien tree invasion: Rhabdomys pumilio limits establishment of Acacia cyclops

Generalist indigenous herbivores resist alien tree invasion: Rhabdomys pumilio limits establishment of Acacia cyclops

Daily electrical activity in the master circadian clock of a diurnal mammal.

Circadian rhythms in mammals are orchestrated by a central clock within the suprachiasmatic nuclei (SCN). Our understanding of the electrophysiological basis of SCN activity comes overwhelmingly from a small number of nocturnal rodent species, and the extent to which these are retained in day-active animals remains unclear. Here, we recorded the spontaneous and evoked electrical activity of single SCN neurons in the diurnal rodent Rhabdomys pumilio, and developed cutting-edge data assimilation and mathematical modeling approaches to uncover the underlying ionic mechanisms. As in nocturnal rodents, R. pumilio SCN neurons were more excited during daytime hours. By contrast, the evoked activity of R. pumilio neurons included a prominent suppressive response that is not present in the SCN of nocturnal rodents. Our modeling revealed and subsequent experiments confirmed transient subthreshold A-type potassium channels as the primary determinant of this response, and suggest a key role for this ionic mechanism in optimizing SCN function to accommodate R. pumilio's diurnal niche.

Bachelor groups form due to individual choices or environmental disrupters in African striped mice

In several mammal species, bachelor groups occur as a regular life history stage between dispersal and becoming the breeding male of a multifemale group. How such groups come into existence and how males that choose this strategy differ in life history traits from other males is rarely investigated. Males of the socially flexible African striped mouse, Rhabdomys pumilio , have been historically reported to adopt one of three alternative tactics: small group-living philopatric males, intermediate solitary roaming males or large group-living territorial males. Here, we describe for the first time, bachelors as a fourth male tactic. A long-term study on 13 generations of striped mice revealed two types of bachelor groups: (1) kin bachelor groups formed when all females disappeared, probably due to predation, and (2) nonkin bachelor groups formed by unrelated males that originated from different groups. Whereas kin bachelor groups occurred more frequently during the nonbreeding season, nonkin bachelor groups were most common in the breeding season and had a shorter tenure, since most of these males soon switched to the solitary roaming tactic or the territorial breeder tactic. Importantly, we found that nonkin bachelors were heavier and older than kin bachelors and that they did not differ from solitary roaming males in body mass and age. We therefore identified two different forms of bachelor groups, small kin bachelors whose female group members disappeared and larger nonkin bachelor groups showing traits of an alternative reproductive tactic. Both types of bachelor groups differed in multiple traits, demonstrating that it is important to follow the life histories of individuals to understand the mechanisms leading to alternative tactics. • We describe bachelor groups as a fourth male tactic in striped mice. • Kin bachelor groups form when all females disappear. • Nonkin bachelor groups are formed by unrelated males from different groups. • Both types of groups differ in body mass, age and seasonality of occurrence.