Xerus Inauris Research Articles

Lovers, not fighters: docility influences reproductive fitness, but not survival, in male Cape ground squirrels, Xerus inauris

Over their lifetime, individuals may use different behavioural strategies to maximize their fitness. Some behavioural traits may be consistent among individuals over time (i.e., ‘personality’ traits) resulting in an individual behavioural phenotype with different associated costs and benefits. Understanding how behavioural traits are linked to lifetime fitness requires tracking individuals over their lifetime. Here, we leverage a long-term study on a multi-year living species (maximum lifespan ~ 10 years) to examine how docility (an individual’s reaction to trapping and handling) may contribute to how males are able to maximize their lifetime fitness. Cape ground squirrels are burrowing mammals that live in social groups, and although males lack physical aggression and territoriality, they vary in docility. Males face high predation risk and high reproductive competition and employ either of two reproductive tactics (‘natal’ or ‘band’) which are not associated with different docility personalities. We found that although more docile individuals sired more offspring on an annual basis, docility did not affect an individual’s long-term (lifetime) reproductive output. Survival was not associated with docility or body condition, but annual survival was influenced by rainfall. Our findings suggest that although docility may represent a behavioural strategy to maximize fitness by possibly playing a role in female-male associations or female mate-choice, variations in docility within our study population is likely maintained by other environmental drivers. However, individual variations in behaviours may still contribute as part of the ‘tool kit’ individuals use to maximize their lifetime fitness.

Temperature-associated morphological changes in an African arid-zone ground squirrel

Abstract The ecology, life histories, and physiology of many animals are changing in response to human-induced climate change. As the Earth warms, the ability of an animal to thermoregulate becomes ecologically and physiologically significant. Morphological adaptations to warmer temperatures include larger appendages and smaller bodies. We examined morphological features in a ground squirrel, Xerus inauris, living in the arid zones of South Africa, to examine whether squirrels have responded to increases in temperature and changes in seasonal rainfall with morphological modifications over the last 18 years. We found that over time, absolute hindfoot length and proportional hindfoot length increased, while spine length decreased. These changes are consistent with ecogeographical rules (Allen’s rule and Bergmann’s rule) and provide evidence in support of “shape-shifting” in response to climatic warming. Body mass also increased with time; however, these changes were not consistent with Bergmann’s rule, indicating that mass is influenced by other ecological factors (e.g., resource availability). Our study adds to the growing evidence that animal morphologies are changing in response to changing climatic conditions, although it remains to be seen whether these changes are adaptive.

Personalities are not associated with different reproductive tactics in male Cape ground squirrels, Xerus inauris

Personality may influence social living and the maintenance of alternative reproductive tactics (ARTs). In some species, suppressing aggression may be important for facilitating social living, and different personalities may be linked with different types of social associations. Yet, few studies have examined personality in species with low levels of aggression. In Cape ground squirrels, males have two discrete ARTs. Males either live in family groups (‘natal’) or all-male groups (‘band’) and lack physical aggression and territoriality. We measured docility (during trapping and handling in 2014–2019, N males = 275) and activity and exploration (during an open field test in 2015, N males = 34) in adult males to determine whether personality contributes to the maintenance of ARTs. We found repeatability in docility (adjusted repeatability = 0.25–0.26) but not in activity or exploration, and docility was not associated with different ARTs. However, docility and ARTs were influenced by abiotic and biotic factors. Males were more docile after their first capture, and older males (longer on-site tenure) tended to be less docile. In years of higher rainfall, there were more band males, suggesting that ARTs may depend on ecological conditions. • Cape ground squirrels are a highly social species with low rates of aggression. • Males have two discrete reproductive tactics; ‘natal’ and all-male ‘band’ groups. • Males have docile personalities. • Personalities are not associated with different reproductive tactics. • Males became less docile with longer on-site tenure (years captured).

Engineering by cape ground squirrels affects biodiversity in semi-arid grasslands

Burrowing mammals that disproportionately affect their physical environment, creating habitat and providing resources for other organisms, are considered ecosystem engineers. Such modifications are particularly important in dry grassland environments, where low precipitation and soil nutrients limit plant growth. We tested 5 hypotheses about the impact of Cape ground squirrels (Xerus inauris) on plants and animals in a semi-arid grassland of South Africa. At each burrow cluster and paired control site without burrows, we estimated plant cover, height, and richness using quadrats, and invertebrate and small mammal abundance and richness using pit-fall traps and mark-recapture, respectively. We determined nitrogen concentrations in grasses on and off burrows and measured carbon and nitrogen stable isotopes in plants and squirrel hair to determine squirrel diet. Burrows had greater plant cover and richness, particularly more shrubby vegetation, but plant height and nitrogen concentrations did not differ on and off burrows. Invertebrate and small mammal abundance and richness were greater on burrows. Squirrel disturbances in semi-arid grassland improved conditions for disturbance-dependent shrubs, which were rarely consumed by squirrels but are valuable forage for antelope and provide cover for invertebrates and small mammals. By altering habitat for plants reliant on disturbance, Cape ground squirrels enhance grassland biodiversity.

Intraspecific variation in male mating strategies in an African ground squirrel (Xerus inauris).

Male mating strategies respond to female availability such that variation in resources that affect spatial distribution can also alter cost–benefit tradeoffs within a population. In arid‐adapted species, rainfall alters reproduction, behavior, morphology, and population density such that populations differing in resource availability may also differ in successful reproductive strategies. Here, we compare two populations of Cape ground squirrels (Xerus inauris), a sub‐Saharan species with year‐round breeding and intense mating competition. Unlike most mammals where males resort to aggressive interactions over females, male X. inauris are tolerant of one another, relying instead on other nonaggressive pre‐ and postcopulatory strategies to determine reproductive success. Our findings suggest that differences in resource availability affect female distribution, which ultimately leads to intraspecific variation in male reproductive tactics and sexual morphology. Sperm competition, assessed by reproductive morphometrics, was more pronounced in our high resource site where females were distributed evenly across the landscape, whereas dominance seemed to be an important determinant of success in our low resource site where females were more aggregated. Both sites had similar mating intensities, and most males did not sire any offspring. However, our low resource site had a higher variance in fertilization success with fewer males siring multiple offspring compared with our high resource site where more individuals were successful. Our results lend support to resource models where variations in female spatial distribution attributed to environmental resources ultimately impact male reproductive behaviors and morphology.

Engineering Effects of Cape Ground Squirrels on Biodiversity in Semi-Arid Grasslands

Engineering Effects of Cape Ground Squirrels on Biodiversity in Semi-Arid Grasslands

Alternative tactics in male African ground squirrels: the impact of variable rainfall on condition and physiology

Abstract Alternative reproductive tactics occur when conspecifics of the same sex use different behavioral processes to maximize reproductive success. Resource availability can have significant impacts on the proximate factors impacting the success and persistence of alternative tactics, such as an individual’s physiology, immunity, and body condition. Male Cape ground squirrels (Xerus inauris) display two alternative tactics, with some mature males dispersing from their natal groups and joining bands of nonrelated males (band males), whereas others do not disperse and remain philopatric in their natal groups past sexual maturation (natal males). Despite differences in metabolism, home ranges, and behavior, there is no difference in reproductive success between the two tactics, allowing us to test if rainfall (as a measure of primary productivity) influences body condition and physiological indices in tactics when fitness is equal. Over a period of 6 years, rainfall was positively related to body condition (mass–spine length residuals) in band males (N = 76), but not in natal males (N = 75). When we followed 18 males prior to and after dispersal, we also found a positive relationship between body condition and age following dispersal, but not prior to dispersal, and natal males maintained a better body condition in low rainfall years. During 2 years of low rainfall, band males (N = 39) had higher total ectoparasite abundance, and white blood cell differentials, implying they are less able to tolerate parasitic infection than natal males (N = 31). We found no difference in bacterial growth inhibition between tactics, suggesting that band and natal males both are equally resistant to parasites. The poorer body condition of band males during lower rainfall suggests they are less tolerant to parasites in these years. Dispersal during years of low rainfall thus may increase the costs to body condition and parasite infection, but the reproductive benefit of overlapping with more females may contribute to maintaining equal fitness between tactics.

Eavesdropping of an African ground squirrel on the heterospecific alarm calls of a noisy ground‐nesting bird

AbstractAnimals gather information about their environment from a variety of sources to enable adaptive decision‐making behaviour. Eavesdropping on heterospecific alarm calls enhances predator avoidance, reduces time spent vigilant and allows for more time on daily activities such as foraging. If the information is relevant and reliable, individuals that respond to heterospecific signals may benefit from a wider range of information at a low marginal cost. The Cape ground squirrel (Xerus inauris) and crowned lapwing (Vanellus chilensis) are ground‐dwelling species that are taxonomically distant but share similar predators, habitat and anti‐predatory behaviours. We used playback experiments of the alarm calls produced by conspecifics and lapwings to investigate the vigilance responses of adult female Cape ground squirrels. Squirrels responded with greater vigilance to both squirrel and lapwing alarm calls, and no changes of vigilance levels were observed in response to a control sound. However, contrary to our predictions, changes in vigilance and time to relax did not differ between conspecific versus heterospecific playbacks. The results from our study suggest that squirrels perceive lapwing alarm calls as relevant and reliable information and that responding to it could increase their survival.

Not playing by the rules: mixed support of ecogeographic rules in an arid‐adapted African ground squirrel

AbstractBody size impacts nearly all aspects of an animal's life and can be subject to considerable variation in response to differences in climate and resource availability. We studied the impact of temperature and resource availability on arid‐living Cape ground squirrels (Xerus inauris), relative to body size and degree of sexual dimorphism, over three locations differing in annual rainfall and temperature to test Bergmann's rule, the resource rule and Rensch's rule. We found that squirrels were the largest where resources were the highest and temperatures were the lowest but squirrels were similar in mass where resources were medium or low and temperatures medium and highest, partially supporting Bergmann's rule and the resource rule. Hind‐feet were the largest where resources were medium and temperatures were medium and similarly small in low and high resource and high‐ and low‐temperature areas. The degree of sexual dimorphism of hind‐foot and mass was constant no matter the resource abundance or temperature, suggesting no impact of resource availability or temperature on the degree of sexual dimorphism, contradicting Rensch's rule. Our findings suggest that, while resource availability and temperature may have an impact on body size, other mechanisms may be important in limiting both body size and degree of sexual dimorphism in this species.

Social organization in a North African ground squirrel

AbstractResearch on sociality in temperate ground-dwelling squirrels has focused on female philopatry and other life history trade-offs, which are influenced by constraints in the duration of the active growing season. Temperate ground-dwelling squirrels that experience high predation pressure, are large in body size, and have a short active season, show a more complex social organization. In contrast, African ground squirrels are active year-round, suggesting that instead of a short active season, distinct selective pressures influence their social organization. We examined the social organization of Barbary ground squirrels, Atlantoxerus getulus, and compared the social organization of temperate and African ground-dwelling sciurids. Anecdotal accounts on Barbary ground squirrels’ social organization suggested that they were either solitary or gregarious, or live in small family groups. We recorded the group size, composition, cohesion, and genetic relatedness, of the population on the arid island of Fuerteventura, Spain. Our data indicate that females live in small (1–8) all-female kin groups separate from adult males, and that unrelated adult males share sleeping burrows with immature individuals of either sex. We observed sex-biased dispersal with males primarily the dispersing sex and females primarily philopatric. Females sleep solitarily during gestation and lactation and nest either communally or singly after juvenile emergence. During the day, males and females can be active in the same area. Barbary ground squirrels are social because the squirrels share sleeping burrows and show spatiotemporal overlap. Barbary ground squirrels’ social organization resembles that of the closely related Cape ground squirrel rather than that of the temperate ground-dwelling sciurids, although the former are more temperate, seasonal breeders. In addition to describing the social organization of a previously unstudied species, this paper sheds light on the ecological drivers of sociality, and the evolution of distinct social organizations in ground-dwelling sciurids.

Understanding the relationship between farmers and burrowing mammals on South African farms: are burrowers friends or foes?

Burrowing mammals are ubiquitous on farms in South Africa and can hinder agricultural practices. This study explored farmer perspectives of these species, and specifically the factors that influence these perspectives. Forty-four farmers responded to a questionnaire that assessed their ecological knowledge of, tolerance towards and lethal management of burrowing mammals that occur on their farms. The results from generalised linear models showed that neither farmer age, nor level of education are accurate predictors of ecological knowledge, overall tolerance towards burrowers, or their lethal management. Knowledge of burrowing mammals showed a significant relationship with tolerance, with more knowledgeable individuals displaying higher levels of tolerance. However, a farmer’s overall tolerance towards burrowing species did not affect the number of species managed. Our results also suggest that different values are attached to different species when it comes to lethal management. Thus, farmers commonly controlled the numbers of the problem rodent species, Highveld gerbil (Gerbilliscus brantsii) and Cape ground squirrel (Xerus inauris), but were less likely to manage black-backed jackal (Canis mesomelas) and warthog (Phacochoerus africanus), even when experiencing these as problematic. We suggest that the larger, more charismatic species possibly evoke more sympathy from farmers. Agro-ecosystems are likely to become increasingly important for conservation in the future, and we encourage continued studies on the environmental attitudes and approaches of agricultural practitioners as a means to understanding the current status and future trends in ecologically sustainable agriculture.

Both familiarity and kinship influence odour discrimination by females in a highly social African ground squirrel

Kin recognition can be important in species where inbreeding avoidance or nepotism (favouritism towards kin) rely on identifying kin, particularly in species with alloparental care. The mechanisms that facilitate kin discrimination, where recognition is determined through cues that correlate with relatedness, usually include either prior association (familiarity) or phenotype matching or both. Odour is an important cue used in a number of mammalian species to discern kin, particularly the ground-dwelling squirrels. Cape ground squirrels, Xerus inauris, are a cooperative-breeding species, living in tight-knit family groups. However, group fission, promiscuity and the large home ranges of breeding males result in a high variance in relatedness both within and among social groups, making them a good species to investigate kin discrimination. We examined whether females are capable of discriminating between the odours of familiar versus unfamiliar females that varied in their relatedness to the focal female using odour experiments. Overall, the average duration of sniffing of the odours of familiar and unfamiliar females did not differ. Similarly, females did not adjust their sniff duration relative to the degree of relatedness of familiar females. However, females appeared to discriminate by the degree of relatedness of unfamiliar (stranger) females, spending longer sniffing odours from females that were not related to them. Thus, females were capable of discriminating the degree of relatedness from odour but they did not do so within their family group. We conclude that Cape ground squirrels are able to discriminate kin. However, whether females in this facultative cooperative breeder use the degree of relatedness in direct social interactions and nepotistic behaviours remains to be investigated.

Unusual cases of Taenia crassiceps cysticercosis in naturally infected animals in the Czech Republic

The tapeworm Taenia crassiceps has an indirect life cycle. Occasionally, metacestode stages have been reported from aberrant hosts as dogs, cats, lemurs and humans. This study describes an unusual series of serious cysticercosis cases: an 18-month-old male Yorkshire terrier dog with pleural cysticercosis accompanied by a cough, a 10-year-old male Shih Tzu dog with subcutaneous cysticercosis as well as a Cape ground squirrel and a Senegal bushbaby, both with generalised cysticercosis. Surgery was successful only in the Shih Tzu. The Yorkshire terrier died a few hours after surgery, while the Cape ground squirrel was euthanised and the Senegal bushbaby died before surgery. Cysticerci from the four cases were identified morphologically and using molecular methods. Fragments of genes coding for cytochrome oxidase subunit 1 were sequenced for each of the four isolates. Their affiliation to T. crassiceps was confirmed by comparison with the sequence data of other isolates available in the GenBank database. In general, the comparison of sequences of all isolates showed low variability in nucleotide composition (at most five positions). The cases from captive zoo animals represent the first findings of T. crassiceps in the Cape ground squirrel and Senegal bushbaby. The optimal treatment of cysticercosis caused by T. crassiceps remains unclear. Successful attempts usually include extensive surgical interventions and prolonged anthelmintic treatment. Chemotherapeutic options are limited. Although regular deworming targeting intestinal helminths of dogs is not effective against T. crassiceps cysticerci, it may help to prevent contamination of the environment by tapeworm eggs contained in dog faeces and reduce the risk of infection for susceptible animals and humans.

Trade-offs between immunity and testosterone in male African ground squirrels.

The immunocompetence handicap hypothesis (ICHH) proposes that testosterone has both beneficial effects on male reproductive potential and negative effects by suppressing the immune system. However, support for the ICHH has been variable and an alternative hypothesis suggests that testosterone may be acting indirectly via cortisol to suppress immunity (the stress-linked ICHH). A third hypothesis is that increased energetic investment in immunity results in the suppression of testosterone. We tested these hypotheses in male Cape ground squirrels (Xerus inauris) through two separate manipulations: first, by triggering a strong immune response using a lipopolysaccharide (LPS) injection and, secondly, by increasing circulating testosterone using silastic testosterone implants. Responding to an immune challenge significantly reduced testosterone, supporting the immune suppression hypothesis, while increasing circulating testosterone had no effect on immunocompetence, body mass, ectoparasite abundances or cortisol levels, failing to support either the ICHH or stress-linked ICHH. Our results add to the increasing body of literature that challenges the ICHH, and we conclude that the trade-off between testosterone and immunity is mediated through immune activation and not through testosterone in male Cape ground squirrels. Being able to test the ICHH, stress-linked ICHH and immune suppression hypotheses in a free-ranging mammal gives us a unique opportunity to examine the mechanisms mediating this trade-off.

The effects of familiarity and reproductive status on olfactory discrimination by female Cape ground squirrels (Xerus inauris)

The ability to differentiate among conspecifics on the basis of genetic relatedness can be advantageous in kin and mate selection. Selection of mates that are of an intermediate degree of relatedness maximizes the propagation of shared genes to offspring, while minimizing the accumulation of deleterious recessive alleles that can result from close inbreeding. Odors produced from various glandular surfaces of the body have been shown to influence discrimination of conspecifics in numerous taxa, including the order Rodentia. We investigated whether female Cape ground squirrels (Xerus inauris) discriminate between the odors of familiar and foreign males by conducting scent experiments. We simultaneously presented odors that had been collected on acrylic cubes from the anal gland of a familiar (non-dispersed) and a foreign male as well as an unscented control, and recorded the response of focal pregnant and non-pregnant females (n = 19). Non-pregnant females responded differently to the odors of the scent cubes, sniffing the scent collected from the foreign male significantly longer than either the familiar male or control odor, whereas there was no difference in the response of pregnant females. We conclude that male familiarity may influence female mate choice, as familiarity is reliably correlated with relatedness in this population. Based on prior knowledge about the social behavior of Cape ground squirrels, the ability to discriminate between familiar and foreign males may be used by females as an inbreeding avoidance mechanism, as close inbreeding can be avoided by mating with foreign males. Olfactory cues are one method of social communication among conspecifics, and can play an important role in nepotism, territory defense, and mate choice. We studied olfactory discrimination in the Cape ground squirrel, a highly social, semi-fossorial mammal that occurs in South Africa. We assessed the response of pregnant and non-pregnant females to the odors of familiar and unfamiliar males. We found that non-pregnant females displayed a preference for unfamiliar males, whereas pregnant females displayed no preference. Cape ground squirrels are non-territorial and exhibit low levels of intraspecific aggression; therefore, our results indicate that odor may be involved in mate selection by females, rather than territoriality, as relatively low levels of inbreeding are maintained in this population.

Use of the sun as a heading indicator when caching and recovering in a wild rodent.

A number of diurnal species have been shown to use directional information from the sun to orientate. The use of the sun in this way has been suggested to occur in either a time-dependent (relying on specific positional information) or a time-compensated manner (a compass that adjusts itself over time with the shifts in the sun’s position). However, some interplay may occur between the two where a species could also use the sun in a time-limited way, whereby animals acquire certain information about the change of position, but do not show full compensational abilities. We tested whether Cape ground squirrels (Xerus inauris) use the sun as an orientation marker to provide information for caching and recovery. This species is a social sciurid that inhabits arid, sparsely vegetated habitats in Southern Africa, where the sun is nearly always visible during the diurnal period. Due to the lack of obvious landmarks, we predicted that they might use positional cues from the sun in the sky as a reference point when caching and recovering food items. We provide evidence that Cape ground squirrels use information from the sun’s position while caching and reuse this information in a time-limited way when recovering these caches.

Are Cape Ground Squirrels (Xerus inauris) Sensitive to Variation in the Pay‐offs from Their Caches?

AbstractFor food caching to be adaptive, the benefits of recovery must outweigh the costs of storing an item. One of the costs to cachers is the risk of theft, and therefore, it is predicted that individuals may be sensitive to this theft and show various behavioural strategies to minimise it. In this study, we gave wild Cape ground squirrels (Xerus inauris) a choice between two different coloured items of the same food type: one item with a specific colour that was always artificially removed when cached and the other item with a different colour that was not removed when cached. During the choice presentations, subjects reduced the amount they consumed and cached of the food items with the colour that was experimentally removed when cached, despite the two items only differing in caching pay‐off. This avoidance to choose the food with the colour that was removed occurred over time, which suggests that subjects were using information about the item's pay‐off during cache recovery and this then impacted on successive decisions. This study highlights how the sensitivity to a food item's pay‐off can affect an individual's choice towards items that offer the greater overall reward.

Cape ground squirrels as ecosystem engineers: modifying habitat for plants, small mammals and beetles in Namib Desert grasslands

AbstractBurrowing and foraging of semi‐fossorial rodents can affect species distribution and composition. Ground squirrels dig large burrow systems for refuge from predators and temperature extremes. Burrowing and foraging around burrows by squirrels may affect habitat and resource distributions for other organisms. We examined the impact of Cape ground squirrels (Xerus inauris) on vegetation, small mammals and beetles during winter and summer in grasslands on the edge of the Namib Desert. At each burrow system and paired control site without burrows, we estimated plant cover and height using quadrats (N = 8 paired sites), small mammal abundance and species richness using mark‐recapture techniques (N = 8 paired sites) and beetle abundance and species richness using pitfall traps (N = 6 paired sites, winter only). Squirrel burrowing and foraging activities resulted in lower plant cover and height, higher small mammal abundance and lower beetle abundance and species richness. Squirrels also reduced more plant cover in winter compared to summer, but had no effect on small mammal species richness. Furthermore, plant cover and height were higher in summer, whereas small mammal abundance and species richness were higher in winter. Our results suggest that Cape ground squirrels are important ecosystem engineers that influence plant and animal communities in the Namib Desert grasslands.

Caching in the presence of competitors: Are Cape ground squirrels (Xerus inauris) sensitive to audience attentiveness?

When social animals cache food close to their burrow, the potential for an audience member to observe the event is significantly increased. As a consequence, in order to reduce theft it may be advantageous for animals to be sensitive to certain audience cues, such as whether they are attentive or not to the cache event. In this study, observations were made on three groups of Cape ground squirrels (Xerus inauris) in their natural habitat when they cached provisioned food items. When individuals cached within 10m of conspecifics, we recorded the attentiveness (i.e. whether any audience members were orientated towards the cacher, had direct line of site and were not engaged in other activities) and identity of audience members. Overall, there was a preference to cache when audience members were inattentive rather than attentive. Additionally, we found rank effects related to cache avoidance whereby high-ranked individuals showed less avoidance to cache when audience members were attentive compared to medium- and low-ranked individuals. We suggest this audience sensitivity may have evolved in response to the difference in competitive ability amongst the ranks in how successful individuals are at winning foraging competitions. This study demonstrates that Cape ground squirrels have the ability to not only monitor the presence or absence of conspecifics but also discriminate individuals on the basis of their attentive state.

“Failure to launch”: is there a reproductive cost to males living at home?

Differential reproductive success commonly reflects variations in reproductive physiology, behavior, and morphology. In some species, competition among males results in the evolution of alternative reproductive tactics that confer a fitness advantage relating to social status, density, or myriad other factors. In the Cape ground squirrel (Xerus inauris), a species that is highly competitive but lacks typical mammalian aspects of intrasexual competition (e.g., territoriality and aggression), 2 alternative reproductive tactics occur relating to dispersal. While physiological and behavioral differences have been demonstrated between dispersed males and males that delay dispersal, we used microsatellite markers to quantify variations in reproductive success between tactics. We found that dispersed males are in better body condition with larger home ranges likely allowing greater encounter frequencies with estrous females. However, we found no difference in copulation frequency between tactics, and the decisio...