Microcavia Australis Research Articles

Social Environment and Agonistic Interactions: Strategies in a Small Social Mammal

In group-living species, the development of agonistic interactions among conspecifics may be affected by socio-ecological factors, such as size and composition of social group, and availability of nests and food. We analysed the importance of size and composition of social groups on agonistic interactions among males in the Southern mountain cavy (Microcavia australis). We made behavioural observations in four social groups of different size and composition. We recorded two types of agonistic interactions: agonistic displays and direct agonistic behaviours; both types increased in the breeding season. A social group composed of a high number of males was associated with high frequency of agonistic displays. Direct agonistic behaviours were also influenced by the interaction of season and number of males per social group and number of females per social group. Agonistic interactions were also recorded among males of different socials groups in the breeding season. Agonistic displays were most frequent among males of the same social group, whereas direct agonistic behaviours were most common among males of different social groups. These results suggest that social factors affect agonistic interactions among males of Southern mountain cavy and that in a conflict situation, males develop different strategies, such as increased frequency of agonistic behaviours in breeding season and intragroup cooperation for defence of oestrous females.

High genetic differentiation among populations of the small cavy Microcavia australis occupying different habitats

The small cavy Microcavia australis, a social and fossorial rodent, inhabits a large distribution range in South American arid zones. The species is versatile in coping with the seasonal and spatial variability typical of these environments through changes in morphology, physiology, and behavior. In order to explore whether phenotypic variations are related to the evolutionary history of the species, we analyzed the levels of genetic variability and divergence among four populations that differ in climate and habitat characteristics, two belonging to highlands and the other two from lowlands. We sequenced the mitochondrial control region and used the Inter Simple Sequence Repeats technique to study variability in the noncoding nuclear genome. Results from both genetic markers were consistent. Variability levels were high for all populations, and even higher for lowland ones. Pairwise genetic differentiation varied greatly, all comparisons being statistically significant except for the two highland populations. Seventeen haplotypes were detected which displayed three clear lineages: two corresponding to each lowland population and one to those in the highlands. Levels of genetic differentiation between population pairs varied widely. Haplotypes showed a mean sequence divergence of 1.4% between lowland populations and 0.2% between highland ones, whereas divergence was around 9% when populations from different altitudes were compared. Results from BEAST analysis support extant hypotheses suggesting that lowland forms are clearly older than the highland group. The deep genetic divergence between lineages poses the need to search for new evidence for properly defining the taxonomic status of divergent populations of M. australis.

Small mammal remains recovered from two archaeological sites in the middle and lower Negro River valley (Late Holocene, Argentina): Taphonomic issues and paleoenvironmental implications

This paper presents the results of a taphonomic and paleoenvironmental analysis of small mammal remains recovered from the Negro Muerto and Angostura 1 archaeological sites. These sites (ca. 0.5 and 0.95 ka BP, respectively), are located in the middle and lower Negro River valley in northern Patagonia, Argentina. Based upon the presence of several types of evidence (cut marks, bone tools, and thermal alteration), it is proposed that Holochilus brasiliensis and cavies were acumulated by humans. At the Angostura 1 site, some remains also show evidence of having been generated by carnivores (digestion, breakage patterns, and relative skeletal element abundances). This indicates that carnivores (e.g., Puma concolor) could have contributed to the formation of the small mammal assemblages. Other small mammal species recovered at both sites (e.g., Galea leucoblephara, Microcavia australis, Akodon molinae, and Graomys griseoflavus) suggest semi-desert environmental conditions, similar to those found today. The presence of Reithrodon auritus and Oligoryzomys sp. indicate the development of open herbaceous steppe environments in proximity to bodies of water. However, the discovery of H. brasiliensis at both sites, an orizomyine of amphibious habitats and subtropical origin, and which is now absent in the area, suggests warmer and wetter conditions during this period.

Influence of predation risk and plant structure on vigilance and intermittent locomotion in Microcavia australis (Rodentia, Caviidae)

The aim of this study was to analyze and compare vigilance behavior and intermittent locomotion at two sites (El Leoncito and Nacunan, Argentina) that differ in predation risk, plant structure, and plant resource availability. Subjects were lesser cavies (Microcavia australis), a social species that is semi-fossorial, diurnal, and native to South America. Continuous focal sampling was conducted during the day, at times of food shortage, food abundance, and reproduction from 2003 to 2005. The proportion of time spent vigilance was significantly higher at Nacunan, where vigilance peaked at midday and reached a minimum in the evening. This midday peak of vigilance at Nacunan was associated with a midday peak of danger from raptors as indicated by a raptor activity peak at that time. In contrast, both vigilance and predator activity at El Leoncito were constant through the day. Records of intermittent locomotion and number and duration of pauses in locomotion were significantly higher at El Leoncito, a difference that may have been due to the need for greater vigilance while moving across areas of less protective cover at this site.

Geographic and seasonal variability in feeding behaviour of a small herbivorous rodent

Foraging strategies have traditionally been modelled as a result of food selection in response to one factor, as for instance resource availability, deterrent compounds or nutrients. Thus, a trade-off is assumed between plasticity (generalist strategy) and efficiency (specialist strategy). Nevertheless, several studies have demonstrated that animals cope behaviourally with food supply variation. For instance, desert-dwelling rodents partially compensate for nutritional bottlenecks through diet selection. The aim of our study was to test how foraging behaviour matches spatial and temporal variations in the trophic environment and how modelling hypotheses help us to understand the resultant foraging strategy. Our animal study model was the small cavy Microcavia australis, a widely distributed herbivorous rodent. Fieldwork was carried out in four places, in wet and dry seasons. We found significant differences in plant cover, plant diversity and niche breadth, and diet selection revealed a complex foraging strategy. M. australis shows a behavioural repertoire that exceeds single-criterion categories; therefore, we appeal to theoretical models that consider ecological and physiological perspectives. We classified the small cavy as a facultative specialist displaying a thoroughly opportunistic strategy based on the plasticity of the behavioural phenotype. We finally discuss the evolutionary relevance of our results and propose further investigation avenues.

Effect of climatic variables on seasonal morphological changes in the testis and epididymis in the wild rodent Microcavia australis from the andes mountains, Argentina

It has been shown that seasonal changes, especially in arid areas have a large influence on gonadal changes of the species that inhabit these areas. We studied a wild hystricomorph Microcavia australis in its natural habitat in the arid Andes Mountains. Sampling of adult males was carried out every 2 months. After autopsy, testes and epididymides were weighed and processed to obtain histological samples. Testes were analyzed with a microscope to measure seminiferous tubule area and diameter for each sampled month. Epididymides were used to determine spermatozoon storage in the cauda region. Results illustrate morphological changes in the testis and epididymis along the year. A high output of sperm cells was detected from middle winter to middle summer and a complete shutdown of spermatogenesis at the end of summer. The initiation of testicular activity coincided with month with the shortest day length, in dry season and very low temperature. On the other hand, gonadal regression started in the middle of summer with long day length, in the wet season, and high temperatures. Rainfall, temperature, and day length seem to be important for the testis cycle. We suggest that photoperiod could be a good predictor for an oncoming period suitable for breeding, and males may probably use it as a signal to regulate gonadal activity.

Plasticity in food assimilation, retention time and coprophagy allow herbivorous cavies ( Microcavia australis) to cope with low food quality in the Monte desert

Energy balance depends on the efficiency with which organisms make use of their trophic resources, and has direct impact on their fitness. There are environmental variations that affect the availability as well as the quality of such resources; energy extraction also depends on the design of the digestive tract. It is expected that features associated with food utilization will be subjected to selective pressures and show some adjustment to the variability of the environment. Since energetic constraints challenge animals to display digestive compensatory mechanisms, the objective of this study is to determine the physiological and behavioral responses to spatial and seasonal heterogeneity in food quality. We investigated digestive strategies (digestive efficiency and coprophagy) in cavies inhabiting two different populations, and hence naturally experiencing different levels of diet quality. Cavies under experimentally different quality diets showed changes in dry matter digestibility and intake, digesta retention time and coprophagy. Our results partially support the expectations from theory and also reveal interpopulation differences in the ability to cope with changes in food quality, and may explain the capability of Microcavia australis to colonize extreme habitats.

Is communal burrowing or burrow sharing a benefit of group living in the lesser cavy Microcavia australis?

Burrow systems play an important role in the life of rodents in arid environments. The objectives of this study were to examine the hypothesis that group living is beneficial to the semifossorial rodent, and determine whether Microcavia australis (Geoffroy and d’Orbigny, 1833) burrows communally and/or shares burrow systems. I related the structure of burrow systems to the number of cavies inhabiting them, in two habitats with different soil hardness and different plant cover (El Leoncito and Ñacuñán). El Leoncito has a harsh climate, with lower plant density and softer soil than Ñacñuán. A total of 18 burrow systems were characterized at Ñacuñán, and 12 at El Leoncito. Social groups at El Leoncito have a higher number of individuals than at Ñacuñán, but the structure of burrow systems in softer soil is narrower (small area size), with fewer holes, less slope and depth of galleries, and with no relationship between the number of holes and burrow area. Therefore, considering the development of the burrow system as an indicator of the cost of burrowing, I conclude that communal burrowing to reduce the energetic cost of burrowing per capita is not the primary cause of cavy sociality. M. australis were not active diggers, because digging behaviour was rarely recorded at either site. Burrow systems of cavies persisted over the years of study, occupied by the same cavies and new offspring, and digging new burrow systems and tunnels was a relatively rare event at both sites. Under the burrow-sharing hypothesis, sociality could prevail in M. australis that regularly dig to build and maintain a burrow system which they use for a long time.

Vergleichend quantitative Untersuchungen an Organen von Caviomorpha

Comparative quantitative investigations of organs of Caviomorpha. The weights of the organs: heart, liver, lung, spleen, kidneys and stomach-intestines were measured in nine species of caviomorph rodents. The sizes of these organs were compared using allometry formulae calculated for each organ from the Caviomorpha to the allometric lines of mammals (mouse-to-elephant line). The slopes of the two sets were nearly equal, except for the lung/body slope. In organ sizes, independently from body size, most of the caviomorph species were found to be outlying with respect to the reference Mammalia. Thus, compared to the general mammalian-line the organ sizes of the caviomorph vary between an increase of 47% in the kidneys of Microcavia australis and a decrease of 68% in the spleen weight of Lagostomus maximus. It is argued that these differences in size suggest a strong correlation to the functional importance of the organs, and that the large range of variation in organ size is regarded as a process of functional adaptation to different life styles within caviomorph rodents.

Comparing composition of social groups, mating system and social behaviour in two populations of Microcavia australis

Microcavia australis is a semifossorial, diurnal and social rodent, native to South America. The objective was to determine and compare the composition of social groups, mating system and social behaviours of cavies in two populations of the Monte (El Leoncito and Ñacuñán). The two sites differ in climate conditions and plant resource availability. Trapping was carried out on 7–11 consecutive days at three times of the year (food abundance, food shortage, reproduction), from 2003 to 2005. Individuals were identified with metal ear tags. Continuous focal samplings were performed during 4 days. The female/male proportion per group was 1/1 at both sites which, together with the absence of sexual dimorphism in body size (0.94), the accomplishment of oestrus synchronization, the large size of scrotal testes during the reproductive season and sexual patterns, suggests a promiscuous mating system. Social groups were larger and with more adults at the site with more severe climate conditions (El Leoncito). The index of association among individuals was higher at El Leoncito. Cavies could use seismic communication to avoid encounters ending in fights at El Leoncito, and the agonistic behaviour was significantly lower in this population.

Vigilance and foraging behaviour in a social desert rodent, Microcavia australis (Rodentia Caviidae)

Microcavia australis is a social species, diurnal and native to South America. This rodent provides an opportunity for analyzing the relationship between group size and the vigilance and foraging behaviour of the lesser cavy in two populations inhabiting two risky sites (El Leoncito and Ñacuñán). The study should reveal the mechanisms used by M. australis to reduce predation risk (many-eyes effect, cooperative vigilance or/and simple dilution of per capita risk). Continuous focal sampling was conducted at times of food shortage, food abundance and reproduction, from 2003–2005. A negative correlation was found between number of individuals per group and frequency of individual vigilance, and a positive correlation between rate and proportion of total group vigilance and the number of individuals per group of both sites. There was no correlation between the number of individuals per group and group foraging at either site. A benefit of social grouping in cavies is an increased probability of survival with group vigilance, although this implies no favourable impact on foraging activity. This should reveal an effect of group in the antipredator response, i.e. groups of larger size show lower levels of individual vigilance and improved efficiency in their vigilance behaviour. That is to say that a predator would be detected earlier when approaching a group than when approaching a solitary individual and could thus be avoided (many-eyes effect and cooperative vigilance).

Utilization of food resources by small and medium-sized mammals in the Monte Desert biome, Argentina

Theoretical models of species coexistence between desert mammals have generally been based on a combination of food and microhabitat selection by granivorous rodents. Although these models are applicable in various deserts of the world, they cannot explain resource use by mammals in Neotropical deserts. The present study examines diet composition in a mammal assemblage in the Monte desert, Argentina. The results show that two main strategies are used by these mammals: medium-sized species (hystricognath rodents: Dolichotis patagonum, Lagostomus maximus, Microcavia australis and Galea musteloides; and an exotic lagomorph: Lepus europaeus) are herbivores, whereas small-sized species (a marsupial: Thylamys pusillus; and sigmodontine rodents: Graomys griseoflavus, Akodon molinae, Calomys musculinus, Eligmodontia typus) are omnivorous. Small mammals also show a tendency towards granivory (C. musculinus), insectivory (A. molinae and T. pusillus) and folivory (G. griseoflavus).

Large males dominate: ecology, social organization, and mating system of wild cavies, the ancestors of the guinea pig

Ecological factors differently affect male and female animals and thereby importantly influence their life history and reproductive strategies. Caviomorph rodents are found in a wide range of habitats in South America and different social and mating systems have evolved in closely related species. This permits to study the impact of ecological factors on social evolution. In this study, we investigated the social organization and the mating system of the wild cavy (Cavia aperea), the ancestor of the domestic guinea pig, in its natural habitat in Uruguay. Based on our laboratory investigations, we expected a polygynous system with large males controlling access to females. Results from radiotelemetry and direct observations showed that females occupied small stable home ranges which were largely overlapped by that of one large male, resulting in a social organization of small harems. In some cases, small satellite males were associated with harems and intermediate-sized roaming males were occasionally observed on the study site. However, microsatellite analyses revealed that offspring were exclusively sired by large males of the same or neighboring harems, with a moderate degree of multiple paternity (13–27%). Thus, the mating system of C. aperea can be described as polygynous and contrasts with the promiscuous organization described for other species of cavies (Cavia magna, Galea musteloides and Microcavia australis) living under different ecological conditions. Our findings stress the strong impact of environmental factors on social evolution in Caviomorphs as resource distribution determines female space use and, thereby, the ability of males to monopolize females.

Different antipredator responses by Microcavia australis (Rodentia, Hystricognate, Caviidae) under predation risk

[The antipredator response of rodents may depend on the species of predator and the structure of the vegetation. To investigate these effects, we compared the antipredator response of Microcavia australis to two predator models. We used two populations occurring at sites of the Monte desert that differ in plant structure and availability, and in predation risk. At Nacunan plant cover is 54.3%, the major risk of predation is from raptors. At El Leoncito plant cover is 21.9%, the predation risk is similar by raptors and carnivores. In addition we investigated whether olfactory cues for different predators may elicit different antipredator responses in absence of visual cues. This was done by presenting feces of two predators and controls in an experimental set-up. The exposed individuals reduced their activity in response to feces of both predators and not in response to the control, but they did not respond in the same way to each predator (their response to each predator was not the same). The results show that M. australis recognizes different predators through both sight and smell, and that the response may be influenced by vegetation structure., The antipredator response of rodents may depend on the species of predator and the structure of the vegetation. To investigate these effects, we compared the antipredator response of Microcavia australis to two predator models. We used two populations occurring at sites of the Monte desert that differ in plant structure and availability, and in predation risk. At Nacunan plant cover is 54.3%, the major risk of predation is from raptors. At El Leoncito plant cover is 21.9%, the predation risk is similar by raptors and carnivores. In addition we investigated whether olfactory cues for different predators may elicit different antipredator responses in absence of visual cues. This was done by presenting feces of two predators and controls in an experimental set-up. The exposed individuals reduced their activity in response to feces of both predators and not in response to the control, but they did not respond in the same way to each predator (their response to each predator was not the same). The results show that M. australis recognizes different predators through both sight and smell, and that the response may be influenced by vegetation structure.]

Rodents from southern Patagonian semi-arid steppes (Santa Cruz Province, Argentina)

The little-known mammalian fauna of southern Santa Cruz Province is studied by means of live-trapping and examination of owl pellets at 11 localities. Thirty-nine individuals of seven species were recorded in a total of 753 trap nights during the years of 2004 and 2005. Additionally, we identified 376 prey items from a total of 130 pellets cast by Barn owls ( Tyto alba) and Magellanic horned owls ( Bubo magellanicus). Abrothrix olivaceus [Waterhouse, 1839. The zoology of the Voyage of the Beagle. Part II: Mammalia., London.] and Eligmodontia sp. were the most abundant trapped species and the best represented in pellet samples. Other rodents identified were Ctenomys sp., Euneomys sp., Loxodontomys micropus, Microcavia australis, Mus musculus, Notiomys edwardsii, Oligoryzomys magallanicus, and Phyllotis xanthopygus. The mammal sampling effected by live-traps and owls was rarely coincident, with some species collected only by traps or by owls. New recording localities for N. edwardsii and O. magellanicus enlarge the known distribution of these species in Santa Cruz province by 270 km west and 70 km north, respectively.

Spatial and Seasonal Plasticity in Digestive Morphology of Cavies (Microcavia australis) Inhabiting Habitats with Different Plant Qualities

Ecological physiology examines how animals cope with changing environmental demands. In low-productivity desert habitats, small mammals should consume low-quality, high-fiber food as a consequence of necessity rather than by choice. Diet quality of populations can differ at both spatial and temporal scales. Nevertheless, spatial and temporal variation in the digestive system has not been extensively studied in the field. We captured individuals from 4 populations of Microcavia australis and measured their digestive morphological traits. Fieldwork was carried out in 4 localities belonging to arid and semiarid regions, in dry and wet seasons. We also estimated diet quality for each population and season. We found significant effects of sex, season, and site on the size of digestive organs. The concentration of fiber and nitrogen in the plants consumed differed between populations and varied seasonally: dietary fiber was higher in the dry season and nitrogen concentration was higher in the wet season. As predicted by theory, the cecum, the organ most closely related to cellulose fermentation, was significantly larger in animals facing the lowest quality diet. The other organs also were affected by reproductive state and water requirements. Intraspecific variation in the digestive morphology of M. australis probably helps this species cope with remarkable seasonal and geographical variability.

NEST AND SPACE USE IN A HIGHLAND POPULATION OF THE SOUTHERN MOUNTAIN CAVY (MICROCAVIA AUSTRALIS)

We examined the spatial and social structure of a high-altitude population of the scarcely known southern mountain cavy (Microcavia australis) in Argentina. We used radiotelemetry techniques to monitor nest use at night and daily home ranges and examine whether southern mountain cavies form nesting associations that are socially cohesive groups. We further timed our observations to breeding time ofour study population (September–November) to assess opportunities for communal breeding. The nighttime telemetry of 24 radiotagged cavies revealed 7 nesting associations (i.e., communal nesting). These included 1–4 breeding females and 1 or 2 breeding males. Nesting associations were stable in terms of identity of individual members and in the location of putative nest sites. Most associations used a single nest site, but some shared 2 or 3. We noted that all nest sites were located under dominant shrubs, but use of nest sites was unrelated to variation in shrub cover. Nest sites with more burrow entrances were more frequently used by radiocollared cavies. During the day, home ranges of cavies overlapped more with ranges of nest mates than with those of non–nest mates, implying that nesting groups were socially cohesive units. This study confirmed that southern mountain cavies are communally nesting, and, because communal nesting occurs during breeding time, our findings support the idea that cavies engage in communal care of young.

Utilization of food resources by small and medium‐sized mammals in the Monte Desert biome, Argentina

AbstractTheoretical models of species coexistence between desert mammals have generally been based on a combination of food and microhabitat selection by granivorous rodents. Although these models are applicable in various deserts of the world, they cannot explain resource use by mammals in Neotropical deserts. The present study examines diet composition in a mammal assemblage in the Monte desert, Argentina. The results show that two main strategies are used by these mammals: medium‐sized species (hystricognath rodents: Dolichotis patagonum, Lagostomus maximus, Microcavia australis and Galea musteloides; and an exotic lagomorph: Lepus europaeus) are herbivores, whereas small‐sized species (a marsupial: Thylamys pusillus; and sigmodontine rodents: Graomys griseoflavus, Akodon molinae, Calomys musculinus, Eligmodontia typus) are omnivorous. Small mammals also show a tendency towards granivory (C. musculinus), insectivory (A. molinae and T. pusillus) and folivory (G. griseoflavus).

Molecular Relationships Among Octodontidae (Mammalia: Rodentia: Caviomorpha)

We examined ten species of octodontid rodents and representatives of three outgroups in a complete 13 × 13 DNA-hybridization matrix. The results were indexed as differences in median melting-point depressions (ΔT,ms), symmetrized, subjected to phylogenetic analysis using FITCH, bootstrapped, and exhaustively taxon-jackknifed. Within Octodontidae, four clades were recovered with 100% bootstrap and complete jackknife support: Tympanoctomys barrerae with Octomys mimax, Octodontomys gliroides alone, Octodon spp., and Aconaemys spp. with Spalacopus cyanus; the latter two clades were closer to each other than either was to Octodontomys or Octomys-Tympanoctomys, but were slightly nearer to and united with Octodontomys, with 89% bootstrap support. However, relationships among the three Aconaemys species and Spalacopus were not completely resolved by our experiments. Ctenomys coyhaiquensis, Abrocoma bennetti, and Lagostomus maximus represented successive outgroups to Octodontidae, while one-way comparisons with Cavia porcellus and Microcavia australis suggested that these caviids are almost as distant from octodontoids as is the chinchilloid Lagostomus. When the data were suitably corrected for percentage hybridization and saturation, division of the distances by the rate previously determined for most amniotes (∼0.48%/myr) suggested that the basal divergence among the caviomorph rodents examined occurred about 59 myrbp, and that Octodontidae originated 40 myrbp and diversified into extant lineages beginning 14 myr ago. Calibration against the date of the earliest known caviomorph (late Eocene or about 37.5 myrbp) gave a rate of 0.75%/myr, which would suggest later dates for subsequent caviomorph cladogenesis. It is notable that, based respectively on the slower or faster rates, the tetraploid Tympanoctomys barrerae must have diverged from its sister-taxon Octomys mimax ∼10 or 6.5 myr ago.

Effect of herbivorous rodents (cavies and tuco-tucos) on a shrub community in the Monte Desert, Argentina

The importance of tuco-tucos (Ctenomys eremophilus) and cavies (Microcavia australis) as herbivores in the Monte Desert was assessed on a creosotebush community dominated byLarrea cuneifolia. Herbivory by tuco-tucos or cavies affected 35% of the total plants. The most highly damaged plant species wasAtriplex lampa, followed byLarrea cuneifoliaandLyciumsp. The level of damage caused byCtenomyswas higher than that produced by cavies.