Jaime Polop

Factors affecting home range size and overlap in Calomys venustus (Muridae: Sigmodontinae) in Argentine agroecosystems

Summary In this study, information concerning home range size and overlap of Calomys venustus (Thomas, 1894), in relation to sex, population size, and breeding periods is provided. The present study was carried out on a railway bank in southern Cordoba Province (Argentina), between October 1994 and September 1997, using the capture-mark-recapture method. Home range size in C. venustus depended on breeding period and population size, and was independent of sex. The degree of home range overlap was dependent on breeding and non-breeding periods and overlap type (intra- or intersexual), but was independent of population density. During the breeding period, females showed a small degree of intrasexual home range overlap. In general, male home ranges largely overlapped with females. The conclusion is that differences in home range size of C. venustus could be determined by season and population size. Moreover, the degree of inter- and intrasexual home range overlap during the breeding period suggested that males and females of C. venustus use space differently. Females did not share their home range with other females, while males fully shared it with both sexes, and male spacing is influenced by female distribution.

Commensal and wild rodents in an urban area of Argentina

The aim of this study was to determine the rodent species, distribution, and abundance in an urban area, in relation to epidemiology risk or damage, so as to elaborate a control program. The first sampling was done between May and July of 1998 on 31 vacant lots, 5 rubbish dumps, 15 stream banks, 18 railway banks and 28 vacant areas. Between August 1999 and June 2000 seasonal samples were taken in the same habitats. At each capture site 20 snap traps and 10 live traps were installed. Of 1253 animals captured, 74% were commensal rodents (Mus domesticus, Rattus rattus and Rattus norvergicus) and 26% were wild rodents (Calomys musculinus, Akodon dolores, A. azarae and C. venustus). M. domesticus was the population that numerically predominated in every sampled habitat. C. musculinus was the second most abundant species and its distribution was related to open space (vacant areas, railway banks, stream banks and rubbish dumps). The basic information found by this work will allow us to consider and measure the risk of a possible human infection in a specific area. Thus, human diseases can be prevented by controlling rodent reservoirs and/or by avoiding contact between rodents and humans.

Size and overlap of home range inCalomys musculinus (Muridae: Sigmodontinae)

Home range size and overlap ofCalomys musculinus (Thomas, 1913) was examined in relation to sex and breeding periods. The study was carried out in four 0.25 ha enclosures, in a natural pasture, between October 2002 and July 2003. The four enclosures functioned as independent populations and each was considered a replicate. The capture, mark and recapture method was used. Home range size and overlap inC. musculinus depended on sex and period. Home range size of males was always larger than that of females. Females showed a small degree of intra-sexual home range overlap during the breeding period. In general, male home ranges overlapped with females. We conclude that differences in home range size inC. musculinus is determined by sex and breeding period. Moreover, the degree of inter- and intra-sexual home range overlap during the breeding period suggests that both males and females ofC. musculinus use space differently. Females did not share their home range with other females, while males fully shared it with both sexes, and male spacing is influenced by the distribution of females. A promiscuous-polygynous mating system is suggested forC. musculinus.

Territorial behaviour in corn mice, Calomys musculinus (Muridae: Sigmodontinae), with regard to mating system

We studied territorial behaviour of Calomys musculinus, a promiscuous-polygynous species, in order to test the predictions that during the breeding period, home-range-owner females are more aggressive than home-range intruders and that males do not display territorial behaviour. At the core of the breeding season, we conducted 136 intrasexual and 66 intersexual encounters. The study was carried out in four 0.25-ha enclosures, each containing one independent population. We studied territorial behaviour utilising focal animal sampling to record behaviour. Encounters were conducted in a circular opaque arena (COA) near the home-range’s activity mathematical centre (AMC). Amicable behaviour was not observed in any of the 78 trials among females. The rates of aggressive and submissive behaviour per female–female encounters varied in relation to whether they were home-range owners or intruders, the former being aggressive, the latter submissive. So we could link these drives to the territorial behaviour of C. musculinus. This result fits well with the already known territoriality of C. musculinus during the breeding season. In contrast, the 58 intrasexual male encounters did not show direct aggressive interactions between them. The rates of the different behaviours between males did not vary in relation to whether they were home-range owners or intruders. In our study, which took place during the breeding period, C. musculinus males were nonterritorial, and they never exhibited aggressiveness towards females.

Temporal and Spatial Host Abundance and Prevalence of Andes Hantavirus in Southern Argentina

Andes virus (AND) is a hantavirus hosted by the sigmodontine rodent Oligoryzomys longicaudatus in southern Argentina, where it is responsible for most cases of hantavirus pulmonary syndrome (HPS). Our study provides data about the spatial variation in abundance of the rodent host of AND hantavirus. We report results of a longitudinal study performed in a locality of the Andean region of Chubut Province. From November 2003 (spring) to July 2006 (winter), O. longicaudatus was the most common species captured (63%) and it showed significant differences in abundance among habitats and seasons. Most antibody-positive rodents were O. longicaudatus (9.2%), followed by A. longipilis (3.6%) and A. olivaceus (1.5%). The highest number of antibody-positive animals was observed for males that belonged to the heaviest mass classes. Antibody-positive O. longicaudatus were more abundant in brush habitats. We found low richness of rodents and abundance of O. longicaudatus in areas affected by anthropogenic activity. The infection seems to be regionally persistent, but the risk to humans in a landscape would be localized. To develop accurate models for predicting HPS outbreaks, further research is needed to characterize rodent movement patterns across the landscape.

Summer–autumn distribution and abundance of the hantavirus host, Oligoryzomys longicaudatus, in northwestern Chubut, Argentina

Abstract We examined population density of Oligoryzomys longicaudatus (colilargo) and prevalence of Andes virus (ANDV) antibody at regional and landscape spatial scales in northwestern Chubut Province (Argentina) and contrasted it with climatic variables recorded by meteorologic stations near the study area. Mice were trapped in late summer–early fall (March–April) for 3 years (2007–2009). The composition of the rodent assemblage and species representation in the community varied among years, regions (forest, ecotone, and steppe), and landscape units (Nothofagus and Austrocedrus forests, sweet briar shrublands, and without sweet briar shrublands). Colilargos occurred in all regions and landscape units within the study area, from dense forest to open habitats such as steppe. The species dominated the rodent assemblages of ecotone and forest at a regional scale and the assemblages in sweet briar shrublands and Austrocedrus forests at a landscape scale. Abundance of colilargos also varied among periods, regions, and landscape units. Antibodies to ANDV were found in all regions but not in every landscape unit. Thus there is a potential for human hantavirus pulmonary syndrome (HPS) cases to occur not only in forests and shrublands, but also in steppe. At a landscape scale, Nothofagus forests appeared to pose a higher risk than Austrocedrus in wet years, because colilargo abundance and ANDV antibody prevalence were significantly greater. Within ecotone, sweet briar shrublands posed greater risk than habitats without sweet briar. Sweet briar shrublands were the landscape unit with the highest colilargo abundances during the driest periods. Sweet briar shrublands may play an important role in HPS dynamics, and should be considered when designing prevention policies. Resumen Nuestro objetivo fue examinar la densidad poblacional de Oligoryzomys longicaudatus (colilargo) y la prevalencia de virus Andes (ANDV) a escala regional y de paisaje en el noroeste de la provincia de Chubut, Argentina. Los muestreos se llevaron a cabo durante el verano tardío–otoño temprano (Marzo–Abril) por un período de 3 años (2007 a 2009). La composición de la comunidad de roedores y la representación de cada especie en la misma varió entre años, regiones (bosque, ecotono y estepa) y unidades de paisaje (bosques de Nothofagus y de Austrocedrus, matorrales de rosa mosqueta y matorrales sin rosa mosqueta). O. longicaudatus fue encontrado en todas las regiones y unidades de paisaje del área de estudio. Esta especie dominó los ensambles de roedores de bosques y ecotono a escala regional y los ensambles de los matorrales de rosa mosqueta y bosques de Austrocedrus a escala de paisaje. La abundancia de colilargos varió entre períodos, regiones y unidades de paisaje. Se detectaron anticuerpos contra ANDV en todas las regiones, pero no en todas las unidades de paisaje. Por lo tanto, el riesgo de enfermedad en humanos existe no sólo en bosque y ecotono, sino también en estepa. Además, a escala de paisaje, los bosques de Nothofagus parecieron implicar un mayor riesgo que los de Austrocedrus en años húmedos, ya que las abundancias de colilargos y la prevalencia de ANDV fueron significativamente mayores en los primeros. Dentro del ecotono, los matorrales de rosa mosqueta significaron un mayor riesgo que los matorrales sin rosa mosqueta. Los primeros constituyeron la unidad de paisaje con las mayores abundancias de colilargos durante los períodos secos. Estos matorrales podrían tener un papel importante en la dinámica del Síndrome Pulmonar por Hantavirus y debieran ser considerados a la hora de diseñar medidas de prevención.

Modeling potential distribution of oligoryzomys longicaudatus, the andes virus (Genus: Hantavirus) reservoir, in Argentina

We constructed a model to predict the potential distribution of Oligoryzomys longicaudatus, the reservoir of Andes virus (Genus: Hantavirus), in Argentina. We developed an extensive database of occurrence records from published studies and our own surveys and compared two methods to model the probability of O. longicaudatus presence; logistic regression and MaxEnt algorithm. The environmental variables used were tree, grass and bare soil cover from MODIS imagery and, altitude and 19 bioclimatic variables from WorldClim database. The models performances were evaluated and compared both by threshold dependent and independent measures. The best models included tree and grass cover, mean diurnal temperature range, and precipitation of the warmest and coldest seasons. The potential distribution maps for O. longicaudatus predicted the highest occurrence probabilities along the Andes range, from 32°S and narrowing southwards. They also predicted high probabilities for the south-central area of Argentina, reaching the Atlantic coast. The Hantavirus Pulmonary Syndrome cases coincided with mean occurrence probabilities of 95 and 77% for logistic and MaxEnt models, respectively. HPS transmission zones in Argentine Patagonia matched the areas with the highest probability of presence. Therefore, colilargos presence probability may provide an approximate risk of transmission and act as an early tool to guide control and prevention plans.

Reproductive characteristics of free-livingCalomys venustus (Rodentia, Muridae)

Calomys venustus showed a cyclic seasonal pattern of reproductive activity characterized by a period of repose and a variable length of the period of sexual activity between August—September to May—June. The study was done from 1983 to 1999. During this time the population density increased from October—November to the end of autumn and sharply decreased in winter. Three peaks in rate of pregnancy were recognized in the breeding period: spring, summer and late summer. The average litter size was different among the three peaks in rate of pregnancy. The reproductive pattern had a peak at the beginning of the spring produced by overwintering animals, and another peak in summer-autumn caused by the reproductive activity of young born in the same period in which they breed. The spring cohort exhibited the greatest breeding contribution suggesting that this cohort is principally responsible for the yearly peak in abundance.

On the relationship between the environmental history and the epidemiological situation of Argentine hemorrhagic fever

The aim of this work was to establish the relationship between different Argentine hemorrhagic fever (AHF) epidemiological situations found at different sites and the related large-scale environmental conditions. Large-scale environmental records (vegetation index, temperature, precipitation and elevation) were obtained from a series of monthly NOAA satellite images and global databases considered suitable for modeling climatic and other environmental determinants of large-scale biogeographical regions. The temporal variation in vegetation for cycles of winter-summer showed a greater variation in the nonendemic region than in the other two regions. On the other hand, the average of the temporal variation in precipitation in cycles of spring–autumn was more different in the historic region than in the other two regions, and land surface temperatures in cycles of spring–autumn showed differences between the epidemic region and the other two regions. We found good separation among the epidemic, historic and nonendemic sites, with the greatest difference found between epidemic and nonendemic sites. The classification of sites showed a tendency for grouping according to the epidemiological situation, but there was some variation. It seems possible to establish a close relationship between the state of AHF incidence and the environmental history of sites suggesting the possibility of predicting epidemiological behavior using environmental conditions derived from satellite data.

Isolation and characterization of microsatellite markers in Oligoryzomys longicaudatus (Muridae, Sigmodontinae, Oryzomini), the natural reservoir of genotype Andes hantavirus

The rodent Oligoryzomys longicaudatus or long‐tailed pygmy rice rat is the reservoir of the aetiological agent of the hantavirus pulmonary syndrome in southern Argentina and Chile. We characterize 11 polymorphic microsatellite loci which would be useful for studies on microgeographical population structure in the species. Amplification of these loci in 42 individuals from four natural populations revealed four to 21 alleles per locus, and values of observed heterozygosities ranging from 0.371 to 0.896. Cross‐species amplifications showed that some of the primers designed may be useful for other species of the genus Oligoryzomys.