Patterns of macro and microhabitat use of two rodent species in relation to agricultural practices

Orthohantavirus Infection in Two Rodent Species that Inhabit Wetlands in Argentina

Previous research conducted in central-east region of Argentina recorded potential orthohantavirus host rodents in diverse environments, but no research has focused particularly on islands, the environments that present the greatest risk to humans. For this reason, the aims of this research were to determine the orthohantavirus host in the rodent community focused on islands of Paraná River Delta, central-east region of Argentina, to identify temporal and spatial factors associated with orthohantavirus prevalence variations, to compare the functional traits of seropositive and seronegative rodents, and to explore the association between orthohantavirus prevalence and rodent community characteristics between August 2014 and May 2018. With a trapping effort of 14,600 trap-nights, a total of 348 sigmodontine rodent specimens belonging to seven species were captured 361 times. The overall antibody prevalence was 4.9%. Particularly, 14.9% of Oligoryzomys flavescens and 1.5% of Oxymycterus rufus, mainly reproductively active adult males, had antibodies against orthohantavirus. Even though O. flavescens inhabit all islands, our results suggest spatial heterogeneity in the viral distribution, with two months after periods of low temperature presenting increases in seroprevalence. This could be a response to the increased proportion of adults present in the rodent population. In addition, an association was found between the high seroprevalence and the diversity of the rodent assemblage. We also found 1.5% of O. rufus exposed to orthohantavirus, which shows us that further investigation of the ecology of the virus is needed to answer whether this species act as a spillover or a new competent host.

Population survey of small rodents on islands located inside a region of endemism for hantavirus pulmonary syndrome

Ecological studies of rodent species, especially as reservoirs of zoonoses, can identify spatiotemporal conditions associated with irruptions of abundances, as well as predict areas and times with higher risk of disease transmission. The aims of this research were to describe and identify (i) the rodent community composition; (ii) their population structure and breeding season; (iii) temporal and spatial variations in their population abundance; and (iv) the environmental factors associated with these variations on islands of upper Paraná River Delta, a zone of endemism for hantavirus pulmonary syndrome (HPS) in Argentina (Entre Ríos and Santa Fe provinces). We carried out seasonal surveys over 3 years (2014–2017) with live capture traps on seven islands (natural protected areas and under livestock grazing). Three hundred seventy-seven sigmodontine rodents of seven species were captured. While the maximum richness was seven, only four species coexisted at most on an island at the same time. Although changes in reproduction were detected throughout the year, seasonality, land use, and vegetation structure did not explain changes in abundance of rodents. Rodent abundances were affected mainly by flooding-related factors and meteorological conditions (rainfall and temperatures). The recovery of rodent populations after river flooding was species-specific and heterogeneous. The abundance of Oxymycterus rufus and Akodon azarae was affected by El Niño Southern Oscillation (ENSO); A. azarae did not recover after the flood at least during the study period. After the flood, populations of Oligoryzomys flavescens, the reservoir of HPS, also declined; however, this species’ populations were the first to recover its numbers, becoming dominant in the post-flood rodent community.

Small mammals in high fragmented landscape in Cerrado/Atlantic Forest ecotone, Southeastern Brazil

ABSTRACT Exploratory human activities have resulted in small fragments inserted into a matrix which is inhospitable to small non-flying mammals. The effects of landscape changes alter the distribution patterns of species. Landscape fragmentation patterns for small mammals are controversial, especially considering small fragments and ecotonal regions. Based on these arguments, we investigated the diversity patterns of small mammals in small fragments in the ecotonal Cerrado/Atlantic Forest region. A total of 24 fragments (<40 ha) were studied using tomahawk, sherman and pitfall traps. We found low species richness (11 species, six marsupials and five rodents), which was not expected because it is an ecotonal region. It was verified that composition and community structure are simplified by the marked presence of generalist species and with the increase of species turnover. The small forest fragments present a microhabitat structure with lianas and streams as main environmental filters of groups with ecological similarities. Our findings suggest that these fragments must be managed in order to conserve the local biodiversity and maintain the needed characteristics to enable the occurrence of different ecological groups.

Helminth community from Azara's grass mouse (Akodon azarae) in three habitats with different land use in farming systems of Argentina

In the Pampa region of Argentina, farming activities have been performed since the beginning of the 20th century, but in the 1990s, land-use patterns rapidly changed towards intensive agriculture and poultry breeding. This study compares the helminth community of Akodon azarae (Rodentia) among three habitats with different land use in pampean agroecosystems: poultry farms, mono-cultivated fields and abandoned fields (not used for 35 years), under the prediction that there will be greater helminth richness and diversity in mice from abandoned fields compared to those from the other habitats. Nevertheless, the highest abundance of A. azarae occurred on poultry farms, the habitat most disturbed by human activity, while cultivated fields showed the lowest. Helminth richness and diversity were significantly higher on poultry farms than in the other habitats, due to the presence of Trichuris laevitestis, Protospirura numidica criceticola and cysts of Taenia taeniaeformis. We suggest that the helminth fauna of A. azarae can survive on poultry farms despite disturbance from farming activities, because rodents can move and get shelter within farm perimeter fences, where dense and high vegetation grows. This farm area could offer good conditions for geohelminth development, while chicken sheds could attract insects that are intermediate hosts of helminths with indirect life cycles. On the contrary, agrochemicals applied in cultivated fields would negatively influence helminth diversity and composition, by decreasing host populations (arthropods and rodents) and affecting free larval stages of geohelminths.

Evaluation of habitat requirements of small rodents and effectiveness of an ecologically-based management in a hantavirus-endemic natural protected area in Argentina

Hantavirus pulmonary syndrome is a severe cardio pulmonary disease transmitted to humans by sylvan rodents found in natural and rural environments. Disease transmission is closely linked to the ecology of animal reservoirs and abiotic factors such as habitat characteristics, season or climatic conditions. The main goals of this research were: to determine the biotic and abiotic factors affecting richness and abundance of rodent species at different spatial scales, to evaluate different methodologies for studying population of small rodents, and to describe and analyze an ecologically-based rodent management experience in a highly touristic area. A 4-year study of small rodent ecology was conducted between April 2007 and August 2011 in the most relevant habitats of El Palmar National Park, Argentina. Management involved a wide range of control and prevention measures, including poisoning, culling and habitat modification. A total of 172 individuals of 5 species were captured with a trapping effort of 13 860 traps-nights (1.24 individuals/100 traps-nights). Five rodent species were captured, including 2 hantavirus-host species, Oligoryzomys nigripes and Akodon azarae. Oligoryzomys nigripes, host of a hantavirus that is pathogenic in humans, was the most abundant species and the only one found in all the studied habitats. Our results are inconsistent with the dilution effect hypothesis. The present study demonstrates that sylvan rodent species, including the hantavirus-host species, have distinct local habitat selection and temporal variation patterns in abundance, which may influence the risk of human exposure to hantavirus and may have practical implications for disease transmission as well as for reservoir management.

Environmental Variables Associated with Hantavirus Reservoirs and Other Small Rodent Species in Two National Parks in the Paraná Delta, Argentina: Implications for Disease Prevention

Hantavirus pulmonary syndrome (HPS) is a severe zoonotic disease caused by hantaviruses hosted in various rodents species. In Argentina, its transmission to humans has been associated to exposure during activities such as farming, recreation, and tourism which are carried out in wild and rural areas. The aim of this study was to analyze the macro- and micro-habitat use and spatio-temporal variation of small sylvan rodents in Pre Delta and Islas de Santa Fe national parks, located in an HPS-endemic area of Argentina. Rodent communities were studied at six sites: two islands, a riparian forest, an inland forest, a marsh, and the margins of a pond. A total of 453 individuals of five species were captured with a trapping effort of 9471 trap-nights. Maximum species richness was found at the marsh and the pond margin sites. Abundance of rodents was influenced by flooding events. Two hantavirus reservoirs, Oligoryzomys flavescens and Akodon azarae, were identified in the area. O. flavescens was captured in every habitat, but it was dominant in Islas de Santa Fe National Park where its abundance was strongly influenced by flooding. A. azarae was captured in every habitat except on the islands. A. azarae behaved as a generalist species at a micro-habitat scale in every habitat of Pre Delta National Park except for the marsh where it selected patches with low vegetation height. Based on these results, several disease prevention measures, including the use of rodent-proof containers for food, and keeping the grass short in the camp site, are proposed in order to reduce the risk to visitors and residents of contracting HPS.

Microhabitat of small mammals at ground and understorey levels in a deciduous, southern Atlantic forest

Each animal species selects specific microhabitats for protection, foraging, or micro-climate. To understand the distribution patterns of small mammals on the ground and in the understorey, we investigated the use of microhabitats by small mammals in a deciduous forest of southern Brazil. Ten trap stations with seven capture points were used to sample the following microhabitats: liana, fallen log, ground litter, terrestrial ferns, simple-trunk tree, forked tree, and Piper sp. shrubs. Seven field phases were conducted, each for eight consecutive days, from September 2006 through January 2008. Four species of rodents (Akodon montensis, Sooretamys angouya, Oligoryzomys nigripes and Mus musculus) and two species of marsupials (Didelphis albiventris and Gracilinanus microtarsus) were captured. Captured species presented significant differences on their microhabitat use (ANOVA, p = 0.003), particularly between ground and understorey sites. Akodon montensis selected positively terrestrial ferns and trunks, S. angouya selected lianas, D. albiventris selected fallen trunks and Piper sp., and G. microtarsus choose tree trunks and lianas. We demonstrated that the local small-mammal assemblage does select microhabitats, with different types of associations between species and habitats. Besides, there is a strong evidence of habitat selection in order to diminish predation.