Abrothrix Olivaceus Research Articles

First record of <i>Abrothrix olivacea</i> (Waterhouse, 1837) in Peru based on historical material from Tacna

Abrotrichini is the sigmodontine tribe with the fewest species in Peru, known only from two species: Abrothrix andina and Ab. jelskii, both distributed in the high Andean regions of Peru above 3000 m in altitude. A detailed review of the morphology of historical specimens collected in the Tacna department and identified as Akodon mollis was conducted. As a result, we found that the examined specimens corresponded to Abrothrix olivacea, a species previously known only from Chile and Argentina. This discovery represents the first record of this species in Peru, extending its distribution range 165 km north of its previous northernmost record in Quebrada Camarones, Arica-Parinacota, Chile. Furthermore, this finding significantly reduces the distribution range of Akodon mollis to the northwestern region of Peru. We also provide key craniodental characters to differentiate species of Abrothrix and Akodon in southwestern Peru and northern Chile. For Peru, this record increases the diversity of mammals to 588 species and rodents to 201 species. In the case of the Tacna department, mammalian diversity increases to 47 species. This work highlights the value of natural history museum collections in enhancing our understanding of species diversity.

Are Rattus rattus fleas invasive? Evaluation of flea communities in invasive and native rodents in Chile.

Co-invasion, characterized by the simultaneous introduction of hosts and parasites with the latter establishing themselves in native hosts, is a phenomenon of ecological concern. Rattus rattus, a notorious invasive species, has driven the extinction and displacement of numerous avian and mammalian species and serves as a key vector for diseases affecting both humans and wildlife. Among the parasites hosted by R. rattus are fleas, which exhibit obligate parasitic behaviour, a generalist nature and high prevalence, increasing the likelihood of flea invasion. Simultaneously, invasive species can serve as hosts for native parasites, leading to potential amplification or dilution of parasite populations in the environment. In Chile, R. rattus has been present since the 17th century because of the arrival of the Spanish colonizers through the ports and has spread throughout urban, rural and wild Chilean territories. This study aims to evaluate whether co-invasion of native fleas of invasive rats occurs on native rodents in Chile and to determine whether black rats have acquired flea native to Chile during their invasion. For this, we captured 1132 rodents from 26 localities (20° S-53° S). Rattus rattus was found coexisting with 11 native rodent species and two species of introduced rodents. Among the native rodents, Abrothrix olivacea and Oligoryzomys longicaudatus exhibited more extensive sympatry with R. rattus. We identified 14 flea species associated with R. rattus, of which only three were native to rats: Xenopsylla cheopis, Leptopsylla segnis and Nosopsyllus fasciatus. These three species presented a higher parasite load in black rats compared to native fleas. Leptopsylla segnis and N. fasciatus were also found associated with native rodent species that cohabit with R. rattus. The remaining species associated with R. rattus were fleas of native rodents, although they were less abundant compared to those associated with native rodents, except for Neotyphloceras pardinasi and Sphinctopsylla ares. Although there has been evidence of flea transmission from rats to native species, the prevalence and abundance were relatively low. Therefore, it cannot be definitively concluded that these fleas have established themselves in native rodent populations, and hence, they cannot be classified as invasive fleas. This study underscores R. rattus' adaptability to diverse environmental and geographical conditions in Chile, including its capacity to acquire fleas from native rodents. This aspect has critical implications for public health, potentially facilitating the spread of pathogens across various habitats where these rats are found.

Assessing Ecogeographic Rules in Two Sigmodontine Rodents along an Elevational Gradient in Central Chile.

Bergmann's and Allen's rules are two classic ecogeographic rules concerning the physiological mechanisms employed by endotherm vertebrates for heat conservation in cold environments, which correlate with adaptive morphological changes. Thus, larger body sizes (Bergmann's rule) and shorter appendages and limbs (Allen's rule) are expected in mammals inhabiting cold environments (higher latitudes). Both rules may also apply to elevational gradients, due to the decrease in external temperature as elevation increases. In this study, we evaluated whether these patterns were true in two coexisting sigmodontine rodents across an elevational gradient in central Chile. We analyzed whether the size of the skull, body, and appendages of Abrothrix olivacea (n = 70) and Phyllotis darwini (n = 58) correlated with elevation, as predicted by these rules in a range between 154 and 2560 m. Our data revealed weak support for the Bergmann and Allen predictions. Moreover, we observed opposite patterns when expectations of Bergmann's rules were evaluated, whereas Allen's rule just fitted for ear size in both rodent species. Our results suggest that morphological changes (cranial, body, and appendage sizes) may play a minor role in the thermoregulation of these two species at high elevations, although behavioral strategies could be more critical. Other ecological and environmental variables could explain the morphological trends observed in our study. These hypotheses should be assessed in future studies to consider the relative contribution of morphology, behavior, and physiological mechanisms to the thermal adaptation of these two rodent species at high elevations.

Small mammal records from Limay river basin (Northwestern Patagonia) in the Anthropocene from a taphonomical and paleoecological perspective

The studies of the small mammal fossil and recent assemblages from the Limay river basin (Northwestern Patagonia) have strongly increased during the last decade. Taxonomic, taphonomic, and paleoecological information about small rodents and marsupials recovered from fossil sites offers the opportunity to discuss the periods of change and stability in the conformation of their communities through the Anthropocene. Here, we used two large data matrix of fossil and recent small mammal samples. As starting point, we considered the small mammal record of Epullán Grande cave (LL thereafter), which covers the Early Holocene/Post-hispanic Period, in order to assess the impact of anthropic activities on the small mammal communities during the Anthropocene. The taphonomic analysis performed on the newest samples from LL confirms the predatory activity of Tyto furcata on sigmodontines and human consumption on caviomorphs (mostly for the last ca. 1000 years). The analysis of manganese oxide staining suggested higher levels of moisture during the earliest formation of the LL sequence. The taxonomic results indicate a major diversity in the small mammal fossil assemblages to the later periods of LL and other fossil sequences of the Limay basin of the Anthropocene. Conversely, opportunistic sigmodontines ( Abrothrix olivacea, Calomys musculinus, Eligmodontia spp. and Oligoryzomys longicaudatus) experienced a growth in the recent samples. Some stenoic and specialist species ( Euneomys spp., Lestodelphys halli, Loxodontomys micropus and Reithrodon auritus) were abundant in the temporal units associated with the Anthropocene, but now are in retraction. Additionally, the drop in the diversity of recent assemblages supports a restructuration of small mammal communities from Limay river basin occurred in the 20th century.

Late-Holocene stability and recent changes in small mammal communities in north-central Andean forests of Patagonia

Past and current climatic and environmental changes have contributed to configure actual species distributions and abundances. Knowing their evolution over time allows discrimination between natural and anthropogenic causes in current composition of faunal communities. We evaluate the changes in small mammal assemblages from the north-central Patagonian Andean forests since the Late-Holocene to recent times and their relationship with the environmental modifications driven by human activities. A bone sequence from Población Anticura archaeological site (lower Manso river valley, Río Negro province, Argentina) was studied, which encompasses a time span from the early Late-Holocene (3350 ± 100–2270 ±80 years BP) to final Late-Holocene (1420 ± 70–530 ±50 years BP) and Historical times (480 ± 70–280 ±40 years BP). The species composition indicates that forest environment established in the area from at least the Late-Holocene (dominance of Loxodontomys micropus, with subordinate frequencies of Abrothrix olivacea, A. hirta, Geoxus valdivianus, Irenomys tarsalis, and Paynomys macronyx), with patches of (or near to) open environments (presence of Reithrodon auritus and cavids). It is remarkable the presence of cavids, which increased their abundance in the sequence towards Historical times but disappeared nowadays. The low frequencies (<10%) of the rodent Oligoryzomys longicaudatus along the entire sequence is also relevant, since this rodent is the reservoir of the Andes strain of the Hantavirus (ANDV), which causes pulmonary syndrome. This mouse dominates the small mammal assemblages from forests and ecotonal shrublands of northwestern Patagonia (abundances exceed 50% in owl pellets recently collected from the study area). Current configuration of forest and ecotonal assemblages, particularly the high abundance of O. longicaudatus, should be mainly linked to anthropogenic causes, including the introduction of cattle, land clearing, and the advance of introduced plant species such as the sweet briar ( Rosa eglanteria). Particularly, this exotic shrub offers shelter and additional food for O. longicaudatus, turning their shrublands into spaces of high epidemiological risk.

Molecular detection and characterization of Bartonella spp. in rodents from central and southern Chile, with emphasis on introduced rats (Rattus spp.)

Bartonella spp. was screened in 155 rodents from Chile, mainly the invasive rats Rattus norvegicus and Rattus rattus. A total of 155 spleen and 50 blood samples were analyzed through real-time PCR for Bartonella spp. (nuoG gene). Positive samples were subjected to amplification of fragment of loci gltA, rpoB and ITS by conventional PCR (cPCR). Overall, 43 spleen samples (27.7%) and 6 rodent blood samples (12%) were positive for nuoG-Bartonella spp. Positive samples were found in R. norvegicus, R. rattus, Abrothrix olivacea and Oligoryzomys longicaudatus. Bartonella spp. DNA was amplified by cPCR in 16 samples, resulting in 21 sequences (6 gltA, 5 ITS and 10 rpoB). Sequencing and phylogenic analyses identified genotypes from Rattus spp., potentially belonging to Bartonella coopersplainsensis, Bartonella henselae, Bartonella tribocorum, and an undescribed Bartonella sp. From native rodents, one sequence was identified, being related B. machadoae. In conclusion, this work describes diverse and potentially zoonotic Bartonella spp. genotypes in Rattus spp. Additionally, this is the first report of Bartonella in O. longicaudatus, including a potentially novel Bartonella genotype or species.

Survey and Molecular Characterization of Sarcocystidae protozoa in Wild Cricetid Rodents from Central and Southern Chile.

In Chile, studies of parasites from the family Sarcocystidae (Apicomplexa) have mostly been related to domestic animals. We aimed to assess the presence of Sarcocystidae taxa in cricetid rodents from Central and Southern Chile. We studied 207 rodents, encompassing six species, from 13 localities. We isolated DNA from tissue samples, amplified the Sarcocystidae 18S rRNA gene with polymerase chain reaction, and performed phylogenetic analyses using maximum likelihood and Bayesian inferences. In addition, we examined blood smears and performed histological studies in organs from Sarcocystidae DNA-positive animals. Three specimens were DNA-positive and three genotypes were retrieved and named: Sarcocystis sp. P61, related to Sarcocystis strixi, was detected in two Abrothrix olivacea. Toxoplasmatinae gen. sp. P99 was retrieved from those same two specimens, and was related to Toxoplasma and other genera, although it branched independently. Besnoitia sp. R34 was detected in one Abrothrix hirta, and was clustered with congeneric species associated with rodents. No protozoa were found during microscopic studies; thus, it was not possible to confirm parasitic interactions rather than accidental encounters. However, the close relatedness of the retrieved genotypes to parasites of rodents supports the hypothesis of host-parasite associations. All three genotypes are suggested as potential new taxa, including a putative new genus.

The skull variation of the olive field mouse Abrothrix olivacea (Cricetidae: Abrotrichini) is localized and correlated to the ecogeographic features of its geographic distribution.

The relationship between phenotypic variation and landscape heterogeneity has been extensively studied to understand how the environment influences patterns of morphological variation and differentiation of populations. Several studies had partially addressed intraspecific variation in the sigmodontine rodent Abrothrix olivacea, focusing on the characterization of physiological aspects and cranial variation. However, these had been conducted based on geographically restricted populational samples, and in most cases, the aspects characterized were not explicitly contextualized with the environmental configurations in which the populations occurred. Here, the cranial variation of A. olivacea was characterized by recording twenty cranial measurements in 235 individuals from 64 localities in Argentina and Chile, which widely cover the geographic and environmental distribution of this species. The morphological variation was analyzed and ecogeographically contextualized using multivariate statistical analyses, which also included climatic and ecological variation at the localities where the individuals were sampled. Results indicate that the cranial variation of this species is mostly clustered in localized patterns associated to the types of environments, and that the levels of cranial differentiation are higher among the populations from arid and treeless zones. Additionally, the ecogeographical association of cranial size variation indicate that this species does not follow Bergmann's rule and that island populations exhibit larger cranial sizes compared to their continental counterparts distributed at the same latitudes. These results suggest that cranial differentiation among the populations of this species is not homogeneous throughout its geographic distribution, and that the patterns of morphological differentiation are also not completely consistent with the patterns of genetic structuring that have been described recently. Finally, the analyses performed to ponder morphological differentiation among populations suggest that the contribution of genetic drift in the formation of these patterns can be ruled out among Patagonian populations, and that the selective effect imposed by the environment could better explain them.

Variable interspecific competition under megadrought conditions: rodent population dynamics in semiarid Chile

Deciphering how climatic variability modulates the interspecific interactions in natural systems is one of the most interesting and least studied ecological processes. Rodent outbreaks or irruptions in semiarid Chile are associated with rainfall pulses driven by the El Niño Southern Oscillation (ENSO). During the last decade, north‐central Chile has experienced an almost uninterrupted sequence of > 10 dry years, the so‐called megadrought, which had led to a new ecological benchmark in this region. We employ a diagnostic approach to analyze abundance data regarding two rodent species, Phyllotis darwini and Abrothrix olivacea, using a 33 year time series spanning from 1987 to 2019. Our population dynamic models provide evidence of competitive interactions within and between both species. This result is novel because we show that rainfall variability influences the degree of interspecific competition and that it is asymmetric. The diagnostic approach used here offers a way to develop simple population models that are useful for understanding the causes of population fluctuations and for predicting population changes under a climate change scenario.

Gastrointestinal parasites in wild rodents in Chiloé Island-Chile.

Gastrointestinal parasites are well-documented in small mammals from north-central Chile, but little is known about endoparasites of rodents in southern Chile. A survey was conducted between January and February 2018 to evaluate gastrointestinal parasites and risk factors of wild rodents that live in rural areas in Northern Chiloé Island, Chile. A total of 174 fecal samples from rodents of six native and one introduced species were collected and examined using the Mini-FLOTAC method. Also, 41 individuals of four native wild rodent species were examined furtherly to determinate adult parasites from gastrointestinal tracts. The overall prevalence of endoparasites was 89.65% (156). Helminth egg types included: Rodentolepis spp., Capillariidae, Trichuris sp., Syphacia sp., oxyurid-type eggs, Strongyloides sp., Spirurid-type eggs, Strongilid-type eggs, Moniliformis sp., and an unidentified nematode egg and larvae. Protozoa comprised coccidia, amoeba, and unidentified cysts. From necropsies, adult parasites involved Syphacia sp. Trichuris sp., Protospirura sp. and Physaloptera sp. In Abrothrix olivacea, individuals with low-body-mass index exhibited reduced infection probability for Spirurid-type and Strongilid-type eggs. Some parasites in this study may affect human health. In rural settings where environmental conditions are changing, more research should be undertaken to understand parasitic infections in wildlife and implications for public health and conservation.

Climate influences the genetic structure and niche differentiation among populations of the olive field mouse Abrothrix olivacea (Cricetidae: Abrotrichini)

Even when environmental variation over time and space is commonly considered as an important driver of population divergence, few evaluations of intraspecific genetic variation explicitly assess whether observed structure has been caused by or is correlated with landscape heterogeneity. Several phylogeographic studies have characterized the mitochondrial diversity of Abrothrix olivacea, but none has incorporated landscape genetics analyses and ecological niche modeling, leaving a gap in the understanding of the species evolutionary history. Here, these aspects were addressed based on 186 single nucleotide polymorphisms, extracted from sequences of 801 bp of Cytb gene, gathered from 416 individuals collected at 103 localities in Argentina and Chile. Employing multivariate statistical analyses (gPCA, Mantel and Partial Mantel Tests, Procrustes Analysis, and RDA), associations between genetic differences and geographic and climatic distances were evaluated. Presence data was employed to estimate the potential geographic distribution of this species during historical and contemporary climatic scenarios, and to address differences among the climatic niches of their main mitochondrial lineages. The significant influence of landscape features in structuring mitochondrial variability was evidenced at different spatial scales, as well as the role of past climatic dynamics in driving geographic range shifts, mostly associated to Quaternary glaciations. Overall, these results suggest that throughout geographic range gene flow is unevenly influenced by climatic dissimilarity and the geographic distancing, and that studied lineages do not exhibit distributional signals of climatic niche conservatism. Additionally, genetic differentiation occurred by more complex evolutionary processes than mere disruption of gene flow or drift.

Correction to: The Mitochondrial Genetic Diversity of the Olive Field Mouse Abrothrix olivacea (Cricetidae; Abrotrichini) is Latitudinally Structured Across Its Geographic Distribution

Correction to: The Mitochondrial Genetic Diversity of the Olive Field Mouse Abrothrix olivacea (Cricetidae; Abrotrichini) is Latitudinally Structured Across Its Geographic Distribution

Apicomplexans in small mammals from Chile, with the first report of the Babesia microti group in South American rodents.

Small mammals play an essential role as disseminators of pathogens because they reach high population densities and have ubiquitous distributions. In the Northern Hemisphere rodents are well recognized as reservoirs for tick-borne bacteria of the Anaplasmataceae family and also apicomplexan protozoans. In contrast, South American rodents hosting these microorganisms have been rarely identified. In this study, we collected blood from rodents and marsupials in northern Chile and screened for Anaplasmataceae bacteria and apicomplexan protozoa. Overall, 14.7% of the samples were positive for Babesia, Hepatozoon, and Sarcocystidae using conventional PCR assays targeting the structural 18S rRNA locus (18S). Phylogenetic analyses performed with amplicons derived from 18S and cytochrome c oxidase (COI) gene provided evidence of a Babesia sp. belonging to the Babesia microti group in Phyllotis darwini, and a novel Babesia genotype in P. darwini and Abrothrix jelskii. Furthermore, four novel genotypes of Hepatozoon retrieved from Abrothrix olivacea, P. darwini, and Oligoryzomys longicaudatus, formed independent lineages within a clade that includes additional Hepatozoon spp. detected in South American rodents. Moreover, an incidental finding of a previously detected apicomplexan, herein designated as Sarcocystidae sp., was recorded in Thylamys opossums with a high prevalence, indicating a possible specific association with these mammals. Phylogenetic analysis of Sarcoystidae sp. clearly demonstrated its relatedness to apicomplexans detected in Australian marsupials. Our results expand the range of mammals hosting tick-borne apicomplexans in South America, highlight a novel clade consisting of South American babesias, and report for the first time the B. microti group infecting rodents in the region.

The Mitochondrial Genetic Diversity of the Olive Field Mouse Abrothrix olivacea (Cricetidae; Abrotrichini) is Latitudinally Structured Across Its Geographic Distribution

The Mitochondrial Genetic Diversity of the Olive Field Mouse Abrothrix olivacea (Cricetidae; Abrotrichini) is Latitudinally Structured Across Its Geographic Distribution

Activity patterns and interactions of rodents in an assemblage composed by native species and the introduced black rat: implications for pathogen transmission

BackgroundThe degree of temporal overlap between sympatric wild hosts species and their behavioral interactions can be highly relevant to the transmission of pathogens. However, this topic has been scantly addressed. Furthermore, temporal overlap and interactions within an assemblage of wild rodents composed of native and introduced species have been rarely discussed worldwide. We assessed the nocturnal activity patterns and interactions between rodent taxa of an assemblage consisting of native species (Oligoryzomys longicaudatus, Abrothrix hirta, and Abrothrix olivaceus) and the introduced black rat (Rattus rattus) in a temperate forest from southern Chile. All rodent species in this study are known hosts for various zoonotic pathogens.ResultsWe found a high nocturnal temporal overlap within the rodent assemblage. However, pairwise comparisons of temporal activity patterns indicated significant differences among all taxa. Rattus rattus showed aggressive behaviors against all native rodents more frequently than against their conspecifics. As for native rodents, agonistic behaviors were the most common interactions between individuals of the same taxon and between individuals of different taxa (O. longicaudatus vs Abrothrix spp.).ConclusionsOur findings reveal several interactions among rodent taxa that may have implications for pathogens such as hantaviruses, Leptospira spp., and vector-borne pathogens. Furthermore, their transmission may be facilitated by the temporal overlap observed between rodent taxa.

Genomic footprints of Quaternary colonization and population expansion in the Patagonian‐Fuegian region rules out a separate southern refugium in Tierra del Fuego

AbstractAimDuring the glacial phases, the Andean slopes of southern South America were covered by ice sheets, causing the isolation of many species in glacial refugia. This work aimed to test the number and putative location of glacial refugia in southern South America and establish the sources, timing and direction of post‐glacial colonization events.LocationSouthern South America, Patagonia.TaxonOlive mouse (Abrothrix olivacea).MethodsUsing exome capture, we genotyped 7339 SNPs in 172 specimens of A. olivacea collected at 21 localities distributed across the steppe, grasslands, and forests in the Patagonian‐Fuegian region and seven specimens from two other species of Abrothrix. Based on the effective migration rate, principal component analysis, and admixture composition, we first study the population structure of A. olivacea. The source and direction of colonization events were inferred using the directionality index and standard population genetic analyses. To study the role of the glacial phases, we performed a bayesian demographic analysis to infer divergences times and ancestral population sizes.ResultsPopulation genomic analyses based on SNPs of more than 7000 exons identified three Patagonian genetic clusters: Valdivian forests, continental Magellan forests, and a combination of continental open biomes and Tierra del Fuego. The directionality index supports a single source in northwestern forests, in line with a Valdivian forest refugium, from which the post‐glacial colonization may have started. The effective diversity rate, the onset of population expansions and divergence times also support a Valdivian forest refugium and rule out a separate southern refugium in Tierra del Fuego.Main conclusionsOur results support a coastal refugium located in or near the previously proposed Valdivian refugium and reject in situ differentiation in Tierra del Fuego. More in general, our demographical analysis reveals the role of the Last Glacial Maximum in affecting the population dynamics (i.e., contraction and expansion) of A. olivacea and in fostering the geographical diversification of populations.

Morphological similarity and dental homologies in two sigmodontine rodents (Mammalia, Cricetidae) from different tribes: A topological analysis to explore convergence.

We present a topological analysis of the third upper molars (M3) using the recently developed ICAMER nomenclatural system as a way to understand the dental morphological similarity in sigmodontine rodents, the most speciose subfamily of cricetids. The method is explored in Scapteromys aquaticus and Abrothrix olivacea, taxa belonging to two diverse tribes, Akodontini and Abrotrichini, respectively, which exhibit high similarity regarding several craniodental traits as well as external anatomy. Both species show morphologically similar M3 in adults characterized by cylindrification and the isolation of a large central fossette arising from the marginal fusion of the anterior and posterior lobes. The results indicate that, before the wear, these rodents have a strongly different topological pattern at the cuspal level, mostly involving production of the connection between the main cusps. The central fossette derives from the isolation of part of the metaflexus in Scapteromys, while in Abrothrix it originates from the hypoflexus. The topological analysis provides a new approach to sigmodontine systematics, including the ability to detect diagnostic characters of both tribes. More important, it constitutes a new step toward an integrative phylogeny of fossil and living cricetids.

Trypanosoma cruzi-infected triatomines and rodents co-occur in a coastal island of northern Chile.

Trypanosoma cruzi, the cause agent of Chagas disease, is transmitted mainly by blood-feeding insects of the subfamily Triatominae. The T. cruzi life cycle alternates between triatomines and mammalian hosts, excluding birds and reptiles. Triatomines of Mepraia genus are wild vectors of T. cruzi in Chile. Mepraia specimens infected with T. cruzi have been detected in Pan de Azúcar and Santa María islands. The most common vertebrates that inhabit these islands are birds and reptiles, and it is unknown whether small mammals are present. Consequently, it is relevant to know whether there are any T. cruzi-infected small mammals on those islands to elucidate the T. cruzi cycle. To clarify this crossroads, islands of northern Chile were explored to determine if T. cruzi-infected triatomines and rodents co-occur in islands of northern Chile. T. cruzi DNA was detected by conventional and real-time PCR in three islands: on Santa María and Pan de Azúcar islands T. cruzi was detected in Mepraia sp samples, while on Pan de Azúcar (6.1%) and Damas islands (15%) was detected in the rodent Abrothrix olivacea. We show for the first time in Chile the occurrence of insular rodents infected with T. cruzi, and a complete T. cruzi life cycle in a coastal island. Our results provide new insights to understand the T. cruzi infection in the wild cycle.

Morphological variation in two sigmodontine rodents along the mainland and the Fuegian archipelago in Chilean southern Patagonia

BackgroundAnalysis of morphological variation in archipelagos has been essential to understand the evolution of terrestrial vertebrates. In particular, these natural scenarios allow to assess morphological changes experienced by insular fauna compared to their mainland counterparts. In mammals, morphological changes of insular forms have been observed in size and shape of body and cranial traits. The southern Patagonia of Chile represents a unique scenario to analyze morphological variation in two of the most widely distributed small rodents along western southern South America: Abrothrix olivacea and Oligoryzomys longicaudatus.MethodsWe applied linear and three-dimensional geometric morphometric tools to analyze the variation in cranial morphology of A. olivacea (N = 80) and O. longicaudatus (N = 49). Sampled localities were distributed in the mainland and islands of the Fuegian archipelago in Chilean Patagonia. Standard multivariate methods, as Principal Components Analysis, and Logistic Regression models were carried out to evaluate differences in size and shape of crania.ResultsWe detected higher levels of morphological variation in the crania of A. olivacea if compared to O. longicaudatus. The variation was associated to cranial size instead of shape.We observed significant differences between insular and mainland individuals in A. olivacea, being the cranium size of this species significantly bigger on islands. Indeed, specimens of A. olivacea from “Isla Wellington”, exhibited the higher increment in cranium size compared to any other mainland and insular site sampled for this species. In contrast, insular and mainland forms of O. longicaudatus did not show significant differences in cranial morphology.ConclusionsWe suggest that the patterns of morphological variation observed in these two small rodents along Patagonia, could be explained in terms of the historical biogeography of the region, and the different ecological features of the studied species.

FOOD HABITS AND TROPHIC ATTRIBUTES OF THE MAGELLANIC HORNED OWL (BUBO MAGELLANICUS) IN PATAGONIAN STEPPE, SOUTHERNMOST CHILE

For most of southern South America, the food habits of Magellanic Horned owls (Bubo magellanicus) are well known. In Chile, several researchers have reported the owl’s diet in northern xerophytic environments, as well as subpolar forests; however, other than a short note on the owls’ summer diet in Punta Dungeness, no major studies have documented the food habits of Magellanic Horned owls in the Chilean Patagonian steppe. Based on 278 fresh pellets, we reported the food habits of owls inhabiting two sites located at > 52°S in the southernmost Patagonian steppe in continental Chile, and compared our findings with those reported for owls inhabiting eight localities from 39 to 52°S in the Argentinean Patagonian steppe. Our results indicate that in Patagonian steppe environments of both Argentina and Chile, the Magellanic Horned Owl is a generalist predator, which consumes whatever prey available, ranging in size from inver- tebrates to introduced juvenile lagomorphs. Because all five major vertebrate prey here reported (Abrothrix olivacea, Loxodontomys micropus, Microcavia australis, Reithrodon auritus, Lepus europaeus) are broadly distributed in the Argentinean Patagonian steppe and occur abundantly from 36°S southwards to the Strait of Magellan and Isla Grande de Tierra del Fuego, their generalized occurrence as prey does not allow for expression of latitudinal trends in species composition in the owl’s diet.