South American Rodents Research Articles

Differential climatic niche diversification processes in South American rodents (Octodontoidea) across tropical and extratropical regions

ABSTRACT Studying niche evolution becomes central to understanding the processes driving species diversification along latitudinal gradients. Octodontoidea rodents serve as a model group for understanding how the colonisation of extratropical regions has shaped the climatic niche evolution of species. We analyse the time and mode of climatic niche evolution among different Octodontoidea lineages to understand how niche evolutionary processes operate across the spatial gradient of the Neotropical region. We constructed ecological niche models for living Octodontoidea species to assess the timing and mode of climatic niche evolution across tropical and extratropical lineages. We estimated niche similarity and correlated it with species divergence times, and estimated the rate of climatic niche diversification across lineages. Our results show a trend of greater niche overlap in more recent lineages and lower niche overlap in older lineages. However, extratropical lineages exhibit lower climatic niche overlaps. From diversification analysis, we detected that the Ctenomyidae group shows higher rates of niche diversification, whereas the tropical Echimyidae group exhibits the lowest rates of climatic niche diversification. Our results support the idea that the lineages restricted to tropical regions tend towards niche conservatism. However, some tropical lineages have successfully colonised extratropical regions, and this colonisation has been accompanied by strong selective pressures, leading to higher rates of niche diversification and lower climatic niche overlap among species.

Identification and management of infections caused by Giardia sp., Trichuris sp. and Demodex sp. in captive Brazilian porcupines (Coendou prehensilis)

The Brazilian porcupine (Coendou prehensilis, Rodentia, Erethizontidae) is an arboreal South American nocturnal rodent. Switzerland is home to one of the largest captive colonies in Europe. In June 2022, most of the animals in this colony showed severe diarrhoea, and Giardia sp. cysts were detected. All the animals were treated with metronidazole (75 mg/animal/day orally) for five days, repeating after two weeks. The diarrhoea continued, sometimes containing blood, and further analyses revealed Giardia sp. cysts and Trichuris sp. eggs with a particular undulating eggshell in pooled samples. The soil layer of some enclosures was removed to thoroughly clean and disinfect the underlying concrete floor. The animals were treated with fenbendazole (50 mg/kg/day orally) for 5 days repeating after three days. Giardia sp. cysts were not further detected. However, Trichuris sp. eggs were detected in branch bark samples and in six animals 2–3 months after treatment. The treatment with fenbendazole was repeated and no further Trichuris sp. eggs were detected. A 18S rRNA fragment consensus sequence showed 98.58% identity with Trichuris fossor. The Trichuris sp. in C. prehensilis may represent a new species, specific for arboreal porcupines. Demodex mites were observed in faecal flotations and thereafter in skin scrapings from five animals (four of them being family-related). A 16S consensus sequence showed 86.4% identity with other Demodex species. The animals were initially treated with moxidectin (0.4 and 0.8 mg/kg orally) and afterwards with sarolaner (10 mg/animal) but the treatments were not completely effective since in control scrapings, two animals evidenced few non-motile mites. An individual susceptibility and poor immunological control of the infection is suggested. Treatment with fenbendazole was effective against Giardia sp. and Trichuris sp. infections; however, reinfections may occur if the enclosures and tree branches are not deep cleaned and disinfected or replaced.

A new Late Miocene stem Octodontoid (Rodentia: Caviomorpha: Octochinchilloi) from the Solimões Formation (Brazil): paleobiogeographic implications

ABSTRACT Caviomorphs are the neotropical hystricognathous rodents (Ctenohystrica: Hystricognathi: Caviomorpha). Octodontoidea are today the richest and most speciose clade of caviomorphs. Their fossil record also reveals a wide array of extinct species, including Acarechimys, a taxon with a widespread South American distribution and extensive temporal range. This genus comprises at least five species documented in deposits ranging from the late Oligocene to the Middle Miocene. Here, we report the discovery of a new species of Acarechimys from Upper Miocene deposits of the Envira River (PRE06 outcrop), situated in the Acre State, western Brazilian Amazonia. The new species differs from the other species of the genus in having lower molars with a strong posterior arm of the metaconid, the presence of a mesostylid (usually prominent) and a neomesolophid forwardly directed and connected to the metalophulid I on m1 but not on m2–3, and the absence of posterior arm of the protoconid. This taxon represents the youngest known species of the Acarechimys lineage to date. Its occurrence in Western Amazonia strengthens support for the hypothesis that South American rodent lineages survived longer during the Neogene at low latitudes than in the southern regions of the continent.

The virtual brain endocast of Incamys bolivianus: insight from the neurosensory system into the adaptive radiation of South American rodents

The virtual brain endocast of <i>Incamys bolivianus</i>: insight from the neurosensory system into the adaptive radiation of South American rodents

Searching for common patterns in parasite ecology: species and host contributions to beta-diversity in helminths of South African ungulates and fleas of South American rodents

We searched for common patterns in parasite ecology by investigating species and host contributions to the beta-diversity of infracommunities (=assemblages of parasites harboured by a host individual) in helminths of three species of South African ungulates and fleas of 11 species of South American rodents, assuming that a comparison of patterns in distinctly different parasites and hosts would allow us to judge the generality or, at least, commonness of these patterns. We used data on species’ composition and numbers of parasites and asked whether (i) parasite species’ attributes (life cycle, transmission mode, and host specificity in helminths; possession of sclerotized combs, microhabitat preference, and host specificity in fleas) or their population structure (mean abundance and/or prevalence) and (ii) host characteristics (sex and age) affect parasite and host species’ contributions to parasite beta-diversity (SCBD and HCBD, respectively). We found that parasite species’ morphological and ecological attributes were mostly not associated with their SCBD. In contrast, parasite SCBD, in both ungulates and rodents, significantly increased with either parasite mean abundance or prevalence or both. The effect of host characteristics on HCBD was detected in a few hosts only. In general, parasite infracommunities’ beta-diversity appeared to be driven by variation in parasite species rather than the uniqueness of the assemblages harboured by individual hosts. We conclude that some ecological patterns (such as the relationships between SCBD and parasite abundance/prevalence) appear to be common and do not differ between different host-parasite associations in different geographic regions, whereas other patterns (the relationships between SCBD and parasite species’ attributes) are contingent and depend on parasite and host identities.

Organization of Somatosensory Cortex in the South American Rodent Paca (Cuniculus paca)

Introduction: The study of non-laboratory species has been part of a broader effort to establish the basic organization of the mammalian neocortex, as these species may provide unique insights relevant to cortical organization, function, and evolution. Methods: In the present study, the organization of three somatosensory cortical areas of the medium-sized (5–11 kg body mass) Amazonian rodent, the paca (Cuniculus paca), was determined using a combination of electrophysiological microelectrode mapping and histochemical techniques (cytochrome oxidase and NADPH diaphorase) in tangential sections. Results: Electrophysiological mapping revealed a somatotopically organized primary somatosensory cortical area (S1) located in the rostral parietal cortex with a characteristic foot-medial/head-lateral contralateral body surface representation similar to that found in other species. S1 was bordered laterally by two regions housing neurons responsive to tactile stimuli, presumably the secondary somatosensory (S2) and parietal ventral (PV) cortical areas that evinced a mirror-reversal representation (relative to S1) of the contralateral body surface. The limits of the putative primary visual (V1) and primary auditory (A1) cortical areas, as well as the complete representation of the contralateral body surface in S1, were determined indirectly by the histochemical stains. Like the barrel field described in small rodents, we identified a modular arrangement located in the face representation of S1. Conclusions: The relative location, somatotopic organization, and pattern of neuropil histochemical reactivity in the three paca somatosensory cortical areas investigated are similar to those described in other mammalian species, providing additional evidence of a common plan of organization for the somatosensory cortex in the rostral parietal cortex of mammals.

Esporotriose em porquinho da índia (Cavia porcellus) - relato de caso

ABSTRACT The guinea pig is a South American rodent with a docile behavior that has been gaining popularity as a pet, increasing the search for specialized veterinary care for the species. In the clinical casuistry, about half of the visits are due to dermatological changes, among which fungal infections are uncommon. Sporotrichosis is a zoonosis caused by the fungus of the genus Sporothrix, widely distributed in nature, which contaminates the host from the inoculation of the agent in lesions and mucous membranes and has been reported in several species of animals. Felines with access to the street are the main disseminators of the agent due to the behaviors of the species and can contaminate other animals and humans. The most evident clinical signs are crusted, exudative and difficult to heal lesions, requiring complementary tests such as PCR and culture to confirm the diagnosis. The specific treatment is time-consuming, using antifungal drugs such as itraconazole, which can be associated with topical treatment to aid healing. Given the difficulty of finding references about this zoonosis, it is difficult to obtain reliable data on the epidemiology of this disease. The present work describes the first report of sporotrichosis in guinea pig in Brazil, the complementary examinations that resulted in the definitive diagnosis and the effective therapeutic response, to contribute to possible work and research.

A simple and low-cost environmental enrichment program improves the welfare of Calomys callosus, a species that adapts to animal facilities.

An environmental enrichment protocol is essential for testing experimental models because it upholds animal welfare, aligns with ethical principles in animal experimentation, and reduces the number of animals needed. Calomys callosus, a South American rodent from the Cricetidae family, is bred in rodent animal facilities for its ease of handling, longevity, prolificacy, and effectively mimicking diseases like Toxoplasmosis, Leishmaniasis, Chagas, and Schistosomiasis. There are no reports on environmental enrichments for this species or their impact on reproductive parameters. This study aimed to analyze the influence of the Environmental Enrichment Program (EEP) on the reproductive and zootechnical performance of C. callosus kept in the Rodents Animal Facilities Complex of Universidade Federal de Uberlândia (UFU). Two experimental groups were established: with environmental enrichment EE+ and without environmental enrichment EE-. The materials used in the experimental design were changed weekly and alternated between dietary, occupational, physical/cognitive, and non-enrichment items. After the inclusion of the EEP, an improvement in the reproductive indices of C. callosus was identified in the EE+ group. These improvements included increased female precocity, a decreased interbirth interval, and a higher number of pairs producing more offspring. The postpartum zootechnical indices were also better, such as the number of animals born alive, improved weaning rates, and a reduced average number of deaths from birth to weaning. After the inclusion of the EEP, the general health status of C. callosus improved, reducing cases of non-infectious lumbar alopecia. Therefore, EEP allows C. callosus to express natural reproductive behaviors and improves parental care.

A new species of the highly polytypic South American rodent Ctenomys increases the diversity of the magellanicus clade

The subterranean rodent Ctenomys is the most polytypic South American mammal genus and one of the most speciose and rapidly diversifying mammal genera in the world. Its systematics is unstable due to the underlying accelerated diversification processes that give rise to evolutionary lineages at different stages of differentiation and to remarkable morphological homogeneity even among long-differentiated species. As a result, species boundaries are often difficult to define. Diversity of this genus in the coastal area of central Argentina has been extensively studied, with two independent lineages currently recognized while a distinct third population had not been previously detected. Through a phylogenetic analysis based on combined morphological and molecular evidence, Bayesian estimates of divergence times, and morphometric and morphological assessments, we recognize this third population as an independently evolving lineage. The new species, Ctenomys pulcersp. nov., is here described for both the living fauna and the fossil record of the Pampean region of central Argentina. According to phylogenetic results, Ctenomys pulcersp. nov. belongs to the essentially Patagonian magellanicus clade, and would have diverged from its sister species, Ctenomys bidaui, during the middle Pleistocene (ca. 0.4 Ma). Its current distribution in the fixed and semifixed dunes of the coastal Pampean region is assumed to represent a relict of a wider and continuous distribution of potentially suitable environments during the late Pleistocene. Ctenomys pulcersp. nov. occurs in a particularly fragile natural system subjected to profound disturbances caused by diverse anthropic actions and therefore measures for the conservation of its habitat will be indispensable.

Review of three neglected species of Ctenomys (Rodentia: Ctenomyidae) from Argentina

Abstract Ctenomys is one of the most speciose genera among South American rodents, whose systematics have not yet been fully elucidated. One of the difficulties for clarifying the identity of its species is the limited information available on some of them, erected more than a century ago and of which only the original descriptions are known, generally very poorly detailed. Our study provides new information about Ctenomys coludo Thomas 1920, based on the collection of topotype specimens that allowed us to perform more detailed morphological and molecular analyses, and to compare them with the available information referred to the holotype, with specimens deposited in museum collections, and other species of the genus that have been proposed as related to C. coludo. Our results allow us to place C. coludo as a member of the mendocinus group, proposing C. famosus Thomas, 1920 as a junior synonym for C. coludo. We also recognize Ctenomys johannis as a valid and full species, and provide unpublished information on it from the collection of specimens at the type locality. Thus, we add new areas for the distribution of these species and present their phylogenetic relationships.

An integrative approach to explore species limits in Laelaps mazzai Fonseca, 1939 (Mesostigmata, Laelapidae), a South American widespread mite parasitizing the cricetid Calomys Waterhouse, 1837

Laelaps mazzai Fonseca, 1939 (Mesostigmata, Laelapidae) parasitizes several species of the widespread South American rodent genus Calomys Waterhouse, 1837. Morphological variation has been noticed within this laelapid but has yet to be analyzed. Since several other species of laelapids that initially were considered generalists have resulted in host-specific species, after further analyses, herein we explored, through morphology and genetics, the variation of this parasite across six species of Calomys, trying to establish if it constitutes a polymorphic species or a complex of cryptic host specific-species. An integrative approach was applied, including principal component and discriminant analyses of females and males and DNA sequences (nuclear region ITS and the COI gene). The obtained results indicate that female mites tend to differentiate only the sizes of their dorsal shield among host species but with extensive overlapping. At the same time the males lack metrical differentiation, and the genetic evidence failed to resolve specific-species clades. We conclude that L. mazzai is a single widespread mite with little genetic and phenotypic differentiation.

First virtual endocast description of an early Miocene representative of Pan-Octodontoidea (Caviomorpha, Hystricognathi) and considerations on the early encephalic evolution in South American rodents

AbstractThe study of the cranial endocast provides valuable information to understand the behavior of an organism because it coordinates sensory information and motor functions. In this work, we describe for the first time the anatomy of the encephalon of an early Miocene pan-octodontoid caviomorph rodent (Prospaniomys priscus Ameghino, 1902) found in the Argentinean Patagonia, based on a virtual 3D endocast. This fossil rodent has an endocast morphology here considered ancestral for Pan-Octodontoidea and other South American caviomorph lineages, i.e., an encephalon with anteroposteriorly aligned elements, mesencephalon dorsally exposed, well-developed vermis of the cerebellum, and rhombic cerebral hemispheres with well-developed temporal lobes. Prospaniomys Ameghino, 1902 also has relatively small olfactory bulbs, large paraflocculi of the cerebellum, and low endocranial volume and degree of neocorticalization. Its encephalization quotient is low compared with Paleogene North American and European noncaviomorph rodents, but slightly higher than in several late early and late Miocene caviomorphs. Paleoneurological anatomical information supports the hypothesis that Prospaniomys was a generalist caviomorph rodent with terrestrial habits and enhanced low-frequency auditory specializations. The scarce paleoneurological information indicates that several endocast characters in caviomorph rodents could change with ecological pressures. This work sheds light on the anatomy and evolution of several paleoneurological aspects of this particular group of South American rodents.

Sexual behavior of Ctenomys pearsoni (Rodentia: Ctenomyidae) in “Carrasco” population (Montevideo - Uruguay)

Ctenomys is a genus of South American subterranean rodents that is distributed from Peru to southern Argentina and Uruguay. The present work studies the reproductive behavior (courtship and copula) of Ctenomys pearsoni (Carrasco population, Uruguay). To carry out the characterization, we used an ethogram with 19 behavioral units grouped into different categories. By studying 10 couples we quantified the frequency of occurrence and the time invested in each behavioral unit during the development of the interaction. Through the analysis of the results, the roles of each partner and the importance of each one's role in the development of reproductive behavior are inferred. The results obtained are compared with the data available for other populations of the species and other species of the genus. We discussed the relevance of classifying the reproductive pattern on the basis of the Dewsbury classification. Finally, the importance of each sex in the development and molding of reproductive behavior is discussed.

Spatial maps and oscillations in the healthy hippocampus of Octodon degus, a natural model of sporadic Alzheimer's disease.

The Octodon degus is a South American rodent that is receiving increased attention as a potential model of aging and sporadic late-onset Alzheimer’s disease (AD). Impairments in spatial memory tasks in Octodon degus have been reported in relation to either advanced AD-like disease or hippocampal lesion, opening the way to investigate how the function of hippocampal networks affects behavior across AD stages. However, no characterization of hippocampal electrophysiology exists in this species. Here we describe in young, healthy specimens the activity of neurons and local field potential rhythms during spatial navigation tasks with and without objects. Our findings show similarities between the Octodon degus and laboratory rodents. First, place cells with characteristics similar to those found in rats and mice exist in the CA1 subfield of the Octodon degus. Second, the introduction of objects elicits novelty-related exploration and an increase in activity of CA1 cells, with location specific and unspecific components. Third, oscillations of the local field potential are organized according to their spectral content into bands similar to those found in laboratory rodents. These results suggest a common framework of underlying mechanisms, opening the way to future studies of hippocampal dysfunction in this species associated to aging and disease.

A century of stasis: Taxonomy of Ctenomys (Rodentia: Hystricomorpha) populations in northeastern Patagonia limits, Argentina

The South American rodent genus Ctenomys is well represented throughout much of southern Patagonia by the polytypic “magellanicus” lineage. In western Argentina, members of this lineage occur from 35 °S to 54 °S latitude. In comparison, the taxonomy of Ctenomys in northeastern Patagonia remains poorly known. This ∼160,000 km2 region consists primarily of mostly flat, homogenous tracts of austral Monte desert covering a gravel substrate and is cut by two major fluvial systems associated with the Colorado and the Negro rivers. Here, we use mitochondrial sequences and morphological comparisons to describe phylogenetic relationships among recently sampled populations of Ctenomys from this region. These analyses indicate that the “magellanicus” lineage extends into northeastern Patagonia to at least the Negro river (40°S). Contained within this lineage are three latitudinally distinct clades that are separated by geographic features such as rivers and basaltic plateaus. Identification of these clades generates new insights into the phylogeographic history of the “magellanicus” lineage and marks the end to nearly a century of stasis regarding taxonomic studies of Ctenomys from northeastern Patagonia.

Hymenolepidid cestodes: Diversity, morphological and molecular characterization of a new species, and phylogeny of parasitic species of rodents from North and South America

Rodents are hosts of a wide diversity of cestodes. Fifteen genera included in the family Hymenolepididae parasitize rodents, and only four of these genera have been recorded from the Neotropical region. The purpose of this paper is to update species of Hymenolepididae from rodents, describe a new species of Hymenolepis based on morphological and molecular characterization (ITS1 rDNA and cox1 mtDNA), comparing the features among the species from North and South American rodents, and provide phylogenetic inferences of Hymenolepididae from rodents based on sequences available in the GenBank. Rodents were collected in the Parque Provincial Ernesto Tornquist, Buenos Aires, Argentina. Hymenolepis ivanovae n. sp. differs from other Hymenolepis species registered from North and South American rodents by body size, scolex, suckers, cirrus sac, cirrus, testes, and eggs, among others. Comparative morphometric data for Hymenolepis species from North and South American rodents is provided. Molecular analyses place H. ivanovae n. sp. within the genus Hymenolepis with strong support, and show it close to species of zoonotic importance. The new species is the first species of Hymenolepis described from Sigmodontinae rodents.

Daylength Shapes Entrainment Patterns to Artificial Photoperiods in a Subterranean Rodent.

Photoperiodism plays an important role in the synchronization of seasonal phenomena in various organisms. In mammals, photoperiod encoding is mediated by differential entrainment of the circadian system. The limits of daily light entrainment and photoperiodic time measurement can be verified in organisms that inhabit extreme photic environments, such as the subterranean. In this experimental study, we evaluated entrainment of circadian wheel-running rhythms in South American subterranean rodents, the Anillaco tuco-tucos (Ctenomys aff. knighti), exposed to different artificial photoperiods, from extremely long to extremely short photophases (LD 21:3, LD 18:6, LD 15:9, LD 9:15, LD 6:18 and LD 3:21). Artificial photoperiods synchronized their activity/rest rhythms and clear differences occurred in (a) phase angles of entrainment relative to the LD cycle and (b) duration of the daily activity phase α. These photoperiod-dependent patterns of entrainment were similar to those reported for epigeous species. Release into constant darkness conditions revealed aftereffects of entrainment to different photoperiods, observed in α but not in the free-running period τ. We also verified if animals coming from summer and winter natural photoperiods entrained equally to the artificial photoperiods by evaluating their phase angle of entrainment, α and τ aftereffects. To this end, experimental animals were divided into "Matching" and "Mismatching" groups, based on whether the experimental photoperiod (short-day [L < 12 h] or long-day [L > 12 h]) matched or not the natural photoperiod to which they had been previously exposed. No significant differences were found in the phase angle of entrainment, α and τ aftereffects in each artificial photoperiod. Our results indicate that the circadian clocks of tuco-tucos are capable of photoperiodic time measurement despite their natural subterranean habits and that the final entrainment patterns achieved by the circadian clock do not depend on the photoperiodic history.

DNA barcodes highlight genetic diversity patterns in rodents from lowland desert and Andean areas in Argentina

Rodents are an important component of South America fauna. Their high diversity has motivated researchers to continually review their taxonomy, genetic diversity, species limits, and phylogenetic relationships. Here, we applied DNA-barcodes for assessing the taxonomic and genetic diversity in the two major lineages of South American rodents: caviomorphs and sigmodontines. We analysed 335 COI barcodes in 34morphologically determined species from 39localities along central Andes and arid lands of Argentina. Neighbour-joining and maximum likelihood reconstruction provided clear separation between species. The Barcode Index number and Bayesian Poisson tree processes were used to confirm concordance between sequence clusters and species designations by taxonomy. We found deep divergence within the Phyllotis xanthopygus species complex, with distances up to 13.0% between geographically separated lineages. Minor divergences (3.30% and 2.52%) were found within Abrothrix hirta, and Tympanoctomys barrerae, respectively, with differentiation in their genetic lineages. Also, we documented geographically separated clusters for Akodon spegazzinii and A.oenos with up to 2.3% divergence, but clustering methods failed to distinguish them as different species. Sequence results show a clear barcode gap with a mean intraspecific divergence (0.56%) versus a minimum nearest-neighbour distance averaging (10.1%). Distances between congeneric species varied from 4.1 to 14%, with the exception of two related forms within Euneomys and the sister species Akodon spegazzinii and A.oenos. This study constitutes a substantial contribution to the global barcode reference library. It provides insights into the complex phylogeographic patterns and speciation scenarios in rodents, while highlighting areas that require in-depth taxonomic and integrative research.

The nasal cavity in agoutis (Dasyprocta spp.): a micro-computed tomographic and histological study

Abstract Nasal anatomy in rodents is well-studied, but most current knowledge is based on small-bodied muroid species. Nasal anatomy and histology of hystricognaths, the largest living rodents, remains poorly understood. Here, we describe the nasal cavity of agoutis (Dasyprocta spp.), the first large-bodied South American rodents to be studied histologically throughout the nasal cavity. Two adult agoutis were studied using microcomputed tomography, and in one of these, half the snout was serially sectioned and stained for microscopic study. Certain features are notable in Dasyprocta. The frontal recess has five turbinals within it, the most in this space compared to other rodents that have been studied. The nasoturbinal is particularly large in dorsoventral and rostrocaudal dimensions and is entirely non-olfactory in function, in apparent contrast to known muroids. Whether this relates solely to body size scaling or perhaps also relates to directing airflow or conditioning inspired air requires further study. In addition, olfactory epithelium appears more restricted to the olfactory and frontal recesses compared to muroids. At the same time, the rostral tips of the olfactory turbinals bear at least some non-olfactory epithelium. The findings of this study support the hypothesis that turbinals are multifunctional structures, indicating investigators should use caution when categorizing turbinals as specialized for one function (e.g., olfaction or respiratory air-conditioning). Caution may be especially appropriate in the case of large-bodied mammals, in which the different scaling characteristics of respiratory and olfactory mucosa result in relative more of the former type as body size increases.

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.