Genus Akodon Research Articles

Herodotools: An R package to integrate macroevolution, biogeography and community ecology

AbstractAimSpeciation, extinction and historical dispersal are the ultimate factors generating and maintaining biodiversity. However, methods of macroevolution used to detect historical processes usually ignore the variation of macroevolutionary processes at scales finer than entire regions. Likewise, biogeography and community ecology often ignore deep‐time evolutionary processes. To overcome this problem, it is necessary to integrate data from ancestral state reconstructions, current species distributions and biogeographical regionalization. Herodotools is an R package designed to perform this integration.LocationGlobal application, with an example from Neotropics.Major taxa studiedAny taxa, with an example from small rodents (genus Akodon and subfamily Sigmodontinae).MethodsHerodotools streamline analyses of historical biogeography, including regionalization, calculation of assemblage age, lineage in situ diversification and community phylogenetic metrics, merging species occurrence with macroevolutionary methods of ancestral area and trait reconstruction. The main functions of our R package are presented with toy examples and by analysing the historical biogeography of small rodent assemblages in the Neotropics.ResultsOur package can integrate methods from biogeography, macroevolution and community ecology, allowing us to downscale the effects of historical processes and calculate important historical variables (e.g., age of assemblages, in situ diversification, phylogenetic regionalization, phylogenetic transition zones, metrics of trait macroevolutionary dynamics and new metrics of phylogenetic diversity and endemism) in different scales, from entire regions to communities of co‐occurrent species.Main ConclusionsHerodotools is the first platform to streamline the analysis of historical biogeography, enabling a better understanding of historical processes at different levels of organization, from local assemblages to entire biogeographical regions and incorporating macroevolutionary models in commonly used community phylogenetic metrics. This integration bridges the gap between macroevolutionary, biogeography and community ecology methods.

The importance of the Andes in the evolutionary radiation of Sigmodontinae (Rodentia, Cricetidae), the most diverse group of mammals in the Neotropics

The Andean mountains stand out for their striking species richness and endemicity that characterize many emblematic Neotropical clades distributed in or around these mountains. The radiation of the Sigmodontinae subfamily, the most diversified mammalian group in the Neotropics, has been historically related to Andean orogenesis. We aim to evaluate this interplay between geological processes and biological responses through the diversification dynamics, the biogeographical history, and the range evolution of the subfamily. For these, we built the most comprehensive phylogeny and gathered 14,836 occurrences for the subfamily. We identified one shift in the speciation rate in the genus Akodon, which suffered their Andean radiation after the arrival of non-Andean ancestors. Our biogeographic analyses show multiple dispersal paths throughout the evolution that allowed this subfamily to colonize all Neotropics. The Northern Andes and Central-Southern Andes were the most important sources of diversity. In addition, the Central-Southern Andes were the most relevant sink, receiving the highest number of lineages. The Andean region exhibited higher speciation and turnover rates than non-Andean regions. Thus, our results support the crucial role of the Andean Mountains in the Sigmodontinae radiation, acting as a "macroevolutionary cradle" and "species attractor" for several sigmodontine lineages at different times, and as a "species pump" becoming the biogeographic source of multiple widely distributed neotropical lineages. Then, complex macroevolutionary dynamics would explain these rodents' high extant Andean diversity and their wide distribution in the Neotropics.

Revision and analysis of the chromosome variability in the speciose genus Akodon (Rodentia, Sigmodontinae), including new data from Argentina.

Rodentia has a high species number and chromosomal variability. The South American genus Akodon is one of the most speciose muroids, with more than 40 species included in several species groups. Here, we characterize cytogenetically specimens of Akodon from central-western Argentina. Subsequently, we reviewed and analyzed the cytogenetic data for this genus, build a phylogeny and mapped chromosome changes to interpret its evolution. Specimens of A. dolores from central-western Argentina have 2n=42-44/FNa=44 (46, 48) due to a Robertsonian rearrangement. Our data expand the distribution range known for this polymorphism and confirm its geographic structure. Other specimens had 2n=40/FNa=40, representing populations of A. oenos, A. polopi, and A. spegazzinii. All karyotypes have a low amount of heterochromatin, concentrated in centromeres and sex chromosomes, as in other rodents. The complement with 2n=40/FNa=40 is the most frequent in Akodon and is shared by most species in some groups. Chromosome numbers are very diverse. The FNa shows less variability; FNa=42 was recovered as ancestral, excluding A. mimus, which was connected at the base of the Akodon tree and has FNa=44. This indicates a complex chromosome evolution in Akodon, and suggests that reductions and increases in the 2n and FNa evolved independently in some lineages.

The First Quaternary Record of the Rodent Akodon kadiweu Brandão, Percequillo, D'Elía, Paresque, & Carmignotto, 2021 (Rodentia: Cricetidae: Sigmodontinae).

Rodents of the genus Akodon comprise 41 extant species, and are considered the most diverse genus of the tribe Akodontini. The most recently described extant species is Akodon kadiweu, known exclusively from Serra da Bodoquena, a karstic region located in Mato Grosso do Sul state, Brazil. Some sub-fossil and fossil specimens of Akodon have been reported in recent years for Brazil, but most remain unidentified at the species level. Here we examine the identity of Quaternary specimens of Akodon sp. from the limestone cave Nossa Senhora Aparecida, located in Serra da Bodoquena. Quantitative characters allowed the distinction of Akodon sp. specimens from smaller and larger congeners, and skull qualitative characters of nasal, interorbital region, supraorbital margins, zygomatic notches, zygomatic plate, incisive foramina, mesopterygoid fossa, mandible and molars allowed to identify these individuals as A. kadiweu. Our results revealed the first known past representatives of Akodon to be recorded in Mato Grosso do Sul, as well as western Brazil.

Small mammal glucocorticoid concentrations vary with forest fragment size, trap type, and mammal taxa in the Interior Atlantic Forest

Species that live in degraded habitats often show signs of physiological stress. Glucocorticoid hormones (e.g., corticosterone and cortisol) are often assessed as a proxy of the extent of physiological stress an animal has experienced. Our goal was to quantify glucocorticoids in free-ranging small mammals in fragments of Interior Atlantic Forest. We extracted glucocorticoids from fur samples of 106 small mammals (rodent genera Akodon and Oligoryzomys, and marsupial genera Gracilinanus and Marmosa) from six forest fragments (2–1200 ha) in the Reserva Natural Tapytá, Caazapá Department, Paraguay. To our knowledge, this is the first publication of corticosterone and cortisol levels for three of the four sampled genera (Akodon, Oligoryzomys, and Marmosa) in this forest system. We discovered three notable results. First, as predicted, glucocorticoid levels were higher in individuals living withing small forest fragments. Second, animals captured live using restraint trapping methods (Sherman traps) had higher glucocorticoid levels than those animals captured using kill traps (Victor traps), suggesting that hair glucocorticoid measures can reflect acute stress levels in addition to long-term glucocorticoid incorporation. These acute levels are likely due to urinary steroids diffusing into the hair shaft. This finding raises a concern about the use of certain trapping techniques in association with fur hormone analysis. Finally, as expected, we also detected genus-specific differences in glucocorticoid levels, as well as cortisol/corticosterone ratios.

Neotropical wild rodents Akodon and Oligoryzomys (Cricetidae: Sigmodontinae) as important carriers of pathogenic renal Leptospira in the Atlantic forest, in Brazil

Leptospirosis is an important worldwide zoonosis, caused by a bacterium of the genus Leptospira. For a better understanding of the disease, it is relevant the application of the one health concept. The Atlantic Forest is considered a biodiversity hotspot, with a great endemism of species and despite its importance and proximity to urban areas, the potential role of its fauna as carriers of infectious agents is still poorly understood. Although it is well-known that rats and mice are key reservoirs of leptospires, particularly Rattus norvegicus, wild rodents have also been revealed as reservoirs of leptospiral strains. Thus, the purpose of this study was to investigate the role of the sigmodontine rodents from genera Akodon and Oligoryzomys as pathogenic Leptospira carriers in the Atlantic Forest. We studied 52 Akodon spp. and 15 Oligoryzomys spp. from three areas. Overall 30% were PCR-positive for pathogenic Leptospira, 27% (14/52) Akodon spp. and 40% (6/15) Oligoryzomys spp. DNA sequencing of LipL32 gene confirmed nine species as pathogenic Leptospira. This remarkable incidence of leptospiral carriage within wild genera emphasizes the role of these rodents as carriers of leptospires throughout in this environment.

Pequenos mamíferos (Didelphimorphia, Chiroptera e Rodentia) em egagropilos de Tyto furcata (coruja-das-igrejas) (Aves, Tytonidae) do sul do Brasil

A análise e identificação de pequenos mamíferos em egagropilos de coruja, em especial do gênero Tyto, são consideradas uma ferramenta útil e complementar na mastozoologia. No entanto, poucos estudos deste tipo têm sido desenvolvidos no sul do Brasil. Foram analisados os fragmentos cranianos e mandibulares de pequenos mamíferos encontrados em egagropilos de Tyto furcata coletados em sete localidades dos três estados do sul do país. Ao todo, foram contabilizados 2.382 indivíduos pertencentes a 29 táxons, incluindo cinco marsupiais (Didelphidae; 1,39% dos indivíduos), quatro quirópteros (Molossidae, Phyllostomidae e Vespertilionidae; 0,25%) e 20 roedores (Cricetidae, Muridae, Caviidae e Echimyidae; 98,36%). Os roedores Akodon spp., Oligoryzomys sp. e Mus musculus foram os táxons mais comuns. A amostra inclui espécies com poucos registros para o sul do Brasil, como Bibimys sp., Calomys tener e Wilfredomys oenax. A riqueza de pequenos mamíferos obtida nessas amostras corrobora a utilidade e importância da análise de egagropilos de aves de rapina. Ainda assim, são necessários estudos mais detalhados sobre a morfologia e identificação das espécies, como de Akodon e Oligoryzomys, considerando-se a natureza fragmentária do material nos egagropilos.

Comparative short-term variation of urine concentration among three sigmodontine rodent species from contrasting habitats

We compared urine concentration capacity among three phylogenetically closed sigmodontine rodent species that occur in two distinct habitats: Necromys lasiurus (xeric), Akodon cursor and Akodon lindberghi (mesic). Water conservation ability was evaluated in 30 h-trials, with urine collected every 6 h. A control (I- water and food ad libitum) and a test (II- food and water deprivation) were conducted for each species. Body mass loss (BML), urine volume (UV), urine relative volume (UVr) and urine concentration (UC) were compared between experiments I and II for each species and among species. Changes in urine osmolality between experiments were modeled using exponential and sine functions. Circadian variation of urine concentration was obtained by sine functions fit to the experiments I. Best fit was achieved for sine functions with an accumulation term for experiments II, showing that even in stressful conditions the circadian variation is still present. Highest UC and lowest BML were obtained from Necromys lasiurus individuals, which achieved them at faster rates. The lowest UC with highest BML were obtained for A. cursor individuals at slower rates and values than A. lindberghi, which were intermediate. Necromys lasiurus is more adapted for xeric habitats achieving higher urine concentration in shorter time and faster rate than species of genus Akodon.

A new species of grass mouse, genus Akodon Meyen, 1833 (Rodentia, Sigmodontinae) from central Peruvian Yungas

The genus Akodon is one of the most abundant and species-rich genus of Neotropical mammals. Its species-level taxonomy has been changing actively since its establishment. Currently, the genus is divided into five groups of species: aerosus , boliviensis , cursor , dolores , and varius. Most taxonomic studies of the genus Akodon have focused on boliviensis , varius , and cursor . Taxa from the aerosus group, including A . orophilus , remain largely unknown and poorly studied, even when several authors indicate that most species could constitute species complexes. Here we review populations currently assigned to A. orophilus ; our results allowed the description of a new species of Akodon . We carried out a complete and thorough revision of species of the Akodon aerosus group from the central Peruvian montane forests. We included external and craniodental characters and morphometric data for our analyses. Multivariate statistics and morphological characterizations were performed in order to find differences between species. A new species of Akodon from Peru is described based on combined analyses of cranial morphology and morphometric data. This new species was compared with other taxa from the aerosus species group, it is easily distinguishable from congeners by a unique combination of pelage coloration, body size, and cranial morphology. This new species is most likely endemic to montane forests from Huanuco, and its discovery contributes to uncover the real diversity of Peruvian rodents, adding up to nine species of Akodon from montane cloud forests. Moreover, it supports the previous hypothesis that montane rodent species are complex species; therefore, further research is necessary.

Chromosomal variation in Argentine populations of Akodon montensis Thomas, 1913 (Rodentia, Cricetidae, Sigmodontinae).

The genus Akodon Meyen, 1833 is one of the most species-rich among sigmodontine rodents and has great chromosome variability. Akodon montensis has a relatively broad distribution in South America, and Argentine populations are located in the southernmost region of its range. Brazilian populations have important chromosomal variability, but cytogenetic data from Argentina are scarce. We performed a chromosome characterization of natural populations of Akodon montensis using conventional staining, C-banding, Ag-NORs and base-specific fluorochromes. A total of 31 specimens from five localities of Misiones Province, in Argentina, were analyzed. The 2n=24 chromosomes was the most frequently observed karyotype. However, five individuals presented 25 chromosomes due to a supernumerary B-chromosome; and one individual had 2n=26 due to one B plus a trisomy for chromosome 11. Additionally, two XY females and two variants of the X chromosomes were found. C-positive centromeric bands occurred in all chromosomes; additional C-bands were observed in some autosomes, the X, Y and B chromosomes. Ag-NORs were observed in five autosomes, and the B chromosome was frequently marked. Fluorochrome banding was similar among karyotypes of the analyzed populations. Comparisons of cytogenetic data among populations of Argentina and Brazil showed the presence of high intraspecific variability in Akodon montensis and some differences among regions.

Karyotype description of two species of the genus Akodon (Rodentia, Sigmodontinae) in the northern Rio Grande do Sul state, Brazil

Among the sigmodontine rodents, the genus Akodon is the second in numerical terms, with about 45 recognized species. In the Rio Grande do Sul state, there are 5 registered species. This article shows data on the distribution of the species of the genus Akodon in the northern Rio Grande do Sul state, as well as a description of the karyotypes of species from this region are shown. Six localities were sampled from August 2008 to May 2010. A total of 44 specimens underwent cytogenetic analysis and 2 species were identified ( Akodon montensis and Akodon paranaensis ). The karyotype of A. montensis was 2n = 24, FN = 44 and that of A. paranaensis was 2n = 44, NF = 46. Data on abundance and distribution of these species corroborate the pattern described in other studies with the rodent community in the northern portion of the state, where the Akodon species are seen as dominant. The fact that only A. montensis and A. paranaensis were captured is an indication that these two species are the only ones with confirmed occurrence in the northern portion of this state.

Hantavirus Reservoirs: Current Status with an Emphasis on Data from Brazil

Since the recognition of hantavirus as the agent responsible for haemorrhagic fever in Eurasia in the 1970s and, 20 years later, the descovery of hantavirus pulmonary syndrome in the Americas, the genus Hantavirus has been continually described throughout the World in a variety of wild animals. The diversity of wild animals infected with hantaviruses has only recently come into focus as a result of expanded wildlife studies. The known reservoirs are more than 80, belonging to 51 species of rodents, 7 bats (order Chiroptera) and 20 shrews and moles (order Soricomorpha). More than 80genetically related viruses have been classified within Hantavirus genus; 25 recognized as human pathogens responsible for a large spectrum of diseases in the Old and New World. In Brazil, where the diversity of mammals and especially rodents is considered one of the largest in the world, 9 hantavirus genotypes have been identified in 12 rodent species belonging to the genus Akodon, Calomys, Holochilus, Oligoryzomys, Oxymycterus, Necromys and Rattus. Considering the increasing number of animals that have been implicated as reservoirs of different hantaviruses, the understanding of this diversity is important for evaluating the risk of distinct hantavirus species as human pathogens.

An introduction to the systematics of Akodon orophilus Osgood, 1913 (Rodentia: Cricetidae) with the description of a new species.

The genus Akodon is one of the most species-rich rodent lineages in South America. In Peru, this genus contains 14 species subdivided in two groups: aerosus and boliviensis. Akodon orophilus Osgood, 1913 (Rodentia: Cricetidae) is a member of the Akodon aerosus group that inhabits the northern Peruvian montane forest, but is poorly characterized and its distribution is vaguely known. We review the status of the species based on morphology, morphometric and karyology, and compared with all members of the Akodon aerosus clade from Peruvian montane forests. As a result, we provide a complete redescription of A. orophilus, present new information on its natural history, restrict its distribution to the east of Río Marai6n, and describe a new species of Akodon from Huánuco Department, central Peru, a population previously assigned to A. orophilus.

Taxonomic validity of species groups in the genus Akodon (Rodentia, Cricetidae)

In an effort to evaluate the four Akodon species groups, phylogenetic relationships among individuals of the genus Akodon, selected from throughout South America, were examined using cytochrome b and a concatenated data set consisting of data from cytochrome b, exon 6 of the dentin matrix protein 1 and the nuclear intron thyrotropin. Both the cytochrome b data set and the combined data set were analysed under maximum parsimony, maximum likelihood and Bayesian criteria. Like previous studies, a monophyletic Akodon clade was recovered. Monophyly of the boliviensis and cursor groups was supported, and the two form a strongly supported sister relationship. Akodon azarae is basal to and forms a monophyletic group with the boliviensis + cursor clade, resolving the placement of A. azarae but leaving it unassignable to a current Akodon species group. The aerosus and varius groups are paraphyletic as four members of the varius group (A. glaucinus, A. simulator, A. tartareus and A. varius) fall within the aerosus group. Akodon lindberghi is formally placed in the cursor group. Akodon caenosus is recognized as a species distinct of A. lutescens, A. orientalis is recognized as a species distinct of A. orophilus, and A. aerosus, A. baliolus and A. surdus are recognized as three separate species. Based upon chronophylogenetic analysis, the initial divergence within Akodon likely began during the late Pliocene and ancestors of the four extant species groups (aerosus, boliviensis, cursor and dolores) appeared around the Pleistocene–Pliocene boundary or shortly thereafter.

Akodon cursor(Rodentia: Cricetidae)

Akodon cursor (Winge, 1887) is a Sigmodontinae rodent commonly called the cursorial akodont. This small cursorial mouse has homogenous dorsal pelage that can range from dark to golden brown and it is 1 of 41 species in the genus Akodon. It is endemic to Brazil, South America, and is found in the Atlantic Forest, being the most abundant sigmodontine rodent of this large area. Deforestation within the range of A. cursor may not affect this species, because it is tolerant of human disturbance. Currently the International Union for Conservation of Nature and Natural Resources regards it as a species of “Least Concern.”

Akodon polopi Jayat et al., 2010 is a senior subjective synomym of Akodon viridescens Braun et al., 2010

Two new taxa of species level were recently named for grass mice of the genus Akodon (Cricetidae, Sigmodontinae) from central Argentina: Akodon polopi Jayat, Ortiz, Salazar-Bravo, Pardiñas et D’Elía, 2010 and Akodon viridescens Braun, Mares, Coyner et Van Den Bussche, 2010. Several lines of evidence show that both taxa refer to the same biological species.

No Differences in the Sry Gene between Males and XY Females in Akodon (Rodentia, Cricetidae)

Several species of the South American genus Akodon present fully fertile XY females besides XX ones. To analyze the possibility of a Sry mutation as the cause of sex reversal in A. azarae and A. boliviensis, we determined the sequence of the Sry gene in 2 males and 3 XY females from each of these species. The Sry gene sequence was also studied in A. dolores, a species that does not have XY females. In inter-specific comparisons, the percentage identities with respect to the region analyzed varied between 96.8% and 97.9%. An ORF of 543 nucleotides was identified, and the predicted Sry proteins comprised 180 amino acids, with an HMG domain of 83 amino acids. Our results indicate that female sex reversal in A. azarae and A. boliviensis cannot be explained by sequence differences in the Sry region analyzed here, which includes the complete ORF and, together with previous results concerning the inheritance of the XY condition, show that Sry mutation is not the basis of sex reversal.

Small-mammal consumption by sympatric canids in southern Brazil: niche overlap and prey selection

The crab-eating fox, Cerdocyon thous, and the pampas fox, Lycalopex gymnocercus, are two endemic canids from the neotropics that are sympatric in the Rio Grande do Sul State, southern Brazil. Previous studies indicated that both species feed mainly on small mammals, without marked differences between their diets, at least when small-mammal genera are not determined. In the present study, our objective was to evaluate the similarity in diet composition of those foxes, identifying the genera of small mammal consumed. Besides that, we also investigated potential patterns of prey selection by the canids. We analyzed 222 samples of fox feces from the National Park of Aparados da Serra (NPAS) in southern Brazil (29°10’S, 50°05’W) collected from 2000 to 2005. Fox species were determined by identification of hairs found in scats. We also conducted, between 2000 and 2002, a survey of small mammals using capture-mark-recapture techniques. Our results indicated that the species studied do not differ significantly in relation to the small mammals they consume. We also detected that both canids seem to prefer feeding on rodents of the genus Akodon. On the other hand, rodents of the genus Oligoryzomys were consumed less than would be expected. Our results indicated that prey similarity is very high for the studied canids, even under a more refined analysis of small-mammal preys. This pattern supports the suggestion that niche differentiation between C. thous and L. gymnocercus probably occurs through other mechanisms than diet (e.g. habitat or activity time). Key words: araucaria forest, cerdocyon thous, rodents, feeding habits, niche overlap, lycalopex gymnocercus.

Animal infections by vaccinia-like viruses in the state of Rio de Janeiro: an expanding disease

In the present study we investigated the presence of infections by vaccinia-like viruses in dairy cattle from 12 counties in the state of Rio de Janeiro in the last 9 years. Clinical specimens were collected from adult animals with vesicular/pustular lesions mainly in the udder and teats, and from calves with lesions around the nose and mouth. A plaque reduction neutralization test (PRNT) was applied to search for antibodies to Orthopoxvirus; the vesicular/pustular fluids and scabs were examined by PCR, electron microscopy (EM) and by inoculation in VERO cells for virus isolation. Antibodies to Orthopoxvirus were detected in most cases. The PCR test indicated a high nucleotide homology among the isolates and the vaccinia viruses (VACV) used as controls. By EM, typical orthopoxvirus particles were observed in some specimens. The agents isolated in tissue culture were confirmed as vaccinia-like viruses by EM and PCR. The HA gene of the vaccinia-like Cantagalo/IOC virus isolated in our laboratory was sequenced and compared with other vaccinia-like isolates, showing high homology with the original Cantagalo strain, both strains isolated in 1999 from dairy cattle. Antibodies to Orthopoxvirus were detected in one wild rodent (genus Akodon sp.) collected in the northwestern region of the state, indicating the circulation of poxvirus in this area. Nonetheless, PCR applied to tissue samples collected from the wild rodents were negative. Vesicular/pustular lesions in people in close contact with animals have been also recorded. Thus, the vaccinia-like virus infections in cattle and humans in the state seem to be an expanding condition, resulting in economic losses to dairy herds and leading to transient incapacitating human disease. Therefore, a possible immunization of the dairy cattle in the state should be carefully evaluated.

The use of PCR-RFLP as an identification tool for three closely related species of rodents of the genus Akodon (Sigmodontinae, Akodontini)

Three cryptic species of the rodent Akodon (A. cursor, A. montensis and Akodon sp.) were analyzed. The two former species are sympatric in the Brazilian states of Sao Paulo, Rio de Janeiro and Minas Gerais, where hybrids have already been found. The third species, Akodon sp., occurs in an isolated area in Central Brazil. The identification of these species is difficult by the need of living animals. At present, karyotyping is the only method used in the identification of specimens. We used PCR-RFLP of the mitochondrial cytochrome gene to test the distinctiveness of the three species, which was confirmed by the absence of shared species-specific haplotypes. We also detected a geographical pattern of haplotypes distribution with highly polymorphic populations of A. cursor from Espirito Santo and of A. montensis from Rio Grande do Sul.