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The genus Octodontomys contains only a single species, Octodontomys gliroides (P. Gervais and d'Orbigny, 1844), the mountain degu, found in Andean and Sub-Andean regions of 3 countries, Argentina, Bolivia, and Chile, from elevations of about 1,200-4,400 m. This fossorial octodontid is typical of dry areas, inhabits rocky zones, and is active during the day and the first few hours of night. It is not of special conservation status, being common throughout its distribution, and is considered a species of "Least Concern." [ABSTRACT FROM AUTHOR]

The genome of the red vizcacha rat (Rodentia, Octodontidae, Tympanoctomys barrerae) is the largest of all mammals, and about double the size of their close relative, the mountain vizcacha rat Octomys mimax, even though the lineages that gave rise to these species diverged from each other only about 5Ma. The mechanism for this rapid genome expansion is controversial, and hypothesized to be a consequence of whole genome duplication or accumulation of repetitive elements. To test these alternative but nonexclusive hypotheses, we gathered and evaluated evidence from whole transcriptome and whole genome sequences of T. barrerae and O. mimax. We recovered support for genome expansion due to accumulation of a diverse assemblage of repetitive elements, which represent about one half and one fifth of the genomes of T. barrerae and O. mimax, respectively, but we found no strong signal of whole genome duplication. In both species, repetitive sequences were rare in transcribed regions as compared with the rest of the genome, and mostly had no close match to annotated repetitive sequences from other rodents. These findings raise new questions about the genomic dynamics of these repetitive elements, their connection to widespread chromosomal fissions that occurred in the T. barrerae ancestor, and their fitness effects--including during the evolution of hypersaline dietary tolerance in T. barrerae. [ABSTRACT FROM AUTHOR]

Octodon (Octodontidae) is an endemic genus of rodents that is typical of southwestern South America and represented by 4 species. Octodon pacificus, commonly referred to as the Mocha Island degu, was initially described from specimens collected in 1959 at Mocha Island, a small coastal island located along the central coast of Chile. Fifty-seven years after its original collection, we report the discovery of a female O. pacificus carcass, identified by its morphological characteristics and its specific locality. In addition, based on the cytochrome b (Cytb) gene of the mitochondrial DNA obtained from O. pacificus and other congeneric species, we assessed phylogenetic relationships within the Octodontidae. Bayesian phylogenetic reconstruction indicated that O. degus represented the basal Octodon sp., followed by O. lunatus; O. bridgesii and O. pacificus were identified as sister taxa. Remarkably, the genetic divergence between O. bridgesii and O. pacificus is low, which suggests that 1 of 2 scenarios may be at play: the occurrence of a recent peripatric speciation process in O. pacificus, or the presence of O. bridgesii on Mocha Island. Documented collections of archeozoological material obtained from Mocha Island only include specimens of O. pacificus, a finding that supports our 1st proposed scenario. While the core of Mocha Island is a national reserve, strong anthropogenic landscape modifications have affected the coastal plains-the only known habitat of O. pacificus. Rodent control using killing traps and poison is a common practice on the island; therefore, population surveys and conservation initiatives are needed to conserve this endangered species. [ABSTRACT FROM AUTHOR]

Multiple ecological factors are known to drive variation in social behavior. However, group-living in some species appears to be highly conserved, suggesting a phylogenetic influence. In this study, we evaluated both scenarios using intraspecific and interspecific comparisons across octodontid rodents. We first examined 2 different populations of Andean degu ( Octodontomys gliroides), representing 2 extremes of a climate vegetation gradient across the Andes range. We evaluated how ecological variation in terms of abundance and distribution of food resources, predation risk, and burrowing costs predicted interpopulation variation in group size and range-area overlap (2 proxies of sociality). We estimated these measures of sociality from livetrapping and radiotelemetry. We then used phylogenetic methods to determine whether sociality exhibits a phylogenetic signal and reconstructed the ancestral state of sociality across the family Octodontidae. Overall activity of females and males of O. gliroides was greater during nighttime than daytime. Across populations we found significant differences in ecology, including abundance and distribution of food, predation risk, and burrowing costs. However, populations were similar in terms of group size and range-area overlap. The phylogenetic approach revealed a strong and significant phylogenetic signal associated with sociality, where this behavior was present early during the evolution of octodontid rodents. Together, these findings imply that sociality of O. gliroides is not linked to current population differences in ecology. La variación en la conducta social ha sido atribuida a múltiples factores ecológicos. Sin embargo, la vida en grupo en algunas especies es un rasgo altamente conservado, sugiriendo una influencia filogenética. En este estudio, se evaluó ambos escenarios usando comparaciones intraespecíficas e interespecíficas a través de roedores octodóntidos. En primer lugar se evaluaron 2 poblaciones de degu Andino ( Octodontomys gliroides) que representan 2 extremos de un gradiente climático y de vegetación a través de la Cordillera de los Andes. Se evaluó como la variación en términos de abundancia y distribución de recursos alimenticios, riesgo de depredación, y costos asociados a cavar madrigueras podrían predecir la variación interpoblacional en tamaño de grupo y solapamiento del ámbito de hogar (2 medidas de sociabilidad). Estas medidas fueron estimadas con datos de trampeo y radiotelemetría. Además, se utilizaron métodos filogenéticos para determinar si el rasgo social presenta señal filogenética, y de esta manera reconstruir el estado ancestral de la sociabilidad a través de la familia Octodontidae. Se encontraron diferencias estadísticamente significativas entre las poblaciones en términos de ecología, incluyendo abundancia y distribución de recursos alimenticios, riesgo de depredación, costos asociados a cavar madrigueras. Sin embargo, el tamaño de grupo y solapamiento del ámbito de hogar fueron similares entre ambas poblaciones. El análisis filogenético reveló una fuerte y significativa señal filogenética asociada a la sociabilidad, y que esta conducta estuvo presente temprano en la evolución de los roedores octodóntidos. En conjunto, estos resultados implican que la vida en grupo en O. gliroides no está relacionada a las diferencias en ecología en las poblaciones actuales. [ABSTRACT FROM AUTHOR]

The evolution of sociality across octodontid rodents remains puzzling. Although basal species are solitary living, the most derived octodontids studied so far are social, implying that sociality evolved recently from solitary- living ancestors. However, the social behavior of some octodontids remains anecdotal. We aimed to provide the 1st systematic data on activity, space use, and social behavior of the moon-toothed degu (Octodon lunatus), a derived octodontid rodent. We used livetrapping and radiotelemetry to monitor patterns of aboveground activity, aboveground range areas and overlap, and use of resting locations in a coastal population in north-central Chile. Activity of O. lunatus was statistically similar during nighttime and daytime, implying no clear diurnal or nocturnal activity. During daytime the animals used resting locations that were associated with high shrub cover and Pouteria splendens. Radiocollared males and females shared resting locations on multiple occasions. There was a nonsignificant trend in degus that used same resting locations to exhibit greater range overlap than degus using different resting locations. Associations based on resting locations revealed a total of 5 social groups. Taken together, these results indicate that adult O. lunatus exhibit some sociality, a finding consistent with a trend in which group living is more frequent in the most derived compared with basal octodontids. [ABSTRACT FROM AUTHOR]

A new living species of the desert-adapted tetraploid rodent Tympanoctomys (Caviomorpha, Octodontidae) is described. The new form is restricted to the type locality in Chubut Province, central Patagonia, Argentina, although is known from at least 4 additional Holocene-aged localities along the middle and lower valley of the Chubut River. Tympanoctomys sp. nov. is smaller than the living T. barrerae, its general coloration is yellowish (reddish in T. barrerae) and its tail is equal to ~43-50% of head and body length (,~049-53% in T. barrerae). Its skull and dentition are characterized by a unique combination of morphological traits, including narrow and posteriorly acuminate nasals (broad and barrel-shaped in T. barrerae), supraoccipital not laterally expanded (expanded in T. barrerae), and 8-shaped lower 3rd molar (comma-shaped in T. barrerae and †T. cordubensis). Morphometric and genetic evidence supports the specific distinction of this Patagonian endemic Tympanoctomys, also characterized by smaller sperm than T. barrerae. The reduced range of the new species, coupled with its recent extinction from the Chubut River valley and the potential impact of large uranium mining projects in central Patagonia, suggest that this species faces a severe extinction risk in the short term. [ABSTRACT FROM AUTHOR]

The allotetraploid Tympanoctomys barrerae has a broad, patchy distribution around salt flats in western Argentina. To gain insights into its phylogenetic relationships, phylogeographical patterns, and origin, seven populations of T. barrerae and its allied taxa were studied through a 1075-bp fragment of cytochrome b and cytochrome oxidase I. Matrilineal phylogenetic relationships were explored with maximum likelihood and Bayesian approaches. The intraspecific genealogy was inferred by median-joining networks. The populational structure was assessed by molecular variance, and the demographic history through coalescence. The tree topology depicted sister-group relationship between Octomys mimax to the pair T. barrerae-Pipanacoctomys aureus, suggesting P. aureus belongs to the maternal lineage that gave rise to T. barrerae. High degrees of intrapopulational variation and the several instances of interpopulational polyphyly suggest range shifts and secondary contact. Consistent with the phylogenetic results, the network analysis revealed two haplotypic lineages depicting genetic admixtures unrelated to the current geographical distribution, and a deep split with the southernmost lineage of Chubut. The origin of T barrerae was estimated at approximately 2.52 Mya, whereas the divergence estimate for Chubut coincides with the end of largest Patagonian glaciation, at 1.47 Mya. Apparently, this population remained isolated during a northward Pleistocenic range shift. The historical demographic patterns of the lineages of T. barrerae fit with a contraction-expansion model coincident with Quaternary cycling events. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 108, 453-469. [ABSTRACT FROM AUTHOR]

Octomys mimax O. Thomas, 1920, the viscacha rat, is a surface-dwelling rodent, endemic to the Monte biome of western Argentina. The genus Octomys is monotypic and represents a basal clade within the family Octodontidae. O. mimax is strictly herbivorous and is found in low-elevation arid environments characterized by galleries or rock formations. In these environments, O. mimax nests within rock crevices located inside ravines with relatively low vegetation cover. O. mimax is solitary and mostly nocturnal. Nocturnal activity coupled with a basal metabolic rate and thermal conductance lower than expected for body mass of O. mimax probably represent strategies for water conservation in this species. [ABSTRACT FROM AUTHOR]

The red viscacha rat, Tympanoctomys barrerae, is an octodontid rodent endemic to the arid west-central and southern regions of Argentina. It is solitary, lives in complex burrows built in soft soil, and occurs at low population densities in patches associated with salt basins and sand dunes in lowland habitats of the Monte and Patagonia deserts. The purpose of this study was to investigate the genetic structure and biogeography of this desert specialist. To assess genetic variation an 800-base pair fragment of the mitochondrial control region was sequenced for 60 individuals from 8 localities across the species' range. Relationships among haplotypes were inferred from phylogenetic analyses (maximum parsimony, Bayesian, and networks). Genetic structure and demographic history were analyzed with descriptive statistics, mismatch distributions, neutrality tests (Tajima's and Fu's), and analyses of molecular variance (AMOVAs). In total, 26 haplotypes were found, most restricted to single populations. The presence of unshared haplotypes was consistent with low migration rates. Within the distribution (between 29°S and 39°S) southern and northern populations showed higher genetic diversity values than central populations. Populations of T. barrerae showed moderate to high genetic differentiation on the basis of haplotypes of central populations. AMOVA analyses indicated a moderate level of geographic structure for all populations. Low haplotype and nucleotide diversities in central populations suggest a possible bottleneck associated with Pleistocene glaciations or volcanic activity in this part of the range of the viscacha rat. Phylogeographic structure was moderate, and the analyses recovered 2 principal clades: A (with central and a part of the southern distribution) and B (with northern and another part of the southern distribution). Most populations were polyphyletic, indicating that they have not been isolated long enough to reach reciprocal monophyly. Demographic analyses conducted for clades A and B suggest a recent history of population expansion. [ABSTRACT FROM AUTHOR]

To examine the evolution of burrowing specializations in the sister families Octodontidae and Ctenomyidae (Rodentia: Caviomorpha), we produced a synthetic phylogeny (supertree), combining both molecular and morphological phylogenies, and including both fossil and extant genera. We mapped morphological specializations of the digging apparatus onto our phylogenetic hypothesis and attempted to match morphological diversity with information on the ecology and behaviour of octodontoid taxa. Burrowing for sheltering and rearing is the rule among octodontids and ctenomyids, and adaptations for digging have been known from the Early Pliocene onward. However, only a few taxa have evolved fully subterranean habits. Scratch-digging is widespread among both semifossorial and fully subterranean lineages, and morphological changes associated with scratch-digging are not restricted to subterranean lineages. By contrast, various adaptations for chisel-tooth digging are restricted to some subterranean lineages and are combined differently in the octodontid Spalacopus, the fossil ctenomyid Eucelophorus, and some living Ctenomys. Some octodontid taxa are able to dig complex burrows in spite of having no substantial changes in musculoskeletal attributes. Hence, we suggest that, during the early evolution of those branches giving rise to fully subterranean ctenomyids and octodontids, a change in behaviour probably preceded the origin of structural adaptations. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95, 267–283. [ABSTRACT FROM AUTHOR]

Spalacopus cyanus is a subterranean rodent inhabiting coastal and mountain habitats. Individuals from mountain populations are larger than individuals from the coast, and mountain populations have a more limited geographic range. To investigate the genetic structure and biogeography of this species, we analyzed mitochondrial DNA control region sequences. We found low levels of nucleotide diversity in comparison with other subterranean rodents. Coastal populations had higher nucleotide diversity and effective population size than mountain populations. Phylogenetic analysis using maximum parsimony and a haplotype network generated using statistical parsimony recognized 3 groups of haplotypes: northern coastal and mountain populations, central coastal populations, and southern coastal population. Consistent with the presence of unshared haplotypes, migration rates were practically 0, except from Valparaíso to Ventanas and from La Parva to Huentelauquén. We observed asymmetric migration rates from mountain to coastal populations, suggesting that this species originated in the Andean mountains. A likelihood ratio test could not reject the null hypothesis of a stable population when all sequences were grouped into a single population and when coastal populations were analyzed separately. However, a negative exponential growth parameter was estimated for mountain populations, suggesting that these populations have undergone recent demographic changes. [ABSTRACT FROM AUTHOR]

The discovery of tetraploidy in the red viscacha rat, Tympanoctomys barrerae (4 n = 102) has emphasized the evolutionary role of genome duplication in mammals. The tetraploid status of this species is corroborated here by in situ PCR and Southern blot analysis of a single-copy gene. The species meiotic configuration strongly suggests a hybrid derivation. To investigate the origin of T. barrerae further, the recently described Pipanacoctomys aureus was studied. This 92-chromosome species also has a duplicated genome size, redundant gene copy number and diploid-like meiotic pairing, consistent with an event of allotetraploidization. Phylogenetic analysis of mitochondrial sequences indicates sister-group relationships between these two tetraploid rodents. The new karyotypic data and the phylogenetic relationships suggest the participation of the ancestral lineages of Octomys mimax in the genesis of P. aureus. The high overall DNA similarity and shared band homology revealed by genomic Southern hybridization as well as matching chromosome numbers between O. mimax and the descendant tetraploid species support the notion of introgressive hybridization between these taxa. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82, 443–451. [ABSTRACT FROM AUTHOR]

Molecular phylogenetic relationships were investigated in 6 species of Chinchillidae (Chinchilla lanigera, C. brevicaudata, Lagidium peruanum, L. viscacia, L. wolffsohni, and Lagostomus maximus), 1 species of Dinomyidae (Dinomys branickii), 1 of Abrocomidae (Abrocoma cinerea), and 1 of Octodontidae (Octodon degus) using the first 548 base pairs of the mitochondrial cytochrome-b gene. Maximum-parsimony and maximum-likelihood analyses consistently showed Chinchillidae as a robust clade and confirmed a close relationship with Dinomyidae. Both Chinchilla species differed at 22 sites, and 3 were nonsilent; average genetic distances were approximately 6%. Sequences from domestic C. lanigera and wild C. brevicaudata showed low levels of variation. Although all topologies obtained were congruent with current taxonomy, Lagidium exhibited large genetic distances (range 5.9-8.9%), suggesting the existence of more than the 3 species currently recognized. [ABSTRACT FROM AUTHOR]

The middle ear of the solitary subterranean rodent Ctenomys talarum was studied. The most significant features observed were the enlarged middle-ear cavity, a round and larger eardrum without pars flaccida, no connection between malleus and the tympanic bone, partial fusion of malleus with incus, a nearly flat stapedial footplate, absence of stapedial artery, reduced tensor tympani, and absence of stapedial muscle. Some of these features are shared with unrelated subterranean rodents like Spalax ehrenbergi and geomyids, possibly as adaptations for low-frequency hearing. [ABSTRACT FROM AUTHOR]

Presents a study which investigated the daily patterns of activity of coruros under laboratory conditions, Spalacopus cyanus. Discussion of subterranean mammals; Materials and methods; Results and discussion.

Presents a study which examined the morphological and functional variations in jaws of coastal and mountain populations of subterranean Spalacopus cyanus inhabiting soils with contrasting hardness. Information on Spalacopus cyanus; Materials and methods; Results and discussion.