Sigmodontines comprise one of the most diverse radiations of mammals. The cranial ontogeny has been studied in several mammals, but remains poorly studied in the group. We quantified the ontogenetic pattern for 22 sigmodontine species and 8 outgroups, generating partial reconstructions of ancestral allometric growth patterns, and testing the role of evolutionary history on cranial ontogeny. Sigmodontines were conservative in growth pattern, without unique patterns defining tribes. The allometric growth of the cranium was mostly negative, with Akodontini being the most isometric and Phyllotini the most allometric tribes. Allometry of variables associated with the neurocranium was mostly negative, while those linked to trophic functions showed positive allometry or isometry. A general cranial lengthening was detected, but variables associated with cranial width or height grew at lower rates. Cranial growth and development were associated with changes in the musculature functionally involved in bite and mastication. Most changes occurred in earlier postnatal stages, achieving an early morphological optimum. Few changes in the rate of growth at internal nodes were detected, and the stasis along the backbone was recurrent. Cranial elongation was a pattern widespread in the sample and likely a plesiomorphic condition. The few synapomorphies defining the ancestor of Sigmodontinae conform to a pattern with zygomatic arches little expanded laterally and globose braincases. The conservative pattern may be attributed to the biomechanically optimal morphology for omnivorous diets, suggesting that the generalized morphology allows the exploitation of multiple types of food with minor morphological adjustments.
The taxonomic history of Euryoryzomys legatus has been complex and controversial, being either included in the synonymy of other oryzomyine species or considered as a valid species, as in the most recent review of the genus. Previous phylogenetic analyses segregated E. legatus from E. russatus, its putative senior synonym, but recovered it nested within E. nitidus. A general lack of authoritative evaluation of morphological attributes, details of the chromosome complement, or other data types has hampered the ability to choose among alternative taxonomic hypotheses, and thus reach a general consensus for the status of the taxon. Herein we revisit the status of E. legatus using an integrated approach that includes: (1) a morphological review, especially centered on specimens from northwestern Argentina not examined previously, (2) comparative cytogenetics, and (3) phylogenetic reconstruction, using mitochondrial genes. Euryoryzomys legatus is morphologically and phylogenetically distinct from all other species-level taxa in the genus, but its 2n=80, FN=86 karyotype is shared with E. emmonsae, E. nitidus, and E. russatus. Several morphological and morphometric characters distinguish E. legatus from other species of Euryoryzomys, and we provide an amended diagnosis for the species. Morphological characters useful in distinguishing E. legatus from E. nitidus, its sister taxon following molecular analyses, include: larger overall size, dorsal fur with a strong yellowish brown to orange brown tinge, flanks and cheeks with an orange lateral line, ventral color grayish-white with pure white hairs present only on the chin, presence of a thin blackish eye-ring, tail bicolored, presence of an alisphenoid strut and a well-developed temporal and lambdoid crests in the skull, and a labial cingulum on M3. Molecular phylogenetic analyses recovered E. legatus as a monophyletic group with high support nested within a paraphyletic E. nitidus; genetic distances segregated members of both species, except for an exemplar of E. nitidus. Our integrated analyses reinforce E. legatus as a full species, but highlight that E. macconnelli, E. emmonsae, and E. nitidus each may be a species complex and worthy of systematic attention. Finally, we also evaluated the chromosome evolution of the genus within a phylogenetic context.
The genus Microcavia includes six species of terrestrial, medium-sized, living cavies that occupy arid to semiarid environments at both high and low elevations in western and southern South America. Among these, Microcavia shiptoni is one of the least known species, being recorded only at two isolated localities from northwestern Argentina. Genetic information and a detailed morphological characterization are lacking for this elusive species. In this work, we start filling these gaps by including M. shiptoni in a phylogenetic analysis based on mitochondrial DNA sequences that includes five of the six currently recognized species and place M. shiptoni as sister to M. niata in a clade of highland species. In addition, using both qualitative and quantitative morphological traits, we provided an emended diagnosis for this taxon and a key for the living species of the genus. Finally, we present, the first notes on the natural history of this species.
New geographic distribution records for ten species of sigmodontine rodents (Rodentia: Cricetidae) from Northwestern Argentina. The Sigmodontinae have radiated to encompass all the terrestrial environments and a wide altitudinal gradient through its large geographic distribution. In Northwestern Argentina (NWA) this group constitutes approximately 30% of the mammals of the region. Several works in the last years have contributed to the knowledge of the geographic distribution of the sigmodontine rodents in NWA. Notwithstanding, many of the species are known only by old and scarce records, most of them heavily biased towards more accessible areas. From surveys conducted in the last three years in the area, which include captures and collections of pellets samples of strigiform birds, in this work we report novel distribution records for the species in this group. We contribute with new record for ten species and eight localities. The new records include the addition of Abrothrix illutea and Oxymycterus wayku for Salta province and Andalgalomys cf. A. olrogi for La Rioja province, the first mentions of Calomys lepidus and Phyllotis tucumanus in high altitudinal grasslands located in Monte de Sierras y Bolsones and Akodon boliviensis in the Puna of Argentina, and several distributional records for Abrothrix andina, Neotomys ebriosus, P. anitae, and Reithrodon auritus, four species not well documented in the study area. Finally, we discussed some methodological and taxonomic aspects, and the relevance of each one of the obtained records.
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