Leila Maria Pessôa

Bootstrap Confidence Regions for Canonical Variates: Application to Studies of Evolutionary Differentiation

Theory recently developed to construct confidence regions based on the parametric bootstrap is applied to add inferential information to graphical displays of sample centroids in canonical variate analysis. Problems of morphometric differentiation among subspecies and species are addressed using numerical resampling procedures.

New species of Cerradomys from coastal sandy plains of southeastern Brazil (Cricetidae: Sigmodontinae)

Abstract A new species of Cerradomys is described from the sandy plains of the northeastern littoral of Rio de Janeiro State and the southern littoral of Espírito Santo State, southeastern Brazil. Morphological and karyological characters were used to distinguish the new taxon from the 3 closest related species: C. subflavus, C. vivoi, and C. langguthi. Skull differences include the relatively larger general size, pronounced crests, broader rostrum, broader lacrimals, and wider sphenopalatine vacuities. Canonical variate analyses based on craniometric data showed that the new species has little overlap with C. subflavus, C. vivoi, and C. langguthi in multivariate space. The pelage of the new species has a unique, sparser, and thinner aspect. The diploid number of 54 chromosomes and the autosomal fundamental number of 66 arms (the highest among the 3 related species), added to the morphology of both sexual chromosomes, are diagnostic for the new species. The new taxon is restricted to a particular section of the Brazilian littoral covered by a mosaic of open vegetation locally named restingas, where it is one of the most abundant terrestrial mammals. In the restingas of this region this species is associated more with shrub patches than more forested physiognomies, being captured both on ground and on tree branches, especially of Clusia trees, suggesting a degree of arboreality. The recognition of this species adds further biogeographic uniqueness to the restingas of the northeastern littoral of Rio de Janeiro and southern littoral of Espírito Santo.

Karyological and morphometric variation in the genus Thrichomys (Rodentia: Echimyidae)

Summary We describe two new karyotypes for the echimyid rodent genus Thrichomys , based on samples from the type locality of Thrichomys apereoides (Lund, 1839), Lagoa Santa, Minas Gerais, eastern Brazil, and from the north Pantanal region, near Cuiaba, state of Mato Grosso, western Brazil. These karyotypes are described using GTG- and CBG-banding and silver staining techniques, and compared with karyotypes from northeastern Brazil previously described for the genus. The karyotype of Thrichomys apereoides from Lagoa Santa shows 2n = 28 and FN 50, with constitutive heterochromatin showing pericentromeric bands in all autosomes except in two pairs, and nucleolar organizing regions (Ag-NOR sites) coincident with the secondary constriction on the short arm of pair two. The karyotype of the specimens from the north Pantanal region shows 2n = 34 and FN = 64, with C-bands restricted to the sexual chromosomes, whereas Ag-NOR sites are coincident with the secondary constrictions. A multivariate analysis of craniometric traits including the type series of Thrichomys apereoides (Lund) from Lagoa Santa, deposited in the Copenhagen Museum, the sample from the north Pantanal region (Mato Grosso) and a sample from Jaiba in the north of the state of Minas Gerais was also performed. The results show that the samples from the north Pantanal region and Lagoa Santa are completely separated from each other with respect to a main axis of variation summarizing cranial shape. These results, gauged by the analysis of the karyological variation among samples from different localities support the revalidation of Thrichomys pachyurus (Wagner, 1845).

Morphological variation in the appendicular skeleton of Atlantic Forest sigmodontine rodents.

Rodents of the subfamily Sigmodontinae comprise a highly diversified group in the Atlantic Forest, with semifossorial, terrestrial, semiaquatic, scansorial, and arboreal forms. In this study, we analyzed morphometric variation in humerus, scapula, ulna, radius, femur, tibia, and pelvis to investigate its possible relationship with the different types of locomotion recorded in the literature. Skeletal characters were measured in 321 specimens belonging to 29 species and 19 genera either restricted to or recorded in this ecoregion. Multivariate morphometric analyses (principal component and canonical variate analyses) arranged individuals of different genera in groups congruent with the different types of locomotion. This arrangement was more clearly defined when analyses included only forelimb measurements, indicating that most of the variation in appendicular traits associated with the different locomotor modes occurs in the forelimb skeleton. Semifossorial forms exhibited the most distinct appendicular morphology, as well as the greatest frequency of endemism among analyzed species. These results suggest that this mode of locomotion led to greater differentiation in semifossorial Atlantic forest sigmodontines than in terrestrial and arboreal forms, which were found to have more subtle differentiation and fewer endemics. Scansorial species could not be set apart from terrestrial ones in terms of appendicular morphology, suggesting that these two modes of locomotion are the most similar and generalized for the group, as they occur in most lineages in the subfamily. The results of this study corroborate previous observations on the relevance of appendicular characters in the differentiation of species and genera in the subfamily Sigmodontinae. J. Morphol. 2013.

Phylogenetic and size constrains on cranial ontogenetic allometry of spiny rats (Echimyidae, Rodentia).

Analysis of ontogenetic development is crucial for understanding the emergence of phenotypic discrepancies between animal taxa. The study of allometric trajectories within a phylogenetic context is a feasible approach to assess the morphological change across different evolutionary lineages. Here, we report the disparity of multivariate ontogenetic allometry in the Echimyidae, a taxonomically diverse rodent family, as well as the effects of size on the evolution of skull ontogeny. The ontogenetic trajectories of 15 echimyid operational taxonomic unities (12 genera plus one genus with three species) belonging to all subfamilies and major clades, when plotted in allometric space, revealed strong and significant phylogenetic signals. Allometric trajectories were found to be constrained by phylogenetic ancestry, with changes approximately adjusting to a Brownian motion model of evolution. Moreover, the occupation of allometric space by echimyid taxa was significantly correlated with adult size rather than with shape, suggesting that the variation in adult size might result in critically intrinsic and structural constraints on allometric coefficients. These findings disagreed with the hypothesis that allometric disparities might be mainly adaptive with undetectable phylogenetic signals.

Plio-Pleistocene history of the endangered spiny rat Trinomys eliasi (Echimyidae) from Rio de Janeiro, Brazil

Trinomys eliasi is an endangered species of spiny rat endemic to a small area in the lowlands of Rio de Janeiro state (Brazil). Limited data on its biology and variation are available for designing conservation policies. Here, we provide data on genetic variation of T. eliasi, elucidating aspects of its evolutionary differentiation based on analysis of cytochrome b DNA. Our findings showed that T. eliasi diverged from its sister species T. paratus in the early Pleistocene or late Pliocene (∼2.5 million years ago [mya]). Two T. eliasi mitochondrial lineages diverged in the early Pleistocene (∼2.1 mya) and are currently separated by a large river and Holocene areas previously occupied by a vast Pleistocene internal sea, which may have operated as a historical barrier between populations. The haplotypes of the southern lineage diverged relatively late in the Pleistocene (∼0.6 mya), and diversity of this lineage is not equally distributed across the landscape, but rather, it appears to be concentrated in the rainiest areas, which contain major forest remnants. This region should be considered a priority for conservation. In the northern extreme of Rio de Janeiro state, we found an isolated, highly divergent T. eliasi lineage, which deserves further investigation. This work highlights the need for fine-scale studies of genetic variation in endangered species for the preservation of their evolutionary diversity.

A new karyotype of Wiedomys pyrrhorhinus (Rodentia: Sigmodontinae) from Chapada Diamantina, northeastern Brazil

A new karyotype of Wiedomys pyrrhorhinus (Wied, 1821) is described, including G- and C-banding and Ag-NOR sites from specimens collected in the municipality of Morro do Chapeu, situated in the northern region of the Chapada Diamantina, state of Bahia. Karyological studies of W. pyrrhorhinus have shown a constant diploid number (2n) of 62 with two different numbers of autosomal arms (FNa): 86 and 90, respectively. The new karyotype revealed 2n = 62 and FNa = 104, being the higher autosomal number found so far for this genus. The X chromosome is a large acrocentric and the Y chromosome is a small acrocentric. The analysis of the karyotype morphology suggests that this new karyotype is more closely related to the previous karyotype with 2n = 62 and FNa = 90, described from Caetite, Bahia State. Further studies, comparing different populations of W. pyrrhorhinus, including molecular approaches, may help to better understand the geographical limits of each population and their phylogenetic relationships in the Caatinga biome

Systematics and Acceleration of Cranial Evolution in Cerradomys (Rodentia, Cricetidae, Sigmodontinae) of Quaternary Sandy Plains in Southeastern Brazil

The genus Cerradomys, comprising eight species, is distributed mainly in transitional, dry, open and inland South American biomes like Caatinga, Cerrado, and Chaco. However, Cerradomys goytaca is restricted to very harsh ecosystems along the Quaternary coast sandy plains (restingas) of the Rio de Janeiro and Espírito Santo states, in southeastern Brazil. Cytochrome b and IRBP DNA data were used for elucidating the phylogenetic relationships of Cerradomys and estimating the time of divergence of different evolutionary lineages, while morphometric analyses were carried out for analyzing the rate of phenotypic evolution. Our findings showed that the first speciation events occurred in the Pliocene and early Pleistocene, leading to the C. marinhus, C. maracajuensis, and C. scotti distributed in central and western Brazil while species from eastern Brazil (C. langguthi, C. vivoi, C. subflavus, and C. goytaca) originated in the middle to late Pleistocene. Cerradomys goytaca populations diverged from inland C. subflavus ca. 0.29 MYBP with an accelerated rate of phenotypic evolution resulting in unique craniometric attributes, likely due to the strong selective pressures imposed by harsh habitats.

Small mammals (Chiroptera, Didelphimorphia, and Rodentia) from Jaíba, middle Rio São Francisco, northern Minas Gerais State, Brazil

We report the results of small mammals inventories conducted in the region of Jaiba, northern Minas Gerais state, southeastern Brazil, from 1990 to 1995. This region is located in the southern limit of the Caatinga biome, and harbors a unique set of natural ecosystems and extensive agricultural areas. With a total effort of 2964 trap-nights and 44 net sessions, we captured 893 small mammals from 46 species, including four marsupials, 13 rodents, and 29 bats. We report on species that are endemic to the Caatinga (Wiedomys pyrrhorhinos and Xeronycteris vieirai), and species that are new to the mammal fauna of the state of Minas Gerais (Tonatia saurophila, X. vieirai, and Myotis lavali). We also provide the first valid voucher-supported record of Micronycteris sanborni from southeastern Brazil, and extend the known range of X. vieirai 800 km southward. All bats highlighted here as endemic or representing new records were associated to limestone outcrops, suggesting that preservation of this kind of habitat may be particularly relevant to the conservation of these mammals.

Allometric Patterns and Evolution in Neotropical Nectar-Feeding Bats (Chiroptera, Phyllostomidae)

Within the neotropical bat family Phyllostomidae, species of the subfamilies Glossophaginae and Lonchophyllinae have many derived traits adapted to nectarivory, including elongated snouts and jaws and the ability to perform hovering flight. We compared patterns of cranial variation within and between these groups with respect to within-group allometric trajectories, based on 19 linear morphometric variables collected from 221 specimens representing all genera and 62% of the species in the two subfamilies. In a pooled principal component analysis, species belonging to Lonchophyllinae and Glossophaginae occupy similar regions in morphospace, though the latter species have a greater variance. Principal components and common principal components analyses for separate taxonomic lineages (subfamilies, tribes and subtribes) revealed distinct static allometric trajectories among these groups, with variables associated with elongation of the rostrum having distinct allometric coefficients. Our results indicate that distinct cranial morphotypes associated with the degree of elongation of the rostrum in phyllostomid nectarivores are allometrically characteristic of each lineage. The patterns suggest that cranial integration in phyllostomid nectarivores reflects primarily their phylogenetic history rather than adaptive pressures resulting from specialization to particular feeding resources.