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Morphological evolution and biogeography of Neotropical rodents

Goal: To investigate ecomorphology, macroevolution, macroecology and biogeography of Neotropical rodents. Emphasis on Sigmodontinae and Ctenomys.

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Renan Maestri
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Investigations of phenotypic disparity across geography often ignore macroevolutionary processes. As a corollary, the random null expectations to which disparity is compared and interpreted may be unrealistic. We tackle this issue by representing, in geographical space, distinct processes of phenotypic evolution underlying ecological disparity. Under divergent natural selection, assemblages in a given region should have empirical disparity higher than expected under an evolutionarily‐oriented null model, while the opposite may indicate constraints on phenotypic evolution. We gathered phylogenies, biogeographic distributions, and data on the skull morphology of sigmodontine rodents to discover which regions of the Neotropics were more influenced by divergent, neutral, or constrained phenotypic evolution. We found that regions with higher disparity than expected by the evolutionary‐oriented null model, in terms of both size and shape, were concentrated in the Atlantic Forest, suggesting a larger role for divergent natural selection there. Phenotypic disparity in the rest of South America, mainly the Amazon basin, northeastern Brazil and Southern Andes, was constrained — lower than predicted by the evolutionary model. We also demonstrated equivalence between the disparity produced by randomization‐based null models and constrained‐evolution null models. Therefore, including evolutionary simulations into the null modeling framework used in ecophylogenetics can strengthen inferences on the processes underlying phenotypic evolution. This article is protected by copyright. All rights reserved
Renan Maestri
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We evaluated whether evolution is faster at ecotones as niche shifts may be needed to persist under unstable environment. We mapped diet evolution along the evolutionary history of 350 sigmodontine species. Mapping was used in three new tip-based metrics of trait evolution – Transition Rates, Stasis Time, and Last Transition Time – which were spatialized at the assemblage level (aTR, aST, aTL). Assemblages were obtained by superimposing range maps on points located at core and ecotone of the 93 South American ecoregions. Using Linear Mixed Models, we tested whether ecotones have species with more changes from the ancestral diet (higher aTR), have maintained the current diet for a shorter time (lower aST), and have more recent transitions to the current diet (lower aLT) than cores. We found lower aTR, and higher aST and aLT at ecotones than at cores. Although ecotones are more heterogeneous, both environmentally and in relation to selection pressures they exert on organisms, ecotone species change little from the ancestral diet as generalist habits are necessary toward feeding in ephemeral environments. The need to incorporate phylogenetic uncertainty in tip-based metrics was evident from large uncertainty detected. Our study integrates ecology and evolution by analyzing how fast trait evolution is across space.
Renan Maestri
added 2 research items
The genus Ctenomys is comprised of more than 70 valid living species. It is the largest collection of fossorial mammals that occupy underground habitats, mainly in the grasslands of South America. We investigated different aspects of morphological evolution in the genus Ctenomys, with special attention to the skull. We analyzed 1359 craniums and 830 mandibles of 49 species of Ctenomys. We used geometric morphometric approaches to quantify this morphological diversity across its range. We found geographical structuring in skull shape among the eight clades of Ctenomys structured along east-west and north-south morphological gradients. We observed that many species from the extreme north of the distribution had a robust skull shape, whereas the southern ones had a gracile skull shape. Such structural differences may be following an environmental gradient. The mandible is less variable in shape than the cranium. We found high morphological variation within each of the eight clades and a geographical structuring. The subterranean niche is not homogeneous across space, and morphological adaptation of subterranean species occurs following this spatial gradient.
Tuco-tucos (Ctenomys sp.) are the most speciose genus of octodontoid rodent and are widely distributed in the southern half of South America. Despite their diversity, species of tuco-tucos rarely co-occur in syntopy and most adjacent species pairs are thought to be contiguously allopatric. Greater understanding of their geographic patterns of species diversity, range size, and body size distribution may provide insights on Ctenomys biogeography. In this chapter, we explored spatial patterns of species richness, geographic range size, and body size of tuco-tucos. We recovered a center of geographic range overlap in northern Argentina, and verified that tuco-tucos have a small range size when compared to other caviomorph families. However, we investigated range exclusivity – the proportion of a species range that is not shared with its congeners – and found that the exclusivity of Ctenomys ranges is comparable to that in other species-rich genera of caviomorphs. This finding challenges the idea that tuco-tuco species have a higher degree of allopatry than other genera. The body size distribution of tuco-tucos is right-skewed, as in other mammal groups, and negatively correlated with latitude, as previously documented. Relationships between richness, range size, and body size with geographical variables were presented and briefly discussed.
Renan Maestri
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This book examines the biology of tuco-tucos (Ctenomys) from an evolutionary perspective. Historically, these subterranean rodents have long attracted the attention of scientists due to its remarkable chromosomes variability and rapid diversification. A wealth of knowledge on physiology, ecology, genetics, morphology, paleontology, and taxonomy has been documented in the last 70 years through numerous single publications. In this volume, expert investigators review and frame these essays with the breadth of current understanding. The collection of chapters are presented into the major topics: i) Evolution of Ctenomys, ii) Geographic Patterns, iii) Organismal Biology, and iv) Environmental Relationships. Given its scope, the book will be of interest to both students and researchers and may stimulate further research with this exciting model on a wide range of evolutionary topics.
Renan Maestri
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Evolutionary constraints and ecological pressures influence species’ morphological diversity. The aim of this study was to explore patterns of morphological variation, to investigate the influence of environmental variables on morphological differentiation, and assess the strength of phylogenetic signal for the cranium and mandible in spiny rats of the genus Trinomys. We examined 377 crania and mandibles of all species of the genus Trinomys. We used geometric morphometric methods based on two-dimensional anatomical landmarks to describe cranium and mandible shape and size. Phylogenetic signal was tested using the K statistics and associations between morphology and environmental variables were made using a phylogenetic partial least squares analysis. We found marked differences in size and shape in the synchranium among species, especially in the segregation of T. albispinus and T. yonenagae from the other species, which in turn greatly overlapped both in size and shape spaces. We found a weak phylogenetic signal for size of the synchranium and intermediate phylogenetic signals for shape, a pattern similar to other studies. Differentiation of the synchranium shape in Trinomys was associated largely with precipitation-related variables, while the association between size and environmental variables was weak. Notably, Trinomys species inhabiting xeric environments had relatively larger tympanic bullae.
Bruce D Patterson
added a research item
The mandible of vertebrates serves as insertion area for masticatory muscles that originate on the skull, and its functional properties are subject to selective forces related to trophic ecology. The efficiency of masticatory muscles can be measured as mechanical advantage on the mandible, which, in turn, has the property of correlating with bite force and shape. In the present work, we quantify the mechanical advantage of the mandible of akodontine rodents, which present a diverse radiation of insectivorous specialists, to assess their relationship to the estimated bite force and diet. We also tested the degree of morphofunctional convergence in response to insectivory on the group. We found the mechanical advantages to be convergent on insectivorous species, and associated with the estimated bite force, with higher mechanical advantages in species with a stronger bite and short, robust mandibles, and lower mechanical advantages in insectivorous species with weaker bites and more elongated, dorso‐ventrally compressed mandibles. Insectivorous species of Akodontini are functional specialists for the consumption of live prey and may exploit the resources that shrews, moles, and hedgehogs consume elsewhere.
Bruce D Patterson
added a research item
Stable isotope analyses are frequently used to study trophic interactions, diet, and community processes, but they have seldom been applied to investigate the trophic niche structure of entire clades. In this paper, we assess stable isotopes information in a phylogenetic context to evaluate trophic evolution across the phylogeny of a diversified group of Neotropical cricetid rodents. A total of 139 hair samples of 47 species of Akodontini rodents were collected from five museum mammal collections and submitted to stable isotope analyses for δ13C and δ15N values. The resulting isotopic values were compared among the four main clades within the tribe. The phylogenetic signal of isotope values was estimated using a phylogenetic tree of Akodontini. Our results corroborate previous impressions that, in general, akodontines include more animal matter in their diet than other Neotropical rodents, but the lack of information for some species precludes more specific inferences. Some species appear to have relatively restricted niches, but the large variance observed in other species may be related to dietary and habitat differences related to ecological factors throughout the distribution of wide-ranging species. We found low phylogenetic signal for δ13C and δ15N values, suggesting that different regions within the isotopic niche space were occupied independently many times throughout akodontine evolutionary history. The δ13C/δ15N bi-plot indicates that the four main lineages occupy the trophic niche space in similar ways, although differing in trophic diversity. Our results represent new ecological information and an approach that can be useful in studying the evolution of trophic niches, and highlight the importance of museum specimen-based research for evolutionary ecology studies.
Renan Maestri
added 3 research items
We recorded three individuals of Abrawayaomys ruschii Cunha & Cruz, 1979 in Chapecó, Santa Catarina state, expanding the known geographic distribution of the species in approximately 370 km west from its nearest locality. It is the second record of the species in this type of physiognomy, characterized by the transition of Seasonal Deciduous and Mixed Ombrophilous forests. Additionally, this is the closest record, about 200 km east, from the recently described Abr-awayaomys chebezi Pardiñas, Teta & D'Elía, 2009.
Juliomys ossitenuis Costa, Pavan, Leite and Fagundes, 2007 was previously known in Brazil from the Atlantic Forest of the Southeastern Region to the Dense Ombrophilous Forest and Araucaria Forest of the Southern Region. The new record from Chapecó, in Santa Catarina state, confirmed by morphological and cytogenetic analyses, extends its distribution about 300 km westwards. This is the westernmost record for the species, in a region characterized by the transition between deciduous and Araucaria forests.
The Atlantic Forest is the second most diverse forest system in South America, and only a fraction of its original distribution remains. In this study, we aim to use robust datasets of small mammals along the entire forest system to disentangle the main drivers for diversity along this gradient. More specifically, we aim to disentangle whether deforestation (recent), biogeographical variables, including 19 bioclimatic variables (historic), or historical trapping bias best describe patterns of taxonomic, functional, and phylogenetic diversities using small mammal assembles, from northeastern Brazil to eastern Paraguay. For that, we applied regression tree analyses to determine what environmental variables best describe each of the dimensions of diversity. Additionally, we implemented polynomial regression to test nonlinear relationships between biodiversity metrics and patch size. We found that patterns of overall taxonomic, functional, and phylogenetic diversities; rodent taxonomic diversity; and marsupial functional diversity were better explained by temperature variables. Meanwhile, marsupial taxonomic and phylogenetic diversities, and rodent functional and phylogenetic diversities were best explained by precipitation variables. Furthermore, patch area, trapping, and latitude were never the best descriptors for any of the diversity dimensions. Although all dimensions of biodiversity are correlated, they have unique information and should be considered individually to better understand biodiversity and inform conservation strategies. We found that fragmentation is impactful at a local scale and becomes less important at a biogeographical scale. Therefore, climatic variables drove biogeographical faunal patterns for all clades, probably reflecting important historical assembly process at large spatial scales.
Bruce D Patterson
added a research item
Necromys is a genus of sigmodontine rodent that inhabits grasslands and scrublands in South America. Eight extant species are recognized in the genus; one of these is Necromys lactens, which inhabits high-elevation grasslands in the Yungas from south-central Bolivia to northwestern Argentina. Morphological variation in N. lactens has been recognized by the description of three nominal forms. Geographically structured genetic diversity also has been observed, but a thorough revision of these nominal forms within an integrative framework has yet to be performed. We conducted a phylogeographic assessment based on an 801 base-pair fragment of the cytochrome-b gene that guided morphometric analyses (univariate and multivariate comparisons) of patterns of geographic variation in the species, and the distinction of its nominal forms. Haplotypes of N. lactens form a well-supported and geographically structured clade. Within it, there are two main clades; haplotypes from the northern range form a well-supported clade, sister and allopatric to a weakly supported southern clade, which includes variants collected at or near the type localities of three nominal forms. In turn, both main clades are composed by two allopatric subclades. Morphometric analyses indicated no differences in shape of the skull among the three nominal forms or between the recovered clades and subclades. Taking together all the available evidence, we consider N. lactens to be a monotypic species.
Renan Maestri
added a research item
Reproductive compatibility usually decreases according to increasing genetic difference and the time of divergence between species. However, the amount of modification required to influence hybridization may vary in different species. Thus, it is extremely important to conduct studies that seek to understand what and how variables influence the reproductive isolation of species. We have explored a system involving two species of subterranean rodents that present morphological, karyotypic, and evolutionary history differences and are capable of generating hybrids. To gain insight into the karyotype organization of genus Ctenomys, we examined the chromosome evolution by classical and molecular cytogenetics of both parental species and hybrids. Furthermore, we have used different approaches to analyze the differences between the parental species and the hybrids, and determined the origin of the hybrids. The results of our work demonstrate unequivocally that some species that present extensive differences in chromosome organization, phenotype, evolutionary history, sperm morphology and genetic, which are usually associated with reproductive isolation, can generate natural hybrids. The results also demonstrate that females of both species are able to generate hybrids with males of the other species. In addition, the chromosome-specific probes prepared from Ctenomys flamarioni provide an invaluable tool for comparative cytogenetics in closely related species.
Renan Maestri
added 4 research items
The “resource availability hypothesis” predicts occurrence of larger rodents in more productive habitats. This prediction was tested in a dataset of 1,301 rodent species. We used adult body mass as a measure of body size and normalized difference vegetation index (NDVI) as a measure of habitat productivity. We utilized a cross-species approach to investigate the association between these variables. This was done at both the order-level (Rodentia) and at narrower taxonomic scales. We applied phylogenetic generalized least squares (PGLS) to correct for phylogenetic relationships. The relationship between body mas and NDVI was also investigated across rodent assemblages. We controlled for spatial autocorrelation using generalized least squares (GLS) analysis. The cross-species approach found extremely low support for the resource availability hypothesis. This was reflected by a weak positive association between body mass and NDVI at the order level. We find a positive association in only a minority of rodent subtaxa. The best fit GLS model detected no significant association between body mass and NDVI across assemblages. Thus, our results do not support the view that resource availability plays a major role in explaining geographic variation in rodent body size.
Biogeographic regionalization offers context to the geographical evolution of clades. The positions of bioregions inform both the spatial location of clusters in species distribution and where their most important boundaries are. Nevertheless, defining bioregions based on species distribution alone only incidentally recovers regions that are important during the evolution of the focal group. The extent to which bioregions correspond to centers of independent diversification depends on how clusters of species composition naturally reflect the radiation of single clades, which is not the case when mixed colonization occurred. Here, we showed that using phylogenetic turnover based on fuzzy sets, instead of species composition, led to more adequate detection of evolutionary important bioregions, that is, regions that truly account for the independent diversification of lineages. Mapping those evoregions in the phylogenetic tree quickly reveals the timing and location of major shifts of biogeographic regions. Moreover, evolutionary transition zones are easily mapped, and permits the recognition of regions with high phylogenetic overlap. Our results using the global radiation of rats and mice (Muroidea) recovered four evoregions - three major evolutionary arenas corresponding to the Neotropics, a Nearctic-Siberian, and a Paleotropical-Australian evoregion, and a fourth and fuzzy Afro-Palearctic evoregion. In comparison, an analysis with a method considering species distribution alone found 52 bioregions. Evoregions is a useful framework whenever the question is related to the identification of the most important centers of a group's diversification history and its evolutionary transitions zones.
Daniel Galiano
added 2 research items
The genus Ctenomys comprises approximately 70 recognized living species of subterranean rodents endemic to South America. Phylogenetic studies to date, based on mitochondrial DNA data, place 44 recognized species in eight species groups and provide evidence for a burst of speciation early in the history of the genus. Species from Argentina, Uruguay, Bolivia, and southern Brazil are well studied at the phylogenetic level. However, the taxonomic status of the species inhabiting midwest and northern Brazil remains poorly understood. In this study, we construct phylogenies based on maximum likelihood and Bayesian inference methods with cytochrome b gene haplotypes of Ctenomys from midwest and northern Brazil and with haplotypes representative of the genus Ctenomys to place the sampled haplotypes into a phylogenetic framework; we also evaluate skull geometric morphometrics data among sampling sites to assess whether skull morphology corroborates the phylogenetic patterns observed. The results show that the sampling sites used in this study are represented by two species, namely, Ctenomys bicolor, which is present in the state of Rondônia, and Ctenomys nattereri, which is present in Mato Grosso and Bolivia. The results also reveal two lineages of Ctenomys distinct from C. bicolor and C. nattereri, henceforth called Ctenomys sp. “xingu” and Ctenomys sp. “central.” Both the species and lineages share a most recent common ancestor with C. boliviensis and are part of the boliviensis species group.
A major interest of evolutionary biologists is to understand which environmental features are associated with morphological and behavioural characteristics of species. Intraspecific studies addressing this question provide the best evidence for ecology-driven evolution over short time scales. Here, we evaluated whether two adjacent habitats differ in soil hardness and whether skull and forelimb morphology and estimated bite force differ between populations of a single species from sand fields and sand dunes. We used a total of 39 humeri and 88 skulls and mandibles of Ctenomys minutus from both habitats to estimate the bite force and generate morphometric data. Our results provide strong evidence that parapatric populations, occupying adjacent habitats, can respond differently in particular circumstances. This indicates that C. minutus uses different strategies (i.e. scratch-digging and tooth-digging) in the excavation of tunnels, and both of them respond to changes in soil hardness, establishing that the strategies are not evolutionarily exclusive. This difference is probably a consequence of the harder soils found in the sand fields, which are more difficult to excavate. Our results suggest the presence of divergent selection or strong phenotypic plasticity in the excavation-related morphology of populations occupying different habitats.
Bruno Busnello Kubiak
added a research item
A major interest of evolutionary biologists is to understand which environmental features are associated with morphological and behavioural characteristics of species. Intraspecific studies addressing this question provide the best evidence for ecology-driven evolution over short time scales. Here, we evaluated whether two adjacent habitats differ in soil hardness and whether skull and forelimb morphology and estimated bite force differ between populations of a single species from sand fields and sand dunes. We used a total of 39 humeri and 88 skulls and mandibles of Ctenomys minutus from both habitats to estimate the bite force and generate morphometric data. Our results provide strong evidence that parapatric populations, occupying adjacent habitats, can respond differently in particular circumstances. This indicates that C. minutus uses different strategies (i.e. scratch-digging and tooth-digging) in the excavation of tunnels, and both of them respond to changes in soil hardness, establishing that the strategies are not evolutionarily exclusive. This difference is probably a consequence of the harder soils found in the sand fields, which are more difficult to excavate. Our results suggest the presence of divergent selection or strong phenotypic plasticity in the excavation-related morphology of populations occupying different habitats.
Renan Maestri
added a research item
We investigated spatial patterns of evolutionary relatedness and diversification rates to test hypotheses about the historical biogeographic processes underlying the radiation of Neotropical rats and mice (Sigmodontinae, ~400 species). A negative correlation between mean phylogenetic distance and diversification rates of rodent assemblages reveals a pattern of species co‐occurrence in which assemblages of closely related species are also the fastest diversifying ones. Subregions of the Neotropics occupied by distantly related species that are on average more slowly diversifying include Central America, northern South America, and the Atlantic forest. In southern South America, recent species turnover appears to have been higher. Ancestral locations for the main tribes of sigmodontines were also estimated, suggesting eastern South America and the Amazonian lowlands were colonized before some central Andean regions, even though the latter are now centers of species richness for these rodents. Moreover, a past connection between the tropical Andes and the Atlantic Forest is suggested by our results, highlighting a role for a hypothetical arc connecting the two biomes, which would have impacted many other groups of organisms. Whether rapid, recent speciation in some regions is related to Quaternary climatic fluctuations and the young age of sigmodontines (~12.7 Ma crown age) or instead to intrinsic traits of these rodents remains an open question. If the former is true, we hypothesize that contrasting trends will characterize older Neotropical clades. This article is protected by copyright. All rights reserved.
Bruce D Patterson
added a research item
Ctenomys dorsalis is known only from its type specimen, a female preserved as skin without skull (except for the upper incisors) from an imprecise locality in the “Northern Chaco of Paraguay”. Here, we report additional individuals of this species housed, since the 1940s, at the Field Museum of Natural History (Chicago, USA). Based on these specimens, which fully match the original description of this rodent, we provide novel information regarding its phylogenetic position, external and cranial morphology, and distribution. The analysis of mtDNA sequences supports the distinctiveness of this taxon and suggests its placement within the boliviensis group of Ctenomys . Our study highlights once more the importance of museum collections as repositories of biodiversity.
Rodrigo Fornel
added a research item
We tested the association between chromosomal polymorphism and skull shape and size variation in two groups of the subterranean rodent Ctenomys. The hypothesis is based on the premise that chromosomal rearrangements in small populations, as it occurs in Ctenomys, produce reproductive isolation and allow the independent diversification of populations. The mendocinus group has species with low chromosomal diploid number variation (2n=46-48), while species from the torquatus group have a higher karyotype variation (2n=42-70). We analyzed the shape and size variation of skull and mandible by a geometric morphometric approach, with univariate and multivariate statistical analysis in 12 species from mendocinus and torquatus groups of the genus Ctenomys. We used 763 adult skulls in dorsal, ventral, and lateral views, and 515 mandibles in lateral view and 93 landmarks in four views. Although we expected more phenotypic variation in the torquatus than the mendocinus group, our results rejected the hypothesis of an association between chromosomal polymorphism and skull shape and size variation. Moreover, the torquatus group did not show more variation than mendocinus. Habitat heterogeneity associated to biomechanical constraints and other factors like geography, phylogeny, and demography, may affect skull morphological evolution in Ctenomys.
Daniel Galiano
added 2 research items
Bayesian consensus time-tree based on the Fgb-I7 sequences. Values above nodes correspond to posterior probabilities > 0.90. (TIF)
Percentage of correct classification by discriminant analysis, using Jackknife Cross-validation, for the dorsal, ventral, and lateral views of the O. nasutus skull for the two ecoregions. (DOCX)
Daniel Galiano
added 2 research items
Pleistocene climatic oscillations favoured the expansion of grassland ecosystems and open vegetation landscapes throughout the Neotropics, and influenced the evolutionary history of species adapted to such environments. In this study, we sampled populations of the rodent Oxymycterus nasutus endemic to open areas in the Pampas and Atlantic Forest biomes to assess the tempo and mode of population divergence using an integrative approach, including coalescence theory, ecological niche models, and morphometry. Our results indicated that these O. nasutus populations exhibited high levels of genetic structure. Six major mtDNA clades were found, structuring these biomes into distinct groups. Estimates of their divergence times was indicated to be 0.571 myr. The high degree of genetic structure is reflected in the analyses of geometric morphometric; skull differences between lineages in the two ecoregions were detected. During the last glacial maximum, there was a strong increase in suitable abiotic conditions for O. nasutus. Distinct molecular markers revealed a population expansion over time, with a possible demographic retraction during the post-gla-cial period. Considering that all clades coalesce with the last interglacial maximum, our results indicated that reduction in suitable conditions during this period may have resulted in a possible vicariance associated with refuge isolation.
Bruno Busnello Kubiak
added a research item
Species with similar ecological requirements coexisting in the same geographic region are prone to competitively exclude each other. Alternatively, they may coexist if character displacement acts to change the niche requirements of one or both species. We used two methodological approaches (ecological niche modeling [ENM] and geometric morphometrics) to test two hypotheses: given their behavioral, morphological, and ecological similarities, one species competitively excludes the other; and, character displacement enables their coexistence at two sites in which the species are known to occur in sympatry. The results from the ENM-based approach did not provide evidence for competitive exclusion; however, the morphometric analyses documented displacement in size of C. minutus. This result, suggests that C. minutus might exclude C. flamarioni from areas with softer soils and higher food availability. We stress the importance of using multiple methodological approaches when testing prediction of competitive exclusion. However, both methods had limited explanatory power given that the focal species possess truly peculiar distributions, being largely parapatric and restricted to narrow, small geographic areas with a strange distribution and there is a need to search for additional methods. We discuss the idiosyncrasy of the ENM-based approach when applied to organisms with subterranean habits. Species' distributions are influenced by history, climate biotic interactions, and other factors 1. Among the most studied biotic interactions that affect species' distributions is competition, being competitive exclusion its most extreme manifestation, where a superior competitor excludes another species from a geographic area. According
Renan Maestri
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Coexistence between species with similar niche requirements is often facilitated by displacement of morphological, behavioral, or physiological characteristics. Experiments comparing treatments with and without the presence of potential competitors are ideal for testing hypotheses of interspecific competition. Here, we investigate a fundamental aspect in the natural history of a species: the home range. We determined whether co-occurrence can influence the home range size of 2 subterranean rodent species, Ctenomys flamarioni and C. minutus. We evaluated home range size in populations of both species in allopatry and sympatry along the coastal plain of southern Brazil. Animals were radiotracked, and the home range size of each individual was estimated using grid cells and minimum convex polygon methods. We found no significant differences in home range size between sites or species, and the interaction was nonsignificant. We also found no relationship between home range size and body mass or sex. Our results suggest that co-occurrence may not influence home range size in these species, perhaps due to environmental adaptations that facilitate coexistence (e.g., microhabitat segregation and dietary modifications). Further, the characteristics of the sandy dune habitat may act as environmental filters, favoring similar home range sizes for both species.
Renan Maestri
added a research item
Assemblage-level studies of mean trait variation are com-mon in macroecology. However, how phylogenetic relationships among species affect trait-based macroecological patterns is still un-resolved. I used an approach based on variation partitioning analysis using environmental and phylogenetic lineage variation as predictors to investigate whether variation in mean trait values among Neotrop-ical sigmodontine rodent communities is best explained by macroe-cological adaptation, biogeographical history, or joint effects of both - the latter resulting in phylogenetic niche conservatism (PNC) at the metacommunity scale. Metacommunity PNC best explained mean variation in body size and skull/mandible shape across assemblages, and the pattern of metacommunity PNC suggests that influence of environmental factors on mean trait variation relies heavily on spatial biogeographical clade sorting. This suggests that biogeographical lin-eage distribution should be taken into account in analyses seeking to correlate environmental variables with mean trait variation.
Renan Maestri
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Check out the blog post for our recent published article:
 
Renan Maestri
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Patterns of univariate trait variation across metacommunities are widely explored, as are searches for their underlying causes. Surprisingly, patterns of multivariate shape remain unknown, and the search for drivers of functional traits of communities often neglect the biogeographical distribution of phylogenetic clades. Our aim was to investigate multivariate shape distribution across metacommunities and to determine the main environmental drivers of shape beyond/taking into account the phylogenetic distribution of lineages. We obtained mean skull and mandible shape for 228 species of Neotropical sigmodontine rodents through geometric morphometrics (GM), and then calculated mean shapes for 1°x1° cells across the Neotropics based on the incidence of sigmodontines. We investigated the effects of lineage distribution on mean trait variation by using phylogenetic fuzzy weighting to calculate Principal Coordinates of Phylogenetic Structure (PCPS). Effects of environmental variables on shape variation incorporating phylogenetic composition were realized through redundancy analysis. We found that the different distributions of major lineages throughout the Neotropics were responsible for much of the mean shape variation. The association of landscape features with tribal groupings (Oryzomyini with Amazonia and Phyllotini and Abrotrichini with the Andes) were standouts. Environmental variables and lineage distribution explain the same (i.e. shared) portion of shape variation, suggesting phylogenetic niche conservatism at the metacommunity level. Seasonality in temperature and land cover were the best environmental predictors of mean shape: larger tympanic bullae, incisive foramina, and check teeth are all associated with highly seasonal and less vegetated areas. Our new approach of using GM shape across metacommunities was demonstrably useful in understanding large-scale biogeographical patterns of shape variation and identifying its underlying causes. The overlap between environmental variables and phylogenetic lineage distribution suggests that a process of niche conservatism is likely: the phenotype-environment correlation is mediated by the differential biogeographical distribution of the main clades.
Renan Maestri
added 6 research items
Understanding the spatial distribution of species sheds light on the group's biogeographical history, offers clues to the drivers of diversity, and helps to guide conservation strategies. Here, we compile geographic range information for South America's diverse rodents, whose 14 families comprise ~50% of the continent's mammalian species. The South American rodent fauna is dominated by independent and temporally staggered radiations of caviomorph and sigmodontine groups. We mapped species richness and turnover of all rodents and the principal clades to identify the main predictors of diversity patterns. Species richness was highest in the Andes, with a secondary hotspot in Atlantic Forest and some regions of considerable richness in Amazonia. Differences in richness were evident between the caviomorphs and sigmodontines, the former showing the greatest richness in tropical forests whereas the latter show-and largely determine-the all-rodent pattern. Elevation was the main predictor of sigmodontine richness, whereas temperature was the principal variable correlated with richness of caviomorphs. Across clades, species turnover was highest along the Andes and was best explained by elevational relief. In South America, the effects of the familiar latitudinal gradient in species richness are mixed with a strong longitudinal effect, triggered by the importance of elevation and the position of the Andes. Both latitudinal and elevational effects help explain the complicated distribution of rodent diversity across the continent. The continent's restricted-range species-those seemingly most vulnerable to localized disturbance-are mostly distributed along the Andes and in Atlantic Forest, with the greatest concentration in Ecuador. Both the Andes and Atlantic Forest are known hotspots for other faunal and floral components. Contrasting patterns of the older caviomorph and younger sigmodontine radiations underscore the interplay of both historical and ecological factors in determining present-day diversity patterns.
Evolutionary radiations on continents are less well understood and appreciated than those occurring on islands. The extent of ecological influence on species divergence can be evaluated to determine whether a radiation was ultimately the outcome of divergent natural selection or else arose mainly by non-ecological divergence. Here, we used phylogenetic comparative methods to test distinct hypotheses corresponding to adaptive and non-adaptive evolutionary scenarios for the morphological evolution of sigmodontine rodents. Results showed that ecological variables (diet and life-mode) explain little of the shape and size variation of sigmodontine skulls and mandibles. A Brownian model with varying rates for insectivory versus all other diets was the most likely evolutionary model. The insectivorous sigmodontines have a faster rate of morphological evolution than mice feeding on other diets, possibly due to stronger selection for features that aid insectivory. We also demonstrate that rapid early-lineage diversification is not accompanied by high morphological divergence among sub-clades, contrasting with island results. The geographic size of continents permits spatial segregation to a greater extent than on islands, allowing for allopatric distributions and escape from interspecific competition. We suggest that continental radiations of rodents are likely to produce a pattern of high species diversification coupled with a low degree of phenotypic specialization. This article is protected by copyright. All rights reserved
Body size variation in animal assemblages is a widely addressed pattern in biogeographical studies, and is affected by both environmental gradients and phylogenetic constraints. However, no study has yet explored to what extent the association between body size variation and environmental gradients across broad spatial scales is influenced by the biogeographical distribution of different phylogenetic lineages. In this study, we discriminate the influences of environmental variables and phylogenetic community composition on body size variation in South American sigmodontine rodents.
Renan Maestri
added a project goal
To investigate ecomorphology, macroevolution, macroecology and biogeography of Neotropical rodents. Emphasis on Sigmodontinae and Ctenomys.