Thales R.O. Freitas
Universidade Federal do Rio Grande do Sul, Genetica, Faculty Member
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... more
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.
Research Interests:
For many vertebrate species, bite force plays an important functional role. Ecological characteristics of a species' niche, such as diet, are often associated with bite force. Previous evidence suggests a biomechanical trade-off between... more
For many vertebrate species, bite force plays an important functional role. Ecological characteristics of a species' niche, such as diet, are often associated with bite force. Previous evidence suggests a biomechanical trade-off between rodents specialized for gnawing, which feed mainly on seeds, and those specialized for chewing, which feed mainly on green vegetation. We tested the hypothesis that gnawers are stronger biters than chewers. We estimated bite force and measured skull and mandible shape and size in 63 genera of a major rodent radiation (the myomorph sigmodontines). Analysis of the influence of diet on bite force and morphology was made in a comparative framework. We then used phylogenetic path analysis to uncover the most probable causal relationships linking diet and bite force. Both granivores (gnawers) and herbivores (chewers) have a similar high bite force, leading us to reject the initial hypothesis. Path analysis reveals that bite force is more likely influenced by diet than the reverse causality. The absence of a trade-off between herbivores and granivores may be associated with the generalist nature of the myomorph condition seen in sigmodontine rodents. Both gnawing and chewing sigmodontines exhibit similar, intermediate phenotypes, at least compared to extreme gnawers (squirrels) and chewers (chinchillas). Only insectivorous rodents appear to be moving towards a different direction in the shape space, through some notable changes in morphology. In terms of diet, natural selection alters bite force through changes in size and shape, indicating that organisms adjust their bite force in tandem with changes in food items.
Research Interests:
Knowledge about the ecology of bottlenose dolphins in the Southwestern Atlantic Ocean is scarce. Increased by-catch rates over the last decade in coastal waters of southern Brazil have raised concerns about the decline in abundance of... more
Knowledge about the ecology of bottlenose
dolphins in the Southwestern Atlantic Ocean is scarce.
Increased by-catch rates over the last decade in coastal
waters of southern Brazil have raised concerns about the
decline in abundance of local dolphin communities. Lack of
relevant data, including information on population structure
and connectivity, have hampered an assessment of the
conservation status of bottlenose dolphin communities in
this region. Here we combined analyses of 16 microsatellite
loci and mitochondrial DNA (mtDNA) control region
sequences to investigate genetic diversity, structure and
connectivity in 124 biopsy samples collected over six
communities of photographically identified coastal bottlenose
dolphins in southern Brazil, Uruguay and central
Argentina. Levels of nuclear genetic diversity were
remarkably low (mean values of allelic diversity and heterozygosity
across all loci were 3.6 and 0.21, respectively), a
result that possibly reflects the small size of local dolphin
communities. On a broad geographical scale, strong and
significant genetic differentiation was found between bottlenose
dolphins from southern Brazil–Uruguay (SB–U) and
Bahı´a San Antonio (BSA), Argentina (AMOVA mtDNA
UST = 0.43; nuclear FST = 0.46), with negligible contemporary
gene flow detected based on Bayesian estimates. On a
finer scale, moderate but significant differentiation (AMOVA
mtDNA UST = 0.29; nuclear FST = 0.13) and asymmetric gene flow was detected between five neighbouring
communities in SB–U. Based on the results we
propose that BSA and SB–U represent two distinct evolutionarily
significant units, and that communities from SB–U
comprise five distinct Management Units (MUs). Under this
scenario, conservation efforts should prioritize the areas in
southern Brazil where dolphins from three MUs overlap in
their home ranges and where by-catch rates are reportedly
higher.
dolphins in the Southwestern Atlantic Ocean is scarce.
Increased by-catch rates over the last decade in coastal
waters of southern Brazil have raised concerns about the
decline in abundance of local dolphin communities. Lack of
relevant data, including information on population structure
and connectivity, have hampered an assessment of the
conservation status of bottlenose dolphin communities in
this region. Here we combined analyses of 16 microsatellite
loci and mitochondrial DNA (mtDNA) control region
sequences to investigate genetic diversity, structure and
connectivity in 124 biopsy samples collected over six
communities of photographically identified coastal bottlenose
dolphins in southern Brazil, Uruguay and central
Argentina. Levels of nuclear genetic diversity were
remarkably low (mean values of allelic diversity and heterozygosity
across all loci were 3.6 and 0.21, respectively), a
result that possibly reflects the small size of local dolphin
communities. On a broad geographical scale, strong and
significant genetic differentiation was found between bottlenose
dolphins from southern Brazil–Uruguay (SB–U) and
Bahı´a San Antonio (BSA), Argentina (AMOVA mtDNA
UST = 0.43; nuclear FST = 0.46), with negligible contemporary
gene flow detected based on Bayesian estimates. On a
finer scale, moderate but significant differentiation (AMOVA
mtDNA UST = 0.29; nuclear FST = 0.13) and asymmetric gene flow was detected between five neighbouring
communities in SB–U. Based on the results we
propose that BSA and SB–U represent two distinct evolutionarily
significant units, and that communities from SB–U
comprise five distinct Management Units (MUs). Under this
scenario, conservation efforts should prioritize the areas in
southern Brazil where dolphins from three MUs overlap in
their home ranges and where by-catch rates are reportedly
higher.
Research Interests:
Knowledge about the ecology of bottlenose dolphins in the Southwestern Atlantic Ocean is scarce. Increased by-catch rates over the last decade in coastal waters of southern Brazil have raised concerns about the decline in abundance of... more
Knowledge about the ecology of bottlenose dolphins in the Southwestern Atlantic Ocean is scarce. Increased by-catch rates over the last decade in coastal waters of southern Brazil have raised concerns about the decline in abundance of local dolphin communities. Lack of relevant data, including information on population structure and connectivity, have hampered an assessment of the conservation status of bottlenose dolphin communities in this region. Here we combined analyses of 16 microsatellite loci and mitochondrial DNA (mtDNA) control region sequences to investigate genetic diversity, structure and connectivity in 124 biopsy samples collected over six communities of photographically identified coastal bottlenose dolphins in southern Brazil, Uruguay and central Argentina. Levels of nuclear genetic diversity were remarkably low (mean values of allelic diversity and heterozygosity across all loci were 3.6 and 0.21, respectively), a result that possibly reflects the small size of local dolphin communities. On a broad geographical scale, strong and significant genetic differentiation was found between bottlenose dolphins from southern Brazil–Uruguay (SB–U) and Bahı´a San Antonio (BSA), Argentina (AMOVA mtDNA UST = 0.43; nuclear FST = 0.46), with negligible contemporary gene flow detected based on Bayesian estimates. On a finer scale, moderate but significant differentiation (AMOVA mtDNA UST = 0.29; nuclear FST = 0.13) and asymmetric gene flow was detected between five neighbouring communities in SB–U. Based on the results we propose that BSA and SB–U represent two distinct evolutionarily significant units, and that communities from SB–U comprise five distinct Management Units (MUs). Under this scenario, conservation efforts should prioritize the areas in southern Brazil where dolphins from three MUs overlap in their home ranges and where by-catch rates are reportedly higher.
Research Interests:
Sigmodontinae is a high diverse rodent subfamily with difficult taxonomic identification, which plays a relevant role in environmental impact assessment and public health. We evaluated cytochrome c oxidase subunit I (COX-I) sequence... more
Sigmodontinae is a high diverse rodent subfamily with difficult taxonomic identification, which plays a relevant role in environmental impact assessment and public health. We evaluated cytochrome c oxidase subunit I (COX-I) sequence variability in order to investigate the existence of 'barcoding gap' and to assess its phylogenetic potential in evolutionary studies. We generated 130 sequences from 21 species sampled. Also, we added 58 sequences available in Genbank. Preliminary analysis revealed some field misidentifications. Thus, we reclassified them in order to include in the further analysis. The mean distance was 14.7% overall, 15.2% among genera, and 2.4% among species. The 'barcoding gap' was found and an unexpected phylogenetic signal was recovered. Although it proved to be a useful tool that can enhance the discovery of biodiversity, the barcoding approach must be also supported by taxonomy and museum collections.
Research Interests: Zoology()
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Research Interests: Zoology()
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Research Interests:
Abstract Aim 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... more
Abstract
Aim
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.
Location
South America.
Methods
We computed the mean body mass of sigmodontine species co-occurring in 1 × 1° cells across South America. For each cell we recorded mean values for three environmental variables. We characterized the phylogenetic composition of sigmodontine assemblages within each cell using phylogenetic fuzzy-weighting and principal coordinates of phylogenetic structure (PCPS). We then partitioned out the influence of environmental factors and the phylogenetic community composition on mean body size.
Results
Mean body size variation was mostly explained by shared influence of phylogenetic community composition (PCPS) and environmental factors (68%), while exclusive influence of PCPS was low (19%), and of environment was even lower (0.47%). Increases in body size were related to increases in annual mean temperature, and the influence of environment on body size was mediated by the distribution of sigmodontine lineages across South America.
Main conclusions
Environment alone was not sufficient to explain body size variation in sigmodontine assemblages. Rather, environmental gradients interacted with historical processes to determine body size variation in the Neotropical assemblages. These results have implications for the way we think of body size gradients across species assemblages, because any gradient in a trait may be a result of differences in the biogeographical distribution of lineages across space, which should be considered in an explicit context.
Aim
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.
Location
South America.
Methods
We computed the mean body mass of sigmodontine species co-occurring in 1 × 1° cells across South America. For each cell we recorded mean values for three environmental variables. We characterized the phylogenetic composition of sigmodontine assemblages within each cell using phylogenetic fuzzy-weighting and principal coordinates of phylogenetic structure (PCPS). We then partitioned out the influence of environmental factors and the phylogenetic community composition on mean body size.
Results
Mean body size variation was mostly explained by shared influence of phylogenetic community composition (PCPS) and environmental factors (68%), while exclusive influence of PCPS was low (19%), and of environment was even lower (0.47%). Increases in body size were related to increases in annual mean temperature, and the influence of environment on body size was mediated by the distribution of sigmodontine lineages across South America.
Main conclusions
Environment alone was not sufficient to explain body size variation in sigmodontine assemblages. Rather, environmental gradients interacted with historical processes to determine body size variation in the Neotropical assemblages. These results have implications for the way we think of body size gradients across species assemblages, because any gradient in a trait may be a result of differences in the biogeographical distribution of lineages across space, which should be considered in an explicit context.