Pleistocene expansion and connectivity of mesic forests inside the South American Dry Diagonal supported by the phylogeography of a small lizard*

Geoclimatic drivers of diversification in the largest arid and semi-arid environment of the Neotropics: Perspectives from phylogeography

The South American Dry Diagonal, also called the Diagonal of Open Formations, is a large region of seasonally dry vegetation extending from northeastern Brazil to northern Argentina, comprising the Caatinga, Cerrado, and Chaco subregions. A growing body of phylogeography literature has determined that a complex history of climatic changes coupled with more ancient geological events has produced a diverse and endemic-rich Dry Diagonal biota. However, the exact drivers are still under investigation, and their relative strengths and effects are controversial. Pleistocene climatic fluctuations structured lineages via vegetation shifts, refugium formation, and corridors between the Amazon and Atlantic forests. In some taxa, older geological events, such as the reconfiguration of the São Francisco River, uplift of the Central Brazilian Plateau, or the Miocene inundation of the Chaco by marine incursions, were more important. Here, we review the Dry Diagonal phylogeography literature, discussing each hypothesized driver of diversification and assessing degree of support. Few studies statistically test these hypotheses, with most support drawn from associating encountered phylogeographic patterns such as population structure with the timing of ancient geoclimatic events. Across statistical studies, most hypotheses are well supported, with the exception of the Pleistocene Arc Hypothesis. However, taxonomic and regional biases persist, such as a proportional overabundance of herpetofauna studies, and the under-representation of Chaco studies. Overall, both Pleistocene climate change and Neogene geological events shaped the evolution of the Dry Diagonal biota, though the precise effects are regionally and taxonomically varied. We encourage further use of model-based analyses to test evolutionary scenarios, as well as interdisciplinary collaborations to progress the field beyond its current focus on the traditional set of geoclimatic hypotheses.

Genetic structure and landscape effects on gene flow in the Neotropical lizard Norops brasiliensis (Squamata: Dactyloidae)

One key research goal of evolutionary biology is to understand the origin and maintenance of genetic variation. In the Cerrado, the South American savanna located primarily in the Central Brazilian Plateau, many hypotheses have been proposed to explain how landscape features (e.g., geographic distance, river barriers, topographic compartmentalization, and historical climatic fluctuations) have promoted genetic structure by mediating gene flow. Here, we asked whether these landscape features have influenced the genetic structure and differentiation in the lizard species Norops brasiliensis (Squamata: Dactyloidae). To achieve our goal, we used a genetic clustering analysis and estimate an effective migration surface to assess genetic structure in the focal species. Optimized isolation-by-resistance models and a simulation-based approach combined with machine learning (convolutional neural network; CNN) were then used to infer current and historical effects on population genetic structure through 12 unique landscape models. We recovered five geographically distributed populations that are separated by regions of lower-than-expected gene flow. The results of the CNN showed that geographic distance is the sole predictor of genetic variation in N. brasiliensis, and that slope, rivers, and historical climate had no discernible influence on gene flow. Our novel CNN approach was accurate (89.5%) in differentiating each landscape model. CNN and other machine learning approaches are still largely unexplored in landscape genetics studies, representing promising avenues for future research with increasingly accessible genomic datasets.

Genetic structure of Enyalius capetinga (Squamata, Leiosauridae) in Central Cerrado and transitional areas between the Cerrado and the Atlantic forest, with updated geographic distribution

The Brazilian Cerrado is considered a biodiversity hotspot highly threatened by human activities. Recently, many studies have demonstrated how underestimated is Cerrado's biodiversity considering squamate species, and the identification of divergent and cryptic lineages is essential for the formulation of effective conservation strategies. The transition areas between the Cerrado and the Atlantic Forest are even less known and, consequently, often dismissed in conservation policies. As previous studies suggested the presence of cryptic diversity within E. capetinga, we investigated patterns and processes in the geographic distribution of its genealogical lineages. We used DNA sequences from individuals collected in six localities and sequences publicly available from three mitochondrial markers (CYT-B, 16S and ND4) and one nuclear marker (C-Mos). We tested if the core and ecotone regions of the Cerrado show differences in biotic and abiotic characteristics that could promote genetic structure and divergence among lineages within E. capetinga. We found evidence for divergent lineages within the species, but not congruent with our hypothesis. Similar divergent patterns were observed in other Cerrado lizards, including interspecific divergences within the Enyalius genus. Molecular characterization of field-collected individuals (previously identified as E. bilineatus), allowed us to update the geographic distribution of the species to include the ecotone between the Cerrado and the Atlantic Forest, an area where species distribution overlap.

Diversity patterns of lizard assemblages from a protected habitat mosaic in the Brazilian Cerrado savanna

Differences in habitat complexity and structure can directly influence the composition, diversity, and structure of species assemblages. Measurements of functional and phylogenetic diversity complement the commonly used measurements of taxonomic diversity, elucidating the relationships between species, their traits, and their evolutionary history. In this study, we evaluated how the mosaic of open and forested formations in a federal conservation unit in the western portion of the Brazilian Cerrado savanna influences the taxonomic, functional, and phylogenetic structure of lizard assemblages. Lizards were sampled for 15 months using pitfall traps set in open and forested formations. We recorded 292 lizards distributed among 16 species from eight families, with species composition differing among the formations. Richness was greater in the assemblages from open formations, while functional diversity and phylogenetic variability were greater in those of forested formations. Lizard assemblages in open formations were functionally and phylogenetically clustered, probably as a result of environmental filters acting on species, while the assemblages from forested formations were randomly structured. Different environmental and historical mechanisms have apparently shaped the current diversity of lizards in the region. This study shows that Cerrado vegetation mosaics can promote wide variation in different aspects of the taxonomic, functional, and phylogenetic structure from the lizard assemblages.

Digest: A lizard evolutionary history illustrates a past Neotropical dispersal route

Extensive lineage interchanges among Neotropical biomes are key to understanding their remarkable biodiversity. At a population level, one could expect to observe past cross-regional connections. The description of the phylogeographic history of a forest-associated lizard by Ledo et al. (2020) revealed a likely interbiome dispersal route through networks of riparian forests surrounded by dry habitats. We anticipate that future studies focusing on understudied widespread organisms like plants will build on these findings to better describe the origins of Neotropical diversity.