The Atlantic Forest of Brazil is one of the world's most important biodiversity hot spots; it still harbours a high number of endemic species. To know the processes that generate and maintain biodiversity is a major and controversial topic in evolutionary biology with large implications for conservation management. A research group from the University of Barcelona (UB) has performed a comprehensive phylogeographic study by analysing genetic diversity patterns and levels of land planarians (Cephaloflexa bergi) in 11 site localities, in and out the Serra do Mar biological corridor, in the Atlantic Forest.
The study, published on the cover of the journal Heredity, is signed by Marta Riutort, Julio Rozas, Marta Álvarez Presas and Alejandro Sánchez-Gracia, from the Department of Genetics and the Biodiversity Research Institute of UB (IRBio), together with Fernando Carbayo, from the University of São Paulo (Brazil). The study is focused on a geographic region of the Atlantic Forest which is severely damaged by human activities. Some areas of the region have been protected and some biological corridors have been designed to restore ecosystem functionality.
How is biodiversity originated?
The causes of the origin and maintenance of extant biodiversity in the Neotropics -- an area of high biodiversity value -- have been discussed for decades. Dominating hypotheses point out Pleistocene glaciations -- which took place between 2.5 years ago and 20,000 years ago -- or Tertiary tectonic geological reorganizations Tertiary, which occurred much earlier, as the main factor.
According to the new study, extant biodiversity of the Atlantic Forest of Brazil originated and has been shaped by complex interactions between ancient geological events and more recent evolutionary processes, whereas Pleistocene climate changes had a minor influence in generating present-day diversity, even if they influenced its distribution.
Most studies aimed at defining and studying high biodiversity areas focus on organisms with high-dispersal ability. However, these models could not be good indicators to detect small areas with high biodiversity, so it makes difficult to understand the processes that generate and maintain biodiversity. Innovatively, the study carried out by UB research group is focused on the land planarian (Cephaloflexa bergi), a low-dispersal organism which inhabits soil ecosystems.
Land planarians, an animal model of phylogeographic studies
Authors explain that "to formulate an efficient conservation policy, a good understanding of spatial and temporal biodiversity patterns and their underlying evolutionary mechanisms is required." "For this reason -- they add -- , it is necessary to work with organisms with a low-dispersal ability that are particularly sensitive to changes in the environment."
The research group performed a comparative analysis of DNA sequence variation of land planarian by means of a nuclear and a mitochondrial gene. By applying Bayesian inference methods (Approximate Bayesian Computation, ABC), two scenarios proposed to explain the biodiversity of Southern Atlantic Forest region were evaluated.
Results show that nucleotide diversity levels in this species are very high in most sampled localities. Moreover, most sampled localities harbour high levels of genetic diversity, with lineages sharing common ancestors that predate the Pleistocene (more than 2.5 million years ago). Experts found little evidence of a recent colonization of Brazilian Atlantic forest localities. Nevertheless, some populations might result from very recent secondary contacts; in order words, glacial and interglacial periods might have remodelled diversity distribution.
To improve biodiversity management and conservation
The study published in the journal Heredity highlights that land planarians are an advantageous biological model for making phylogenetic and, particularly, fine-scale evolutionary inferences. Furthermore, the study has enabled experts to propose appropriate conservation policies, for example the need to extend the boundary of the Serra de Mar corridor to the South in order to reconnect some areas that were linked in the past when the Serra do Mar was a continuous forest landscape.
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