What drives speciation? One way to investigate this problem would be to go to where there’s biodiversity, so you can see what causes it all. However, when you do that there’s a danger of getting lost with some many variables. That’s why a study by Bárbara Leal and colleagues has focused on just one plant in the Neotropics. Dr Leal explained: “We focused on a single species, Pitcairnia lanuginosa, to investigate general questions related to speciation processes underlying the astonishing biodiversity found in this region and highlighted that dispersion might be an important mechanism to explain patterns of diversification in the Neotropics.”
“Our research group has been using Pitcairnia as a model system to study diversification processes in the Neotropics since the beginning of this decade. Previous studies have shown for instance restrict gene flow within Pitcairnia species and interspecific gene flow among some species from the Atlantic Forest. This time we wanted to address questions related to connections between neotropical ecoregions, so we focused on one of the most widespread Pitcairnia species that occur in distinct ecoregions.
To get a sample of diverse Pitcairnia plants, the team visited sites in the Cerrado of Brazil and the Yungas of Peru. The Cerrado is thought of as a vast grassland, but there is forest there too. Along the rivers in these forests, the team collected their Pitcairnia samples. In contrast, the Yungas is a narrow habitat, between the Andean highlands and the Amazonian rainforest. Once the team had their plants, they extracted the DNA. They then analysed P. lanuginosa, based on microsatellites, plastid and nuclear
sequence data sets.
What the team expected to find were two distinct lineages. The two sites were very definitely isolated. But the first impressions didn’t seem to back that up. Dr Leal said, “Before sampling plants in the Andean Yungas, we expected to find many morphological differences between populations occurring in such regions, but we realized that the species is surprisingly uniform in terms of morphology across the entire distribution. Despite the lack of obvious morphological differences, our molecular data shows two long-term divergent lineages occupying the Cerrado and the Andean Yungas and no evidence of recent gene flow between them.”
Dr Leal explained that while the plants may look similar, their hidden diversity may play a role in the future. “Lineages associated with riparian forests in the Cerrado (a savanna-like biome) may be pre-adapted to moister conditions and easily spread to neighbor forested biomes. The dispersion may be thus an important mechanism explaining patterns of diversification of many other lineages occurring in both open and forest neotropical biomes.”
In their paper, the authors conclude: “Besides the occurrence of historical population bottlenecks (or founder events) following dispersion events, the species genetic diversity and structure may have been strongly influenced by the combined effect of high rates of selfing and low seed-mediated gene flow among populations. The scenario highlighted here implies strong genetic drift as the major force underlying the species diversification.”
Leal, B. S. S., Graciano, V. A., Chaves, C. J. N., Huacre, L. A. P., Heuertz, M., & Palma-Silva, C. (2019). Dispersal and local persistence shape the genetic structure of a widespread Neotropical plant species with a patchy distribution. Annals of Botany. https://doi.org/10.1093/aob/mcz105