ECR feature: Ricardo Gaytán Legaria on phylogeography of Mexican oaks

Ricardo Gaytán-Legaria is a PhD candidate at the UNAM – National Autonomous University of Mexico. He is broadly interested in the biogeography and evolution of different Mexican taxa, with emphasis in oaks species and other plants. Here, Ricardo shares his recent work on the phylogeography and niche breadh of Mexican oaks.

Ricardo Gaytán-Legaria during field work in a tropical forest.

Personal links. Researchgate | GoogleScholar

Institute. UNAM (National Autonomous University of Mexico).

Academic life stage. PhD candidate.

Major research themes. Biogeography; evolution; molecular ecology; biological conservation.

Current study system. The mountains of Mexico harbour the highest number of oak (Quercus) species of the American continent, which coexist under a wide variety of climatic conditions. Our work assesses the role of ecological niche in shaping their evolutionary patterns, in order to understand the mechanisms that make possible the coexistence of many oak species, as well as the processes that drove the group’s diversification and their phylogeographic implications.

Recent JBI paper. Gaytán-Legaria, R., Oyama, K., Ruiz- Sánchez, E., & González- Rodríguez, A. (2023). The role of niche breadth in oak phylogeography: Quercus glaucoides as a study case. Journal of Biogeography, 50(9), 1653–1667.

Motivation behind this paper. Although several phylogeographical studies have been carried out in Mexican oaks, the eco-evolutionary processes that drive the distribution of genetic diversity in species exhibiting particular climatic affinities is still unclear. Accordingly, we explored and compared the spatial patterns of genetic diversity across species, in order to understand the role of geographical configuration, climatic changes, and adaptation to high temperatures and dry conditions in their diversification.

Key methodologies. As a baseline study system, we chose an oak species (Quercus glaucoides) occurring in unusual climatic conditions, i.e. high temperatures and a long dry season, for which we explored phylogeographic patterns. We then compared the distribution of the oak’s genetic diversity with other species that occur in temperate forests, in the Mexican highlands, associating the niche breadth of the species with the degree of population genetic differentiation and the amount of genetic diversity.

Mature tree of Quercus glaucoides from the transition zone to tropical dry forest in Teotitlan, Oaxaca, Mexico.

Unexpected challenges. At first, we expected a different phytogeographical pattern in this oak (Q. glaucoides) in comparison with oak species from temperate forests, but while analysing the data, we found a previously scarcely explored association between niche breadth and phylogeographic patterns. This made us realize about the need to focus on the importance of niche breadth in explaining the spatial patterns of genetic diversity.

Major results. We found that the niche breadth of Mexican oaks is negatively correlated with their degree of genetic differentiation. This suggests that species occurring in a wider variety of environments present less differentiation, probably as a result of higher connectivity among populations, while populations belonging to species exhibiting a narrower niche could be susceptible to longer periods of isolation. At the same time, we found a positive correlation of niche breadth with an important index of genetic diversity (observed heterozygosity), implying that niche breadth could be a crucial factor behind the evolution of Mexican oaks.

Acorn of Quercus glaucoides with a size of 9 to 16 mm of diameter, generally dispersed mainly by birds (Jays) and gravity.

Next steps for this research. At the current stage, we would like to generate more genetic data, preferentially using next-generation sequencing techniques, that could be comparable among species with different ecological characteristics, as this will help determine how robust is the association of niche breadth and genetic diversity patterns, not only in oak species, but also in other plant groups around Mexico. Additionally, it would be interesting to compare adaptive patterns among species with different niche breadths, since this will shed light on the processes driving plant species diversification and coexistence in a megadiverse country such as Mexico.

If you could study any organism on Earth, what would it be? I would like to study tropical trees and their mechanisms of adaptation, with emphasis in species from tropical dry forests that have evolved to cope with long periods of dry and warm conditions; these species are fascinating!

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