The travel of Costa Rican palms revealed by their genetic footprints

The lower Central American region is widely known for its incredible biodiversity due to its complex topographic and climatic history. One of the region’s most widespread and abundant species of plants is Chamaedorea tepejilote, a small understory palm. Despite its abundance, very few studies have been conducted on the phylogeography of this species in lower Central America. In a new study published in the Open Access journal AoB PLANTS, Fuchs and colleagues tackle Chamaedorea tepejilote, a small understory palm, by examining simple sequence repeat (SSR) and chloroplast DNA (cpDNA) markers. Their results reveal what geography allows genes to flow and what isolates plants.

The lower Central American region is a biodiversity hotspot because it contains a vast number of endemic species, meaning species that are found nowhere else in the world. It is home to a diverse array of habitats, including tropical rainforests, deciduous forests, savannahs, and wetlands. These habitats are home to a wide variety of plants and animals, some of which are considered threatened or endangered. The region is also important for ecotourism and provides livelihoods for many local people. Conservation efforts would be helped by understanding how the ecosystem is connected. 

Chamaedorea tepejilote, commonly known as the Pacaya Palm, is a tropical palm tree native to Central America. It has a tall, slender trunk with long, thin leaves that sprout from the top. It is wind or thrip pollinated, but its fruits are eaten and spread by birds and mammals, including humans. Additionally, its leaves and bark are used for various medicinal purposes. But recent deforestation and urbanisation have probably reduced the size of palm populations. Therefore Chamaedorea tepejilote is an important species to conserve and protect.

Fuchs and colleagues used nuclear microsatellites searching for regions called simple sequence repeat (SSR) markers to assess the genetic diversity and phylogeography of Chamaedorea tepejilote. Nuclear microsatellites are snippets of DNA that vary in length between individuals and are useful for estimating genetic diversity, population structure, and gene flow. They are often used in plants and animals to compare genetic variation between populations. Additionally, they also used Chloroplast DNA (cpDNA) markers. cpDNA markers are maternally inherited and can be used to determine a species’s evolutionary history and phylogeography. 

The botanists found that Chamaedorea tepejilote populations have moderate to high nuclear SSR genetic diversity. This diversity probably comes from the way Chamaedorea tepejilote reproduces. Chamaedorea tepejilote is keen on outcrossing, meaning that the gene pool keeps getting stirred by plants sharing their DNA with each other. However, habitat loss means some genetic structure within slopes may still exist. The team found that the mountains of Central America acted as a very effective barrier to gene flow. Still, results indicated that the palms on either coast weren’t entirely isolated from each other.

Using statistical analysis, Fuchs and colleagues found that they could link populations in the Caribbean and the southern Pacific coast. They found the connection at the southern extreme of the Talamanca Mountain range in Panama. This is not a location that people had previously suggested as a colonisation route for lower Central American plants. 

The results show that the complex topography of the lower Central America region has played a major role in shaping the gene flow patterns of Chamaedorea tepejilote in Costa Rica. This article is the first study of its kind for the genus. The study’s results provide greater insight into the genetic diversity and structure of Chamaedorea tepejilote populations and demonstrate the importance of mountain ranges for the effective gene flow of Neotropical plants. Consequently, this study could inform conservation strategies for the species.

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Fuchs, E.J., Cascante-Marín, A., Madrigal-Brenes, R. and Quesada, M. (2023) “Genetic diversity and phylogeographic patterns of the dioecious palm Chamaedorea tepejilote (Arecaceae) in Costa Rica: the role of mountain ranges and possible refugia,” AoB PLANTS, 15(1), p. lac060. Available at: https://doi.org/10.1093/aobpla/plac060.