Taxonomy & Evolution

Nothofagus macrocarpa populations represent relics of a once-greater range

Today’s remaining isolated populations are highly genetically diverse and extensively hybridized.

Central Chile is home to a highly biodiverse, Mediterranean-type forest that stands as a relic of a wider distribution reduced by past climate oscillations. Nothofagus macrocarpa is a palaeoendemic tree that is both threatened and poorly represented in the protected areas of the forest. Recognition of the tree’s status has been hindered by its similarity to and misidentification as N. obliqua. At present, the tree is only found on mountaintops along the Coastal and Andean ranges. The fossil record, however, hints at a wider distribution in the distant past.

Nothofagus obliqua. Image: Diucón / Wikipedia

In a new article published in Annals of Botany, lead author Paula Mathiasen and colleagues investigated whether today’s populations of N. macrocarpa represent a relic of a larger ancient range, with the goal of improving its identification and conservation, as well as our understanding of the species’ history. The researchers analyzed genetic material from the six remaining populations and used phylogenetic analyses and ecological niche modelling (ENM) to reconstruct the species’ biogeographic history and understand modern patterns of diversity within the populations.

The researchers found that today’s small, isolated populations of N. macrocarpa display a high level of genetic diversity and show signs of extensive hybridization. Though a past latitudinal geographic structure was apparent, modern populations do not show this. ENM showed highly suitable areas for the species scattered throughout the region across different time periods and suggests local expansion and contraction of the tree’s range over time. Overall, the authors write, genetic patterns confirmed that the remaining populations “are indeed relics of an ancient flora that locally withstood climatic oscillations, highlighting its evolutionary and ecological value.”

The ability of N. macrocarpa populations to persist over long periods of a changing climate, combined with their high levels of genetic diversity are determinants of the species’ future in a once-again shifting climate. Still, ENMs pointed to a possible future reduction of the species’ range based on their climatic preferences, leaving them at even greater risk. “We suggest that for a landscape matrix of intense anthropogenic impacts such as that inhabited by N. macrocarpa, it is meaningful to preserve all its current populations, as each of them has unique genetic characteristics, as well as a significant historical geographic structure,” write the authors.