New Study Of Liberica Coffee Genome Redefines Species Boundaries – CoffeeTalk

A genomic analysis has redefined the boundaries of Liberica coffee species, shedding new light on their geographical distribution and evolutionary relationships. The research, led by Davis, Shepherd-Clowes, and Cheek, utilized extensive genomic data and rigorous field collection records to redefine species boundaries within Liberica coffee, a group essential both ecologically and economically. This reassessment addresses long-standing confusion about the natural habitats and ranges of three closely related but distinctly separate species: Coffea liberica, Coffea klainei, and Coffea dewevrei.

For decades, the classification and distribution of these Coffea species have been mired in ambiguity, with many previous records failing to distinguish between truly wild populations and those that originated from cultivation or spontaneous growth near human settlements. By meticulously filtering out such cultivated and self-sown records, the researchers ensured the robustness of their dataset, focusing solely on indigenous, wild populations. This approach has led to definitive evidence that the indigenous distributions of these species do not overlap, exhibiting allopatric patterns across the African continent.

Coffea liberica has been established as predominantly occupying the upper West African region, which spans several countries including Sierra Leone, Liberia, Ivory Coast, Ghana, and Nigeria. The species’ range in these territories forms a distinct population cluster, geographically isolated from its congeners. On the other hand, Coffea klainei is localized exclusively in West-Central Africa, specifically encompassing Cameroon, Gabon, the Republic of Congo, and Angola’s Cabinda enclave. The third species, Coffea dewevrei, dominates habitats in a wider swath of Central Africa, found across the Republic of the Congo, Cameroon, the Democratic Republic of Congo, Central African Republic, South Sudan, and Uganda.

An important analytical tool leveraged in this study is Rapoport’s mean propinquity assessment, which measures the spatial coherence and separation between populations. By applying a barrier distance threshold of 500 kilometers, the researchers identified a clear and robust genetic and demographic separation between Coffea liberica and the combined populations of Coffea dewevrei and Coffea klainei. Intriguingly, this barrier was not observed between Coffea dewevrei and Coffea klainei, indicating a closer geographical and possibly evolutionary proximity between these latter two species.

This finding carries significant implications for both evolutionary biology and conservation strategies. It suggests that while Coffea liberica has evolved and persisted largely independent of its central and west-central African relatives, the contact zones or environmental gradients between Coffea klainei and Coffea dewevrei may be more permeable. Such information is critical in understanding the dynamics of gene flow, species adaptation, and ecological niches in these coffee species, many of which are threatened by habitat loss and climate change.

Interestingly, the revised natural range of Coffea liberica parallels that of two other known Coffea species — Coffea humilis and Coffea stenophylla. Both of these species are native to overlapping regions within upper West Africa, sharing similar ecological constraints and possibly analogous environmental drivers. This parallel distribution hints at a broader ecological pattern influencing Coffea species in this subregion, potentially tied to climatic factors, soil composition, or historical biogeographical events shaping species presence and survival.

The technological foundation underpinning this research is rooted in modern genomic sequencing and intricate population genetic analyses. With advances in next-generation sequencing platforms, researchers were able to unravel the genomic architecture across multiple populations, providing unprecedented resolution in species delimitation. This genomic clarity transcends traditional morphological methods, which often struggle to differentiate closely related or cryptic species, especially in complex rainforest environments where many Coffea species occur.

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