The Origin and Diversification of the Hyperdiverse Flora in the Chocó Biogeographic Region

Abstract

Extremely high levels of plant diversity in the American tropics are derived from multiple interactions between biotic and abiotic factors. Previous studies have focused on macro-evolutionary dynamics of the Tropical Andes, Amazonia, and Brazil's Cerrado and Atlantic forests during the last decade. Yet, other equally important Neotropical biodiversity hotspots have been severely neglected. This is particularly true for the Chocó region on the north-western coast of South and Central America. This geologically complex region is Earth's ninth most biodiverse hotspot, hosting approximately 3% of all known plant species. Here, we test Gentry's [1982a,b] hypothesis of a northern Andean-Central American Pleistocene origin of the Chocoan flora using phylogenetic reconstructions of representative plant lineages in the American tropics. We show that plant diversity in the Chocó is derived mostly from Andean immigrants. Contributions from more distant biogeographical areas also exist but are fewer. We also identify a strong floristic connection between the Chocó and Central America, revealed by multiple migrations into the Chocó during the last 5 Ma. The dated phylogenetic reconstructions suggest a Plio-Pleistocene onset of the extant Chocó flora. Taken together, these results support to a limited extend Gentry's hypothesis of a Pleistocene origin and of a compound assembly of the Chocoan biodiversity hotspot. Strong Central American-Chocoan floristic affinity may be partly explained by the accretion of a land mass derived from the Caribbean plate to north-western South America. Additional densely sampled phylogenies of Chocoan lineages also well represented across the Neotropics could enlighten the role of land mass movements through time in the assembly of floras in Neotropical biodiversity hotspots.

Keywords: Andean uplift; Central America; Chocó; biogeography; hyper-diversity; macroevolution; neotropical region.

Figure 1

Geographical extent of the Chocó biogeographic region (highlighted in blue) in Central and South America as defined by Myers (2000) and its compound geological origin. The geological extensions of the Chucunaque, Atrato, and Tumaco basins are indicated with colour coded polygons. The location of the Uramita suture and the Garrapatas fault are also provided. (A) Lowland wet forest in north-western Colombia in Purricha (Chocó Department); (B) Pre-montane gallery forest in central-western Colombia, near Queremal town (Valle del Cauca department). Photos: R. Cámara-Leret and O. Pérez]

Figure 2

Temporal migration dynamics of selected Neotropical plant lineages represented in the Chocó and their diversification patterns. (A) Mean ages and their corresponding 95% High Density Probabilities (HDP) of Most Recent Common Ancestors (MRCA) of plant species/clades distributed in the Chocó. Ages estimates are colour coded by family and were obtained from published phylogenies of Cymbidieae and Pleurothallidinae (Orchidaceae: Pérez-Escobar et al., 2017a), Amphilophium (Bignoniaceae: Thode et al., 2019), Philodendron (Araceae: Canal et al., 2019), Cremastosperma and Mosannona (Annonaceae: Pirie et al., 2018). Boxplots representing mean values and quartiles were computed whenever four or more observations per plant family were available. [Inset: The proportion of species sampled vs the total known of species diversity in each surveyed phylogeny is provided with a picture of the corresponding plant family (Orchidaceae: Pleurothallis pierryi; Bignoniaceae: Anemopaegma orbiculatum; Araceae: Philodendron sp.; Annonaceae: Cremastosperma sp.)]. The green bar represents the approximate age of the terrestrial ecosystem onset in the Chocó. (B) A schematic phylogeny representing the two most prominent diversification patterns of Chocoan lineages, all of which appear to have occurred during the last ∼8 Ma: 1) migration from adjacent or distant biogeographical areas into the Chocó followed by in-situ diversification (blue arrows); 2) migration into the Chocó without subsequent diversification. Photos: O. Pérez.