Acaulescence promotes speciation and shapes the distribution patterns of palms in Neotropical seasonally dry habitats

• Rainforests have been a source of lineages to open and seasonally dry habitats throughout Angiosperm evolution, especially in the Neotropics. However, the underlying mechanisms that allow such shifts remain poorly understood at large spatial scales. Here, we test whether acaulescence (an underground stem or a very short stem concealed in the ground) has affected the colonization and speciation in Neotropical seasonally dry habitats by cocosoid palms (Cocoseae). Acaulescent species maintain their growth underground, which increases their chances of survival from prolonged seasonal dry season and frequent fires. We use an integrative approach based on trait-dependent diversification models, phylogenetic comparative methods and ecological niche models. We found that shifts towards acaulescent growth form were accompanied by evolutionary transitions to seasonally dry habitats. Acaulescent lineages had higher speciation rates than non-acaulescent ones. However, the interaction between acaulescence and seasonally dry habitats had no significant effect on Cocoseae speciation rates. Acaulescent palms are primarily distributed in Neotropical seasonally dry habitats and non-acaulescent palms are concentrated in Amazonian rainforests. Our results suggest that an underground stem, with high carbohydrate and water storage capacity, is a preadaptation by which rainforest lineages were able to colonize and diversify in new fire-prone, increasingly seasonal and drier adaptive zones. The projected global expansion of dry seasonal habitats requires an understanding of how drought-avoidance functional traits evolve and how they are linked to seasonally dry habitats. Our results are, thus, a step forward in determining plant response mechanisms to drier and seasonal conditions.

Ämnesord

NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

Nyckelord

biome shifts

diversification

ecological niche models

key innovation

macroevolution

tropical rainforest

species distribution models

plant diversity

occurrence records

evolution

diversification

prediction

cerrado

drought

traits

shifts

Biodiversity & Conservation

Environmental Sciences & Ecology

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