RESUMO
Andean uplift and the concomitant formation of the Diagonal Arid of South America is expected to have promoted species diversification through range expansions into this novel environment. We evaluate the evolution of Argylia, a genus belonging to the Bignoniaceae family whose oldest fossil record dates back to 49.4 Ma. Today, Argylia is distributed along the Andean Cordillera, from 15°S to 38.5°S and from sea level up to 4,000 m.a.s.l. We ask whether Argylia's current distribution is a result of a range expansion along the Andes Cordillera (biological corridor) modulated by climatic niche conservatism, considering the timing of Andean uplift (30 Ma - 5 Ma). To answer this question, we reconstructed the phylogenetic relationships of Argylia species, estimated divergence times, estimated the realized climatic niche of the genus, reconstructed the ancestral climatic niche, evaluated its evolution, and finally, performed an ancestral range reconstruction. We found strong evidence for climatic niche conservatism for moisture variables, and an absence of niche conservatism for most of the temperature variables considered. Exceptions were temperature seasonality and winter temperature. Results imply that Argylia had the capacity to adapt to extreme temperature conditions associated with the Andean uplift and the new climatic corridor produced by uplift. Ancestral range reconstruction for the genus showed that Argylia first diversified in a region where subtropical conditions were already established, and that later episodes of diversification were coeval with the of Andean uplift. We detected a second climatic corridor along the coastal range of Chile-Peru, the coastal lomas, which allowed a northward range expansion of Argylia into the hyperarid Atacama Desert. Dating suggests the current distribution and diversity of Argylia would have been reached during the Late Neogene and Pleistocene.
RESUMO
Understanding why some plant lineages move from one climatic region to another is a mayor goal of evolutionary biology. In the southern Andes plant lineages that have migrated along mountain ranges tracking cold-humid climates coexist with lineages that have shifted repeatedly between warm-arid at low elevations and cold habitats at high elevations. Transitions between habitats might be facilitated by the acquisition of common traits favoring a resource-conservative strategy that copes with drought resulting from either low precipitation or extreme cold. Alternatively, transitions might be accompanied by phenotypic divergence and accelerated evolution of plant traits, which in turn may depend on the level of coordination among them. Reduced integration and evolution of traits in modules are expected to increase evolutionary rates of traits, allowing diversification in contrasting climates. To examine these hypotheses, we conducted a comparative study in the herbaceous genus Leucheria. We reconstructed ancestral habitat states using Maximum Likelihood and a previously published phylogeny. We performed a Phylogenetic Principal Components Analysis on traits, and then we tested the relationship between PC axes, habitat and climate using Phylogenetic Generalized Least Squares (PGLS). Finally, we compared the evolutionary rates of traits, and the levels of modularity among the three main Clades of Leucheria. Our results suggest that the genus originated at high elevations and later repeatedly colonized arid-semiarid shrublands and humid-forest at lower elevations. PGLS analysis suggested that transitions between habitats were accompanied by shifts in plant strategies: cold habitats at high elevations favored the evolution of traits related to a conservative-resource strategy (thicker and dissected leaves, with high mass per area, and high biomass allocation to roots), whereas warm-arid habitats at lower elevations favored traits related to an acquisitive-resource strategy. As expected, we detected higher levels of modularity in the clades that switched repeatedly between habitats, but higher modularity was not associated with accelerated rates of trait evolution.