Seasonal droughts during the Miocene drove the evolution of Capparaceae towards Neotropical seasonally dry forests

Abstract

Introduction: Neotropical seasonally dry forest (NSDF) climatic constraints
increased endemism, and phylogenetic niche conservatism in species that are restricted to this
biome. NSDF have a large number of endemic Capparaceae taxa, but it is unknown if
phylogenetic niche conservatism has played a role in this pattern. Objective: We carried out an
evolutionary analysis of the climatic niche of neotropical species of Capparaceae to identify
whether the climatic constraints of NSDF have played a major role throughout the family’s
evolutionary history. Methods: Using three chloroplastic (ndhF, matK, rbcL) and one ribosomal
(rsp3) DNA sequences, we proposed a date phylogeny to reconstruct the evolutionary climatic
niche dynamics of 24 Neotropical species of Capparaceae. We tested the relationship between
niche dissimilarity and phylogenetic distance between species using the Mantel test. Likewise,
we used a set of phylogenetic comparative methods (PGLS) on the phylogeny of Capparaceae to
reconstruct the main evolutionary historic events in their niche. Results: Capparaceae originated
in humid regions and subsequently, convergent evolution occurred towards humid and dry forest
during the aridification phases of the Middle Miocene (16-11 Mya). However, adaptation
towards drought stress was reflected only during the precipitation of the coldest quarter, where
we found phylogenetic signal (Pagel ) for gradual evolution and, therefore, evidence of
phylogenetic niche conservatism. We found convergent species-specific adaptations to both
drought stress and rainfall during the Miocene, suggesting a non-phylogenetic structure in most
climatic variables. Conclusions: Our study shows how the Miocene climate may have
influenced the Capparaceae speciation toward driest environments. Further, highlights the
complexity of climatic niche dynamics in this family, and therefore more detailed analyses are
necessary in order to better understand the NSDF climatic constrictions affected the evolution of
Capparaceae.