Delimitação de espécies e história de diversificação do complexo Pagamea Guianensis (Rubiaceae) na América do Sul Tropical

Abstract

Species complexes are groups in which species limits and hence species numbers are unclear. Untangling species limits within species complexes can be challenging, but is the basis for investigating the processes underlying species differentiation and the discovery of new species. The Pagamea guianensis species complex is one of the most widespread and common taxa in the Amazonian white-sand flora. Previous analysis suggested the occurrence of ten species within this group, but species limits remain unclear due to poor sampling, morphological overlap and low molecular resolution. Here we present the most comprehensive sampling of individuals across the geographical distribution of the P. guianensis complex in order to: test the monophyly of this species complex; clarify species limits within it; reconstruct the spatio-temporal history of the white-sand specialist Pagamea guianensis complex in order to investigate where, when and how diversification events took place. Using a high-throughput DNA sequencing approach, we sequenced 431 loci (>34 M bases) for 179 individuals. We applied phylogenetic and species tree analyses to resolve phylogenetic relationships among the sampled individuals. Species delimitation was estimated based on molecular data, and we subsequently tested whether these hypothesized species could be differentiated by morphological and/or NIR spectroscopy data, and whether they have different ecological niches. Ancestral habitat were reconstructed for the variables vegetation structure, flooding and annual precipitation. We run admixture analysis in order to analyze population structure within the most widely distributed species: Pagamea angustifolia, P. guianensis and P. pilosa. We also run an isolation-by-distance model to investigate the correlation between geographic distance and cophenetic distance among individuals of the clade P. angustifolia+P. guianensis distributed around the Guiana Shield in a ring-like distribution. Our results confirmed the monophyly of the P. guianensis complex and our integrative approach using evidences from independent datasets show 15 distinct and well-supported lineages, here circumscribed as 14 species and one subspecies (six species and one subspecies newly described and one species with new status). All diversification events took place during the Pleistocene (last 2.5 Ma). The ancestral area of the Pagamea guianensis complex was inferred in the Western Amazon around 2.5 Ma, from where it started to disperse eastward reaching the Atlantic Coast on the Guiana Shield around 1.3 Ma and the Northeastern Brazilian Atlantic Coast (Bahia State) the Last Interglacial (~130,000 years). The ancestor was in tall forests over dry soils, with subsequent diversification to lower or open vegetation and to moist or flooded soils. We found a gradient of species diversity following the west-east dispersal route, with higher diversity in the Western and Northwestern Amazon (7 and 5 spp), intermediate in Central Amazon (4) and few species in the Eastern Amazon and Atlantic Forest (1). Population structure analysis revealed more genetic structure in the North of the Amazonas River than in the South region. Populations from the P. angustifolia+P. guianensis clade in the Eastern Guiana Shield follow an isolation-by-distance model with strong correlation among cophenetic and geographical distances around the ring, a pattern never detect before for plants in the Amazon. Finally, in this work we were able to delimit and discover new species using advanced techniques of DNA sequencing and phylogenetic inferences from multiple markers, combining with independent analysis from morphological, spectral and ecological datasets. After species delimitation, we finally could reconstruct a more detailed and less uncertain biogeographic history for the P. guianensis complex.