How important was polyploidy in the diversification of herbs in the Chaquean Domain? The case of the Turnera sidoides autopolyploid complex (Passifloraceae: urneroideae)

Abstract

The evolutionary processes that shape the unique biodiversity of the Neotropical Chaquean Domain are still poorly understood, and choosing an appropriate model to address evolutionary questions is essential for understanding the current patterns of Chaquean diversity. We used the Turnera sidoides autopolyploid complex as a model to assess current and past environmental factors and the processes that shaped and maintain its intraspecific variation in the Chaquean Domain. Based on current and past niche modelling, cytogeographical and genetic divergence analyses, we provide strong evidence that the T. sidoides complex has been in an active process of intraspecific allopatric diversification at the diploid level since the early Pleistocene. Further diversification of the complex involved the emergence of independent polyploid series in each morphologically divergent lineage. Cytotypes in each series do not differ in diagnostic morphological traits, but are reproductively isolated and have different ecological requirements. Currently, each subspecies/morphotype and cytotype are true species according to the biological, evolutionary and ecological concepts; however, they are still considered to be the same morphological species. Our study has clarified the effect of the complex processes of diversification occurring in the Chaquean Domain on T. sidoides and that much diversity is overlooked when only the morphological species concept is considered when estimating the diversity of Neotropical ecoregions.