A snapshot of progenitor-derivative speciation in action inIberodes(Boraginaceae)

Abstract

SUMMARYTraditional classification of speciation modes has focused on physical barriers to gene flow. While allopatry has been viewed as the most common mechanism of speciation, parapatry and sympatry, both entail speciation in the face of ongoing gene flow and thus both are far more difficult to detect and demonstrate. Iberodes (Boraginaceae, NW Europe) with a small number of recently derived species (five) and contrasting morphological traits, habitats and distribution patterns constitutes an ideal system in which to study drivers of lineage divergence and differentiation.To reconstruct the evolutionary history of the genus, we undertook an integrative study entailing: (i) phylogenomics based on restriction-site associated DNA sequencing (RAD-seq), (ii) morphometrics, and (iii) climatic niche modelling.Key results revealed a history of repeated progenitor-derivative speciation, manifesting in paraphyletic pattern within Iberodes. Climatic niche analyses, together with the morphometric data and species distributions, suggest that ecological and geographical differentiation have interacted to shape the diversity of allopatric and parapatric distributions observed in Iberodes.Our integrative study has enabled to overcome previous barriers to understanding parapatric speciation by demonstrating the recurrence of progenitor-derivative speciation in plants with gene flow and ecological differentiation, explaining observed parapatry and paraphyly.

The contribution of the edaphic factor as a driver of recent plant diversification in a Mediterranean biodiversity hotspot

“…Closely related endemic species frequently co‐occur at a regional scale, supporting that speciation of neoendemics may have taken place in situ. The speciation mechanism known as ‘budding’, in which a new range‐restricted species originates within or at the margin of a surviving ancestral species (Crawford, 2010), seems to be common in the Mediterranean‐type region of California (Anacker & Strauss, 2014) and it is probably usual also in the Mediterranean Basin (Otero et al., 2019; Papuga et al., 2018). Plants are particularly prone to strong divergent selection caused by fine‐scale environmental heterogeneity and, as a result, soil properties and microclimatic conditions may play an important role in speciation and ecological segregation at the regional scale (Rundle & Nosil, 2005; Anacker & Strauss, 2014; Molina‐Venegas et al., 2016).…”

Evolution in the Model Genus Antirrhinum Based on Phylogenomics of Topotypic Material

“…Some other species (4) fall in a pattern of paraphyly (A. microphyllum embedded in A. pulverulentum lineages; A. grosii embedded in A. meonanthum lineages) following Sutton's (1988) circumscription of species (Figure 3). This suggests a pattern of budding speciation typically found in Iberia (Otero et al, 2019). The hypothesis of a general pattern of budding speciation in Antirrhinum needs to be tested with a higher number of populations, particularly from widespread species.…”

Plant speciation in the Namib Desert: origin of a widespread derivative species from a narrow endemic

“…Such P-D pairs are often expected to display paraphyletic relationships, with accessions of the derivative species occupying a nested position within those of the ancestral taxon (e.g. Lopéz et al 2012;Otero et al 2019). However, our phylogenetic (ML) analysis of multiple intraspecific ITS sequences of S. englerianus and S. flavus (Figure S2) rsulted in an unresolved (polytomous) crown topolgy, including a weakly supported, potentially derived cluster of northern S. flavus.…”