The keys to plant diversityThe evolutionary investigation of biological diversity must integrate multiple perspectives: morphology, genetics, geography, development, cytogenetics, biotic and abiotic interactions, etc. All these factors generate diversity through evolutionary and speciation processes. Furthermore, the study of plant diversity should be approached at different evolutionary scales, from macroevolution (above the species rank, on a wide spatial and temporal scale), through the transition between macro- and microevolution (represented by the speciation process itself), to microevolution (populations and individuals of the same species). Throughout my research career, I have addressed these three scales using different study systems and a multidisciplinary approach. In particular, an important part of my work has focused on the tribe Antirrhineae (family Plantaginaceae), a clade of c. 30 genera and 300–400 species distributed throughout both the Old and New World, and exhibiting remarkable phenotypic diversity. Since the 20th century, species of this clade have served as a model for numerous studies in genetics, developmental biology, and evolutionary biology, some of them fundamental to our understanding of plant biology. For this reason, we will continue using this group as a study system at different scales, in combination with other evolutionary lineages of great interest, such as the genus Scalesia of the Galápagos Islands.
The macroevolutionary scale
Evolutionary radiation (understood as rapid diversification) is a macroevolutionary pattern that provides essential opportunities to understand the factors driving biological diversity. Thus, a “key innovation” would be an evolutionary change in a trait that is causally associated with an increased rate of diversification in the resulting clade, as has been proposed, for example, for nectar spurs. We have evaluated the role of the nectar spur as a key innovation in the tribe Antirrhineae (where more than 75% of the species and subspecies present this character) in the framework of the deepest phylogenetic analysis of this clade to date. Although the diversification rate was higher, on average, in spurred lineages, this association is not unequivocal or immediate, indicating that diversity asymmetries cannot be explained based on a single trait, but rather by the combined action of multiple factors. |
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The transition from macro- to microevolution: speciation
At this scale, the factors driving speciation and phenotypic divergence between closely related species in a given geographic context are studied. In particular, there is evidence that flower evolution has driven angiosperm diversification through adaptation to diverse pollinating agents. Within the Antirrhineae, we have conducted studies at the scale of speciation mainly in the genus Linaria, the most diverse of the tribe, with a focus on Linaria sect. Versicolores, a clade of about 30 species and subspecies distributed mainly in the western Mediterranean and displaying flowers with highly specialised traits. A clade within Linaria sect. Versicolores formed by eight species endemic or sub-endemic to the Iberian Peninsula is allowing us to investigate speciation processes in great detail using a multidisciplinary approach combining ecological, phylogenetic and evolutionary developmental perspectives (eco-evo-devo). A phylogenomic analysis based on high-throughput sequencing data (genotyping-by-sequencing) revealed a remarkable pattern of divergence in flower traits between geographically close sister species, and of convergence in phylogenetically and geographically distant species. Recent speciation events coincide with remarkable changes in floral traits linked to pollination (corolla colour, tube width, spur length), supporting a hypothesis of pollinator-mediated speciation. Furthermore, at a higher level of detail, the two sister species L. clementei and L. becerrae provide an ideal system to investigate a specific speciation event. These two narrowly distributed endemics from the southern Iberian Peninsula display a remarkable difference in the length of the floral spur (potential key innovation). We are currently studying this speciation event from multiple perspectives: evo-devo, pollination ecology, environmental niche, genetic differentiation, crossing experiments, etc. |
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We have also investigated the diversification of Scalesia, a plant genus known as “Darwin's finches of the plant world” because it is the most representative adaptive radiation of plants in the Galápagos Islands, first observed by Darwin during the voyage of the Beagle. Unlike their zoological counterparts (Darwin’s finches), Scalesia species had barely been investigated from an evolutionary perspective. In collaboration with researchers from Ecuador and the USA, we have used genotyping-by-sequencing to reconstruct phylogenomic relationships and evolutionary patterns of this iconic radiation. Results revealed recent explosive diversification from a common ancestor, lack of compliance with the “progression rule” hypothesis (which predicts a concordance between lineage age and island age), predominance of within-island speciation over between-island speciation, and prevalence of convergent evolution.
Microevolutionary scale
In the Mediterranean Region, Quaternary climatic fluctuations appear to be the main factor driving the recent history of intraspecific lineages and the distribution of genetic diversity, as revealed by phylogeography, population genetics and species distribution modelling. We have applied these approaches to species with a broad range of geographical distributions, from narrow endemics to circum-Mediterranean species, leading to several novel insights. Although it was traditionally assumed that the altitudinal and latitudinal gradients determined the main population movements, our study in the Iberian species Linaria elegans discovered a fundamental role of the oceanic-continental gradient in determining the location of glacial refugia. In a completely different lineage, we have found that oceanic conditions also allowed the Canary Islands to act as a refuge for genetic diversity in the thermophilous species Cistus monspeliensis. This was the first species in which a significantly higher genetic diversity was discovered in oceanic islands than in the continental region of origin (Mediterranean Region), a pattern contradicting the one usually assumed.
In the Mediterranean Region, Quaternary climatic fluctuations appear to be the main factor driving the recent history of intraspecific lineages and the distribution of genetic diversity, as revealed by phylogeography, population genetics and species distribution modelling. We have applied these approaches to species with a broad range of geographical distributions, from narrow endemics to circum-Mediterranean species, leading to several novel insights. Although it was traditionally assumed that the altitudinal and latitudinal gradients determined the main population movements, our study in the Iberian species Linaria elegans discovered a fundamental role of the oceanic-continental gradient in determining the location of glacial refugia. In a completely different lineage, we have found that oceanic conditions also allowed the Canary Islands to act as a refuge for genetic diversity in the thermophilous species Cistus monspeliensis. This was the first species in which a significantly higher genetic diversity was discovered in oceanic islands than in the continental region of origin (Mediterranean Region), a pattern contradicting the one usually assumed.