Macroevolución y microevolución en sistemas insulares: el patrón Rand Flora en el género Canarina

Abstract

Global change and the current biodiversity crisis have increased the need to understand the effect of climate change on patterns of biodiversity distribution and the mechanisms or factors underlying them. To understand the origin of these biodiversity patterns, scientists have resorted to macroevolutionary explanations studying the relationships between organisms and their habitat at large spatial and temporal scales, and microevolutionary explanations, studying the basis of evolutionary change within species or populations locally and over shorter time spans. One of the best-studied effects of the impact of climate change over diversity patterns is Pleistocene glaciations; however, events of global drought or aridification are more interesting under the current climatic scenario. For this, the African continent offers an ideal scenario. Africa has been considered one of the exceptions to the global Latitudinal Diversity Gradient because a dip in biodiversity can be observed in many organisms as one move from the temperate to the tropical regions; species poverty in this continent has been sometimes attributed to extinction, mediated by climate change (gradual aridification) that also presumably generated large-scale, intracontinental disjunctions. In this sense, the socalled Rand Flora pattern, which relates angiosperm lineages that share similar disjunct distributions across the margins of the African continent and adjacent islands (Macaronesia-west Africa, the Horn of Africa-South Arabia, east Africa and Southern Africa), offers us a unique opportunity to study the effects of rapid climate change on patterns of biotic assembly. One of the most extreme representatives of this pattern is the genus Canarina. Belonging to the tribe Platycodoneae, a basal lineage within the Campanulaceae family, this genus comprises only three species with a widely disjunct distribution: the island-endemic Canarina canariensis is associated to the unique laurel habitat of the Canary Islands facing northwest Africa, while at the other end of the Sahara Desert, Canarina abyssinica and Canarina eminii are inhabitants of the East African Mountain forests. Thus, the distribution of Canarina species seems to be restricted to what is considered the last remnants of a subtropical vegetation that was presumably widespread throughout Africa, and which are now confined to island ecosystems on the continental margins of Africa: the Canarian species on oceanic islands, and the East African species "within-continent" islands or sky islands ¿ geographically isolated high-altitude habitats occurring alongside different mountain ranges. The overall objective of this thesis is to study the evolutionary history of the genus Canarina to try to infer the macro- and microevolutionary processes that generated its current distribution. We have used an integrative and multidisciplinary approach encompassing macroevolutionary (phylogeny, biogeography, ecology) and microevolutionary (phylogeography, demography, population genetics) approaches...