Using phylogeography to define conservation priorities: The case of narrow endemic plants in the Mediterranean Basin hotspot
Abstract Rare and vulnerable narrow endemic species represent distinct evolutionary units emerging from various temporal processes, and the preservation of such species is a key issue in biological conservation. Phylogeography has proven to be a relevant tool for distinguishing evolutionary units within species resulting from contrasted biogeographical events, and it can be leveraged to obtain historical and evolutionary perspectives. Yet, despite its usefulness, it is curiously underutilized in plant conservation genetics. Here we provide a comprehensive review of the available case studies on the structure of genetic diversity in the Mediterranean narrow endemic plants (MNEs) of the Mediterranean Basin hotspot. The use of genetic diversity structure for phylogeographical inference and for defining conservation units was examined in eighty-four studies dealing with eighty-three distinct taxa, most of which are perennial herbs occupying a narrow ecological niche. In addition, some 91.5% of the analyzed MNEs are located in the north-western part of the Mediterranean region, and this results in a geographical coverage that is heavily biased. Half of the studied species have moderate to high genetic diversity, and genetic differentiation is geographically structured in 56% of the case studies, indicating that MNEs are not “evolutionary dead-ends,” but rather represent species that have a strong evolutionary legacy. Taken at face value, this would imply conservation planning at the population level. However, it was only a minority of the studies that used these genetic structures to define conservation units. The main insight of the present review is that phylogeography is generally overlooked in conservation genetics. In fact, the design of conservation units has not often been the main goal of these studies, which more commonly is simply to enhance the scope of genetic diversity analyses of rare plants. Nevertheless, the strong phylogeographic structure revealed by several studies of MNEs underlines the relevance of phylogeography. We argue that comparative phylogeography across several co-occurring taxa could greatly improve the proactive conservation planning for threatened endemic plants within biodiversity hotspots.