Phylogeography of an endangered disjunct herb: long-distance dispersal, refugia and colonization routes

Abstract

Quaternary glacial cycles appear to have had a consistent role in shaping the genetic diversity and structure of plant species. Despite the unusual combination of the characteristics of the western Mediterranean–Macaronesian area, there are no studies that have specifically examined the effects of palaeoclimatic and palaeogeographic factors on the genetic composition and structure of annual herbs. Astragalus edulis is a disjunct endemic found in the easternmost Canary Islands and the semi-arid areas of north-eastern Africa and south-eastern Iberian Peninsula. This endangered species shows no evident adaptations to long-distance dispersal. Amplified fragment length polymorphism (AFLP) data and plastid DNA sequences were analysed from a total of 360 individuals distributed throughout the range of this species. The modelled potential distribution of A. edulis under current conditions was projected over the climatic conditions of the Last Interglacial (130 ka BP) and Last Glacial Maximum (21 ka BP) to analyse changes in habitat suitability and to look for associations between the modelling and genetic results. Amplified fragment length polymorphism analysis showed clear phylogeographic structure with four distinct genetic clusters. Approximate Bayesian computation (ABC) models based on plastid DNA sequences indicated a Middle Pleistocene long-distance dispersal event as the origin of the populations of the Canary Islands. The models also suggested south-western Morocco as the ancestral area for the species, as well as subsequent colonization of north-eastern Morocco and the Iberian Peninsula. The data compiled indicated the possibility of the presence of refuge areas at favourable locations around the High Atlas and Anti-Atlas mountain ranges. Moreover, palaeodistribution models strongly support the events inferred by ABC modelling and show the potential distribution of the species in the past, suggesting a putative colonization route.

Phylogeography at the crossroad: Pleistocene range expansion throughout the Mediterranean and back‐colonization from the Canary Islands in the legume Bituminaria bituminosa

“…Our study on Bituminaria also provided new evidence of the Pleistocene biogeographical connections existing between NW Africa and the Canary Islands. Several studies have recurrently documented events of very recent dispersals from the neighbouring mainland to the Canaries (e.g., Bobo‐Pinilla et al, 2018; García‐Aloy et al, 2017). In agreement with this observation, we found little differentiation at nuclear microsatellite loci coupled with haplotype sharing between eastern Canarian and Anti‐Atlas populations of Bituminaria (Figure 3; Table S7).…”

“…Comparative analyses across taxa have allowed biogeographers to pinpoint refuge areas where the negative impact of Quaternary climatic shifts on biodiversity may have been attenuated (Médail & Diadema, 2009). For instance, recent phylogeographical studies have stressed that NW Africa represents a key reservoir of genetic variation in the region (Bobo‐Pinilla et al, 2018; García‐Aloy et al, 2017; Husemann et al, 2013). However, common phylogeographical patterns across taxa are still difficult to describe in the MB, probably due to the occurrence of manifold evolutionary processes across space and time (Conord et al, 2012; Nieto Feliner, 2014).…”

Phylogeographic sampling guided by species distribution modeling reveals the Quaternary history of the Mediterranean–Canarian Cistus monspeliensis (Cistaceae)

“…The climate of these refugial areas has been markedly buffered by oceanic influence, a pattern found in some other Mediterranean plants (Fernández‐Mazuecos & Vargas, 2013; García‐Verdugo et al, 2013). As a result, western Iberia and north‐western Africa emerge as potential Quaternary refugia for angiosperms (Gómez & Lunt, 2007; Bobo‐Pinilla et al, 2018). In addition, these two areas can be considered centers of diversity involved in the recent expansion of C. monspeliensis across the Mediterranean Basin during the Late Quaternary, as the divergence of Mediterranean haplotypes probably occurred after the LIG (Fig.…”

Looking for a successful translocation: the case of Astragalus edulis

“…It occurs in South-Eastern (SE) Iberian Peninsula, Morocco (two main locations in the North East and South West), and the easternmost Canary Islands (Lanzarote and Fuerteventura). Previous studies have assessed intraspecific genetic diversity and phylogeographic patterns of A. edulis, which have led to propose an in situ management plan to preserve the genetic diversity across the entire distribution area of the species (Bobo-Pinilla et al, 2018;Peñas et al, 2016). As described by Peñas (2004), the dispersal ability of the species is very limited.…”

“…As described by Peñas (2004), the dispersal ability of the species is very limited. The low values of diversity and rarity found have been interpreted as a consequence of recent colonization events or reduction of the effective population sizes (Bobo-Pinilla et al, 2018). Moreover, this species represents an ideal study system to test the utility of Species Distribution Modeling (SDMs) and diversity patterns as a tool to assess how climate change will affect the potential distribution of endangered species from semiarid ecosystems and a way to preserve taxa that have highly fragmented populations.…”