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.
Highlights
Current diversity patterns are influenced by both historic and recent environmental conditions
The western Mediterranean–Macaronesian transition area bears an unusual combination of characteristics, which includes a geographical closeness between continents and between oceanic islands and mainland areas, as well as a broad range of geological ages, palaeoclimatic events and palaeogeographic features
Population structure based on Amplified fragment length polymorphism (AFLP) Bayesian clustering conducted using STRUCTURE resulted in a best partition of four clusters with a maximum modal value of ΔK = 249.02 [see Supporting Information— Fig. S1]
Summary
Current diversity patterns are influenced by both historic and recent environmental conditions. Northern Hemisphere phylogeography relies on the idea that Quaternary glacial/interglacial cycles affected the distribution of plant communities and species (Weiss and Ferrand 2007). The nature of colonization and settlement patterns after the last glacial period is of particular interest to conservation (Soliani et al 2015). Investigating the possible historical dispersal routes of endangered species, with relatively wide and fragmented distribution areas, may provide useful information for the effective implementation of affordable conservation measures. A pre-eminent characteristic of oceanic islands is that they furnish clear-cut spatial and temporal limits and act as living laboratories for studies on the effects of historical colonization, dispersal, geographical isolation and other evolutionary patterns of plants A pre-eminent characteristic of oceanic islands is that they furnish clear-cut spatial and temporal limits and act as living laboratories for studies on the effects of historical colonization, dispersal, geographical isolation and other evolutionary patterns of plants (e.g. Fernández-Mazuecos and Vargas 2011; Lo Presti and Oberprieler 2011; and references therein)
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