Hopping or Jumping on the Cliffs: The Unusual Phylogeographical and Demographic Structure of an Extremely Narrow Endemic Mediterranean Plant.

Sandro Strumia,Teresa Rosa Galise,Annalisa Santangelo,Donata Cafasso,Salvatore Cozzolino

doi:10.3389/fpls.2021.737111

Sandro Strumia, Teresa Rosa Galise + Show 3 more

Open Access

https://doi.org/10.3389/fpls.2021.737111

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Abstract

Several past and recent climatic and geological events have greatly influenced the current distribution of coastal species around the Mediterranean Basin. As a consequence, the reconstruction of the distributional history of these species is challenging. In this study, we used both chloroplast and nuclear SNPs to assess the levels of genetic differentiation, contemporary/historical levels of gene flow, and demographic history for the three only known (one mainland and two insular) populations of Eokochia saxicola, a rare Mediterranean coastal rocky halophyte. Plastid genome analysis revealed very low intraspecific haplotype variation and partial admixture among Capri and Palinuro populations with at least two independent colonization events for the Strombolicchio islet. Nuclear SNPs variation consistently identified three distinct genetic clusters corresponding to our sampling localities. Furthermore, strong genetic isolation was confirmed by both historical and contemporary levels of migration among the three populations. The DIYABC analysis identified two introductions temporally separated from Palinuro to Capri (ca.25 Mya) and subsequently to Strombolicchio (ca.09 Mya) as the most likely hypothesis for the current distribution of E. saxicola. Regardless of their small population sizes, all study sites supported high-genetic diversity maintained by outcrossing and random mating between individuals owing largely to wind pollination, an exclusive trait among Mediterranean narrow endemics. In conclusion, the patterns observed confirm that some Mediterranean endemics are not necessarily “evolutionary dead-ends” but rather represent species that have extensive demographic stability and a strong evolutionary legacy.

Highlights

The Mediterranean Basin is one of the Hotspots of Biodiversity on the Earth (Médail and Quézel, 1999; Myers et al, 2000), largely due to the high number of endemic species (Quezel, 1985; Greuter, 1991)
The general pattern largely associated with coastal halophytes inhabiting dune and marshes habitats has not been found in coastal rocky species (Kadereit and Westberg, 2007)
Even if short and long seed dispersion is still possible, why E. saxicola is so rare compared with other littoral halophytes species (Davis, 1951)? the strong genetic differentiation detected among living populations suggests that the longdistance colonization typical of halophytes is merely occasional

Summary

Introduction

The Mediterranean Basin is one of the Hotspots of Biodiversity on the Earth (Médail and Quézel, 1999; Myers et al, 2000), largely due to the high number of endemic species (Quezel, 1985; Greuter, 1991). The subsequent warming phases led to these temporary land bridges being gradually submerged by rising sea levels (Feliner, 2014) This main isolating barrier favored speciation processes, which resulted in the increase of insular endemics in the Mediterranean Basin (Médail, 2017). The general pattern largely associated with coastal halophytes inhabiting dune and marshes habitats has not been found in coastal rocky species (Kadereit and Westberg, 2007) Both inland and coastal rocky areas provide suitable habitats for numerous endemic species often with extremely restricted distribution (Davis, 1951; Lavergne et al, 2004; Thompson, 2005) with many of them being considered “narrow endemics” (Kruckeberg and Rabinowitz, 1985; Médail and Baumel, 2018) and threatened by extinction (Montmollin and Strahm, 2005; Orsenigo et al, 2018). They play a key role in the biodiversity conservation priority setting (Médail and Baumel, 2018)

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