Contrasting Genetic Footprints among Saharan Olive Populations: Potential Causes and Conservation Implications.

Guillaume Besnard,Ahmed El Bakkali,Océane Gorrilliot,Djamel Baali-Cherif,Benoit Génot,Pauline Raimondeau,Fabien Anthelme

doi:10.3390/plants10061207

Abstract

The Laperrine’s olive is endemic to the Saharan Mountains. Adapted to arid environments, it may constitute a valuable genetic resource to improve water-stress tolerance in the cultivated olive. However, limited natural regeneration coupled with human pressures make it locally endangered in Central Sahara. Understanding past population dynamics is thus crucial to define management strategies. Nucleotide sequence diversity was first investigated on five nuclear genes and compared to the Mediterranean and African olives. These data confirm that the Laperrine’s olive has a strong affinity with the Mediterranean olive, but it shows lower nucleotide diversity than other continental taxa. To investigate gene flows mediated by seeds and pollen, polymorphisms from nuclear and plastid microsatellites from 383 individuals from four Saharan massifs were analyzed. A higher genetic diversity in Ahaggar (Hoggar, Algeria) suggests that this population has maintained over the long term a larger number of individuals than other massifs. High-to-moderate genetic differentiation between massifs confirms the role of desert barriers in limiting gene flow. Yet contrasting patterns of isolation by distance were observed within massifs, and also between plastid and nuclear markers, stressing the role of local factors (e.g., habitat fragmentation, historical range shift) in seed and pollen dispersal. Implications of these results in the management of the Laperrine’s olive genetic resources are discussed.

Highlights

The Sahara Desert is an area of 9,200,000 km2 with occidental and oriental boundaries stretching out from the Atlantic coast to the Red Sea [1]
Four non-diploid genotypes were included in this sampling (Table S1) and excluded from population genetics analyses based on nuclear microsatellites
Our observations may have implications for in situ conservation of this endangered taxon in the Saharan mountains, and for its management in ex situ collections to evaluate its potential value as a genetic resource for the improvement of the cultivated olive

Summary

Introduction

The Sahara Desert is an area of 9,200,000 km with occidental and oriental boundaries stretching out from the Atlantic coast to the Red Sea [1]. This hostile environment acts as a major geographic barrier between the Mediterranean Basin and tropical Africa [2,3]. Several successive dry and wet periods have, induced the decline and expansion of suitable habitats for living organisms, including humans [3,4]. Several long-living tree species have persisted in this environment, including a few iconic endemics such as the Tassili’s cypress The long generation time of tree species may limit their ability to evolve, making them vulnerable to abrupt environmental changes

Methods

Results

Discussion

Conclusion