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

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.

Genealogical tracing of Olea europaea species and pedigree relationships of var. europaea using chloroplast and nuclear markers

“…Five out of six subspecies showed peculiar polymorphisms, forming separate clusters when analyzed by Maximum Likelihood and Network methods. Contrariwise, the four samples of subspecies laperrinei , here analyzed, showed a strong similarity at chloroplast level with the subspecies europaea belonging to lineage E1 and therefore to the cultivars, as already described in previous studies [ 27 , 44 , 45 ]. In O. europaea subsp.…”

Limitation of gene flow by distance in the common yellow jasmine (Chrysojasminum fruticans, Oleaceae): implications for the study of its mating strategies

“…However, when the species has a long generation time and/or if perturbations are quite recent, it might be necessary to check these assumptions. In addition, the precision of estimates of genetic differentiation used to infer gene flow depends on the sampling of populations (Petit et al, 2005;Besnard et al, 2021). Although the R estimate can help comparing the relative contribution of pollen and seeds in global gene flow among taxa (Ennos, 1994;Petit et al, 2005), it thus still needs to be interpreted with caution.…”