African olive populations from the invaded range exhibit two South African chlorotypes hence supporting an introduction from South Africa, while populations from South Australia exhibit chlorotypes of Mediterranean cultivars.
We previously showed that invasive olive populations from South Australia and NSW have probably derived from introductions of Mediterranean and southern African trees (Besnard et al. 2007a,b 2007a,b
Our genetic analysis confirmed that all invasive olive populations sampled until now originated from two distinct taxa, as first suggested by Besnard et al.
Second, the Structure analysis based on nuclear SSRs (Fig. 3) confirms that invasive olive populations in South Australia and NSW are closely related to Mediterranean cultivars and South African Olives, respectively.
This is likely due to the strong genetic bottlenecks in invasive African olive populations (for instance, many alleles initially shared between europaea and cuspidata in the native range could have been lost after bottlenecks and may bias assignments).
The majority of cultivars was characterised by the chlorotype CE1, which likely originated from the wild olive populations of the Eastern Mediterranean and was spread to the Western part through cultivar dispersal by humans.
These difficulties prevail even with marker assisted attempts to define the relationship between the cultivated olive (Olea europeae L). and the feral olive populations of the Mediterranean, and the reconstruction of the history of olive domestication (Baldoni et al. 2006; Breton et al. 2006; Bronzini de Caraffa et al. 2002; Lavee and Zohary 2012).
First, the cpDNA variation (Fig. 1) shows that South Australian olive populations have three Mediterranean chlorotypes (which are detected in Mediterranean olive cultivars; Besnard et al. 2011), while populations from NSW (with the exception of Camden Park, Mount Annan no. 17 and Bringelly no. 21) and Maui display two African chlorotypes.
This analysis also revealed differences between all pairs of neighbouring populations, except between Mbita Island and Wonzye Point (both belonging to the light-olive morph), and between Wonzye Point and the dark-olive population from Muzumwa.
Interestingly, neighbouring populations belonging to different colour morphs had highly divergent parasite communities, but neighbouring populations belonging to the same colour morph were also rather divergent in parasitism (with the exception of the light-olive populations - i.e. the only pair without a major barrier to Tropheus dispersal; Figure 1).
