Phylogeographic consequences of different introduction histories of invasive Australian Acacia species and Paraserianthes lophantha (Fabaceae) in South Africa
Le Roux, J.J.
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Aim The genetic makeup and evolutionary potential of alien species can be profoundly influenced by their introduction history, but without detailed historical records, it can be difficult to ascertain the strength of this historical contingency. We explore how the known introduction histories combined with phylogeographic patterns in the native range have affected the genetic diversity in the invasive range for five Australian trees introduced to South Africa (Acacia cyclops, Acacia mearnsii, Acacia pycnantha, Acacia saligna and Paraserianthes lophantha). Location Western Australia, South Australia, Victoria and New South Wales (native and invasive ranges), and South Africa and the Hawaiian Islands (invasive range). Methods DNA sequence data were generated for all study species for either the external transcribed spacer (ETS) or plastid rpl32-trnL(UAG) gene regions (combined total of 180 DNA sequences). Using statistical parsimony networks and genetic diversity indices, we compared genetic structure and variation in native and invasive ranges. Results Australian acacia species tend to have high genetic diversity at the population level in their native ranges, often showing high intra-specific divergence. In most instances, these species have similar levels of population genetic diversity in their adventive ranges in South Africa, but lack structure. For A. cyclops, A. saligna and P. lophantha, we found evidence for intra-specific hybridization between mixed genetic entities in the invasive range, arguably as a result of the structured native range being broadly sampled prior to introduction. Main conclusions Invasive species that have been extensively used in forestry often have complex introduction histories resulting in equally complex genetic signatures in the invasive range. Our results show that extreme caution should be taken when using indirect inferences (molecular genetic data) of introduction histories in the absence of detailed introduction records.