Genetic diversity and structure of the globally invasive tree, Paraserianthes lophantha subspecies lophantha, suggest an introduction history characterised by varying propagule pressure

Genetic analyses reveal complex introduction histories for the invasive tree Acacia dealbata Link around the world

“…In contrast, populations from La Réunion have very low genetic diversity (even lower than South African populations; see Hirsch et al., 2019) and showed genetic structure. Such extremely low genetic diversity levels are likely due to very low propagule pressure (number and size of introduction events) and genetic drift (Thompson et al., 2016; Ward et al., 2008), a notion supported by our ABC model estimates which showed that La Réunion had the lowest estimated introduced population size of all non‐native ranges we considered (i.e. 105 individuals; Table , Appendix ).…”

“…New Zealand populations had similar genetic diversity levels to native and other non‐native ranges and showed no clear genetic structure. We assume that high propagule pressure due to the multiple introductions helped to maintain high levels of genetic diversity in this range (Thompson et al., 2016). As discussed above, such a boost of genetic diversity can be beneficial for the invasion success of an introduced species by providing sufficient genetic variation to overcome founder effects and to cope with environmental conditions in the new range (Dlugosch et al., 2015; Lavergne & Molofsky, 2007).…”

Psidium guajava in the Galapagos Islands: population genetics and history of an invasive species

“…Other plants that are known invaders in island ecosystems, such as Cortaderia jubata and C. selloana in New Zealand [45] and Miconia calvescens in several Pacific islands [46] exhibit a very low genetic diversity, as expected (H E = 0.061, H E = 0.095 and H E = 0.110 respectively). However, other invasive species in island settings, like Senesio madagascarensis [47] and Paraserianthes lophantha [48] in Hawaii, exhibit much higher genetic diversity levels (H E = 0.790 and H E = 0.600 respectively), argued to be a product of gene flow or multiple introductions [42]. By contrast, the P. guajava populations in Galapagos show an expected heterozygosity which is intermediate to these scenarios.…”

“…Finally, one of the best supported scenarios in the ABC analysis (scenario B) confirms that Isabela, along with San Cristobal, contributed to the presentday Santa Cruz population. The multiple origins of the Santa Cruz P. guajava population may explain the absence of bottleneck evidence this island (Table 3), since the effects of genetic bottlenecks are softened when multiple introductions occur [48,49]. The admixture of the San Cristobal and Isabela lineages in Santa Cruz, may also help explain the higher genetic diversity and number of lineages (K=4, S3 Fig) found.…”

The role of hybridization in facilitating tree invasion

“…Novel hybrid invasives that involved only non-native species include Acacia pycnantha , A. saligna and A. cyclops (intraspecific hybrids; Le Roux et al 2011 ; Thompson et al 2012 ; Ndlovu et al 2013 ), Casuarina (interspecific hybrid; Gaskin et al 2009 ), Leucaena (white leadtree; Fabaceae; an intraspecific hybrid with origins in North and Central America and now invading Australia; Raghu et al 2005 ), Olea (interspecific hybrid; Besnard and El Bakkali 2014 ), Paraserianthes (Cape Leeuwin wattle; Fabaceae; an intraspecific hybrid of geographically structured Australian native sources now invading South Africa; Thompson et al 2016 ), Pinus taeda (intraspecific hybrid; Zenni et al 2014 ) , Prosopis (interspecific hybrid; Van Klinken et al 2006 ), Pyrus (intraspecific hybrid; Hardiman and Culley 2010 ), Salix (interspecific hybrid; Greenwood et al 2004 ), Schinus (intraspecific hybrid; Williams et al 2005 ) and Tamarix (interspecific hybrids; Gaskin and Schaal 2002 , Gaskin and Shafroth 2005 ).…”