Clinal variation in life-history traits of the invasive plant species Echium plantagineum L.

Range expansion during the invasion of a novel environment requires that invading species adapt to geographical variation in climate and maintain positive population growth in the face of environmental heterogeneity. Thus, invasive species are expected to undergo adaptive evolutionary changes as they encounter novel selection pressures. The aim of this thesis was to identify adaptive changes in plant growth and reproductive traits throughout the lifecycle of a model invasive species to determine which traits are vital to the success of invasive species encountering novel environments. The model species used in this study was the widespread European invader, Echium plantagineum, which has invaded over 33 million ha across Australia, causing ~$30 million (AUD) damage per annum. I investigated geographic variation in life-history traits of 34 populations of E. plantagineum across a 1,000 km arid-mesic gradient throughout south-eastern NSW, Australia. Seeds were collected for each population along the arid-mesic gradient, germinated in the laboratory and grown in the glasshouse in a common environment. I found that E. plantagineum has rapidly adapted to environmental selection pressures throughout its range, resulting in two major clines linked to plant flowering time and seed size of progeny. Compared with populations from mesic habitats along the arid-mesic gradient, plant populations from arid environments had significantly higher relative growth rate and leaf production which was associated with much earlier flowering time and reduced time between stem production and flower production. Plants from arid regions also produced significantly larger seeds compared with plants from mesic habitats. Interestingly, seeds from all E. plantagineum populations along the arid-mesic gradient germinated rapidly (within 48 hours of water exposure) allowing them to quickly and opportunistically take advantage of available resources. Considered together, these adaptations allow E. pl