UC Riverside

Invasive species are a major component to global change. Recent work suggests that evolutionary processes are often involved in the formation of invasive species. Hybridization and whole genome duplication are evolutionary processes that can contribute to the evolution of invasive species; multiple invasive species are the result of hybridization and whole genome duplication in the same lineage (allopolyploid species). Through this work we evaluate the potential invasiveness of a newly formed allopolyploid species, Salsola ryanii, which evolved by hybridization between S. tragus (an invasive species native to Russia and China) and S. australis (an invasive species native to Australia and/or South Africa). We investigate the potential invasiveness of this newly formed through three studies 1) a study of how the range of this newly formed species has shifted in the decade following initial discovery; 2) a common garden comparison of plant size, mass and phenology between S. ryanii and its progenitors; 3) a study of the number of independent evolutionary origins of S. ryanii as determined through an analysis of genetic structure.

Through a systematic collection of Salsola sp in California we documented a rapid range expansion from three to fifteen populations within the decade following initial discovery. This range expansion included expansion from two floristic provinces to six different floristic provinces. We compare the range expansion in S. ryanii to other systems for

which similar data is available and demonstrate that S. ryanii has experienced the most rapid range expansion of any newly formed allopolyploid invasive for which data is available. A dramatic range expansion provides support for the hypothesis that S. ryanii has the potential to become a problematic weedy and invasive species.

In the common garden comparison of S. ryanii and its progenitors we document a significant increase in mass and plant size in the newly formed allopolyploid species. Which of the progenitor species had the larger mass and size was dependent on year. The high fitness of S. ryanii regardless of year suggests a strong potential for S. ryanii to replace one or both of its progenitors in all or part of their range. Salsola ryanii’s large plant size makes it a more problematic weed and the high seed production associated with a large plant size increases the potential for spread.

Number of independent evolutionary origins of potentially invasive newly formed allopolyploid species is linked to evolutionary potential; species resulting from multiple origins which admix with each other have potentially greater genetic diversity and evolutionary potential than species resulting from a single origin. We use an analysis of genetic structure to determine whether S. ryanii results from a single or multiple origins. From the analysis of genetic structure it appears that S. ryanii is the result of at least three independent origin events followed by wide dispersal and admixture. A species resulting from multiple origins followed by admixture theoretically has a stronger potential to become an invasive species than a species resulting from a single origin.

Together these studies provide strong empirical support for the hypothesis that allopolypolyploidization can lead to the evolution of increased invasiveness; specifically this work provides strong evidence that S. ryanii is likely to become more invasive than its invasive progenitors. Documentation of range extension of S. ryanii provides land managers with information about new areas where this species is present. Land managers can utilize this information to control the spread of this newly formed invasive species. It additionally provides a needed first common garden comparison between a newly formed allopolyploid species and its progenitors and adds to our understanding of allopolyploid origins.