Colonization is a critical filter for the establishment of most introduced populations, and recent work has emphasized that increased genetic diversity in a founder population can enhance colonization success. Yet the mechanisms by which increased genetic diversity may be beneficial for colonization are often not clear; for example, are sampling effects or complementarity more important for driving those patterns? We conducted a field-based seed addition experiment in Texas using the ruderal mustard Arabidopsis thaliana in which we manipulated founder population size (five levels, ranging from 32 to 960 seeds per 0.25 m2plot), genetic diversity (one, four or eight genotypes) and interspecific competition (ambient or reduced). All genotypes were also seeded as single-genotype populations so statistical expectations for mixture plots could be compared to observed colonization success in mixtures. In each of three growing seasons we collected DNA from plants in mixture plots so genetic markers could be used to assess realized genetic diversity in populations over time as well as the per-genotype contributions to colonization success. Knowing the identity of successfully colonizing genotypes also enables tests of whether additive effects (i.e., sampling) or non-additive effects (complementarity) contributed to colonization success in diverse founder populations.
Results/Conclusions
We have reported previously that increased genetic diversity enhanced colonization success in the first generation post-introduction when founder population size (and therefore intraspecific densities) were the greatest and under conditions of apparent resource limitation (low soil nutrient conditions). These patterns have persisted through three generations, including effects on population growth rates (λ). Genetic marker data are now being assessed, and preliminary results indicate that a subset of genotypes appear to have contributed disproportionately to colonization success across the experiment. Many of the most successful genotypes are from source populations towards the southern extent of A. thaliana’s native range, suggesting that sampling effects were strong and related to stressful abiotic conditions in our field site. Further assessments from the genetic marker dataset will be presented, including analyses quantifying the extent to which sampling effects and complementarity contributed to colonization success and analyses designed to identify key characteristics of the most successful genotypes.