A plant’s mating system can influence its success in invading new environments. Self-compatible species benefit from reproductive assurance during the early phases of the invasion process when founding populations are small but may suffer the fitness costs associated with selfing. By contrast, self-incompatible (SI) plants can suffer from mate limitation in small populations but maintain progeny fitness. However, SI plants often have complex s-allele dominance interactions that allow biparental inbreeding which increases mate availability but may result in reduced fitness in the progeny of related individuals. Our goal was to assess if biparental inbreeding is a good ecological strategy for invaders by exploring the tradeoff between mate availability and progeny fitness in five populations spread across three regions of Australia: Western Australia (WA), South Australia (SA) and Eastern Australia (EA). To do this, we used a two-generation controlled cross experiment to generate full-sib, half-sib and unrelated individuals. All plants were also selfed and all recovered selfed individuals were included in the final design. The resulting seeds were grown in an outdoor enclosure in a randomized block design. A variety of fitness attributes were measured throughout the life of the plants and ANOVA was used to test if there were differences among cross types, populations, and regions.
Results/Conclusions
We found a large amount of variation in the proportion of self-compatible plants among populations (range 0.03 to 0.26). Cross type was significant in explaining variation in six out of ten fitness variables. Seed weight, rosette width, number of leaves, plant height and dried root weight (all measures of overall plant vigour) increased with decreased relateness. Days to germination decreased with decreased relateness. Days from germination to bolting and flowering varied by population and region, but not by cross type. Reproductive output is currently being estimated. These results indicate that although mate availability is increased, fitness is decreased through biparental inbreeding depression in wild radish. The implications for invading populations will be tested using a population model that will include rates of inbreeding depression under various demographic scenarios such as small founding populations and multiple source populations.