Colloquia

         Ecological and Evolutionary Consequences of Genome Size Variation in Plants

Plant polyploidy in duckweed (Spirodela polyrhiza) alters the outcome of herbivory

Presenting Author
Hannah Rose Assour
Description
Polyploidy is a widespread mutational process in angiosperms with a myriad of phenotypic and genotypic consequences. In addition to consequences incurred by the plant, polyploidy can also have broader effects on species interactions. Yet, knowledge of how ploidy-induced variation first effects plant-herbivore dynamics is scarce. Here, we test whether aphid herbivores exhibit preference for a diploid or polyploid host cytotype and whether ploidy impacts plant resistance and tolerance to aphids, measured as aphid and plant performance respectively. To answer these questions, we evaluated aphid choice and compared the effects of the water-lily aphid (Rhopalosiphum nymphaeae) herbivore on multiple independently synthesized lines of neopolyploid greater duckweed (Spirodela polyrhiza) and their immediate diploid progenitors in growth chamber experiments. Both aphids and duckweeds are fast-growing organisms, producing multiple asexual generations within several weeks, providing a unique opportunity to evaluate population growth rates of both partners during their interaction. We found that when plants were size matched, aphids did not show a preference for one cytotype over another. We also found that polyploid plants performed as well or worse under aphid herbivory compared to their diploid progenitors. Similarly, aphid growth rates were either the same or higher on polyploid plants. Thus, polyploid plants exhibited lower tolerance and resistance than their diploid progenitors. However, these results varied by genotype, indicating that the effect of polyploidy depends on the plant’s genetic origin. Consequently, it is possible that plant polyploidy may not confer any higher tolerance or resistance to herbivory. Instead, plant polyploidy may contribute to herbivore success and host range expansion, eventually promoting evolutionary diversification of the herbivore.