OOS 57-1 - Conferred evolutionary resistance to invasion: An empirical test of evolutionary invasional meltdowns using duckweed communities (Lemna minor & Spirodela polyrhiza) and invasive Salvinia spp.

Invading species can alter the abiotic and biotic aspects of ecosystems to mutually facilitate each other’s establishment and impact on native communities (i.e. invasional meltdown). While researchers have described the ecological mechanisms of facilitation between multiple invasive species, the reciprocal evolutionary impacts that different invasive species can have on communities remains unexplored. For instance, the presence of an invasive species might alter the evolution of community populations such that these communities become more invasible by another invasive species in the future (evolutionary invasional meltdown). Conversely, exposure to an invasive species might result in the evolution of increased resistance to invasion by populations of the same or different invasive species. To understand the eco-evolutionary consequences of community evolution to invasive species, we evolved genotypically diverse communities of duckweed (Lemna minor and Spirodela polyrhiza) in the presence, absence, or combination (i.e. co-invasion) of invasive aquatic ferns Salvinia natans or Salvinia minima. Following a common garden phase, we reconstituted these communities and conducted reciprocal invasions of Salvinia spp. to measure adaptation and community evolutionary responses to experimental invasion histories.

Our findings show that experimental populations of L. minor and S. polyrhiza exhibit significant and differential evolutionary responses to non-native Salvinia spp. Populations of L. minor invaded by S. minima evolved significantly smaller per capita surface area than pre-evolved populations and those evolving with S. natans (p = 0.001). Populations of S. polyrhiza invaded by co-invasions of S. natans and S. minima evolved significantly larger per capita surface area than their pre-evolved counterparts (p = 0.04). Communities that evolved in the presence of S. minima demonstrated significantly reduced invasibility to future experimental invasions compared to reconstructed communities consisting of the original genotypes and their initial compositions prior to experimental evolution (p = 0.03). These results illustrate the complexity of evolutionary outcomes that can result from the introduction of even closely related invasive species. Contrary to our initial hypothesis, we observed that evolution to a single invasive species can negatively affect the future establishment and impact of the same or different invasive species. This not only suggests that community evolution can result in changes to invasive species’ success over time, but that these eco-evolutionary outcomes are asymmetrical and contingent on the order in which species invade.