The series of papers known as ‘Geron et al.’ has a new addition, marking the final piece of Charly Geron’s PhD trajectory studying the link between urban plant invaders and urban microclimates.

In his earlier chapters, we already demonstrated that urban invaders often originate from warmer and drier native regions, probably benefiting from the warmer urban temperatures due to the urban heat island effects. We found that these species nevertheless prefer shaded environments, which protect them during urban heatwaves. We also explored the traits, phenology and genetics that contribute to these behaviors.

In the latest article by Geron et al. published in Oecologia, we delve deeper into the latter pressing question: do non-native plant species adapt to urban environments? We focused on the delicate little (but make no mistake, this species native to the north Caucasus and Iran can be a real crop pest) flower Veronica persica (bird’s-eye speedwell) as our model species, conducting a combination of field (or better – urban road verges and wastelands) surveys and a ‘common garden’ experiment.

What we were after was straightforward to articulate, but – sorry – bloody difficult to test: was there a difference in the development and performance of Veronica persica between urban and rural settings, and, if differences exist, could they be attributed to either adaptation, mother plant influence or simple plasticity? if plants from urban origin showed a higher reproduction in urban microclimate, it might be the sign of adaptation to urban environments. If not, it could suggest that Veronica persica is highly plastic, resulting in variations in its development following local conditions but not due to genetic changes.

Our findings highlighted the latter scenario. Veronica persica exhibited significant phenotypic plasticity across all measured traits, with reduced germination, growth, and flowering under urban conditions. This suggests significant setbacks to plant success in the more stressful growing conditions of a warmer urban microclimate.

Interestingly, we found no significant differences in how well urban versus rural plants coped with these conditions, indicating a lack of local adaptation. However, we observed notable genetic differences at the population level, influenced by the identity of the mother plant, suggesting genetic diversity among populations.

Does this mean that non-native plant species cannot adapt to urban environments? Certainly not. It’s important not to generalize based on a single species. Our findings did align surprisingly well with previous research on Matricaria discoidea (pineapple weed), however, which also demonstrated strong phenotypic plasticity and maternal effects, but no clear local adaptation.

Two is not yet a crowd, yet they do show clearly that detecting subtle local adaptation amidst the variability introduced by phenotypic plasticity is challenging, especially in highly adaptable ruderal non-native species.

We can only end – as so often necessary – with a call for further research. Urban environments are warming rapidly, and the urban environment creates unique ecosystems. Understanding how both non-native and native species may or may not adapt to these conditions is crucial for protecting future biodiversity.

Read the full story in Oecologia or here on ResearchGate to find out more!