With climate change the frequency and severity of drought in many northern ecosystems has increased. Climate change also promotes range shifts of species from their original range to cooler and wetter regions (higher altitudes and latitudes). During range expansion, plants may lose genetic diversity, and this loss may be particularly detrimental to expanding species adaptation during drought scenarios. However, it still remains unclear how genetic diversity changes during range expansion and if changes affect plant fitness in response to stress. Here, we compare the effect of early- and late-season drought on Geranium lucidum, which is expanding its range northwards within Europe, to Geranium dissectum which is native within the same area. Seeds of both species were collected from southern and northern populations and were grown to test for interacting effects of drought and origin on range expanding plants. After 12 weeks of growth, plants were harvested and measured for above and belowground biomass. Additionally, RADseq was used to assess the genetic diversity of the two species across the range. We hypothesized that range expanding species would perform worse under both drought conditions, compared to native species, because native populations were expected to have higher genetic diversity.
Results/Conclusions
We found that early season drought had a greater negative impact than the late season drought on both species. However, range expanders did not perform considerably worse than natives in response to drought. Interestingly seed origin for both species had a significant effect on drought responses, where seeds collected from the north were more negatively affected by all drought treatments. We also observed an effect of seed origin on the timing of flowering. The drought responses could be partially explained by plant genetic diversity as genotypes form the South (and not present in the Northern range) responded better to drought stress. Overall, this work demonstrates that regardless of the genetic structure, the timing of drought can be very important for plant success and development, yet the interactive effects of drought and genetic diversity are important for the success of range expanders in novel ecosystems. The results of this study provide empirical evidence for genetically homogeneous range-expansion and reveal fundamental insights into the evolutionary processes underlying the ability of range-expanding species to cope with environmental stress. Furthermore, this work in combination with climate predictions can provide insight into the success of range expanding plants under extreme weather events in novel ecosystems.