LB 21-186 - The flower doesn’t flower in the city: Evolution of the plant reproductive traits in an urban population.

Background/Question/

Methods: Recent research indicates that environmental change with urbanization can lead to the evolution of organisms. In urban areas, biotic and abiotic factors differ from rural areas, such as interactions with pollinators and temperature changes caused by urban heat islands, which may drive biological evolutions. Previous studies have mainly focused on leaf traits and plant form to examine plant evolution in urban environments, paying little attention to reproductive traits. This presentation compares plant traits, including reproductive traits, between urban and cultivated lands for Japan's annual herbaceous plant, Portulaca oleracea.Seeds were collected from 98 individuals in urban areas (9 populations) and surrounding cultivated lands (9 populations) in Tokyo, Japan. The F2 generation was used to measure traits of P. oleracea, such as flower type (see results below), phenology, and seed weight. Results/

Conclusions: Previous study (Furukawa et al. 2020. Annals of Botany) has shown that P. oleracea has individuals that produce only open flowers (chasmogamous, hereafter CH) and individuals that produce only closed flowers (cleistogamous, hereafter CL). The present study found that the CL type appeared more frequently in urban areas than CH type individuals. Some environmental variables such as ground surface temperature and potential evapotranspiration were analyzed as predictors to examine the factors influencing each flower type occurrence. The results showed that surface temperature was the most important variable, with CL types being more abundant in areas with higher temperatures. Compared to CH type, CL type started flower bud formation more than ten days earlier, and the average seed weight was significantly heavier. The CL type may have an advantage in urban areas because it can start reproducing before summertime severe heat and dry conditions. This study suggests that the dimorphism in flower production may be genetically differentiated in response to urbanization in P. oleracea.