Allopolyploidy enhances survival advantages for urban environments in the native plant genus Commelina

Urbanization-induced environmental changes affect the geographical distribution of natural plant species. This study focused on how polyploidization, a dynamic genome change, influences the survival and distribution of Commelina communis (Cc) and its subspecies C. communis f. ciliata (Ccfc), which have variable chromosome numbers (e.g. Cc, 2n = 88 for Cc; Ccfc, 2n = 46 for Ccfc). The aim was to investigate polyploidization effects on natural plant distribution in urban environments.

The geographical distribution across urban-rural gradients was investigated at a total of 218 sites in Japan. Stomata size and density were measured and compared between Cc and Ccfc. Flow cytometry determined genome size and polyploidy. Chromosome karyotyping was performed using the genomic in situ hybridization (GISH) method.

Urban areas were exclusively dominated by Cc, while Cc and Ccfc coexisted in rural areas. Cc had larger and fewer stomata and a genome size more than twice that of Ccfc. GISH results indicated that Cc possesses Ccfc and another unknown genome, suggesting allopolyploidy.

Our results show that the ploidy difference affects the geographical distribution, stomata traits and genome size between two distinct taxa in the genus Commelina, C. communis as a neo-tetraploid and C. communis f. ciliata, the diploid. Cc is an allopolyploid and is therefore not only polyploidy but also has an additional genome that provides new sets of genes and alleles, contributing to Cc having enhanced survival potentials in urban environments compared with Ccfc. This is the first investigation to clarify the distribution difference related to urban environments, the difference in stomata traits and genome size, and to study chromosome composition in Commelina species.