Conservation of wet meadow species in an urban context: Lychnis flos-cuculi as study case.
In urban areas, wetland habitats consist of small isolated remnants, embedded in an inhospitable human-used matrix, and incurring strong anthropogenic pressures (e.g., artificialization, pollution, eutrophication, and exotic species invasions). These can lead to detrimental genetic and demographic consequences for the populations, even for common species. This study investigated genetic variation and structure for 12 allozyme loci and reproductive fitness in populations of Lychnis flos-cuculi (Caryophyllaceae), an insect-pollinated perennial herb occurring in wetland fragments and along the Woluwe River, in Brussels urban zone (Belgium), in relation to population size. No effect of population size on genetic variation and usually low between-population genetic differentiation were found for urban populations of L. flos-cuculi. A significant pattern of isolation by distance indicated that beyond a certain distance, especially along the Woluwe, populations might still exchange genes. Floral display and fruit set increased with population size, but this relationship did not seem to be predominant. Significant differences found among populations suggest that other factors (e.g., plant density, neighbour competition and habitat quality) may have a stronger impact on reproductive fitness. Some of the small populations may also be still connected through pollen flow, increasing reproductive success and preventing inbreeding depression. The present findings suggest that populations of L. flos-cuculi in Brussels urban zone are not prone to the detrimental effects of habitat fragmentation, as we may have expected, despite the relative small size of the populations. These genetically diverse and productive populations can still be considered of conservation value, including the small ones, which within a certain spatial distance might be regarded as important connecting components of pollen-exchanging network of populations, buffering populations against the negative effects of small population size. The conservation of L. flos-cuculi in Brussels urban zone should favour the preservation of connected populations rather than only preserving isolated wetlands.