A fig tree in a concrete jungle: fine-scale population genetic structure of the cluster fig Ficus racemosa in an urban environment

Abstract

Urban vegetation is an essential requirement in cities for mitigating pollution, heat island effects and providing food and shelter to urban fauna. Efforts to conserve and augment green cover in cities, however, often lack data on the genetic diversity of urban trees, which could be crucial to the success of such programmes. We investigate the population genetics of the cluster fig Ficus racemosa, which occurs naturally in Indian cities and is a keystone species for urban fauna. Genetic analysis of 51 F. racemosa trees in urban Bangalore, India, shows no evidence of inbreeding; the overall inbreeding coefficient (F is ) across 12 microsatellite markers (0.0366) was non-significant with no evidence of heterozygote deficit. Spatial genetic structure (SGS) analysis of 47 trees showed an overall negative relationship between kinship coefficient and spatial distance, with strong SGS at distances <1 km. The absence of heterozygote deficit is likely due to the fig’s obligate mutualistic association with fig wasps which pollinate their flowers even across long distances. However, the strong SGS at short distances could result from clumped seed dispersal close to natal trees. Therefore, the pattern of population genetics for F. racemosa from urban Bangalore likely results from short-distance seed dispersal and long-distance pollen flow. Despite the scattered and fragmented nature of green areas within cities, these gene mobility factors maintain robust population genetics in F. racemosa even at low population densities. The same may not apply for Ficus species that are planted as vegetative cuttings in cities and therefore may have limited genetic diversity.