Habitat fragmentation negatively affects effective gene flow via pollen, and male and female fitness in the dioecious tree, Spondias purpurea (Anacardiaceae)

Abstract

Habitat fragmentation is recognized as one of main threats to global biodiversity. Habitat fragmentation negatively affects population size and mutualistic interactions that directly impact plant fitness and genetic diversity; however, little is known about effects on dioecious trees. We assessed the effects of forest fragmentation on plant-pollinator interactions, male and female reproductive success, realized gene flow, genetic diversity and spatial genetic structure (SGS) in the dioecious tree Spondias purpurea. The study was performed in continuous and fragmented forest habitats in the region of the Chamela-Cuixmala Biosphere Reserve, Jalisco, Mexico. Stingless bees were the main pollinators followed by wasps and flies. There were no differences in pollinator assemblages between habitat conditions, however visitation rate was higher in continuous habitats. Male trees produced more flowers than female trees in both habitat conditions. Total flower production was higher in fragmented habitats, but a higher fruit-set was observed in continuous habitat. In fragmented habitats, realized pollen flow occurs at a shorter distance and correlated paternity was higher than in continuous habitats. Genetic diversity and SGS were comparable among adult trees between habitat conditions; however, juveniles and seeds had lower heterozygosity levels and higher inbreeding coefficients in fragmented habitats. Our results suggest that mating systems and pollinator dependence are both key elements influencing plant vulnerability to habitat fragmentation. We conclude that conservation efforts should focus on processes that maintain reproductive success and genetic diversity of species to ensure persistence in the long term.