ABSTRACT: Premise of the study: Wild populations of domesticated species constitute a genetic reservoir and are fundamental to the evolutionary potential of species. Wild papaya (Carica papaya) is a rare, short-lived, gap-colonizing, dioecious tree that persists in the forest by continuous dispersal. Theoretically, these life-history characteristics render wild papaya highly susceptible to habitat fragmentation, with anticipated negative effects on its gene pool. Further, species dioecy may cause founder effects to generate local biases in sex ratio, decreasing effective population size. We contrasted the genetic diversity and structure of C. papaya between wild populations from rainforest fragments and continuous forest at Los Tuxtlas, Mexico. We evaluated recent migration rates among populations as well as landscape resistance to gene flow. Finally, we calculated the sex ratio of the populations in both habitats. Populations of wild papaya in rainforest fragments showed lower genetic diversity and higher population differentiation than populations in continuous rainforest. Estimates of recent migration rates showed a higher percentage of migrants moving from the continuous forest to the forest fragments than in the opposite direction. Agricultural land and cattle pasture were found to be the most resistant matrices to gene flow. Finally, biased sex ratios were seen to affect the effective population size in both habitats.The mating system, rarity, and short life cycle of C. papaya are exacerbating the effects of rainforest fragmentation on its genetic diversity, threatening the persistence of its natural populations in the proposed place of origin as well as its genetic reservoir.
