• 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.• Methods: 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.• Key results: 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.• Conclusions: 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.
Heliconia uxpanapensis (Heliconiaceae) is an outcrossing endemic herb that grows within continuous and fragmented areas of the tropical rain forest of southeast Veracrúz (México). The genetic diversity, population differentiation, and genetic structure of seven populations of the studied species were assessed using inter-simple sequence repeat) markers. Population differentiation was moderately high (F ST range: 0.18-0.22) and indirect estimates of gene flow were rather low (Nm = 0.65-0.83). Analysis of molecular variance indicated that the populations explained 22.2 percent of the variation, while individuals within the populations accounted for 77.8 percent. The similar and high level of genetic diversity found within populations of the continuous and fragmented forest suggests that H. uxpanapensis has not suffered yet the expected negative effect of fragmentation. Genetic structure analyses indicated the presence of fewer genetic clusters (K = 4) than populations (N = 7). Three of the four fragmented forest populations were assigned each to one of the clusters found within the continuous forest, suggesting the absence of a negative fragmentation effect on the amount and distribution of genetic variation. Given the significant genetic structure combined with high genetic diversity and low levels of gene flow, theoretical simulations indicated that H. uxpanapensis might be highly susceptible to changes in the mating system, which promotes inbreeding within fragmented populations. Thus, future conservation efforts in this species should be directed to ensure that levels of gene flow among populations are sufficient to prevent an increment in the magnitude of inbreeding within fragments.Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp.
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