Genetic imprints of Brosimum alicastrum Sw. in Mexico

Genomic diversity and structure of a Neotropical microendemic fig tree

Genetic diversity is a key component of evolution, and unraveling factors that promote genetic differentiation in space and time is a central question in evolutionary biology. One of the most diverse and ecologically important tree genera in tropical forests worldwide is Ficus (Moraceae). It has been suggested that, given the great dispersal capacity of pollinating fig wasps (Chalcidoidea; Agaonidae), the spatial genetic structure, particularly in monoecious fig species, should be weak. However, no studies have addressed the factors that determine the genetic structure of Ficus species in regions of high geological, geographic, and climatic complexity, such as the Mexican Transition Zone. Using nuclear single nucleotide polymorphisms (5311 SNPs) derived from low-coverage whole genomes and 17 populations, we analyzed the population genomics of Ficus pringlei to characterize neutral and adaptive genetic variation and structure and its association with geographic barriers such as the Trans-Mexican Volcanic Belt, environmental heterogeneity, and wind connectivity. From genomic data of 71 individuals, high genetic diversity, and the identification of three genomic lineages were recorded (North, South, and Churumuco). The results suggest that genetic variation is primarily determined by climatic heterogeneity. Ficus pringlei populations from the north and south of the Trans-Mexican Volcanic Belt also exhibited minimal genetic differentiation (F ST = 0.021), indicating that this mountain range may not act as an insurmountable barrier to gene flow. Wind connectivity is also highlighted in structuring putative adaptive genetic variation, underscoring the intricate complexity of the various factors influencing genetic variation in the species. This study provides information on the possible mechanisms underlying the genetic variation of endemic species of the tropical dry forest of Western Mexico, such as F. pringlei.

Gone with the wind: Negative genetic and progeny fitness consequences of habitat fragmentation in the wind pollinated dioecious tree Brosimum alicastrum

PREMISE

Habitat fragmentation negatively affects population size and mating patterns that directly affect progeny fitness and genetic diversity; however, little is known about the effects of habitat fragmentation on dioecious, wind pollinated trees. We assessed the effects of habitat fragmentation on population sex ratios, genetic diversity, gene flow, mating patterns, and early progeny vigor in the tropical dioecious tree, Brosimum alicastrum.

METHODS

We conducted our study in three continuous and three fragmented forest sites in a Mexican tropical dry forest. We used eight microsatellite loci to characterize the genetic diversity, gene flow via pollen distances, and mean relatedness of progeny. We compared early progeny vigor parameters of seedlings growing under greenhouse conditions.

RESULTS

Sex ratios did not deviate from 1:1 between habitat conditions except for one population in a fragmented habitat, which was female biased. The genetic diversity of adult trees and their offspring was similar in both habitat conditions. Pollen gene flow distances were similar across habitat types; however, paternity correlations were greater in fragmented than in continuous habitats. Germination rates did not differ between habitat conditions; however, progeny from fragmented habitats produced fewer leaves and had a lower foliar area, total height, and total dry biomass than progeny from continuous habitats.

CONCLUSIONS

Changes in mating patterns because of habitat fragmentation have negative effects on early progeny vigor. We conclude that negative habitat fragmentation effects on mating patterns and early progeny vigor may be a serious threat to the long-term persistence of tropical dioecious trees.