Development and characterization of microsatellite markers for a monoecious Ficus species, Ficus insipida, and cross-species amplification among different sections of Ficus

Pollinator sharing, copollination, and speciation by host shifting among six closely related dioecious fig species

The obligate pollination mutualism between figs (Ficus, Moraceae) and pollinator wasps (Agaonidae, Hymenoptera) is a classic example of cospeciation. However, examples of phylogenetic incongruencies between figs and their pollinators suggest that pollinators may speciate by host shifting. To investigate the mechanism of speciation by host shifting, we examined the phylogenetic relationships and population genetic structures of six closely related fig species and their pollinators from southern China and Taiwan-Ryukyu islands using various molecular markers. The results revealed 1) an extraordinary case of pollinator sharing, in which five distinct fig species share a single pollinator species in southern China; 2) two types of copollination, namely, sympatric copollination by pollinator duplication or pollinator migration, and allopatric copollination by host migration and new pollinator acquisition; 3) fig species from southern China have colonized Taiwan repeatedly and one of these events has been followed by host shifting, reestablishment of host specificity, and pollinator speciation, in order. Based on our results, we propose a model for pollinator speciation by host shifting in which the reestablishment of host-specificity plays a central role in the speciation process. These findings provide important insights into understanding the mechanisms underlying pollinator speciation and host specificity in obligate pollination mutualism.

Phylogenetic and population genetic analyses reveal mechanisms of pollinator sharing, copollination and speciation by host-shift in fig-wasp mutualism.

Spatial Scales of Genetic Structure in Free-Standing and Strangler Figs (Ficus, Moraceae) Inhabiting Neotropical Forests

Wind-borne pollinating wasps (Agaonidae) can transport fig (Ficus sp., Moraceae) pollen over enormous distances (> 100 km). Because of their extensive breeding areas, Neotropical figs are expected to exhibit weak patterns of genetic structure at local and regional scales. We evaluated genetic structure at the regional to continental scale (Panama, Costa Rica, and Peru) for the free-standing fig species Ficus insipida. Genetic differentiation was detected only at distances > 300 km (Jost´s D_est = 0.68 ± 0.07 & F_ST = 0.30 ± 0.03 between Mesoamerican and Amazonian sites) and evidence for phylogeographic structure (R_ST>>permuted R_ST) was only significant in comparisons between Central and South America. Further, we assessed local scale spatial genetic structure (SGS, d ≤ 8 km) in Panama and developed an agent-based model parameterized with data from F. insipida to estimate minimum pollination distances, which determine the contribution of pollen dispersal on SGS. The local scale data for F. insipida was compared to SGS data collected for an additional free-standing fig, F. yoponensis (subgenus Pharmacosycea), and two species of strangler figs, F. citrifolia and F. obtusifolia (subgenus Urostigma) sampled in Panama. All four species displayed significant SGS (mean Sp = 0.014 ± 0.012). Model simulations indicated that most pollination events likely occur at distances > > 1 km, largely ruling out spatially limited pollen dispersal as the determinant of SGS in F. insipida and, by extension, the other fig species. Our results are consistent with the view that Ficus develops fine-scale SGS primarily as a result of localized seed dispersal and/or clumped seedling establishment despite extensive long-distance pollen dispersal. We discuss several ecological and life history factors that could have species- or subgenus-specific impacts on the genetic structure of Neotropical figs.

Dioecy, more than monoecy, affects plant spatial genetic structure: the case study of Ficus

In this analysis, we attempt to understand how monoecy and dioecy drive spatial genetic structure (SGS) in plant populations. For this purpose, plants of the genus Ficus were used as a comparative model due to their particular characteristics, including high species diversity, variation in life histories, and sexual systems. One of the main issues we assessed is whether dioecious fig tree populations are more spatially genetically structured than monoecious populations. Using the Sp statistic, which allows for quantitative comparisons among different studies, we compared the extent of SGS between monoecious and dioecious Ficus species. To broaden our conclusions we used published data on an additional 27 monoecious and dioecious plant species. Furthermore, genetic diversity analyses were performed for two monoecious Ficus species using 12 microsatellite markers in order to strengthen our conclusions about SGS. Our results show that dioecy, more than monoecy, significantly contributes to SGS in plant populations. On average, the estimate of Sp was six times higher for dioecious Ficus species than monoecious Ficus species and it was two times higher in dioecious than monoecious plant species. Considering these results, we emphasize that the long-distance pollen dispersal mechanism in monoecious Ficus species seems to be the dominant factor in determining weak spatial genetic structure, high levels of genetic diversity, and lack of inbreeding. Although Ficus constitute a model species to study SGS, a more general comparison encompassing a wider range of plants is required in order to better understand how sexual systems affect genetic structure.

Nuclear and chloroplast DNA phylogeography of Ficus hirta: obligate pollination mutualism and constraints on range expansion in response to climate change

This study uses a phylogeographic approach to investigate how interspecific interactions in an obligate pollination mutualism enhance or constrain dispersal and the range distributions of species through time. Fifteen populations of Ficus hirta, a bird-dispersed fig pollinated by a species-specific fig wasp, were sampled from Thailand to the northern limits of the tropical forest in China. These populations were assayed for six nuclear microsatellite loci and two intergenic chloroplast DNA sequences. Analyses of range expansion and genetic clustering indicated a relatively slow rate of range expansion from two or more southern glacial refugia. Low nuclear differentiation, combined with high interpopulation differentiation, and phylogeographic structuring of chloroplast variation indicated that seed dispersal has had a greater constraint than obligate interactions with fig wasps on the rate of post-glacial range expansion. This study is the first to investigate the phylogeographic history of a widely distributed southeast Asian tropical plant whose distribution extends to the northern limits of tropical forest habitat in China. It is also the first study of Ficus utilizing molecular data to evaluate whether species-specific pollination is a limitation or an aid to range expansion in response to climate change.

Anonymous and EST-based microsatellite DNA markers that transfer broadly across the fig tree genus (Ficus, Moraceae)

PREMISE OF THE STUDY

We developed a set of microsatellite markers for broad utility across the species-rich pantropical tree genus Ficus (fig trees). The markers were developed to study population structure, hybridization, and gene flow in neotropical species.

METHODS AND RESULTS

We developed seven novel primer sets from expressed sequence tag (EST) libraries of F. citrifolia and F. popenoei (subgen. Urostigma sect. Americana) and optimized five previously developed anonymous loci for cross-species amplification. The markers were successfully tested on four species from the basal subgenus Pharmacosycea sect. Pharmacosycea (F. insipida, F. maxima, F. tonduzii, and F. yoponensis) and seven species of the derived subgenus Urostigma (F. citrifolia, F. colubrinae, F. costaricana, F. nymphaeifolia, F. obtusifolia, F. pertusa, and F. popenoei). The 12 markers amplified consistently and displayed polymorphism in all the species.

CONCLUSIONS

This set of microsatellite markers is transferable across the phylogenetic breadth of Ficus, and should therefore be useful for studies of population structure and gene flow in approximately 750 fig species worldwide.

Polymorphic microsatellite loci from Dacryodes edulis (Burseraceae), a Central African rainforest and fruit-tree species

PREMISE OF THE STUDY

Microsatellite markers were isolated and characterized from Dacryodes edulis (Burseraceae), a tropical rainforests fruit tree of central Africa.

METHODS AND RESULTS

Using an enrichment protocol, six microsatellites loci were developed from Dacryodes edulis. We investigated polymorphism using 45 trees from three widely separated populations in Cameroon. All loci were polymorphic, with the number of alleles ranging from 2 to 15. Polymorphism was widely variable among loci and expected heterozygosities ranged from 0.06 to 0.84 with a mean value of 0.49.

CONCLUSIONS

These loci will be useful for the in-depth analysis of population structure and phylogeographic variation throughout the distribution range of Dacryodes edulis and other related taxa, Dacryodes buettneri and D. normandii, in which all loci were also amplified. Furthermore, they will offer the opportunity to study early domestication processes acting on the genetic diversity of Dacryodes edulis.

Development of microsatellite loci for Blastophaga javana (Agaonidae), the pollinating wasp of Ficus hirta (Moraceae)

PREMISE OF THE STUDY

To investigate genetic structure of the pollinator and, indirectly, gene flow in its plant host, Blastophaga javana microsatellite primers were developed.

METHODS AND RESULTS

Ten polymorphic microsatellite loci were developed using the Fast Isolation by AFLP of Sequences Containing (FIASCO) repeats protocol. Numbers of alleles per locus ranged from 2 to 19, with observed and expected heterozygosities ranging from 0.000 to 0.800 and from 0.000 to 0.925, respectively.

CONCLUSIONS

These markers may be useful for further investigation of population genetics of Blastophaga javana and other congeneric species.

Cross species amplification ability of novel microsatellites isolated from Jatropha curcas and genetic relationship with sister taxa: cross species amplification and genetic relationship of Jatropha using novel microsatellites

The present investigation was undertaken with an aim to check the ability of cross species amplification of microsatellite markers isolated from Jatropha curcas--a renewable source of biodiesel to deduce the generic relationship with its six sister taxa (J. glandulifera, J. gossypifolia, J. integerrima, J. multifida, J. podagrica, and J. tanjorensis). Out of the 49 markers checked 31 markers showed cross species amplification in all the species studied. JCDS-30, JCDS-69, JCDS-26, JCMS-13 and JCMS-21 amplified in J. curcas. However, these markers did not show any cross species amplification. Overall percentage of polymorphism (PP) among the species studied was 38% and the mean genetic similarity (GS) was found to be 0.86. The highest PP (24) and least GS (0.76) was found between J. curcas/J. podagrica and J. curcas/J. multifida and least PP (4.44) and highest GS (0.96) was found between J. integerrima/J. tanjorensis. Dendrogram analysis showed good congruence to RAPD and AFLP than nrDNA ITS data reported earlier. The characterized microsatellites will pave way for intraspecies molecular characterization which can be further utilized in species differentiation, molecular identification, characterization of interspecific hybrids, exploitation of genetic resource management and genetic improvement of the species through marker assisted breeding for economically important traits.

Transferability and characterization of microsatellite markers in two Neotropical Ficus species

Microsatellite markers were transferred and characterized for two Neotropical fig tree species, Ficus citrifolia and Ficus eximia. Our study demonstrated that microsatellite markers developed from different subgenera of Ficus can be transferred to related species. In the present case, 12 of the 15 primer pairs tested (80%) were successfully transferred to both of the above species. Eleven loci were polymorphic when tested across 60 F. citrifolia and 60 F. eximia individuals. For F. citrifolia, there were 4 to 15 alleles per locus, whereas expected heterozygosities ranged from 0.31 to 0.91. In the case of F. eximia, this was 2 to 12 alleles per locus and expected heterozygosities from 0.42 to 0.87.