Landscape genetic structure of natural populations of Acacia caven in Argentina

Acacia caven is a South American species which shows remarkable climate tolerance and ecological adaptability; as such, this species is suitable for colonizing anthropogenically degraded sites. This species is widely distributed, and six varieties have been described based on both morphological traits and molecular markers. Moreover, Aronson (1992) suggests that, for this species, geographical separation could be associated with ecological differentiation. In this study, amplified fragment length polymorphisms were used to study genetic variation within and among 15 populations of A. caven from five eco-regions of Argentina and to investigate (1) whether the varieties are genetically coherent, (2) whether the varieties correspond consistently to a single eco-region, (3) the proportion of the species diversity explained within and among varieties and eco-regions. Eight of the 225 bands appear to be under positive selection. The remaining 217 neutral loci showed a high percentage of polymorphism (99.1%). The estimates of genetic diversity H _j were generally high. The F _ST (0.315) was highly significant, providing evidence for genetic structure among populations. Hierarchical analysis of molecular variance indicated that variation among eco-regions was 8.2% and highly significant. The higher component of variance was found within populations (67.5%). STRUCTURE analysis suggested that the optimal number of K?=?11. The results showed that, in most cases, geographic separation is associated with ecological differentiation. Since differentiation of A. caven populations studied here in eco-regions was highly significant, sampling should include a large number of trees within populations as well as covering the wide ecological diversity of the species.     

Size variation ofAcacia caven (leguminosae) pods along a climatic gradient in Chile

A southward tendency of increment in pod-length is shown for 11 populations ofAcacia caven (Mol.) Hook et Arn. localized along a climatic gradient of increasing annual rainfall in Chile. This fact would suggest thatA. caven populations occurring in the south are in better conditions for reproduction than northern populations, since pod-length is related to the amount of seeds inside the pods. The possible bearing of this southward tendency of increasing seed production upon the expansion ofA. caven toward the more humid zones in southern Chile is discussed.     

Extensive long-distance pollen dispersal and highly outcrossed mating in historically small and disjunct populations of Acacia woodmaniorum (Fabaceae), a rare banded iron formation endemic

Background and Aims

Understanding patterns of pollen dispersal and variation in mating systems provides insights into the evolutionary potential of plant species and how historically rare species with small disjunct populations persist over long time frames. This study aims to quantify the role of pollen dispersal and the mating system in maintaining contemporary levels of connectivity and facilitating persistence of small populations of the historically rare Acacia woodmaniorum.

Methods

Progeny arrays of A. woodmaniorum were genotyped with nine polymorphic microsatellite markers. A low number of fathers contributed to seed within single pods; therefore, sampling to remove bias of correlated paternity was implemented for further analysis. Pollen immigration and mating system parameters were then assessed in eight populations of varying size and degree of isolation.

Key Results

Pollen immigration into small disjunct populations was extensive (mean minimum estimate 40 % and mean maximum estimate 57 % of progeny) and dispersal occurred over large distances (≤1870m). Pollen immigration resulted in large effective population sizes and was sufficient to ensure adaptive and inbreeding connectivity in small disjunct populations. High outcrossing (mean t_m = 0·975) and a lack of apparent inbreeding suggested that a self-incompatibility mechanism is operating. Population parameters, including size and degree of geographic disjunction, were not useful predictors of pollen dispersal or components of the mating system.

Conclusions

Extensive long-distance pollen dispersal and a highly outcrossed mating system are likely to play a key role in maintaining genetic diversity and limiting negative genetic effects of inbreeding and drift in small disjunct populations of A. woodmaniorum. It is proposed that maintenance of genetic connectivity through habitat and pollinator conservation will be a key factor in the persistence of this and other historically rare species with similar extensive long-distance pollen dispersal and highly outcrossed mating systems.     

Comparison of mating system parameters and genetic structure in three natural scenarios of Acacia visco (Leguminosae, Mimosoideae)

Acacia visco is a native South American tree species that has been extensively used for ornamental purposes and in carpentry, bodywork and parquet due to the hardness and durability of its wood. Little is known about genetic diversity and mating system of A. visco. The main aims of this study were to (1) estimate outcrossing rates in natural Argentinean populations using AFLP markers, (2) test for any difference in mating patterns among a large a patchy and relict population, and (3) compare the mating system of A. visco with other Acacia species. The three primer pairs used in the AFLP analysis revealed a total of 569 variable loci. Most genetic variation was observed among individuals within families (61.2 %). The estimate of multilocus outcrossing rate (t _m) was high (≥0.971) in all populations. Average pairwise coancestry between progenies within families for each population ranged from 0.082 to 0.105 or from 0.125 to 0.136, depending on the method θ was estimated. In the three populations studied, the progenies of open pollination were constituted mainly for half-sibs (94.3 %). This work shows a similar mating system in all populations of A. visco in spite of their size differences, hypothesizing that the entire species has a similar mating system of outcrossing preferential. Considering the results obtained here where a high percentage of individuals were half-sibs, sampling large numbers of pods from individual trees for ex situ conservation will result in a genetically diverse sample as a consequence of high outcrossing rates.     

Mating system parameters in species of genus Prosopis (Leguminosae)

The section Algarobia of genus Prosopis involves important natural resources in arid and semiarid regions of the world. Their rationale use requires a better knowledge of their biology, genetics and mating system. There are contradictory information about their mating system. Some authors claim they are protogynous and obligate outcrosser. However, some evidence have been shown indicating that they might not be protogynous and that they might be somewhat self-fertile. The current paper analyses genetic structure and mating system parameters in populations of seven species of this section from South and North America based on isozyme data. In all species a significant homozygote excess was found in the offspring population but not in mother plant genotypes. Multilocus and mean single locus outcrossing rates (tm, ts) indicated that about 15% selfing can occur in the studied populations. The heterogeneity between pollen and ovule allele frequencies was low suggesting population structuration, in agreement with the estimates of correlation of tm within progeny (rt) and correlation of outcrossed paternity (rp). The difference of FIS estimates between offspring and mother plants suggest some selection favouring heterozygotes between seedling and adult stages.     

Extensive pollen flow in a natural fragmented population of Patagonian cypress Austrocedrus chilensis

Habitat fragmentation might significantly affect mating and pollen dispersal patterns in plant populations, contributing to the decline of remnant populations. However, wind-pollinated species are able to disperse pollen at longer distances after opening of the canopy. Our objectives were to characterize the mating system parameters and to estimate the average distance of effective pollen dispersal in the wind-pollinated conifer Austrocedrus chilensis. We sampled 19 “mother trees,” 200 progeny, and 81 additional adults (both male and female), in a fragmented population at the Argentinean Patagonian steppe. We registered the spatial positions of individuals and genotyped all samples with five microsatellite markers. We found a high genetic diversity, a moderated rate of biparental inbreeding (t _m? ??t _s?=?0.105), and a complete absence of correlated paternity (r _p?=??0.015). The effective number of pollen donors contributing to a single mother (N _ep) was 13.9. Applying TWOGENER, we estimated a low but significant differentiation among the inferred pollen pools (Φ_FT?=?0.036, p?=?0.001) and a very large average pollen dispersal distance (d?=?1,032.3 m). The leptokurtic distribution (b?=?0.18) presumes a potential for even larger dispersal distances. The high genetic diversity, the mating patterns, and the extensive pollen dispersal presume that habitat fragmentation did not have a negative impact on pollen movement in this population of A. chilensis. Genetic connectivity among fragmented populations scattered in the Patagonian region is possible, and we stress the need of management policies at the landscape level.     

Morphometric analysis of varieties of Acacia caven: (Leguminosae, Mimosoideae): Taxonomic inferences in the context of other Argentinean species

The aims of this study were to evaluate the degree of morphological differentiation between six varieties of Acacia caven and to examine their taxonomic validity in the context of other Argentinean species of the genus. To accomplish these purposes, morphological traits have been analyzed using multivariate methods (non parametric ANOVA, phenetic analysis and principal component analysis) on the varieties of A. caven and other six species of the genus, represented in Argentina. The phenogram obtained showed two principal clusters, one grouping all the species of subg. Acacia and the other grouping the species of subg. Aculeiferum. This result agreed with Vassal's infrageneric classification. However, the results of the principal PCA gathered the seven species here included in three groups, which were consistent with Bentham's infrageneric treatment. The ANOVA method indicated that most of the morphometric characters used were statistically sound for differentiation between varieties of A. caven. Further studies, including more species and characters, must be performed in order to clarify the position of Acacia boliviana and the relationships between A. caven and A. curvifructa.     

Outcrossing rates and organelle inheritance estimated from two natural populations of the Japanese endemic conifer Sciadopitys verticillata

The Japanese endemic conifer Sciadopitys verticillata is one of the most phylogenetically isolated species of all plants. Occurring in small and scattered populations, the species is currently classified as Near Threatened by the International Union for Conservation of Nature and Natural Resources (IUCN) and as Vulnerable in three prefectures of Japan. This study investigated two major factors that should impact the genetic structure of the species at both the nuclear and organelle DNA level, the mating system and the inheritance of both the chloroplast and mitochondrial genomes. The mating system is crucial to determining the degree of outcrossing of plant species and thus should have a key role in shaping the species’ population level genetic diversity and gene flow between populations but as yet has not been studied in S. verticillata. Nine mother trees and their seedling progeny from two natural populations were genotyped using genetic markers from three plant genomes (eight nuclear microsatellites and DNA sequence for the chloroplast and mitochondria). Using a maximum likelihood method implemented in the software MLTR, the study found an outcrossing rate in the seedling stage of 0.49 and 0.79 for Aburazaka and Mount Shirotori populations, respectively, and an average of 0.66 at the species level. These outcrossing rates were low for conifers and therefore may have potential deleterious implications for the conservation of the species. The test of organelle inheritance supported paternal transmission of both the chloroplast and mitochondria consistent with previous microscopic evidence.     

Jatropha curcas L. (Euphorbiaceae) exhibits a mixed mating system, high correlated mating and apomixis

The hierarchical mating system among and within fruits of Jatropha curcas was investigated in a base population using five microsatellite loci, employing mixed mating and correlated mating models. Open-pollinated fruits were collected from 15 randomly selected seed trees, sampling seven fruits per tree for a total of 21 seeds from each tree. We detected multilocus genotypes identical to the mother tree in 13 % of offspring, implying the occurrence of apomixis in J. curcas. The presumed apomictic individuals were excluded from the analysis of the remaining results. Evidence of substantial selfing was provided by the average multilocus outcrossing rate (t _m?=?0.683), showing that the species exhibits a mixed mating system. The outcrossing rate showed a large variation among seed trees, ranging from 0.21 to 1.0, indicating that the species is not self-incompatible. Significant differences were detected between the multilocus and the single locus outcrossing rates (t _m???t _s?=?0.347) that suggested mating among related individuals, possibly because of the presence of individuals from the same progeny (sibs) in the base population. The multilocus paternity correlation was extremely high for the population (r _p(m)?=?0.999), indicating that the progenies were manly composed of full-sibs. As a consequence of selfing and a high paternity correlation, the co-ancestry coefficient within the progeny was higher (Θ?=?0.369) than expected for panmictic populations. Our results indicated that J. curcas produces seeds asexually by apomixis and sexually by a mixed mating system, combining selfing and outcrossing.     

Strategies for conservation for disturbed Prosopis alba (Leguminosae, Mimosoidae) forests based on mating system and pollen dispersal parameters

Prosopis species forests in Argentina are increasingly fragmented in the last years mainly by the deforestation activity without any reforestation strategy, the establishment of different crop plantations, and natural fires. The consequence of habitat fragmentation on the genetic potential of Prosopis alba requires a fine-scale analysis of population structure, in particular mating system and pollen dispersal. By means of short sequences repeats, we analyzed a fragmented population of this species in Santiago del Estero (Argentina). Most genetic variation was observed among families within zones (65.5%), whereas the lowest proportion corresponded to the differentiation among zones (2.8%). The fine analysis of structure at family level suggests that this population is complete outcrosser and there is a low but significant biparental inbreeding. Outcrossing rates differ among mother plants and the proportion of full sibs within mother plants ranged from 64% for seeds proceeding from the same pod to 10% for seeds from different pods. The average pollen dispersal distance was estimated to be among 5.36 and 30.92 m by using the KinDist or TwoGener approach. About seven pollen donors are siring each progeny array and the number of seed trees necessary for seed collection aiming to retain an effective population size of 100 was estimated in 16–39 individuals depending on the relatedness estimator used. Pollen and seed dispersal would be limited, what determines the need of conserving short distant patches to avoid the effects of inbreeding and drift within populations as a consequence of intensive use resource for agriculture.     

Mating system and population genetic structure of Bruguiera gymnorrhiza (Rhizophoraceae), a viviparous mangrove species in China

In order to explain the diversity patterns and develop the conservation strategies, the population genetic structures and the mating systems of Bruguiera gymnorrhiza from the coastlines of south China were investigated in this study. The mating system parameters were analyzed using progeny arrays for allozyme markers. The multilocus outcrossing rates (tm) ranged from 0.845 (Fugong) to 0.267 (Dongzhai harbor). High allozyme variations within the five collected populations were determined and compared with the published data of other plant species with the mixed mating systems. At species level, the percentage of polymorphic loci (P) was 80%, the average number of alleles per locus (A) was 2.440, and the heterozygosity (He) was 0.293. The total gene diversity within each population (H_S = 0.2782) and the coefficient of genetic differentiation (G_ST = 0.0579) among the populations were estimated. On the basis of this population genetic structure, it is suggested that the gene flow (Nm = 3.85) is quite high, which is possibly related to its water-dispersed hypocotyls. It is also suggested that the mating system of this species is of mixed mating.     

Wild sorghum from different eco-geographic regions of Kenya display a mixed mating system

Knowledge of mating systems is required in order to understand the genetic composition and evolutionary potential of plant populations. Outcrossing in a population may co-vary with the ecological and historical factors influencing it. However, literature on the outcrossing rate is limited in terms of wild sorghum species coverage and eco-geographic reference. This study investigated the outcrossing rates in wild sorghum populations from different ecological conditions of Kenya. Twelve wild sorghum populations were collected in four sorghum growing regions. Twenty-four individuals per population were genotyped using six polymorphic simple sequence repeat (SSR) markers to compute their indirect equilibrium estimates of outcrossing rate as well as population structure. In addition, the 12 populations were planted in a field in a randomised block design with five replications. Their progeny (250 individuals per population) were genotyped with the six SSR markers to estimate multi-locus outcrossing rates. Equilibrium estimates of outcrossing rates ranged from 7.0 to 75.0%, while multi-locus outcrossing rates (t _m) ranged from 8.9 to 70.0% with a mean of 49.7%, indicating that wild sorghum exhibits a mixed mating system. The wide range of estimated outcrossing rates in wild sorghum populations indicate that environmental conditions may exist under which fitness is favoured by outcrossing and others under which selfing is more advantageous. The genetic structure of the populations studied is concordant with that expected for a species displaying mixed mating system.     

Development of microsatellite markers in an amphicarpic species,Amphicarpaea edgeworthii Benth. (Leguminosae)

Eight polymorphic simple sequence repeats (SSRs) markers were developed for Amphicarpaea edgeworthii Benth., an amphicarpic species in East Asia. The low level of heterozygosity in populations and the high level of population differentiation found in this study suggest that A. edgeworthii has a mixed mating system that is predominantly selfing. The findings also indicate that the new markers can be used in genetic analyses of the mating system and the estimation of the construction of progeny populations contributed by chasmogamously and cleistogamously produced seeds.     

Analysis of genetic population structure in Acacia caven (Leguminosae,Mimosoideae), comparing one exploratory and two Bayesian-model-based methods

Bayesian clustering as implemented in STRUCTURE or GENELAND software is widely used to form genetic groups of populations or individuals. On the other hand, in order to satisfy the need for less computer-intensive approaches, multivariate analyses are specifically devoted to extracting information from large datasets. In this paper, we report the use of a dataset of AFLP markers belonging to 15 sampling sites of Acacia caven for studying the genetic structure and comparing the consistency of three methods: STRUCTURE, GENELAND and DAPC. Of these methods, DAPC was the fastest one and showed accuracy in inferring the K number of populations (K = 12 using the find.clusters option and K = 15 with a priori information of populations). GENELAND in turn, provides information on the area of membership probabilities for individuals or populations in the space, when coordinates are specified (K = 12). STRUCTURE also inferred the number of K populations and the membership probabilities of individuals based on ancestry, presenting the result K = 11 without prior information of populations and K = 15 using the LOCPRIOR option. Finally, in this work all three methods showed high consistency in estimating the population structure, inferring similar numbers of populations and the membership probabilities of individuals to each group, with a high correlation between each other.     

No loss of genetic diversity in small and isolated populations of Medicago sativa subsp. falcata

Molecular allozyme markers of three polymorphic isozymes were used to estimate the genetic diversity among the seed progeny in fragmented Estonian populations of sickle medic Medicago sativa ssp. falcata L. depending on the population size and the isolation degree. Genetic diversity H_e was high in all populations, ranging between 0.795 and 0.893. No correlation between the genetic diversity measures and population size or isolation distance was found. Even the smallest population had equally high genetic diversity as about a hundred times larger population. Genetic differentiation of populations into two major groups was associated with the geographic position of populations, except one remote population. Elimination of seed progeny of reduced fitness by embryo abortion and continuous yearlong contribution of the highly heterozygous progeny through the soil seed bank are considered as important supplementary factors that have contributed to maintaining high levels of genetic diversity in populations of sickle medic in addition to its autotetraploid nature and perennial life form.     

Random amplified polymorphic DNA analysis of kinship within host-associated populations of the symbiotic water mite Unionicola foili (Acari: Unionicolidae)

Kinship relations within populations of unionicolid water mites are not well known, owing to their complex life cycles and the fact that interactions between active and resting stages for some species are transitory. A number of species of unionicolid water mites are, however, obligate symbionts of freshwater mussels and spend most of their life cycle in association with these hosts. Among these species of mites, parents and offspring are more likely to co-occur and thus provide opportunities to address questions related to the structure of the mating system. The present study employs random amplified polymorphic DNA (RAPD) analysis to address kinship within populations of Unionicola foili living in symbiotic association with the host mussel Utterbackia imbecillis. DNA was amplified from adult mites and a representative number of eggs or larvae (n = 20-30) that were removed from mussels collected on three separate occasions (July, November, and March) over a 12-month period. Parsimony analyses of the molecular data for adults and progeny collected from mussels during July, November, and March revealed distinct groupings, that for the most part, corresponded to mites collected from each of the sampling periods. Many of the genetic markers obtained for male and female U. foili were not evident among the larvae or eggs, suggesting that adults obtained from a host mussel at the time of collection were not the parents of a majority of the progeny. However, female mites and eggs collected from mussels during March and November shared more markers than did females and progeny examined during July. Furthermore, many offspring in the July sampling period were found to have one or more parents absent from the sampled population. Overall, RAPD profiling appears to have limited usage in determining kinship within populations of U. foili, due to its recruitment patterns, and the relatively large number of adults and progeny per mussel. It may, however, prove to be a useful method for assessing genetic relatedness among unionicolid mussel-mites that have substantially lower population densities.     

Increased inbreeding but not homozygosity in small populations of Sabatia angularis (Gentianaceae)

Understanding how the mating system varies with population size in plant populations is critical for understanding their genetic and demographic fates. We examined how the mating system, characterized by outcrossing rate, biparental inbreeding rate, and inbreeding coefficient, and genetic diversity varied with population size in natural populations of the biennial Sabatia angularis. We found a significant, positive relationship between outcrossing and population size. Selfing was as high as 40% in one small population but was only 7% in the largest population. Despite this pattern, observed heterozygosity did not vary with population size, and we suggest that selection against inbred individuals maintains observed heterozygosity in small populations. Consistent with this hypothesis, we found a trend of lower inbreeding coefficients in the maternal than progeny generation in all of the populations, and half of the populations exhibited significant excesses of adult heterozygosity. Moreover, genetic diversity was not related to population size and was similar across all populations examined. Our results suggest that the consequences of increased selfing for population fitness in S. angularis, a species that experiences significant inbreeding depression, will depend on the relative magnitude and consistency of inbreeding depression and the demographic cost of selection for outcrossed progeny in small populations.     

Genetic diversity within and among two Argentinean and one Mexican species of Acacia (Fabaceae)

Acacia is a pantropical genus comprising > 1450 species. Following Vassal's treatment Acacia is considered as a single genus with three subgenera (Acacia, Aculeiferum and Phyllodineae). Acacia caven, A. curvifructa and A. farnesiana belong to subgenus Acacia and the relationship between them is controversial. The aim of this study was to elucidate the relationship between the three species using amplified fragment length polymorphism, analysing 15 populations of these species, and to compare the results obtained with those from a morphological analysis. Genetic diversity indices (percentage of polymorphic loci, genetic diversity) showed that genetic variation in A. caven is higher than that in A. curvifructa and A. farnesiana. Of the total genetic diversity in A. caven and A. farnesiana, most is found within populations (∼70%). Analysis with STRUCTURE showed that the optimal number of clusters (K) was ten, and in all cases where populations were grouped they were geographically close and/or belong to the same variety. The morphological canonical discriminant analysis did not result in a separation between all individuals, indicating that they do not harbour consistent morphological discontinuities. Altogether, the results of our molecular analyses showed the existence of significant differences between A. caven, A. curvifructa and A. farnesiana, which argues for recognizing them as different species. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 593–606.     

Pollen dispersal and breeding structure in a hawkmoth-pollinated Pampa grasslands species Petunia axillaris (Solanaceae)

Background and Aims The evolution of selfing is one of the most common transitions in flowering plants, and this change in mating pattern has important systematic and ecological consequences because it often initiates reproductive isolation and speciation. Petunia axillaris (Solanaceae) includes three allopatric subspecies widely distributed in temperate South America that present different degrees of self-compatibity and incompatibility. One of these subspecies is co-distributed with P. exserta in a restricted area and presents a complex, not well-understood mating system. Artificial crossing experiments suggest a complex system of mating in this sympatric area. The main aims of this study were to estimate the pollen dispersal distance and to evaluate the breeding structure of P. axillaris subsp. axillaris, a hawkmoth-pollinated taxon from this sympatric zone.Methods Pollen dispersal distance was compared with nearest-neighbours distance, and the differentiation in the pollen pool among mother plants was estimated. In addition, the correlation between genetic differentiation and spatial distance among plants was tested. All adult individuals (252) within a space of 2800 m² and 15 open-pollinated progeny (285 seedlings) were analysed. Genetic analyses were based on 12 polymorphic microsatellite loci.Key Results A high proportion of self-pollination was found, indicating a mixed-mating system. The maximum pollen dispersal distance was 1013 m, but most pollination events (96 %) occurred at a distance of 0 m, predominantly in an inbreeding system. Both parents among sampled individuals could be identifed in 60–85 % of the progeny.Conclusions The results show that most pollen dispersal in the hawkmoth-pollinated P. axillaris subsp. axillaris occurs within populations and there is a high proportion of inbreeding. This mating system appears to favour species integrity in a secondary contact zone with the congener species P. exserta.