Remnant Pachira quinata pasture trees have greater opportunities to self and suffer reduced reproductive success due to inbreeding depression

Habitat fragmentation is extensive throughout the world, converting natural ecosystems into fragments of varying size, density and connectivity. The potential value of remnant trees in agricultural landscapes as seed sources and in connecting fragments has formed a fertile area of debate. This study contrasted the mating patterns of bat-pollinated Pachira quinata trees in a continuous forest to those in pasture through microsatellite-based paternity analysis of progeny. The breeding system was determined by analysis of pollen tube growth and seed production from controlled pollinations. Fitness of selfed and outcrossed seed was compared by germination and seedling growth. There was more inbreeding within pasture trees (outcrossing=0.828±0.015) compared with forest trees (0.926±0.005). Pasture trees had fewer sires contributing to mating events, but pollen dispersal distances were greater than those in the forest. Paternity analysis showed variation in outcrossing rates among pasture trees with high proportions of external and self pollen sources detected. A leaky self-incompatibility system was found, with self pollen having reduced germination on stigmas and slower growth rate through the style. Controlled pollinations also showed a varied ability to self among trees, which was reflected in the selfing rates among pasture trees shown by the paternity analysis (0–80% selfing). Self pollination resulted in lower seed set, germination and seedling growth compared with outcrossing. While remnant trees in agricultural landscapes are involved in broader mating patterns, they show increased but varied levels of inbreeding, which result in reduced fitness.     

Outcrossing between an agroforestry plantation and remnant native populations of Eucalyptus loxophleba

Gene dispersal among populations of a species is an important force influencing their genetic structure. Dispersal may also occur between taxa that would normally be isolated when nonendemic, domesticated or transgenic species are planted within the natural range of interfertile taxa. Such a mosaic of populations is typical of many agricultural landscapes, and investigations are needed to assess the risks of genetic contamination of the endemic populations but a combination of approaches may be necessary because of the limitations of research in this landscape. This study used microsatellite markers and a range of analyses (mating system, paternity exclusion, Bayesian assignment) to examine gene dispersal between remnants of the endemic Eucalyptus loxophleba ssp. supralaevis and a plantation of a nonendemic subspecies. Our results indicate that remnant populations are connected by significant dispersal to pollen sources up to 1.94 km away including the plantation. The combined analyses showed that the pollen pool and outcrossing rates of individuals within remnants varied significantly probably because of asynchronous flowering and that the likelihood of paternity was not correlated with spatial proximity. More than half of all progeny had male parents from outside their stand with the largest proportions estimated to come from the plantation by exclusion (42.4%) or Bayesian analyses (18.8–76%). Fragmentation may not be associated with decreased gene dispersal between populations of tree species, natural or planted, so that the distances required to buffer endemic trees in fragmented rural landscapes are likely to be large.     

Outcrossing rates and relatedness estimates in pecan (Carya illinoinensis) populations

Estimates of single and multilocus outcrossing rates as well as relatedness among progeny of individual seed trees were obtained for 14 populations of pecan [Carya illinoinensis (Wangenh.) K. Koch]. Mean outcrossing estimates were not significantly different from 1.0 and relatedness values indicate that most progeny within families are half sibs. Biparental inbreeding was insignificant in all study sites, and inbreeding coefficients indicated that populations were close to inbreeding equilibrium.     

Pollen Dispersal in Fragmented Populations of the Dioecious Wind-Pollinated Tree,Allocasuarina verticillata (Drooping Sheoak,Drooping She-Oak; Allocasuarinaceae)

Vegetation clearing, land modification and agricultural intensification have impacted on many ecological communities around the world. Understanding how species respond to fragmentation and the scales over which functionality is retained, can be critical for managing biodiversity in agricultural landscapes. Allocasuarina verticillata (drooping sheoak, drooping she-oak) is a dioecious, wind-pollinated and -dispersed species with key conservation values across southeastern Australia. But vegetation clearing associated with agricultural expansion has reduced the abundance and spatial distribution of this species in many regions. Spatial genetic structure, relatedness among trees, pollen dispersal and mating patterns were examined in fragmented A. verticillata populations selected to represent the types of remnants that now characterise this species. Short scale spatial genetic structure (5–25 m) and relatedness among trees were observed in most populations. Unexpectedly, the two male trees closest to each female did not have a reproductive advantage accounting for only 4–15% of the seed produced in larger populations. Biparental inbreeding was also generally low (<4%) with limited evidence of seed crop domination by some male trees. More male trees contributed to seed crops in linear remnants (mean 17) compared to those from patch remnants (mean 11.3) which may reflect differences in pollen dispersal within the two remnant types. On average, pollen travels ~100 m irrespective of remnant type but was also detected to have dispersed as far as 1 km in open landscapes. Low biparental inbreeding, limited reproductive assurance for near-neighbour and probably related males and variability in the distances over which females sample pollen pools suggest that some mechanism to prevent matings between relatives exists in this species.     

Do Eucalyptus plantations host an insect community similar to remnant Eucalyptus forest?

Abstract We examined the potential of forest plantations to support communities of forest‐using insects when planted into an area with greatly reduced native forest cover. We surveyed the insect fauna of Eucalyptus globulus (Myrtaceae) plantations and native Eucalyptus marginata dominated remnant woodland in south‐western Australia, comparing edge to interior habitats, and plantations surrounded by a pastoral matrix to plantations adjacent to native remnants. We also surveyed insects in open pasture. Analyses focused on three major insect orders: Coleoptera, Lepidoptera and Hymenoptera. Plantations were found to support many forest‐using insect species, but the fauna had an overall composition that was distinct from the remnant forest. The pasture fauna had more in common with plantations than forest remnants. Insect communities of plantations were different from native forest both because fewer insect species were present, and because they had a few more abundant insect species. Some of the dominant species in plantations were known forestry pests. One pest species (Gonipterus scutellatus) was also very abundant in remnant forest, although it was only recently first recorded in Western Australia. It may be that plantation forestry provided an ecological bridge that facilitated invasion of the native forest by this nonendemic pest species. Plantation communities had more leaf‐feeding moths and beetles than remnant forests. Plantations also had fewer ants, bees, evanioid wasps and predatory canopy beetles than remnants, but predatory beetles were more common in the understory of plantations than remnants. Use of broad spectrum insecticides in plantations might limit the ability of these natural enemies to regulate herbivore populations. There were only weak indications of differences in composition of the fauna at habitat edges and no consistent differences between the fauna of plantations adjacent to remnant vegetation and those surrounded by agriculture, suggesting that there is little scope for managing biodiversity outcomes by choosing different edge to interior ratios or by locating plantations near or far from remnants.     

Genetic and reproductive consequences of forest fragmentation for populations of <Emphasis Type="Italic">Magnolia obovata</Emphasis>

In order to evaluate the consequences of forest fragmentation on populations of Magnolia obovata, we compared genetic diversity and reproductive characteristics at two nearby sites, one conserved and one fragmented. The genetic diversity between adults trees of the different sites was not significantly different. However, saplings in the conserved site showed a significantly higher genetic diversity than both adult trees in the conserved site and saplings in the fragmented sites; this was found to be the result of the larger gene flow into the conserved site. The density of the adult trees was significantly related to all of the reproductive traits analyzed (fertilization of ovules, insect attack to seeds, ovules that developed into seeds and outcrossing at the stage of seeds) at both sites. At both sites, fertilization of ovules and insect attack on seeds were positively correlated to adult tree density while outcrossing rate was negatively correlated to adult tree density. The fertilization of ovules and outcrossing were more dependent on adult tree density in the fragmented site than in the conserved site. The probability of ovules developing into outcrossed seeds showed a negative correlation with adult tree density at both sites, indicating the advantage of low density for this species and possibly implying a resilience to habitat fragmentation. A two-generation-analysis did not identify significant differences between sites in terms of the structure of the pollen pool and the number of pollen donors. Although fragmentation affected reproductive characteristics, the effect on seedling establishment and subsequent survival remains to be determined. Proposals for future studies that will assist in the development of management strategies for forests suffering fragmentation are made.     

Temporal heterogeneity of outcrossing rates in alpine ash (Eucalyptus delegatensis R.T. Bak.)

Summary Three seed crops of a Eucalyptus delegatensis population were assayed for their allozyme genotype at three loci to determine estimates of mating system parameters. In the pollen the allelic frequencies at each of the three loci were similar to those in the parents and the progeny. Overall there was a significant amount of inbreeding (23%) in the population. The levels of outcrossing in each crop were significantly different from each other indicating apparent temporal variation in outcrossing rates. The outcrossing rate was greatest in the oldest crop (85%) and lowest in the most recent crop (66%). Mean heterozygosity in the progeny of all three crops was less than the heterozygosity in the parents indicating that selection favours heterozygotes during the life cycle. The implications of a balanced mixed mating system for a eucalypt breeding program are discussed.     

Genetic polymorphism of plus-tree clones and their seed progeny in the scotch pine clone plantation

The genetic variability at 12 allozyme (ten were found to be polymorphic) loci was studied in the archive-clone plantation of 23 plus-trees of Pinus sylvestris and their seed progeny in the southeast of Ukraine. More than half of the clones possessed four to eight heterozygous loci, while their seed progeny was characterized by a lower degree of variation as compared with maternal trees. Seed progeny was obtained from high outcrossing rate (t _m = 95%). The clone progeny was characterized by a high rate of distortions of allele segregation in megagametophytes and a high percentage of significant deviations in distribution of genotypes of seed embryos from that theoretically expected in accordance with the Hardy-Weinberg ratio.     

Allozyme polymorphisms, outerossing rates, and hybridization of South AmericanNothofagus

Electrophoretically detectable genetic variation was used to describe the genetic structure of three South American species ofNothofagus: the widespreadN. betuloides andN. dombeyi, and the geographically restrictedN. nitida. Although the widespread species possess higher levels of genetic variation, the three species have more genetic variation within than among populations. These results are consistent with the theoretical expectations for woody, presumably highly outerossed species with wind-borne seeds.Estimates of outcrossing rates from progeny arrays yielded slightly higher average t-values forN. nitida (1.158) andN. dombeyi (range 0.873–1.045) than forN. betuloide (0.878). Hierarchical analysis of population structure revealed values of F_IS and FIT that were positive and significantly different from zero at most loci and for each species. The levels of inbreeding detected by F-statistics indicate some degree of self-fertilization and/or population substructuring into discrete family groups. Reduced seed vagility and regeneration of natural stands after disturbance by a few remnant individuals would probably generate the recruitment of related seedlings underneath parent trees.The analysis of a putative hybrid population betweenN. nitida andN. betuloides indicated that individuals clearly segregated intonitida-like orbetuloides- like individuals. The reduced outcrossing rate ofbetuloides-like individuals from the hybrid site (t=0.585) is interpreted in concert with low pollen availability and the increased probability of selfing and/or hybridization inNothofagus.     

Genetic diversity and mating system of the threatened plant <Emphasis Type="Italic">Kirengeshoma palmata</Emphasis> (Saxifragaceae) in Korea

The endangered herb Kirengeshoma palmata, from eastern Asia, has had its population severely reduced in number through habitat loss and fragmentation. All of the individuals within five subgroups at Mt. Baek-un-san, in the southern part of Korea, were genetically surveyed by allozyme analysis. Genetic diversity levels within subgroups were relatively high, and a consistently high outcrossing rate as well as a negligible biparental mating rate were confirmed by this study. Several groups of visibly connected ramets were observed in a clustered distribution which suggested cloning. Absence of mating partner rather than pollinators decreased seed production in small mating groups. The present genetic structure of the five subgroups was probably the result of local extinction of intervening populations. Because K. palmata may be a self-incompatible species, populations with few genets face lowered seed set due to mate scarcity. Thus, this type of population may be at an increased risk of extinction as a result of inbreeding depression, loss of genetic variability, and reduced sexual reproduction. The small, genetically depauperate subgroups may need an input of seeds or plants from other populations in China or Japan in order to regenerate, but the possibility of outcrossing depression leads us to recommend outbreeding among the local subgroups of Mt. Baek-un-san to restore genetic variability.     

Protecting evolutionary significant units for the remnant populations of <Emphasis Type="Italic">Berchemiella wilsonii</Emphasis> var. <Emphasis Type="Italic">pubipetiolata</Emphasis> (Rhamnaceae)

Berchemiella wilsonii var. pubipetiolata (Rhamnaceae) is an endangered tree in eastern China. Habitat destruction has resulted in fragmentation of remnant populations and extinction of local populations. AFLP and cpDNA markers were used to determine the population structure of remnant populations of B. wilsonii var. pubipetiolata. Moderate nuclear genomic diversity was found within each of the four remnant populations (H _S = 0.141–0.172), while the cpDNA haplotype diversity in each population ranged from 0.356 to 0.681. Six haplotypes were identified by a combined cpRFLP and cpSSR analysis in a total of 89 individuals. AMOVA revealed significantly AFLP genetic differentiation within and between regions (Φ_SC = 0.196, Φ_CT = 0.396, respectively), and a high cpDNA haplotype differentiation between regions (Φ_CT = 0.849). The results suggest low gene flow between populations of B. wilsonii var. pubipetiolata. Strong genetic divergence between two regional populations as revealed by both AFLP and cpDNA markers provided convincing evidence that two distinct evolutionary lineages existed, and should be recognized as ‘evolutionary significant units’ (ESUs) for conservation concerns.     

INBREEDING EFFECTS IN CLARKIA TEMBLORIENSIS (ONAGRACEAE) POPULATIONS WITH DIFFERENT NATURAL OUTCROSSING RATES

Inbreeding depression is commonly observed in natural populations. The deleterious effects of forced inbreeding are often thought to be less pronounced in populations with self-pollinating mating systems than in primarily outcrossing populations. We tested this hypothesis by comparing the performance of plants produced by artificial self- and cross-pollination from three populations whose outcrossing rate estimates were 0.03, 0.26, and 0.58. Outcrossing rates and inbreeding coefficients were estimated using isozyme polymorphisms as genetic markers. Analysis of F statistics suggests that biparental inbreeding as well as self-fertilization contribute to the level of homozygosity in the seed crop. Biparental inbreeding will reduce the heterozygosity of progeny produced by outcrossing, relative to random outcrossing expectations, and hence will reduce the effects of outcrossing versus self-fertilization. Heterotic selection may increase the average heterozygosity during the life history. Selfed and outcrossed seeds from all three populations were equally likely to germinate and survive to reproduce. However, inbreeding depression was observed in fecundity traits of plants surviving to reproduction in all three populations. Even in the population whose natural self-fertilization rate was 97%, plants grown from seed produced by self-pollination produced fewer fruits and less total seed weight than plants grown from outcrossed seed. There was no detectable inbreeding depression in estimated lifetime fitness. Inbreeding effects for all reproductive yield characters were most severe in the accession from the most outcrossing population and least severe in the accession from the most self-fertilizing population.     

Capturing Genetic Variation during Ecological Restorations: An Example from Kankakee Sands in Indiana

Genetic variation in populations, both natural and restored, is usually considered crucial for response to short‐term environmental stresses and for long‐term evolutionary change. To have the best chance of successful long‐term survival, restored populations should reflect the extant variation found in remnants, but restored sites may suffer from genetic bottlenecks as a result of founder effects. Kankakee Sands is a large‐scale restoration being conducted by The Nature Conservancy (TNC) in northwestern Indiana. Our goal was to test for loss of genetic variation in restored plant populations by comparing them with TNC’s seed source nursery and with local remnant populations that were the source of nursery seed and of the first few restored sites. Allozyme analysis of Baptisia leucantha, Asclepias incarnata, Coreopsis tripteris, and Zizia aurea showed low levels of allozyme diversity within all species and reductions in polymorphism, alleles per locus, and expected heterozygosity between remnants and restorations for all species except A. incarnata. Almost all lost alleles were rare; restored populations contained almost 90% of alleles at polymorphic loci that occurred in remnants at frequencies greater than 1%. Allele frequencies for most loci did not differ between remnants and restored sites. Most species showed significant allele frequency differentiation among remnant populations and among restored sites. Our results indicate that seed collection techniques used at Kankakee Sands captured the great majority of allozyme variation present in seed source remnant populations.     

Structural features of fragmented woodland communities affect leaf litter decomposition rates

Disruption to the physical structure of plant communities by habitat fragmentation can change microclimates, so leaf litter decomposition rates, being dependent on temperature and moisture, may also be affected. Similarly, smaller-scale structural features of plant communities can modify microclimates, and so may produce distinctive spatial patterns in decomposition rates. We investigated the effects of three types of structural feature having the potential to alter litter layer microclimates: fragmentation-induced modification that diminishes with distance from remnant edges (edge-core); concentric zones of locally modified conditions imposed by individual trees (Belsky–Canham); and highly localised abiotic modification collectively imposed by herbaceous plants (ground cover). We conducted a litter bag experiment in woodland remnants, testing whether the observed spatial variability in litter decomposition was attributable to one or more of these three structural features. The data provided the strongest support for the Belsky–Canham hypothesis, and the least support for the ground cover hypothesis. However, the hypotheses were not mutually exclusive, for each explained a component of the observed variability not explained by either of the other two. Proximity to remnant edge, proximity to trees, canopy light penetration, and ground cover density each explained part of the observed variability between plots. Decomposition rates did not differ with remnant area per se, for the effects of fragmentation were weak, and differed with cardinal direction. In contrast, the effects of individual trees were much stronger, and accounted for most of the between-plot variability. We found that litter decomposition rates in small remnants are only weakly affected by fragmentation, and we consider that the contributions of small remnants to landscape-scale functioning warrant closer attention.     

Mating system and early viability resistance to habitat fragmentation in a bird-pollinated eucalypt

Habitat fragmentation has been shown to disrupt ecosystem processes such as plant-pollinator mutualisms. Consequently, mating patterns in remnant tree populations are expected to shift towards increased inbreeding and reduced pollen diversity, with fitness consequences for future generations. However, mating patterns and phenotypic assessments of open-pollinated progeny have rarely been combined in a single study. Here, we collected seeds from 37 Eucalyptus incrassata trees from contrasting stand densities following recent clearance in a single South Australian population (intact woodland=12.6 trees ha⁻¹; isolated pasture=1.7 trees ha⁻¹; population area=10 km²). 649 progeny from these trees were genotyped at eight microsatellite loci. We estimated genetic diversity, spatial genetic structure, indirect contemporary pollen flow and mating patterns for adults older than the clearance events and open-pollinated progeny sired post-clearance. A proxy of early stage progeny viability was assessed in a common garden experiment. Density had no impact on mating patterns, adult and progeny genetic diversity or progeny growth, but was associated with increased mean pollen dispersal. Weak spatial genetic structure among adults suggests high historical gene flow. We observed preliminary evidence for inbreeding depression related to stress caused by fungal infection, but which was not associated with density. Higher observed heterozygosities in adults compared with progeny may relate to weak selection on progeny and lifetime-accumulated mortality of inbred adults. E. incrassata appears to be resistant to the negative mating pattern and fitness changes expected within fragmented landscapes. This pattern is likely explained by strong outcrossing and regular long-distance pollen flow.     

Reproductive ecology of tropical forest trees in logged and fragmented habitats in Thailand and Costa Rica

Invertebrates mediate several important ecological processes, including pollination and seed predation, and events that affect invertebrate diversity or behaviour can potentially disrupt forest regeneration processes. This study investigates the impact of logging in Thailand and forest fragmentation in Costa Rica on the pollination and seed production of two self-incompatible forest trees. Logging in a dry deciduous dipterocarp forest in Thailand resulted in reduced densities of the common dipterocarp treeShorea siamensis and variably isolated individual trees. The number of flower visits to S. siamensis by pollinating Trigona bees was not affected by logging disturbance. However, pollinators did spend longer periods of time foraging in the canopies of isolated trees which were more prevalent in logged areas where tree density had been reduced. Consequently, at the logged site few cross-pollinations were effected and fruit set of S. siamensis was considerably lower than at nearby unlogged sites where distances between flowering conspecifics were smaller. Reduced fruit set has long-term implications for the recovery of S. siamensis populations in disturbed areas, and local population genetic structure is likely to be affected as reduced outcrossing rates among trees in disturbed regions results in relatively inbred seed. In Costa Rica forest fragmentation has restricted the once widespread tree Anacardium excelsum to forest patches located in an agriculturally-dominated landscape. As with S. siamensis, the abundance of pollinators, also Trigona bees, in the canopies of A. excelsum was largely unaffected by fragment size. Nevertheless, pollination success and seed production was positively correlated with fragment size. We propose that small bees rarely move between forest fragments and gene exchange through pollination occurs predominantly among trees within fragments and, together with likely low genetic variability in small fragments, that this contributes to the observed reduced fertilisation and seed set of A. excelsum. Thus increased tree isolation tree through selective logging or habitat fragmentation by forest clearance can result in reduced seed set due to changes in the foraging patterns of poorly mobile pollinators. Even if population sizes of the pollinators are maintained following environmental perturbation, this study shows that disturbance may disrupt pollination processes through changes in pollinator foraging behaviour. More attention needs to be focussed on changes in the behaviour of species involved in key ecological interactions following disturbance events in tropical forests.     

Primary pollinator exclusion has divergent consequences for pollen dispersal and mating in different populations of a bird‐pollinated tree

Pollination by nectarivorous birds is predicted to result in different patterns of pollen dispersal and plant mating compared to pollination by insects. We tested the prediction that paternal genetic diversity, outcrossing rate and realized pollen dispersal will be reduced when the primary pollinator group is excluded from bird‐pollinated plants. Pollinator exclusion experiments in conjunction with paternity analysis of progeny were applied to Eucalyptus caesia Benth. (Myrtaceae), a predominantly honeyeater‐pollinated tree that is visited by native insects and the introduced Apis mellifera (Apidae). Microsatellite genotyping at 14 loci of all adult E. caesia at two populations (n = 580 and 315), followed by paternity analysis of 705 progeny, revealed contrasting results between populations. Honeyeater exclusion did not significantly impact pollen dispersal or plant mating at Mount Caroline. In contrast, at the Chiddarcooping site, the exclusion of honeyeaters led to lower outcrossing rates, a threefold reduction in the average number of sires per fruit, a decrease in intermediate‐distance mating and an increase in near‐neighbour mating. The results from Chiddarcooping suggest that bird pollination may increase paternal genetic diversity, potentially leading to higher fitness of progeny and favouring the evolution of this strategy. However, further experimentation involving additional trees and study sites is required to test this hypothesis. Alternatively, insects may be effective pollinators in some populations of bird‐adapted plants, but ineffective in others.     

Diversity Assessment of an Endemic <i>Carpinus oblongifolia</i> (Betulaceae) Using Specific-Locus Amplified Fragment Sequencing and Implications for Conservation

Carpinus oblongifolia is an endemic species and the extant wild populations show a fragmentation distribution in the Baohua Mountain of Jiangsu Province in eastern China. Understanding of genetic diversity plays an important role in C. oblongifolia survival and sustainable development. The wild C. oblongifolia population was artificially divided into four subpopulations according to the microhabitats, and another two subpopulations were constructed by progeny seedlings cultivated with the mature seeds. Then, the leaf buds of 80 individuals from six subpopulations were sampled to develop single nucleotide polymorphisms (SNPs) using specific-locus amplified fragment sequencing (SLAF-seq). Based on these SNPs, we aimed to characterize the genetic diversity and population structure of C. oblongifolia and provide an illumination and reference for effective management of such a small endemic population. The level of genetic diversity was low at the species level, and the progeny subpopulations had a relatively higher genetic diversity than the wild subpopulations. This may be attributed to a high gene flow and an excess heterozygosity to reduce the threat of genetic drift-based hazards. Moreover, the progeny subpopulations had the ability to form new clusters and a great contribution to the genetic structure variation of C. oblongifolia. These results will assist with the development of conservation and management strategies, such as properly evacuating competitive trees to provide more chance for pollen and seed flow in situ conservation, and establishing sufficient seedling plantlets under laboratory conditions for reintroduction to enlarge the effective population size.     

Flexible mating system in a logged population of <Emphasis Type="Italic">Swietenia macrophylla</Emphasis> King (Meliaceae): implications for the management of a threatened neotropical tree species

Microsatellites were used to evaluate the mating system of the remaining trees in a logged population of Swietenia macrophylla, a highly valuable and threatened hardwood species, in the Brazilian Amazon. A total of 25 open pollinated progeny arrays of 16 individuals, with their mother trees, were genotyped using eight highly polymorphic microsatellite loci. Genotypic data analysis from the progeny arrays showed that 373 out of the 400 seedlings (93.25%) were unambiguously the result of outcrossed matings and that the remaining 6.75% had genotypes consistent with self-fertilisation. Apomixis could be ruled out, since none of the 400 seedlings analysed had a multi-locus genotype identical to its mother tree. The high estimate of the multi-locus outcrossing rate (t _m = 0.938 ± 0.009) using the mixed mating model also indicated that the population in this remnant stand of S. macrophylla was predominantly allogamous. The relatively large difference between the multi-locus and single-locus outcrossing estimates (t _m −t _s = 0.117 ± 0.011) provides evidence that, in spite of the high outcrossing rate, a considerable degree of biparental inbreeding has contributed to the genetic structure of this population. Levels of outcrossing were not evenly distributed among maternal trees (t _m ranging from 0.39 to 1.00), suggesting the occurrence of a variable degree of self-incompatibility and/or dichogamy among individual trees of this monoecious species. Due to its generalist pollination system and some level of tolerance for selfing, S. macrophylla seems to be resilient to environmental disturbances such as those caused by logging, since it sets fruits with predominantly outcrossed seeds even at low stand densities. Therefore, the remaining individuals in logged areas or in relict fragments may be very important for long-term population recovery and genetic conservation programmes.     

Reproductive ecology of a perennial outcrosser with a naturally dissected distribution

We surveyed four populations of contrasting size (two isolated and two large stands) of a woody outcrossing species, Discaria trinervis (Rhamnaceae), which has a naturally dissected distribution. Our main goal was to investigate the floral biology, breeding system and pollination mechanism of the species, which in turn may help to explain the mechanisms underlying the survival of the isolated populations. Discaria trinervis is both wind- and insect-pollinated, showing interactions with a large fraction of the available flower visitors at both stand sizes. In the larger populations, stigmatic loads were larger, more pollen tubes reached the ovules, and fruit and seed set were higher; however, the reproductive output in the smaller populations (over 2000 seeds per plant per year) seemed adequate for population persistence. Human disturbance (e.g. destruction of trees for wood extraction) may put these smaller populations at risk through loss of incompatibility alleles. The results suggest that plant species with naturally dissected distributions may provide clues about which reproductive mechanisms ensure survival under fragmentation.