Outcrossing Estimates Research Articles

Will Benchtop Sequencers Resolve the Sequencing Trade-off in Plant Genetics?

Will Benchtop Sequencers Resolve the Sequencing Trade-off in Plant Genetics?

An AFLP estimation of the outcrossing rate of <i>Spondias tuberosa</i> (Anacardiaceae), an endemic species to the Brazilian semiarid region

The umbu tree (Spondias tuberosa) is one of the most important endemic species to the Brazilian tropical semiarid region. The umbu tree has edible fruits with a peculiar flavor that are consumed in natura or in a semi-industrialized form, such as jams, candies and juices. The majority of endemic species to Brazilian semiarid region have not been studied or sampled to form germ-plasm collections, which increases the risk of losing genetic variability of the adapted species to xerophytic conditions. The aim of this study was to estimate outcrossing rates in S. tuberosa using a multilocus mixed model in order to guide genetic resources and breeding programs of this species. DNA samples were extracted from 92 progenies of umbu trees, which were distributed among 12 families. These trees were planted by seed in 1991 in Petrolina, PE, Brazil. The experimental design was a randomized block, with a total of 42 progenies sampled in three regions. The experimental units were composed by five plants and five replications. The outcrossing rate was estimated by the multilocus model, which is available in the MLTR software, and was based on 17 polymorphic AFLP bands obtained from AAA_CTG and AAA_CTC primer combinations. The observed heterozygotes ranged from 0.147 to 0.499, with a maximum frequency estimated for the AAA_CTC 10 amplicon. The multilocus outcrossing estimation (t(m)) was 0.804 +/- 0.072, while the single-locus (t(s)) was 0.841 +/- 0.079, which suggests that S. tuberosa is predominantly an outcrossing species. The difference between t(m) and t(s) was -0.037 +/- 0.029, which indicates that biparental inbreeding was nearly absent. The mean inbreeding coefficient or fixation index (F) among maternal plants was--0.103 +/- 0.045, and the expected F was 0.108, which indicates that there was no excess of heterozygotes in the maternal population. The outcrossing estimates obtained in the present study indicate that S. tuberosa is an open-pollinated species. Biometrical models applied to this species should therefore take into account the deviation from random outcrossing to estimate genetic parameters and the constitution of broad germplasm samples to preserve the genetic variability of the species. Outcrossing rates based on AFLP and the mixed-mating model should be applied to other studies of plant species in the Brazilian semiarid region.

Reduced Petal Size and Color Associated with Transitions from Outcrossing to Selfing inCamissoniopsis Cheiranthifolia(Onagraceae)

Floral traits used to attract and reward pollinators should become vestigial during the evolution of self-fertilization from outcrossing due to the reduced fitness benefits of investing in pollinator attraction. However, few traits have been studied, and covariation with outcrossing is rarely evaluated using genetic estimates of the mating system. We examined covariation between petal size and color and genetic estimates of outcrossing among populations of the yellow-flowered, bee-pollinated Camissoniopsis cheiranthifolia that exhibit striking variation in the mating system. We measured brightness, chroma, and hue, using a spectrophotometer, and petal size, using image analysis for flowers sampled in the field from 25 populations across the species’ geographic range. Petals were brighter with higher chroma and lower hue (less red) in large-flowered populations than in small-flowered populations. Petal size, brightness, and chroma also correlated positively with the proportion of seeds outcrossed estimated...

Estimation of mating systems in Short and Tall ecomorphs of the coral Favia fragum

We used 15 microsatellite markers to estimate the selfing rate (s), outcrossing rate (t(O) ) and hybridization between partially sympatric ecomorphs (t(H) ) of the coral Favia fragum. Genotyping of progeny arrays revealed complete self-fertilization in the Tall ecomorph and low outcrossing (t(O) + t(H) < 1%) in the Short ecomorph. Further, all larvae could be assigned with high probability to the same population as their parental dam, indicating no hybridization between ecomorphs (t(H) = 0). Despite low ecological estimates of outcrossing, Q values from highly structured adult populations indicated that 9% of the adult samples were the products of outcrossing, and an additional 11% were hybrids. Reproductive isolation appears to have a strong geographical component, as we did not detect hybrids at a second site where the two ecomorphs were distributed in complete microallopatry. Adult estimates of gene flow within ecomorphs may be positively biased by ecomorph-specific patterns of inbreeding depression, but cryptic gene flow between ecomorphs is most likely explained by undetected outcrossing and the fact that hybrid lineages persist after repeated generations of self-fertilization. Our microsatellite data show that phenotypic differences between ecomorphs are maintained in sympatry despite evidence for hybridization.

Genetic evaluation of seeds of highly endangered Pinus uliginosa Neumann from Węgliniec reserve for ex-situ conservation program

Peat-bog pine &lt;em&gt;Pinus uliginosa&lt;/em&gt; Neumann has become extinct or rare in many parts of Europe. We have investigated the levels of genetic variation and inbreeding in seeds collected from a highly endangered reserve of this species in Poland, using allozymes as genetic markers. Generally, a high level of genetic variation was observed. The mean expected heterozygosity was 0.376, while average (Na) and effective (Ne) numbers of alleles per locus were 2.45 and 1.67, respectively. Nevertheless, we have detected relatively low levels of outcrossing, and potential biparental inbreeding. The population-wide multilocus outcrossing rate was estimated to be 0.706 (±0.091), while the minimum variance mean of single-locus estimates was distinctly lower (ts=0.611). The estimates of outcrossing calculated for individual trees ranged widely from 0.051 to 1.017, indicating the complexity of outcrossing patterns. The investigated population of &lt;em&gt;P. uliginasa&lt;/em&gt; from Węgliniec is small and surrounded by extensive forest stands of &lt;em&gt;P. sylvestris&lt;/em&gt;. Our three-year records of phenological observations demonstrated that flowering periods for &lt;em&gt;P. uliginosa&lt;/em&gt; and &lt;em&gt;P. sylvestris&lt;/em&gt; overlap, allowing for cross-pollination. The possibility of &lt;em&gt;P. uliginosa&lt;/em&gt; pollination by &lt;em&gt;P. sylvestris&lt;/em&gt; creates a potential danger of genetic erosion of the &lt;em&gt;P. uliginosa&lt;/em&gt; gene pool. Nonetheless, based on a species specific cpDNA marker we have found that among 533 seedlings of &lt;em&gt;P. uliginosa&lt;/em&gt; there were only six seedlings carrying cpDNA marker specific for &lt;em&gt;P. sylvestris&lt;/em&gt;, indicating that such hybridization seems to be rare.

Gene frequency-based estimation of natural outcrossing in opium poppy (Papaver somniferum L.)

Mating systems are generally thought to be important factors in determining the amount and nature of genetic variability in a population. Nearly 1,000 individuals at a single location (Lucknow) and over two years were crossed and subsequently scored for selfing versus outcrossing in 9–10 monohybrid populations of opium poppy (Papaver somniferum). Three different alleles of two marker loci (two—R/r and P/p—for anthocyanin locus and B/b for capsule size locus) were used to determine the male gametes that had effected fertilizations in F2 recessives (rr, pp and bb). The estimates of the gene frequency-based outcrossing parameter (α) were found to vary with year, cross and marker locus used (α range: 7.21–71.03%). Study of the two dihybrid crosses concerning the two marker loci simultaneously, further confirmed that outcrossing at the R/r or P/p locus was significantly greater than that at the B/b locus. The nature of the outcrossing was, in general, nonrandom. In this species, in general, selfing predominated, with one exception in respect of monohybrid crosses involving the purple form of anthocyanin locus, in which outcrossing predominated.

Corrigendum

New PhytologistVolume 178, Issue 2 p. 459-459 Free Access Corrigendum This article corrects the following: Effect of inbreeding depression on outcrossing rates among populations of a tropical pine R. F. Del Castillo, S. Trujillo, Volume 177Issue 2New Phytologist pages: 517-524 First Published online: November 7, 2007 First published: 26 March 2008 https://doi.org/10.1111/j.1469-8137.2008.02398.xCitations: 1AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat New Phytologist 177 (2008), 517–524 Since its publication, the authors of del Castillo & Trujillo (2008) have brought to our attention two errors in the text. In the Summary (last bullet point) and in the Discussion ‘Inbreeding depression and its impact on outcrossing estimates’ (final paragraph) the text should read ‘accuracy but not precision’ and not ‘precision but not accuracy’. The corrected Summary bullet point and section of the Discussion are printed below. We apologize to our readers for these mistakes. Summary • Inbreeding depression may be an uneven source of bias for outcrossing estimates even at the infraspecific level. Accuracy but not precision may be gained by including inbreeding depression in outcrossing estimates. Therefore, caution should be taken when comparing tm among species or even populations within the same species. Discussion Inbreeding depression and its impact on outcrossing estimates ... The distribution of outcrossing rates among plant species have been subject to much attention in particular after the influential study of Lande & Schemske (1985) predicting a bimodal distribution. Several works have pinpointed sources of bias in empirical studies testing such predictions (Ugic & Kohn, 2006). Here we illustrate two additional problems. First, the distribution of outcrossing is traditionally investigated by assigning a single outcrossing category to each species analysed (Schemske & Lande, 1985; Vogler & Kalisz, 2001). The great variation in outcrossing rates observed in P. chiapensis populations indicates that classifying species on the basis of their t-value detected in a single or few populations can be misleading. Very little is known about the true range of variation in outcrossing rates among populations within species. Second, outcrossing rates used in empirical studies testing Lande and Schemske predictions are not usually corrected for inbreeding depression. In our study, the correction for inbreeding depression altered outcrossing rates by only 10% or less. Nonetheless, this distortion will operate unevenly among populations, making correct outcrossing estimates across populations difficult to achieve. Furthermore, correcting for inbreeding depression adds an extra source of random error to outcrossing estimates. Therefore, we may gain accuracy not precision by including inbreeding depression in outcrossing estimation. In this regard, we provide additional information that supports the notion that conclusions of empirical studies analysing the frequency of mixed mating or the shape of the distribution of outcrossing rates in nature are premature and a good comprehensive study would be very difficult to accomplish. Reference Del Castillo RF, Trujillo S. 2008. Effect of inbreeding depression on outcrossing rates among populations of a tropical pine. New Phytologist 177: 517– 524. Wiley Online LibraryCASPubMedWeb of Science®Google Scholar Citing Literature Volume178, Issue2April 2008Pages 459-459 ReferencesRelatedInformation

얼치기완두(콩과) 집단의 교배계와 내교잡 압력

The mating systems of natural populations of Vicia tetrasperm in Korea were determined using allozyme analysis. The result suggests that V. tetrasperm is low rates of outcrossing or mix-mating outcrossing (self-fertilization, s ＜ 0.5). At the population levels, the values of inbreeding coefficient of ten populations in Korea varied from 0.131 to 0.176, giving an average 0.154. For ten natural populations, multi-locus estimates of outcrossing (tm) was 0.333 across fifteen polymorphic loci, with individual population values ranging from 0.269 to 0.423. The differences between the tm and ts values were not close to zero (tm - ts ＞ 0.154), indicating that biparental inbreeding was significant in the loci. The reason for relatively low outcrossing rates of some populations could be attributed to extensive consanguineous mating and isolation of flowering mature plants. Although heterozygote excess was observed in one natural population, most populations exhibited varying degrees of inbreeding and heterozygotes deficit. Thus, selection against homozygotes operated in the progeny populations throughout the life cycle.

Effect of inbreeding depression on outcrossing rates among populations of a tropical pine

Inbreeding depression is common among plants and may distort mating system estimates. Mating system studies traditionally ignore this effect, nonetheless an assessment of inbreeding depression that may have occurred before progeny evaluation could be necessary. In the neotropical Pinus chiapensis inbreeding depression was evaluated using regression analysis relating progeny F-values with seed germinability, the mating system was analysed in three populations with contrasting size, using isozymes, obtained a corrected outcrossing rate. Selfing decreased seed viability by 19%, relative to an outcrossed plant. Multilocus outcrossing rates, t(m), varied widely among populations. In the two smallest populations t(m) congruent with 1. Therefore, inbreeding depression did not affect the estimates, but overestimated t(m) by 10% in the third population, which has a true mixed mating system (selfing was the major source of inbreeding), and an unusually low t(m) for pines (t(m) = 0.54, uncorrected, t(m) = 0.49, corrected). Inbreeding depression may be an uneven source of bias for outcrossing estimates even at the infraspecific level. Accuracy [corrected] but not precision [corrected] may be gained by including inbreeding depression in outcrossing estimates. Therefore, caution should be taken when comparing t(m) among species or even populations within the same species.

Mating system variation in the hermaphroditic brooding coral, Seriatopora hystrix

Self-compatible, hermaphroditic marine invertebrates have the potential to self-fertilize in the absence of mates or under sperm-limited conditions, and outcross when sperm is available from a variety of males. Hence, many hermaphroditic marine invertebrates may have evolved mixed-mating systems that involve facultative self-fertilization. Such mixed-mating strategies are well documented for plants but have rarely been investigated in animals. Here, I use allozyme markers to make estimates of selfing from population surveys of reef slope and reef flat sites, and contrast this with direct estimates of selfing from progeny-array analysis, for the brooding coral Seriatopora hystrix. Consistent heterozygote deficits previously reported for S. hystrix suggests that inbreeding (including the extreme of selfing) may be common in this species. I detected significant levels of inbreeding within populations (F(IS)=0.48) and small but significant differentiation among all sites (F(ST)=0.04). I detected no significant differentiation among habitats (F(HT)=0.009) though among site differentiation did occur within the reef slope habitat (F(SH)=0.06), but not within the reef flat habitat (F(SH)=0.015). My direct estimates of outcrossing for six colonies and their progeny from a single reef flat site revealed an intermediate value (t(m) (+/-s.d.)=0.53+/-0.20). Inbreeding coefficients calculated from progeny arrays (F(e)=0.31) were similar to indirect estimates based on adult genotype frequencies for that site (F(IS)=0.38). This study confirms that the mating system of this brooding coral is potentially variable, with both outcrossing and selfing.

Do inbreeding depression and relative male fitness explain the maintenance of androdioecy in white mangrove, Laguncularia racemosa (Combretaceae)?

Mathematical models predict that to maintain androdioecious populations, males must have at least twice the fitness of male function in hermaphrodites. To understand how androdioecy is maintained in Laguncularia racemosa (white mangrove), outcrossing, inbreeding depression, and relative male fitness were estimated in two androdioecious populations and one hermaphroditic population. Outcrossing was estimated based on length of pollinator foraging bout and pollen carryover assumptions. Inbreeding depression was measured at three life stages: fruit set, seedling emergence, and seedling survivorship. The relative fitnesses of males and the male component of hermaphrodites were compared at these three stages and at the pollen production stage. Male frequency predictions generated by Lloyd's model were compared with observed frequencies in two androdioecious subpopulations. Outcrossing estimates were moderate for all populations (0.29-0.66). Inbreeding depression varied among populations (-0.03-0.86), but the strength of inbreeding depression did not increase with male frequency. Males produced significantly more flowers/inflorescence than hermaphrodites, but pollen production/flower did not differ. Male and hermaphroditic progeny did not differ significantly at other life stages. Populations of white mangrove with male plants were functionally androdioecious. Lloyd's model accurately predicted male frequency in one androdioecious subpopulation, but underestimated male frequency in the second subpopulation.

Effects of floral display size and biparental inbreeding on outcrossing rates in Delphinium barbeyi (Ranunculaceae)

Floral display size represents a tradeoff between the benefits of increased pollinator visitation and the quantity of pollen received vs. the costs of increased self-pollination and reduced pollination quality. Plants with large floral displays often are more attractive to pollinators, but pollinators visit more flowers per plant. Intraplant foraging movements should increase self-pollination through geitonogamy, lowering outcrossing rates in large plants. Local genetic structure should also increase inbreeding and decrease outcrossing estimates, if pollinators move between neighboring, related plants. These predictions were tested in a population of larkspurs (Delphinium barbeyi) in Colorado. Allozymes were used to estimate outcrossing rates of plants varying in display size. Floral displays varied widely (2-1400 flowers; 1-26 inflorescences per plant), and outcrossing rate decreased significantly with increasing display size. Large, multistalked plants self over twice as frequently as single-stalked plants (46 vs. 21%). Local population structure is significant, and biparental inbreeding depresses outcrossing in plants surrounded by genetically similar neighbors. Protandry, coupled with stereotypical bottom-up pollinator foraging, reduces self-fertilization by autogamy or geitonogamy within inflorescences. Selfing is predominantly (>60%) by geitonogamy between inflorescences in large plants. Geitonogamy may be a significant cost to plants with large floral displays if inbreeding depression and/or pollen and ovule discounting results. If so, floral display size, particularly inflorescence number, may be under contrasting selection for pollination quantity vs. quality.

Comparison of Reproductive Modes in Populations of Potentilla freyniana

The mating systems of natural populations of Potentilla freyniana in Korea were determined using allozyme analysis. The result suggests that P. freyniana is outcrossing as well as employing vegetative reproduction by stolon (self-fertilization rate, s < 0.5). The values of the inbreeding coefficient of eight populations in Korea varied from 0.244 to 0.331, with an average value of 0.274. For eight natural populations, multi-locus estimates of outcrossing (tm) was 0.603 across 13 polymorphic loci, with individual population values ranging from 0.530 to 0.652. The relatively low outcrossing rates of some populations could be attributed to extensive vegetative reproduction by stolon and the isolation of flowering mature plants. Although P. freyniana usually propagated by asexually-produced ramets, I could not rule out the possibility that sexual reproduction occurred at a low rate because each ramet may produce terminal flowers. Although heterozygote excess was observed in some natural populations, most populations exhibited varying degrees of inbreeding and a heterozygote deficit.

Flexible mating system in a logged population of Swietenia macrophylla 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.

Comparison of Mating Systems in Populations of Gleditsia japonica var. koraiensis

The mating systems of two groups of natural populations of Gleditsia japonica var. koraiensis in Korea were determined using allozyme analysis. The result suggests that G. japonica var. koraiensis is predominantly outcrossing. The tm values of eight populations in Korea varied from 0.667 (Mdh-1) to 0.938 (ldh-1), giving an average 0.820. Population and individual outcrossing estimates were associated with flowering tree density or degree of spatial isolation. The reason for relatively low outcrossing rates of some populations could be attributed to reduction of effective population sizes of sib for the medicine, small population size, and isolation of flowering mature trees. The heterozygote excesses were observed in some natural populations, whereas other populations exhibited varying degrees of inbreeding and heterozygotes deficit. Thus, selection against homozygotes operated in the progeny populations throughout the life cycle.

Impacts of forest fragmentation on the mating system and genetic diversity of white spruce (Picea glauca) at the landscape level

We studied the mating system of white spruce (Picea glauca) in a landscape fragmented by agriculture in northern Ontario, Canada. We sampled 23 stands that ranged in size from 1 to >500 trees isolated by 250-3000 m from the nearest other stand. Six polymorphic allozyme loci from four enzyme systems were used to genotype approximately 10 000 embryos from 104 families. We detected no allele frequency heterogeneity in the pollen pool among stands or families (Phi(FT)=-0.025). Overall, estimates of outcrossing were high (t(m)=94% and mean t(s)=91%) but significantly different from unity. Bi-parental inbreeding (t(m)-t(s)=3.2%) was low but significantly different from zero. Allozyme-based outcrossing estimates did not differ significantly among three stand-size classes (SSCs): small (<10 trees), medium (10-100 trees) and large (> or =100 trees). The number of effective pollen donors was high in all SSCs, but was significantly lower in small stands (N(ep)=62.5) than in medium-sized and large stands (both N(ep)=143). The primary selfing rate was significantly higher in medium stands than in large stands. We found no significant difference in genetic diversity measures in the filial (seed) population among SSCs. Overall, these results indicate that white spruce stands in this fragmented landscape are resistant to genetic diversity losses, primarily through high pollen-mediated gene-flow and early selection against inbred embryos. We discuss the importance of using seed data, in conjunction with genetic data, to evaluate the impacts of fragmentation on natural populations.

Fine-scale estimation of outcrossing in western redcedar with microsatellite assay of bulked DNA.

Western redcedar (Thuja plicata, Cupressaceae) is a self-fertile conifer with a mixed mating system and significant variation for outcrossing among populations. In this paper, we conducted a fine-scale study of mating system variation to identify correlates of outcrossing in natural populations. We examined variation for outcrossing within and among individual trees, and describe a new method to estimate outcrossing using bulked DNA samples. Bulking (assaying DNA tissues from several individuals simultaneously) increases the experimental power without increasing the experimental effort. We sampled 80 trees from four natural populations in southwestern British Columbia. From each tree, we sampled from up to six crown positions (three heights and inner vs outer branches). From each position, two samples of three seedlings each were bulked before DNA extractions. Using four microsatellite loci, we obtained outcrossing rates for each tree and for each of the six crown positions. We found individual tree selfing rates to increase with tree height in all four populations, but selfing rates did not differ among crown positions. The higher selfing rate of larger trees is probably due to their greater proportional contribution to local pollen clouds. Individual tree outcrossing rates ranged from 22 to 100% and the population outcrossing rates from 66 to 78%. Missed alleles due to bulking and the estimation method used both cause a downward bias in outcrossing rates, so that these estimates are probably lower than the actual outcrossing rates. Nevertheless, the trends we observed are not affected by systematic biases of estimation.

Mating System and Genetic Variability in the Simultaneously Hermaphroditic Terrestrial Gastropod Balea Perversa on the Baltic Island of Öland, Sweden

Random amplified polymorphic DNA (RAPD) technique was used to analyse the mating system of the simultaneously hermaphroditic land snail Balea perversa and to examine the level of genetic variability in eight natural populations of this rock-dwelling gastropod on the Baltic island of Oland, Sweden. The mode of reproduction was assessed in parent-offspring comparisons, in which parents (virgin at the beginning of the breeding experiment or wild-caught individuals with prior reproductive experience) were kept either singly or in pairs. Snails with no prior reproductive experience produced 1–10 offspring exclusively by selfing, no matter whether they were kept singly or in pairs. In contrast, low rates of outcrossing occurred in snails with prior reproductive experience. Minimum estimates of outcrossing were 10 % for snails kept singly and 16 % for snails kept in pairs. Corresponding maximum likelihood estimates of outcrossing ranged from 16 to 25 %. The results indicated that sperm stored from previous matings were used for cross-fertilization. At the population level, AMOVA analysis showed that most of the genetic variability (84 %) occurred among populations of B. perversa and only 16 % within populations. In two populations genetic variability was completely absent in the DNA fragment patterns examined. This finding agrees with the mode of reproduction in B. perversa. Frequent selfing may account for the low within-population variability compared with the moderate among-population variability in this species.

A comparison of Direct and Indirect Measures of Gene Flow in the Bat‐Pollinated TreeHymenaea courbarilin the Dry Forest Life Zone of Southwestern Puerto Rico

Gene flow was estimated in the tropical tree Hymenaea courbaril using indirect measures based on the proportion of total genetic diversity from differences among populations (FST) and using direct paternity analyses. Outcrossing estimates ($$t_{\mathrm{m}\,}=1.07$$) are consistent with indications that H. courbaril is self‐incompatible. Direct estimates of pollen gene flow into two small ($$n< 6$$) stands of trees indicate that 42% and 62% of the pollen came from outside the stand. Despite this level of external gene flow, genetic drift is expected to cause divergence of populations over time (migration rate $$N_{\mathrm{e}\,}m=0.40$$ and 0.63), mainly because of the small number of adult trees within each population. Indirect estimates of gene flow based on nine larger populations of 21–48 trees gave estimates of 2.91 migrants per generation, but the absence of migration‐drift equilibrium renders this estimate unreliable. Analysis of pollen movement among 21 adult trees indicated that the effective number of fathers was only 6.9, with the majority of pollinations coming from just three trees. Asynchronous flowering, and perhaps restricted use of flowering resources by bats, the primary pollinators of H. courbaril, is the likely cause of this low number. Genetic diversity values based on 31 allozyme loci were lower than those reported for other outcrossing, gravity‐dispersed tree species. Few effective fathers, and a relatively low population density, are the likely reasons.

Sistema de reprodução em população natural de Chorisia speciosa A. St.-Hil. (Bombacaceae)

This study aims to analyse by isozymes the outcrossing rate in a Chorisia speciosa population. Thus, open-pollinated seeds from 28 trees and leaves from 53 adult trees were sampled in a C. speciosa population at the Bauru Ecological Station, Sao Paulo State, Brazil. Eighteen alleles were observed distributed in seven polymorphic loci. The fixation index () was smaller in adult trees than in families, suggesting selection against homozygous. The multilocus outcrossing estimate () was 0.816, revealed that this species is a mixed mating system, predominantly alogamous. Heterogeneity of pollen pool was observed in outcrossing individual tree indicating that mating were not random. The paternity correlation () revealed that families are constituted of a high proportion of full sibs (71.4%). There was also detection of crossing among relatives in population (5.6%), indicating the possibility of family structure within population.