Short-distance pollen dispersal and high self-pollination in a bat-pollinated neotropical tree

We investigated pollen dispersal and breeding structure in the tropical tree species Caryocar brasiliense Camb. (Caryocaraceae), using genetic data from ten microsatellite loci. All adult trees (101) within a patch of 8.3 ha were sampled, and from these adults 18 open-pollinated maternal progeny arrays were analyzed (280 seeds from 265 fruits). Most fruits presented only one seed (median equal to 1.000) and mean number of ripened seeds per fruit was 1.053 (SD = 0.828). Our results showed that C. brasiliense presents a mixed-mating system, with 11.4% of self-pollination, multilocus outcrossing rate of t _m = 0.891 ± 0.025, and high probability of full-sibship within progeny arrays (r _p = 0.135 ± 0.032). Outcrossing rate and self-pollination varied significantly among mother trees. We could detect a maximum pollen dispersal distance of ∼500 m and a mean pollen dispersal distance of ∼132 m. However, most pollination events (80%) occurred at distances less than 200 m. Our results also indicated that pollen dispersal is restricted to a neighborhood of 5.4 ha with rare events of immigration (∼1% N _e m = 0.35). C. brasiliense also presents a significant but weak spatial genetic structure (Sp = 0.0116), and extension of pollen dispersal distance was greater than seed dispersal (N _b = 86.20 m). These results are most likely due to the foraging behavior of pollinators that may have limited flight range. The highly within-population synchronous flowering, high population density, and clumped distribution reinforce pollinator behavior and affect residence time leading to a short-distance pollen dispersal.     

Short-distance pollen dispersal in a protogynous Annonaceae tree species from the Brazilian Cerrado

Annona crassiflora (Annonaceae) is a protogynous beetle-pollinated savannah tree species, widely distributed in the savannahs of the Cerrado biome. Studies on the mating system and pollen dispersal of protogynous species are very scarce. Here, we used six microsatellite loci to assess the mating system and pollen dispersal of A. crassiflora in a savannah remnant in Central Brazil. We mapped and sampled leaves of 112 adult trees and collected 74 fruits from 20 mother trees (1–4 fruits per plant) to obtain the seeds used (460) for mating system and parentage analyses. Annona crassiflora has predominantly allogamous mating systems, with a high multilocus outcrossing rate (t_m?=?0.974, SE?=?0.011) that did not differ among mother trees (F?=?1.32, p?=?0.165). However, t_m–t_s was variable among seed trees, indicating that some seeds were produced by mating among relatives. Our results also showed multiple paternity within fruits. Multilocus correlation of outcrossed paternity was high (r_p?=?0.302, SE?=?0.045), indicating that for each mother tree, the probability that the same pollen donor sired two random sibs was 30.2%, and the mean number of pollen donors per mother tree was high (6.3). We detected a maximum pollen dispersal distance of 360.7 m and an average of 124.3 m (SD?=?80 m), but most pollination events (73%) occurred at shorter distances (<?160 m), indicating short-distance pollen dispersal, most likely due to the pollinator behaviour.     

Temporal variation in pollen dispersal and breeding structure in a bee-pollinated Neotropical tree

Variation among flowering seasons in the time of flowering, synchrony and length of flowering, and fluctuations in the abundance of pollinators may cause a variation in pollen dispersal distance. In this study, we analyzed the temporal variation in pollen dispersal and breeding structure in the Neotropical tree species Tabebuia aurea (Bignoniaceae) and evaluated pollen dispersal between a population inside the reserve and a patch of isolated individuals on the edge of the reserve, and tested the hypothesis that isolated individuals are sinking for pollen. All adult trees (260) within a population of 40 ha and 9 isolated individuals on the edge of the reserve were sampled, and from these adults, 21 open-pollinated progeny arrays were analyzed in 2 flowering seasons (309 seeds in 2004 and 328 in 2005). Genetic analyses were based on the polymorphism at 10 microsatellite loci. A high proportion of self-pollination found in both flowering seasons indicated a mixed-mating system. The mean pollen dispersal distance differed significantly between the two flowering seasons (307.78 m in 2004 and 396.26 m in 2005). Maximum pollen dispersal was 2608 m, but most pollination events (65%) occurred at distances <300 m. Our results also showed that isolated individuals are sinking for pollen, with high pollen flow between the population inside the reserve and individuals on the edge. These results are most likely due to the large pollinator species, which can potentially fly long distances, and also due to temporal variation in individual fecundity and contribution to pollen dispersal.     

Maintenance of high pollen dispersal in Eucalyptus wandoo, a dominant tree of the fragmented agricultural region in Western Australia

Pollen dispersal was investigated in five remnant populations of Eucalyptus wandoo, a dominant insect-pollinated tree in the fragmented agricultural region of southern Western Australia. Paternity analysis using six microsatellite loci identified a pollen source for 45% of seedlings, and the remainder were assumed to have arisen from pollen sources outside the stands. Outcrossing was variable, ranging from 52 to 89%, and long distance pollen dispersal was observed in all populations with up to 65% of pollen sourced from outside the populations over distances of at least 1 km. Modelling dispersal functions for pollination events within the two larger populations showed little difference between the four two-parameter models tested and indicated a fat-tailed dispersal curve. Similarity of direct and indirect historical estimates of gene flow indicates maintenance of gene flow at levels experienced prior to fragmentation. The study revealed extensive long distance pollen dispersal in remnant patches of trees within a fragmented agricultural landscape in the southern temperate region and highlighted the role of remnant patches in maintaining genetic connectivity at the landscape scale.     

Mating patterns and pollen dispersal in a heterodichogamous tree, Juglans mandshurica (Juglandaceae)

Mating patterns in heterodichogamous species are generally considered to be disassortative between flowering morphs, but this hypothesis has hitherto not been vigorously tested. Here, mating patterns and pollen dispersal were studied in Juglans mandshurica, a heterodichogamous wind-pollinated species that is widely distributed in northern and north-eastern China. Paternity analyses carried out on 11 microsatellite loci were used to estimate morph-specific rates of outcrossing and disassortative mating. Pollen dispersal and genetic structure were also investigated in the population under study. The mating pattern of J. mandshurica was highly outcrossing and disassortative. Pairwise values of intramorph relatedness were much higher than those of intermorph relatedness, and a low level of biparental inbreeding was detected. There was no significant difference in outcrossing and disassortative mating rates between the two morphs. The effective pollen dispersal distribution showed an excess of near-neighbor matings, and most offspring of individual trees were sired by one or two nearby trees. These results corroborate the previous suggestion that mating in heterodichogamous plant species is mainly disassortative between morphs, which not only prevents selfing but also effectively reduces intramorph inbreeding.     

Pollen dispersal and representation in a neotropical rain forest

Results of 3 years of pollen trapping on Barro Colorado Island, Panama, are presented. Minimum pollen dispersal distances are estimated for the most abundant pollen taxa. Dispersal distances for some taxa appear to be as low as 5 m, while for other taxa at least 50% of the trapped pollen had travelled more than 40 m. No consistent pattern of spatial variation was reflected in the pollen rain, however, samples close to large canopy gaps had exceptional abundances of 'disturbance' taxa. A preliminary analysis of the representation of canopy components indicates that as much as 19% of pollen caught in the traps was derived from large tree species.     

Effects of pollen shortage and self-pollination on seed production of an endangered tree, Magnolia stellata

BACKGROUND AND AIMS: Pollen limitation is a significant determinant of seed production, and can result from both insufficient pollen quantity (pollen shortage) and quality (mainly relating to self-pollination). For animal-pollinated tree species with large floral displays, pollen limitation may be determined by a balance between increased pollen quantity due to increased attractiveness for pollinators, countered by increased self-pollination due to increased geitonogamy. The contributions of pollen shortage and self-pollination on seed production were quantitatively examined in the natural pollination of an insect-pollinated, dichogamous, endangered tree, Magnolia stellata, which has a large, showy floral display. METHODS: Manual self- and cross-pollinations were conducted to determine the effects of selfing on seed production. The outcrossing rate was measured using microsatellite analyses of open-pollinated seeds, and the embryo mortality rate caused by self-pollination was indirectly estimated. The frequency of ovule mortality due to pollen shortage was also inferred using the embryo mortality and ovule survival rates from natural pollination. KEY RESULTS: The average fruit set, seed set per fruit, and ovule survival rate per tree from hand cross-pollination were 1.37, 3.15, and 3.34 times higher than those from hand self-pollination, respectively, indicating that self-pollination causes inbreeding depression for fruit and seed set. The multilocus-outcrossing rate (t(m)) was intermediate, 0.632, and the primary selfing rate was 0.657. This indicates that frequent geitonogamous selfing occurs. The ovule mortality rate due to pollen shortage and the embryo mortality rate due to self-pollination were estimated to be 80.8 % and 45.9 %, respectively. CONCLUSIONS: It is concluded that seed production of M. stellata is strongly limited by both pollen shortage and self-pollination. Inefficient beetle-pollination and the automimicry system via asynchronous flowering might be responsible for the high level of pollen shortage and frequent geitonogamy. This is despite a large, showy floral display and the dichogamous system of the species.     

A genetic evaluation of seed dispersal in the neotropical tree Jacaranda copaia (Bignoniaceae)

Seed dispersal is a critical but poorly understood life-history stage of plants. Here we use a genetic approach to describe seed dispersal patterns accurately in a natural population of the Neotropical tree species Jacaranda copaia (Bignoniaceae). We used microsatellite genotypes from maternally derived tissue on the diaspore to identify which individual of all possible adult trees in the population was the true source of a given seed collected after it dispersed. Wind-dispersed seeds were captured in two different years in a large array of seed traps in an 84-ha mapped area of tropical forest on Barro Colorado Island, Panama. We were particularly interested in the proportion of seeds that traveled long distances and whether there was evidence for direct dispersal into gaps, which are required for successful recruitment of this pioneer tree species. Maximum likelihood procedures were used to fit single- and multiple-component dispersal kernels to the distance data. Mixture models, with separate distributions near and far, best fit the observed dispersal distances, albeit with considerable uncertainty in the tail. We discuss the results in light of different mechanisms responsible for separate distributions near the adult source and in the tail of the curve.     

Aspects of variation in a neotropical seed dispersal system

This paper explores the causes and consequences of seed and seedling mortality of the tree Virola nobilis (Myristicaceae) Central Panama in order to understand the advantage to local seed dispersal by birds and monkeys. Post-dispersal mortality due to insects (primarily Conotrachelus spp., Curculionidae) accounts for 30–35% of seed and seedling death during the first 12 weeks after seed fall. Because more seeds and seedlings are killed under and near fruiting trees than 15–45 m away, seed dispersal confers a 20–40 fold advantage on seeds carried 45 m from fruiting adults. In contrast, >60% of seed and seedling death during the first year is due to seed predation by mammals, with >90% due to mammals among the <2% seeds that survive until maternal endosperm is exhausted ±12 weeks after seed fall. Mortaliy due to mammals is independent of distance from parent trees, confering no advantage to seed dispersal. Insects account for variation in mortality attributable to distance effects, mammals to between site effects.Early weevil infestations put a premium on seed removal by large birds (Ramphastos swainsonii, R. sulfuratus, Penelope purpurascens), which carry >50% of the seeds that they eat >40 m, as compared with smaller birds (Baryphthengus martii, Tityra semifasciata, Trogon massena) and monkeys (Ateles geoffroyi), which leave most or all of the seeds that they eat under or near the tree crown.     

Air pollen dispersal in a tropical area

Volumetric data on airborne pollen have been gathered for two consecutive years at a neotropical location (Caracas). Among the 65 taxa which were identified, pollen from aCupressus species (introduced) and from aCecropia species (indigenous) were dominant. Less numerous but also abundant (daily averages ≥5 grains/m³ air) were pollen from Gramineae, Urticaceae,Alcalypha, Pinus, Piperaceae andMimosa. Pollen grains were recorded daily throughout the year. They increased in numbers during April–May and again during November–December. The first peak was contributed mainly by indigenous species, the second peak mainly by introduced species.     

Centres of dispersal and evolution in the neotropical region

For the first time, centres of dispersal in the sense of De Lattin (1957) have been analysed for South and Central America. According to the results of this analysis, at least 40 centres have to be considered, the situation of which has been influenced by quaternary climatic fluctuations and vegetation fluctuations. The latest rate of differentiation of the faunal elements, which have to be associated with the centres (subspecific level) can be understood for a temporary indicator of the last function of the centres in the sense of centres of preservation of faunas and floras during regressive phases. The isolation of the montane forest centres occured before that of most of the lowland forest centres of the central and northern part of South America. During a postglacial arid phase, there has been a gene flow, via open migration roads, between numerous Amazonian Hylea‐Campo populations and populations of the costal savanna of Guiana, Venezuela and the Campo Cerrados. At the same time, these migration roads played the role of barriers of dispersal to the forest fauna and were reconquered by the forest at the end of the aridity phase. At the present time, transition zones of subspecificly differentiated forest populations can be found within the range of these old migration roads. Although the Campo Cerrado has been acting as a barrier of dispersal to forest species since the beginning of the postglacial arid phase, it had obviously been passed through by Amazonian and Serra‐do‐Mar faunal elements prior to that time. The location of the centres of dispersal and the differentiation of their faunal elements support the assumption that the great richness in species of neotropic biomes may be attributed to a large extent to quaternary biochore shifts and the resulting constant isolation of populations. Independent of this, however, numerous faunal elements indicate that this latest phase of differentiation is, in many cases, based on much older ones.     

Airborne dispersal ofCecropia peltata L. (Moraceae) pollen,a neotropical species,in the vicinity of Caracas,Venezuela

In this paper, airborne dispersion of the pollen ofCecropia peltata L. (Moraceae) in a location close to the Equator is described. The Cecropias are fast-growing pioneer trees unique to the Neotropics, where they grow within a large altitude range, from Mexico to Brazil.Cecropia pollen was the most abundant grain throughout the year. The highest recovery occurred during April–May. As widely distributed members of the Moraceae family and because of their small pollen size, the Cecropias are prime suspects for being the source of inhalant allergens. The numbers ofCecropia airborne pollen grains that were recorded are well above those deemed necessary for human sensitization.     

Patterns of pollen and seed dispersal in a small, fragmented population of the wind-pollinated tree Araucaria angustifolia in southern Brazil

Paternity analysis based on eight microsatellite loci was used to investigate pollen and seed dispersal patterns of the dioecious wind-pollinated tree, Araucaria angustifolia. The study sites were a 5.4 ha isolated forest fragment and a small tree group situated 1.7 km away, located in Paranalpha State, Brazil. In the forest fragment, 121 males, 99 females, 66 seedlings and 92 juveniles were mapped and genotyped, together with 210 seeds. In the tree group, nine male and two female adults were mapped and genotyped, together with 20 seeds. Paternity analysis within the forest fragment indicated that at least 4% of the seeds, 3% of the seedlings and 7% of the juveniles were fertilized by pollen from trees in the adjacent group, and 6% of the seeds were fertilized by pollen from trees outside these stands. The average pollination distance within the forest fragment was 83 m; when the tree group was included the pollination distance was 2006 m. The average number of effective pollen donors was estimated as 12.6. Mother-trees within the fragment could be assigned to all seedlings and juveniles, suggesting an absence of seed immigration. The distance of seedlings and juveniles from their assigned mother-trees ranged from 0.35 to 291 m (with an average of 83 m). Significant spatial genetic structure among adult trees, seedlings, and juveniles was detected up to 50 m, indicating seed dispersal over a short distance. The effective pollination neighborhood ranged from 0.4 to 3.3 ha. The results suggest that seed dispersal is restricted but that there is long-distance pollen dispersal between the forest fragment and the tree group; thus, the two stands of trees are not isolated.     

Ontogenetic shifts in habitat-association of tree species in a neotropical wetland

Plant and Soil - We evaluated whether habitat association is consistent between two tree life history stages, young and adult, and whether spatial gradients explain species composition variation....     

Short-distance pollen dispersal for an outcrossed, wind-pollinated southern beech (Nothofagus nervosa (Phil.) Dim. et Mil.)

The mating system (outcrossing, selfing, and biparental inbreeding) and the extent of pollen flow are two of the most important genetic features that determine the genetic structure of plant populations, and both are crucial for the design of conservation strategies. The objectives here were to estimate mating system parameters and to fit the pollen dispersal kernel for the southern beech, Nothofagus nervosa. We sampled 25 mothers and 372 progeny from two stands in the Tromen Lake region of Argentina. We registered spatial positions of the maternal trees, and genotyped mothers and offspring for five simple sequence repeat markers. We estimated single-locus (t _s?=?0.95) and multilocus (t _m?=?0.99) outcrossing rates and biparental inbreeding (t _m-t _s?=?0.04). The species is strongly outcrossing, but correlated paternity within maternal sibships (r _p?=?0.10) indicates that each maternal parent is sampling a different and restricted array of pollen donors. We used two protocols (twogener and kindist) to fit an exponential power dispersal kernel to the structure of pollen clouds sampled by different mothers. The estimated effective number of pollen donors contributing to a single mother was N _ep?=?9.9. The twogener and kindist analyses yielded slightly different estimates, but both indicated short average distances for pollen dispersal (<35?m), indicating that the dispersal kernel was strongly leptokurtic (???=?0.36). While short-distance pollen dispersal predominates, there remains a nontrivial probability of long-distance dispersal. The results are discussed in the context of ongoing conservation and management programs.     

Mating system,pollen and propagule dispersal,and spatial genetic structure in a high-density population of the mangrove tree Kandelia candel

Mangrove tree species form ecologically and economically important forests along the tropical and subtropical coastlines of the world. Although low intrapopulation genetic diversity and high interpopulation genetic differentiation have been detected in most mangrove tree species, no direct investigation of pollen and propagule dispersal through paternity and/or parentage analysis and spatial genetic structure within populations has been conducted. We surveyed the mating system, pollen and propagule dispersal, and spatial genetic structure in a natural population of Kandelia candel, one of the typical viviparous mangrove tree species, using nuclear and chloroplast microsatellite markers. High diversity and outcrossing rates were observed. Paternity and parentage analysis and modelling estimations revealed the presence of an extremely short-distance component of pollen and propagule dispersal (pollen: 15.2 ± 14.9 m (SD) by paternity analysis and 34.4 m by modelling; propagule: 9.4 ± 13.8 m (SD) by parentage analysis, and 18.6 m by modelling). Genetic structure was significant at short distances, and a clumped distribution of chloroplast microsatellite genotypes was seen in K. candel adults. We conclude that the K. candel population was initiated by limited propagule founders from outside by long-distance dispersal followed by limited propagule dispersal from the founders, resulting in a half-sib family structure.     

The effects of pollen composition on fitness components in a neotropical herb

Summary Experimental pollinations of Costus allenii (Zingiberaceae) were conducted to assess the effects of pollen composition on fitness. Plants were selfed, outcrossed with the first nearest neighbor, and outcrossed with pollen mixtures obtained from the nearest 2, 3, and 5 plants. Cross type had a significant effect on seed production, seed weight and total-plant dry weight. Progeny from crosses with 3, and 5 parents grew significantly larger than selfed progeny, or those from 1-parent crosses. Competition experiments indicated the superiority of progeny from 3-, and 5-parent crosses over progeny from 1-parent crosses, but no differences in competitive ability were observed between progeny from 3-, and 5-parent crosses. Relative fitness, based on 1) seed production, 2) percent germination, and 3) dry weight, varied significantly among crosses, and was greatest for crosses with 3 parents and lowest for selfs. The relative fitness of progeny from 5-parent crosses was lower than that of all other outcrossed classes. We suggest that the significant effect of pollen composition on fitness results from variation in the genetic similarity of seed and pollen parents, which is a function of spatial distribution and population structure.