Long-distance seed dispersal in a metapopulation of Banksia hookeriana inferred from a population allocation analysis of amplified fragment length polymorphism data

There is currently a poor understanding of the nature and extent of long-distance seed dispersal, largely due to the inherent difficulty of detection. New statistical approaches and molecular markers offer the potential to accurately address this issue. A log-likelihood population allocation test (AFLPOP) was applied to a plant metapopulation to characterize interpopulation seed dispersal. Banksia hookeriana is a fire-killed shrub, restricted to sandy dune crests in fire-prone shrublands of the Eneabba sandplain, southwest Australia. Population genetic variation was assessed for 221 individuals sampled from 21 adjacent dune-crest populations of B. hookeriana using amplified fragment length polymorphism. Genetic diversity was high, with 175 of 183 (96%) amplified fragment length polymorphism markers polymorphic. Of the total genetic diversity, 8% was partitioned among populations by amova and FST. There was no relationship between genetic diversity within populations and population demographic parameters such as population size and sample size. A population allocation test on these data unambiguously assigned 177 of 221 (80.1%) individuals to a single population. Of these, 171 (77.4% of total) were assigned to the population from which they were sampled and 6 (2.7% of total) were assigned to a known population other than the one from which they were sampled. A further 9 (4.1% of total) were assigned to outside the sampled metapopulation area, and 35 individuals (15.8%) could not be assigned unambiguously to any particular population. These results suggest that both the extent [15 of 221 (6.8%) individuals originating from a population other than the one in which they occur] and distance (1.6 to > 2.5 km), of seed dispersal between dune-crest populations is greater than expected from previous studies. The extent of long-distance interpopulation seed dispersal observed provides a basis for explaining the survival of populations of the fire-killed B. hookeriana in a landscape experiencing frequent fire, where local extinctions and recolonizations may be a regular occurrence.     

Dispersal mode constrains allocation of carbon and mineral nutrients in seeds of forest and savanna trees

• Species vary in seed size and content of stored reserves, which can be related to dispersal strategies and type of habitat in which they are found. We compare seed carbon and nutrient reserves of anemochorous and zoochorous trees from the Cerrado of central Brazil.
• We measured seed dry mass, lipids, non‐structural carbohydrates (starch and total soluble sugars), carbon and mineral nutrients in ten forest and 13 savanna species, each classified as having wind‐ or animal‐dispersed seeds. We used phylogenetically independent contrasts to test for correlations among these traits.
• Seeds of anemochorous species were lighter, with higher concentrations of C, N, P, Ca and Mg. Lipids were the dominant carbon reserve for most anemochorous species, underpinning the importance of allocation to compact carbon reserves. Starch, lipids or soluble sugars were the major carbon reserve in zoochorous seeds. Savanna and forest species did not differ in seed mass or in total carbon reserves. However, seeds of forest species had higher concentrations of starch than seeds of savanna species. Lipid and starch negatively correlated across species, suggesting a trade‐off between starch and lipids as major seed carbon reserves. Calcium was positively correlated with Mn and B, while Mg was positively correlated with C, N, P, K, S, Zn and B. Potassium, S and Cl were positively correlated, while P was positively correlated with Mg and Zn.
• Dispersal mode rather than vegetation type constrained seed mass and seed storage allocation patterns in forest and savanna trees. We provide evidence that similar mechanisms are involved in seed storage of carbon and mineral nutrients across species.

     

Performance and allocation patterns of the perennial herb,Plantago lanceolata,in response to simulated herbivory and elevated CO2 environments

Summary We tested the prediction that plants grown in elevated CO₂ environments are better able to compensate for biomass lost to herbivory than plants grown in ambient CO₂ environments. The herbaceous perennial Plantago lanceolata (Plantaginaceae) was grown in either near ambient (380 ppm) or enriched (700 ppm) CO₂ atmospheres, and then after 4 weeks, plants experienced either 1) no defoliation; 2) every fourth leaf removed by cutting; or 3) every other leaf removed by cutting. Plants were harvested at week 13 (9 weeks after simulated herbivory treatments). Vegetative and reproductive weights were compared, and seeds were counted, weighed, and germinated to assess viability.Plants grown in enriched CO₂ environments had significantly greater shoot weights, leaf areas, and root weights, yet had significantly lower reproductive weights (i.e. stalks + spikes + seeds) and produced fewer seeds, than plants grown in ambient CO₂ environments. Relative biomass allocation patterns further illustrated differences in plants grown in ambient CO₂ environments. Relative biomass allocation patterns further illustrated differences in plant responses to enriched CO₂ atmospheres: enriched CO₂-grown plants only allocated 10% of their carbon resources to reproduction whereas ambient CO₂-grown plants allocated over 20%. Effects of simulated herbivory on plant performance were much less dramatic than those induced by enriched CO₂ atmospheres. Leaf area removal did not reduce shoot weights or reproductive weights of plants in either CO₂ treatment relative to control plants. However, plants from both CO₂ treatments experienced reductions in root weights with leaf area removal, indicating that plants compensated for lost above-ground tissues, and maintained comparable levels of reproductive output and seed viability, at the expense of root growth.     

Reproductive allocation of an annual,<Emphasis Type="Italic"> Xanthium canadense</Emphasis>, at an elevated carbon dioxide concentration

Stimulation of vegetative growth by an elevated CO₂ concentration does not always lead to an increase in reproductive yield. This is because reproductive yield is determined by the fraction of biomass allocated to the reproductive part as well as biomass production. We grew Xanthium canadense at low N (LN) and high N levels (HN) under an ambient (360 mol mol^-1) and elevated (700 mol mol^-1) CO₂ concentration ([CO₂]) in open-top chambers. Reproductive yield was analysed as the product of: (1) the duration of the reproductive period, (2) the rate of dry mass acquisition in the reproductive period, and (3) the fraction of acquired biomass allocated to the reproductive part. Elevated [CO₂] increased the total amount of biomass that was allocated to reproductive structures, but this increase was caused by increased capsule mass without a significant increase in seed production. The increase in total reproductive mass was due mainly to an increase in the rate of dry mass acquisition in the reproductive period with a delay in leaf senescence. This positive effect was partly offset by a reduction in biomass allocation to the reproductive part at elevated [CO₂] and HN. The duration of the reproductive period was not affected by elevated [CO₂] but increased by HN. Seed production was strongly constrained by the availability of N for seed growth. The seed [N] was very high in X. canadense and did not decrease significantly at elevated [CO₂]. HN increased seed [N] without a significant increase in seed biomass production. Limited seed growth caused a reduction in biomass allocation to the reproductive part even though dry mass production was increased due to increased [CO₂] and N availability.     

Population structure and reproductive status of two Banksia shrubs at various times after fire

Populations of the obligate-seeder, Banksia ericifolia, were even-aged. Seedling recruitment occurred only after fire. Mean genet size (height + canopy diameter; H+D) increased progressively with elapsed time since fire in stands last burnt 2–23 years before 1981. Populations of a co-occurring resprouter, B. oblongifolia, were mixed-aged. Genet size varied significantly between stands, but this variation was not explained by regressions of H+D on years since fire. In addition B. oblongifolia seedlings were recruited both after fire and in patches of heath unburnt for 16 years.Most flower and seed production in B. oblongifolia occurred in the stands last burnt less than 10 years previously. More than 30% of genets had not produced cones since the last fire, irrespective of how many years had elapsed. In contrast, few B. ericifolia genets had produced cones five years after fire, but by 16 years after fire nearly 100% had. Overall, about 51% of B. ericifolia inflorescences and about 28% of B. oblongifolia inflorescences set seed. The number of seeds in seed-bearing cones was not significantly different between species.Resprouting B. oblongifolia genets began flowering sooner after fire, but B. ericifolia subsequently overtook them in accumulating a bank of serotinous seeds. In the stand unburnt for 23 years the largest B. ericifolia genets had more than twice as many cones as the largest co-occurring B. oblongifolia. However, when accumulated cone production was compared for genets of equal H+D over all stands, there was no difference between species.We thank the New South Wales National Parks & Wildlife Service for permission to do this work in Ku-ring-gai Chase National Park. We are grateful to Don Adamson, Lynn Day, David Haig and James Sim for constructive comments on earlier drafts.     

Reproductive allocation strategies in desert and Mediterranean populations of annual plants grown with and without water stress

Reproductive effort (relative allocation of biomass to diaspore production) was compared in matched pairs of Mediterranean and desert populations of three unrelated annual species, Erucaria hispanica (L.) Druce, Bromus fasciculatus C. Presl. and Brachypodium distachyon (L.) Beauv., grown under high and low levels of water availability in a common-environment experiment. Desert populations in all three species showed higher reproductive effort than corresponding Mediterranean populations, as expressed by both a reproductive index (RI= reproductive biomass/vegetative biomass), and a reproductive efficiency index (REI=number of diaspores/total plant biomass). Moreover, in E. hispanica and Brachypodium distachyon, inter-populational differences in reproductive effort were greater under water stress, the main limiting factor for plant growth in the desert. These results indicate that variability in reproductive effort in response to drought is a critical and dynamic component of life history strategies in annual species in heterogeneous, unpredictable xeric environments. When subjected to water stress the Mediterranean populations of E. hispanica and B. distachyon showed greater plasticity (e.g. had a greater reduction) in reproductive effort than the desert populations, while in Bromus fasciculatus both populations showed similar amounts of plasticity.     

Individual resource allocation to vegetative growth and reproduction in subgenus <Emphasis Type="Italic">Cyclobalanopsis</Emphasis> (<Emphasis Type="Italic">Quercus</Emphasis>, Fagaceae) trees

The resource allocation for vegetative growth and female reproduction in three tree species of subgenus Cyclobalanopsis (Quercus, Fagaceae), i.e., Q. salicina, Q. sessilifolia, and Q. acuta, were examined on a per-individual basis in two consecutive reproductive seasons, in order to test whether these trees fit the predictions of the masting hypotheses about resource matching versus resource switching. Since the three Quercus species have a biennial fruiting habit, it takes 3 years for the observation of two reproductive events. Female flower and acorn production per tree were investigated by using a seed-trap method and a numerical analysis of seed dispersal. The net production of each individual was estimated as the sum of the annual increase in the dry mass of vegetative organs and reproductive investment per tree. In the data analyses, the three species were pooled, since all 12 sample trees of the subgenus apparently showed masting in the same year, with no exceptions. Female flower and acorn production per individual tree changed considerably between years. The net production per tree increased with tree size, but did not differ between years. Therefore, the reproductive allocation (proportion of a plant’s annual assimilated resources which are used for reproduction) differed dramatically between years. On the other hand, within a year, the reproductive allocation increased with increasing net production per tree. These results suggest that the switching of resource allocation between years within an individual are occurring in subgenus Cyclobalanopsis species, and the intensity of the switching increases with increasing tree size.     

Sexual differences in biomass and nutrient allocation of first-year Silene dioica plants

Reproductive and somatic biomass, nitrogen (N), and phosphorus (P) pools were compared between females and males in 1st-year plants of Silene dioica. We estimated irretrievable resources allocated to seeds, pollen, flowers, and unrecovered summer leaf investment by collecting plant parts at abscission throughout the season. At the end of the season, we determined resources lost through senescent stems and autumn leaf turnover and resources stored in perennial roots and overwintering buds. Sexual differences in allocation patterns depended on the resource used for comparison, and whether absolute or proportional resource pools were assessed. Total resource pools in terms of biomass and N were similar for females and males. However, male plants acquired relatively more P. The proportional reproductive investment, i.e., reproductive effort, was similar for males and females in terms of biomass and N. In terms of P, male reproductive effort was higher. There was no difference between sexes in the proportional and relative biomass allocated to perennial roots and overwintering buds. However, in terms of absolute and relative N allocation to below-ground parts, females had larger reserves than males. Females, moreover, had a larger proportion of their P in below-ground parts. However, as male total P pools were larger, absolute P reserves did not differ between sexes. The high reproductive effort and N depletion of below-ground parts in males resulted largely from higher flower production compared to females. In females, seeds were the major component of reproductive effort. These results show that if biomass and nutrient allocation are assessed in parallel for dioecious plants, we obtain a more complete view of their sexual differences. Received: 07 May 1998 / Accepted: 30 October 1998     

Significance of the simultaneous growth of vegetative and reproductive organs in the prostrate annual Chamaesyce maculata (L.) Small (Euphorbiaceae)

To elucidate the significance of the simultaneous growth of vegetative and reproductive organs in the prostrate annual Chamaesyce maculata (L.) Small (Euphorbiaceae) from the standpoint of meristem allocation, we investigated plant architecture, meristem allocation, and the spatial and temporal patterns in vegetative growth and reproduction in the reproductive stage. The numbers of secondary and tertiary shoots successively increased by branching in the reproductive stage, and the sum of shoot length was greater in secondary shoots than in primary shoots. The specific shoot length (shoot length per shoot biomass) was greater in lateral shoots than in primary shoots, indicating efficient lateral shoot elongation. The internode length was shorter in secondary shoots than in primary shoots, increasing the number of nodes per shoot length in secondary shoots. Many nodes on a shoot generated two meristems, one of which committed to a flower and one to a lateral shoot. The number of reproductive meristems was greatest in tertiary shoots, and 96% of total reproductive meristems on shoots were generated in lateral shoots. On almost all nodes, the reproductive meristem developed into a flower, and 95–98% of the flowers produced a fruit. Therefore, vegetative growth by branching in the reproductive stage contributed to the increase in reproductive outputs. From the standpoint of meristem allocation, the simultaneous growth of vegetative and reproductive organs in prostrate plant species might be important for increasing the number of growth and reproductive meristems, resulting in the increase in reproductive outputs.     

The association between rank,mating effort,and reproductive success in male Barbary macaques (Macaca sylvanus)

The association between social rank, mating effort, and reproductive success of male Barbary macaques (Macaca sylvanus) has been evaluated by longterm behavioral observations and subsequent paternity determination via oligonucleotide DNA fingerprinting in a large semifreeranging group. All offspring born between 1985 and 1988 that survived to at least 1 year of age (n=75) were available for paternity testing. The exclusion of all but one of the potential fathers from paternity was possible in 70 cases (93%). Mating activities were recorded using ad lib. and focal female sampling techniques. The analysis of male mating effort was restricted to the most likely days of conception. Male rank correlated significantly with male mating success in all four breeding seasons and with male reproductive success in three of the four seasons. Mating success and reproductive success also showed a significant correlation, with the exception of one breeding season, in which the proportion of males per fertilizable female was especially high. Poor mating success was almost always associated with poor reproductive success, while good mating success was less predictive for a male's actual reproductive success. This was apparently a consequence of sperm competition, resulting from the promiscuous mating system. Male mating success is not necessarily an unreliable indicator for reproductive success, provided that sufficient sample sizes are available and that conception periods can be determined. Sperm competition and other factors may weaken the association, however.     

A comparison of reproductive allocation and reproductive effort between semelparous and iteroparous fucoids (Fucales,Phaeophyta)

Reproductive allocation, the proportion of total dry weight allocated to receptacle tissue and reproductive effort, the proportion of reproductive carbon requirement contributed by receptacle photosynthesis, were measured in two fucoid algal species Fucus serratus and Himanthalia elongata at sites in NE Scotland. Reproductive development takes over ten months in H. elongata, a semelparous (single reproductive event) species, and reproductive allocation at receptacle maturity is over 98%. Following gamete release, the whole thallus dies. In contrast, reproductive development in F. serratus takes four months. Fucus serratus is iteroparous (capable of multiple reproductive events), reproductive allocation is 38.6% for the first reproductive event and 50.5% for the following year's event. In Fucus serratus, the receptacles appear to make a major contribution to their own carbon requirements after the first month of reproductive development. The receptacles of Himanthalia elongata contribute only a small proportion of the receptacle carbon requirements in the first four months of reproductive development, after which the contribution made through receptacle photosynthesis increases.     

Litter-fall and reproductive seasonalities in aLeucaena leucocephala forest at Chichijima,Ogasawara (Bonin) Islands

Seasonal changes in litter components were measured in a closedLeucaena leucocephala forest stand in Chichijima, Ogasawara (Bonin) Islands, situated in a wet subtropical climate. The phytomass of the stand was estimated as 5.62, 1.47 and 0.448 kg d.w. m⁻² for stems, branches and leaves, respectively. Litter from the canopy was collected semimonthly by ten 0.5 m² traps. Leaf-litter production rate was low in spring, medium in summer and autumn, and peaked in mid-winter. Annual production of leaf-litter was 498 g d.w. m⁻². Annual turnover rate of canopy leaves was 1.1. Flower-litter showed biannual production with peaks in spring and autumn, and the former peak largely exceeded the latter one in quantity. Seed maturation needed about 3 months. Annual production of reproductive organs was 89.2, 89.4, 19.1 and 99.4 g d.w. m⁻² for flowers, mature seeds, immature ones and pods, respectively. Number, of mature seeds disseminated exceeded 2,500 m⁻². Annual production of branch- and bark-litter was 345 g d.w.m⁻². Annual amount of plant litter from the canopy was as large as 1,150 g d.w. m⁻², showing higher productivity and higher rate of matter turnover in this forest than in temperate forests.     

Patterns of resource allocation in male and female plants of Rumex acetosa and R. acetosella

Summary Patterns of resource allocation in the dioecious Rumex acetosa and R. acetosella were investigated. Males were found to allocate more to reproduction during flower production than females, whereas females invested considerably more in reproduction during seed production. Altogether, females allocated both a higher total amount and a higher proportion of energy to reproduction than did males. By regression analysis, the influence of plant size on reproductive effort was examined separately for males and females. The results indicated that while reproductive effort is sometimes lower for tall plants than for small plants, size-independent effects have a greater influence on reproductive effort than size distribution. An analysis of variance was conducted to investigate the effects of population, season, sex and their interactions on plant size, and an analysis of covariance was used to study differences in resource allocation patterns. Different interaction effects were found to be most important in the two species of Rumex.     

Timing of seed germination and the reproductive effort in Xanthium canadense

The effect of different dates of germination on the timing of flowering and the final reproductive yield was examined in a short-day annual plant Xanthium canadense (cocklebur). Delays in germination of 30 and 60 days deferred flower initiation by 2 and 9 days, respectively. Although plants that germinated later were smaller because of the shorter growing period, the reproductive yields did not show as much reduction as the vegetative biomass. The reproductive effort (RE, defined as the ratio of final reproductive yield to the vegetative biomass at the end of the growing season) increased 1.5 and 2.5 times with delays in germination of 30 and 60 days, respectively. A simple model of plant growth was used to analyse the factors involved in the control of RE, which depends only on the dry mass productivity and its partitioning in the reproductive phase, and is independent of the productivity and partitioning in the vegetative phase. Since relative allocation of dry mass to the reproductive part in the reproductive phase was similar for plants with different germination dates, the different REs could be ascribed mainly to differences in productivity of the vegetative parts in the reproductive period. The dependence of RE on plant size is discussed.     

Size-dependent sex allocation in hermaphroditic plants: the effects of resource pool and self-incompatibility

The effects of the resource pool and resource obtained during a season for seed maturation and self-incompatibility on the size-dependency of evolutionarily stable sex allocation were analysed theoretically. In hermaphroditic plants, reproductive resources allocated between male and female function may not be paid from a single resource pool, because plants can mature seeds using not only reserved resources but also newly gained resources after flowering. But the resource investment to male function is limited to the flowering stage. Under the assumption of constant reserve efficiency and diminishing resource return per investment to leaves, large plants should use both reserved and newly gained resources for seed maturation, while small plants should use only new resources. When both reserved and new resources are used, the optimal allocation for self-compatible species is to invest a constant amount of resources into male function irrespective of resource size, because the female fitness curve increases linearly and the male curve decelerates due to local mate competition. In self-incompatible species, on the other hand, fitness gain per investment through male function and the optimal amount of resources invested in male function decrease with size. Thus a decrease in maleness with size should be emphasized more in self-incompatible species than in self-compatible one. When only new resources are used for seed growth, the female fitness curve as well as male one decelerates with investment. Consequently, the investment in both male and female functions should increase with size, in both self-compatible and self-incompatible species. The magnitude of reserve efficiency relative to efficiency of resource gain after flowering affects size-dependent pattern of sex allocation, while the cost of seed maturation relative to ovule production has little effect on it. The plant size variation in a population emphasizes size-dependency of sex allocation. When size variation is large enough, it is possible that large plants become complete female in self-incompatible species, but it is not in self-compatible species.     

5种甘草属植物花序和种子生产的位置效应及繁殖资源分配模式初步研究

以种植于新疆石河子的光果甘草( Glycyrrhiza glabra Linn.)、胀果甘草( G. inflata Batal.)、乌拉尔甘草( G. uralensis Fisch.)、黄甘草( G. eurycarpa P. C. Li)和蜜腺甘草( G. glabra var. glandulosa X. Y. Li)为研究对象,对植株不同部位的花序数量、花序正常发育率、每花序单花数量和果穗干质量,以及植株不同部位和花序不同部位的生物量投入比、座果率、结籽率、种子投影面积和种子千粒质量进行测定;在此基础上,对供试5种甘草属( Glycyrrhiza Linn.)植物的繁殖资源分配模式和种子生产策略进行分析。结果表明：同一植株内,光果甘草、乌拉尔甘草、黄甘草和蜜腺甘草的花序数量、花序正常发育率、每花序单花数量和果穗干质量从植株下部到上部总体上依次递减,而胀果甘草植株不同部位间这4项指标总体上无显著差异。同一植株内,胀果甘草植株中部的生物量投入比和座果率均较高,但其生物量投入比、座果率和结籽率在植株不同部位间均无显著差异;而供试另4种植物的生物量投入比、座果率和结籽率从植株下部到上部总体上依次递减。同一花序内,胀果甘草花序中部的生物量投入比明显高于花序上部和下部,座果率从花序下部到上部依次递减,结籽率则在花序不同部位间无显著差异,而供试另4种植物的生物量投入比、座果率和结籽率从花序下部到上部总体上依次递减。供试5种植物的种子投影面积和种子千粒质量在植株不同部位间和花序不同部位间均无显著差异。综合研究结果显示：在资源竞争、结构效应和花粉限制的影响下,供试5种甘草属植物存在2种不同的资源分配模式和种子生产格局。其中,光果甘草、乌拉尔甘草、黄甘草和蜜腺甘草通过减少对晚发育的花或果实的资源投入来保障早发育的花或果实获得较多的资源,达到繁殖成功的目的;而胀果甘草则采取对花和果实随机败育的方式减小资源竞争的压力,这2种繁殖资源分配模式和种子生产策略对提高甘草属植物的繁殖成功率具有重要作用。