REPRODUCTIVE CAPACITY AND SEED SIZE IN LUPINUS TEXENSIS

The average number of ovules produced per individual of Lupinus texensis is much greater than the average number of seeds per plant. Each plant produces approximately 2,000 ovules but only 2.5% develop into seeds. One fourth of the seeds is lost due to abortion and 0.3% is lost due to predation on the plant. Mature seeds from this population exhibit a five-fold range in weight, from 10 to 56 mg. The distribution of seed weights in the field population is skewed and leptokurtic. Seed wt is positively correlated with both seed germination and seedling survivorship. Heritability of seed wt is 0.09. There is no correlation between average seed wt per plant and total number of seeds per plant, seeds per pod, or legumes per plant.     

Patterns of Seed Size,Germination and Seed Viability of Tropical Tree Species in Southern India1

Seed weight, days to germination and seed viability were observed for 99 species growing in the Western Ghats of Karnataka, India. Seed size was strongly correlated with days to germination; smaller seeds germinated faster than larger seeds. Species which flowered during the rainy season had lighter seeds than species which flowered during the dry season. It was also found that seed size and viability of seeds were related to the season of fruiting. Species which fruit during the rainy season had heavier seeds and shorter viability than species which fruit during the dry season. These flowering and fruiting patterns and varying seed sizes are argued to be adaptations to the time of dispersal, time of moisture availability in the habitat and seedling survival.     

Seed size variation in the palm Euterpe edulis and the effects of seed predators on germination and seedling survival

Intraspecific variation in seed size is common in wild plant populations and has important consequences for the reproductive success of individual plants. Multiple, often conflicting evolutionary forces mediated by biotic as well as abiotic agents may maintain such a variation. In this paper we assessed seed size variation in a population of the threatened, commercially important palm Euterpe edulis in southeast Brazil. We investigated (i) how this variation affects the probability of attack by vertebrate and invertebrate post-dispersal seed predators, and (ii) if seed size influences the outcome of seeds damaged by beetles in terms of seed germination and early survival of seedlings. Euterpe edulis seeds varied in diameter from 8.3 to 14.1 mm. Neither insects nor rodents selected the seeds they preyed upon based on seed size. Seed germination and total, shoot and root biomasses of one-year seedlings were significantly and positively affected by seed size. Root biomass and seedling survival were negatively affected by seed damage caused by a scolytid beetle (Coccotrypes palmarum) whose adults bore into seeds to consume part of the endosperm, but do not oviposit on them. Seed size had a marginally significant effect on seedling survival. Therefore, if any advantage is accrued by E. edulis individuals producing large seeds, this is because of greater seed germination success and seedling vigor. If this is so, even a relatively narrow range of variation in seed size as observed in the E. edulis population studied may translate into differential success of individual plants.     

Rainfall seasonality predicts the germination behavior of a tropical dry‐forest vine

Seed dormancy is considered to be an adaptive strategy in seasonal and/or unpredictable environments because it prevents germination during climatically favorable periods that are too short for seedling establishment. Tropical dry forests are seasonal environments where seed dormancy may play an important role in plant resilience and resistance to changing precipitation patterns. We studied the germination behavior of seeds from six populations of the Neotropical vine Dalechampia scandens (Euphorbiaceae) originating from environments of contrasting rainfall seasonality. Seeds produced by second greenhouse‐generation plants were measured and exposed to a favorable wet environment at different time intervals after capsule dehiscence and seed dispersal. We recorded the success and the timing of germination. All populations produced at least some dormant seeds, but seeds of populations originating from more seasonal environments required longer periods of after‐ripening before germinating. Within populations, larger seeds tended to require longer after‐ripening periods than did smaller seeds. These results indicate among‐population genetic differences in germination behavior and suggest that these populations are adapted to local environmental conditions. They also suggest that seed size may influence germination timing within populations. Ongoing changes in seasonality patterns in tropical dry forests may impose strong selection on these traits.     

DEVELOPMENTAL AND GENETIC SOURCES OF SEED WEIGHT VARIATION IN RAPHANUS RAPHANISTRUM L. (BRASSICACEAE)

Seed weight is known to have a marked impact on emergence and post-emergence productivity in wild radish (Raphanus raphanistrum). In this paper, I describe several levels of seed weight variation in plants taken from a natural population in Hamden, Connecticut. Six maternal plants from the 1981 season were analyzed in detail: the weights and positions of all seeds within a fruit were recorded, and some of these seeds were used the following summer for competition studies and progeny analysis. Within a plant, average seed weight decreased as the number of seeds within a fruit increased, suggesting that developing embryos compete for maternal resources. Seed weight also varied significantly among the six maternal plants used in the study. Comparison of the average weights of seeds produced by offspring of those six plants with the average weights of seeds borne by the maternal plant revealed a significant genetic component to seed weight variation. Seed weight varied up to six-fold within single fruits of R. raphanistrum; large seeds tend to occur near the pedicel or in the middle positions. Seed size variation seen within single fruits is of sufficient magnitude to result in differential reproductive output among closely related seeds under competitive field conditions.     

EXPERIMENTAL STUDIES OF THE EVOLUTIONARY SIGNIFICANCE OF SEXUAL REPRODUCTION. III. MATERNAL AND PATERNAL EFFECTS DURING SEEDLING ESTABLISHMENT

To determine whether genetic differences in fitness components exist among seeds and seedlings in a natural population, weighed propagules of six parents of Anthoxanthum odoratum from a reciprocal diallel cross were planted into the parental source population, a mown field. Seed families of maternal genotypes differed in germination success, while paternal families showed no detectable differences. Differential germination success could not be attributed to propagule weight. Seed families ranked differently in germination percentage in different blocks. No survivorship differences among parental seed families could be detected. There were significant cross × block × germination and cross × block × survivorship interactions; different crosses performed better or worse in different blocks. In some cases, crosses sired by different fathers within a maternal seed family differed in germination or survivorship, suggesting that natural selection may be capable of discriminating among juvenile genotypes within a maternal family despite the presence of large overall maternal effects. These results indicate that seedling establishment may differ according to genotype and that microsite heterogeneity may maintain genetic variation in juvenile traits in natural plant populations.     

The effects of seed size and pericarp on seedling recruitment and biomass in Cryptocarya alba (Lauraceae) under two contrasting moisture regimes

Establishment success of plants derived from large seeds has been proposed to be greater than that of those derived from smaller ones, particularly under unfavourable conditions of moisture. Therefore, the advantages conferred by large seeds in terms of seedling performance may be modulated by abiotic conditions. The effect of seed size on Cryptocarya alba seedling performance (as determined by seedling recruitment and seedling size) was evaluated under two contrasting rainfall regimes (wet and dry year regime), simulated in the laboratory. It was also determined whether the presence of a pericarp, which had been shown to reduce germination, decreases desiccation and if this counterbalances the greater recruitment of seeds without a pericarp, especially under unfavourable conditions of moisture. Large seeds had a greater probability of recruitment and their seedlings attained a greater biomass, independently of the amount of water applied. In the simulated wet year regime, seeds with a pericarp showed a greater probability of recruitment than those lacking a pericarp. However, seedlings derived from both seed types attained a similar biomass. Under the dry year regime, seeds with and without a pericarp showed similar recruitment probabilities and their seedlings had similar biomasses. These results do not support the assumption that under favourable conditions of moisture, individual differences in seed size would not matter in term of seedling performance. A possible explanation in this case, is the presence of recalcitrant seeds in C. alba, which determines a very short time period for germination following dispersal. Therefore, any attribute that increases germination (e.g., large seeds) would be advantageous, independently of the prevailing abiotic conditions.     

Effects of seed dispersal on Juniperus communis recruitment on a Mediterranean mountain

Abstract. The recruitment of the relict shrub Juniperus communis on a mountain in SE Spain was studied during the period 1994–1998. The main objective was to determine both the quantitative and qualitative effects of bird dispersal on seedling establishment. Seed removal by birds, seed rain, post‐dispersal seed predation, germination, and seedling emergence and survival were analysed in different microhabitats. Birds removed 53 ‐ 89% of the seeds produced by plants. Seed rain was spatially irregular as most seeds accumulated near stones used by birds as perches and below mother plants while a few seeds were dropped in wet meadows and open ground areas. Post‐dispersal seed predation by rodents affected < 10% of dispersed seeds but varied significantly among microhabitats. Only 3.6 ‐ 5.5% of dispersed seeds appeared viable, as many seeds had aborted or showed wasp damage. Seeds germinated in the second and third springs after sowing, reaching a germination percentage of 36%. Seedling emergence was concentrated in wet meadows. Seedling mortality was high (75–80%), but significantly lower in wet meadows, the only microhabitat where seedlings could escape from summer drought, the main mortality cause. Seed abortion, germination and seedling mortality proved to be the main regeneration constraints of J. communis on Mediterranean mountains. Birds exerted a strong demographic effect, although their qualitative effect was limited by abiotic factors which caused the pattern of seed rain to differ from the final pattern of recruitment between microhabitats.     

Seed mass versus seedling performance in Scots pine: a maternally dependent trait

It is generally accepted that larger seeds give rise to seedlings with better performance. On the other hand, the size that a seed reaches is genetically determined by at least two different traits ; the genetic variability of the developing embryo and the genetic variability of the maternal plant. Thus, the relative contributions of these two traits affect seedling performance by influencing seed size. In this paper, I investigate the effect of seed size on seedling performance in the Scots pine ( Pinus sylvestris ). From eight maternal plants, 50 seeds were planted in each of two soil types (800 seeds in total), and seedling performance was monitored for 1 yr. Seed mass proved to be highly constant within maternal plants. Soil type influenced emergence and survival; however, the effect of soil type differed depending on maternal origin. Seed mass was positively correlated with seedling emergence, although this relationship was not found for seedling survival or date of emergence. The initial growth of the shoot was also positively correlated with seed mass. However, after one growing season, seed mass had no effect on seedling performance, which depended exclusively on maternal origin. Nevertheless, the mean mass of seeds produced by plants was positively correlated with mean values of growth parameters. Thus, first-year seedling performance seems to be a maternal trait indirectly associated with seed size.     

Development of pepper (Capsicum annuum) seed quality

Changes in seed quality in pepper (Capsicum annuum L.) were monitored during seed development and maturation in two seasons. Seed quality was assessed by a number of different tests, but principally by determining seed storage longevity in laboratory tests and seedling growth in glasshouse tests. Mass maturity (defined as the end of the seed-filling phase) occurred 49–53 days after anthesis (DAA) in 1989 (varying among fruit layers) and 53 DAA in 1990 when seed moisture contents were 51–53%. The onset of both germinability and desiccation tolerance occurred either just before or at mass maturity. Maximum potential longevity (assessed by the value of the seed lot constant K_i) was achieved 63–65 DAA, i.e. not until 10–12 days after mass maturity (DAMM), in both years. Seedling dry weights in the glasshouse growth tests were maximal later still - for seeds harvested 17–21 DAMM in 1989 and 17 DAMM in 1990; the effects on seedling weight arose from differences in times from sowing to emergence (P < 0.005) among different seed harvests, with no significant differences in subsequent relative growth rates (P > 0.25). Seed priming reduced mean germination times for seeds harvested at all stages of development, but had little effect on germination capacity and potential longevity, and did not affect the pattern of changes in potential longevity during seed development and maturation. The results contradict the hypothesis that seed quality is maximal at the end of the seed-filling phase and that viability and vigour begin to decline immediately thereafter.     

干旱胁迫下白刺花种子大小与萌发对策

种子大小与种子萌发及其与环境因子的关系是植物种子萌发对策研究中的重要科学问题之一。采用PEG模拟干旱法研究不同干旱胁迫强度(0,5%,10%,15%,20%)下,白刺花(Sophora davidii)种子萌发进程、种子大小与种子萌发及种子命运的关系。结果表明:不同干旱胁迫下,白刺花种子具有相似的萌发进程,但中度干旱处理(10%PEG)萌发率显著高于零干旱(0%PEG)和重度干旱处理(P0.05),重度干旱处理(20%PEG)种子萌发开始时间晚于零干旱和中度干旱处理;种子大小与种子萌发开始时间的关系表现为零干旱处理下呈极显著负线性关系,中度干旱处理(5%PEG,10%PEG)下无相关关系,重度干旱处理(15%PEG,20%PEG)下呈负二次曲线关系;种子大小对种子命运的影响表现为零干旱处理有利于大、小种子萌发和小种子休眠,中度干旱处理(10%PEG)增加中等种子萌发、大种子休眠和小种子死亡风险,重度干旱处理(15%PEG,20%PEG)增加大种子死亡风险、中等种子和小种子休眠。综合分析表明,白刺花种子大小与萌发行为及种子命运的关系具有较强的环境依赖性,即种子萌发行为表现为顺境下种子越大萌发越快,逆境下小种子和大种子较中等种子萌发更快;种子命运表现为顺境增加种子死亡的风险,中度干扰有利于种子萌发,逆境则有利于种子休眠。     

The Influence of Seed Size Variation on Seed Germination and Seedling Vigour in Diploid and Tetraploid Dactylis glomerata L.

In this study the effects of seed size variation on germinationand seedling vigour have been investigated within and betweenploidy levels of diploid and related autotetraploid Dactylixglomerata. Rates of seed germination and seedling growth werecompared in two contrasting environments using diploid and tetraploidseeds of equal and also different biomass. Within each ploidylevel, seed biomass had no effect on either the overall percentagenor the rate of germination. In contrast, the comparison ofseeds of equal biomass but differing in ploidy level showedthat seeds from tetraploid plants germinated faster and to ahigher percentage than those from diploid plants. With respectto seedling growth, heavier seeds from the tetraploid genotypesgave seedlings of significantly higher biomass than those fromlighter tetraploid and diploid seeds throughout the 2 monthsof study. Interestingly, seeds of equal biomass but from differentploidy levels produced seedlings more similar than those fromthe extreme seed weight categories. These differences were maintainedin two different environmental conditions. These results suggestthat there is a complex interdependance of seed size and ploidyon seed germination and seedling growth but is not a simpleconsequence of differences in seed size between diploids andtheir related tetraploids.Copyright 1995, 1999 Academic Press Dactylis glomerata, polyploidy, seed size, germination, seedling     

Seed Dispersal of a High Quality Fruit by Specialized Frugivores: High Quality Dispersal?1

Dispersal quality, as estimated by the cumulative effects of dispersal, germination, seed predation, and seedling survival, was examined for Beilschmiedia pendula (Lauraceae) in Monteverde, Costa Rica. I determined the pattern of dispersal by finding seeds deposited by birds, protected the seeds from seed predators with cages to assess germination and seedling survival, and examined seed predation rates with marked seeds. Seed predation, germination, and seedling survival were compared between seeds naturally dispersed by birds and seeds placed at randomly located sites. Approximately 70 percent of seeds dispersed by birds (N= 244) were deposited <10 m from crown edges of fruiting B. pendula trees, although some seeds were dispersed at least 70 m away. Larger seeds were more likely to be dispersed under or close to the parent trees, and larger seeds produced larger seedlings. Seed size was not correlated directly with seedling survival, but larger seedlings at three months were most likely to survive one year. Seed predation by mammals and insects and seedling mortality due to fungal pathogens were concentrated beneath the crowns of parent trees. Seedlings and saplings were more abundant beneath fruiting B. pendula trees, but individuals farther away were taller on average. Thus, dispersal is beneficial for B. pendula, but such benefits appear most pronounced at a small spatial scale; seeds dispersed >30 m from the crown edges actually had a lower probability of survival than those dispersed 10–20 m. Only 10 percent of B. pendula. seeds received high‐quality dispersal in terms of landing in the zone with the highest per seed probability of seedling survival 10–20 m from parental crowns.     

Cryptic seed heteromorphism in Packera tomentosa (Asteraceae): differences in mass and germination

Seed mass variation and heteromorphism may afford plant species differential germination behavior and ultimately seedling success, particularly in disturbed habitats. We asked whether such variation occurs in Packera tomentosa (Michx.) C. Jeffrey (Asteraceae), a clonal species of the southeastern USA. Seed mass was compared within and among genetic individuals differentiated using amplified fragment length polymorphisms. We compared central and peripheral seeds produced by disc and ray florets, respectively, for their morphology, mass, and germination behavior, including response to water availability, aging, and cold stratification. Seed mass was highly variable both within and among individuals and influenced germination behavior. We found cryptic seed heteromorphism in P. tomentosa. Central and peripheral seeds had similar morphologies but dissimilar mass and biomass allocation. We used failure time analysis to detect different germination behavior. Central seeds were heavier, contained larger embryos, and germinated faster and at a higher proportion in most germination studies. Highly variable mass and heteromorphism of seeds may allow persistence of P. tomentosa in its disturbed habitats. Based on our results, some future studies of Asteraceae species with disc and ray florets may need to account for possible differences between seed types, even when morphological differences are not apparent. Evaluation of individual seed mass and maternal differences in germination studies may assist in the detection of cryptic seed heteromorphism, a phenomenon thought to be common, yet rarely documented.     

Consequences of a mixed reproductive system in the hog peanut,Amphicarpaea bracteata, (Fabaceae)

Summary The forest annual, Amphicarpaea bracteata L. can reproduce via aerial chasmogamous, aerial cleistogamous, and subterranean cleistogamous flowers. Both plant size and light intensity influenced the utilization of the three modes of reproduction. chasmogamous and aerial cleistogamous flower number and the ratio of chasmogamous flowers to the total number of aerial flowers increased with plant size. The latter demonstrated a shift to xenogamy and outbreeding in larger plants. Light intensity indirectly influenced reproductive modes through its infuence on plant size. Seed set by both types of aerial flowers was low and unrelated to plant size. Subterranean seed number and the total dry weight of subterranean seeds per plant increased with size. The subterranean seeds of Amphicarpaea bracteata are thirty-four times larger than the aerial seeds (fresh weight). Under field conditions, subterranean seeds had greater germination after one year than acrial seeds. The plants arising from subterranean seeds were significantly larger and more fecund than those from aerial seeds. Seeds produced by aerial cleistogamous, hand selfpollinated chasmogamous, and naturally pollinated chasmogamous flowers had equivalent germination rates and produced plants of equal size and fecundity. This suggests that the outbred progeny from chasmogamous flowers have no advantage over the inbred progeny from aerial cleistogamous flowers.     

Ingestion by an endemic frugivore enhances seed germination of endemic plant species but decreases seedling survival of exotics

Aim To test whether ingestion by endemic frugivores differentially affects the seed germination time, germination percentage and seedling survival of endemic, native and exotic fleshy fruited plant species, and to identify the principal processes and attributes driving such effects. Location Round Island, Mauritius. Methods We conducted a germination and seedling survival experiment for 3 months to test whether ingestion (gut passage and deposition in faeces) by the endemic Telfair’s skink (Leiolopisma telfairii) had a differential effect on the germination time, germination percentage and seedling survival of two endemic, four native and two exotic fleshy fruited plant species. To assess the importance of factors involved in the ingestion process, we used a factorial design with gut passage (gut‐passed vs. not gut‐passed), depulping (whole fruit vs. manually depulped seed) and the presence of faecal material (faeces vs. without faeces). In addition, the roles of species‐specific traits, seed size and deposition density (average number of seeds per faeces) were examined. Results Exotic species had a higher germination percentage than indigenous (native and endemic) species when not ingested. Following skink ingestion, there was no longer a difference, as ingestion enhanced germination percentage most in endemic species. The exotic species still germinated faster overall than the indigenous species, despite ingestion accelerating the germination time of endemics. However, ingestion strongly reduced seedling survival of the exotic species, while having no negative effect on the survival of indigenous seedlings. Overall, ingested indigenous seeds were more likely to germinate and the seedlings more likely to survive than ingested exotic seeds and seedlings. Seed size, deposition density and the removal of fruit pulp by either manual depulping or gut passage were important predictors of germination time, germination percentage and seedling survival. Main conclusions These endemic frugivores can enhance the competitiveness of endemic compared with exotic fleshy fruited plants at the critical germination and seedling establishment stage. Consequently, conservation and restoration of mutualistic endemic plant–animal interactions may be vital to mitigating the degradation of habitats invaded by exotic plants, which is of particular relevance for island ecosystems in which large numbers of endemics are threatened by exotic invaders.     

沙埋和种子大小对固沙禾草沙鞭的种子萌发与幼苗出土的影响

该文研究了野外条件下不同深度的沙埋对沙鞭(Psammochloa villosa)种子萌发和幼苗出土的影响,以及温室条件下种子大小对不同深度沙埋后的种子萌发和幼苗出土的影响。结果表明,沙埋深度显著影响沙鞭的种子萌发率、幼苗出土率和种子休眠率。沙子表面的种子不能萌发。2 cm的浅层沙埋时的种子萌发率和幼苗出土率最高,1 cm 沙埋的种子萌发率和幼苗出土率次之。沙埋深度超过2 cm之后,沙鞭的种子萌发率和幼苗出土率与沙埋深度呈负相关。2 cm的种子休眠率最低。从2 ~12 cm,种子休眠率随着沙埋深度的增加而增加。在幼苗能够出土的深度(1~6 cm),幼苗首次出土所需的时间随着沙埋深度的增加而延长。种子大小对沙鞭的种子萌发率没有显著影响。但是在深层沙埋(6 cm)时,与小种子相比,大种子产生的幼苗的出土率较高。从2~6 cm,大种子形成的幼苗的茎长度都较长。     

Seed size as an indicator of seed quality: a case study of Primula veris

Seed size is a widely accepted measure of seed quality, because many earlier studies have shown that large seeds have high seedling survival, growth and establishment. We tested whether ovule loss increases size of the remaining seeds and whether such size increase affects seedling establishment. We removed all except one flower from inflorescences of Primula veris L. (Primulaceae), a perennial hemicryptophyte herb, at a late stage of flowering. Flower removal (FR) increased seed size by 33% compared to the control plants. We then divided the seeds within each treatment to small, middle-sized and large seeds and carried out a sowing experiment in the field. Within each experimental group, seedling establishment was positively associated with seed size. However, despite size differences, seeds from the FR and control groups had the same seedling establishment probability. Seeds from FR plants had a higher seedling emergence in May than those from control plants, but the number of seedlings alive per sowing plot in the late summer was the same in both experimental groups. Increase in seed mass after partial FR thus did not enhance seedling performance, although seed size variation due to other causes was positively correlated with seedling establishment. Further studies are needed to show whether plastic changes of seed size are usually adaptive or not.     

Consumption of wheat seed reserves during germination and early growth as affected by soil water potential

Seed size and weight are important criteria for determining seedling vigour and stand establishment. Evolution of seed dry weight of wheat (Triticum aestivum L.) during germination and early growth was examined because poor stands are often associated with the depletion and exhaustion of seed reserves. Two laboratory experiments were conducted on filter paper and in soil at three water potentials using wheat seeds. Seed, root, and shoot dry weights were recorded at approximately one-day intervals. Coleoptile and first leaf lengths were also measured at all sampling periods. Wheat seedlings grown on filter paper in the dark grew to a length of 90 to 100 mm with 50% of the initial seed weight remaining after eight days when the experiment was terminated. In soil, wheat seedlings grew 15 mm with 25% of the initial seed weight remaining. Seed reserves were depleted more quickly when the soil was wet because seedlings grew more quickly. There were significant and similar negative relationships between seed weight and coleoptile length of wheat seedlings grown on filter paper and in soil. There was no effect of soil water potential on the relationship between seed weight and shoot length. Therefore, it was concluded that poor wheat stands are not likely to occur due to depletion of seed reserves under field conditions without mechanical obstacles.     

Seed dispersal effectiveness in a plant–lizard interaction and its consequences for plant regeneration after disperser loss

Mutualistic disruptions, such as those promoted by the loss of seed dispersers, can have negative effects on the plant regeneration of those species that strongly depend upon them. In order to adequately assess how plant communities are affected by such disruptions, we need to know the importance of the dispersal phase, both in its quantitative and qualitative components. We examined this in the narrow interaction between the shrub Daphne rodriguezii and its (only) disperser, the lizard Podarcis lilfordi. We quantified fruit removal and the effect of fruit/seed-size selection, seed treatment in the disperser’s guts and seed deposition patterns on seedling emergence and survival. In the only locality in which lizards persist, they removed most fruits and showed preference for larger ones in one of the two study years. Seed treatment in lizard’s guts had no effect on germination, although it tended to reduce the effect of seed size on germination (differences between large vs. small seeds in seed germination were higher for non-ingested seeds). Probability of seedling emergence, but not survival, was higher in the locality with lizards. Dispersed seeds under heterospecific shrubs showed higher seedling survival than those under conspecifics in all localities, especially the year with higher rainfall. Our findings support that the movement of seeds to nurse shrubs by lizards is the most important component of the seed dispersal process in the only remaining locality where both species coexist.