Life History Evolution in Amphicarpic Plants

Abstract Plants with dimorphic flowers or seeds provide excellent material for the study of life history evolution because the dimorphism often involves measurable differences in morphology, size, number, or genetic relatedness. For amphicarpic plants, the proportion of aerial: subterranean morphs produced is highly variable (from 0 to > 100) and related to both environmental and genetic factors. Plants from aerial seeds produce lower ratios of aerial: subterranean morphs than those from subterranean seeds. Despite substantial variation, subterranean seeds are generally heavier than aerial seeds (but fewer) and produce vigorous seedlings with high survivorship and high fitness. Adaptive advantages of subterranean seeds include retention of offspring in favorable parental microhabitats, protection of seeds from herbivory, predation, or fire, and avoidance of desiccating conditions on the soil surface; potential disadvantages include lack of gene exchange, high energy costs, limited dispersal, and sibling competition. For the few species studied, aerial reproduction is more plastic than subterranean reproduction and more likely to be affected by environmental conditions. Quantitative genetic analyses of a population of the annual grass Amphicarpum purshii have revealed lower heritabilites for subterranean relative to aerial reproductive traits. Subterranean seed number and mass show genetic correlations with shoot mass while aerial seed number and mass do not; seed set percentages of both seed types as well as percentage allocation to both reproductive morphs show negative genetic correlations with shoot mass. In this Amphicarpum population, directional selection on shoot mass may indirectly select for increased subterranean (but not aerial) seed output.     

Amphicarpic plants: definition,ecology, geographic distribution,systematics, life history,evolution and use in agriculture

Although most plants produce all of their fruits (seeds) aboveground, amphicarpic species produce fruits (seeds) both above‐ and belowground. Our primary aims were to determine the number of reported amphicarpic species and their taxonomic, geographic, life form and phylogenetic distribution, to evaluate differences in the life history of plants derived from aerial and subterranean seeds, to discuss the ecological and evolutionary significance of amphicarpy, to explore the use of amphicarpic plants in agriculture, and to suggest future research directions for studies on amphicarpy. Amphicarpy occurs in at least 67 herbaceous species (31 in Fabaceae) in 39 genera and 13 families of angiosperms distributed in various geographical regions of the world and in various habitats. Seeds from aerial and subterranean fruits differ in size/mass, degree of dormancy, dispersal and ability to form a persistent seed bank, with aerial seeds generally being smaller, more dormant and more likely to be dispersed and to form a seed bank than subterranean seeds. In addition, plants produced by aerial and subterranean seeds may differ in survival and growth, competitive ability and biomass allocation to reproduction. Amphicarpic plants may exhibit a high degree of plasticity during reproduction. Subterranean fruits are usually formed earlier than aerial ones, and plants may produce only subterranean propagules under stressful environmental conditions. Differences in the life histories of plants from aerial and subterranean seeds may be an adaptive bet‐hedging strategy.     

REPRODUCTIVE BEHAVIOR OF AMPHICARPAEA BRACTEATA (LEGUMINOSAE), AN AMPHICARPIC ANNUAL

Amphicarpaea bracteata, an annual legume common in woodland communities in the eastern United States, produces three distinct types of flower: subterranean cleistogamous (SCL), aerial cleistogamous (ACL), and aerial chasmogamous (ACH). We sought to quantitatively describe the growth and reproduction of four diverse A. bracteata populations in an effort to explain the adaptive significance of this species’ variable reproductive modes. Virtually all plants develop 1 to 3 SCL seeds on subterranean cotyledonary shoots, starting in late July. Larger plants produce additional SCL seeds later from the tips of axillary shoots which bury. Seeds produced by SCL flowers are large (39 to 134 mg), have restricted dispersal, lack dormancy, have high germination , and produce relatively vigorous seedlings. ACL flowers develop from early August through plant senescence in early October, while ACH flowers appear in a pulse in late August. The number of each aerial flower type was positively correlated with plant size. The ACL flowers take significantly less time to develop mature fruits than do ACH flowers. Both aerial seeds are smaller than the subterranean (mean weights: ACL 12.1, ACH 8.7 mg), have lower germination (ACL 20.2%, ACH 15.3%), appear relatively resistant to environmental extremes, and have the potential for more widespread dispersal. Plants derived from subterranean seeds are much larger than plants derived from aerial seeds, which makes them more likely to produce axillary SCL and aerial seeds. Only larger plants derived from subterranean seeds and growing in favored sites produce ACH flowers. This imposes an alternation of selfing with outcrossing generations. This pattern of reproductive behavior in A. bracteata is similar to that found in several other amphicarpic species.     

Differences in seed dormancy and germination in amphicarpic legumes: manifold bet-hedging in space and time

两型结实豆科植物种子休眠和萌发的差异：空间和时间上多样性的两头下注策略 通过休眠而实现的在空间或时间上的传播是生物体对它们所经历的环境施加影响的主要过程之一。在植物中，由于这两种传播都是通过种子进行的，而且两者在适应性方面发挥的作用也是类似的，因此预测它们之间存在较强的进化相关性。在本研究中，我们使用了两型结实的植株来研究这些进化相关性，这类植株能同时产生具有高度空间传播力的种子以及不会传播的地下种子。我们对经不同组合的休眠过程破坏处理(即干燥后熟、冷积层和物理划伤)后的种子的萌发百分比进行了评估，以研究两种两型结实豆科植物——野豌豆(Vicia amphicarpa L.)和山黧豆(Lathyrus amphicarpos L.)，以及同它们亲缘关系很近的两种单型结实类群——救荒野豌豆(Vicia sativa L.)和红山黧豆(Lathyrus cicera L.)的飞播种子和地下种子在休眠和萌发方面的变化情况。研究结果表明，空间传播和时间传播之间存在着复杂的相互作用。在刚完成传播时，空播种子比地下种子更具休眠性，但当种子经后熟处理而开始物理休眠时，这种趋势也随之逆转。单型结实植株种子的萌发百分比高于其两型结实的同属植株，并在后熟处理后都同样失去了休眠性。相反，两型结实植株的种子则表现出同时受生理休眠和物理休眠调节的不同休眠性策略，预计这可能使出苗时间发生变化，从而提供了多层次多样化的两头下注策略(bet-hedging)。这一策略能够使植株依赖于丰产季中的历史有利区域而不阻碍空间和时间上的迁移，从而有可能在不可预测性很高的条件下具有适应性。     

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.     

Amphicarpum purshii and the “pessimistic strategy” in amphicarpic annuals with subterranean fruit

Summary Amphicarpum purshii Kunth is an annual amphicarpic grass of recently disturbed sandy areas in the Coastal Plain of eastern North America, producing small aerial and larger subterranean seeds. At study sites on the eastern edge of the Pine Barrens of New Jersey, the temporal aspects of reproductive allocation were investigated through biweekly whole-plant field harvests of 25 plants each throughout the 1980 growing season, and the survivorship of plants arising from aerial and subterranean seeds was monitored in a total of 10 high and 10 low density quadrats at two sites differeing in soil moisture. Plants arising from subterranean propagules began to allocate early (July 16) considerable energy to subterranean reproduction (ca 40% of whole-plant dry weight by the last half of August); allocation to aerial culms and flowers did not begin until mid-August and never exceeded 3% on a population basis. Plants arising from aerial propagules (aerial plants) produced only subterranean flowers, and these flowers first appeared 2 wk later than they did on subterranean plants. Survivorship was greater for the subterranean seedlings at both the dry and wet sites and at low and high densities, and aerial plants showed significantly less total growth and seed production than subterranean plants. The pessimistic strategy (early allocation of energy to large subterranean propagules) in the annual Amphicarpum has its selective basis in the relative vigor, survival, and timing and amount of reproduction of the two types of seedlings, and appears comparable to the allocation strategies of at least eight other amphicarpic annuals in at least five other families of plants.     

QUANTITATIVE VARIATION OF LIFE HISTORY TRAITS IN AMPHICARPIC PEANUTGRASS (AMPHICARPUM PURSHII) AND ITS EVOLUTIONARY SIGNIFICANCE

Peanutgrass, Amphicarpum purshii, is a predominantly selling annual that exhibits an amphicarpic reproductive strategy, producing spikelets (and seeds) both above and below the soil surface. Both aerial and subterranean spikelets are self-fertile, but only the aerial spikelets are chasmogamous and capable of cross-pollination. This species mostly grows in disturbed areas of the New Jersey Pine Barrens. To examine life history variation, 60 quantitative characters were measured on twelve families raised from seeds collected from the aerial panicles of twelve parents grown in the greenhouse. Only 19 (= 31.7%) of the traits showed significant between-family phenotypic variation, and the mean percentage of the total variation due to family was 14.9 (N = 60 characters). Percentage biomass allocation and vegetative characters showed the highest narrow-sense heritabilities. Traits directly relevant to fitness such as subterranean seed set and seed weight of both seed types showed the least genetic variation. This low variation could reflect genetic fixation and/or developmental canalization of those fitness components important to survival in disturbed, early-successional habitats.     

Genetic diversity of an amphicarpic species, Amphicarpaea edgeworthii Benth. (Leguminosae) based on RAPD markers

Amphicarpaea edgeworthii Benth. is an amphicarpic legume widespread in China. Amphicarpy describes the phenomenon that a plant produces aerial as well as subterranean fruits. A. edgeworthii can reproduce via three kinds of flowers: aerial chasmogamous flowers, aerial cleistogamous flowers, and subterranean cleistogamous flowers. Although there are some studies on the population genetic structure of species with both chasmogamous and cleistogamous flowers, none has been done for that of an amphicarpic species so far. The present study uses random amplified polymorphic DNA (RAPD) to assess level and pattern of genetic variation in 15 natural populations of A. edgeworthii. A total of 131 stable and clearly scored RAPD bands were achieved from 13 primers. The average genetic diversity within populations estimated by Shannon's information index was 0.218 at the population level, but ranged from 0.119 to 0.302, which was significantly different (P < 0.01). Different statistical analyses revealed a high level of genetic differentiation among populations (G_ST = 0.473–0.527). Thus, the pattern of genetic structure of A. edgeworthii is consistent with that of an inbreeding species.     

Reproductive Biology of an Amphicarpic Annual, Polygonum thunbergii (Polygonaceae): Spatio-temporal Changes in Growth, Structure and Reproductive Components of a Population over an Environmental Gradient

Abstract The process and mechanisms of spatio-temporal changes in growth, population structure, as well as various yield and reproductive components of a population of an amphicarpic annual, Polygonum thunbergii (Polygonaceae), with two reproductive systems (aerial chasmogamous flowers and subterranean cleistogamous flowers) along an environmental gradient (light, moisture and soil nitrogen levels) were investigated in the field.
The results clearly demonstrate that growth and allocation patterns, population structure, and reproductive output of individuals changed sharply along the environmental gradient in response to seasonal and spatial changes in resource availability. Models predicted that light conditions bring about one-sided competition, whereas nutrient conditions in the soil engender two-sided competition. As expected, the degree of one-sided competition was prominent in the case of a planophile, Polygonum thunbergii. Allocation patterns, seed outputs, individual seed size as well as relative energy costs of chasmogamous and cleistogamous seed as affected by light and nutrient levels were also critically analyzed. The most noteworthy finding was that the size of chasmogamous seeds sharply decreased in response to a decrease in the light regime, while cleistogamous seed size remained constant along the gradient. However, relative cost of both chasmogamous and cleistogamous seeds sharply increased with decrease in the light level, reflecting different degrees of environmental stress, biotic interference, or both.     

DISPERSAL OF HETEROMORPHIC SEEDS IN AMPHICARPAEA BRACTEATA (FABACEAE)

The dispersal of the chasmogamous, aerial cleistogamous, and subterranean cleistogamous seeds of Amphicarpaea bracteata was examined. The chasmogamous and aerial cleistogamous seeds are ballistically dispersed. Chasmogamous seeds were dispersed farther than the aerial cleistogamous seeds due to the height advantage of the chasmogamous pods. There was no difference in the firing angle or the initial velocity of the seeds discharged from the two aerial pod types. The subterranean cleistogamous seeds are “dispersed” the shortest distance by the elongation of runners. Differential dispersal of the three types of seeds may be a factor involved in the evolution of cleistogamy in A. bracteata.     

The selection of cleistogamy and heteromorphic diaspores

Models for the evolution of a mixture of cleistogamous (closed, autogamous) flowers and chasmogamous (open) flowers are described. The 'basic' model takes into account features associated with cleistogamous self-pollination, including the greater economy and certainty of cleistogamous fertilization and the inability of cleistogamous flowers to contribute pollen to the outcrossed pollen pool. Complete cleistogamous selfing is favoured when allocation to maternal function, fertilization rate, and viability of progeny are sufficiently greater for the cleistogamous component, and when the resources spent on ancillary structures in cleistogamous flowers, cleistogamous seed costs, and inbreeding depression are low. The result is discussed with respect to the cost of sex argument and relevant ecological data. Suggestions for the apparent rarity of cleistogamy are presented. The 'complex habitat' model extends the basic model to situations in which the success of reproduction by cleistogamy or chasmogamy varies according to the environment of the parent. In this situation, reproduction by both cleistogamy and chasomogamy is sometimes selected. A 'near and far dispersal' model addresses the question of the evolution of dual modes of dispersal, which occur in some cleistogamous and non-cleistogamous plants. A dual mode of dispersal may evolve if a narrowly dispersed seed type is more successful in establishing at the sites located within its dispersal range compared with a second, more widely dispersed seed type which experiences less sib competition. The prediction is discussed with respect to data from amphicarpic plants.     

Analysis of mating system and genetic structure in the endangered,amphicarpic plant,Lewton’s polygala (<Emphasis Type="Italic">Polygala lewtonii)</Emphasis>

Polygala lewtonii is a federally endangered, amphicarpic plant with a mixed mating system and three types of flowers: (1) aboveground, chasmogamous flowers (i.e., open-pollinated; CH), (2) aboveground, cleistogamous flowers (i.e., closed, selfing; CL) and (3) CL flowers on belowground stems (amphicarpy). Aboveground seeds are ant-dispersed, whereas belowground seeds are spaced across the length of the rhizome. Here, we collected individuals of P. lewtonii at both range-wide and fine geographic scales and genotyped them at 11 microsatellite loci. We analyzed patterns of genetic diversity and structure to understand: (1) the predominant mating system (selfing or outcrossing), (2) the movement of pollen and seeds across the landscape, and (3) the optimal strategy to conserve the full range of genetic variation. P. lewtonii reproduces predominantly by selfing or bi-parental inbreeding, but reproduction occurred through each of the three flower types. Some individuals produced by selfing/inbreeding were tightly clustered spatially, and were likely produced either by belowground flowers or by aboveground flowers with limited seed dispersal. Other selfed/inbred individuals were spatially separated (maximum of 15 m), and were likely produced by aboveground flowers followed by seed dispersal by ants. Fine-scale patterns of genetic structure indicate that some gene flow is occurring among aboveground CH flowers but both pollen and outcrossed seeds are moving limited distances (maximum of 0.5 km). Because genetic variation is structured at a fine spatial scale, protecting many populations is necessary to fully conserve the genetic variation in P. lewtonii. Conservation seed banking, if accompanied by research on seed germination requirements, may also contribute to the effective protection of genetic variation in P. lewtonii.     

黄土丘陵沟壑区主要物种植冠种子库动态及其生态策略

植冠种子库是植物适应环境并应对外界干扰的种子生态策略之一,研究了黄土丘陵沟壑区12种主要植物植冠种子库动态,结果表明:杠柳不具有植冠种子库,其他11种植物均具有植冠种子库;除了黄刺玫种子在翌年5月达到脱落高峰,其他植物大部分种子在冬季脱落,其中杠柳、达乌里胡枝子、茭蒿、黄柏刺和水栒子的大部分种子脱落集中偏早,铁杆蒿和土庄绣线菊的大部分种子脱落集中偏晚;植冠宿存对大部分植物种子的萌发特性表现为促进作用;但不同植物种子的萌发时滞对植冠宿存响应差异较大;9种植物种子在植冠上宿存至翌年2月底,其种子活力仍能维持达60%以上;该区植物表现出不同的植冠种子库策略,通过不同的方式来减少干扰的威胁,提高成功萌发与更新的几率,它们或具有较大规模的宿存量、或调控种子萌发特性、或提高种子维持活力的百分比。此外,全面了解该区植物形成植冠种子库的机理及对应的生态策略还有待于全面、深入的研究。     

Do Meyer’s Parrots Poicephalus meyeri benefit pollination and seed dispersal of plants in the Okavango Delta,Botswana?

Recent studies of new world parrots repeatedly document, with few exceptions, that parrots are wasteful and destructive predispersal seed predators that are unlikely to contribute towards pollination and seed dispersal. Few detailed studies, however, have assessed the contribution of African parrots to forest ecology by quantifying the potential net benefit of seed and flower predation by parrots for most tree species in their diet. Due to the incidence of pollen on the heads of Meyer’s Parrots when feeding on Leguminosae flowers and the dispersal of viable seeds to the ground during seed predation, we compared destruction rates, when feeding on pods, fruits and flowers, with dispersal rates of viable seeds to the ground and frequency of head contact with reproductive apparatus to estimate net benefit from Meyer’s Parrot feeding activity. Meyer’s Parrots were not implicated in endo‐ or epizoochory, but they dropped uneaten fruit pulp and seeds to the ground during feeding bouts, thus providing ripe, undamaged seeds to secondary seed dispersers. This link with forest recruitment was weak, as all tree species utilized by Meyer’s Parrots either had more significant primary dispersal agents or were primarily wind‐dispersed. In most cases, the negative effect of seed predation outweighed any positive effects in terms of dispersal, whereby almost three times more seeds were consumed or destroyed than were dispersed to the ground. Significantly, only Sclerocarya birrea caffra recorded marginal net dispersal benefit from utilization by Meyer’s Parrots. Due to low relative resource abundance and high destruction rate, feeding activity on Berchemia discolor may be significant enough to influence its spatial distribution and abundance. Utilization of flowers of Kigelia africana and Adansonia digitata by parrots likely had a significant negative impact on pollination. Feeding on Acacia nigrescens flowers, however, was potentially advantageous to their pollination. We conclude that Poicephalus parrots are net consumers of ripe, undamaged seeds and flowers, thus having an overall negative impact on forest recruitment in subtropical Africa.     

The role of seed depth,litter, and fire in the seedling establishment of amphicarpic peanutgrass (Amphicarpum purshii)

Summary Amphicarpum purshii is an annual grass which mostly grows in disturbed areas of the New Jersey Pine Barrens, USA. It is amphicarpic, producing spikelets (and seeds) both above and below the soil surface. Previous research has shown that subterranean seed production ensures reproduction in the event of a major disturbance such as fire and results in rapid post-burn colonization of these sandy habitats. The effects of fire, litter, and seed depth were further examined by planting subterranean seeds at four depths in 16 litter-covered flats buried at ground level and comparing plants arising from burned flats with those in undisturbed litter-covered flats. At 0 and 1 cm depth, rates of seedling emergence were lowest in burned flats. Surface-sown seeds produced seedlings more likely to desiccate. Sowing depth had a greater influence on most measured characters than burning treatments. The mean depth of subterranean seed placement by Amphicarpum is 3.5 cm and this coincides with the seed depth from which plants showed the greatest height growth, shoot biomass, and reproductive output. In a second experiment, subterranean seeds on the bare soil surface in clay pots were more likely to lose viability and less likely to germinate than seeds protected by litter or burial in soil. In addition to providing protection from fire, placement of seeds below ground in the sandy habitat of peanutgrass provides conditions more suitable for seed survival and subsequent seedling establishment.     

Origins of variance in seed number and mass: interaction of sex expression and herbivory in Lomatium salmoniflorum

Summary As in many plant species, Lomatium salmoniflorum (Umbelliferae) individuals produce many flowers, only a subset of which produce mature seeds that escape seed parasitism and enter the seed bank. The interrelationships between the timing and number of flowers produced, sex expression, seed set, and seed parasitism were studied for their direct and indirect effects on the numbers and masses of viable seeds produced by individual plants. In a sample population of 369 plants that produced 161 386 flowers, 76% of the plants produced some hermaphroditic flowers. The percentage of hermaphroditic flowers increased significantly with the total number of flowers produced by a plant. Seed set was 65–90% in plants producing >600 flowers, but was highly variable in plants producing fewer flowers. Hand-pollinated plants showed the same pattern of seed set, suggesting that variable seed set in small plants may result from insufficient resources for seed development. The majority of schizocarps was produced by only 12% of the plants. Parasites killed 24.5% of the seeds prior to dispersal. Another 14.5% of the seeds lacked endosperm. Hence, the initial 161 386 flowers, which included 25874 hermaphroditic flowers each capable of producing two seeds, produced 42 468 seeds of which an estimated 25906 entered the seed bank as undamaged seeds with fully developed endosperm. Path analysis indicated that the number of hermaphroditic flowers on a plant and the percentage of seeds attacked by seed parasites had the greatest direct effects on the number of viable seeds entering the seed bank. The date at which a plant began flowering and the percentage of flowers setting seed had smaller or only indirect effects on viable seed production. Mean seed mass for plants was not significantly related to any of the factors that affected seed number, but little of the variance in seed mass occurred among plants. Masses of intact seeds in the population ranged 9-fold in both 1987 and 1988. Thirty-five percent of the variance was among seeds within umbels, 46% was among umbels within plants, and only 19% was among plants. The large variation among umbels within plants resulted from a seasonal pattern in which seeds from umbels produced late in the spring had lower mean seed masses than seeds from umbels produced early in the spring. Overall, the results indicate that both direct and indirect interactions between number of flowers, the date of initiation of flowering, seed set, and seed parasitism affect the number of viable seeds entering the seed bank. These interactions strongly bias viable seed output to a small minority of plants that produce many seeds with a wide range of masses over the growing season.     

Breeding systems of the Japanese-endemic carnivorous sundew species Drosera makinoi and Drosera toyoakensis (Droseraceae)

In response to unfavorable environmental conditions, some Drosera species in the northern hemisphere do not open their flowers but form bud-like flowers. The bud-like flowers exhibit pseudo-cleistogamous behavior and produce similar numbers of seeds as open flowers. However, it is not clear how common this type of reproduction is in the genus Drosera. In this study, we examined the effects of flowering (opening flowers/forming bud-like flowers) and pollinator visitation on seed production in Drosera makinoi and D. toyoakensis, two endemic species in Japan. D. makinoi and D. toyoakensis plants did not open 20%–40% chasmogamous flowers to form bud-like flowers. The numbers of mature seeds produced by bud-like flowers were significantly lower than those produced by open flowers (0%–2% of open flowers). In D. makinoi, the percentage of bud-like flowers correlated negatively with the seed production per plant, suggesting that the production of bud-like flowers decreased the lifetime reproductive success. In both D. makinoi and D. toyoakensis, pollinator-excluded flowers produced similar numbers of seeds as control flowers. Our results suggest that pseudo-cleistogamy does not occur in D. makinoi and D. toyoakensis, and they produce seeds without pollinator visits once flowers open.     

Fruit dimorphism inPhaseolus sublobatus (Fabaceae) and its evolutionary significance

Populations of the annualPhaseolus sublobatus from different ecogeographical zones are genetically differentiated. In twelve populations from the western ghats (Maharashtra range) chasmogamous flowers are arranged in peduncled capitate racemes borne in leaf axils of higher nodes. One population (Poona Race S₄) has additional inflorescences, also with chasmogamous flowers, on the main axis between the cotyledonary node and the ground. When the pods of these flowers ripen, the inflorescence gradually coils and, eventually, gets bury the fruits in the soil. This phenomenon is not known in any other plant.—The seed-coat patterns as revealed by SEM, and germination behaviour of both aerial and subterranean seeds are similar, and both types of seeds lack dormancy.—Heavy seed predation selection pressure is probably the principal cause for the evolution of fruit dimorphism inP. sublobatus. The origin of geocarpy in relation to fruit dimorphism and seed predation is discussed.     

SPATIAL PATTERNS OF SEED DISPERSAL AND POSTDISPERSAL SEED PREDATION OF CRYPTANTHA FLAVA (BORAGINACEAE)

I examined the spatial patterns of seed dispersal and postdispersal seed predation of the semidesert perennial Cryptantha flava (A. Nels.) Payson (Boraginaceae) at two sites in north-eastern Utah. Most flowers mature only one seed (nutlet) which is permanently retained within a pubescent calyx. The calyx and enclosed seed abscise from the plant as a unit. These dispersal units are effectively dispersed by wind as evidenced by the highly directional seed shadows and the long distances some of them travel (up to 31.3 m). Potential seed predators at the sites include five species of rodents, of which Peromyscus maniculatus is the most common, and two species of ants, Pogonomyrmex occidentalis and an undescribed species of Conomyrma. There were no strong spatial patterns of postdispersal seed predation. More seeds were removed from dishes placed at the bases of fruiting adults than from dishes ≥ 1.0 m away in one of three experiments. More seeds were removed from under shrubs or clumps of grass than in the open in one of four experiments. After 3–4 days, there was a consistent tendency for more seed removal from high density (75 seeds per .25 m²) quadrats than from low density (75 seeds per 6.25 m²) quadrats, but the difference was not always significant. There was a similar nonsignificant difference between high- and low-density quadrats exposed for 21 days. The pubescent calyx greatly discourages seed predation by ants, and probably also reduces predation by rodents. In addition, by increasing the surface area of the dispersal unit, the calyx may facilitate dispersal by wind.     

INFLUENCE OF ENVIRONMENT AND POPULATION ORIGIN ON SURVIVORSHIP AND REPRODUCTION IN RECIPROCAL TRANSPLANTS OF AMPHICARPIC PEANUTGRASS (AMPHICARPUM PURSHII)

Reciprocal transplants of both seeds and seedlings were utilized to determine whether populations of the annual grass Amphicarpum purshii have become locally adapted to specific habitats due to the consistent production of cleistogamous subterranean seeds from year to year. The hypothesis was that subterranean seeds placed in the same habitat as the parents will produce seedlings of greater vigor and adults of higher reproductive capacity than plants from seeds transplanted to a different habitat far removed from the parents. For both seed and seedling transplant experiments involving three sites in the Pine Barrens of New Jersey, the effects of site on shoot dry weight and production of aerial spikelets, subterranean spikelets, and seeds were generally much more significant than the effects of population origin. With one exception, there was no tendency for seedlings (or plants from seeds) replanted into their home sites to outperform alien seedlings (or plants from seeds) transplanted into these same sites. The overriding importance of environmental factors (relative to genetic differences among populations) in determining the phenotypic expression of life history characters, and selection occurring during succession at a site may retard the evolution of genetic adaptation to local habitat conditions in this species.