Selection of Reference Genes for Normalizing Gene Expression During Seed Priming and Germination Using qPCR in Zea mays and Spinacia oleracea

Quantitative real-time RT-PCR (qPCR) has been widely used to investigate gene expression during seed germination, a process involving seed transition from dry/physiologically inactive to hydrated/active state. This transition may result in altered expression of many housekeeping genes (HKGs), conventionally used as internal controls, thereby posing a challenge about selection of HKGs in such scenarios. The objectives of this study included identifying valid reference genes for seed priming and germination studies, both of which involve the transition of seed hydration status, and assessing whether or not findings derived from the “seed model” used in this study would also be applicable to other plant species. Eight commonly used HKGs were evaluated in maize seeds during hydropriming and germination. Using Bestkeeper, geNorm, and NormFinder, we provided a rank of stability for these HKGs. Actdf, UBQ, βtub, 18S, Act, and GAPDH were adjudged as valid internal controls by geNorm and NormFinder. Under the second objective, we conducted a case study with spinach seeds collected during osmopriming and germination. Our results indicate that the conclusions derived from maize were applicable to spinach as well, in that 18S exhibited greater expression stability than GAPDH in osmoprimed and germinated seeds; this held true even under stress conditions. While both of these genes were rejected by BestKeeper, we found that 18S exhibited stable expression when “dry” and “hydrated” seeds were analyzed as separate data sets. Although this approach precludes the comparison between “hydrated” and “dry” seeds, it still provides effective comparison among samples of same hydration status.     

Assessment of Gene Flow from Genetically Modified Anthracnose-Resistant Chili Pepper (Capsicum annuum L.) to a Conventional Crop

We conducted a 2-year field assessment of the gene flow from genetically modified (GM) chili pepper (Capsicum annuum L.), containing the PepEST (pepper esterase) gene, to a non-GM control line “WT512” and two commercial hybrid cultivars, “Manidda” and “Cheongpung Myeongwol (CM).” After seeds were collected from the pollen-recipient non-GM plants, hybrids between them and the GM peppers were screened by a hygromycin assay. PCR with the targeting hpt gene was performed to confirm the presence of transgenes in hygromycin-resistant seedlings. Out of 7,071 “WT512” seeds and 6,854 “Manidda” seeds collected in 2006, eight and 12 hybrids, respectively, were detected. In 2007, 33 hybrids from 3,456 “WT512” seeds and 50 hybrids from 3,457 “CM” seeds were found. The highest frequency of gene flow, 6.19%, was observed in that 2007 trial. These results suggest that a limited isolation distance would be sufficient to prevent gene flow from GM to conventionally bred chili peppers.     

Induction of free radicals in seeds by high intensive flashes and the relevant phosphorus metabolism in the seedling

Influence of high intensive flashes on the yield of free radicals in intact seeds and excised embryonic axis, endosperm, and seed coat, and its resulting effect on seedling growth, total biomass production and phosphorus metabolism in wheat (Triticum aeativum), vetch (Vicia sativa L.) and onion (Allium cepa L.) was studied. Free radicals (f.r.) were formed mainly in seed coat and not in the endosperm. Vetch seeds after irradiation had 20.76 X 10¹³ f.r. g^-1 dry intact seed and 17.30 X 10¹³ f.r. g^-1 dry seed coat. Excised seed coats exposed to irradiation also yielded 17.28 × 10¹³ f.r. g^-1 dry matter. High irradiance “white light” flashes induced more f.r. than a monochromatic one of the same photon content. Red (650 nm), farred (750 nm) and even infra-red (1100 nm) radiation did not initiated f.r. formation but resulted in their decay in samples irradiated earlier by “white”, blue and green parts of the spectrum. Blue irradiation of seeds led to the decrease in the length of shoots and roots in comparison to “white”, green and red irradiation but their biomass increased faster than in the seedlings obtained from non-irradiated or irradiated with “white” and green radiation. The quantity of total acid soluble phosphorus followed a sequence with respect to wavelength of radiation: 436 nm > 650 nm> > 540 nm > non-irradiated > 300–800 nm. Quantity of inorganic phosphorus remained unaffected by different spectral character of radiation. The quantity of organic acid soluble nucleic phosphorus and acid insoluble polyphosphates was higher in samples irradiated with red beams (650 ± 6 nm).     

Sibling rivalry between seeds within a fruit: Some population genetic models

Competition between seeds within a fruit for parental resources is described using one-locus-two-allele models. While a “normal” allele leads to an equitable distribution of resources between seeds (a situation which also corresponds to the parental optimum), the “selfish” allele is assumed to cause the seed carrying it to usurp a higher proportion of the resources. The outcome of competition between “selfish” alleles is also assumed to lead to an asymmetric distribution of resources, the “winner” being chosen randomly. Conditions for the spread of an initially rare selfish allele and the optimal resource allocation corresponding to the evolutionarily stable strategy, derived for species with n-seeded fruits, are in accordance with expectations based on Hamilton’s inclusive fitness criteria. Competition between seeds is seen to be most intense when there are only two seeds, and decreases with increasing number of seeds, suggesting that two-seeded fruits would be rarer than one-seeded or many-seeded ones. Available data from a large number of plant species are consistent with this prediction of the model. Based on a talk given at the Haldane Centenary Symposium held on 6 November 1992 at Ahmedabad as part of the 58th Annual Meeting of the Indian Academy of Sciences.     

Germination and seedling survival in fens undergoing succession

We studied mechanisms of vegetation change in fens subject to succession from open water to floating mats and finally herbaceous rich-fens. Earlier research showed that these systems are characterized by transient seed banks. Our main question was whether seedlings of later successional fen stages are already present in earlier stages, remaining subordinate in the vegetation until conditions become suitable for them. If, however, conditions during succession change in a way that only a limited set of species can survive as seedlings during each of the successional stages, no seedling bank will exist. The transient character of the seeds would then imply that seeds will not germinate and will subsequently die and that seeds that have germinated in the “wrong” stage will not become established. We hypothesized that: (1) germination and seedling survival of fen species are significantly better in the successional fen stage for which these species are characteristic, (2) as a consequence no seedling banks occur in these fens. In a field experiment, seeds of five characteristic fen species in the standing vegetation of three successional fen stages i.e. raft fen, quaking fen and rich fen were sown in each of these stages in a turf pond in the Tienhoven area, The Netherlands. Germination and seedling survival were measured over two growing seasons together with environmental variables. Germination was higher in the “own” stage for all species groups as was survival for quaking fen species and rich fen species. For both these stages, percentage of germination and survival of four out of five characteristic species were significantly higher in the “own” stage. Germination and survival can be considered stage-dependent and it was concluded that seedling banks do not exist in these fens. Site-specific environmental variables act as a sieve and differentiate on species presence already during early life history stages. We found clues that the environmental sieve acts at the level of nutrient availability, tolerance for high sulphide concentration and light climate. Because of the transient seed bank and absence of a seedling bank in these fen wetlands, successful establishment of species necessitates a continuous dispersal of characteristic species until the environmental conditions permit establishment. This also implies that species of the whole successional sere should be present within dispersal distance.     

Scale-dependent neighborhood effects: shared doom and associational refuge

A resource’s susceptibility to predation may be influenced by its own palatability and the palatability of its neighbors. We tested for effects of plant chemical defenses on seed survival by manipulating the frequency of palatable and less palatable sunflower seeds in food patches subject to harvest by fox squirrels (Sciurus niger) and gray squirrels (Sciurus carolinensis). We varied resource distributions at three scales: among stations (aggregates of patches ca. 50 m apart), among patches immediately adjacent to each other, and within patches. When food patches were segregated into high-palatability and low-palatability stations (Experiment 1), seeds suffered greater mortality at stations with high levels of palatable seeds. In the same experiment, within patches, squirrels selected strongly for palatable seeds over less palatable seeds. When high- and low-palatability food patches were placed together at the same stations (Experiment 2), increasing densities of co-occurring palatable seeds amplified the mortality of less palatable seeds, indicating “shared doom.” When palatable and less palatable seeds were partitioned into micropatches (Experiment 3), associational effects disappeared, as predicted. Furthermore, selectivity in less palatable patches increased as the initial densities of palatable seeds increased, and selectivity in palatable patches decreased as the initial densities of less palatable seeds increased. Foraging theory predicts associational effects among prey that vary in palatability. Our results show how the type and magnitude of associational effects emerge from the interplay among the spatial scale of prey heterogeneity, the diet selection strategy, and the scale-dependent foraging responses of the consumer.     

Detection of gene flow from GM to non-GM watermelon in a field trial

Gene flow from genetically modified (GM) crops to conventional non-GM crops is a serious concern for protection of conventional and organic farming. Gene flow from GM watermelon developed for rootstock use, containing cucumber green mottle mosaic virus (CGMMV)-coat protein (CP) gene, to a non-GM isogenic control variety “Clhalteok” and grafted watermelon “Keumcheon” was investigated in a small scale field trial as a pilot study. Hybrids between GM and non-GM watermelons were screened from 1304 “Chalteok” seeds and 856 “Keumcheon” seeds using the duplex PCR method targeting theCGMMV- CP gene as a marker. Hybrids were found in all pollen recipient plots. The gene flow frequencies were greater for “Chaiteok” than for “KeumcheonD; with 75% outcrossing in the “Chaiteok” plot at the closest distance (0.8 m) to the GM plot. A much larger scale field trial is necessary to identify the isolation distance between GM and non-GM watermelon, as the behaviors of insect pollinators needs to be clarified in Korea.     

An anatomical study of anther development in Acorus L.: Phylogenetic implications

 Critical morphological synapomorphies have not been found in support of the Acoranan hypothesis, the molecular phylogenetic discovery that Acoranae are the basal monocots. The previously undetermined pattern of anther wall development in Acorus has been suggested to be one such character. Two main types of anther wall development have been recognized: 1) the “monocotyledonous” type, which characterizes both monocots and dicots, and 2) the “dicotyledonous” type, which is almost exclusively found among dicots. An anatomical study of anther wall development in Acorus was here undertaken using the electron microscope. Development of the anther wall in Acorus was found to be somewhat irregular or perhaps even intermediate between the two types although largely consistent with the “monocotyledonous” type. The presumed significance of anther wall development and other critical morphological characters to the Acoranan hypothesis in the absence of knowledge about the sister group to the monocots is evaluated. Received August 28, 2000 Accepted February 19, 2001     

SYSTEMATIC SIGNIFICANCE OF SEED-SURFACE FEATURES IN ORTHOCARPUS (SCROPHULARIACEAE—SUBTRIBE CASTILLEJINAE)

Scanning electron microscope and light microscope examination of seed-coat features of 26 species of Orthocarpus have allowed recognition of many species-level differences (summarized in a key) and of three seed-coat types that parallel taxonomic subgroups but support realignments at generic and infrageneric levels. Type 1 seeds (subg. Orthocarpus, sect. Orthocarpus) have a lateral hilum, sculptured inner tangential seed-coat walls, and a tightly fitting outer seed coat. They are very similar to seeds of Cordylanthus. Seeds of Types 2 and 3 have a terminal hilum and membranous inner tangential cell walls. Type 2 seeds (subg. Orthocarpus, sects. Castillejoides and Cordylanthoides, with one exception) have a net-like, loosely fitting outer seed coat that shows close relationship to seeds of Castilleja. Inner tangential walls of Type 2 seeds normally rupture. Type 3 seeds (subg. Triphysaria, with two exceptions) have a tightly fitting outer seed coat and inner tangential walls are always retained. Seed features support evidence from floral morphology and chromosome numbers that Orthocarpus as currently recognized is not a monophyletic lineage.     

Pollen and resource limitations to lifetime seed production in a wild population of the endangered plant Disanthus cercidifolius var. longipes H. T. Chang (Hamamelidaceae)

Disanthus cercidifolius Maxim. var. longipes H. T. Chang, a plant species that only occurs in a few counties in Hunan, Jiangxi and Zhejiang Provinces and with a relatively small number of individuals, is ranked as a second Class endangered species for conservation in China. We have studied the effect of pollen and resources available to female reproduction, and the reproductive mechanism of “excess flowers with low fruit set” in Disanthus cercidifolius Maxim. var. longipes H. T. Chang was discussed. Results are as follows Pollen from different sources has significant effects on fruit set and seed set of Disanthus cercidifolius Maxim. var. longipes H. T. Chang. The pollen source rather than pollen numbers significantly affected reproduction of this species. In wild populations, producing one fruit needs about 54.8 flowers, and one satiation seed needs about 6.60 flowers or 83.19 ovules. After fertilizing, which was propitious to flower development, the abortion rate of flower buds was decreasing, but the flowering rate was increasing. The fruit set and seed set was also significantly increasing, while abortion rate of fruit was significantly decreasing. With the increasing percentages of cutting leaves, the fruit set decreased, but the abortion rate of fruit shows no significant differentiation among treatments. After cutting branches that were puny, broken and insectin-fested branches, the flower number seemed to be decreasing, but the fruit set and seed set all increased significantly. After removing some flowers, the fruit set was calculated with respect to the number of flowers remaining after the treatment increased with increasing of percentages of flower removal, whereas fruit set calculated with respect to the initial number of flowers remained constant, and the mean weights of per fruit and per seed all decreased significantly. Sufficient spatial or temporal heterogeneities in nutrient levels might allow limitation of seed set by resources and pollen in a natural population, while supplying resources may indirectly affect pollination by increasing attraction of the flowers to pollinators. There were very low fruit and seed sets in natural populations of Disanthus cercidifolius Maxim. var. longipes H. T. Chang. Different factors may have interacted to effect a low fruit set. A joint adoption of the “selection abortion hypothesis”, “ovary reserve hypothesis” and “male function hypothesis” seems to be the most likely explanation for the reproductive strategy of “excess flowers with few fruit sets” in Disanthus cercidifolius Maxim. var. longipes H. T. Chang. __________ Translated from Acta Ecologica Sinica, 2006, 26(2): 496–502 [译自: 生态学报]     

Experiments on competitiveness of three endomycorrhizal fungi

Summary This paper examines competition between three VA endophytes places respectively as “inoculant” fungus in an inner compartment (300 ml) below the germinating seed, and as “indigenous” fungus in an outer compartment (900 ml). Previously prepared infested soil was used as source of the endophytes. Inner and outer compartment roots were harvested separately and percentage infection determined for each fungus, using diagnostic anatomical features of each fungus. Changes in colonisation patterns were followed up to 4 and 5 months. Treatments with non-infested soil in the outer compartment were used to compare infectivity and spread of the different endophytes. All three endophytes were able to invade soil already colonised by either of the other two, butGlomus fasciculatum (E₃) was more invasive thanGlomus tenue. This pattern appeared to be related to rates of spread of the fungi in the non-infested soil. The pattern was not affected by host, clover or sorghum, or by position, immediately below the seed or in the outer compartment. It seemed that the endophyte in the inner compartment had overriding and persistent effects on plant growth, unrelated to its dominance pattern or share of overall root infection at the later harvests.     

Defense Proteins from Vigna Unguiculata Seed Exudates: Characterization and Inhibitory Activity Against Fusarium Oxysporum

Plants exude a variety of substances through their roots, germinating seeds and aerial parts. Some of these released compounds seem to have an inhibitory effect against pathogens. The aim of this work was to investigate and identify antifungal proteins present in exudates from imbibed cowpea seeds (Vigna unguiculata (L.) Walp). The obtained exudation was analyzed in regard to specific protein activities by enzymatic or immunological assays for plant defense proteins, from 4 h to 48 h of seed imbibition. Our results show that cowpea seeds exudates present several defense related proteins characterized as β-1,3-glucanases, cystatins, vicilins and lipid transfer proteins (LTPs), as well as a storage vacuole membrane α-TIP protein, since the very first hours of imbibition. These exudates also have an “in vitro” inhibitory effect on the growth of the fungus Fusarium oxysporum f. sp. phaseoli. Our results suggest that seed exudates should promote seed protection from soil pathogens.     

Reproductive biology of Abies cephalonica Loudon in Mount Aenos National Park, Cephalonia, Greece

The reproductive biology of the endemic to Greece Abies cephalonica Loudon, including the phenology of the reproductive life cycle, cone production in relation to plant age and the required seed germination conditions, was studied. All individuals growing within 20 permanent plots of 100 m² each established in 11 different locations covering the entire strictly protected area of Mount Aenos National Park (Cephalonia) were monitored over a period of 4 years. The cones are formed on the upper part of the previous year’s branches, mostly at the upper crown half of the reproductive individuals (over 53 years old). Female flowers are pollinated in spring and cone maturation lasts until the beginning of autumn, when seed dispersal occurs. The annual production of cones per individual varied significantly, revealing masting behavior for this tree. This behavior was also expressed in the number of trees producing cones, as well as the percentage of sound seeds per cone. A significant difference in the mass and the length of the cones between the years of low and high cone production was observed, being higher in the years of massive cone production. Similar germination percentages were observed in full darkness or under “canopy light” and “sun light”, provided that the seeds were previously stratified for 6 weeks. It is concluded that A. cephalonica exhibits plasticity expressed in its reproductive behavior for alternating years of high to low cone production and in its seed germination for an array of habitat light conditions.     

Separated at Birth: The Interlinked Origins of Darwin’s Unconscious Selection Concept and the Application of Sexual Selection to Race

This essay traces the interlinked origins of two concepts found in Charles Darwin’s writings: “unconscious selection,” and sexual selection as applied to humanity’s anatomical race distinctions. Unconscious selection constituted a significant elaboration of Darwin’s artificial selection analogy. As originally conceived in his theoretical notebooks, that analogy had focused exclusively on what Darwin later would call “methodical selection,” the calculated production of desired changes in domestic breeds. By contrast, unconscious selection produced its results unintentionally and at a much slower pace. Inspiration for this concept likely came from Darwin’s early reading of works on both animal breeding and physical ethnology. Texts in these fields described the slow and unplanned divergence of anatomical types, whether animal or human, under the guidance of contrasting ideals of physical perfection. These readings, it is argued, also led Darwin to his theory of sexual selection as applied to race, a theme he discussed mainly in his book The Descent of Man (1871). There Darwin described how the racial version of sexual selection operated on the same principle as unconscious selection. He thereby effectively reunited these kindred concepts.     

Lectin fromCanavalia brasiliensis (MART.). isolation,characterization and behavior during germination

A lectin was isolated fromCanavalia brasiliensis Mart. seeds by combining solubility fractionation with affinity chromatography on Sephadex G-50. The lectin showed a carbohydrate specificity for D-mannose (D-glucose) binding and a requirement for Ca²⁺ and Mn²⁺. All the hemagglutinating activity was found in the cotyledons and the presence of the lectin was followed during the first 15 days of plant germination, through the activity against rabbit erythrocytes, the presence of the “lectin peak” in Sephadex G-50 affinity chromatography, presence of the “lectin bands” in SDS-polyacrylamide gel electrophoresis and the “lectin arcs and rockets” in immunoelectrophoresis in agarose gel. On application of all these methods the lectin showed a differentiated metabolism, disappearing more slowly than the other high molecular weight proteins of the seed.     

Use of microsatellite DNA and otolith Sr:Ca ratios to infer genetic relationships and migration history of four morphotypes of <Emphasis Type="Italic">Rhinogobius</Emphasis> sp. OR

The genetic diversity and relationship among four morphotypes of Rhinogobius sp. OR, Gobiidae (“Tōshoku,” “Shinjiko,” “Gi-tōshoku,” and “Shimahire”) were investigated with seven microsatellite DNA loci, and amphidromy of these morphotypes was verified by strontium (Sr) and calcium (Ca) deposition in the otolith. Samples of “Tōshoku,” “Shinjiko,” “Gi-tōshoku,” and “Shimahire” were collected from, respectively, three, three, two, and four locations in Japan. Microsatellite analysis detected high genetic diversity (based on the number of alleles, allelic richness, and average observed heterozygosity) in the “Tōshoku” and “Shinjiko” morphotypes relative to the “Shimahire” morphotype; the “Gi-tōshoku” morphotype had an intermediate level of variation. Almost all pairwise F _ST values were significantly different from zero (P < 0.001), except between two populations of “Tōshoku.” Clear genetic independence was observed between the “Shinjiko” and “Shimahire” morphotypes in the Maruyama River. A principle component analysis based on microsatellite data indicated that the “Tōshoku,” “Shinjiko,” and “Gi-tōshoku” morphotypes were genetically similar. Furthermore, the three populations of “Tōshoku” were closely related each other, and two of those collected from the Lake Biwa system were a single population. There was, however, a high degree of genetic differentiation between “Shimahire” and the other morphotypes; moreover, there was high genetic divergence among four populations of the “Shimahire” morphotype. Amphidromous migratory histories were indicated by Sr:Ca ratios in two of three populations of the “Shinjiko” morphotype and in one of two “Gi-tōshoku” morphotypes, whereas all populations of the “Shimahire” morphotype were freshwater residents. The large genetic divergence and low genetic diversity in “Shimahire” are likely related to migration history.     

Dung beetle distribution patterns in the Iberian peninsula

A canonical variate analysis was used to summarize the distribution pattern of 30 species of dung beetles (Scarabaeinae) from 162 sites in the Iberian peninsula (Spain and Portugal) in relation to 4 site variables. The best separation of beetle species, obtained using a xerothermic climatic index, was into 3 groups called “mediterranean”, “unrestricted” and “temperate”. Little further separation was achieved using altitude, dung type or soil type. These data are used to select dung beetles for introduction to south-western Australia for bush fly control.

---

Résumé On a fait appel à l'analyse de variables canoniques pour résumer le plan de distribution, relatif à 4 variables de localité, de 30 espèces de bousiers (Scarabaeinae) de 162 localités de la Péninsule ibérique (l'Espagne et le Portugal). La meilleure division des espèces, obtenue à l'aide d'un indice xérothermique climatique, se faisait en 3 groupes désignés respectivement comme “méditerranéen”, “ubiquiste” et “tempéré”. Peu de séparation supplémentaire a été obtenue en ayant recours à des facteurs d'altitude, de nature de la bouse ou de type de sol. Ces données ont été employées pour aider à la sélection de bousiers destinés à être introduits en Australie Occidentale pour y combattreMusca vetustissima Walker[Diptera].

     

Seed Morphology of Plantago in China and Its Taxonomic Significance

Studied in this work was seed morphology of the genus Plantago (2 subgenera, 8 sections, 17 species and １ variety )in China. The sculpture was observed under scanning election microscope. Four forms of seed morphology are recognized as follows: (1)Multi-angular type: seeds are variously angulate, yellow-brown or black, 6-30 in a fruit; seed-coat sculpture ranges from reticulate to papillate. It occurs in Subgen. Plantago Sect. Polyneuron: P. scheideri, P. denstflorus, P. major, P. hostifolia, P. asiatica, P. erosa and P. centralis. (2) Navicular type: seeds are navicular, yellow, brown to black, 2 in a fruit; seed-coat sculpture is reticulate. It was found in Subgen. Plantago Sect. Novorbis: P. virginica; Sect. Arnoglossum: P. lanceolata; Sect. Leucopsyllium: P. minuta, P. lessingii and P. aristata and Subgen. Psyllium Sect. Psyllium: P. indica. (3)Ovoid type: seeds are long-ovoid, yellow-brown, black and lustrous. Seed-coat sculpture scali-ratiform. P. maxima in Subgen. Plantago Sect. Lamprosantha belongs to this type. (4)Recti-circular type: seeds are recti-circular, yellow-brown, black, 1-2 or 4-5 in a fruit; seed-coat sculpture is reticulate and papillate. It was found in P. maritima var. salsa of Subgen. Plantago Sect. Coronopus and P. depressa, P. camtschatica and P. arachnoidea of Sect. Mesembrynia. The seed morphology and seed-coat sculture exhibit specific characters, by which some of confused species can be clarified and a new species, P. densiflorus J. Z. Liu. is established. The present author’s seed morphology classification is in accordance with Pilger’s systemof the genus, which was established using other features.     

Contrast adaptation to time constraints on development of two pre-dispersal predators of dandelion (<Emphasis Type="Italic">Taraxacum officinale</Emphasis>) seed

Pre-dispersal seed predators of quickly maturing inflorescences of Asteraceae are constrained by shortage of development time. At seed dispersal, they should pupate or, if still immature, relocate into another inflorescence. To investigate how dominant coleopteran predators of dandelion seed, Glocianus punctiger (Curculionidae) and Olibrus bicolor (Phalacridae), cope with time limitation we combined observation (development and temperature of dandelion capitulum, thermal constants of predator development, age structure of larval populations at seed dispersal) and analogy (“rate isomorphy” in predator development, comparing “model” coleopteran species with similar temperature requirements). Development of a dandelion capitulum takes 21 days. The time available to G. punctiger (140–190 day degrees, development threshold 6.3°C) is sufficient to complete development and pupate after seed dispersal. By contrast, only 30–50 day degrees are available to O. bicolor (threshold 13.5°C) and this is not enough to complete development and consequently immature larvae should move to other capitula to continue feeding until pupation. These contrast strategies which are determined by this thermal adaptation, are accompanied by differences in larval morphology. The “cold adapted” G. punctiger has an apodous larva not capable of migrating between capitula while the “warm adapted” O. bicolor has a mobile campodeiform larva capable of migration.     

Seed dispersal in Cakile edentula var. lacustris : decoupling the fitness effects of density and distance from the home site

A factorial design of three densities of siblings at three local distances from seed parents was employed to distinguish effects of density from effects of dispersal distance on lifespan and fruit production of Cakile edentula var. lacustris, a plant with heteromorphic seeds. The segmented fruits produce two seed types: proximal and distal, with distal seeds having greater mass and greater dispersibility. Effects of longer distances (0.5 km and 30 km) on lifespan and fruit production were investigated using plants at low density. The prediction was tested that the greater seed mass of distal seeds increases fitness when seeds are dispersed into sites of unknown quality away from the home site or when seeds are dispersed to low density. High density caused earlier mortality and lower probability of reproduction. Distance from the maternal plant did not influence lifespan or reproduction at distances of 15 m or less, but lifespan was longer 0.5 km from the home site. No interaction was detected between the effects of density and distance on either lifespan or total fitness. Environmental conditions that influence fitness did not vary as a function of dispersal distance in this system, and favorable conditions at the home site did not persist between generations. Therefore, selection on dispersion patterns in natural conditions is likely to be through effects of density rather than dispersal distance. Proximal seeds had greater reproduction than distal seeds at the home site, and distal seeds had greater reproduction at the more distant sites (but not the most distant site), as expected, but these performance differences could not be attributed to differences in mass between the two seed types. Reduced seed mass was favored at the most distant site, but larger seed mass was favored most strongly at low density. Seeds that are dispersed to low density are larger, suggesting that although kin selection may limit the effectiveness of individual selection to increase seed mass under conditions of sibling competition, density-dependent individual selection on seed mass, rather than distant-dependent selection, also contributes to the observed associations among seed type, seed mass and dispersal ability. Received: 21 October 1996 / Accepted: 4 December 1996