Differential dispersal of Chamaesyce maculata seeds by two ant species in Japan

Seed dispersal by ants (myrmecochory) is a widely distributed plant–animal interaction in many ecosystems, and it has been regarded as a generalized (multiple species) interaction in which specialization on specific ant partners is uncommon. In this paper, we demonstrate species-specific seed dispersal of spotted spurge (Chamaesyce maculata) by ants in Japan. C. maculata produces seeds from summer to autumn in Japan. The seeds produced in autumn are carried by two ant species, Tetramorium tsushimae and Pheidole noda. We performed laboratory experiments to investigate the fate of C. maculata seeds in the nests of T. tsushimae and P. noda. P. noda consumed the seeds in the nest and rarely carried seeds out of the nest, while T. tsushimae consumed only the seed coat, and subsequently carried the seeds out of the nest. Removal of the seed coat by T. tsushimae may increase seed survival by reducing their susceptibility to infection by fungi. We also observed ant responses to filter paper soaked with an aqueous extract of the seed coat. P. noda did not react to the filter paper, but T. tsushimae carried the filter paper into their nest. Analysis by high-pressure liquid chromatography revealed that the aqueous extract contained at least four sugars and one unknown substance. Myrmecochory has been regarded as a generalized interaction with specialization for specific ant partners uncommon. However, our study suggests there is a species-specific interaction in seed dispersal by ants in autumn-flowering individuals of C. maculata in Japan.     

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

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

Vegetation diversity influences endozoochoric seed dispersal by moose (Alces alces L.)

Research on moose-mediated seed dispersal is limited. However, its potential role in transferring seeds in patchy landscapes may be of great importance. In this work we examined how seasons and vegetation diversity influence the species richness and abundance of seeds dispersed endozoochorically by moose. Samples of moose faeces were collected year-round, fortnightly, from contrasting vegetation types, dominated by diverse, species-rich wetland or poor, dry pine forest. The viable seed content of dung was studied by the seedling emergence method. The mean number of emerged seedlings per 0.8 L sample and the mean number of plant species per 0.8 L sample were several times higher in the diverse wetland vegetation than in the poor pine forest vegetation. Maximum species richness and seed abundance was observed during the fructification period, and the minimum during spring. The species richness of samples did not differ between winter and the growing season, although the composition of plant species was different. The results of this study suggest that moose are efficient seed vectors, especially of grasses typical for grasslands and wetlands. The species richness and abundance of dispersed seeds coincides with the diversity of the vegetation of the animal’s habitat.     

Secondary seed dispersal in Montrichardia arborescens (L.) schott dominated wetlands in Laguna Grande, Venezuela

Laguna Grande, Monagas State, Venezuela, is a shallow, V-shaped lake created by the confluence of two rivers. Montrichardia arborescens (L.) Schott. dominated wetlands cover most of the north and south arms and the littoral zone of the main body of the lake. The vegetation and seed banks of Montrichardia wetland sites were sampled in the north arm, south arm and main body five times from the end of the dry season in 1991 to beginning of the rainy season in 1992. The composition of the vegetation was similar and changed very little at all three sites during the course of the study. These wetlands had 53 species. Besides M. arborescens, other common species were Hamelia patens Jacq., Mikania cordifolia (L.) Wild., Sarcostemma clausum (Jacq.) Roem. & Schult., and Vitis caribaea L. In both the vegetation and seed banks, species richness was highest during the dry season. Altogether, the seed banks contained the seeds of 61 species of which 35 were also found in the vegetation. Seeds of three tree species were found in the seed banks that did not grow anywhere in the lake. In the seed bank, seeds of Cyperus odoratus L., Eleocharis interstincta (Vahl.) R&S, Ludwigia hyssopifolia (G. Don.) Excell, L. lithospermifolia (Mich.) Hara, Polygonum acuminatum H.B.K., and Sacciolepis striata (L.) Nash were the most abundant. Mean total seed density over the entire study was 6,500, 3,800, and 6,000 seeds/m² in the north arm, south arm, and main basin, respectively. Seed production and dispersal occur primarily during the dry season, and the highest seed densities at all sites were found in the dry season when there was no or little standing water. The lowest seed densities at all sites were found during the rainy season during which seed densities declined over 80% at the north and south arm sites. In the main body of the lake, however, seed densities during the rainy season, although lower than during the dry season, actually increased significantly from 3,600 seeds/m² in August 1991 to 6,000 seeds/m² in October 1991. A significant decrease in seed density in either the north or south arms or both and a significant increase in the main body site during the rainy season occurred for 5 of the 8 species whose seeds were the most abundant, for all life-form guilds, except hydrophytes and for the entire seed bank. Secondary dispersal by water currents during the rainy season appears to be transporting seeds from the north and south arms into the seed bank of the main body of the lake.     

Seasonally different modes of seed dispersal in the prostrate annual, <Emphasis Type="Italic">Chamaesyce maculata</Emphasis> (L.) Small (Euphorbiaceae), with multiple overlapping generations

The modes of seed dispersal in the prostrate annual, Chamaesyce maculata, with multiple overlapping generations were investigated. We found that C. maculata has two modes of seed dispersal; autochory in the summer and myrmecochory in the autumn. Seasonally different modes of seed dispersal have not been known in other plant species. The large proportion of seeds produced in the summer was positioned further than the expanse of the parent plants by automatic mechanical seed dispersal. Therefore, autochory would be effective for avoiding competition between parent and offspring plants. No autochory occurred in the seeds produced in the autumn. The seeds of C. maculata without an elaiosome were dispersed by seed-collecting ants in the autumn. Although 18 ant species in total visited the plants of C. maculata at the 50 sites investigated, only two ant species, Tetramorium tsushimae and Pheidole noda frequently carried the seeds of C. maculata. The low frequency of seeds carried out of the nest by P. noda suggests that the workers of P. noda carry the seeds as food into their nest. So, P. noda might be a less effective seed disperser for C. maculata, corresponding to the effectiveness of seed dispersal by harvester ants. However, T. tsushimae ants frequently carried the seeds into and out of their nest, suggesting that T. tsushimae do not regard the seeds of C. maculata as a food resource. Thus, T. tsushimae may be an effective seed disperser for C. maculata.     

Regional dynamics and dispersal in the vascular plant Silene viscosa (L.) inhabiting small islands

We investigated and compared the patch occupancy and colonisation and extinction over a 40-yr period in the vascular plant Silene viscosa in two archipelagos off the Swedish east coast. We also assessed the importance of regional vs local dynamics for regional persistence by examining factors affecting colonisation and extinction processes.
We found an effect of isolation on the patch occupancy in 1957, but this effect disappeared 1997. The effect of isolation was not detected when analysing colonisations and extinctions during the 40-yr period separately, which suggests that the colonisations and extinctions since 1957 have changed the patch occupancy of S. viscosa . The change in the patch occupancy is attributed to an increased colonisation, presumably mediated by the increase of the greylag goose Anser anser . The large amplitude of population size change, the high persistence of populations during a 40-yr period, and the long term persistence for some populations all suggest that the distribution pattern approximates a distribution that is expected to be generated from an Island-Mainland model, where a number of large populations are persistent and a number of smaller populations are more prone to extinction due to catastrophes (nesting cormorants) and environmental stochasticity (summer drought). Most evidence suggests that regional processes are of less importance than local processes for regional persistence on a time scale of 40 yr for S. viscosa .     

Interactions of seed water content with phytochromeinitiated germination of Rumex crispus (L.) seeds

Light-initiated germination levels of Rumex crispus L. seedswere reduced equally by imbibition in mannitol or polyethyleneglycol 6000 (PEG 6000) solutions of the same w, indicating thatthe effects of each were through w. Reduction of the water contentof the seeds with these osmotica decreased the effectivenessof the far-red absorbing form of phytochrome (P_tr) in causinggermination. However, reduced water content had no effect onthe slopes or saturation points of fluence/response curves whichindicates that has no effect on the number of P_tr receptor sites.The time during which a portion of the seeds were still photoreversibleby far-red light was increased by imbibition in PEG 6000, indicatinga direct effect of w on a reaction involving phytochrome. Noqualitative effect of PEG 6000 on the Onset of secondary dormancywas seen; however, its effect on the relative rate of appearanceof secondary dormancy was equivocal. ¹ Mississippi Agricultural and Forestry Experiment Station cooperating. (Received February 23, 1978; )     

Prevalence and control of wheat (Triticum aestivum L.) seed borne fungi in farmer-saved seeds

High incidence of diseases associated with the use of seeds saved from previous harvests as desire of maintaining local varieties with special attributes is of increased concern in wheat industry worldwide. Prevalent of seed-borne fungi in farmer-saved seeds and seed dressing fungicides to prevent infection from seeds to seedlings was studied in Northern Tanzania. One hundred and thirty five untreated farmer-saved seed lots were collected randomly from farmers. Alternaria alternata, Bipolaris sorokiniana, Drechslera tritici, Fusarium graminearum, Fusarium moniliforme, Aspergillus flavus, Cladosporium sphaerospermum, Epicoccum purpurascens, Pyricularia oryzae and Penicillium corylophilum were fungi isolated in farmer-saved seeds. Mean seed infection was 29% causing average grain yield loss of 1.2 mt/ha^?1. Seed dressing with Metalaxy plus (Methyl carboxaitide), Mancozeb (Manganase-zinc salt) and Baytan (Chlorophenoxy ethanol) increased seed germination by 14, 13 and 17%, respectively, and grain yield by 28, 20 and 18%, respectively. Farmer-saved seeds were heavily infected by fungi with low grain yield performance.     

Immunocytochemical localization of the Lathyrus ochrus (L.) DC seed lectin in seeds and seedlings

Lathyrus ochrus (L.) DC lectin was found to be localized within the protein bodies of both the cotyledons and embryo axis of mature seeds, by using immunocytochemical-labelling techniques involving rabbit antibodies against lectin, followed by goat antibodies against rabbit immunoglobulins (IgG) either fluoresceine-labelled (light microscopy) or adsorbed on colloidal gold particles (electron microscopy). Deposition of lectin inside the protein bodies was studied during seed development, together with its disappearance associated with the protein bodies coalescence occurring during seed germination. In both cases, a parallel quantification of lectin in ripening seeds and seedlings was carried out by radial immunodiffusion with rabbit antibodies against lectin. Our failure to detect lectin in other parts of the plant during its life-cycle suggests that lectin remains associated only with the protein bodies of seeds and seedlings.     

Dispersal ecology of Nuphar luteum (L.) Sibthorp & Smith: abiotic seed dispersal mechanisms

Nuphar luteum (Nymphaceae) is a water lily indigenous to the glacial lakes of the Rocky Mountains of the western United States. The seeds are negatively buoyant, but are dispersed across the water surface in two different manners: (1) within the floating fruits, and (2) within a buoyant, but water-soluble matrix that surrounds the seeds. Seed dispersal via fruits results in a clumped distribution, while seed dispersal mediated by the buoyant matrix results in scattered seed distributions. Experimental release of tagged fruits and seeds in nature show that fruit and seeds can travel up to 80 m/h on the water surface. Although seeds only float for about 72 h, this is adequate time for dispersal, especially in small glacial lakes that are connected via streams. By comparing historical lake-specific population distributions of N. luteurn using aerial photographs taken over a 36 year period we found little change in the overall intralake distribution of each population. We believe these historical patterns to be related to the mechanisms of fruit and seed dispersal.     

Effect of the seed coat on water uptake and electrolyt leakage of sorghum (Sorghum bicolor (L.) Moench) seeds

Four seed lots of sorghum cultivar IS 34213 were obtained which had been harvested early or at full maturity and then dried either swiftly in the sun or slowly in the shade. The earlier harvested seeds were lighter, smaller and of lower density. Earlier harvested seeds had pericarps which permitted faster water uptake and greater leakage of electrolytes. Water uptake and electrolyte leakage were positively correlated. The method of seed drying had no effect on water uptake or leakage. Greater leakage was associated with lower final germination. The results are interpreted in relation to germination testing.     

Queen size dimorphism in the ant Tetramorium moravicum (Hymenoptera, Formicidae): Morphometric, molecular genetic and experimental evidence

Summary. By combining different methods we evaluate whether the ant Tetramorium rhenanum is specifically separated from T. moravicum or whether it is a conspecific microgyne form. High-precision morphometry shows a clear difference in queen size. Sequence comparison of 1031 bp of COI reveals that T. rhenanum falls into a clade with T. moravicum, which is significantly separated from T. forte and T. chefketi. T. rhenanum shares at least two haplotypes with T. moravicum and is considered as a junior synonym. Sexual behaviour and colony foundation experiments corroborate conspecificity. The queen dimorphism is discussed in the context of social parameters such as queen number and reproductive strategy.Received 10 June 2004; revised 28 October 2004; accepted 12 November 2004.     

The role of natural agents in the removal of coat-imposed dormancy in Dichrostachys cinerea (L.) Wight et Arn. seeds

Dichrostachys cinerea seeds are impermeable to water and do not germinate readily. The plant, however, contributes to a bush encroachment problem, minimising visibility in wildlife reserves and reducing the area available for grazing. Natural dormancy-breaking conditions must therefore exist, promoting the germinability of these normally dormant seeds. Diurnal temperature fluctuations (50°C/15°C), especially when combined with moisture were found to break dormancy. High temperatures, such as those generated by fire, destroyed seeds. Seeds ingested by herbivorous browsers such as nyala, became permeable. Seed burial for 48 weeks, was a more effective treatment than storage in promoting permeability. Distribution of D. cinerea will therefore be restricted to areas in which these conditions or factors occur. Seeds germinated optimally at 30C in the laboratory.     

Nutritional function of replete workers in the pharaoh's ant, Monomorium pharaonis (L.)

Summary: Queens of the pharaoh's ant Monomorium pharaonis (L.), like several other ant species, feed on larval secretions as their main nourishment and their fecundity is positively correlated with the number of large larvae present in the nest. The surplus of secretions produced by larvae is stored in a temporary caste of replete workers, which comprises young workers who remain in the nest and store liquid nourishment. Repletes are characterised by a conspicuously large gaster, caused by large amounts of liquid food stored in the crop, from which it may be regurgitated and distributed among colony members. In this study, repletes of pharaoh's ants were demonstrated to be functioning as buffers, smoothing fluctuations in availability of high quality food to the reproductive queens when larvae are scarce or missing, thus temporarily keeping up the egg production of queens.¶In undisturbed two-queen colonies with 20 large worker larvae and 30 workers (15 young and 15 old workers), approximately 10 repletes developed (one replete per two larvae). Development of older workers into repletes, when some or all repletes had been removed from the colonies, demonstrated that their temporal polyethism exhibits great plasticity in this trait.¶This study confirmed that, in pharaoh's ants, the regulation of fecundity depends not only on the food flow to the queen from larvae or from repletes but also on an unknown larval stimulus.¶The term crop repletes is suggested for replete workers which use their crop to store nourishment, as opposed to fat-body repletes, which store nourishment in their fat body.¶The presence of brood tending crop repletes in nests in several European ant species of Leptothorax, Myrmica, and Lasius, show that repletism is a common trait in ants, and that it may play an important role in regulation of nutrition in ant colonies, as demonstrated in Monomorium pharaonis.     

Quantity,quality and the effectiveness of seed dispersal by animals

Disperser effectiveness is the contribution a disperser makes to the future reproduction of a plant. Although it is a key notion in studies of seed dispersal by animals, we know little about what determines the effectiveness of a disperser. The role of the present paper is to review the available information and construct a hierarchical framework for viewing the components of disperser effectiveness.Effectiveness has both quantitative and qualitative components. The quantity of seed dispersal depends on (A) the number of visits made to the plant by a disperser and (B) the number of seeds dispersed per visit. The quality of seed dispersal depends on (A) the quality of treatment given a seed in the mouth and in the gut and (B) the quality of seed deposition as determined by the probability that a deposited seed will survive and become an adult. In this paper I review the ways disperser behavior, morphology and physiology can influence these major components of disperser effectiveness, and when data permit present preliminary analyses of relationships among components.     

The interaction of food distribution and the caste composition of an ant colony (Myrmica rubra L.)

The distribution of food between members of a Myrmica rubra L. Society was investigated by varying the ratios of queens, workers and medium-sized larvae. Observations revealed patterns in colony behaviour which could be of importance in a polygyne system.
Queens had little effect upon the rate of food transmission, but the worker/larva ratio was of significance. Many workers effectively fed all larvae present in a colony, but a small number of workers fed only a few. If larvae and/or queens were in abundance, the workers were partly deprived of access to them. Competition between the queens and larvae for food and worker attention occurred when their numbers were high. In this situation, queens fed themselves while the workers cared for the larvae. The significance of overcrowding, not only upon the administration of food, but upon the queen effect acting on the workers to stimulate or inhibit worker egg-laying and brood-rearing, is discussed.