Ecological Interactions Shape the Dynamics of Seed Predation in Acrocomia aculeata (Arecaceae)

Background

The complex network of direct and indirect relationships determines not only the species abundances but also the community characteristics such as diversity and stability. In this context, seed predation is a direct interaction that affects the reproductive success of the plant. For Acrocomia aculeata, the seed predation by Pachymerus cardo and Speciomerus revoili in post-dispersal may destroy more than 70% of the propagules and is influenced by the herbivory of the fruits during pre-dispersal. Fruits of plants with a higher level of herbivory during pre-dispersal are less attacked by predators in post-dispersal. We proposed a hypothesis that describes this interaction as an indirect defense mediated by fungi in a multitrophic interaction. As explanations, we proposed the predictions: i) injuries caused by herbivores in the fruits of A. aculeata favor fungal colonization and ii) the colonization of A. acuelata fruit by decomposing fungi reduces the selection of the egg-laying site by predator.

Methodology/Principal Findings

For prediction (i), differences in the fungal colonization in fruits with an intact or damaged epicarp were evaluated in fruits exposed in the field. For prediction (ii), we performed fruit observations in the field to determine the number of eggs of P. cardo and/or S. revoili per fruit and the amount of fungal colonization in the fruits. In another experiment, in the laboratory, we use P. cardo females in a triple-choice protocol. Each insect to choose one of the three options: healthy fruits, fruits with fungus, or an empty pot. The proposed hypothesis was corroborated. Fruits with injuries in the epicarp had a higher fungal colonization, and fruits colonized by fungi were less attractive for egg-laying by seed predators.

Conclusion/Significance

This study emphasizes the importance of exploring the networks of interactions between multitrophic systems to understand the dynamics and maintenance of natural populations.     

Greater mycorrhizal colonization of unisexual morphs than of hermaphroditic morphs of Jacaratia mexicana during flowering and fruiting in central Mexico

Different sexual morphs of dimorphic and trimorphic populations of plants have different demands for resources correlating with phenotypic and ecological dissimilarities among morphs. Few studies have investigated the variations in mycorrhizal symbiosis across the sexual morphs of trimorphic plant populations. Here, we report seasonal variations in the mycorrhizal colonization of the roots of female, male and hermaphroditic trees of Jacaratia mexicana under field conditions in central Mexico. Mycorrhizal colonization was low in the rainy season, when J. mexicana bears only leaves, but high in the dry season when it flowers and fruits. In the dry season, the mycorrhizal colonization of female and male trees was over twofold higher than that of the hermaphroditic trees, and all three morphs had low mycorrhizal colonization in the rainy season. The lack of seasonal variation in the mycorrhizal colonization of hermaphroditic trees, together with other available evidence, supports the idea that hermaphroditic trees of J. mexicana might have some physiological disadvantages compared with male and female trees.     

Species of Penicillium causing decay of stored fruits and vegetables in Israel

Penicillia species were isolated from postharvest decays of fruits of pear, apple, grapes, strawberry, melon, pepper, eggplant and tomato, after 3–5 days' shelf-life following cold storage.Penicillium cyclopium was the most common species in storage and was isolated from all fruits except eggplants. Next in frequency wereP. expansum, P. puberulum, P. viridicatum andP. brevi-compactum, naturally occurring on various types of stored fruits.P. expansum, P. stecki andP. cyaneo-fulyum showed the highest pathogenic potential, being capable of infecting all inoculated tested fruits.P. cyclopium, P. puberulum, P. viridicatum, P. crustosum andP. granulatum were also among the non-selective species, capable of infecting all fruits except eggplant or pepper.P. citrinum, P. purpurogenum, P. frequentans, P. chrysogenum, P. stolonifer, andP. italicum constitute a category characterized by both limited natural distribution and selective pathogonicity after artificial fruit inoculations. Fruit tissues of pears, grapes and tomatoes were found the most suitable for colonization and development of the Penicillia, whereas those of eggplant and pepper were most resistant to infection.     

Colonization of rye green manure and peanut fruit debris by Aspergillus falvus and Aspergillus niger group in field soils.

Aspergillus flavus and Aspergillus niger group colonization of deep-plowed, decomposing rye green manure cover crops in peanut field soils was studied in four fields during 1972 and 1973; colonization of decomposing peanut fruits was studied in 1972 in two fields. A. flavus colonization of rye and peanut fruits was greater in soils of heavy texture, and an A. flavus population as high as 165 propagules per g of soil was observed in soil adjacent to rye, whereas A. flavus populations in soils not associated with rye were 18 propagules per g of soil or lower. Highest A. flavus populations in soil adjacent to decomposing peanut fruits were usually comparable to populations associated with rye. Little decomposing rye or peanut fruit colonization was generally observed by the A. flavus competitor, A. niger group. A. flavus may maintain or increase its inoculum potential by colonization of these and other moribund plant tissues.     

Biocontrol of Postharvest Rhizopus Decay of Peaches with Pichia caribbica

A new yeast antagonist, Pichia caribbica, isolated in our laboratory from the soil collected from unsprayed orchards, was evaluated for its biocontrol capability against Rhizopus stolonifer on peaches and the possible mechanisms involved. The decay incidence and lesion diameter of Rhizopus decay of peaches treated by P. caribbica were significantly reduced compared with the control fruits, and the higher the concentration of P. caribbica, the better the efficacy of the biocontrol. Rapid colonization of the yeast in peach wounds stored at 25 °C was observed. In peaches, the activities of peroxidase (POD), catalase (CAT), and phenylalanine ammonia-lyase (PAL) were significantly induced by P. caribbica treatment compared to those of the control fruits. All these results indicated that P. caribbica has a great potential for the development of commercial formulations to control postharvest Rhizopus decay of peaches. Its modes of action were based on competition for space and nutrients with pathogens, inducement of activities of defense-related enzymes such as POD, CAT, and PAL of peaches.     

Eggs survive through avian guts—A possible mechanism for transoceanic dispersal of flightless weevils

How flightless animals disperse to remote oceanic islands is a key unresolved question in biogeography. The flightless Pachyrhynchus weevils represent repetitive colonization history in West Pacific islands, which attracted our interests about how some weevils have successfully dispersed in the reverse direction against the sea current. Here, we propose endozoochory as a possible mechanism that the eggs of the weevils might be carried by embedded in the fruits as the food of frugivorous birds. In this study, Pachyrhynchus eggs were embedded in small pieces of persimmon fruits (Diospyros kaki) and fed to captive frugivorous birds. After digestion, 83%–100% eggs were retrieved from the feces of a bulbul (Hypsipetes leucocephalus) and two thrushes (Turdus chrysolaus). The retrieved eggs had hatching rates higher than 84%, which were not different from the control. In contrast, no egg was retrieved from the feces of the frugivorous pigeon (Treron sieboldii), which took a longer retention time in the guts. Our study identified that the eggs of Pachyrhynchus weevils are possible to be transported by internal digesting in some bird species.     

内生细菌在荔枝体内的定殖及其防病保鲜功能

用含有GFP基因标记的内生细菌菌株BS-2-gfp和TB2-gfp,采用喷雾接种的方法,研究其在荔枝叶片、花、幼果及成熟果实果皮内的定殖动态及其与防病保鲜之间的关系.结果表明:内生细菌BS-2-gfp和TB2-gfp能在荔枝叶片、花、幼果及采后果皮上定殖,能在各组织内繁殖并可在花和幼果间传导.内生细菌在荔枝叶片上的定殖因季节和荔枝生长期的不同而异,与秋季相比,春季定殖期限长,定殖量大.内生细菌在荔枝不同部位的定殖时间和定殖量也不同,在叶片上接种37d后还可分离回收到接种的2种目标细菌,在花上接种10d后就回收不到BS-2-gfp,而成熟荔枝果皮上2种菌的定殖量最大.防病试验表明,当荔枝霜疫病的病情指数急剧上升时,TB2-gfp在荔枝果皮的定殖量达到最大,为1.90×106CFU.g-1FM;保鲜试验发现,TB2-gfp菌株的保鲜效果优于BS-2-gfp,菌株在荔枝果皮内的定殖量也高于菌株BS-2-gfp,表明供试内生细菌在荔枝果皮的定殖量与其防病及保鲜效果呈正相关.     

A Microscopic Characterization of the Infection of Green and Red Pepper Fruits by an Isolate of Colletotrichum gloeosporioides

Colletotrichum gloeosporioides is a common pathogenic fungus in many plants. To investigate the specificity of the isolate C. gloeosporioides to green fruits, fungal behaviours and anthracnose development on green and red pepper fruits were compared using light and stereo microscopic techniques. When the isolate of C. gloeosporioides was inoculated on both green and red fruits, conidial germination, appressoria, and infection hyphae were observed on both fruits within 24 h after inoculation. The fungal invasion and colonization continued to the epidermal cells of green fruits, but not to those of red ones. Initial anthracnose symptoms were detected only on green fruits at 2 days after inoculation resulting in typical sunken necrosis within 5 days after inoculation. Thus the specificity of the isolate to green fruits may be due to successful invasion and colonization of the infection hyphae from appressoria into the epidermal cells through epicuticular layers of green pepper fnats, but not on red ones.     

On the Limited Potential of Azorean Fleshy Fruits for Oceanic Dispersal

How plants arrived to originally sterile oceanic islands has puzzled naturalists for centuries. Dispersal syndromes (i.e., diaspore traits that promote dispersal by long-distance dispersal vectors), are generally considered to play a determinant role in assisting island colonization. However, the association between diaspore traits and the potential vectors by which diaspores are dispersed is not always obvious. Fleshy fruits, in particular, are considered to have evolved to promote the internal dispersal of seeds by frugivores (endozoochory), however some fleshy fruits can also float in saltwater, and thus be potentially transported by oceanic current (thalassochory). We performed saltwater floatation and viability experiments with fruits of the 14 European fleshy-fruited species that naturally colonized the Azores archipelago (North Atlantic Ocean). We show that only Corema album (a berry) and Juniperus oxycedrus (a fleshy cone) floated for as long as 60 days, the estimated minimum time needed to reach the Azores by oceanic currents. Regardless the floatation potential, exposure to saltwater largely reduced the viability of most seeds of the 14 species (46% of viability decline within 15 days and 77% within 60 days of immersion), including those of Corema album (61%) and Juniperus oxycedrus (83%). Floatability and viability trials suggest that while some fleshy-fruited species might have arrived to the Azores by oceanic currents, such would have required extreme meteorological events that could largely reduce the duration of the trip. Thus, the alternative hypothesis that fleshy-fruited species were mostly dependent on animal dispersers (endozoochory) to colonize these remote islands is reinforced.     

Characterization of Tuber borchii and Arbutus unedo mycorrhizas

For the first time, arbutoid mycorrhizas established between Tuber borchii and Arbutus unedo were described. Analyzed mycorrhizas were from one T. borchii natural truffle ground, dominated by Pinus pinea, as well as synthesized in greenhouse conditions. A. unedo mycorrhizas presented some typical characteristics of ectomycorrhizas of T. borchii. However, as in arbutoid mycorrhizas, ramification was cruciform and intracellular colonization in epidermal cells was present. The ability of T. borchii to form ectomycorrhizas with A. unedo opens up the possibility to also use this fruit plant for truffle cultivation. This represents an important economic opportunity in Mediterranean areas by combining both the cultivation of precious truffles and the production of edible fruits which are used fresh or in food delicacies.     

Effect of AMF inoculum from field isolates on the yield of green pepper,parsley, carrot,and tomato

Inoculum of an indigenous mixture of arbuscular mycorrhizal fungi (AMF) containingGlomus mosseae, Glomus fasciculatum, Glomus etunicatum, Glomus intraradices andScutellospora sp. was applied to four of the most frequently used crop species in Slovenia: green pepper (Capsicum annuum), parsley (Petroselinum crispum), carrot (Daucus carrota) and tomato (Lycopersicon esculentum). A simple, feasible, and effective protocol for application of AMF biotechnology in horticulture was adopted.Mycorrhizal inoculation significantly increased the plant biomass parameters of pepper, and parsley and the root biomass of carrots. Statistically significant correlations between biomass parameters of pepper, parsley, and the root biomass of carrots with mycorrhizal colonization parameters (mycorrhizal frequency (F%), global mycorrhizal intensity (M%) and arbuscular richness (A%) were calculated. A significant increase in chlorophyll content was observed in mycorrhizal parsley and a significant increase in carotenoids was observed in mycorrhizal parsley, carrots, and tomato fruits. A significant increase in titratable acidity of fruits from inoculated tomato plants indicates prolonged fruiting period of mycorrhizal tomatoes. In addition, inoculation with an indigenous AMF mixture significantly increased the mycorrhizal potential of soil and thus the growth of non-inoculated plants in the second season. Thus, the results confirmed the potential of applying mycorrhizal biotechnology in sustainable horticulture.     

Free Methionine Levels in rin and Normal Isogenic Tomato Fruits Ripened in the Field or in Storage

Free methionine levels in rin and normal tomato fruits were determined microbiologically. Similar levels (1750 μg/100 g fresh weight) for mature green fruits of both rin and a normal isogenic line suggest that the lack of ripening of rin fruits is not due to low methionine levels. Methionine levels of mature green rin and normal fruits were 1750 μg/ 100 g fresh weight. Normal fruits ripened either on or off the vine were 2860 and 2500 μg/100 g fresh weight, respectively. The rin fruits which were left on the plant or held in air at 20 C until soft and yellow were significantly lower in methionine than C₂H₄-treated rin fruits or any normal fruits. Harvested rin and normal fruits held at 20 C in continuously applied ethylene (10 μl/l) had higher methionine levels than comparable air controls; levels in treated rin fruits were significantly higher than those in normal fruits.     

Pericarp formation in early divergent species of Arecaceae (Calamoideae,Mauritiinae) and its ecological and phylogenetic importance

Lepidocaryum tenue, Mauritia flexuosa and Mauritiella armata belong to the subtribe Mauritiinae, one early divergent lineage of the Arecaceae and one of the few of Calamoideae that occur in South America. These species occur in swampy environments and have fruits that are characteristically covered with scales. The objective of this study was to describe the formation of the layers of the pericarp within this subtribe and attempt to correlate fruit structure with the environment where species typically occur. Toward this goal, flowers in pre-anthesis and anthesis and fruits throughout development were analyzed using standard methods for light microscopy. The ontogeny of the layers of the pericarp of all three species was found to be similar. The scales were formed from non-vascularized emergences composed of exocarp and mesocarp. The median mesocarp accumulates lipids only in M. flexuosa and M. armata. The inner mesocarp together with the endocarp becomes papyraceous and tenuous in all species. This internal region of pericarp showed collapsed cells due to seed growth at the end of fruit development. Fruits of Mauritiinae are baccate, and the characters of the pericarp, especially the inner mesocarp and endocarp, help to maintain moisture. On the other hand, many species close to Mauritiinae show pericarp with sclerenchyma adjacent to the seed. This variation can contribute to understand the importance of this striking character in dispersal, germination and colonization in Arecaceae.     

Vibrio cholerae Response Regulator VxrB Controls Colonization and Regulates the Type VI Secretion System

Two-component signal transduction systems (TCS) are used by bacteria to sense and respond to their environment. TCS are typically composed of a sensor histidine kinase (HK) and a response regulator (RR). The Vibrio cholerae genome encodes 52 RR, but the role of these RRs in V. cholerae pathogenesis is largely unknown. To identify RRs that control V. cholerae colonization, in-frame deletions of each RR were generated and the resulting mutants analyzed using an infant mouse intestine colonization assay. We found that 12 of the 52 RR were involved in intestinal colonization. Mutants lacking one previously uncharacterized RR, VCA0566 (renamed VxrB), displayed a significant colonization defect. Further experiments showed that VxrB phosphorylation state on the predicted conserved aspartate contributes to intestine colonization. The VxrB regulon was determined using whole genome expression analysis. It consists of several genes, including those genes that create the type VI secretion system (T6SS). We determined that VxrB is required for T6SS expression using several in vitro assays and bacterial killing assays, and furthermore that the T6SS is required for intestinal colonization. vxrB is encoded in a four gene operon and the other vxr operon members also modulate intestinal colonization. Lastly, though ΔvxrB exhibited a defect in single-strain intestinal colonization, the ΔvxrB strain did not show any in vitro growth defect. Overall, our work revealed that a small set of RRs is required for intestinal colonization and one of these regulators, VxrB affects colonization at least in part through its regulation of T6SS genes.     

Patch size drives colonization by aquatic insects,with minor priority effects of a cohabitant

Patch size is one of the most important factors affecting the distribution and abundance of species, and recent research has shown that patch size is an important niche dimension affecting community structure in aquatic insects. Building on this result, we examined the impact of patch size in conjunction with presence of larval anurans on colonization by aquatic insects. Hyla chrysoscelis (Cope''s gray treefrog) larvae are abundant and early colonists in fishless lentic habitats, and these larvae can fill multiple ecological roles. By establishing larvae in mesocosms prior to colonization, we were able to assess whether H. chrysoscelis larvae have priority effects on aquatic insect assemblages. We conducted a series of three experiments in naturally colonized experimental landscapes to test whether (1) H. chrysoscelis larval density affects insect colonization, (2) variation in patch size affects insect colonization, and (3) the presence and larval density of H. chrysoscelis shift colonization of insects between patches of different size. Larval density independently had almost no effect on colonization, while patch size had species‐specific effects consistent with prior work. When larvae and patch size were tested in conjunction, patch size had numerous, often strong, species‐specific effects on colonization; larval density had effects largely limited to the assemblages of colonizing beetles and water bugs, with few effects on individual species. Higher larval densities in large mesocosms shifted some insect colonization to smaller patches, resulting in higher beta diversity among small patches in proximity to high density large mesocosms. This indicates establishing H. chrysoscelis larvae prior to insect colonization can likely create priority effects that slightly shape insect communities. Our results support the importance of patch size in studying species abundances and distributions and also indicate that colonization order plays an important role in determining the communities found within habitat patches.     

Do frugivorous birds concentrate their foraging activities on those alien plants with the most abundant and nutritious fruits in the South African Mediterranean-climate region?

Alien plants with abundant and nutritious fruits may compete more effectively for avian dispersal services than native shrubs. This premise was examined by comparing daily foraging activity (visitation frequency, foraging bird number and foraging period) by four frugivorous bird species of different size on fruits of two native and two alien shrub species co-occurring at four different sites. Also, the quantities of seeds consumed daily by each of the four birds species from fruits of the four shrub species were measured and compared with the numbers of fruits and seeds, and the mass of fruits present in the shrub canopies as well as with their fruit monosaccharide concentrations. The quantities of seed consumed daily by four different size bird species (Columba arquatrix, Colius striatus, Pycnonotus capensis, Zosterops pallidus subsp capensis) were positively correlated with the numbers of seeds per m² of canopy area and with fruit mass and fruit monosaccharide content per m² of canopy area, as well as with the monosaccharide concentration of individual fruits, except in the C. arquatrix (African olive pigeon). All four bird species displayed the highest daily visitation frequencies on fruits of the alien Solanum mauritianum which were more abundant and nutritious than fruits of the other alien Lantana camara and fruits the natives Olea europaea subsp africana and Chrysanthemoides monilifera. They also all consumed greater quantities of seed daily from fruits of the alien S. mauritianum than from fruits of the other shrub species. These results corroborate proposals that frugivorous birds concentrate their foraging activities on those alien plants with the most abundant and nutritious fruits.     

Under pressure from above: Overgrazing decreases mycorrhizal colonization of both preferred and unpreferred grasses in the Patagonian steppe

Arbuscular mycorrhizal fungi (AMF) are related to plant community dynamics and ecosystem functioning. Overgrazing can negatively affect plant performance, and consequently unbalance the association with AMF. We studied the grazing effect on AMF colonization for preferred (Bromus pictus and Poa ligularis) and unpreferred grasses (Pappostipa speciosa and Pappostipa humilis) by sheep in the Patagonian steppe. For each species, AMF colonization in ungrazed, moderate and intense grazing sites was quantified. In ungrazed areas, B. pictus showed the highest extent of AMF colonization. Mycorrhizal colonization was higher during the active season, and largely reduced by intense grazing conditions. The decrease of AMF colonization was maximal for the most preferred species, but also significant for the unpreferred species. Our results suggest that overgrazing could reduce mycorrhizal benefits for the plant by reduction of AMF colonization, which can be a good indicator of ecosystem functioning, eventually revealing an increasing degree of environmental degradation.     

Colonization of Crystalline Cellulose by Clostridium cellulolyticum ATCC 35319

Cellulose colonization by Clostridium cellulolyticum was studied by using [methyl-³H]thymidine incorporation. The colonization process indicated that a part of the bacterial population was released from cellulose to the liquid phase before binding and colonizing another adhesion site of the cellulose. We postulate that cellulose colonization occurs according to the following process: adhesion, colonization, release, and readhesion.     

Field Evaluation of Bt Cotton Crop Impact on Nontarget Pests: Cotton Aphid and Boll Weevil

Bt cotton plants expressing Cry1Ac protein have high specificity for the control of lepidopteran larvae. However, studies conducted in several countries have shown these plants have a differential impact on nontarget herbivores. The aim of this study was to compare the colonization rates and population abundance of the cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae) and the boll weevil, Anthonomus grandis Boheman (Coleoptera: Curculionidae), in plots of Bt (Nuopal) and non-Bt cotton (Delta Opal) in an experimental field in Brasilia, DF, Brazil. No difference was observed in the preference and colonization by winged aphids to plants from the two treatments. There was no significant difference in abundance of wingless aphids or in the production of winged aphids between treatments. Apparently, the parameters that control factors such as fecundity, survival, and dispersal were similar on both Bt and non-Bt plants. Monitoring of plants for coccinellids, a specialist predator of aphids, and ants that act on the dispersal of aphids among plants showed no significant difference between Bt and non-Bt plants, supporting the inference above. Regarding the effect on boll weevil, there was also no significant difference between treatments in the total number of fruiting structures attacked in each plot, the percentage of fruiting structures attacked per plant or on the number of weevils emerging from fruits with boll weevil damage from egg-laying, when damaged fruit samples were held in the laboratory. Based on these results, we conclude that there is no impact of Bt cotton crop expressing Cry1Ac on the nontarget herbivores tested under field conditions.