The birds, the bees, and the virtual flowers: can pollinator behavior drive ecological speciation in flowering plants?

Biologists have long assumed that pollinator behavior is an important force in angiosperm speciation, yet there is surprisingly little direct evidence that floral preferences in pollinators can drive floral divergence and the evolution of reproductive (ethological) isolation between incipient plant species. In this study, we expose computer-generated plant populations with a wide variation in flower color to selection by live and virtual hummingbirds and bumblebees and track evolutionary changes in flower color over multiple generations. Flower color, which was derived from the known genetic architecture and phenotypic variance of naturally occurring plant species pollinated by both groups, evolved in simulations through a genetic algorithm in which pollinator preference determined changes in flower color between generations. The observed preferences of live hummingbirds and bumblebees were strong enough to cause adaptive divergence in flower color between plant populations but did not lead to ethological isolation. However, stronger preferences assigned to virtual pollinators in sympatric and allopatric scenarios rapidly produced ethological isolation. Pollinators can thus drive ecological speciation in flowering plants, but more rigorous and comprehensive behavioral studies are required to specify conditions that produce sufficient preference levels in pollinators.     

Sugar secretion and ant protection in Ficus benguetensis: Toward a general trend of fig–ant interactions

The relationship between plants and ants is often mediated by the presence of extrafloral nectaries (EFNs) that attract ants and provide rewards by protecting plants from herbivores or parasites. Ficus trees (Moraceae) and their pollinators (Hymenoptera: Agaonidae) are parasitized by many nonpollinating fig wasp species (Hymenoptera: Chalcidoidea) that decrease the reproductive output of the mutualistic partners. Previous studies have shown that ants living on and patrolling Ficus species can efficiently deter parasitic wasps. The aim of this study was to verify the presence of EFNs on figs of Ficus benguetensis and test the hypothetical protection service provided by ants. Figs in different developmental stages were collected from Fu-Yang Eco Park, Taipei, Taiwan. Sugars on the fig surface were collected and analyzed through high-performance anion-exchange chromatography. Moreover, ants were excluded from the figs to determine the effect of ants on the nonpollinating fig wasps. We identified three oligosaccharides whose relative proportions varied with the fig developmental phase. In addition, results showed that the ant-excluded figs were heavily parasitized and produced three times less pollinators than did the control figs. Finally, the specific interactions of Ficus benguetensis with ants and the relationship between figs and ants in general are discussed.     

The conundrum of CD40 function: host protection or disease promotion?

T cells regulate the immune responses to pathogens and autoantigens. The immune responses are tolerizing or anti-inflammatory against autoantigens but are inflammatory against pathogens and allografts. Such contradictory immune responses have been attributed to two counteracting effector cell types or to two counterregulatory sets of molecules: cell-surface expressed or secreted. By contrast, recent reports suggest that CD40, a co-stimulatory molecule on antigen-presenting cells, is a crucial controller of these counteractive immune responses, and emphasize reciprocal inhibition as an essential feature of biological responses. The molecular mechanism of such reciprocity in CD40 functions is the basis of immunotherapy in many diseases.     

Bamboo flowers visited by insects: do insects play a role in the pollination of bamboo flowers?

Relatively little is known about pollination and other aspects of the reproductive biology of bamboos, but wind pollination is assumed to be the rule, at least in woody bamboos. Documenting the reproductive biology of woody bamboos is a complex task due to the long periods of time between flowering cycles, which range from 3 to 120 years. Insects visiting Guadua paniculata and G. inermis flowers were collected in the field. Scanning electron micrographs were taken of the visiting insects. Four species of bees, three from tribe Meliponini (Geotrigona acapulconis, Plebeia frontalis and Trigona fulviventris) and one from tribe Apini (Apis mellifera), along with a syrphid fly (Toxomerus teligera) were found visiting bamboo flowers. Some species of Hemiptera were also found feeding on the flowers, such as Neortholomus jamaicensis (Lygaeidae), or preying on the flower visitors (Apiomerus pictipes (Reduviidae)). Insects visiting bamboo inflorescences may facilitate the release of pollen grains into the air, promoting outcrossing and genetic flow among the individuals of the flowering bamboo populations.     

The nuclei of cellular organelles and the formation of daughter organelles by the “plastid-dividing ring”

It has been established that organelles, such as mitochondria and plastids, contain organelle-specific DNA and arise from the division of pre-existing organelles (e.g., Possingham and Lawrence, 1983). We propose that organelle DNAs, such as mitochondrial DNA and plastid DNA are not naked in organellesin situ but are organized in each case to form an “organelle nucleus” with basic proteins (Kuroiwa, 1982). The concept of organelle nuclei has changed our ideas about the division of organelles. Thus, the process of organelle division must be composed of two main events: division of the organelle nucleus and organellekinesis (division of the other components of the mitochondrion or plastid). The latter term has been adopted as an appropriate analogue of cytokinesis. We were the first to identify the plastid-dividing ring (PD-ring), which is located in the cytoplasm close to the outer envelope membrane at the constricted isthmus of dividing chloroplasts in the red algaCyanidium caldirum. The PD-ring is about 60 nm in width and 25 nm in thickness, and is a circular bundle of actin-like, fine filaments, each about 4–5 nm in diameter. Since cytochalasin B, an inhibitor of polymerization of actin filaments, inhibits the formation of the PD-ring and, thus, prevents subsequent division of chloroplasts, the PD-ring is thought to be a structure that is essential for the division of plastids (plastidkinesis). The behavior of the PD-ring during a cycle of chloroplast division can be classified into the following four stages on the basis of morphological and temporal differences. The chloroplast growth stage: the small, spherical chloroplast increases in volume and becomes a football-like structure, while the PD-ring from the previous division disappears. Formation of the PD-ring: the somewhat electron-dense body (see below) is fragmented into many, somewhat electron-dense granules, which are aligned along the equatorial region of the chloroplast and fine filaments are formed from the somewhat electron-dense granules in the equatorial region. The fine filaments of the PD-ring align themselves according to the longest axis of their overall domain, i.e., circumferentially. Contraction stage: a bundle of fine filaments begins to contract and generates a deep furrow. Conversion stage: after chloroplast division, the remnants of the PD-ring are converted into somewhat electron-dense bodies. Similar events occur during the second cycle of chloroplast division. Since similar structures are observed extensively in the plastids of algae, moss and higher plants, the PD-ring appears to be an essential structure for the division of plastids in plants.     

The ecological effects of the ant–hemipteran mutualism: A meta-analysis

Ant–hemipteran mutualism has a variety of ecological effects on the host plants, but the magnitude and moderators of those effects are poorly known. We evaluated this issue by conducting a meta-analysis based on 49 published studies. Results showed that the mutualism had significant protective effects on the host plans, although those effects did not lead to enhanced plant growth or reproductive performance. Both herbivores and predators on plants were strongly suppressed by the mutualism; a similar pattern was also detected for fruit removal. The ecological effects of the mutualism tended to be more consistent and stronger in tropical and subtropical regions, whereas in temperate regions, none of the tested variables was significantly affected by the mutualism. The protective effects of the mutualism on plants were independent of plant life form and the invasiveness of ants. The effect of the mutualism on predators varied with plant life form. The study confirmed that the ant–hemipteran mutualism has a wide range of ecological influences on plants and highlights the significance of a common and wide-spread mutualism.     

First screening of bacterial communities of Microdon myrmicae and its ant host: do microbes facilitate the invasion of ant colonies by social parasites?

Many studies have highlighted how numerous bacteria provide their hosts essential nutrients or protection against pathogens, parasites and predators. Nevertheless, the role of symbiotic microorganisms in the interactions between social insects and their parasites is still poorly known. Microdon (Diptera, Syrphidae) is a peculiar fly genus whose larvae are able to successfully infiltrate ant colonies and feed upon the ant brood. Using high throughput 16S rRNA gene amplicon sequencing, we provide the first microbiome survey of Mi. myrmicae larvae and larvae and workers of its host, Myrmica scabrinodis, collected from two sites in England. We analyzed the microbiome of the external surface of the cuticle and the internal microbiome of the body separately. The results clearly show that the Mi. myrmicae microbiome significantly differs from that of its host, while no substantial dissimilarity was detected across the microbiome of ant workers and ant larvae. Microdon myrmicae microbiome varies across the two analyzed sites suggesting that bacteria communities of Mi. myrmicae are derived from the environment rather than by horizontal transmission between hosts and parasites. Families Streptococcaceae, Carnobacteriaceae and Rizhobiaceae are dominant in My. scabrinodis, and Spiroplasma is dominant in ant workers. Microbiome of Mi. myrmicae larvae is mainly characterized by the family Anaplasmataceae, with Wolbachia as predominant genus. Interestingly, we found Serratia within both Mi. myrmicae and Myrmica larvae. Bacteria of this genus are known to produce a family of pyrazines commonly involved in ant communication, which could play a role in Microdon/ant interaction.     

Is nectar reabsorption restricted by the stalk cells of floral and extrafloral nectary trichomes?

Reabsorption is a phase of nectar dynamics that occurs concurrently with secretion; it has been described in floral nectaries that exude nectar through stomata or unicellular trichomes, but has not yet been recorded in extrafloral glands. Apparently, nectar reabsorption does not occur in multicellular secretory trichomes (MST) due to the presence of lipophilic impregnations – which resemble Casparian strips – in the anticlinal walls of the stalk cells. It has been assumed that these impregnations restrict solute movement within MST to occur unidirectionally and exclusively by the symplast, thereby preventing nectar reflux toward the underlying nectary tissues. We hypothesised that reabsorption is absent in nectaries possessing MST. The fluorochrome lucifer yellow (LYCH) was applied to standing nectar of two floral and extrafloral glands of distantly related species, and then emission spectra from nectary sections were systematically analysed using confocal microscopy. Passive uptake of LYCH via the stalk cells to the nectary tissues occurred in all MST examined. Moreover, we present evidence of nectar reabsorption in extrafloral nectaries, demonstrating that LYCH passed the stalk cells of MST, although it did not reach the deepest nectary tissues. Identical (control) experiments performed with neutral red (NR) demonstrated no uptake of this stain by actively secreting MST, whereas diffusion of NR did occur in plasmolysed MST of floral nectaries at the post‐secretory phase, indicating that nectar reabsorption by MST is governed by stalk cell physiology. Interestingly, non‐secretory trichomes failed to reabsorb nectar. The role of various nectary components is discussed in relation to the control of nectar reabsorption by secretory trichomes.     

On the structure and function of “chlorosomes” of green bacteria

An assertion is substantiated that what is widely termed the chlorosomes of green bacteria are not bioparticles, but simply microscopic bacteriochlorophyll c crystals. Apparently, formation of a ??chlorosome?? represents the first, largely unsuccessful, evolutionary attempt to create a regulatory mechanism that would respond to variations in the intensity of solar light reaching the earth surface. Without bacteriochlorophyll cooperation with proteins, this was a dead end.     

Ant–plant interaction in the Neotropical savanna: direct beneficial effects of extrafloral nectar on ant colony fitness

Current evidence suggests that ant–plant relationships may influence species composition, abundance, and interactions at the community scale. The main resource that plants offer to ants is extrafloral nectar (EFN) and the major part of published studies shown benefits from ants to plants possessing EFNs. However, the complementary question of whether and how ants benefit from EFNs is rarely addressed. Here, we present the results of a long-term study to demonstrate whether EFN has a positive effect on ant colony fitness. We quantified colony growth rate, survival and the final weight of individuals as measures of benefit derived from EFN. Our results provide clear evidence that EFN can have a significant positive impact on the survivorship, growth and reproduction of the Myrmicinae Cephalotes pusillus. In fact, a diet rich in EFN (providing at least 30 cal per day) resulted in five times more individuals per colony, greater body weights, and more eggs. These results have shed new light on the relationships between ants and EFN-bearing plants such as in tropical and temperate systems. The ant C. pusillus is the first case in which we have firm evidence that EFN improves colony growth and development, corroborating more than 100 years of experimental evidence of benefits to plants in these widespread relationships.     

What is the function of mitochondrial networks? A theoretical assessment of hypotheses and proposal for future research

Mitochondria can change their shape from discrete isolated organelles to a large continuous reticulum. The cellular advantages underlying these fused networks are still incompletely understood. In this paper, we describe and compare hypotheses regarding the function of mitochondrial networks. We use mathematical and physical tools both to investigate existing hypotheses and to generate new ones, and we suggest experimental and modelling strategies. Among the novel insights we underline from this work are the possibilities that (i) selective mitophagy is not required for quality control because selective fusion is sufficient; (ii) increased connectivity may have non‐linear effects on the diffusion rate of proteins; and (iii) fused networks can act to dampen biochemical fluctuations. We hope to convey to the reader that quantitative approaches can drive advances in the understanding of the physiological advantage of these morphological changes.

     

Brief communication: Why sleep in a nest? empirical testing of the function of simple shelters made by wild chimpanzees

All great apes build nightly a structure ("nest" or "bed") that is assumed to function primarily as a sleeping-platform. However, several other nest function hypotheses have been proposed: antipredation, antipathogen, and thermoregulation. I tested these simple shelter functions of chimpanzee nests in an experiment for which I was the subject in Fongoli, Senegal. I slept 11 nights in chimpanzee nests and on the bare ground to test for differences in sleep quality, potential exposure to disease through bites from possible vectors, and insulation. No difference was found in the total amount of sleep nor in sleep quality; however, sleep was more disturbed on the ground. Differences in sleep disturbance between arboreal and ground conditions seemed primarily due to causes of anxiety and alertness, e.g., vocalizations of terrestrial mammals. Arboreal nest-sleeping seems to reduce risk of bites from possible disease vectors and provide insulation in cold conditions. This preliminary, but direct, test of chimpanzee nest function has implications for the evolutionary transition from limb-roosting to nest-reclining sleep in the hominoids, and from tree-to-ground sleep in the genus Homo.     

Are flowers physiological sinks or faucets? Costs and correlates of water use by flowers of Polemonium viscosum

Water loss through inflorescences may place extreme demands on plant water status in arid environments. Here we examine how corolla size, a trait known to influence pollination success, affects the water cost of flowering in the alpine skypilot, Polemonium viscosum. In a potometry experiment, water uptake rates of inflorescences were monitored during bud expansion and anthesis. Corolla volume of fully expanded flowers predicted water uptake during bud expansion (R ²=0.61, P=0.0375) and corolla surface area predicted water uptake during anthesis (R ²=0.59, P=0.044). To probe mechanisms underlying the relationship between corolla size and water uptake, cell dimensions and densities were measured in several regions of fully expanded corollas. Corolla length was positively correlated with cell length in the middle of the corolla tube and cell diameter in the corolla lobe (Pearson's r from 0.26–0.33, n=86, P ≤ 0.05). Cell density was negatively correlated with cell dimensions in the upper corolla tube and lobe (Pearson's r from –0.39 to –0.42, P ≤ 0.0015). These findings suggest that more water may be required to maintain turgor in large corollas in part because their tissues have lower cell wall densities. The carbon cost of water use by flowers was assessed in krummholz and tundra habitats for P. viscosum flowering, respectively, during dry and wet portions of the growing season. For plants in full flower, average leaf water potentials were significantly more negative (P=0.0079) at mid-day in the krummholz (June) than in the tundra (July), but were similar before dawn (P=0.631). Photosynthetic rate at the time of flowering declined significantly with increasing corolla size in the krummholz (P=0.0376), but was unrelated to corolla size on the tundra (P>0.72). Plants losing water through large corollas may close leaf stomata to maintain turgor. If photosynthesis limits growth in this perennial species, then the water cost of producing large flowers should exacerbate the cost of reproduction under dry conditions. Such factors could select for flowers with smaller corollas in the krummholz, countering pollinator-mediated selection and helping maintain genetic variation in corolla size components of P. viscosum. Received: 5 May 1998 / Accepted: 2 October 1998     

The game of “gossip” analyzed by the theory of information

This paper deals with an analysis of a distributed model of the game of “gossip”, in which a message is passed through a line of individuals, and the final (in general, garbled) result is compared with the original ungarbled message. The deterioration of information (defined in the sense of Shannon and Wiener) along the line is calculated, and exact as well as asymptotic formulas suggesting approximate linear electric network analogues are obtained.