Fluctuating asymmetry,fecundity and development time in Drosophila: is there an association under optimal and stress conditions?

A number of studies have reported a significant negative association between fluctuating asymmetry (FA) of bilateral morphological traits and individual fitness traits, but almost all of these are unreplicated and based on small sample sizes using single trait estimates of FA. We therefore tested if there was a relationship between the FA of five bilateral traits and fecundity and development time in Drosophila in a multiple replicated experimental design. Stressed treatments were included to increase the variability of traits and to test whether associations among traits were affected by changes in the environment. Significant positive relationships were found between the size of wing characters and mean fecundity for the 5‐day period and this relationship tended to be stronger in the stress treatments. No association was found between FA and mean fecundity for any of the traits measured. Similarly, a significant positive relationship was detected between wing trait size and development time but no association was detected between trait FA and development time. There were no differences between mean fecundity or development time of extreme asymmetry phenotypes compared with modal phenotypes. These results are discussed with reference to suggestions in the literature that FA can be used to estimate individual fitness.     

How many symbionts are provided by mothers,acquired by offspring,and needed for successful vertical transmission in an obligate insect–bacterium mutualism?

Vertical symbiont transmission is among the most pivotal processes for maintenance of symbiotic associations. However, it is poorly understood whether and how the levels of resource allocation and investment upon vertical transmission are regulated. The stinkbug Megacopta punctatissima is obligatorily associated with the gut symbiotic bacterium 'Candidatus Ishikawaella capsulata', whose transmission is mediated by a unique mechanism called 'symbiont capsule'. We investigated the population dynamics of the symbiont during vertical transmission in the host-symbiont mutualism. The stinkbug mothers produced one capsule for around 3.6 eggs irrespective of clutch size, suggesting a strict maternal control over symbiont supply for the offspring. However, experimental manipulation of egg/capsule ratios revealed that one capsule is sufficient for symbiont transmission to six nymphs. Quantitative polymerase chain reaction analyses demonstrated that a capsule contains 1.2 x 10(8) symbionts, a newborn nymph possesses 2 x 10(7) symbionts from a capsule, and thus one capsule certainly contains a sufficient amount of symbiont cells for six nymphs. These results indicated that the stinkbug mothers produce 1.7 times more symbiont capsules than needed. The newborn nymphs consistently harboured around 2 x 10(7) symbionts, also suggesting a nymphal control over symbiont transmission. The threshold symbiont titre minimally needed for successful vertical transmission was estimated to be 1.9 x 10(6) symbionts, which is only 1/10 of the actual symbiont titre detected in a newborn nymph. These results illuminate several ecological factors that may be relevant to parental and offspring controls over symbiotic resource allocation through host insect generations.     

Who is where in the Plastisphere,and why does it matter?

To fully understand how plastic is affecting the ocean, we need to understand how marine life interacts directly with it. Besides their ecological relevance, microbes can affect the distribution, degradation and transfer of plastics to the rest of the marine food web. From amplicon sequencing and scanning electron microscopy, we know that a diverse array of microorganisms rapidly associate with plastic marine debris in the form of biofouling and biofilms, also known as the “Plastisphere.” However, observation of multiple microbial interactions in situ, at small spatial scales in the Plastisphere, has been a challenge. In this issue of Molecular Ecology Resources, Schlundt et al. apply the combination labelling and spectral imaging – fluorescence in situ hybridization to study microbial communities on plastic marine debris. The images demonstrate the colocalization of abundant bacterial groups on plastic marine debris at a relatively high taxonomic and spatial resolution while also visualizing biofouling of eukaryotes, such as diatoms and bryozoans. This modern imaging technology provides new possibilities to address questions regarding the ecology of marine microbes on plastic marine debris and describe more specific impacts of plastic pollution in the marine food webs.     

The more,the merrier? Obligate symbiont density changes over time under controlled environmental conditions,yet holds no clear fitness consequences

Symbiotic bacteria are highly diverse, play an important role in ecology and evolution, and are also of applied relevance because many pest insects rely on them for their success. However, the dynamics and regulation of symbiotic bacteria within hosts is complex and still poorly understood outside of a few model systems. One of the most intriguing symbiotic relationships is the obligate, tripartite nutritional mutualism in sap‐feeding, economically‐destructive mealybugs (Hemiptera: Sternorrhyncha: Pseudococcidae), which involves γ‐proteobacteria hosted within β‐proteobacteria hosted within the mealybugs. The present study examines whether there is population variation in symbiont density (i.e. infection intensity, or titre) in the citrus mealybug Planococcus citri (Risso) and how this impacts host life‐history. Symbiont density is found to differ significantly between populations when reared under controlled environmental conditions, indicating that the density of symbiont infections is influenced by host or symbiont genotype. However, symbiont density changes in populations over multiple generations, indicating that symbiont densities are dynamic. Surprisingly, given that the symbionts are essential nutritional mutualists, the density of the symbionts does not correlate significantly with either host fecundity or development. Higher levels of symbionts have no clear benefit to hosts and therefore appear to be superfluous, at least under constant, optimized environmental conditions. Excessive symbiont density may be an evolutionary artefact from a period of inefficient vertical transmission when the balance of conflict between host and symbiont was still being established.     

The interspecific biomass–density relationship for terrestrial plants: where do clonal red seaweeds stand and why?

For crowded stands of terrestrial plants, ranging from mosses to trees, plant (or ramet, for clonal plants) density is negatively related to stand biomass. Stand biomass and ramet density were determined for Mazzaella cornucopiae and for Pterocladiella capillacea , two morphologically distinct intertidal clonal red seaweeds, to compare them with terrestrial plants. For these seaweeds, ramet densities were similar to the highest values reported for terrestrial plants (mosses, specifically). Stand biomass was higher than average values expected from the terrestrial interspecific biomass–density relationship, but lower than the limits expected from the terrestrial ultimate biomass–density line. These seaweeds show unexpectedly low ramet slenderness and high biomass packing per unit of volume, compared with the trend observed for terrestrial plants. Possible explanations for these differences are related to the particular physiology and habitat of intertidal clonal seaweeds.     

Life history interactions with environmental conditions in a host–parasite relationship and the parasite's mode of transmission

The microsporidian parasite Edhazardia aedis is capable of vertical or horizontal transmission among individuals of its host, the mosquito Aedes aegypti, and either mode of transmission may follow the other. We show that following the horizontal infection of host larvae, the parasite's subsequent mode of transmission largely depends on host life history traits and their responses to different environmental conditions. In two experiments the intensity of larval exposure to infection and the amount of food available to them were simultaneously manipulated. One experiment followed the dynamics of host development and the parasite's production of spores while the other estimated the outcome of their relationship. Host life history traits varied widely across treatment conditions while those of the parasite did not. Of particular importance was the host's larval growth rate. Horizontal rather than vertical transmission by the parasite was more likely as low food and high dose conditions favoured slower larval growth rates. This pattern of transmission behaviour with host growth rate can be considered in terms of reproductive value: the potential vertical transmission success that female mosquitoes offer the parasite decreases as larval growth rates slow and makes them more attractive to exploitation for horizontal transmission (requiring host mortality). However, the lack of variation in the parasite's life history traits gave rise in some conditions to low estimates for both its vertical and horizontal transmission success. We suggest that the unresponsive behaviour of the parasite's life history traits reflects a bet-hedging strategy to reduce variance in its overall transmission success in the unpredictable environmental conditions and host larval growth rates that this parasite encounters in nature.     

The relationship between larval size and fitness in the tapeworm Schistocephalus solidus: bigger is better?

In organisms with complex life cycles, fitness often increases with body size at the transition from larva to adult. The translation of larval size into fitness, however, can depend on the source of size variation, with size, per se, not always increasing adult success. In parasitic worms, many factors influence larval growth, but little is known about the consequences of this growth variation. We examined how the size of the tapeworm Schistocephalus solidus in its copepod first intermediate host affects infection success and growth in the stickleback second host. Moreover, we assessed whether the conspicuous growth variation caused by copepod size is fitness‐relevant. Using larvae of the same age, we found that larger worms had a substantially higher infection probability and they tended to still be slightly larger after several months of growth in fish. However, big larvae from bigger copepods did not have higher fitness, suggesting that being large relative to the host, but not necessarily large in general, is important. These findings clarify some aspects of the life history strategy of S. solidus (e.g. why there is a flat ontogenetic reaction norm across copepod stages), but also raise questions (e.g. why growth costs have been hard to document). More generally, our results indicate that larval size can correlate with fitness in helminths, but that not all size variation is predictive of success in the next host.     

Neuropeptide Y, peptide YY and aluminum in Alzheimer's disease: is there an etiological relationship?

Neuropeptide Y (NPY) and peptide YY (PYY) are members of the pancreatic polypeptide family which have a high degree of primary and tertiary structural homology. They function as neurotransmitters and humoral agents in central nervous system and gastrointestinal function. During the last two decades, NPY body fluid concentrations and NPY/PYY brain receptor numbers have been demonstrated to be altered during the course of Alzheimer's disease. Recent research has shown that both NPY and PYY may be involved in aluminum metabolism in animal models. A brief discussion of the structure, biological activity and possible involvement of these peptides in aluminum metabolism and Alzheimer's disease is contained herein.     

What is the usual internal carbon dioxide concentration in C<Subscript>4</Subscript> species under midday field conditions?

The carbon dioxide concentrating system in C₄ photosynthesis allows high net photosynthetic rates (P _N) at low internal carbon dioxide concentrations (C _i), permitting higher P _N relative to stomatal conductance (g _s) than in C₃ plants. This relation would be reflected in the ratio of C _i to external ambient (C _a) carbon dioxide concentration, which is often given as 0.3 or 0.4 for C₄ plants. For a C _a of 360 μmol mol⁻¹ that would mean a C _i about 110–140 μmol mol⁻¹. Our field observations made near midday on three weedy C₄ species, Amaranthus retroflexus, Echinochloa crus-galli, and Setaria faberi, and the C₄ crop Sorghum bicolor indicated mean values of C _i of 183–212 μ mol mol⁻¹ at C _a = 360 μmol mol⁻¹. Measurements in two other C₄ crop species grown with three levels of N fertilizer indicated that while midday values of C _i at high photon flux were higher at limiting N, even at high nitrogen C _i averaged 212 and 196 μmol mol⁻¹ for Amaranthus hypochondriacus and Zea mays, respectively. In these two crops midday C _i decreased with increasing leaf to air water vapor pressure difference. Averaged over all measurement days, the mean C _i across all C₄ species was 198 μmol mol⁻¹, for a C _i/C _a ratio of 0.55. Prior measurements on four herbaceous C₃ species using the same instrument indicated an average C _i/C _a ratio of 0.69. Hence midday C _i values in C ₄ species under field conditions may often be considerably higher and more similar to those of C₃ species than expected from measurements made on plants in controlled environments. Reducing g _s in C₄ crops at low water vapor pressure differences could potentially improve their water use efficiency without decreasing P _N.     

Tissue transglutaminase, inflammation, and cancer: how intimate is the relationship?

Despite significant advances in surgery and biology, cancer remains a major health problem. It is now well accepted that metastasis and cancer cells’ acquired or inherent resistance to conventional therapies are major roadblocks to successful treatment. Chronic inflammation is an important driving force that provides a favorable platform for cancer’s progression and development and suggests a link between inflammation and metastatic transformation. However, how chronic inflammation contributes to metastatic cell transformation is not well understood. According to the current theory of cancer progression, a small subpopulation of cancer stem cells (CSCs) in tumors is responsible for their metastasis, resistance, and sustenance. Whether CSCs originate from normal stem cells or from dedifferentiation of terminally differentiated cells remains unknown. Recent evidence indicates that stem cells are not unique; malignant or nonmalignant cells can reprogram and de-differentiate to acquire a stemness phenotype. Thus, phenotypic plasticity may exist between stem cells and non-stem cells, and a dynamic equilibrium may exist between the two phenotypes. Moreover, this equilibrium may shift in one direction or another on the basis of contextual signals in the microenvironment that influence the interconversion between stem and non-stem cell compartments. Whether the inflammatory microenvironment influences this interconversion and shifts the dynamic equilibrium towards stem cell compartments remains unknown. We recently found that aberrant tissue transglutaminase (TG2) expression induces the mesenchymal transition (EMT) and stem cell characteristics in epithelial cells. This finding, in conjunction with the observation that inflammatory signals (e.g., TGFβ, TNFα, and NF-κB) which induce EMT, also induce TG2 expression, suggests a possible link between TG2, inflammation, and cancer progression. In this review, we summarize TG2-driven processes in inflammation and their implications in cancer progression.     

Interspecific difference in the photosynthesis–nitrogen relationship: patterns,physiological causes,and ecological importance

The photosynthesis–nitrogen relationship is significantly different among species. Photosynthetic capacity per unit leaf nitrogen, termed as photosynthetic nitrogen-use efficiency (PNUE), has been considered an important leaf trait to characterise species in relation to their leaf economics, physiology, and strategy. In this review, I discuss (1) relations between PNUE and species ecology, (2) physiological causes and (3) ecological implications of the interspecific difference in PNUE. Species with a high PNUE tend to have high growth rates and occur in disturbed or high productivity habitats, while those with a low PNUE occur in stressful or low productivity habitats. PNUE is an important leaf trait that correlates with other leaf traits, such as leaf mass per area (LMA) and leaf life span, irrespective of life form, phylogeny, and biomes. Various factors are involved in the interspecific difference. In particular, nitrogen allocation within leaves and the mesophyll conductance for CO₂ diffusion are important. To produce tough leaves, plants need to allocate more biomass and nitrogen to make thick cell walls, leading to a reduction in the mesophyll conductance and in nitrogen allocation to the photosynthetic apparatus. Allocation of biomass and nitrogen to cell walls may cause the negative relationship between PNUE and LMA. Since plants cannot maximise both PNUE and leaf toughness, there is a trade-off between photosynthesis and persistence, which enables the existence of species with various leaf characteristics on the earth.     

Endopterygote systematics – where do we stand and what is the goal (Hexapoda,Arthropoda)?

Abstract. Impressive progress has been made recently in the systematics of holometabolous insects. Nevertheless, important questions remain controversial, and uncertainties concerning the relationships of major lineages may even have increased. New analytical techniques have been developed and an immense wealth of molecular data has accumulated. Although no decisive breakthrough has yet been achieved, recent analyses of large molecular datasets have contributed greatly to the reconstruction of the phylogeny of several holometabolous lineages. Extensive combined analyses with substantial morphological datasets and molecular data comprising several genes (‘total evidence’) are still required for a well‐founded phylogenetic hypothesis for the entire group. Endopterygota monophyly is supported mainly by the specific and derived mode of development, which may be considered as a new evolutionary level within Hexapoda. The basal branching pattern remains controversial. A division into two large clades comprising Coleoptera (+ Strepsiptera?) + Neuropterida, on the one hand, and Hymenoptera + [Amphiesmenoptera + Antliophora (including Strepsiptera?)], on the other, appears plausible. Alternative hypotheses have been proposed based on wing characters and molecular data. The position of Strepsiptera remains unsolved. Mecoptera almost certainly is not monophyletic, as Siphonaptera are probably sister to Boreidae. Immense progress has been made in the reconstruction of the intraordinal relationships of all orders, thanks to increasing studies based on combined datasets. Common efforts of morphologists and molecular systematists probably will lead to further rapid progress. Several discoveries of new higher ranking taxa during recent years have revealed that large‐scale habitat destruction will not only have disastrous effects on global biodiversity, but also on the study of insect phylogeny and evolution.     

The relationship between signal quality and physical condition: is sexual signalling honest in the three-spined stickleback?

Honest sexual signalling requires that the level of advertisement reveals mate quality. In the three-spined stickleback, Gasterosteus aculeatus, females base their mate choice mainly on the intensity of the males' red breeding coloration. Different results have, however, been obtained on the relationship between red breeding coloration and physical condition. In this study, the relationship was curvilinear in a natural population, with males in good and poor condition (measured as lipid content) having larger red areas than males of intermediate condition. By manipulating food intake and thus male condition prior to breeding, I further show that poor condition can induce an increase in signalling effort. This effect was further strengthened when the predation cost of signalling was increased by exposing the males to predators. This suggests that the reason for the high signalling effort of males in poor condition is their low probability of future reproduction and thus lower cost of signalling in terms of loss of future reproductive opportunities. Males in poor condition signal as a terminal effort and take larger risks and invest more in current reproduction than males in good condition. Finally, I discuss whether an effect of decreasing residual reproductive value on signalling effort could result in the breakdown of the honesty of the signal. Copyright 1999 The Association for the Study of Animal Behaviour.