Maternal age as a source of variation in the ability of an aphid to produce dispersing forms

Summary Apterous parthenogentic females of the pea aphid,Acyrthosiphon pisum (Harris), begin to produce alate offspring soon after they have been subjected to crowding. Females which were born early in their own parent’s reproductive period respond most strongly to crowding, producing much larger numbers of alatae than their late-born sisters. In contrast, the early-born daughters of most alate females do not produce winged offspring after being crowded. Some of their later-born sisters may produce a few winged individuals, resembling in this respect the late-born daughters of the apterous females. Control of the production of alatae thus begins in the grandparental generation. Risk-spreading by means of differential dispersal becomes a less uncertain venture when local populations can modify their responses to environmental changes by utilizing past as well as present signals from their surroundings.     

Seasonal variation in the photoperiodic responses of a pea aphid population: evidence for long-distance movements between populations

Summary The purpose of the study was to quantify long distance movements in populations of pea aphid, Acyrthosiphon pisum (Harris), by estimating origins and distances travelled by immigrants into a southern Manitoba population. A strong relationship was demonstrated between latitude of origin and photoperiods at which pea aphid populations are stimulated to produce the diapause stage (Smith 1987). Therefore, the approach was to use photoperiodic response as a physiological marker to identify the source of immigrant aphids. The responses of 89 clones from Glenlea, Manitoba (49°38N), sampled 5 times over 2 seasons, were measured. One sample of clones collected the first season had photoperiodic responses similar to those of a population about 300 km to the south, and significantly different from clones collected in spring of the same year at the same site. Weather analysis corroberates that the migrants were probably carried into Manitoba on a southerly flow of air during the previous 24 to 36 h.     

Nutrient regulation in the pea aphid Acyrthosiphon pisum: application of a novel geometric framework to sugar and amino acid consumption

Abstract. A recently developed framework was applied to investigate the responses of newborn pea aphids, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), to simultaneous variations in dietary suerose and amino acid levels. The location of functional 'targets' for intake and growth were determined experimentally using performance criteria. Behavioural rules employed by insects to approach these targets were investigated by reference to the geometry of arrays of intake and growth across a range of diets. First-instar aphids were fed one of thirty-one chemically-defined diets ranging in sucrose concentration from 200 to 1000 mM and amino acid concentration from 25 to 250 mM. Insect survivorship, dry weight, protein- and carbohydrate-derived growth were high for all diets except those with the lowest nutrient levels. Peaks in final dry weight and protein content identified the intake target as the point reached by larvae fed the 600 mM sucrose, 75 mM amino acid diet. Aphids regulated sucrose primarily by consumption (i.e. behaviourally), whereas amino acids were regulated post-ingestively (i.e. by physiological mechanisms).     

Maternal body-volume as a constraint on reproductive output in lizards: evidence from the evolution of viviparity

A few species of squamate reptiles contain both oviparous (egg-laying) and viviparous (live-bearing) populations, and thus offer exceptional opportunities to test adaptationist hypotheses on the determinants of reproductive output. We focus on the hypothesis that maternal body-volume constrains reproductive output in squamate reptiles. If females are “full” of eggs, what happens when viviparity evolves within a lineage? Eggs increase in volume and mass during development, primarily due to the uptake of water, so how can they be accommodated within the mother's abdomen? We predict that the resultant increase in relative clutch mass (RCM) will be lessened by (1) a decrease in reproductive output (by reducing the number or size of offspring), and/or (2) an increase in maternal body-volume (via modifications of size or shape of adult females). Our comparisons of conspecific oviparous and viviparous lizards (Lerista bougainvillii) confirm that live-bearers carry heavier clutches (in both absolute and relative terms) and show the predicted shifts in body size and shape of reproductive females. However, offspring size and number were unaffected by the evolution of viviparity, and the shifts in maternal morphology were too small to fully offset the increase in clutch mass. Thus, RCMs increased by 50%, indicating that viviparous females produced clutches which more completely filled the space available in the abdominal cavity. We conclude that maternal body-volume does play a role in determining reproductive output, but that the observed clutch masses may be optimized, rather than maximized, with respect to the abdominal space available.     

Individual variation in the ability of Columbian ground squirrels to select an optimal diet

Summary Columbian ground squirrels (Spermophilus columbianus) were examined for ability to select a diet that maximizes daily energy intake (optimal diet) under free-living field conditions. The optimal diet for each squirrel was determined given constraints (e.g. body size, feeding time) on individual foraging behavior. Most squirrels (63%) consumed a diet not significantly different from one that would maximize their daily energy intake. The remainder (37%) approached an energy maximized diet but appeared to make some incorrect foraging decisions. Both males and females appeared to approach energy maximized diets. An individual's deviation from its optimal diet is relatively constant within a season and not significantly affected by immediate environmental influences such as food abundance, thermal conditions and social environment. The energy cost of deviating from an optimal diet may be large enough to affect fitness. These results suggest that the ability to select an optimal diet can be viewed as a behavioral trait that might be subject to natural selection.     

Concurrence of losing a chromosome and the ability to produce destruxins in a mutant of Metarhizium anisopliae

In a previous study, a spontaneous subtilisin pr1A and pr1B gene-deficient mutant of the entomopathogenic fungus Metarhizium anisopliae strain V275 has been identified [Wang, C.-S. et al. (2002) FEMS Microbiol. Lett. 213, 251-255]. The insecticidal metabolites of this mutant were studied further. High-performance liquid chromatography (HPLC) analysis indicated that the mutant isolate lost the ability to produce cyclic peptide toxins, destruxins, both in vitro and in vivo. Pulsed-field gel electrophoresis revealed that the mutant concurrently lost a 1.05 Mb (approximately) chromosome, demonstrating for the first time that a conditionally dispensable (CD) chromosome exists in the insect pathogenic fungus, M. anisopliae. Concurrence of losing the ability to produce destruxins and a CD chromosome in the mutant suggests that the toxin synthetase genes of M. anisopliae are located on this CD chromosome, as similarly described for plant pathogenic fungi. Semi-quantitative api ZYM analysis showed more biochemical disparities between the mutant and the wild-type strain.     

Mobility of salivary components as a possible reason for differences in the responses of alfalfa to the spotted alfalfa aphid and pea aphid

The spotted alfalfa aphid (SAA), Therioaphis trifolii maculata (Buckton), causes a characteristic veinal chlorosis and necrosis in the growing tips of susceptible cultivars of alfalfa. The pea aphid, Acyrthosiphon pisum (Harris), causes general degenerative changes in alfalfa but no specific, local symptoms. Biochemical and electrophoretic analyses detected similar enzymes in the ejected saliva of either species: pectin methylesterase, endopolygalacturonase and at least three isozymes of a copper dependent oxido-reductase that showed both catechol oxidase and peroxidase activity. Pectinase and catechol oxidase activities per unit of soluble protein were much greater in the saliva of pea aphid compared with that of SAA. The isozymes of the oxidase from SAA were roughly half the molecular weights of the corresponding isozymes from pea aphid, however, and radiotracer studies showed that soluble secretions injected into alfalfa by SAA travelled to growing tips considerably faster than the secretions of pea aphid. It is suggested that differences in the lesions caused by these aphids may be due to reaction kinetics rather than specific salivary toxins; that the rate of arrival of salivary components, possibly the oxidases, at phloem unloading sites may determine whether the plant's local defensive system is able to repress the immediate challenge or undergoes a run-away reaction leading to necrosis.     

Investigation into the ability of Gluconacetobacter sacchari to live as an endophyte in sugarcane

The relatively low numbers and sporadic pattern of incidence of the acetic acid bacterium Gluconacetobacter sacchari with the pink sugarcane mealybug (PSMB) Saccharicoccus sacchariCockerell (Homoptera: Pseudococcidae) over time and from different sugarcane-growing regions do not indicate that Glac. sacchari is a significant commensal of the PSMB, as has been previously proposed. This study was conducted to investigate the hypothesis that Glac. sacchari is, like its closest relative Glac. diazotrophicus, an endophyte of sugarcane (Saccharum officinarum L.). In this study, bothGlac. sacchari and Glac. diazotrophicus were isolated from internal sugarcane tissue, although the detection of both species was sporadic in all sugarcane-growing regions of Queensland tested. To confirm the ability of Glac. sacchari to live endophytically, an experiment was conducted in which the roots of micropropagated sugarcane plantlets were inoculated with Glac. sacchari, and the plantlets were subsequently examined for the presence of the bacterium in the stem cells. Pure cultures of Glac. sacchari were grown from homogenized surface sterilized sugarcane stems inoculated withGlac. sacchari.Electron microscopy was used to provide further conclusive evidence that Glac. sacchari lives as an endophyte in sugarcane. Scanning electron microscopy of (SEM) sugarcane plantlet stems revealed rod-shaped cells of Glac. sacchari within a transverse section of the plantlet stem cells. The numbers of bacterial cells inside the plant cell indicated a successful infection and colonization of the plant tissue. Using transmission electron microscopy, (TEM) bacterial cells were more difficult to find, due to their spatial separation. In our study, bacteria were mostly found singularly, or in groups of up to four cells inside intercellular spaces, although bacterial cells were occasionally found inside other cells.     

Hybridization of two forms of ninespine stickleback,Pungitius pungitius and P. platygaster,under experimental conditions and an attempt to predict the consequences of their contact in nature

Synopsis In aquaria and in ponds crosses were made between two closely related allopatric forms of ninespine stickleback of the genus Pungitius (P. pungitius and P. platygaster). There were no ethological isolation mechanisms; F₁, F₂ and F₃ hybrids are fertile; experimental hybrid stocks as well as backcrosses maintain themselves for at least three generations. F₁ hybrids are readily distinguishable from parental forms by a combination of morphological characters; F₂ hybrids grown in the north near the Arctic circle, are morphologically similar to P. pungitius. The southern form P. platygaster does not survive in northern conditions; eggs of the northern form P. pungitius die at a temperature of 28°C, normal for the spawning of the southern form. By 9 out of 19 studied morphological characters there are distinctions between the two forms. Therefore, ecologically and morphologically the two forms have diverged rather significantly. On the other hand, ethologically and genetically (as judged by the absence of postmating isolating mechanisms) the forms have diverged only slightly. As a result, the differences between the two forms are considered not to exceed the subspecies or at least semispecies rank.In recent years, due to a disturbance of the ranges of both these forms in Eurasia, a tendency for a secondary contact between P. pungitius and P. platygaster appeared in the basins of the rivers Volga and Irtysh. In the immediate future the two forms are expected to come into contact. From our data we predict possible introgressive hybridization between the northern and sourthern forms in natural conditions.     

Seasonal extension of the soldier instar as a route to increased defence investment in the social aphid Pemphigus spyrothecae

Abstract.  1. The possibility that the duration of the soldier instar could be extended over the course of the galling season was examined in Pemphigus spyrothecae Passerini (Hemiptera: Aphididae). In this species, the individuals of one morph of the dimorphic first instar are non-sterile specialised defenders known as soldiers.
2. In the face of a declining birth rate, the proportion of first-instar soldiers to first-instar non-soldiers was found to increase. This provides strong evidence of extension of the soldier instar over time.
3. Instar extension provides a mechanism for post-natal investment in soldiers and allows individuals with insufficient time to mature to remain in the defensive stage so that they may continue to make an indirect contribution to their clone's reproductive success.     

Genetic differentiation as a result of adaptation to the phenologies of individual host trees in the galling aphid Kaltenbachiella japonica

Abstract.

• 1 The adaptation of the non-migratory galling aphid Kaltenbachiella japonica (Matsumura) to the budburst phenologies of individual host trees (Ulmus davidiana var. japonica Nakai) was investigated. There was a large variation in budburst time between individual host trees. We tested a hypothesis that aphid populations on respective host trees are genetically differentiated through adaptation to the budburst phenologies of host trees.
• 2 There was significant correlation between the budburst time of eight host trees in two successive years.
• 3 Tree-associated populations differed significantly in egg-hatching time, and the mean hatching time was significantly correlated with the mean budburst time of respective host trees.
• 4 Mating was made between male and female sexuales of the same clone (i.e. self-mating) to obtain selfed eggs. Hatching patterns of selfed eggs showed that there was a substantial amount of genetic variance in hatching time between clones (galls). Nested ANOVA demonstrated that the between-tree component contributed more to the phenotypic variance than the within-tree or within-gall components.
• 5 Reciprocal crosses between males and females of different clones furthermore demonstrated significant differences in hatching time between cross combinations, but no significant differences between the two reciprocals within combinations. This result suggests that there are no maternal effects for the timing of egg hatch and that the differences between selfed lines are attributable to genetic variance.
• 6 The fine-scale adaptation hypothesis was supported by egg-hatching experiments, which further suggest that budburst phenology varying between individual trees is acting as intense selective pressure on the egg-hatching time of associated insects.

     

Using eggshell membranes as a non-invasive tool to investigate the source of nutrients in avian eggs

Development of minimally invasive techniques to collect nutritional information from free-living birds is desirable for both ethical and conservation reasons. Here, we explore the utility of waterfowl eggshell membranes to determine the nutrient source of egg formation by using stable isotope ratios. We compared δ¹³C and δ¹⁵N of membranes from complete king eider (Somateria spectabilis) eggs to membranes of hatched or depredated eggs of the same clutch remaining after incubation. Despite large variation among membranes (δ¹³C: −26 to −14‰) we found a highly predictable relationship between δ¹³C of complete egg membranes and remaining (hatched or depredated) membranes from the same clutch. We did not find a consistent change in either δ¹³C or δ¹⁵N of eggshell membranes during incubation. We suggest that isotope ratios of membranes can be used to determine the source of exogenous nutrients for egg production in income breeders, and that membranes may offer a clutch-specific reference point for dietary nutrients (‘income endpoint’) in isotopic mixing models quantifying nutrient allocation in capital or mixed-strategy breeders.     

Competitive ability as a function of sensitivity to the environment I. Competition betweenTribolium castaneum andTribolium confusum in a deteriorating environment

Summary Tribolium castaneum lines selected for high and for low sensitivity to the environment were observed in pure strain culture and in mixed 1∶1 cultures withTribolium confusm. Since the medium was not refreshed during the experiment, the environment was continuously deteriorating and ultimately both species became extinct. Both time until extinction and total dry weight were used as a measure of competitive ability. AllTribolium castaneum lines showed higher competitive ability thanTribolium confusum. As interference was noted in all the mixed cultures, competition here demonstrates both exploitation and interference. Comparisons between theT. castaneum lines indicates higher competitive ability for lines with shorter developmental time.     

Comparison of the photoreduction of protochlorophyllide to chlorophyllide in leaves and cotyledons from dark-grown bean as a function of age

77 K fluorescence spectra of bean (Phaseolus vulgaris cv Commodore) leaves and cotyledons show the presence of active and inactive protochlorophyllides. The first detected product of the protochlorophyllide photoreduction is the chlorophyllide emitting fluorescence at 690 nm (C690) which is observed one day (leaves) and three days (cotyledons) after sowing. In cotyledons, C690 undergoes the rapid and Shibata shifts; in leaves, these spectral changes are age-dependent. In order to characterize the formation of C690, we have recorded 298 K fluorescence kinetics at 690 nm and the corresponding absorbance kinetics at 440 nm. The amplitude of the variations of both kinetics increases with the sample age. The absorbance and fluorescence kinetics can be modelized as a monoexponential law. The rate constant of the absorbance and fluorescence kinetics does not significantly change during the studied period (except for old cotyledons). The results presented in this paper give evidences for a low energy transfer between pigments during the photoreduction of protochlorophyllide at room temperature.     

The marine microalgaChlorella stigmatophora as a potential source of single cell protein: Enhancement of the protein content in response to nutrient enrichment

Summary Mass cultures ofChlorella stigmatophora were carried out in order to obtain maximum protein production and to study the chemical variations in function of the nutrient concentration. Cultures reached maximum cellular densities of 2.2·10⁸ cells/ml, with a growth velocity between 0.49 and 0.55 doublings/day. Carbohydrate content in the stationary phase ranged between 2.23 and 2.74 pg/cell, RNA between 0.78 and 1.36 pg/cell and DNA between 0.013 and 0.016 pg/cell. The maximum value for chlorophylla was 0.13 pg/cell. Maximum protein content was obtained with a nutrient concentration of 16 mM of NaNO₃, giving 4.85 pg/cell and a protein concentration of 0.7 g/l. The protein content can be manipulated by changes in the nutrient concentration, showing differences up to a 9.2-fold increase. This characteristic makesChlorella stigmatophora a suitable source of single cell protein.     

Interactions of plant stress and herbivory: intraspecific variation in the susceptibility of a palatable versus an unpalatable seaweed to sea urchin grazing

Summary Interactions among environmental stresses, plant defensive characteristics, and plant nutrient status may significantly affect an alga's susceptibility to herbivores. Following desiccation, the palatable seaweed Gracilaria tikvahiae was less susceptible to grazing by the sea urchin Arbacia punctulata while the unpalatable alga Padina gymnospora became more susceptible. Increased grazing on desiccated Padina appeared to result from a loss of chemical defenses following desiccation. Palatable plants treated with organic extracts from desiccated Padina plants were consumed at more than twice the rate of plants treated with extracts from undesiccated plants. Increased susceptibility of Padina did not correlate with changes in protein content of the alga; reduced grazing on desiccated Gracilaria was associated with a decrease in protein content. When Padina was grazed by Arbacia or mechanically damaged to mimic urchin grazing, its susceptibility to Arbacia decreased within 1 to 5 days. These results demonstrate that history of physical or biological stress may affect a plant's susceptibility to herbivory. We hypothesize that urchins cue primarily on attractiveness features (e.g. nutrient content) of highpreference algae and deterrent features (e.g. chemical defenses) of low-preference algae. Stresses may therefore increase, decrease, or not affect a plant's susceptibility to herbivory depending upon the primary feeding cues used by the herbivore, the defensive mechanisms used by the plant, and the way these are altered by various environmental stresses.     

Photo-induction of an NADPH dehydrogenase which functions as a mediator of electron transport to the intersystem chain in the cyanobacterium Synechocystis PCC6803

Illumination of the dark-incubated cells of Synechocystis PCC6803 caused recovery of both respiratory activity of oxygen uptake and PS I-cyclic electron flow, which was monitored by the dark reduction of P700⁺ in the presence of DCMU after a 50 ms pulse light (MT) under background far-red light, but the effects were much smaller in those of the mutant M55, which has an ndh-B defective gene. Activity of an NADPH-NBT oxidoreductase with a higher molecular mass (around 380 kDa), which was only found in wild type but not in M55, became evident after the dark-incubated cells were exposed to the light. Immuno-blotting analysis indicated that the NADPH-NBT oxidoreductase contains the NdhB subunit of NDH. The expression of NdhB decreased in dark-incubated cells and increased upon transfer of the cells back to light. These results indicate that an NADPH-specific NDH participates in the light-regulated cyclic electron transport around Photosystem I as well as in respiratory electron transport to the intersystem chain in Synechocystis 6803. This revised version was published online in August 2006 with corrections to the Cover Date.     

Inoculation experimental animals withParacoccidioides brasiliensis strains: An attempt to reestablish the dimorphic process and variation in pathogenicity as a function of time of preservation under mineral oil

In an attempt to reestablish the dimorphic process in strains ofParacoccidioides brasiliensis in the transition phase (Y ⇄ M) and to reisolate them, five strains in the transitional phase due to the long time of preservation under mineral oil and two strains in the yeast-like phase were inoculated into male albino rats. The animals were then studied for the presence of paracoccidioidomycotic granulomata. Of the seven strains inoculated, five caused granulomatous nodules in several organs of the animals and only two of these five strains, which had been preserved for the shortest period of time (9 years) were reisolated in culture. Two strains were unable to provoke infection, with no lesions detected in any organ. It is assumed that the long period of time during which the strains were left under oil favored the alteration of celt wall contents, leading to differences in pathogenicity.     

Issues in determining factors influencing bacterial attachment: a review using the attachment of Escherichia coli to abiotic surfaces as an example

The emergence of an increasing number of antibiotic resistant human clinical bacteria has been a great cause of concern for the last decades. As an example, Staphylococcus aureus isolates in the hospital environment are becoming more and more resistant to antibiotics including vancomycin which is considered as a last line of defence in treatment of Staphylococcus aureus -resistant methicillin. On the other hand, food safety is threatened by development of pathogenic bacteria including Listeria monocytogenes, Campylobacter jejuni, Salmonella enteritidis, Escherichia coli O157:H7 and Staphylococcus aureus. The use of antimicrobial peptides such as glycopeptides, semi-synthetic peptides, bacteriocins including lantibiotics offers a hope to face these clinical and food microbiology concerns. Clinical approval of new chemotherapeutic agents requires a long period of time. Research on bacteriocins has demonstrated potential use to fight against undesired foodborne pathogens but the use industrial use of bacteriocins is limited. To date only lantibiotic nisin and in class IIa bacteriocin Pediocin PA-1 are legally used as food preservative in many countries. The present minireview is focused on divercin V41 (DvnV41), a class IIa bacteriocin naturally produced by Carnobacterium divergens V41. The last decade has been the witness of intensive investigations carried out on this cationic peptide tempting to answer multiple questions covering basic and applied aspects. DvnV41 has shown a wide spectrum of activity either alone or in combination with nisin and/or polymixins (synergistic effect). This outcome indicates that Cb. divergens V41 could potentially be used for safe and efficient prevention of L. monocytogenes growth in cold smoked salmon.