Photoreceptors and signals in the photoperiodic control of development

Many plant species are sensitive to changes in the seasons, especially with regard to their reproductive behaviour. Sexual or vegetative reproductive structures are often only formed at times of the year when days are sufficiently long, or short. Plants perceive daylength in the leaves, but reproductive changes occur in shoot apices in response to the movement of signals throughout the plant. There is good evidence that phytochrome A is an essential component of the daylength-sensing mechanism in long-day plants, and preliminary evidence suggests a potential interaction between phytochrome C and daylength sensitivity in short-day plants. The sensitivity of reproductive processes to photoperiodic control is directly altered by photoreceptor action, particularly in the case of phytochrome B, which has a major influence on whether flowering or tuberization occurs under non-inductive conditions in both long- and short-day plants, but is not involved in daylength measurement. The signals which move from leaves to the sites of reproductive development are not known, but there is good evidence that gibberellins may be important and some preliminary indication that brassinosteroids might also be involved in photoperiodic signalling.     

Size scaling of whole‐body metabolic activity in the noble crayfish (Astacus astacus) estimated from measurements on a single leg

1. Use of electron transport system (ETS) activity in a single leg for estimating whole‐body ETS activity was explored in the noble crayfish Astacus astacus. Oxygen consumption and ETS activity of the whole body and of a walking leg were measured in different‐sized animals at 10 °C to compare the size scaling of oxygen consumption, whole‐body ETS activity and the ratio of whole‐body ETS activity to oxygen consumption (ETS/R). 2. Electron transport system activity of a leg and the ratio of ETS activity of a whole crayfish to that of a leg were correlated with wet mass of animals. Therefore, metabolic potential in whole noble crayfish can be estimated on the basis of the measured ETS activity in a single leg and crayfish mass. This approach provides a valuable tool for determining metabolic characteristics of crayfish without killing them. 3. Mass‐specific oxygen consumption decreased with increasing wet mass, while ETS activity of whole crayfish showed no significant correlation with wet mass. Both oxygen consumption and ETS activity correlated significantly with protein mass. 4. The increase in ETS/R with increasing wet mass of the noble crayfish indicates that small organisms exploit a greater proportion of their metabolic potential for standard metabolism than larger ones. This is the first report on ETS/R in crayfish.     

Vector competence of Coquillettidia linealis (Skuse) (Diptera: Culicidae) for Ross River and Barmah Forest viruses

Abstract Coquillettidia linealis is a severe pest on some of the Moreton Bay islands in Queensland, Australia, but little is known of its breeding habitats and biology. Because of its high abundance and its association with Ross River (RR) and Barmah Forest (BF) viruses by field isolation, its vector competence was evaluated in the laboratory by feeding dilutions of both viruses in blood. For RR, Cq. linealis was of comparable efficiency to Ochlerotatus vigilax (Skuse), recognised as being a major vector. Results were as follows for Cq. linealis and Oc. vigilax , respectively: dose to infect 50%, 10^2.2 and <10^1.7 CCID₅₀/mosquito; 88% and 90% disseminated infection at 4 days postinfection; transmission at 4 days with rates of 68−92% and 25−60%. For BF dose to infect 50%, 10^2.7 and 10^2.0; disseminated infection rates on first transmission day (day 6), 40% and 70%; transmission rates of 8−16% and 0−10%. As a capillary-tube method was used rather than suckling mice to demonstrate transmission, transmission rates may be underestimates. This, the first study of the vector competence of Cq. linealis in Australia, demonstrates that this species deserves control on the southern Moreton Bay islands.     

Breeding dispersal and site-fidelity in three monogamous wader species in the Western Isles, U.K.

Adult and post-natal breeding-dispersal movements of Redshank Tringa totanus , Dunlin Calidris alpina and Ringed Plover Charadrius hiaticula were quantified in west Scotland. Data from 373 returning birds marked as breeding adults and 142 returning birds marked as chicks are presented. Unlike most previous studies, this study measured dispersal movements up to 40 km and attempted to overcome distance-related biases. For each species, adult males were significantly more nest site-faithful between years than were adult females. Likewise, first-time breeding males bred significantly closer to their natal site than did females. The settlement intensity per unit area of habitat showed marked differences between species, age classes and sex in the relative attractiveness of potential areas at different distances to settling birds. Adult dispersal was negatively and significantly related to breeding success in the previous year and positively related to capture on the nest in the previous year. Dispersal movements of adult Ringed Plover breeding on unstable cultivated habitats were significantly related to habitat quality (measured in terms of nest survival) and were always to habitat of better or equal quality.     

Variation in genetic structure among populations of the caddisfly Helicopsyche borealis from three streams in northern California, U.S.A.

1. Allozyme electrophoresis was used to describe the genetic structure of Helicopsyche borealis caddisflies collected from three sites in each of three streams in northern California, U.S.A.: the Rice Fork of the Eel River; Big Sulphur Creek; and Alameda Creek. Between 7 and 11km separated adjacent sites within these three streams. Helicopsyche borealis from three additional streams in eastern North America (Christiana Creek, Indiana; Byrd's Mill Creek, Oklahoma; Susquehanna River, Pennsylvania) were also analysed electrophoretically to address taxonomic questions that arose during the study. 2. Four genetically distinct groups of individuals were identified (i.e. Helicopsyche types A, B, C, and D). Lack of interbreeding between sympatric groups (as evidenced by fixed allelic differences) and large genetic differences (mean Nei's genetic distances = 0.396–0.693) indicate that these four groups of Helicopsyche were actually reproductively isolated species rather than genetic variants of a single species. 3. Occurrence of Helicopsyche type A at multiple sites permitted an analysis of spatial variation in genetic structure. Within a drainage basin, small differences in allele frequencies were observed among sites in the Rice Fork and Big Sulphur Creek, but not in Alameda Creek. Larger genetic differences were found among sites in separate drainage basins. Genetic distances (Nei's) between Helicopsyche type A from California and from eastern North America sites (mean = 0.236) were greater than interpopulation differences commonly observed for insects, which suggests that Helicopsyche type A from California may represent a different species than Helicopsyche type A from eastern North America. 4. Geographical and taxonomic differences observed in this study underscore the importance of understanding both population structure and genetic relationships among populations in the design and interpretation of stream faunal studies.     

Nitrogen-stimulated potassium influx into maize roots: differential response of components resistant and sensitive to ambient ammonium1

Abstract Potassium (⁸⁶Rb) influx from 200 mmol m ^?3 KCl into dark grown, decapitated maize seedlings 6 d old) was stimulated by nitrate pretreatment. The stimulus was clearly evident by 6h exposure to nitrate and required 12–24 h for maximal expression. Decay of the nitrate-stimulated potassium influx was more than 50% complete within 3 h after transfer to nitrogen-free solutions. The stimulation of potassium influx was entirely accounted for by an increase in the influx component that was resistant to inhibition by presence of 200 mmol m^?3 ambient ammonium. In contrast, the component of potassium influx that was sensitive to inhibition by ambient ammonium was unaffected by nitrate pretreatment. Exposure to the glutamine synthetase inhibitor L-methionine-dl-sulphoximine (MSX) during nitrate pretreatment stimulated the resistant component but the sensitive component was nearly eliminated. Pretreatment with ammonium increased the resistant component of potassium influx within 3 h, i.e. before it was increased by nitrate pretreatment, but the sensitive component was concomitantly restricted. The latter recovered partially during extended pretreatment with ammonium. The data indicate that the resistant component responded positively to increases in tissue ammonium concentrations whereas the sensitive component was unaffected by tissue ammonium except at concentrations in excess of 10μmol g^?1. Ammonium influx was also stimulated by nitrate pretreatment and to a greater extent than potassium influx. Presence of MSX with nitrate during pretreatment resulted in a further stimulation in ammonium influx. The parallel increases in root ammonium concentrations with the two pretreatments imply that part of the increase in ammonium influx was a consequnce of increased counter-transport with endogenous ammonium.     

Seasonal patterns of food storing in the Jay Garrulus glandarius

This study investigated seasonal patterns in food consumption and food storage in six captive Jays Garrulus glandarius. In the first experiment, seasonal changes in food-storing intensity were tested by presenting acorns (oak seeds, Quercus spp.) in spring, summer and autumn. There were no significant differences between the seasons in the amount of food eaten. However, significantly more food was taken and stored in the autumn than in the spring and summer months. In the spring and summer, the acorns were stored between the doorframes, on the ledges of the aviaries and under the bark of branches. In the autumn, Jays also began to hoard underneath the plastic sheeting covering the hard-board flooring by ripping the polythene to create a hidden cache site. The length of time over which the stored food was left before retrieval increased from summer to autumn. Food storing also occurred in spring and summer but was short term. The second experiment tested whether or not there were seasonal changes in food preference by presenting birds with acorns, peanuts and mealworms in the summer and autumn. More peanuts were eaten, taken and stored in the autumn than in the summer, and, as in the first experiment, significantly more acorns were taken and stored in the autumn. In the autumn, only a few mealworms were eaten before the birds stored acorns and peanuts, whereas in the summer, birds tended to eat most of the mealworms before they began to store. As in the first experiment, items tended to be buried in the ground in the autumn and left for longer periods before retrieval. These results are discussed in relation to the demand that each food type places on the Jay's time.