Limnochemical and phytoplankton studies on Nyumba ya Mungu reservoir, Tanzania

This publication reports on the chemical and phytoplankton aspects of a three month biological survey of Nyumba ya Mungu reservoir, Tanzania.
The lake had a total salt concentration of about 8 meq dm^-3 and specific conductivity of 900 μS cm^-1. The main salt in solution was sodium bicarbonate, and when the lake level fell it sometimes formed a crust on the exposed shore. The concentrations of major nutrient ions were probably not limiting to algal growth and good nutrient replenishment was provided by the two inflow rivers.
Nyumba ya Mungu supports a rich phytoplanton dominated by Melosira and blue-green algae. Acetone extractions gave chlorophyll 'a' concentrations ranging from 20–40 mgm^-3 in the vertical profiles, and light and dark bottle experiments indicated a maximum gross photosynthesis of about 800 mg O₂ m^-3h^-1. There was evidence of chemical stratification in the open water and diurnal stratification in the sheltered bays, but discontinuities were short-lived and the Trade Winds ensured regular mixing of the water. The lake appeared to have a higher primary production than the larger Rift Valley lakes and it was considered that this level of production would continue.     

Analysis of growth during geotropic curvature in seedling hypocotyls

Abstract. The patterns of growth in organs curving under the influence of gravity were analysed by time-lapse photography of cress and cucumber hypocotyls which were delimited into 1 mm zones by ion-exchange beads. Geotropic curvature resulted from changes in growth rate on both sides of the organ. Growth inhibition of varying degrees of intensity occurred in all the previously growing zones of the upper (concave) side. An absolute reduction in length due to compression frequently occurred in some zones. Also, in both species growth stimulation was observed on the lower (convex) side. The disparity in growth rate between the upper and lower surfaces varied with time, being more apparent in the subapical region in the first hour of curvature. A later promotion of growth rate on the lower surface subsequently increased the curvature of the more basal zones. Autotropic straightening occurred as a consequence of growth changes, both inhibitory and stimulatory, in the apical zones. These events indicate a polarity of response in which apical zones have precedence over basal zones.     

Coelenterate Neuropeptides: Structure, Action and Biosynthesis

Evolutionary "old" nervous systems such as those of coelenteratesare peptidergic: Using various radioimmunoassays we have nowisolated 13 novel neuropeptides from sea anemones and severalothers from hydrozoan polyps and medusae. These peptides areall structurally related and contain the C-terminal sequenceArg-X-NH₂ or Lys-X-NH₂, where X is Ala, Asn, Ile, Phe, Pro orTrp. Three neuropeptides have a novel N-terminal L-3-phenyllactylresidue, which protects against degradation by nonspecific aminopeptidases.The neuropeptides from sea anemones are produced by differentsets of neurones and have excitatory or inhibitory actions onisolated muscle preparations, suggesting that they are neurotransmittersor neuromodulators. We have also cloned the precursor proteinfor the sea-anemone neuropeptide Antho-RFamide (<Glu-Gly-Arg-Phe-NH₂).In Calliactis parasitica this precursor harbours 19 copies ofimmature Antho-RFamide (Gln-Gly-Arg-Phe-Gly) together with 7other, putative neuropeptide sequences. The precursor of Anthopleuraelegantissima contains 14 copies of Antho-RFamide and 19 other,putative neuropeptides. This shows that the biosynthetic machineryfor neuropeptides in coelenterates, the lowest animal grouphaving a nervous system, is already very efficient and similarto that of higher invertebrates, such as molluscs and insects,and vertebrates.     

Modelling the lineage of a growing population as an age-dependent branching process

A new model for population growth as a branching process is described. It requires knowledge of the population's age-specific survivorship and fecundity curves. The total population size at any time is calculated by summing across all branches of the tree representing the population's lineage and thus the model also allows the lineage of the developing population to be traced. Use of the model is demonstrated by a hypothetical example. The model could be of particular value in tracing the phylogenetic development of populations and/or species.     

Analysis of growth during light-induced hook opening in cress

Abstract. Growth in various regions of the hypocotyls of dark-grown cress seedlings before and after exposure lo continuous white light has been analysed by time-lapse photography. In the dark, growth in the hook was minimal, the upward growth of the seedling being sustained by extension of the shank, especially the uppermost zones. Following irradiation, the hook and the remainder of the hypocotyl showed dissimilar growth responses. Previously growing regions of the shank were inhibited while zones within the hook, especially the apical end of the inner (concave) side, showed marked growth stimulation. These changes in growth rates commenced within 1 h from exposure to the light stimulus and thus considerably preceded any observable changes in hook angle.     

Comparisons of habitat structure and plant,arthropod and bird diversity between mainland and island sites near Perth,Western Australia

Detailed estimations of habitat structure, plant species diversity and diversity of arthropods were made at six 4.0 ha sites, two on mainland Western Australia near Perth and four on adjacent islands. The number of resident passerine bird species was also recorded at each site. Plant species diversity, and horizontal foliage diversity (=patchiness) varied only slightly between sites. There were significant positive correlations between arthropod Order diversity and bird diversity, and between vertical foliage diversity and bird diversity. In both Acacia and dune scrub, the Rottnest Island sites had more individuals of arthropods than the mainland sites but these belonged to fewer Orders. Numerical imbalance between arthropod Orders on Rottnest Island probably results from diminution of predators (passerine birds) there. As the actual number of arthropods is higher on the islands, the absence of so many species of passerine birds may result from other factors (ecological and historical).     

Phenology determines seasonal variation in ectoparasite loads in a natural insect population

1. The extent to which individuals are parasitised is a function of exposure to parasites and the immune response, which in ectotherms may be associated with temperature. 2. We test the hypothesis that seasonal variation in ectoparasite burden is driven by temperature using an extensive mark‐release‐recapture study of adult Coenagrion puella (L.) (Zygoptera) as a model system. Mite counts were taken both at capture and on a subset of subsequent recaptures over two entire, consecutive breeding seasons. 3. Emergence date was the most significant factor in determining individual differences in mite burden, and mean counts for individuals emerging on the same days showed strong unimodal relationships with time of season. Subsequent recounting of mites on a subset of individuals showed that patterns of loss of mites were similar between seasons. 4. While temperature did not significantly affect mite burdens within seasons and ectoparasite prevalence was very similar across the two seasons, intensity of infection and rate of mite gain in unparasitised individuals were significantly higher in the cooler season. 5. We demonstrate that, while temperature may modulate the invertebrate immune response, this modulation does not manifest in variations in mite burdens in natural populations.     

Flexible responses of insects to changing environmental temperature – early season development of Craspedolepta species on fireweed

Developmental response to temperature during the critical early season growing period was investigated in two congeneric species of Craspedolepta feeding on Epilobium angustifolium at three sites at different altitudes in Norway and the UK. The larval development reaction norm to temperature, measured as accumulated day degrees, was not significantly different between Craspedolepta nebulosa and Craspedolepta subpunctata at sites where they co‐occurred but C. nebulosa development was consistently more advanced at any site. For individual species the reaction norms at the lowest site (Ainsdale, UK) were similar to the intermediate site (Geilo, Norway): and there were no differences between years. Insect size remained relatively constant. However, at the highest site (Haugastøl, Norway), where C. subpunctata is unable to complete its development, the reaction norm for C. nebulosa was significantly higher than at Geilo and the individual insects produced were smaller. These adaptations allow life‐history completion under limiting temperature conditions. An experiment at Ainsdale, to raise the mean temperature by around 2.5°C during the early growing season, resulted in accelerated development in both C. nebulosa and C. subpunctata but development in C. nebulosa was accelerated proportionately more. C. nebulosa thus displays the greater plasticity in developmental response to environmental temperature that allows it to occupy a greater altitudinal and latitudinal range than C. subpunctata, in which the response is less plastic and more canalized. The likely individualistic responses of the two species to climate warming are considered.