The relative importance of temperature and diet to larval development and adult size of the winter stonefly, Soyedina carolinensis (Piecoptera: Nemouridae)

SUMMARY. 1. Soyedina carolinensis Claassen, a leaf shredding stonefly, was reared in a series of three laboratory experiments from early instar to adult on different species of deciduous leaves and at various constant and fluctuating temperature regimes.
2. Experiment 1, which involved rearing larvae on fourteen different leaf diets at ambient stream temperatures, showed that diet significantly affected larval growth and adult size but did not affect overall developmental time.
3. Experiment 2, which involved rearing larvae on five different leaf diets at each of three fluctuating temperature regimes (viz ambient White Clay Creek (WCC), ambient WCC+3°C, and ambient WCC+6°C), showed that: (i) adding 6°C to the normal temperature regime of WCC was lethal to 99% of the larvae regardless of diet; and (ii) warming WCC by 3°C did not affect developmental time but did significantly reduce adult size relative to adults reared at WCC temperatures on certain diets.
4. Experiment 3, which involved rearing larvae on five different leaf diets at each of five constant temperatures (viz 5, 10, 15, 20, 25°C), showed that: (i) temperature significantly affected the mortality, growth, and development time of larvae whereas diet only affected larval growth and mortality; (ii) temperatures at or near 10°C yielded maximum larval growth and survival for most diets; (iii) at 5°C, larval mortality was high and growth was low resulting in a few small adults for most diets; (iv) larval mortality was at or near 100% at 15°C regardless of diet; and (v) no larvae survived at 20 and 25°C.     

Ethylene Evolution from Bracts and Leaves of Poinsettia, Euphorbia pulcherrima Willd

Woodrow, L. and Grodzinski, B. 1987. Ethylene evolution trombracts and leaves ol Poinsettia, Euphorbia pulcherrima Willd.—J.exp. Bot. 38: 2024–2032. Ethylene release from fully expanded, red and white bracts andleaves of poinsettia, Euphorbia pulcherrima Willd., was compared.On a laminar (area) basis leaves contained about 50 times morechlorophyll and demonstrated 10 times the photosynthetic rateof the bracts. Both tissues contained starch, however, solublecarbohydrate in the bracts consisted primarily of reducing hexoseswhile the leaves contained mainly sucrose for translocation.The total free alpha-amino nitrogen content of the bract tissuewas twice that of the leaf tissue. The leaves contained moreACC (1-aminocyclopropane-1-carboxylic acid) and produced proportionallymore endogenous C²H⁴ than either the red or white bracts. ACC-stimulated₂H₄ release was also greatest from the green tissue indicatingthat the EFE (ethylene forming enzyme) was most active in theleaves. The specific activity of the ¹⁴C₂H₄/¹²C₂H₄ releasedfrom [2,3-¹⁴C]ACC confirmed ACC as the primary precursor ofC₂H₄ in this tissue. Ethylene release from the non-photosynthetic,bract tissue was not markedly affected by alterations in CO₂or light conditions. In green leaf tissue endogeneous ethylenerelease increased from 1·5 to 6·0 pmol C₂H₄ cm^–2h^–1 while ACC-stimulated ethylene release increased from10 to 35 pmol C₂H₄ cm^2– h^1– as the CO₂ partial pressureincreased from 100 to 1 200 µbar. Key words: Poinsettia, ethylene, bracts     

Pronophiline butterflies (Satyridae) of the Cordillera de Mérida, Venezuela

The 36 species of the tribe Pronophilini known from the Cordillera de Merida, the main Andean mountain range in Venezuela, are listed, together with three others probably erroneously described or labelled as from the range. The general ecological characteristics of the tribe are described, using the Merida species as examples. These include its restriction to high altitudes, endemism in mountain 'islands', species partitioning up the altitude gradient, mimicry within the tribe, and seasonality. The evolutionary relationships of the 16 endemic species are analyzed. Two new genera, six new species, two new subspecies and one new form are described. Three new synonymies are established, three new combinations made, new status is given to two taxa and the status of one taxon is revised.     

Evidence for Distinct Aggregation Factors and Receptors in Cells

SINCE the original observations by Wilson¹ that dissociated sponge cells could reassociate in vitro, cell aggregation (or reaggregation) has been widely used as an operational criterion for the study of intercellular adhesion². The introduction of rotation-mediated methods to promote cell aggregation^3,4 led to the possibility of obtaining reproducible quantitative data. In these methods, suspensions of dissociated single cells are shaken under defined conditions of speed and temperature and cell aggregation is measured by either the size of aggregates or the number of single cells. The aggregation of dissociated cells from sponges⁵, chick and mouse embryos⁴ and tissue culture cells⁶ has been investigated with this method. Cells maintained in vitro seemed particularly suitable for studying mechanisms of cell aggregation as they represent a histotypically homogeneous population.     

Dynamic Properties of Giant Muscle Fibers of the Barnacle

Giant muscle fibers of the barnacle give graded, relativelyslow contractions, A plateau level, termed the unit response,occurs with stimuli of 3 msec, but pulses longer than 10–15msec give much greater tension or shortening. Repetitive stimulationwith pulses of 3 msec leads to a tetanus. The magnitude of activestate was determined, and found to be also graded in natureand slow to develop, though early in onset. The full developmentof active state requires 80–120 msec. A high level ofeffective series-elasticity was associated with the sarcomeresthemselves.     

Isolation Conditions for High Yields of Protoplasts from Laminaria saccharina and L. digitata (Phaeophyceae)

In an investigation of the main factors determining protoplastyield in Laminaria saccharina and L. digitata, protoplasts wereisolated from epidermal, cortical and medullary cells of vegetativethallus by incubation with commercial cellulases, crude andpurified mannuronate lyases and purified guluronate lyases.Treatment of the tissue with the calcium chelator EGTA beforeenzymatic digestion greatly increased the protoplast yield.Preplasmolysis was also necessary to obtain large numbers ofhealthy protoplasts and this was most effective when carriedout during chelation with EGTA. Purification of the mannuronatelyases by ion exchange chromatography reduced the toxicity ofthe crude enzyme preparation. The activities of the wall degradingenzymes were differentially influenced by pH and the optimumfor alginate-lyase activity (8.0) was higher than that for cellulaseactivity (<6.0). Protoplast yield decreased linearly withincreasing pH in the enzyme medium over the range tested (6.0–8.0),and this suggests that cellulases are more critical to walldigestion than alginate-lyases. Ionic osmotica gave improvedyields compared with sugar alcohols or sugars. Increasing thecalcium concentration of the enzyme medium brought about anexponential decrease in protoplast yield and wall digestionwas almost completely inhibited at concentrations exceeding8.0 mol m^–3. However, low levels of calcium (<2.0 molm^–3) were beneficial to protoplast viability. Yields of10⁷ to 10⁸ protoplasts g^–1 fr. wt. were consistently obtainedand 20% to 30% of these regenerated new cell walls within 1–2d of culture. Key words: Laminaria protoplasts, cell wall, alginate-lyases     

Aphid–ant mutualism: how honeydew sugars influence the behaviour of ant scouts

Honeydew is the keystone on which ant–aphid mutualism is built. The present study investigates how each sugar identified in Aphis fabae Scopoli honeydew acts upon the feeding and the laying of a recruitment trail by scouts of the aphid‐tending ant Lasius niger Linnaeus, and thus may enhance collective exploitation by the ant mutualists. The feeding preferences shown by L. niger for honeydew sugars are: melezitose = sucrose = raffinose > glucose = fructose > maltose = trehalose = melibiose = xylose. Although feeding is a prerequisite to the launching of trail recruitment, the reverse is not necessarily true: not all ingested sugar solutions elicit a trail‐laying behaviour among fed scouts. Trail mark laying is only triggered by raffinose, sucrose or melezitose, with the latter sugar being specific to honeydew. By comparing gustatory and recruitment responses of ant foragers to sugar food sources, the present study clarifies the role of honeydew composition both as a source of energy and as a mediator in ant–aphid interactions. Lasius niger feeding preferences can be related to the physiological suitability of each sugar (i.e. their detection by gustatory receptors as well as their ability to be digested and converted into energy). Regarding recruitment, the aphid‐synthesized oligosaccharide (melezitose) could be used by ant scouts as a cue indicative of a long‐lasting productive resource that is worthy of collective exploitation and defence against competitors or aphid predators.