Behaviour of drifting insect larvae

The larval drift behaviour of 23 species representing Ephemeroptera, Plecoptera and Trichoptera was investigated in the laboratory using different current regimes. Mayfly nymphs often performed swimming, while caddis larvae were reluctant to do so. Stonefly nymphs were intermediate. In mayflies swimming seemed to be used to reach the substrate as soon as possible. In contrast most stonefly nymphs by swimming prolonged the time spent in the water column. Modes of swimming and sinking posture differed markedly between the orders. Living passively sinking animals often reached bottom faster than dead control specimens, so consequently behaviour did not always express itself in activity. Some caddis larvae spun adherent anchor lines. Differences among taxa seemed more important in explaining swimming activity compared to preferred habitats (as stream, river and lake) in each species. However, observed differences among closely related species indicated subtle differences related to microhabitat to be of profound importance in explaining the alternative behavioural strategies used.     

Some observations on the swimming and feeding of the nauplius larvae of Lepas pectinata (Girripedia: Crustacea)

Limb movements of restrained stage VI nauplii of Lepas pectinata were studied by cine-photography. Outline drawings were made of successive limb positions in both swimming and grooming activity. The antennae appeared to act as leaky paddles performing both propulsion and food gathering. Free-swimming nauplii averaged 120 limb beats min^-1 and a speed of c. 4 mm s^-1. Grooming occurred every 7–20 beats.
It was concluded that lack of streamlining favours filtration at the expense of propulsion. The grooming sequence differs from that of balanid nauplii and is one method of transferring food to the vicinity of the mouth, where sorting and rejection take place prior to ingestion. Fine- and coarse-mesh filters presumably exploit different plankton types. The overall behaviour pattern is well-designed for exploitation of scarce food in the oligotrophic conditions of the ocean-surface habitat.     

Migratory and reproductive behaviour of female adult Atlantic salmon, Salmo salar L., in a spawning stream

Migration and spawning behaviour of eight Atlantic salmon adult females were analysed by radio-tracking in relation to the degree of sexual maturity in a spawning tributary of the R. Sélune. Six of them were grilse and four of them were ripe. All the fish migrated upstream until reaching their spawning site at a distance of 4–12 km from the trap. The daily migration rate up to this site was inversely correlated with the length of the female. Spawning occurred in all fish at the same time when the water temperature increased dramatically. Spawning lasted 1–10 days according to the fish. After spawning, females quickly moved downstream only small distances and then stayed in approximately the same location until death. This study concluded that ripeness did not influence behaviour on the spawning migration and describes certain characteristics of the reproductive phase in a spawning tributary.     

Notes on the use of wood refugia by Physella heterostropha (say) in a thermally disturbed swamp

Physella heterostropha size distributions and densities were measured in Pen Branch delta, a thermally altered swamp of the Savannah River, South Carolina. During cessation of thermal input, measurements were taken in a highly impacted area and more natural area. Of the three substrates sampled, logs, small woody material and benthos, snail density was highest on small pieces of submerged wood and < 20% of the snails on logs were out of the water. Following resumption of thermal input, snail density was four times higher on logs than previously measured. Snails responded to elevated water temperatures by congregating in a narrow band slightly above the water. Snail size did not appear to affect their response. However, the thermal history of the snails influenced their behaviour and survival rates. Logs may be a potential refuge for snails when water temperature are greater greater than 38°C. However, our results indicate that long-term survival in this manner may be impossible.     

Turnover of organic nitrogen in soils and its availability to crops

The root development of barley seedlings grown for one week in an aerated nutrient solution was studied in the presence of dissolved organic matter from an aqueous chestnut leaf litter extract. In particular, the different effects of low and high molecular weight fractions (small molecules: molecular weight <1000; large molecules: >10,000) of the leaf litter extract were examined. In the presence of large molecules root growth was inhibited, an irregular root tip morphology was observed, and Ca and Mg concentrations in the shoots were lower than in control plants. These phytotoxic effects were not caused by the formation of an impermeable layer of large molecules on the root surfaces that lower accessibility for nutrient cations as inferred from voltammetric experiments. A germination assay using spruce seeds, however, indicated allelochemical effects of large molecules, which exhibit a higher aromaticity than the small molecules as indicated by spectroscopic characterisation. In the growth experiments with small molecules, no influence on the root development of barley was evident, but an increase of Ca and Mg in the shoots was detected. During these growth experiments, a large amount of the small molecules, mainly simple phenols and amino acids, disappeared from the nutrient solution. The loss of small molecules was most likely the effect of mineralisation.Abbreviations DOC dissolved organic carbon - DOM dissolved organic matter - LLE leaf litter extract - MW molecular weight - HMDE hanging mercury drop electrode     

Complex ecological models with simple dynamics: From individuals to populations

The aim of this work is to study complex ecological models exhibiting simple dynamics. We consider large scale systems which can be decomposed into weakly coupled subsystems. Perturbation Theory is used in order to get a reduced set of differential equations governing slow time varying global variables. As examples, we study the influence of the individual behaviour of animals in competition and predator-prey models. The animals are assumed to do many activities all day long such as searching for food of different types. The degree of competition as well as the predation pressure are dependent upon these activities. Preys are more vulnerable when doing some activities during which they are very exposed to predators attacks rather than for others during which they are hidden. We study the effect of a change in the average individual behaviour of the animals on interspecific relationships. Computer simulations of the whole sets of equations are compared to simulations of the reduced sets of equations.     

Behavioural specialization in pre-reproductive colonies of the allodapine beeExoneura bicolor (Hymenoptera: Anthophoridae)

Summary Exoneura bicolor is a univoltine allodapine bee common in montane forests of southern Australia, where it exhibits a semisocial/quasisocial colony organization. Within-nest behaviour in postemergence autumn nests ofExoneura bicolor was recorded with the aim of studying behavioural specialization in pre-reproductive colonies. Ten complete colonies were transferred to purpose-built observation nests shortly before brood eclosion in late summer. Behaviour within observation nests was recorded for periods of up to 44 days after establishment, covering a period when colonies are preparing for overwintering. Dispersal of females and brood rearing do not occur at this time, although some females may become inseminated. Analyses of data using multivariate techniques indicated four distinguishable behavioural castes, designated here as Guards, Nest Absenters, Nest Modifiers and Non-recruits. This represents a higher degree of behavioural specialization than recorded to date for other allodapines. Behaviours performed by Guards and Nest Absenters are likely to involve considerable risks, but benefit the colony as a whole, so that some nestmates in prereproductive colonies exhibit altruism that frequently aids adult siblings or cousins. The males in our study were fed by females via trophallaxis and two of the males participated in nest maintenance tasks. Our results suggest that autumn colonies ofE. bicolor form well-integrated behavioural units even though brood rearing does not commence until the following spring.     

Cold-induced Chromosome Regions and Karyosystematics in Sambucus and Viburnum

The genera Viburnum, Sambucus and Lonicera have been investigated for chromosome number and karyomorphology including Giemsa-C-banding, fluorochrome (DAPI/CMA) banding and cold treatment. Cold-induced undercontracted chromosome regions (CIRs) are found in Viburnum and Sambucus for the first time and are apparently identical with larger hc regions, shown by Giemsa C-banding. Certain narrow C-bands are not cold-sensitive. CIRs frequently react brightly CMA-positive in Viburnum and Sambucus, while DAPI fluorescence is virtually ineffective. The occurrence of CIRs within plants is possibly linked to certain nuclear characters such as large chromosomes and continuous condensation behaviour. Cold-induction has possibly also some influence on euchromatin condensation characteristics in prophasic chromosomes. Several karyological characters point to a closer relationship between Viburnum, Sambucus and Adoxa: Relatively large chromosomes, continuous condensation behaviour, reticulate to semireticulate interphase nuclei and presence of CIRs. These genera appear isolated from Lonicera and the Caprifoliaceae s.str., which differ remarkably in karyomorphology.     

The speckled wood butterflies Pararge xiphia and P. aegeria (Satyridae) on Madeira: distribution, territorial behaviour and possible competition

Madeira is home to two species of speckled wood butterfly. Pararge xiphia is endemic and is common at mid to high altitudes, within and around the edges of the indigenous laurel forest. In 1976 P. aegeria colonized the island and anecdotal reports suggest that it may have been responsible for the loss of P. xiphia from some of its former haunts. The aims of this paper were (1) to provide comprehensive data on the distribution, habitat preferences and recent changes of range of the two species and (2) to examine territorial behaviour to see if inter-specific competition is taking place. Census results show that there are basic differences between the species in altitudinal range and habitat, but they are found together at high densities at habitat boundaries. Repetition of some of the census routes after a 4-year gap suggests that P. aegeria is expanding its range into the areas dominated by P. xiphia. Behavioural data demonstrate that the males may be competing by causing each other to expend more energy in defence of territories. Although competition may be present, it is not yet possible to establish which species is more affected and how competition may have contributed to the recent changes in the species' ranges.     

Cryptic coloration and choice of escape microhabitats by grasshoppers (Orthoptera: Acrididae)

Cryptic coloration is found in many Orthoptera, especially in Acrididae, showing a great variety of forms. In a grasshopper assemblage in southeastern Brazil, preferences for escape places were detected; grasshoppers tended to escape to backgrounds in which they seem to be more cryptic. Coloration was measured using the Simpson diversity index, to quantify 'aspect diversity' (diversity of colours and shapes of patches along the insect's body). A weak positive correlation was found between grasshoppers' aspect diversity and diversification in use of escape places (use of many backgrounds to escape). Grasshoppers with similar colour patterns tended to use the same structures (leaves, sandy soil, stones) to escape.