Evolutionary implications of swimming behaviour in meiobenthic copepods

Body morphology is said to be the all important factor in determining swimming prowess in copepods. Fusion and differentiation of the body (tagmosis) is coupled with advance into the pelagic realm of the Gymnoplea and is thought, by the provision of a rigid thoracic tagma, to promote swimming efficiency. Thus pelagic copepods are believed to be secondarily derived from bottom dwelling predecessors. Experimental evidence is presented to show that the majority of bottom dwelling harpacticoid families, including the most primitive and the most advanced, have representatives that undergo active sustained swimming movements. Such a widespread occurrence is indicative of a conservative evolutionary trait. This primitive behaviour is linked to precopulatory association which takes place necessarily in the water column; it is a feature retained by representatives of all copepod orders. The implication of cephalic appendage vibration (feeding currents) is the essential feature in the swimming success of the Gymnoplea; planktonic efficiency in these is suggested to have evolved coincident with, rather than because of increased tagmosis.     

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.     

黄海车牛山岛白腰雨燕的繁殖习性及种群动态

本文为作者于1980—1981年对黄海车牛山岛白腰雨燕Apuspacificus pacificus (Latham)的初步研究。内容包括对繁殖习性的观察;对繁殖周期、卵孵化率、雏鸟成活串以及出生率等的统计。并对海岛生态环境下白腰雨燕种群数量的变动及其影响因素,作初步探讨。     

A hybrid zone between Chorthippus parallelus parallelus and Chorthippus parallelus erythropus (Orthoptera: Acrididae): behavioural characters

Two subspecies of the grasshopper Chorthippus parallelus have ranges that abut in the Pyrenees. Males produce two types of song—calling song and courtship song. We have examined the use and structure of these songs in males from nine sites near Mont-Louis, Pyrénées-Onentales, France. These sites were previously used to identify the position of the hybrid zone on morphological characters. The subspecies differ in the use and structure of both types of song. Clines in these characters correspond in position with the morphological cline. At least one character may be relevant to mate choice but none of the characters show evidence of reinforcement.     

Techniques for studying the execution of foreign queens by temporal subcastes in fire ants (Solenopsis invicta)

Using monogynous and polygynous colonies of the fire ant, Solenopsis invicta Buren, we developed methodology to determine which behavioural subcaste of workers was responsible for executing unfamiliar queens that were introduced to them. Separation of subcastes and introduction of queens to each of these separately was partly effective, but more accurate results were obtained by removing workers that were in the act of executing queens, marking them individually, and returning them to the colony. Their subsequent behaviour was then recorded to determine whether they behaved like nurses, reserves, or foragers. The results showed that foragers are dominant in execution behaviour and that all morphological subcastes (minors, medias, and majors) are involved. This methodology may be applied to other social insect species.

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Résumé A l'aide de colonies monogynes de S. invicta Buren, nous avons testé la sensibilité de deux méthodes: Premièrement, nous avons isolé les trois sous-castes temporelles des ouvrières (nurses, réserves et fourrageuses) auxquelles nous avons introduit des reines étrangères. Nous avons trouvé que les fourrageuses étaient le groupe le plus agressif, exécutant un pourcentage élevé des reines qui leur étaient présentées. Le degré de physogastrie de la reine étrangère, sa colonie d'origine et la présence de couvain n'avaient pas d'effet visible sur sa destinée. La sensibilité de cette méthode était limitée par la difficulté d'une séparation complète des souscastes temporelles.Deuxièmement, nous avons capturé des ouvrières exécutant activement des reines étrangères, après marquage nous les avons remises dans leur colonie pour observations ultérieures. Nous avons remarqué que leur localisation dans le nid et leur comportement correspondaient aux séquences trouvées pour les fourrageuses bien plus qu'à celles des ouvrières réserves ou nurses. Cette méthode est plus sensible. Des mesures de la largeur de la capsule céphalique de ces ouvrières ont montré qu'aucune des sous-caste morphologiques (mineurs, moyennes et majeurs) étaient dominantes dans le comportement d'exécution. Nos résultats indiquent que la sensibilité des ouvrières à certaines phéromones de la reine et odeur de la colonie augmente avec leur âge.

     

A test of a model for planktivorous filter feeding by bream Abramis brama

Synopsis The planktivorous feeding of bream, Abramis brama on Daphnia hyalina and Bosmina coregoni was analyzed in a stepwise regression analysis with the average size (and standard deviation) of consumed organisms as dependent variable and the size of the fish, the average size (and standard deviation) of the organisms and their density in the environment as independent variables. Three basic predictions on filter feeding were formulated and tested. It was predicted that the (average) prey size should increase with fish size, but that the standard deviation should decline. Secondly the prey size should be strongly correlated with the prey size available and thirdly the prey density should have little effect on the size selection. These hypotheses could not be rejected for bream>10 cm feeding on B. coregoni and for bream>20 cm feeding on D. hyalina. The hypotheses were not valid for smaller bream as these acted as particulate or combined filter- and particulate feeders.     

Quantitative field investigations of feeding and territorial behaviour of young-of-the-year brook charr,Salvelinus fontinalis

Synopsis Direct observations of young-of-the-year brook charr, Salvelinus fontinalis, in a second-order woodland stream indicated that most of their feeding effort was directed toward sub-surface, drifting prey (83% of feeding time). Feeding from the substrate and water surface was much less frequent (17% of feeding time). Comparisons of gut contents to drift net and substrate fauna samples corroborated that the most commonly consumed prey (chironomid and trichopteran larvae, ostracods, and ephemeropteran nymphs) were captured primarily from sub-surface, invertebrate drift. The disproportionate numbers of some prey species in the guts of several fish indicate that some prey selection occurred. Territories appeared to be cardioid-shaped, and were often contiguous, with dominance hierarchies evident among the residents. Agonistic interactions were frequent. Charges and chases predominated (91% of interactions) while lateral displays were infrequent (9% of interactions). Overall, these fish spent most of the daylight hours station-holding (77%) and feeding (18%). While only 3% of total time was spent in aggression, this amounted to 14% of the time a fish spent away from its station. There was some indication that territories were defended at a cost of feeding time.     

The influence of food plant dispersion on caterpillar searching success

Abstract. 1. Collards (Brassica oleracea L.) grown in clumps were more difficult for unstarved, early instar cabbage white caterpillars (Pieris rapae L.) to find than collards spaced at regular intervals, although total plant densities were identical.
2. Early instar, unstarved larvae are less mobile than later instar larvae (our data) or starved larvae (Jones' 1977 data).
3. Starved larvae and late instar larvae tend to find plants more readily than do unstarved or younger larvae.
4. We contend that larval mobility governs the success of searching caterpillars and their sensitivity to variations in plant dispersion.
5. Our results show that the dispersion of targets can influence searching success even though target density is constant. This means that the degree of clumping in host plants is capable of influencing their availability to herbivores.     

A model of a myelinated nerve axon: threshold behaviour and propagation

A model of a myelinated nerve axon is developed on the basis of FitzHugh-Nagumo dynamics under the assumption that the nodes of Ranvier are of small but finite width. It is shown that a periodic excited state may not exist if the width of the nodes is too small and the leakage across the myelin sheath is too great. The propagation of a super threshold pulse is prevented in the absence of nodes. Global stability of the resting equilibrium state is investigated as well as the propagation of wave front, type solutions.