Swimming In Circles Research Articles

Diffraction gratings in gyrinid beetles

The primitive surface pattern of the cuticle of insects and the way in which diffraction gratings are formed is discussed. The appearance of plane and convex gratings when illuminated by parallel light at an arbitrary angle is described. It does not appear to have been previously noted that the direction of the streak of spectra and the apparent direction of the grating rulings form an orthogonal system. The form and distribution of grating lines in the family Gyrinidae are described. Species of Gyretes are the only insects that have diffraction gratings at right angles to each other on the dorsal surface. It is suggested that their unique system of grating lines is related to their habit of swimming in circles.

Courtship, locomotion, feeding, and miscellaneous behaviour of pacific bonito ( Sarda chiliensis)

Establishment of Pacific bonito ( Sarda chiliensis (Cuvier) in captivity at Marineland of the Pacific, Palos Verdes, California, has made it possible to study and describe in detail their swimming, feeding, courtship, and miscellaneous behaviours. The oval tank in which the fish were kept was 33 m long, 16·3 m wide, and 11 m deep at the deepest point. Sea water was pumped from the ocean and was held at 22°C. Fish were viewed through 170 windows in the sides of the tank. The oval tank was part of a public display, a circumstance which limited experimental manipulation of the fish. Swimming speeds and tail-beat frequencies were measured from movie films and direct observation. Frequencies of behaviour patterns were recorded either as the numbers observed among all fish by a stationary observer over 10 min periods or the number observed for a single fish for periods of time averaging 71 sec. With the latter method, data were kept separately for individual fish. They swam continuously against the current at an average speed of 88·2 cm/sec and at a tailbeat frequency of 1·42 beats/sec when not feeding or courting. The linear regression of speed ( y ) in body lengths/sec on the number of tail beats/sec ( x ) was y=0·4905+0·6394 x among feeding S. chiliensis . When food (frozen osmerids) was tossed onto the surface, S. chilensis was the first species to reach and ingest it. During feeding, schooling was disrupted, and each S. chiliensis took on a vertically barred coloration and a yellowish middorsal stripe. Courtship included temporary pairing, aggressive defense of females by males, and a sequence of behaviour leading to the simultaneous and adjacent release of gametes. A wobbling swimming motion by a female released a following by males, and likewise, if a male swam immediately behind a female, she began a wobbling type of swimming. Sexual discrimination was mediated by the wobbling and following movements. If more than one male was in the following position, agonistic behaviour occurred which included the transient vertically barred coloration observed in both sexes at feeding time. During courtship, only males assumed the coloration. Gametes were released during a circle swimming behaviour in which the female with the male in tandem swam in a circular path about three body lengths in diameter. If aggression occurred during the wobbling-following portion of the sequence, the sequence usually terminated and did not result in circle swimming and spawning. S. chiliensis had nine miscellaneous behaviour patterns: mouth closure (long), mouth closure (short), snap, yawn, quick swim, lean, bend, jerk, and defecation. Often such movements have been considered as comfort movements, but in the present paper each was discussed separately in terms of association with some vital process of the fish. Mouth closure (long) movements may be associated with olfaction or gill ventilation; snaps following a yawn or a quick swim may be a drinking movement; leans may be a social releaser in schooling; and bends and jerks may be associated with passage of food through the alimentary canal.

Reproductive Behaviour of the Cod (Gad Us Callarias L.)

AbstractThree weeks before spawning, aggressive and reproductive behaviour was seen in a group of thirteen captive cod. By aggression directed against males and females the most vigorous males were able to establish territories in the pre-spawning period. Less vigorous males and unripe females formed an inactive group outside the territory. All spawning observed occurred in the territory of the dominant male. The amount of reproductive activity was closely linked with dominance in the males. Behaviour culminating in spawning was initiated by a female entering the territory of the male. Males were able to distinguish the sex of mature intruding fish during the spawning period. The distinction appeared to be based on the slow swimming, unafraid approach of the female compared with the quick movements and readiness to flee shown by the males. The male approached ripe females and presented a lateral view of the flaunting display. In this display the median fins are fully erected and the male moves in front of the female with many unnecessary turns sometimes accompanied by a low grunting sound. Ripe females followed flaunting males for ten to fifteen minutes. Then if the female became stationary at the bottom of the tank it was prodded ventrally by the male, which caused it to swim upwards. At the surface the male mounted the female dorsally and then immediately slipped down one side into a ventral mount with the male inverted below the female. In this position the cod spawned while swimming in circles at the surface. No interest was shown by the rest of the group in the spawning. After spawning the spent female returned to the bottom of the tank and rejoined the group of inactive cod. The pattern of spawning behaviour was often initiated but failed to reach completion because of the inappropriate response of the female at some stage. During successive entries the courtship behaviour was carried to later stages until the female swam to the surface and spawned. Aggressive behaviour during the spawning period seems to be important in allowing only the most vigorous males to spawn and preventing interference by other males in the courtship pattern. The production of sounds by the males was used to enforce aggressive behaviour and stimulated the female. It is suggested that, as much of the behaviour leading to spawning involves vertical movements, natural cod shoals may be stratified with a layer of vigorous males above a group of females and less vigorous males.

Goslings Descend from Aerial Nest

Goslings Descend from Aerial Nest