Long-duration whirling of Pholcus phalangioides (Araneae, Pholcidae) is specifically elicited by Salticid spiders.

Long-duration whirling (gyrating of the body during several hours a day) was shown by the pholcid spider Pholcus phalangioides to salticid spiders and hardly ever to predatory spiders from eight other families in laboratory arenas. Long-duration whirling has not been reported so far, in contrast to short-duration whirling lasting less than a few minutes. Long-duration whirling may have the anti-predatory function of disturbing continual visual fixation of prey in attacking salticids, in contrast to short-duration whirling that has been demonstrated to favour survival of pholcids in the presence of all sorts of predatory spiders.

Transitive predatory relationships of spider species (Arachnida, Araneae) in laboratory tests.

Interspecific predation of spiders was studied in the laboratory in view of possible competition in the wild. Certain species killed other species even if handicapped by smaller size. Thirty eight spider species were involved in such a relationship and their predatory relationships were significantly reliable and transitive ('linear' or 'non-triangular'). A theridiid species (Theridion tinctum) showed the highest rank in terms of killing seven 'beta species', i.e. species capable of killing at least one alien species of larger size than themselves. Another theridiid (Steatoda grossa) obtained the second rank by killing five beta species. Experiments in both the wild and laboratory may, further, investigate other factors than body size that may be relevant to competition, such as behaviour-related characteristics (e.g. web structure and biting speed) and ecological factors (e.g. different susceptibilities of the species to parasite or predator attack).

Lateralization of trunk muscle volume, and lateralization of swimming turns of fish responding to external stimuli.

A significant bias towards right-hand startle C-bends was found in vibration-stimulated zebra- and goldfish, but not in guppies and four Cichlid species. The goldfish right bias was significantly larger if they turned their head towards than away from the vibratory stimulus. In an undisturbed situation the fast swimming-turns of isolated goldfish and grouped zebrafish were significantly right-biased, especially so when attacked by group mates. In contrast, the slow turns were significantly left-biased, except for female zebrafish showing significantly right-biased slow turns during periods of non-attack by group mates. The contrast in left-right-bias between fast and slow turns may perhaps be explained by a white-muscle-mass bias to the right versus a red-muscle bias to the left, especially so in the anal region of the trunk of the zebrafish, because fast swimming is mainly powered by white muscle in contrast to red-muscle-powered slow swimming. Fish taxa that occur in open-water habitats and which are more often exposed to predatory fish might have evolved stronger muscular and behavioral lateralizations than more substrate-bound fish taxa.

Aggressive behaviour of two swordtail colour breeds (Xiphophorus, Poeciliidae) in a prior residence situation.

Males of two swordtail colour breeds (Xiphophorus) were tested for differences related to aggression in a prior residency situation. The median latency time of the first dominance sign, the first attack, and the first approach was significantly shorter in the red than in the black breed, while these differences were not present when resident and newcomer or the larger and the smaller member of the pair were compared, either in the two breeds separately, or in the two breeds combined. The significance of these differences in agonistic behaviour is discussed in relation to resource holding power and colour variants in fish.