Sublethal copper toxicity and food response in the freshwater crayfish Cambarus bartonii (Cambaridae, Decapoda, Crustacea).

Food response preceding and following exposure to Cu concentrations of 0.00, 0.02, and 0.2 mg/L was observed in male and female Cambarus bartonii from an uncontaminated, freshwater lake. The animals were tested in a Y-maze. Control animals demonstrated food localization, and the treated animals, either no localization or slight food avoidance. The latency for localization in the Cu-exposed males increased. Females revealed slight increases in latency. There were no significant differences between the low and the high Cu concentration groups in food detection or latency. However, there was an increase in mortality in the higher concentration group and significant difference in mortality among three copper concentrations (P<0.02). Females seem to recover from Cu-induced impairment slightly faster than males, suggesting a more efficient mechanism for detoxifying copper. Female mortality, however, remained equally high in the high Cu concentration group. The toxic effects of copper persist after removal of the toxicant and occur at concentrations much lower than reported lethal levels.

Different aggressive behaviours are exaggerated by facing vs. broadside subliminal stimuli shown to socially isolated Siamese fighting fish, Betta splendens.

We report and analyse some features of a new phenomenon: socially isolated Betta splendens become extremely hyper-aggressive after seeing brief glimpses of fish models or mirrors. These brief glimpses are below the threshold for releasing aggressive display, so they are considered subliminal aggressive stimuli. The hyper-aggressiveness was observed to last for weeks. To confirm that hyper-aggressiveness was dependent upon the aggressive significance of the subliminal stimuli, we presented socially isolated Betta splendens with subliminal models in either a `facing' posture (used mainly in aggressive contexts), or a `broadside' posture (used in many social contexts). The fish shown the aggressive `facing' subliminal stimuli became more aggressive, while those shown `broadside' stimuli performed more generalized advertisement behaviours. The display posture of the model, which may incorporate specific features relevant to aggression, therefore determined how the subliminal aggressive stimuli altered subsequent aggressiveness. This difference was also persistent. Subliminal stimuli may thus be implicated in the hyper-aggressiveness so often reported after social isolation.

Increased aggressiveness after brief social isolation of adult fish: a connectionist model which organizes this literature.

We examine the literature on fishes' aggressive behaviour after social isolation, in the light of a connectionist adaptive control system model for robot motivation and learning. If animals used the model's motivation modules, then social isolation would cause two simultaneous processes to occur-one progressively increasing motivation, the other decreasing display readiness. The readiness decrement would have the temporal flexibility typical of motivation changes, and would disappear soon after social stimuli reappeared. The incremental effect would be synaptic, and would be temporally more stable. Due to this stability difference, brief post-isolation aggression tests would tend to show that social isolates have depressed attack readiness, but longer tests would uncover the underlying increase in aggressiveness. In reviewing the literature, we find that this has been overwhelmingly the case. A new hypothesis about the adaptive value of the increase of aggression during isolation is outlined, which may help make the phenomenon more understandable.

Chemical sex discrimination in the crayfishProcambarus clarkii: Role of antennules.

Chemical sex discrimination of conspecifics by male and female crayfish (Procambarus clarkii) was tested. Intact female subjects were more attentive in the presence of stimulus water from males than from females and showed more aggressive postures in the presence of stimulus water from females than from males. Intact males showed more aggressive postures in the presence of stimulus water from males than from females. Females and males with only one inner antennule ramus and one outer ramus performed discrimination and localization almost as well as intact subjects. Subjects with only the two inner rami or only the two outer rami were disadvantaged in either responding to the stimuli or localizing them. The relevance of this outcome to previous conflicting reports on the use of antennules in sex discrimination in crayfish is discussed.

Social isolation increases social display after priming in Betta splendens but decreases aggressive readiness.

We socially isolated adult, male Siamese fighting fish for 0 to 7 weeks but avoided sensory deprivation, and then measured aggressive display as the fish responded to a series of novel models. Isolates displayed much more strongly than non-isolates to the last model of the series, and display intensity became monotonically stronger with longer social isolation. By contrast, display to the first model seen after isolation was weaker the longer the social isolation. A second experiment compared responses of fish after three weeks during which controls displayed to a conspecific for two minutes every two days, while isolates saw a complex visual stimulus which did not release display. Again, isolates had depressed display readiness, but higher display rates once they were primed. This result supports the hypothesis that social isolation has two effects on aggressive display in Betta, causing decreasing readiness to display, but leading to greater display rates once fish are 'primed'. We discuss two models which predict these phenomena, and show that one of them suggests a new understanding of the function of motivational increases when aggression is 'dammed up'. Methodological issues relevant for examining the rodent behavior literature in the light of the new model are discussed.

Chemical detection of conspecifics in the crayfishProcambarus clarkii: Role of antennules.

Tests with female crayfish (Procambarus clarkii) confirm that conspecifics can be detected chemically. The subjects were more attentive in the presence of water from a stranger's tank than in the presence of water from their own tank. Animals with intact antennules performed this discrimination best, but animals with one intact inner ramus and one intact outer ramus also clearly responded. Conspecific chemical discrimination after loss of both inner or both outer rami was weak (trial 2) or absent (trial 1). The relevance of this outcome to previous conflicting reports on the use of antennules in sex and species discrimination in crayfish is discussed.

Observations of a probable change in the solar radius between 1715 and 1979.

Solar eclipses were observed from locations near both edges of the paths of totality in England in 1715, in Australia in 1976, and in North America in 1979. Analysis of these observations shows that the solar radius has contracted by 0.34 +/- 0.2 arc second in 264 years.

The adaptive role of maladaptive neurosis.

A hypothesis is proposed which postulates that repeated failure in social competition may lead to a "neurotic" maladaptive vicious cycle. It is proposed that by magnifying genetically transmitted differences in fitness, this mechanism emphasizes the superiority of the better endowed, both in mate choice and in fitness of offspring. Species displaying high plasticity and flexibility, the concomitants of high intellectual ability, may be more susceptible to neurosis, hence may be more likely to be influenced by the vicious cycle mechanism operating at the ontogenetic level. Such species would display an accelerated rate of adaptation and intelligence. Some of the implications of the hypothesis for sexual selection, change in status, and preventive mental health are discussed.