Client fish ectoparasite loads and cleaner shrimp Urocaridella sp c hunger levels affect cleaning behaviour

Cleaning is a classic example of mutualism and determining the factors that maintain the balance between the costs and benefits for mutualist partners can assist our understanding of how cleaning relationships are maintained. Optimal foraging theory suggests two factors that might help to maintain the relationship between cleaners and their clients: client ectoparasite load and cleaner hunger levels. The ecological relevance and importance of foraging by cleaner fish in marine systems has been demonstrated repeatedly, yet there is little information available on this behaviour in cleaner shrimp. To determine whether cleaner shrimp base their choice of client fish on food patch quality (i.e. client fish ectoparasite load) we offered the yellow-beaked cleaner shrimp Urocaridella sp. c a choice of parasitized and unparasitized rock cods, Cephalopholis cyanostigma. To determine whether cleaner shrimp hunger levels influence cleaning time, we manipulated hunger levels in Urocaridella sp. c and examined their behaviour towards parasitized client fish. Cleaner shrimp preferred parasitized to unparasitized client fish and food-deprived cleaner shrimp cleaned parasitized rock cods more frequently than satiated cleaner shrimp did. Therefore, variations in client fish ectoparasite load and cleaner shrimp hunger level are two factors that affect the balance in this mutualism. Finally, our results meet some of the assumptions of biological market theory, a framework used to understand cooperative interactions, and thus this framework is suggested for future studies on this cleaning system.

Do chimpanzees (Pan troglodytes) understand single invisible displacement?

Previous research suggests that chimpanzees understand single invisible displacement. However, this Piagetian task may be solvable through the use of simple search strategies rather than through mentally representing the past trajectory of an object. Four control conditions were thus administered to two chimpanzees in order to separate associative search strategies from performance based on mental representation. Strategies involving experimenter cue-use, search at the last or first box visited by the displacement device, and search at boxes adjacent to the displacement device were systematically controlled for. Chimpanzees showed no indications of utilizing these simple strategies, suggesting that their capacity to mentally represent single invisible displacements is comparable to that of 18-24-month-old children.

A possible smoking susceptibility locus on chromosome 11p12: Evidence from sex-limitation linkage analyses in a sample of Australian twin families

Many twin studies have identified sex differences in the influence of genetic and environmental factors on smoking behaviors. We explore the evidence for sex differences for smoking initiation and cigarette consumption in a sample of Australian twin families, and extend these models to incorporate sex differences in linkage analyses for these traits. We further examine the impact of including or excluding non-smokers in genetic analyses of tobacco consumption. Accounting for sex differences improved linkage results in some instances. We identified one region suggestive of linkage on chromosome 11p12. This locus, as well as another region identified on chromosome 6p12, replicates regions identified in previous studies.

Do chimpanzees (Pan troglodytes) and 2-year-old children (Homo sapiens) understand double invisible displacement?

Chimpanzees (Pan troglodytes) and young children (Homo sapiens) have difficulty with double invisible displacements in which an object is hidden in two nonadjacent boxes in a linear array. Experiment 1 eliminated the possibility that chimpanzees' previous poor performance was due to the hiding direction of the displacement device. As in Call (2001), subjects failed double nonadjacent displacements, showing a tendency to select adjacent boxes. In Experiments 2 and 3, chimpanzees and 24-month-old children were tested on a new adaptation of the task in which four hiding boxes were presented in a diamond-shaped array on a vertical plane. Both species performed above chance on double invisible displacements using this format, suggesting that previous poor performance was due to a response bias or inhibition problem rather than a fundamental limitation in representational capacity.

The effects of assessment type on verbal ratings of conditional stimulus valence and contingency judgments: Implications for the extinction of evaluative learning

Recent research on causal learning found (a) that causal judgments reflect either the current predictive value of a conditional stimulus (CS) or an integration across the experimental contingencies used in the entire experiment and (b) that postexperimental judgments, rather than the CS's current predictive value, are likely to reflect this integration. In the current study, the authors examined whether verbal valence ratings were subject to similar integration. Assessments of stimulus valence and contingencies responded similarly to variations of reporting requirements, contingency reversal, and extinction, reflecting either current or integrated values. However, affective learning required more trials to reflect a contingency change than did contingency judgments. The integration of valence assessments across training and the fact that affective learning is slow to reflect contingency changes can provide an alternative interpretation for researchers' previous failures to find an effect of extinction training on verbal reports of CS valence.

Hyperlocomotion associated with transient prenatal vitamin D deficiency is ameliorated by acute restraint

Transient prenatal vitamin D deficiency produces hyperlocomotion in the adult rat. The aim of this study was to examine the effects of acute restraint on the behaviour of DVD and control rats in the open field. Rats were conceived and born to developmentally vitamin D (DVD) deficient or replete (control) dams and, at 8 weeks of age, were monitored for 30 min in an open field using automated video tracking software. Half of the rats were restrained within a towel for 5 min immediately before the open field test. The remainder received minimal handling prior to the open field test. Repeating previous findings, DVD deficient animals had enhanced locomotion during the first 10 min of the open field test compared to control rats. By contrast, there were no differences in locomotor activity after acute restraint stress. The time rats spent in the corners and side of the open field was affected by prenatal diet. DVD rats spent less time in the corners and more time in the side than control rats across the whole 30 min test. This difference was not seen in rats with acute restraint stress. The time spent in the centre was not altered by prenatal diet or acute restraint. Thus, transient prenatal vitamin D deficiency induces a transient spontaneous hyperlocomotion in adulthood that is modulated by acute restraint stress. (c) 2006 Elsevier B.V. All rights reserved.

Evaluation of universal, indicated, and combined cognitive-behavioral approaches to the prevention of depression among adolescents

A cluster, stratified randomized design was used to evaluate the impact of universal, indicated, and combined universal plus indicated cognitive-behavioral approaches to the prevention of depression among 13- to 15-year-olds initially reporting elevated symptoms of depression. None of the intervention approaches differed significantly from a no-intervention condition or from each other on changes in depressive symptoms, anxiety, externalizing problems, coping skills, and social adjustment. All high-symptom students, irrespective of condition, showed a significant decline in depressive symptoms and improvement in emotional well-being over time although they still demonstrated elevated levels of psychopathology compared with the general population of peers at 12-month follow-up. There were also no significant intervention effects for the universal intervention in comparison with no intervention for the total sample of students in those conditions.