PubMed · 15412675
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F GREWEL. 1950. [Aggression and aggressivity].. https://pubmed.ncbi.nlm.nih.gov/15412675/
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An F (5) generation of an advanced inter-cross between red junglefowl (wild-type) and White Leghorn (domesticated) was used to investigate earlier findings suggesting that a mutation in the plumage color gene PMEL17 protects against victimization to feather pecking (FP). F (4) parents were selected according to genotype to produce PMEL17 homozygous offspring (i/i and I/I respectively). Birds were raised and their behavior recorded in groups of either two wild-type i/i (dark colored) and one white I/I, or two I/I and one i/i. In addition each bird was tested for feather preference, reaction to novelty, open-field activity, fear for humans, and tonic-immobility. In the home-pens, i/i birds were more feather pecked and had poorer feather condition than I/I birds. No pecking preference for immobile dark colored feathers was observed. In the open-field test i/i birds vocalized more and earlier than I/I birds, and in the fear-for-human test I/I birds had higher activity at 21 weeks of age. No other behavior differences were observed, but clearly, genotypes of PMEL17 affected some aspects of behavior. Such behavioral differences might be important aspects of the mechanism which predispose i/i individuals for being victims of FP.
This study examined associations between victimization by peers and intention to respond to provocative events as a function of anger arousal and motivation to improve the situation in a cross-sectional sample of school-age children (N = 506, 260 males, 246 females). Results demonstrated that more intense anger and more retaliatory motivation were positively associated with intentions to aggress and with frequency of victimization. The association between aggressive intentions to respond to anger provocation and victimization could be accounted for by subjective feelings of anger and motivation to retaliate. The contribution of emotion processes was stronger for boys than for girls. A post hoc examination of non-bullying participants revealed that motivation accounted for aggressive intentions among the non-bullies. Results support including anger management programs in prevention efforts that target the school climate and victims' risk for psychopathology.
Defended insects often advertise their unprofitability to potential predators using conspicuous aposematic coloration. Many aposematic insects are also gregarious, and it has been suggested that the aggregation of defended prey may have facilitated the evolution of aposematic coloration. Empirical studies have demonstrated that birds are more wary of aggregated aposematic prey, and learn to avoid them more quickly than solitary prey. However, many aposematic insects survive being attacked by birds, and the effect of aggregation on post-attack survival has not previously been investigated. Using domestic chicks as predators and artificially manipulated mealworms as prey, we provide empirical evidence that predators attack aggregated aposematic prey more forcefully than solitary prey, reducing the likelihood of prey surviving an attack. Hence, we suggest that previous works concluding that aggregation was an important pre-requisite for the evolution of aposematism may have overestimated the fitness benefits of aggregation, since aggregated prey may be attacked less but are also less likely to survive an attack.