The Social Life of Pigs: Changes in Affiliative and Agonistic Behaviors following Mixing

This study investigated potentially affiliative behaviors in grow-finish pigs, how these behaviors changed over time and their relationship to agonistic behaviors. A total of 257 Yorkshire barrows were observed for agonistic (reciprocal fights, attacks) and affiliative (nosing, play, non-agonistic contact) behaviors after mixing (at 10 weeks of age), and weeks 3, 6, and 9 after mix. The least square means of affiliative behaviors were compared across time points. Relationships among affiliative and agonistic behaviors were assessed using generalized linear mixed models. Non-agonistic contact with conspecifics increased until week 6 then remained stable between weeks 6 and 9. Nosing was highest at mix, then decreased in the following weeks. Play was lowest at mix and highest at week 3. Affiliative behaviors were negatively related with aggression at mix (p < 0.001). Pigs who engaged in play and nosing behaviors were more likely to be involved in agonistic interactions in the weeks after mixing (p < 0.05), while pigs engaging in non-agonistic contact were less likely to be involved in agonistic interactions (p < 0.001). There appear to be relationships between affiliative and agonistic behaviors in pigs, with contact being the most predictive of less aggression. Future studies could focus on promoting positive non-agonistic contact in unfamiliar pigs as a way to mitigate aggressive interactions.

Costs dictate strategic investment in dominance interactions

Dominance is important for access to resources. As dominance interactions are costly, individuals should be strategic in whom they interact with. One hypothesis is that individuals should direct costly interactions towards those closest in rank, as they have most to gain—in terms of attaining or maintaining dominance—from winning such interactions. Here, we show that male vulturine guineafowl ( Acryllium vulturinum ), a gregarious species with steep dominance hierarchies, strategically express higher-cost aggressive interactions towards males occupying ranks immediately below themselves in their group's hierarchy. By contrast, lower-cost aggressive interactions are expressed towards group members further down the hierarchy. By directly evaluating differences in the strategic use of higher- and lower-cost aggressive interactions towards competitors, we show that individuals disproportionately use highest-cost interactions—such as chases—towards males found one to three ranks below themselves. Our results support the hypothesis that the costs associated with different interaction types can determine their expression in social groups with steep dominance hierarchies. This article is part of the theme issue ‘The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies’.

Factors Affecting Human-Directed Aggression Resulting in Dog Bites: Contextual Aspects of the Biting Incidents

Using a web-based questionnaire with 29 close- and open-ended questions about 400 self-reported dog-biting incidents in Slovenia, this research investigated the contexts of dog bites, focusing on characteristics of the dogs and the descriptions of the situations to identify the main risk factors for the occurrence of dog bites. Even though it has been suggested that most dog bites occur during initially non-aggressive interactions with the dog (e.g., during petting, playing), in our study we discerned a wide variety of contexts, including those in which the person did not intend to interact with the dog. Most victims reported unprovoked bites during fast movements near the dog, while coming into close proximity, and during incidents without a reason. These incidents more likely occurred in public than private places and were associated with purebred dogs with a history of aggression.

7 Behavioral Indicators of Post-weaning Stress Susceptibility in Cross-fostered Pigs

Cross-fostering is a common swine husbandry practice; however, little research has focused on the effects of foster stress on piglets post-weaning. This study evaluated the effect of cross-fostering on behavioral indicators of post-weaning stress susceptibility. Litters (n = 40) were allocated to 1 of 2 treatments: control (CON) and foster. Three piglets (FOS) from each CON litter were randomly selected and moved to a foster litter 12–24 h post-farrowing, where they were nursed along resident (RES) piglets until weaning (approximately 18 d of age). At 21- and 28-d post-weaning, a male and female piglet from each treatment (FOS, RES, CON) underwent 1 of 2 behavior tests: social isolation and social confrontation. Both tests were conducted in an isolated 1.22 × 1.22 m novel pen. For social isolation, escape attempts, movement between floor quadrants (i.e. locomotion), defecation, and urination events were counted. For social confrontation, the latency to first aggressive interaction and the number of aggressive interactions were quantified. All data were analyzed using the GLIMMIX procedure in SAS. The CON piglets moved between quadrants more frequently than RES piglets (P = 0.02), while FOS piglets moved between quadrants intermediate to (but not different from) CON and RES piglets (P = 0.44 and 0.12, respectively). Females moved between quadrants more frequently than males (P &lt; 0.0001). The latency to first aggressive interaction was shorter in FOS piglets compared to CON piglets (P = 0.048). There was a treatment by sex interaction (P &lt; 0.01) for number of aggressive interactions, with CON and RES females having more aggressive interactions than their male counterparts (P = 0.04 for both) while FOS females had fewer aggressive interactions than FOS males (P = 0.007). No additional differences were detected (all P &gt; 0.05). Overall, these results provide little evidence that FOS piglets exhibit an increase in behavioral stress susceptibility post-weaning. However, future work should expand upon and clarify the social confrontation findings.

Sex-dependent resource defense in a nectar-feeding bat

Aggressive resource defense spans from the transient monopolization of a resource up to the long-term maintenance of a territory. While such interference competition is common in nectar-feeding birds, reports in nectar-feeding bats are rare. Glossophaga bats have been observed to temporarily defend flowers but the extent of this monopolization, its effects on nectar intake, and underlying sexual differences remain unknown. We investigated resource defense behavior of Glossophaga mutica in the laboratory. We presented bats with two patches of computer-controlled artificial flowers and tracked individual nectar intake. Furthermore, we established an automated method for detecting aggressive interactions at the artificial flowers. Theoretical models of interference competition predict more aggressive interactions when resources are spatially more clumped. To test this, we varied resource distribution across two patches from clumped to distributed and monitored bats' interactions in one male, one female, and four mixed-sex groups. Males engaged in aggressive interactions more often than females and in each group some individuals defended clumped artificial flowers against others. Subordinate males experienced a substantial decrease in nectar intake, while females were only marginally affected by male aggression. These results suggest that aggressive interactions and their effect on nectar intake are sex-dependent in G. mutica. Furthermore, aggressive interactions were more frequent and resource defense was only successful when resources were clumped. Our experimental set-up allowed us to perform an automated test of models of interference competition with a mammal under controlled laboratory conditions. This approach may pave the way for similar studies with other animals.

A resource-poor developmental diet reduces adult aggression in male Drosophila melanogaster

Aggressive behaviours occur throughout the animal kingdom and agonistic contests often govern access to resources. Nutrition experienced during development has the potential to influence aggressive behaviours in adults through effects on growth, energy budgets and an individual’s internal state. In particular, resource-poor developmental nutrition might decrease adult aggression by limiting growth and energy budgets, or alternatively might increase adult aggression by enhancing motivation to compete for resources. However, the direction of this relationship—and effects of developmental nutrition experienced by rivals—remains unknown in most species, limiting understanding of how early-life environments contribute to variation in aggression. We investigated these alternative hypotheses by assessing male-male aggression in adult fruit flies, Drosophila melanogaster, that developed on a low-, medium- or high-resource diet, manipulated via yeast content. We found that a low-resource developmental diet reduced the probability of aggressive lunges in adults, as well as threat displays against rivals that developed on a low-resource diet. These effects appeared to be independent of diet-related differences in body mass. Males performed relatively more aggression on a central food patch when facing rivals of a low-resource diet, suggesting that developmental diet affects aggressive interactions through social effects in addition to individual effects. Our finding that resource-poor developmental diets reduce male-male aggression in D. melanogaster is consistent with the idea that resource budgets mediate aggression and in a mass-independent manner. Our study improves understanding of the links between nutrition and aggression.Significance statementEarly-life nutrition can influence social behaviours in adults. Aggression is a widespread social behaviour with important consequences for fitness. Using the fruit fly, Drosophila melanogaster, we show that a poor developmental diet reduces aspects of adult aggressive behaviour in males. Furthermore, males perform more aggression near food patches when facing rivals of poor nutrition. This suggests that early-life nutrition affects aggressive interactions through social effects in addition to individual effects.

Intersexual behaviour and effect of male and female intruders in the Tenerife skink (Chalcides viridanus). Is there any mate guarding?

Individuals avoid potential competitors accessing mates during reproductive periods staying close to the mate and chasing same-sex intruders. We studied intersexual relationships and the effect of intruders of each sex in male-female pairs of Chalcides viridanus. We analysed: (1) behaviour patterns of each pair member and the time they spent together during three successive days in March, April and May; and (2) interactions of intruder-resident of the same sex, during each of the three months. Sexual and monthly differences appeared in intersexual behaviour as the breeding season progressed. In each month, time together was significantly larger on the third trial day than in the two previous days but did not significantly change between months. Sexes did not significantly differ in intruder-resident behaviours, but male aggressive interactions were significantly larger in May. Intruder females performed higher frequencies of non-agonistic behaviours than residents. We discuss all these results considering the predictions of mate guarding hypothesis.