Is leadership a reliable concept in animals? An empirical study in the horse

International audienceLeadership is commonly invoked when accounting for the coordination of group movements in animals, yet it remains loosely defined. In parallel, there is increased evidence of the sharing of group decisions by animals on the move. How leadership integrates within this recent framework on collective decision-making is unclear. Here, we question the occurrence of leadership in horses, a species in which this concept is of prevalent use. The relevance of the three main definitions of leadership - departing first, walking in front travel position, and eliciting the joining of mates - was tested on the collective movements of two semi-free ranging groups of Przewalski horses (Equus ferus przewalskii). We did not find any leader capable of driving most group movements or recruiting mates more quickly than others. Several group members often displayed pre-departure behaviours at the same time, and the simultaneous departure of several individuals was common. We conclude that the decision-making process was shared by several group members a group movement (i.e., partially shared consensus) and that the leadership concept did not help to depict individual departure and leading behaviour across movements in both study groups. Rather, the different proxies of leadership produced conflicting information about individual contributions to group coordination. This study discusses the implications of these findings for the field of coordination and decision-making research

The Role of relA and spoT in Yersinia pestis KIM5+ Pathogenicity

The ppGpp molecule is part of a highly conserved regulatory system for mediating the growth response to various environmental conditions. This mechanism may represent a common strategy whereby pathogens such as Yersinia pestis, the causative agent of plague, regulate the virulence gene programs required for invasion, survival and persistence within host cells to match the capacity for growth. The products of the relA and spoT genes carry out ppGpp synthesis. To investigate the role of ppGpp on growth, protein synthesis, gene expression and virulence, we constructed a ΔrelA ΔspoT Y. pestis mutant. The mutant was no longer able to synthesize ppGpp in response to amino acid or carbon starvation, as expected. We also found that it exhibited several novel phenotypes, including a reduced growth rate and autoaggregation at 26°C. In addition, there was a reduction in the level of secretion of key virulence proteins and the mutant was>1,000-fold less virulent than its wild-type parent strain. Mice vaccinated subcutaneously (s.c.) with 2.5×104 CFU of the ΔrelA ΔspoT mutant developed high anti-Y. pestis serum IgG titers, were completely protected against s.c. challenge with 1.5×105 CFU of virulent Y. pestis and partially protected (60% survival) against pulmonary challenge with 2.0×104 CFU of virulent Y. pestis. Our results indicate that ppGpp represents an important virulence determinant in Y. pestis and the ΔrelA ΔspoT mutant strain is a promising vaccine candidate to provide protection against plague

Cues of control modulate the ascription of object ownership

Knowing whether an object is owned and by whom is essential to avoid costly conflicts. We hypothesize that everyday interactions around objects are influenced by a minimal sense of object ownership grounded on respect of possession. In particular, we hypothesize that tracking object ownership can be influenced by any cue that predicts the establishment of individual physical control over objects. To test this hypothesis we used an indirect method to determine whether visual cues of physical control like spatial proximity to an object, temporal priority in seeing it, and touching it influence this minimal sense of object ownership. In Experiment 1 participants were shown a neutral object located on a table, in the reaching space of one of two characters. In Experiment 2 one character found the object first; then another character appeared and saw the object. In Experiments 3 and 4, spatial proximity, temporal priority, and touch are pitted against each other to assess their relative weight. After having seen the scenes, participants were required to judge the sensibility of sen- tences in which ownership of the object was ascribed to one of the two characters. Responses were faster when the objects were located in the reaching space of the characterto whom ownership was ascribed in the sentence and when ownership was ascribed to the character who finds the object first. When contrasting the relevant cues, results indicate that touch is stronger than temporal priority in modulating the ascription of object ownership. However, all these effects were also influenced by contextual social cues like the gender of both characters and participants, the presence of a third-party observer, and the co-presence of characters. Consistent with our hypothesis, our results provide evidence that many different cues of physical control influence the ascription of ownership in daily social contexts