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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2008.10.016 Byline: Colby J. Tanner (a), Frederick R. Adler (a)(b) Abstract: Animals assess many factors when choosing how aggressively to behave during interspecific competitive interactions. Aggressive behaviour can help win resources, but it can also be costly. Here we tested how context such as competitor familiarity, habitat type and resource value affect competitive behaviour using two ant species, Formica xerophila and F. integroides. We found that competitive encounters within an individual's territory yielded more aggressive interactions than encounters in a neutral arena, and aggression towards competitors increased with resource value. Using a recently developed design combining behaviour assays between live ant dyads and ants paired with glass beads chemically resembling competitors, we isolated an individual's behaviour during an encounter to show that its behaviour can be significantly affected by the behaviour of its competitor during the interaction. Furthermore, we determined that context can affect each species differently, and that these differences are consistent with differences in overall fighting abilities. Formica integroides from trees (but not from nests) behaved differently towards live and artificial F. xerophila. Formica integroides are behaviourally dominant, which facilitates a strategy wherein individuals aggressively defend the nest but reciprocate the behaviours of their opponents (showing an interspecific Tit-for-Tat strategy) when defending less valuable locations. Formica xerophila are generally submissive, which favours a highly context-dependent strategy. In particular, F. xerophila discriminate between familiar and unfamiliar F. integroides, and behave more aggressively towards foreign competitors than towards neighbouring competitors. Differences between species' behaviours suggest that these interspecific interactions are dynamic context-dependent associations that cannot be reduced to a static dominance hierarchy. Author Affiliation: (a) Department of Biology, University of Utah (b) Department of Mathematics, University of Utah Article History: Received 5 September 2008; Revised 17 October 2008; Accepted 24 October 2008 Article Note: (miscellaneous) MS. number: A08-00574

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2008.04.022 Byline: Colby J. Tanner Abstract: In fights between groups of social animals, willingness of an individual to fight increases with group size. To better understand how individuals assess numerical state and coordinate group behaviour, I investigated how individual ants, Formica xerophila collect information about group size prior to a competitive encounter, and how this information affects F. xerophila behaviour towards a closely related competitor, F. integroides. To determine how F. xerophila collect information regarding numerical state, I performed aggression bioassays between F. xerophila and F. integroides in which F. xerophila individuals were experimentally exposed to isolated communication pathways (either physical contact or potential chemical interactions) with group members prior to a competitive encounter. I found that individual F. xerophila in direct contact with group members prior to encountering F. integroides were more aggressive during the interaction than were F. xerophila individuals in contact with group members via potential pheromones either in the air or on the ground prior to the encounter. Additionally, individual F. xerophila exposed directly to group member surface hydrocarbons prior to a competitive encounter were just as aggressive as ants exposed to live group members. Aggression towards competitors, however, was only induced after approximately 25min of direct exposure, but individuals remained aggressive for at least 25min after hydrocarbon stimuli were removed. The same compounds that allowed individual ants to distinguish group members from nonmembers also induced aggressive behaviour. These results provide detail into how animals can collect and use information regarding group size to coordinate a group response. Author Affiliation: Department of Biology, University of Utah, Salt Lake City, U.S.A. Article History: Received 18 February 2008; Revised 31 March 2008; Accepted 14 April 2008 Article Note: (miscellaneous) MS. number: A08-00098

Arbuscular mycorrhizal fungi (AMF) are among the most abundant symbionts of plants, improving plant productivity and diversity. They are thought to mostly grow vegetatively, a trait assumed to limit adaptability. However, AMF can also harbor genetically different nuclei (nucleotypes). It has been shown that one AMF can produce genotypically novel offspring with proportions of different nucleotypes. We hypothesized that (1) AMF respond rapidly to a change of environment (plant host) through changes in the frequency of nucleotypes; (2) genotypically novel offspring exhibit different genetic responses to environmental change than the parent; and (3) genotypically novel offspring exhibit a wide range of phenotypic plasticity to a change of environment. We subjected AMF parents and offspring to a host shift. We observed rapid and large genotypic changes in all AMF lines that were not random. Genotypic and phenotypic responses were different among offspring and their parents. Even though growing vegetatively, AMF offspring display a broad range of genotypic and phenotypic changes in response to host shift. We conclude that AMF have the ability to rapidly produce variable progeny, increasing their probability to produce offspring with different fitness than their parents and, consequently, their potential adaptability to new environmental conditions. Such genotypic and phenotypic flexibility could be a fast alternative to sexual reproduction and is likely to be a key to the ecological success of AMF. [ABSTRACT FROM AUTHOR]