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Social heterosis is when individuals in groups or neighbourhoods receive a mutualistic benefit from across-individual genetic diversity. Although it can be a viable evolutionary mechanism to maintain allelic diversity at a given locus, its efficacy at maintaining genome-wide diversity is in question when multiple loci are being simultaneously selected. Therefore, we modelled social heterosis in a population of haploid genomes of two- or three-linked loci. With such linkages, social heterosis decreases gametic diversity, but maintains allelic diversity. Genomes tend to survive as complimentary pairs, with alternate alleles at each locus (e.g. the pair AbC and aBc). The outcomes of selection appear similar to fitness epistasis but are novel in the sense that phenotypic interactions occur across rather than within individuals. The model’s results strongly suggest that strong linkage across gene loci actually increases the probability that social heterosis maintains significant genetic diversity at the level of the genome. [ABSTRACT FROM AUTHOR]

Genetic diversity in species is often high in spite of directional selection or strong genetic drift. One resolution to this paradox may be through fitness benefits arising from interactions of genetically diverse individuals. Advantageous phenotypes that are impossible in single individuals (e.g. being simultaneously bold and shy) can be expressed by groups composed of genetically different individuals. Genetic diversity, therefore, can produce mutualistic benefits shared by all group members. We define this effect as ‘social heterosis’, and mathematically demonstrate maintenance of allelic diversity when diverse groups or neighbourhoods are more reproductively successful than homogenous ones. Through social heterosis, genetic diversity persists without: frequency dependence within groups, migration, balancing selection, genetic linkages, overdominance, antagonistic pleiotropy or nonrandom allele assortment. Social heterosis may also offer an alternative evolutionary pathway to cooperation that does not require clustering of related individuals, nepotistic favouritism towards kin, or overt reciprocity. [ABSTRACT FROM AUTHOR]

The invasive success of the exotic Argentine ant [ Linepithema humile (Mayr)] is often closely tied to year-round availability of water sources. Previous studies suggest that the location of such water sources can strongly influence activity patterns of colonies and may be a key predictor of building infestations. We studied activity patterns of Argentine ants in relation to water and food resources in two open-air structures (aviaries). In one series of manipulations, ant activity inside the aviaries was significantly reduced with the placement of numerous water sources around the outside. Inside activity increased again when the outside water sources were removed. A second series of manipulations involved the placement of water sources at targeted locations outside of the structures. Ant activity inside the aviaries consistently shifted significantly closer to these targeted sites. The results suggest that providing a reliable water source to Argentine ant colonies exterior to buildings can be a non-chemical method of integrated pest management for reducing ant infestations. Independent of our manipulations, L. humile activity levels predictably declined with time of day, but these changes were uncorrelated with observed surface temperatures. In fact, activity was often noted at surface temperatures higher than those that cause worker mortality under laboratory conditions. This suggests that L. humile exhibits a consistent temperature-independent circadian activity pattern of reduced foraging in afternoons relative to mornings. [ABSTRACT FROM AUTHOR]