Supercolonial structure of invasive populations of the tawny crazy ant Nylanderia fulva in the US

Background: Social insects are among the most serious invasive pests in the world, particularly successful at monopolizing environmental resources to outcompete native species and achieve ecological dominance. The invasive success of some social insects is enhanced by their unicolonial structure, under which the presence of numerous queens and the lack of aggression against non-nestmates allow high worker densities, colony growth, and survival while eliminating intra-specific competition. In this study, we investigated the population genetics, colony structure and levels of aggression in the tawny crazy ant, Nylanderia fulva, which was recently introduced into the United States from South America. Results: We found that this species experienced a genetic bottleneck during its invasion lowering its genetic diversity by 60%. Our results show that the introduction of N. fulva is associated with a shift in colony structure. This species exhibits a multicolonial organization in its native range, with colonies clearly separated from one another, whereas it displays a unicolonial system with no clear boundaries among nests in its invasive range. We uncovered an absence of genetic differentiation among populations across the entire invasive range, and a lack of aggressive behaviors towards conspecifics from different nests, even ones separated by several hundreds of kilometers. Conclusions: Overall, these results suggest that across its entire invasive range in the U.S.A., this species forms a single supercolony spreading more than 2000 km. In each invasive nest, we found several, up to hundreds, of reproductive queens, each being mated with a single male. The many reproductive queens per nests, together with the free movement of individuals between nests, leads to a relatedness coefficient among nestmate workers close to zero in introduced populations, calling into question the stability of this unicolonial system in which indirect fitness benefits to workers is apparently absent.Fil: Eyer, Pierre André. Texas A&M University; Estados UnidosFil: McDowell, Bryant. Texas A&M University; Estados UnidosFil: Johnson, Laura N. L.. Texas A&M University; Estados UnidosFil: Calcaterra, Luis Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fundación para el Estudio de Especies Invasivas; ArgentinaFil: Fernández, María Belén. Fundación para el Estudio de Especies Invasivas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Shoemaker, Dewayne. University of Tennessee; Estados UnidosFil: Puckett, Robert T.. Texas A&M University; Estados UnidosFil: Vargo, Edward L.. Texas A&M University; Estados Unido

Causes and Consequences of Intraspecific Variation in Behavior of the Red Imported Fire Ant

Organisms vary at the individual and population level in many ecologically relevant traits. This study documents and quantifies colony-level variation in ecologically important behaviors of a widespread invasive social insect, demonstrates multitrophic ecological effects of this colony-level variation, and explores genetic factors that may affect and predict behavior at the colony-level. I quantified significant, persistent regional and colony-level variation in the red imported fire ant (Solenopsis invicta) in behaviors such as extra-nest activity, exploration, and resource discovery speed and recruitment effort. Colony behavior correlated with both colony productivity and colony growth. Using single-lineage colonies, I estimated broad-sense heritability of between 0.45 and 0.5 for the observed colony behaviors. I created experimental microcosms comprised of fire ant colonies, plants, and insect herbivores. Differences in fire ant colony behavior linked to carbohydrate attraction directly impacted herbivore mortality and indirectly impacted plant damage. I quantified colony differences colony differences in the expression of the fire ant foraging gene (sifor) as well as colony-level differences in behavior for fire ant colonies collected from across a large area of Texas. Expression of sifor was more than three-fold higher in fire ant foragers than in fire ant workers in the interior of the nest, and colony-level differences in sifor expression of foragers and interior workers correlated with colony behavior. Higher sifor expression in foragers correlated with higher foraging activity, exploratory activity, and recruitment to nectar in fire ant colonies. Finally, I explored the hypothesis that fire ant foundress groups could maximize inclusive fitness benefits and alter cooperative and competitive behaviors in response to cues indicating higher relatedness of foundresses. I found that group and queen performance was significantly affected by group composition. Groups composed of foundresses that were less likely to be related produced no more workers than queens founding alone, while groups composed of foundresses from the same site produced the most workers of all group types. The conclusions of this study have widespread implications for many social insects and their ecological interactions. By further exploring these effects at the mechanistic, organismal, and ecological level we will improve our understanding of collective behavior, social evolution, and intraspecific variation

Information Processing in Social Insect Networks

abstract: Investigating local-scale interactions within a network makes it possible to test hypotheses about the mechanisms of global network connectivity and to ask whether there are general rules underlying network function across systems. Here we use motif analysis to determine whether the interactions within social insect colonies resemble the patterns exhibited by other animal associations or if they exhibit characteristics of biological regulatory systems. Colonies exhibit a predominance of feed-forward interaction motifs, in contrast to the densely interconnected clique patterns that characterize human interaction and animal social networks. The regulatory motif signature supports the hypothesis that social insect colonies are shaped by selection for network patterns that integrate colony functionality at the group rather than individual level, and demonstrates the utility of this approach for analysis of selection effects on complex systems across biological levels of organization.The article is published at http://journals.plos.org/plosone/article?id=10.1371/journal.pone.004033

The Wisdom of the Acorn: Social Foraging in Temnothorax ants

abstract: The coordination of group behavior in the social insects is representative of a broader phenomenon in nature, emergent biological complexity. In such systems, it is believed that large-scale patterns result from the interaction of relatively simple subunits. This dissertation involved the study of one such system: the social foraging of the ant Temnothorax rugatulus. Physically tiny with small population sizes, these cavity-dwelling ants provide a good model system to explore the mechanisms and ultimate origins of collective behavior in insect societies. My studies showed that colonies robustly exploit sugar water. Given a choice between feeders unequal in quality, colonies allocate more foragers to the better feeder. If the feeders change in quality, colonies are able to reallocate their foragers to the new location of the better feeder. These qualities of flexibility and allocation could be explained by the nature of positive feedback (tandem run recruitment) that these ants use. By observing foraging colonies with paint-marked ants, I was able to determine the `rules' that individuals follow: foragers recruit more and give up less when they find a better food source. By altering the nutritional condition of colonies, I found that these rules are flexible - attuned to the colony state. In starved colonies, individual ants are more likely to explore and recruit to food sources than in well-fed colonies. Similar to honeybees, Temmnothorax foragers appear to modulate their exploitation and recruitment behavior in response to environmental and social cues. Finally, I explored the influence of ecology (resource distribution) on the foraging success of colonies. Larger colonies showed increased consistency and a greater rate of harvest than smaller colonies, but this advantage was mediated by the distribution of resources. While patchy or rare food sources exaggerated the relative success of large colonies, regularly (or easily found) distributions leveled the playing field for smaller colonies. Social foraging in ant societies can best be understood when we view the colony as a single organism and the phenotype - group size, communication, and individual behavior - as integrated components of a homeostatic unit.Dissertation/ThesisPh.D. Biology 201

A proactive-reactive syndrome affects group success in an ant species

Social insects have been particularly evolutionarily successful: they dominate terrestrial ecosystems all over the globe. Their success stems from their social organization, where one or a few individuals reproduce, whereas others carry out different colony tasks. From an evolutionary standpoint, social species are particularly interesting because natural selection acts at both the individual and colony levels. Therefore, we might expect to see selection acting simultaneously on personality at the individual level and colony level. In this study, we tested whether captive colonies of the ant Aphaenogaster senilis exhibited different behavioral types and evaluated their consequences for intraspecific competition. Our results demonstrate that colonies of the same age exposed to standardized laboratory conditions did indeed have different personalities. In addition, we found that A. senilis demonstrated a behavioral syndrome that included proactive and reactive behaviors: colonies varied in their approaches to exploration, risk taking, food retrieval, and conspecific interactions. This syndrome appears to be associated with a trade-off between competition for food resources and temperature-related foraging risks. >Bold> colonies contained individuals who more readily explored novel environments, exhibited aggressive behaviors, and demonstrated higher food-retrieval efficiency during intraspecific competition trials. However, such colonies were also more risk prone: workers suffered higher mortality rates because they more frequently foraged over their critical thermal maximum. The trade-off we observed under laboratory conditions might be key in maintaining colony-level personality, thus driving local-level adaptations in collective behavior.Peer Reviewe