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Final Report Summary - SOCIAL INVASIONS (Evolution of sociality in invasive fire ant populations)

The objective of this study was to reveal the underlying genetic elements that constitute the basis of adaptation in a social invasive species. Evolutionary theory provides an understanding of general, abstract principles of social evolution but the molecular mechanisms that facilitate this process were out of reach until very recently. The field of social insect evolutionary genomics was born about eight years ago, with the advent of genome sequencing technologies, thereby opening up opportunities to address open questions relating to the mechanisms that underlie the evolution of sociality. Our research approached these questions by studying molecular evolution and adaptation in native and introduced populations of the red and black imported fire ants. A population genomics approach using next generation sequencing was used to identify specific genomic loci under natural selection. The population demographic and recent evolution of these populations was reconstructed and selective pressures were inferred in the native and introduced populations. A selection survey identified genomic regions that may be the target of recent natural selection in the native and introduced ranges. These regions contain genes involved in molecular functions related to social biology and behavior, such as pheromone synthesis and caste determination. These results complement the abstract theory on social evolution that provides ultimate explanations with proximate explanations of the molecular mechanisms that make this theory a reality. Furthermore, these genes are inferred to be of ecological importance in these invasive populations, providing new insights into the biology of ant invasions.

The population genomic data were also used for a detailed reconstruction of the demographic history of these invasive ant population. These analyses were successful in showing that two closely related fire ant species speciated in their native range in South America, and have been genetically isolated for more than a million years. This results is valuable in light of the extensive hybridization of these two invasive species in the USA. This is a unique and powerful system for the study of the evolutionary processes of speciation, the formation of reproductive barriers, and their breakdown following introduction of invasive species.

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Life Sciences
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