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ARS Home » Southeast Area » Gainesville, Florida » Center for Medical, Agricultural and Veterinary Entomology » Imported Fire Ant and Household Insects Research » Research » Publications at this Location » Publication #192833
Title: POPULATION GENETICS OF THE INVASIVE FIRE ANT SOLENOPSIS INVICTA (HYMENOPTERA: FORMICIDAE) IN THE U.S.A.

Author
item Shoemaker, David
item DEHEER, CHRISTOPHER - NC STATE UNVI.
item KRIEGER, MICHAEL - ROCKEFELLER UNIV.
item ROSS, KENNETH - UNIV. OF GEORGIA

Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/19/2006
Publication Date: 8/14/2007
Citation: Shoemaker, D.D., Deheer, C.J., Krieger, M.J., Ross, K.G. 2007. Population genetics of the invasive fire ant solenopsis invicta (hymenoptera: formicidae) in the U.S.A.. Annuals of the Entomological Society of America. 99(6):1213-1233.

Interpretive Summary: The red imported fire ant is considered a significant ecological, agricultural, and public health pest throughout its invasive range in the U.S.A. While previous studies have analyzed patterns of genetic structure in this pest ant at local scales, no study to date has examined structure at multiple scales in both the single queen and multiple queen social forms over a broad geographic area using numerous highly informative genetic markers. The resulting lack of a detailed picture of population genetic structure in the U.S.A. has hindered progress on several fronts, including our ability to discern predicted genetic signatures of recently founded populations, to reconstruct the origin and spread of each social form, and to fully understand the role of this social polymorphism in driving population divergence. A primary aim of our study was to use genetic information in conjunction with data on the invasion history to refine our knowledge of the processes that have led to the current distribution of the red imported fire ant in the U.S.A. The overall patterns of genetic variation we detected, combined with historical and other observational data, suggest early colonization from the initial site of establishment (Mobile Bay) often involved long-distance, human-mediated dispersal. Sub-founder populations of each social form typically were established by queens of the same social form, perhaps often derived from very distant localities. Range expansion from Mobile generally occurred by means of sequential outward sub-founder events, with the result that more peripheral populations are the most genetically distinctive and least resemble the hypothesized original founder population. Secondary introductions of the red imported fire ant may also have occurred, the best evidence for which is the genetic distinctiveness and signal of admixture between two discrete populations discerned for ants sampled near the deepwater port of Port Arthur, Texas. The results of this study are important because they new shed light on the invasion history of each social form of this ant in the U.S.A. Additionally, elucidation of the large-scale genetic structure of introduced fire ants provides a necessary framework for future efforts aimed at pinpointing the native source population(s), a task crucial to focusing biological research aimed at developing new methods of control of this invasive pest.

Technical Abstract: Analyses of population genetic variation in invasive species can provide information on the history of the invasions, breeding systems, and gene flow patterns. We surveyed genetic variation in both social forms of the red imported fire ant, Solenopsis invicta, throughout the species’ introduced range in the U.S.A. to learn how the unique breeding biology of each form shapes genetic structure at various scales, to discern genetic footprints of the invasion process, and to reconstruct the origin and spread of each form. Our analyses revealed significant local mtDNA differentiation in the polygyne (multiple colony queens) but not the monogyne (single colony queen) social form, as well as pronounced mtDNA differentiation coupled with weaker nuclear differentiation between sympatric populations of the two forms. At a larger scale, we found no mtDNA but significant nuclear regional differentiation. In general, populations were most similar to other populations of the same social form at their mtDNA genomes. These higher-level patterns of structure are consistent with the spread of the ant by long-distance, human-mediated dispersal, with sub-founder populations of each form typically established by queens of the same form. Bayesian analyses showed that study populations most distant from the claimed site of entry, Mobile, Alabama, have diverged most from the hypothetical founder population, consistent with an invasion scenario in which the ants spread outward from Mobile through repeated sub-founder events. Several lines of evidence raise the possibility of secondary introductions of S. invicta into the U.S.A.