Progress 12/15/99 to 12/31/03
Outputs
Five objectives were accomplished based on detailed morphological analyses of the S. saevissima species complex. 1) A new classification was erected by replacing the unwieldy earlier terminology of complexes and subcomplexes with species-group terminology, a change also consistent with current uncertainties regarding the monophyly of fire ants. The newly delineated species groups were thoroughly characterized to aid researchers in identification. 2) The different life stages and castes in each species were associated with the adult workers, the material on which original species descriptions typically were based, after collecting a large amount of new material from the native ranges. The new material led to improved species descriptions, new range maps, and description of a new fire ant species from Brazil. 3) Multiple morphological character systems from all castes and life stages were evaluated to discover characters of taxonomic and phylogenetic utility in the S.
saevissima species group. These included many previously unutilized characters of the immatures and adult sexuals. 4) Updated dichotomous and tabular keys were developed using these new characters along with traditional worker characters. 5) A cladistic analysis was performed using the new and traditional characters, and the resulting tree of relationships was used to reconstruct the evolution of several important social features of fire ants, including social parasitism and worker gigantism. MtDNA sequence data representing a portion of the cytochrome oxidase I gene were generated for multiple individuals representing nine Solenopsis species. All methods of phylogenetic analysis resulted in the same well-resolved tree that generally supports the relationships inferred from the morphological data. Sequences from most species were monophyletic; however, those from S. invicta and S. saevissima were paraphyletic. These two species are exceptional within the S. saevissima species group in
terms of their extensive geographic ranges and the breadth of morphological variation each encompasses. Explanations for the paraphyly of S. invicta haplotypes are that historical introgression among lineages has occurred or that this nominal species comprises multiple, morphologically cryptic species. Screens of a DNA library from S. invicta revealed the presence of a transposable element with high sequence identity to mariner elements. The entire element was recovered by inverse PCR and was PCR-amplified and sequenced in seven Solenopsis species. Phylogenetic trees based on these sequences showed that they form a clade within the mauritiana subfamily that is part of a larger monophyletic group of elements derived from other Hymenoptera. Phylogenetic relationships for the deeper branches were concordant with relationships inferred from the morphological characters, but the more recently derived species (including S. invicta) possessed paraphyletic assemblages of mariner elements.
This may be due to recent horizontal transfer of these elements or to paralogous relationships of the mariner copies that were sequenced.
Impacts
The S. saevissima complex, which includes the exotic pest fire ants, remains in surprisingly poor taxonomic condition despite the significance of fire ants as serious agricultural, medical, and ecological pests. Our studies have resolved many of the fundamental taxonomic problems in the group and so provided stable links between the organisms, their taxonomic names, and the scientific literature. The resulting classification and phylogeny serves to remove substantial impediments to future studies of fire ant biology and control.
Publications
- Krieger, M. J. B. and K. G. Ross. 2003. Molecular evolutionary analyses of mariners and other transposable elements in fire ants (Hymenoptera: Formicidae). INSECT MOLECULAR BIOLOGY 12: 155-166.
- Ross, K. G. and D. D. Shoemaker. 2003. Reproductive isolation and species boundaries in native south american fire ants. EVOLUTION (submitted).
- Pitts, J. P., J. V. McHugh, and K. G. Ross. 2004. A cladistic analysis of the fire ants of the Solenopsis saevissima species-group (Hymenoptera: Formicidae). SYSTEMATIC ENTOMOLOGY (submitted).
- Pitts, J. P., J. V. McHugh, and K. G. Ross. 2004. Revision of the fire ants of the Solenopsis saevissima species-group (Hymenoptera: Formicidae). ZOOTAXA (submitted).
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Progress 01/01/02 to 12/31/02
Outputs
Morphological and molecular data were combined using modern systematics methodology to resolve the persistent problems in the taxonomy of fire ants in the S. saevissima species complex. Results were based on analyses of new morphological character systems from all life stages and castes, as well as analyses of DNA sequences from the mitochondrial and nuclear genomes. A new classification was erected that replaced the unwieldy earlier terminology and classification, and newly delineated species groups were thoroughly characterized to aid researchers in identification. The different life stages and castes in each species were associated with the adult workers, the material on which original species descriptions typically were based, after collecting a large amount of new material from the native ranges. The new material led to improved species descriptions, new range maps, and description of a new fire ant species from Brazil. Multiple morphological character systems
from all castes and life stages were evaluated to discover characters of taxonomic utility in the S. saevissima species complex. These included many previously unutilized characters of the immatures and adult sexuals. Updated dichotomous and tabular keys were developed using these new characters along with traditional worker characters. A first reconstruction of evolutionary relationships of fire ants was achieved using morphological and DNA data.
Impacts
The classification and nomenclature of fire ants has been in disarray for many decades because of the lack of careful systematic studies of all life stages and castes in this difficult group of species. The result has been continuing uncertainty in the scientific literature as to which species have been introduced to the U.S., where these species' native ranges occur, and which species are especially closely related in their evolution. This project has succeeded in clarifying the classification and nomenclature of fire ants and has generated a first synthetic hypothesis of their evolutionary relationships.
Publications
- Krieger, M. J. B. and K. G. Ross. 2002. Molecular characterization and evolutionary relationships of mariner and other transposable elements in fire ants (Hymenoptera: Formicidae). Insect Molecular Biology (in press).
- Pitts, J. P. 2002. A cladistic analysis of the Solenopsis saevissima species-group (Hymenoptera: Formicidae). Ph.D. dissertation, University of Georgia.
- Shoemaker, D. D., G. Keller, and K. G. Ross. 2003. Effects of Wolbachia on mtDNA variation in native populations of the fire ants Solenopsis invicta and S. richteri. Molecular Ecology (submitted).
- Mescher, M. C., K. G. Ross, D. D. Shoemaker, L. Keller, and M. J. B. Krieger. 2003. Distribution of the two social forms of the fire ant Solenopsis invicta (Hymenoptera: Formicidae) in the native South American range. Annals of the Entomological Society of America (submitted).
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Progress 01/01/01 to 12/31/01
Outputs
The project is in its early stages. We have collected extensive samples of fire ants from their native ranges in South America and are currently subjecting these samples to exhaustive morphological and genetic analyses. We have identified a large number of useful morphological and genetic characters that can be used to distinguish the various fire ant species from one another and that illuminate their evolutionary relationships.
Impacts
The project will yield significant data to be used to determine and define species of fire ants and understand their evolutionary relationships to one another. Such information is crucial to developing new control strategies and predicting the impact of new biological control agents for managing populations of this introduced pest species.
Publications
- No publications reported this period
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Progress 01/01/00 to 12/31/00
Outputs
This project should have a term date of 09/30/2003. A call has been placed to Washington to correct this error on 03/02/2001. The project is in its initial stages, during which we are collecting samples of fire ants from their native ranges in South America and subjecting these samples to initial morphological and genetic analyses. Extensive samples are now in hand so that this work can proceed in earnest, although two additional trips are planned for next year to complete the samples.
Impacts
The project will yield significant data to be used to determine and define species of fire ants and understand their evolutionary relationships to one another. Such information is crucial to developing new control strategies and predicting the impact of new biological control agents for managing populations of this introduced pest species.
Publications
- No publications reported this period
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