Submitted to: Systematic Biology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/5/2009
Publication Date: 12/14/2009
Publication URL: http://sysbio.oxfordjournals.org/cgi/content/full/syp089v1?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=Ross&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT
Citation: Ross, K.G., Gotzek, D., Ascunce, M.S., Shoemaker, D.D. 2009. Species delimitation: A case study in a problematic ant taxon. 59(2):162-184. Interpretive Summary: Fire ants are considered significant ecological, agricultural, and public health pests. Scientists at the Center for Medical, Agricultural, and Veterinary Entomology, USDA-ARS, Gainesville, Florida and scientists from the University of Georgia and the University of Lausanne describe here the results of a study aimed at distinguishing evolutionarily independent lineages within a widespread and highly variable fire ant species. The integrated approach using diverse data types and methods of analysis revealed a range in levels of divergence and evolutionarily distinctiveness among regional populations of this single nominal fire ant species. The ranges of several such independent lineages overlap with other populations, suggesting that intrinsic premating or postmating barriers to gene flow have developed. The genetic data further suggest that regional genetic differentiation in this ant has been influenced by interspecific hybridization with other nominal species. Our results illustrate the importance of employing different classes of genetic data, different methods of genetic data analysis, and different sources of data to provide robust delimitation of species boundaries in groups of recently diverged lineages.
Technical Abstract: Species delimitation has been invigorated as a discipline in systematics by an influx of new character sets, analytical methods, and conceptual advances. We use genetic data from 68 markers, combined with distributional, bioclimatic, and coloration information, to distinguish evolutionarily independent lineages within the widespread and highly variable fire ant species Solenopsis saevissima, a member of a species-group containing invasive pests as well as organisms regarded as models for ecological and evolutionary studies. Our integrated approach using diverse data types and methods of analysis reveals a range in levels of divergence and evolutionarily distinctiveness among regional genetic clusters (populations) of nominal S. saevissima. While two broadly distributed populations evidently are linked by substantial levels of historical and recent gene flow, other clusters are evolutionarily independent, or clearly on a trajectory to be so, based on phylogenetic and multidimensional scaling analysis of individual genetic relationships, gene flow and genetic differentiation statistics, and ecological niche modeling. Several such independent lineages are parapatric with other populations, suggesting that intrinsic premating or postmating barriers to gene flow have developed. The genetic data further suggest that regional genetic differentiation in S. saevissima has been influenced by interspecific hybridization with other nominal species occurring in sympatry or parapatry, including the quite distantly related S. geminata. Our results illustrate the importance of employing different classes of genetic data (coding and non-coding regions; nuclear and mtDNA markers), different methods of genetic data analysis (tree-based and non-tree-based methods), and different sources of data (genetic, morphological, and ecological data) to provide robust delimitation of species boundaries in clades of recently diverged lineages, while warning against over reliance on any single data type (e.g., mtDNA sequence variation) when drawing inferences.