Friday, November 25, 2005

Don't throw away that old poster...

..send it to Martin Pfeiffer's Online Poster Exhibition at the Ants of Borneo website.

Tuesday, November 22, 2005

Ant Invasions: Many ants introduced, not all establish.

Andrew V. Suarez, David A. Holway, and Philip S. Ward. 2005. The role of opportunity in the unintentional introduction of nonnative ants PNAS 102: 17032-35.

A longstanding goal in the study of biological invasions is to predict why some species are successful invaders, whereas others are not. To understand this process, detailed information is required concerning the pool of species that have the opportunity to become established. Here we develop an extensive database of ant species unintentionally transported to the continental United States and use these data to test how opportunity and species-level ecological attributes affect the probability of establishment. This database includes an amount of information on failed introductions that may be unparalleled for any group of unintentionally introduced insects. We found a high diversity of species (232 species from 394 records), 12% of which have become established in the continental United States. The probability of establishment increased with the number of times a species was transported (propagule pressure) but was also influenced by nesting habit. Ground nesting species were more likely to become established compared with arboreal species. These results highlight the value of developing similar databases for additional groups of organisms transported by humans to obtain quantitative data on the first stages of the invasion process: opportunity and transport.

Thursday, November 17, 2005

A Cautionary Note For DNA Barcoders...

A pair of papers from the fire ant folks show just how complicated ant speciation and delineation of species boundaries may be:

D. DeWayne Shoemaker, Michael E. Ahrens and Kenneth G. Ross, Molecular phylogeny of fire ants of the Solenopsis saevissima species-group based on mtDNA sequences, Molecular Phylogenetics and Evolution, Early Online.

Abstract: The systematics of South American fire ants (Solenopsis saevissima species-group) has been plagued by difficulties in recognizing species and their relationships on the basis of morphological characters. We surveyed mtDNA sequences from 623 individuals representing 13 described and undescribed species within the species-group and 18 individuals representing other major Solenopsis lineages to generate a phylogeny of the mitochondrial genome. Our analyses support the monophyly of the S. saevissima species-group, consistent with a single Neotropical origin and radiation of this important group of ants, as well as the monophyly of the socially polymorphic species within the group, consistent with a single origin of polygyny (multiple queens per colony) as a derived form of social organization. The mtDNA sequences of the inquiline social parasite S. daguerrei form a clade that appears to be distantly related to sequences from the several host species, consistent with the view that advanced social parasitism did not evolve via sympatric speciation of intraspecific parasites. An important general finding is that species-level polyphyly of the mtDNA appears to be the rule in this group of ants. The existence of multiple divergent mtDNA lineages within several nominal species (including the pest S. invicta) suggests that the pattern of widespread polyphyly often stems from morphological delimitation that overcircumscribes species. However, in two cases the mtDNA polyphyly likely results from recent interspecific hybridization. While resolving species boundaries and relationships is important for understanding general patterns of diversification of South American fire ants, these issues are of added importance because invasive fire ants are emerging as global pests and becoming important model organisms for evolutionary research.


KENNETH G. ROSS, D. DEWAYNE SHOEMAKER. Species delimitation in native South American fire ants. Molecular Ecology 2005 14:11 3419.

Abstract: The taxonomy of fire ants has been plagued by difficulties in recognizing species on the basis of morphological characters. We surveyed allozyme markers and sequences of the mtDNA COI gene in several closely related nominal species from two areas of sympatry in the native ranges to learn whether the morphology-based delimitation of these species is supported by genetic data. We found that Solenopsis invicta and Solenopsis richteri, pest species whose distinctiveness has been debated, appear to be fully reproductively isolated at both study sites. This isolation contrasts with the extensive hybridization occurring between them in the USA, where both have been introduced. We also found strong genetic differentiation consistent with barriers to gene flow between Solenopsis quinquecuspis and the other two species. However, several lines of evidence suggest that nuclear and mitochondrial genes of S. invicta and S. richteri are introgressing into S. quinquecuspis. The latter apparently is a recently derived member of the clade that includes all three species, suggesting that there has been insufficient time for its full development of intrinsic isolating mechanisms. Finally, our discovery of genetically distinct populations within both S. invicta and S. richteri suggests the presence of previously unrecognized (cryptic) species. Their existence, together with the difficulties in developing diagnostic morphological characters for described species, imply that the group is actively radiating species and that morphological divergence generally does not keep pace with the development of reproductive isolation and neutral genetic divergence in this process.

For those of you intent on using mitochondrial DNA for quick and easy species identification, I'd not recommend trying it in the fire ants.