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SI Entomology Staff
Scott E. Solomon, Visiting Scientist
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Research Interests:
- Phylogenetics, phylogeography, and paleodistribution modeling
- Systematics and biogeography of fungus-growing ants
- Evolutionary causes for high species diversity in the Amazon
I am generally interested in how evolutionary and ecological processes produce patterns in geographical space, a field known as biogeography. I use ants as a model system, which are useful because they are widespread and abundant, and because ant species diversity is a good indicator of diversity in other groups.
- Leafcutter ant phylogeography and the origins of tropical species diversity.
My dissertation research tested a number of hypotheses that have been proposed to explain the preponderance of species diversity in tropical regions. These hypotheses, known as the Pleistocene refugia hypothesis, the riverine barrier hypothesis, and the marine incursion hypothesis are concerned specifically with the origin of diversity in the tropics through allopatric speciation. They each claim to explain tropical biodiversity by proposing a different mechanism for how geographic barriers arise among tropical biota. However, previous studies have used only vertebrates as test systems, despite the preponderance of invertebrates in tropical habitats. I used three species of leafcutter ants (Atta cephalotes, Atta sexdens, and Atta laevigata) to test these hypotheses, employing a combination of methods from population genetics, phylogenetics, and paleodistribution modeling. The results suggested that rivers do not play a role in diversification of Amazonian leafcutter ants, but could not rule out Pleistocene refugia or marine incursions. Future work using additional Amazonian species - especially other invertebrates - will help determine whether these conclusions apply more generally.
- Systematics of the “Higher Attines”
I am especially interested in the transition between the phylogenetically basal, or “lower” fungus–growing ants (attines) and the highly derived leafcutter ants (Acromyrmex and Atta). This evolutionary event has been described as “the event of greatest importance in the history of the Attini” (Hölldobler and Wilson, 1990, p. 605). The shift to exclusive use of fresh vegetation as a substrate for fungal cultivation by the leafcutters is associated with several radical changes in the biology of these ants, such as dramatically larger colony sizes, increased worker polymorphism, and increased queen mating frequency. Although the transition to cutting leaves was a unique occurrence, limiting the tools that can be used to examine causation, much can be gleaned about the evolution of the leafcutters and about the co-evolutionary dynamics of the attine symbiosis by a detailed examination of the closest living relatives to the leafcutters. This critical position is occupied by Trachymyrmex, one of the most diverse genera of fungus-growing ants, with 48 currently recognized species. Trachymyrmex species share several biological and ecological traits with the lower attines, and others with the more derived leafcutters, emphasizing their position as transitional species.
The evolutionary relationships, as well as the natural history of many Trachymyrmex species are not well known, especially in the Neotropics. In collaboration with researchers in the USA and in Brazil, I am working to elucidate the evolutionary relationships among this important group of attine ants and their microbial symbionts using molecular systematic techniques. We are using currently conducting extensive fieldwork in Brazil to collect samples of Trachymyrmex species and document their geographic range and natural history.
- The ants of Cocos Island, Costa Rica
Since 2003, I have been studying the ant fauna of Cocos Island, a small, volcanic island 500 kilometers off the coast of Costa Rica, in collaboration with Alexander Mikheyev, a graduate student at The University of Texas at Austin. Cocos is the only island in the tropical eastern Pacific Ocean that supports a rainforest environment. Its isolation has given rise to several endemic species of plants, insects, birds, and lizards.
We conducted a systematic survey of the ants of Cocos Island in July 2003, during the wet season, and collected 19 species of ants. Of these, the majority were widespread tramp species. However, one endemic species, Camponotus cocosensis, was found in abundance. Another endemic, Camponotus biolleyi, first collected by expeditions in the early 1900s, was not found. Wasmannia auropunctata, a highly invasive species of fire ant, was found in extremely high densities (up to 1000/sq. m) near disturbed areas, but in low densities or absent from more pristine habitat.
We recently returned to Cocos Island during the dry season, to re-survey the island's ants. We are currently working to analyze the samples collected during this trip.
- Publications
Bacci, M., Solomon, S.E., Silva-Pinhati, A.C.O., Mueller, U.G. Martins, V.G., Carvalho, A.O.R., Vieira, L.G.E. (2008) Phylogeny of leafcutter ants in the genus Atta Fabricius (Formicidae: Attini) based on mitochondrial and nuclear DNA sequences. Molecular Phylogenetics and Evolution, published online Nov 13, 2008, doi:10.1016/j.ympev.2008.11.005
Solomon, S.E., Bacci, M., Martins, J., Gonçalves Vinha, G., Mueller, U.G.
(2008) Paleodistributions and comparative molecular phylogeography of leafcutter ants (Atta spp.) provide new insight into the origins of Amazonian diversity. PLoS ONE 3(7) e2738.
Martins, J., Solomon, S.E., Mikheyev, A.S., Mueller, U.G., Ortiz, A., Bacci, M. (2007) Nuclear mitochondrial-like sequences in ants: evidence from Atta cephalotes (Formicidae: Attini). Insect Molecular Biology 16(6): 777-784.
Solomon, S.E. and Mikheyev, A. (2005) The ant (Hymenoptera: Formicidae fauna of Cocos Island, Costa Rica. Florida Entomologist 88: 415–423.
Solomon, S.E., Mueller, U.G., Schultz, T.R., Currie, C.R., Price, S.L., Bacci, M., Oliveira da Silva-Pinhati, A.C., Vasconcelos, H. (2004) Nesting biology of the fungus growing ants Mycetarotes Emery (Attini, Formicidae), Insectes Sociaux 51:333-338.
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