Projects in this laboratory focus on species interactions and life history evolution.

My students and I study the symbiosis between ants and larvae of the Lycaenidae (Lepidoptera) as a model system to elucidate the dynamics of species interactions and the evolution of life history traits. Our approach involves both field work and laboratory research. With well over 6000 species, the Lycaenidae is among the largest and most diverse of all butterfly families. The life histories of many species have been well documented, making this a group of particular value in comparative evolutionary studies. Historically, they have featured in evolutionary research on topics that include polymorphism and mimicry, ecological genetics, mutualism, and coevolution with host plant species.

Because fossil evidence is scarce, we know little about factors promoting the diversification of butterflies in general or lycaenids in particular. We do know, however, that lycaenids are characterized by a number of ecological features that may be related to their diversity. They are small and short-lived. They also have remarkable dietary breadth: a considerable number of species are carnivorous, a habit that is exceedingly rare in the Lepidoptera, and herbivorous species consume an unusually wide array of different plant families. Finally, the caterpillars of the majority of described species have intimate associations with ants, which vary in nature and intensity. Typically, these interactions are mutualistic: caterpillars secrete food for attendant ants from specialized glands, and in return, are protected by ants against predators and parasites. Some can be facultative interactions in which caterpillars are only occasionally tended by ants and often by many species, while others are complex, obligate associations in which caterpillars are always tended by ants, often by only a single species. Very occasionally, the tables turn and lycaenids actually become parasites of their host ants by preying upon the ant brood.

Current work on lycaenid/ant intereactions addresses three main areas of research. First, we are conducting field and laboratory studies to understand the behavioral mechanisms that promote and maintain species-specific ant associations. Our aim is to determine why certain species of lycaenids have general interactions with many kinds of ants whereas others associate exclusively with only one species. Lycaenid caterpillars secrete chemicals that gain favorable recognition by ants, and we are characterizing the compounds used in this interspecific communication. Both the larvae and pupae of many species produce vibrations, or stridulations, and we are also investigating the role of these acoustical signals in interspecific and intraspecific communication.

Second, we are interested in the evolutionary consequences of specialization, and the role of ant associations in the diversification of the Lycaenidae. What are the mechanisms that have generated the impressive biodiversity we see today? Overlapping requirements of protective ant species and appropriate host plants may result in population restriction and subdivision of ant-associated lycaenids, and this has possibly led to faster rates of evolution. We can test this idea by reconstructing a molecular phylogeny, or family tree, and using this to ‘calibrate’ the relative rates of divergence within and between particular lineages. We are also using molecular techniques to assess levels of polymorphism within and between species that may correlate with particular life history parameters measured in the field. The behavioral and ecological diversity of the Lycaenidae makes this group particularly amenable to comparative studies of life history evolution, but an evolutionary framework is essential to evaluate hypotheses.

Third, we are investigating why many lycaenids are rare. Although the Lycaenidae is only one of many families of Lepidoptera, as many as 30%of endangered or threatened species are lycaenids. Worldwide, individual lycaenids serve as flagship species for conservation organizations. In Britain, an emblem of the Nature Conservancy is the Large Blue. In South Africa, conservation efforts focus on Brenton’s Blue, and in Australia, Illidge’s Blue. In North America, the Xerces Society was named after the Xerces Blue, and much attention has been paid to the plight of the Mission Blue in California and Karner’s Blue in the Northeast. The most threatened species are those whose caterpillars are parasites of ants. In some cases, the caterpillars induce ants to carry them into the nest, where, chemically camouflaged to avoid detection, the caterpillars feast on the brood. In others, the caterpillars convince their ant hosts to feed them mouth-to-mouth by trophallaxis. With their fascinating but highly complex life histories, it is not surprising that these species are particularly sensitive to perturbations of their environment: there is simply more that can go wrong. This makes them a model system for learning about extinction and how to prevent it. What features of the biology of these species make them most vulnerable? Are there diagnostic population genetic indicators that can help us predict vulnerability in advance? The conservation lessons we learn from the lycaenids are applicable to other systems, and the more we understand the factors promoting extinction, the more effective our potential countermeasures.

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For lycaenid-related projects, see:

Graduate students: Glenn Adelson, Sandra Andaluz, Mathew Baylis, Dana Campbell, Ann Fraser, Nikolai Kandul, David Lohman, Richard Macniven, David Nash, Tiago Quental, Diane Wagner

Postdoctoral fellows, research associates and visiting students: Thomas Als, Annkristin Axen, Michael Braby, James Costa, Phil DeVries, Karen van Dorp, Rod Eastwood, Lesley Hughes, John Mathew, Jan Hendrik Megens, James Morris, Kathrin Sommer, Roger Vila

Undergraduates: Michael Blair, John Braverman, Robin Carper, James Coleman, Belinda Chang, Francine Laden, David Merrill , Andre Mignault, Douglas Rand, Leslie Shenkel, Tamara Suderman, Mark Travassos.

Curatorial and research assistants: Mark Cornwall, Ada Kaliszewska, Andre Mignault, Karen Nutt and Tamara Suderman

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Interactions between plants, microbial pathogens and insect herbivores.

A second project in the lab involves a collaboration with the Ausubel lab at Harvard Medical School to analyze three-way species interactions among plants, pathogens and insects. This research combines molecular and ecological approaches to elucidate mechanisms involved in three-way interactions and identify genetic factors underlying variation in these associations. Using a model system comprised of the plant Arabidopsis thaliana, the bacterial pathogen Pseudomonas syringae, and the insect herbivore Trichoplusia ni (cabbage loopers), we have demonstrated significant interaction effects between microbial infection and insect attack on individual plants. We are currently extending this research by analyzing plant gene expression profiles following pathogen and/or insect attack, and by exploring interactions involving additional pathogens and herbivores (see Adam Bahrami, Jianping Cui, and Georg Jander).

 

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Research picture gallery

Research in the Pierce lab features a wide variety of organisms; here are some examples. Click on the icons below to view full-size images.

 

 

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