Wendy Marussich

Department of Ecology and Evolutionary Biology
Phone: (520) 626-7009
Email: wmarussi@email.arizona.edu

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Research Interests

I am a field-based community ecologist currently using molecular techniques to address the evolutionary genetics of the fig-fig wasp mutualism, although my research focus spans four distinct areas:

• Evolutionary genetics of the fig-fig wasp mutualism
• Costs and benefits of ant-plant seed dispersal mutualisms
• Tri-tropic dynamics of arthropod communities in urban and desert areas
• Comparisons of urban ecological footprints based on water usage

Although I am broadly trained as a community ecologist, I have often felt limited by the questions I can ask, especially in my main areas of interest—mutualisms and coevolution. Molecular techniques are becoming standard in ecological research, and thus I am currently learning the tools and the language of evolutionary genetics to address ecological questions. I am using PCR and DNA sequencing to examine both pollinating and non-pollinating fig wasps collected from Panama, and will combine these molecular data with ecological data collected in the field to address questions in mutualisms and coevolution.

Mutualisms are characterized as interactions between species in which participating individuals from both species receive a fitness benefit from the interaction. Figs (Ficus spp., Moraceae) and their pollinating wasps (Hymenoptera, Agaonidae, Chalcidoidea) are a classic example of an obligate mutualism, and are an ideal system for addressing basic questions in ecology and evolutionary biology on coevolution, speciation, and the maintenance of mutualisms. Both the figs and their pollinating wasps are entirely dependent on each other for their survival and reproduction. The fig depends on pollen-bearing female wasps to pollinate its flowers and initiate seed production, whereas mated female wasps depend on the fig for reproduction because each wasp offspring develops within an inflorescence and consumes the contents of a developing fig seed. Natural selection should favor pollinating wasps that increase their own reproductive success at the expense of the fig's viable seed production, but the fig-fig wasp interaction has existed for over 90 million years without overexploitation by the pollinators. Strict one-to-one coevolution has been assumed for all figs and their pollinating wasps. However, recent genetic data demonstrate the coexistence of cryptic pollinator wasp species in at least 50% of the Panamanian host fig species, suggesting that the one-to-one relationship between wasps and their hosts is not as common as had been assumed, and challenging current theory on evolution and stability of mutualisms.

In addition to pollinating wasps, most figs host several non-pollinating wasp species that provide no pollination benefit, but are dependent on the figs for survival and reproduction. Unlike pollinating wasps, many non-pollinating wasps have extremely long ovipositors, and oviposit from outside the fruit wall into the seeds or into the larvae of other pollinator or non-pollinator wasps. Other non-pollinators have shorter ovipositors and lay eggs in the fruit wall, generating large galls. Non-pollinators generally emerge from their flowers at approximately the same time as the pollinators, and exit through a hole chewed in the fruit wall by pollinator males. Molecular work has shown that both the pollinator and non-pollinator wasp species are usually specific to a given fig host species. The phylogenies of the Neotropical pollinator and non-pollinators are largely congruent, suggesting strict-sense coevolution on shared hosts, but recent work on a group of Old World species has shown evidence of host-switching and co-speciation among the non-pollinators. Based on ecological and morphological data, it has been proposed that the pollinating and non-pollinating wasps form a monophyletic group; however, initial molecular studies have been unable to substantiate this hypothesis. Additional molecular data on the non-pollinating species will help to test these hypotheses and could have profound implications for the understanding of the coevolution and maintenance of obligate mutualisms in the presence of non-mutualistic species.

Figs come in many sizes. Shown here: Ficus pertusa. (Photo by E.A. Herre.)

Fig wasps. Left: Pegoscapus estherae, a pollinating figs wasp. Right: Idarnes sp., a non-pollinating fig wasp. Pegoscapus enter the fig and lay eggs inside, whereas Idarnes lay eggs from the outside of the fig by inserting their long ovipositors through the wall of the fig. Both types of fig wasps commonly occur in the same fig. (Photo by E.A. Herre.)

I received my bachelor's degree in biology from Vassar College in May 1998. While at Vassar I worked with Dr. Robert S. Fritz on the tri-trophic dynamics of beetle larvae on hybrid willow trees. After graduating from Vassar College, I went to Arizona State University to pursue a Ph.D. in biology. At Arizona State my research focused on the costs and benefits of an ant-plant seed dispersal mutualism between jimsonweed (Datura wrightii, D. discolor, and D. quercifolia) and several species of desert seed harvester ants (Pogonomyrmex, Messor, and Aphaenogaster). While at Arizona State, I also established a long-term ecological research project in conjunction with Dr. Stanley H. Faeth and the Central Arizona Phoenix Long-Term Ecological Research (CAP-LTER) project. This project focuses on the trophic dynamics of arthropod communities in urban and desert areas.

I received my Ph.D. from Arizona State University in August 2004 and am currently examining the evolutionary genetics of the fig-fig wasp pollination mutualism as a PERT Postdoctoral Fellow at the University of Arizona with Dr. Carlos A. Machado.

More Research Photos:

A single Datura wrightii fruit. The white appendages on the seeds (elaiosomes) are protein- and lipid-rich appendages that are highly attractive to ants. Elaiosomes are thought to induce seed dispersal by ants (myrmecochory) in which ants gather the seeds and carry them back to their nests where they consume the elaiosomes and discard the seeds unharmed either inside the nest or on an external refuse pile. The plants are thought to benefit from dispersal away from their parent plant, transportation to nutrient-rich microsites, and protection from seed predators and fire. The ants are thought to receive nutritional benefits from consuming elaiosomes. However, in many cases, such as the interactions between desert seed harvester ants and Datura, the ants and the plants do not necessarily receive benefits.

A desert seed harvester ant (Pogonomyrmex californicus) queen (bottom left) with her brood (3 larvae, 2 pupae, and 3 workers)

Datura wrightii seedlings during a greenhouse experiment testing the effects of seed scarification by several species of desert seed harvest ants on seed survival and germination.

Photo of a long-term experiment examining the trophic dynamics of arthropod communities on brittlebush (Encelia farinosa). Cages are used to exclude birds, metal flashing rings are used to exclude ground predators, and plants with blue tags receive bimonthly supplemental watering. Arthropods are collected every six weeks and identified to species. Experimental plots containing 40 plants each are currently in three habitat types: mesic residential, native edge desert, and urban desert remnant (pictured above).