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| Research Interests |
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| Current Research:
I am beginning my second year as a National Parks Ecological Research (NPER) Postdoctoral Fellow and am working with Bob Denno in the Department of Entomology at the University of Maryland. I am investigating how nutrient subsidies affect foodweb dynamics within salt marsh communities. Natural wetlands are increasingly threatened by nutrient pollution and invasive plant species. I am studying the contrasting effects of a short-term increase in nutrient availability (pulse) versus a long-term increase in nutrients (press) on the productivity of the cordgrass Spartina alterniflora, with extended consequences for species interactions, food-web structure and food chain length. As a dominant species, Spartina is an important component of the vegetation of Atlantic coastal marshes. Conservation of coastal wetlands, particularly salt marshes, is a major concern because these play a critical role in the ecology and geology of wave-protected shorelines and are the nursery grounds for commercial fish and shellfish. The treatments that I have imposed are specifically designed to mimic nutrient-runoff from agricultural fields and golf courses in order to understand, for conservation and management purposes, how variable nutrient regimes influence community structure over time. Graduate Research: 1) Chemical facilitation of a host shift - Host shifts by herbivorous insects have contributed substantially to current patterns of association between insects and plants by influencing the diversification and speciation of plant-feeding insects. Furthermore, many of our major agricultural pests have colonized crop plants by shifting from native food-plants to an abundant crop host. Despite their evolutionary and agricultural interest, however, the plant traits that predispose insects to colonize some plants instead of others are poorly understood. My research on a fairly recent host shift within a closely related group of swallowtail butterflies known as the Papilio machaon group, experimentally tests the mechanisms by which host shifts are thought to occur. In collaboration with my graduate advisor, Paul Feeny, I fractionated and isolated chemical stimulants in the ancestral and novel host plants used by two P. machaon swallowtails (P. m. aliaska and P.oregonius). After a series of behavioral bioassays, we found that the novel and ancestral host plants share similar chemical stimulants that may have facilitated the host shift by swallowtails within the P. machaon group. Chemical similarities between plants have often been suggested as a possible explanation for insect host shifts but our research is the first experimental test to document the role of plant chemistry during an insect host-shift. Our research supports the chemical facilitation hypothesis of host race formation (Murphy and Feeny, 2006 in Ecological Monographs). 2) The role of enemy-free space during a host shift - Natural enemies can be significant sources of mortality for herbivorous insects and therefore important agents of natural selection. One might expect selection to favor herbivores that escape from their natural enemies into enemy-free space (EFS). While this is an appealing idea, it has received little empirical support and no studies have documented EFS as part of a non-agricultural, naturally-occurring host shift. I designed a field experiment to test whether the novel host plants offer P. m. aliaska larvae EFS that is not found on the ancestral host plant. I found that P. m. aliaska larvae find refuge from their natural enemies by feeding on novel host plants; this appears to be an example of EFS via host-plant dispersion rather than via host-plant chemistry. This study is the first to experimentally demonstrate that EFS can play an important role in maintaining a host expansion or shift in a natural system (Murphy, 2004 in Proceedings of the National Academy of Sciences; Murphy, in press in Entomologia Experimentalis et Applicata.) 3) Do host races exist in the Alaskan swallowtail system? – Specialized insect species that feed on unrelated host plants may be composed of separate host races, with populations that specialize on the different host plants. The Alaskan swallowtail butterfly (P. m. aliaska) uses three unrelated plant species as hosts. I investigated variation in adult oviposition preferences for the three host species to identify whether host races may exist in this swallowtail species. The experiments were designed to test two predictions associated with the presence of host races: 1) P. m. aliaska host preference should be constant and not change from day to day and 2) the offspring from a single dam should prefer the same host plant species. A final experiment investigated whether the food plant on which a female is reared as a larva influences her future choices when she is searching for host plants for her own offspring (Hopkins Host Selection Principle). The results from all of these experiments indicate that P. m. aliaska females vary greatly in their oviposition behavior and in their preferences for the three host plants. Most populations appear to be comprised of generalists; there is no evidence to support the hypothesis that P. m. aliaska populations in central Alaska are divided into host races. The results of this research suggest an explanation for why P. m. aliaska continues to use all three host plants in nature. I propose that the generalized selection of host plants by P. m. aliaska females is a ‘bet-hedging’ strategy and this strategy may maximize reproductive fitness in an unpredictable environment. Finally, my work found no evidence to support the Hopkins Host Selection Principle as a mechanism to promote host shifts (Murphy, in press in Ecological Entomology). | |||||||||||||||||||
| Education |
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| 2005 Ph.D. Cornell University
Ecology and Evolutionary Biology Advisor: Paul Feeny Committee: Monica Geber, Alan Renwick and Marina Caillaud 1997 B.A. University of Colorado at Boulder Environmental, Population and Organismic Biology (EPOB) Major, Biochemistry Minor, Summa Cum Laude Advisor: Yan Linhart Committee: Dave Armstrong and Bert Covert | |||||||||||||||||||
| Representative Publications | |||||||||||||||||||
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Murphy, S. M. In Press. Inconsistent use of host plants by the Alaskan swallowtail butterfly:
Adult preference experiments suggest labile oviposition strategy. Ecological Entomology.
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Murphy, S. M. In Press. The effect of host plant on larval survivorship of the Alaskan
swallowtail butterfly (Papilio machaon aliaska). Entomologia Experimentalis et Applicata.
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Murphy, S. M. and P. P. Feeny. 2006. Chemical facilitation of a naturally-occurring host shift
by Papilio machaon butterflies (Papilionidae). Ecological Monographs 76(3): 399-414. | |||||||||||||||||||
Murphy, S. M. 2004. Enemy-free space maintains swallowtail butterfly host shift. Proceedings
of the National Academy of Sciences 101(52): 18048-18052. | |||||||||||||||||||
Murphy, S. M. and Y. B. Linhart. 1999. Comparative morphology of the gastrointestinal tract in the feeding specialist Sciurus aberti and several generalist congeners. Journal of
Mammalogy 80(4): 1325-1330. | |||||||||||||||||||
Awards and Recognition | |||||||||||||||||||
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