Dr. Julie Alexander, Bartholomew Lab, Postdoctoral Scholar

  Alexander portrait    Office  Nash Hall 522
Phone  541-737-1849
FAX  541-737-0496
Email  alexanju@science.oregonstate.edu
Education  PhD Montana State University

RESEARCH

Generally, my research interests lie within the field of disease ecology.  I am fascinated by parasites that exploit multiple hosts during their life cycles as a means of ensuring their reproductive success.  I am interested in factors that drive and determine the outcomes of host-parasite interactions, how interactions may change under different environmental contexts, and how ecological and life history variables influence the evolution of host-parasite dynamics. I am also interested in multivariate and time series data analyses.

I recently joined the Bartholomew lab as a postdoctoral scholar.  Using the Ceratomyxa shasta life cycle as a model, I am using field and laboratory studies to answer questions about the ecology of the polychaete host.  Ceratomyxa shasta is a myxozoan parasite that alternates between a salmonid host and the freshwater polychaete and two waterborne spore stages during its life cycle.  Salmonids become infected by actionspores, which are released by infected polychaetes, and polychaetes become infected by myxospores, which are released from infected fish (life cycle).  Interactions between the parasite and the salmonid hosts have been well studied – and factors that drive the outcome of these interactions (e.g., disease – transmission to next host, or no disease- no transmission) are reasonably well understood.  However, our understanding of these same factors in the polychaete host stage is hampered by a lack of understanding of the ecology of the polychaete host. 

I am interested in the influence of environmental heterogeneity on polychaete population processes and how these processes in turn influence disease dynamics including encounter and infection rates and transmission to the fish host.  I am currently involved in several projects:  I work closely with several of the Bartholomew Lab’s research pillars (the graduate students, of course!), which I really enjoy.  For one of these projects, we employ a combination of SCUBA and snorkel surveys to collect the cryptic polychaeteThis aim of this project is to examine relationships among environmental features of river habitats (e.g., pools, runs, and eddys) and polychaete host and parasite abundance in the Klamath River.

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Getting acquainted with my current study species.  We use a combination of snorkeling and diving to collect the tube building freshwater polychaete, Manayunkia speciosa.   Collecting polychaetes is made simpler by the use of SCUBA in deep eddys.
I am also involved in other field-based research that encompasses sampling sites in the Klamath River as well as other drainages in the Pacific Northwest that are (or have historically been) important native salmonid habitat.  I plan to use long term monitoring data from at least one of these drainages to begin exploring spatial and temporal patterns in disease.
 
Polychaetes may be processed live or preserved (stained bright pink to facilitate sorting).  This polychaete was collected from an eddy in the Klamath River, the adult is still partly inside its tube and several juveniles hae been expelled while dissecting the upper portion of the tube.   A juvenile polychaete--note the eyespots!
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Polychaetes on a slide coverslip.  They will be weighed and counted prior to inclusion in an experiment.   Polychaete experimental chambers.  Polychaetes are held in small aerated containers in an incubator in order to control temperature and oxygen.
  Al;exander 8
We are investigating population dynamics such as size structure in different river habitats as part of a larger study.  Preliminary data suggests polychaetes may be larger in eddys than other habitat features, which may be a function of food availability or decreased predation.   We are also investigating parasite dynamics in different river habitats as part of a larger study, preliminary data suggest habitats may be characterized by differences in parasite densities in some reaches of the river.

 

Previous Research

I previously worked extensively on Tubifex tubifex, the oligochaete host of Myxobolus cerebralis in Yellowstone National Park.  Myxobolus cerebralis causes whirling disease in salmonid fishes.  The processes that govern interactions between M. cerebralis and T. tubifex are not well understood but environment and genotype effects (and interactions between these) appear to strongly influence disease dynamics.

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Yellowstone cutthroat fry from Yellowstone National Park exhibiting blacktail and deformed vertebrae, characteristic signs of whirling disease.   Tubifex tubifex worms collected from a tributary in Yellowstone National Park where Myxobolus cerebralis, the parasite that causes whirling disease, has been detected.  These worms were tested for parasite DNA by molecular methods.
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Field work in Yelllowstone National Park--summer.   Field work in Yellowstone National Park--winter
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 Tubifex tubifex collected during winter sampling.   Tubifex tubifex progeny reside in cocoons until they hatch, typically in late winter to early spring.  Reproductive adults produce multiple cocoons, filled with up to 15 progeny, when conditions permit.  When conditions become stressful, adults may reabsorb their reproductive structures to conserve energy.

 

Affiliations

  • Society for Freshwater Science (formerly the North American Benthological Association)- this is a wonderful organization to belong to- particularly as a student member!
  • Ecological Society of America (ESA)
  • The Wildlife Society
  • American Fisheries Society (AFS)

Publications

Alexander, J.D., B.L. Kerans, T.M. Koel, and C. Rasmussen (2011).  Context-specific parasitism in Tubifex tubifex in geothermally influenced stream reaches in Yellowstone National Park.  Journal of the North American Benthological Society 30(3):853-867.

Alexander, J.D. and B.L. Kerans (in review).  Substrate determines outcomes of host parasite interactions between Tubifex tubifex and Myxobolus cerebralis.  

Alexander, J.D., S. L. Hallett, L. Xue, and J. L. Bartholomew.  (in prep)  Population dynamics of the polychaete, Manayunkia speciosa, and the myxozoan parasite Ceratomyxa shasta in the Klamath River.

Alexander, J.D., B.L. Kerans, and T.M. Koel (in prep).  Phylogeography of Tubifex tubifex from Yellowstone National Park and their susceptibility to Myxobolus cerebralis

Alexander, J.D. and B.L. Kerans (in prep) Stream geomorphology and disease risk in Yellowstone National Park:  environmental features influence Myxobolus cerebralis infection in Tubifex tubifex