Community ecology - Original Paper


, Volume 166, Issue 4, pp 1029-1041

First online:

Individual and combined effects of multiple pathogens on Pacific treefrogs

  • John M. RomansicAffiliated withDepartment of Zoology, Oregon State University Email author 
  • , Pieter T. J. JohnsonAffiliated withDepartment of Ecology and Evolutionary Biology, University of Colorado
  • , Catherine L. SearleAffiliated withDepartment of Zoology, Oregon State University
  • , James E. JohnsonAffiliated withDepartment of Biological Sciences, Central Washington University
  • , Tate S. TunstallAffiliated withDepartment of Ecology, Evolution and Marine Biology, University of California, Santa Barbara
  • , Barbara A. HanAffiliated withOdum School of Ecology, University of Georgia
  • , Jason R. RohrAffiliated withDepartment of Integrative Biology, University of South Florida
  • , Andrew R. BlausteinAffiliated withDepartment of Zoology, Oregon State University

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In nature, individual hosts often encounter multiple pathogens simultaneously, which can lead to additive, antagonistic, or synergistic effects on hosts. Synergistic effects on infection prevalence or severity could greatly affect host populations. However, ecologists and managers often overlook the influence of pathogen combinations on hosts. This is especially true in amphibian conservation, even though multiple pathogens coexist within amphibian populations, and several pathogens have been implicated in amphibian population declines and extinctions. Using an amphibian host, Pseudacris regilla (Pacific treefrog), we experimentally investigated interactive effects among three pathogens: the trematode Ribeiroia sp. (hereafter, Ribeiroia), the fungus Batrachochytrium dendrobatidis (hereafter, BD), and the water mold Achlya flagellata. We detected no effects of A. flagellata, but did find effects of Ribeiroia and BD that varied depending on context. Low doses of Ribeiroia caused relatively few malformations, while higher Ribeiroia doses caused numerous deformities dominated by missing and reduced limbs and limb elements. Exposure to low doses of BD accelerated larval host development, despite there being no detectable BD infections, while exposure to higher BD doses caused infection but did not alter developmental rate. Hosts exposed to both Ribeiroia and BD exhibited the highest mortality, although overall evidence of interactive effects of multiple pathogens was limited. We suggest further research on the influence of multi-pathogen assemblages on amphibians, particularly under a variety of ecological conditions and with a wider diversity of hosts and pathogens.


Coinfection Concomitant infections Polyparasitism Emerging infectious disease Amphibian decline