Abstract:
Contemporary environmental change encompasses massive biodiversity loss and
increasing numbers of emerging diseases worldwide. As part of a global biodiversity
crisis, amphibians are disappearing at unprecedented rates. Batrachochytrium
dendrobatidis is an emerging infectious pathogen prominently associated with many
declines. Chapter 1 reviews the past decade of research on this system and highlights
areas where knowledge is notably lacking.
Host behavior remains a crucial determinant of host-pathogen dynamics yet
studies addressing the effects of Batrachochytrium on amphibian behaviors are
virtually nonexistent. Remaining chapters examine behavioral responses of host
species to Batrachochytrium. Chapter 2 examines how ancient behaviors that have
persisted in amphibians for millions of years change with exposure to
Batrachochytrium. I examined thermoregulatory behavior in tadpoles of four species
(Pseudacris regilla, Rana aurora, Bufo boreas, Rana cascadae), and aggregation
behavior in two species that school as tadpoles (B. boreas, R. cascadae). Results
suggest that some amphibians will continue seeking optimal temperatures and
continue aggregating regardless of infection risk. I discuss the importance of
behavioral plasticity and evolutionary inertia in interpreting host behavioral responses
to infection.
Chapter 3 examines Batrachochytrium dynamics when multiple host species
interact. I manipulated infection status in tadpoles of three naturally co-occurring hosts
(P. regilla, B. boreas, R. cascadae) in various combinations and measured growth,
survival and infection severity. There were strong interactions between species
combinations and infection leading to pathogen-mediated mutualism and competition.
Results also suggest that both species richness and species identity may be important
factors moderating a dilution effect in this system.
Coexisting, interacting hosts must also contend with predators in a community.
Chapter 4 explores Batrachochytrium-induced changes in antipredator behaviors in
four species (P. regilla, R. aurora, B. boreas, R. cascadae). I also examined whether
antipredator behaviors increased survivorship in the presence of lethal predators in R.
cascadae, R. aurora. Exposure to Batrachochytrium changed activity rate and refuge
use in Bufo, but not in the other species. Nonselective predation of Batrachochytriumexposed
prey by susceptible predators adds an unexplored dimension of complexity to
this system.
Chapter 5 summarizes the ecological implications of studies presented in this
dissertation.
