Data from: Effects of pesticide mixtures on host-pathogen dynamics of the amphibian chytrid fungus

Anthropogenic and natural stressors often interact to affect organisms.
Amphibian populations are undergoing unprecedented declines and
extinctions with pesticides and emerging infectious diseases implicated as
causal factors. Although these factors often co-occur, their effects on
amphibians are usually examined in isolation. We hypothesized that
exposure of larval and metamorphic amphibians to ecologically relevant
concentrations of pesticide mixtures would increase their post-metamorphic
susceptibility to the fungus Batrachochytrium dendrobatidis (Bd), a
pathogen that has contributed to amphibian population declines worldwide.
We exposed five anuran species (Pacific treefrog, Pseudacris regilla;
spring peeper, Pseudacris crucifer; Cascades frog, Rana cascadae; northern
leopard frog, Lithobates pipiens; and western toad, Anaxyrus boreas) from
three families to mixtures of four common insecticides (chlorpyrifos,
carbaryl, permethrin, and endosulfan) or herbicides (glyphosate,
acetochlor, atrazine, and 2,4-D) or a control treatment, either as
tadpoles or as newly metamorphic individuals (metamorphs). Subsequently,
we exposed animals to Bd or a control inoculate after metamorphosis and
compared survival and Bd load. Bd exposure significantly increased
mortality in Pacific treefrogs, spring peepers, and western toads, but not
in Cascades frogs or northern leopard frogs. However, the effects of
pesticide exposure on mortality were negligible, regardless of the timing
of exposure. Bd load varied considerably across species; Pacific
treefrogs, spring peepers, and western toads had the highest loads,
whereas Cascades frogs and northern leopard frogs had the lowest loads.
The influence of pesticide exposure on Bd load depended on the amphibian
species, timing of pesticide exposure, and the particular pesticide
treatment. Our results suggest that exposure to realistic pesticide
concentrations has minimal effects on Bd-induced mortality, but can alter
Bd load. This result could have broad implications for risk assessment of
amphibians; the outcome of exposure to multiple stressors may be
unpredictable and can differ between species and life stages.