<p>In the Anthropocene, amphibians must not only cope with natural
stressors but also a suite of human-made stressors that have been experienced
relatively recently within their evolutionary history. Because it has become
increasingly common for natural and anthropogenic stressors to co-occur in aquatic
ecosystems, the study of their separate and combined effects on ecosystems and
their component species is increasingly necessary. This is especially important for amphibians,
which have experienced global declines and can be highly sensitive to both
natural and anthropogenic stressors. Pesticides and parasites are two commonly
co-occurring stressors that can have complex individual and synergistic
detrimental effects in amphibian populations. Here, I conducted three studies
to broadly assess the separate and interactive effects of pesticides and
parasites on amphibians. More specifically, I explored: 1) the underlying physiological
mechanism allowing amphibians to induce increased tolerance to a pesticide
within a single generation, 2) the effects of exposure timing to two
functionally similar cryptic parasite species on infection outcomes, and 3) population-level
variation in susceptibility to parasites and whether prior exposure to
pesticides influenced the outcome of host-parasite interactions. First, to test
the hypothesis that
induced pesticide tolerance is the result of a generalized stress response, I
exposed tadpoles to an anthropogenic stressor (sublethal pesticide dose), a
natural stressor (cues from a caged predator), or a simulated stressor via
exogenous exposure to the stress hormone corticosterone (CORT). I then exposed
the larvae to a lethal carbaryl treatment to assess how the stressor exposures
influenced survival. I found that prior exposure to exogenous CORT and predator
cues induced tolerance to a lethal concentration of carbaryl, providing
evidence that pesticide tolerance can be induced by a generalized stress
response both in the presence and absence (exogenous CORT) of specific cues. Second,
I explored how the timing of host exposure to two co-occurring cryptic
echinostome species influences infection outcomes. I found that echinostome infection success in
larval anurans can differ significantly based on the parasite species makeup,
density, and exposure timing. I also found that priority effects can occur even
between functionally similar cryptic species, with an early exposure to <i>Echinoparyphium
</i>lineage 3 reducing the infection success of <i>Echinostoma trivolvis </i>three
days later. Finally, I assessed the influence of pesticide exposure on
host-parasite interactions and population-level variation in these responses.
This was accomplished by exposing wood frog larvae from eight
populations to one of two treatments (a
sublethal carbaryl concentration or a pesticide-free control) followed by controlled
parasite exposures to either echinostome trematodes or ranavirus. Then, I
assessed how pesticide exposure influenced infection loads, infection
prevalence, and survival in each population. I found significant population-level
variation in infection outcomes. Interestingly, however, I found no significant
effects of pesticide exposure on disease outcomes. Together, these three
studies demonstrate the wide-ranging and surprising outcomes that can result
from interactions among and between natural and anthropogenic stressors.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/12156165 |
| Date | 24 April 2020 |
| Creators | Logan S Billet (8734638) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/Exploring_the_Separate_and_Interactive_Effects_of_Pesticides_and_Parasites_on_Amphibians/12156165 |
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