Effects of varying environments on the ecology and evolution of the New Zealand Mud Snail and its interactors

Sarah M. Redd

Changes in environmental variables have long been known to influence biological interactions, and neglecting to account for environmental differences can lead to disastrous environmental scenarios. Here, I present the results of two studies looking at environmental effects on interactions involving the New Zealand Mud Snail (Potamopyrgus antipodarum), a worldwide invasive species. Chapter 1 describes an infection experiment designed to test for environmental effects on the interaction between the mud snail and its trematode parasite, Microphallus sp. I used parasites from different environments (lake versus stream) and snails raised under different food regimes in a laboratory infection experiment. Both parasite origin and food level impacted snail growth, and snails raised under high food levels also exhibited higher infection rates, indicating that environment is important to the snail host. Results failed to find evidence of environmental influence on the genotypic specificity of the snail-parasite interaction, indicating an absence of geographic selection mosaics for the tested variables. In chapter 2, I investigated environmental impacts on ecological interactions between invasive populations of the New Zealand Mud Snail, the narrowly endemic Jackson Lake Spring Snail (Pyrgulopsis robusta), and Rainbow Trout (Oncorhynchus mykiss). Presence of the mud snail negatively impacts the spring snail, currently known in only a single stream. Previous work indicates the existence of predator avoidance behavior in the mud snail, and I was interested in the effect this might have on resource use and competition. In a laboratory experiment, I tested for indirect effects of Rainbow Trout on the consumer-resource interactions of both snails at different competitive densities. Snails of both species were more likely to exhibit predator avoidance behaviors when competition was low, indicating that strong competition may pose a greater threat to snails than weak predation. I found strong effects of snail density on chlorophyll density, but consumer-resource interaction strengths indicated stronger per biomass interactions at low snail density. Combined results indicate the importance of quantifying environmental effects to prediction and management of the New Zealand Mud Snail.

Effects of varying environments on the ecology and evolution of the New Zealand Mud Snail and its interactors

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