Question: Are reproductive output and age at first reproduction explained by the prevalence of ca... more Question: Are reproductive output and age at first reproduction explained by the prevalence of castrating parasites in a population? Life-history theory predicts this relationship. Data studied: Reproductive output over 21 days in field-caught freshwater snails from 12 lake populations in Wisconsin. I also measured age at first reproduction and reproductive output over 27 weeks in laboratory-reared snails from the same populations. I determined the prevalence of parasites in each of 2 years as the proportion of snails infected with digenean trematodes. Search method: Field-caught: I regressed mean reproductive output on mean prevalence. Laboratory-reared: I regressed mean reproductive output and mean age at first reproduction on mean prevalence. Conclusions: Neither measure of reproductive output, nor age at first reproduction, was predicted by the mean prevalence of trematode parasites.
Understanding invasive species impacts is critical to determining how an ecosystem may function a... more Understanding invasive species impacts is critical to determining how an ecosystem may function after an introduction. Invasive species can alter the structure and function of ecosystems, reduce biological diversity, and alter communities through predation, facilitation and competition. In the past 30 years, the invasive New Zealand mud snail (Potamopyrgus antipodarum) has established in areas of conservation concern in the American West including Yellowstone National Park. To develop a greater understanding of the impact of P. antipodarum on the native co-occurring snail, Fossaria (Bakerilymnaea) bulimoides group, we conducted two experiments to assess the interactions occurring between these snails. We found that F. bulimoides growth was reduced by all interactors, but especially by P. antipodarum. In addition, growth of F. bulimoides was much more affected by high biomass of snails than P. antipodarum. P. antipodarum grew more in the presence of interactors and their growth was facilitated by the presence of the native snail F. bulimoides.
Animals require food adequate in quantity and quality to grow and reproduce. Therefore, environme... more Animals require food adequate in quantity and quality to grow and reproduce. Therefore, environments limited in key nutrients may promote competitive interactions, with the organisms best equipped to exploit these resources gaining a competitive advantage. We compared the foraging behavior of the New Zealand mudsnail (Potamopyrgus antipodarum), a worldwide invader that can dominate secondary productivity to Fossaria (Bakerlymnaea) bulimoides which is native to western North America to determine whether either of these animals modify their behavior to compensate for nutrient limitation. We used the amount of dietary phosphorus (P) as a measure of food quality, because P is often a limiting resource in freshwater ecosystems. We compared the feeding rate and food preference of each snail species to food containing two levels of P. Because potential competitors can also affect foraging decisions, we conducted additional experiments comparing the effects of conspecifics and heterospecifics under low and high biomass. Consistent with predictions, both species increased feeding rate of low P food, and P. antipodarum consumed more food per unit mass than Fossaria. However, only Fossaria displayed a preference for high P food. The two snails also differed in their response to interacting snails. Fossaria significantly reduced foraging activity in the presence of both conspecifics and heterospecifics, while P. antipodarum spent more time feeding under high conspecific density. Although the presence of high densities of P. antipodarum may negatively impact Fossaria in its native habitat, Fossaria’s ability to locate and preferentially feed on higher quality resources may mitigate some of the impact, potentially facilitating coexistence between these two species.
demonstrate a strong signature of the P environment in the lake of origin on how this snail respo... more demonstrate a strong signature of the P environment in the lake of origin on how this snail responds to P limitation as well as preliminary evidence for intraspecific variation of AP expression in animals.
Why some species and lineages are more likely to be invasive than others is one of the most impor... more Why some species and lineages are more likely to be invasive than others is one of the most important unanswered questions in basic and applied biology. In particular, the relative contributions to the invasion process of factors like preadaptation to invasiveness in the native range, evolution post-colonization, and random vs. non-random sampling of colonist lineages remain unclear. Here, we use a powerful common garden approach to address the potential for a role for sensitivity to nutrient limitation in determining the invasiveness of particular lineages of Potamopyrgus antipodarum, a New Zealand freshwater snail that has become globally invasive. We quantified specific growth rate (SGR), an important fitness-related trait in this species, under high phosphorus (P) vs. low-P conditions for a diverse set of native and invasive P. antipodarum.
Exploitation of shared resources often mediates the impacts of invasive species on native species... more Exploitation of shared resources often mediates the impacts of invasive species on native species. In a field experiment, we compared the ability to graze periphyton and the genera of diatoms removed by the invasive New Zealand mudsnail, Potamopyrgus antipodarum, a native caddisfly larva (Brachycentrus sp.), and a native mayfly nymph (Ephemerella sp.) over 1 week. P. antipodarum removed as much or slightly more periphyton than the native grazers, depending on whether chlorophyll a or ash-free dry mass was used to measure periphyton biomass. When we examined the diatoms in the periphyton, P. antipodarum altered the diatom assemblage more than the native grazers. Effective grazing of periphyton by P. antipodarum may impact native grazers by consuming shared algal resources. In particular, because Ephemerella sp. were also effective grazers, these mayflies may compete for periphyton with P. antipodarum in the western United States. Taken together, these results suggest that ability to procure food resources may contribute to the invasion success of P. antipodarum.
Whether or not organisms become infected by parasites is likely to be a complex interplay between... more Whether or not organisms become infected by parasites is likely to be a complex interplay between host and parasite genotypes, as well as the physiological condition of both species. Details of this interplay are very important because physiology‐driven susceptibility has the potential to confound genetic coevolutionary responses. Here we concentrate on how physiological aspects of infection may interfere with genetic‐based infectivity in a snail–trematode (Potamopyrgus antipodarum/Microphallus sp.) interaction by asking: (1) how does host condition affect susceptibility to infection? and (2) how does host condition affect the survival of infected individuals? We manipulated host condition by experimentally varying resources. Contrary to our expectation, host condition did not affect susceptibility to infection, suggesting that genetics are more important than physiology in this regard. However, hosts in poor condition had higher parasite‐induced mortality than hosts in good condition. Taken together, these results suggest that coevolutionary interactions with parasites may depend on host condition, not by altering susceptibility, but rather by affecting the likelihood of parasite transmission.
Local adaptation-typically recognized as higher values of fitness-related traits for native vs. n... more Local adaptation-typically recognized as higher values of fitness-related traits for native vs. non-native individuals when measured in the native environment-is common in natural populations because of pervasive spatial variation in the intensity and type of natural selection. Although local adaptation has been primarily studied in the context of biotic interactions, widespread variation in abiotic characteristics of environments suggests that local adaptation in response to abiotic factors should also be common. Potamopyrgus antipodarum, a freshwater New Zealand snail that is an important model system for invasion biology and the maintenance of sexual reproduction, exhibits local adaptation to parasites and rate of water flow. As an initial step to determining whether P. antipodarum are also locally adapted to phosphorus availability, we examined whether populations differ in their responses to phosphorus limitation. We found that fieldcollected juvenile P. antipodarum grew at a lower rate and reached an important size threshold more slowly when fed a relatively low vs. a relatively high-phosphorus diet. We also detected significant across-population variation in individual growth rate. A marginally significant population-by-dietary phosphorus interaction along with a twofold difference across populations in the extent of suppression of growth by low phosphorus suggests that populations of P. antipodarum may differ in their response to phosphorus limitation. Local adaptation may explain this variation, with the implication that snails from lakes with relatively low phosphorus availability should be less severely affected by phosphorus limitation than snails from lakes with higher phosphorus availability.
The predominance of sexual reproduction despite its costs indicates that sex provides substantial... more The predominance of sexual reproduction despite its costs indicates that sex provides substantial benefits, which are usually thought to derive from the direct genetic consequences of recombination and syngamy. While genetic benefits of sex are certainly important, sexual and asexual individuals, lineages, or populations may also differ in physiological and life history traits that could influence outcomes of competition between sexuals and asexuals across environmental gradients. Here, we address possible phenotypic costs of a very common correlate of asexuality, polyploidy. We suggest that polyploidy could confer resource costs related to the dietary phosphorus demands of nucleic acid production; such costs could facilitate the persistence of sex in situations where asexual taxa are of higher ploidy level and phosphorus availability limits important traits like growth and reproduction. We outline predictions regarding the distribution of diploid sexual and polyploid asexual taxa across biogeochemical gradients and provide suggestions for study systems and empirical approaches for testing elements of our hypothesis.
When species are introduced to novel environments, abiotic conditions must be suitable for specie... more When species are introduced to novel environments, abiotic conditions must be suitable for species to become invasive. For example, water chemistry must be acceptable for aquatic non-natives to colonize and persist. In two laboratory experiments, we measured growth and survival of Potamopyrgus antipodarum, a worldwide invasive snail from New Zealand, and two co-occurring native snails [Pyrgulopsis robusta and Galba (Bakerilymnaea) bulimoides group] to contrast the relative sensitivity of the three species to aspects of water chemistry (specific conductivity and concentration of multiple cations). Low conductivity reduced growth and survival of Potamopyrgus but did not affect growth of native snails and only reduced survival of one native species, Pyrgulopsis, at extremely low conductivity. In contrast, neither specific cations nor concentration affected growth and survival of Potamopyrgus, but both affected native snails; Pyrgulopsis, grew more at higher concentrations of cations, and Galba grew nine times faster with added potassium than with added magnesium and had higher survival in concentrated than in diluted solutions. Thus, the invasive and native snails differed in their sensitivity to water chemistry: the invasive snail is more sensitive to conductivity, and the native snails are more sensitive to the concentration of specific cations. Our conclusions are consistent with previous studies and with the distribution of Potamopyrgus in the western USA, and parts of Europe, where density of the invasive snail increases with conductivity. Thus, native snails may be able to escape negative effects of the invasive snails by inhabiting areas with low conductivity, when ion concentrations are sufficient.
Understanding the mechanisms that species use to succeed in new environments is vital to predicti... more Understanding the mechanisms that species use to succeed in new environments is vital to predicting the extent of invasive species impacts. Food quality is potentially important because it can affect population dynamics by affecting life history traits. The New Zealand mudsnail, Potamopyrgus antipodarum, is a worldwide invader. We examined how mudsnail growth rate and fecundity responded to the C:P ratio of algal food in laboratory conditions. Mudsnails fed low-P algae (C:P 1,119) grew more slowly, matured later, produced smaller offspring, and grew to a smaller adult size than snails reared on algae with high levels of P. A relatively small increase in algal C:P (203-270) significantly increased mudsnail age at maturity. We suggest that the relatively high body P requirements of mudsnails make them susceptible to allocation trade-offs between growth and reproduction under P-limited conditions. The elemental composition of algae varies greatly in nature, and over half of the rock biofilms in streams surveyed within the introduced range of mudsnails in the Greater Yellowstone Area had C:P ratios above which could potentially pose P limitation of life history traits. High growth rate and fecundity are common traits of many species that become invasive and are also associated with high-P demands. Therefore, fast-growing consumers with high P demands, such as mudsnails, are potentially more sensitive to P limitation suggesting that limitation of growth and reproduction by food quality is an important factor in understanding the resource demands of invasive species.
Question: Are reproductive output and age at first reproduction explained by the prevalence of ca... more Question: Are reproductive output and age at first reproduction explained by the prevalence of castrating parasites in a population? Life-history theory predicts this relationship. Data studied: Reproductive output over 21 days in field-caught freshwater snails from 12 lake populations in Wisconsin. I also measured age at first reproduction and reproductive output over 27 weeks in laboratory-reared snails from the same populations. I determined the prevalence of parasites in each of 2 years as the proportion of snails infected with digenean trematodes. Search method: Field-caught: I regressed mean reproductive output on mean prevalence. Laboratory-reared: I regressed mean reproductive output and mean age at first reproduction on mean prevalence. Conclusions: Neither measure of reproductive output, nor age at first reproduction, was predicted by the mean prevalence of trematode parasites.
Understanding invasive species impacts is critical to determining how an ecosystem may function a... more Understanding invasive species impacts is critical to determining how an ecosystem may function after an introduction. Invasive species can alter the structure and function of ecosystems, reduce biological diversity, and alter communities through predation, facilitation and competition. In the past 30 years, the invasive New Zealand mud snail (Potamopyrgus antipodarum) has established in areas of conservation concern in the American West including Yellowstone National Park. To develop a greater understanding of the impact of P. antipodarum on the native co-occurring snail, Fossaria (Bakerilymnaea) bulimoides group, we conducted two experiments to assess the interactions occurring between these snails. We found that F. bulimoides growth was reduced by all interactors, but especially by P. antipodarum. In addition, growth of F. bulimoides was much more affected by high biomass of snails than P. antipodarum. P. antipodarum grew more in the presence of interactors and their growth was facilitated by the presence of the native snail F. bulimoides.
Animals require food adequate in quantity and quality to grow and reproduce. Therefore, environme... more Animals require food adequate in quantity and quality to grow and reproduce. Therefore, environments limited in key nutrients may promote competitive interactions, with the organisms best equipped to exploit these resources gaining a competitive advantage. We compared the foraging behavior of the New Zealand mudsnail (Potamopyrgus antipodarum), a worldwide invader that can dominate secondary productivity to Fossaria (Bakerlymnaea) bulimoides which is native to western North America to determine whether either of these animals modify their behavior to compensate for nutrient limitation. We used the amount of dietary phosphorus (P) as a measure of food quality, because P is often a limiting resource in freshwater ecosystems. We compared the feeding rate and food preference of each snail species to food containing two levels of P. Because potential competitors can also affect foraging decisions, we conducted additional experiments comparing the effects of conspecifics and heterospecifics under low and high biomass. Consistent with predictions, both species increased feeding rate of low P food, and P. antipodarum consumed more food per unit mass than Fossaria. However, only Fossaria displayed a preference for high P food. The two snails also differed in their response to interacting snails. Fossaria significantly reduced foraging activity in the presence of both conspecifics and heterospecifics, while P. antipodarum spent more time feeding under high conspecific density. Although the presence of high densities of P. antipodarum may negatively impact Fossaria in its native habitat, Fossaria’s ability to locate and preferentially feed on higher quality resources may mitigate some of the impact, potentially facilitating coexistence between these two species.
demonstrate a strong signature of the P environment in the lake of origin on how this snail respo... more demonstrate a strong signature of the P environment in the lake of origin on how this snail responds to P limitation as well as preliminary evidence for intraspecific variation of AP expression in animals.
Why some species and lineages are more likely to be invasive than others is one of the most impor... more Why some species and lineages are more likely to be invasive than others is one of the most important unanswered questions in basic and applied biology. In particular, the relative contributions to the invasion process of factors like preadaptation to invasiveness in the native range, evolution post-colonization, and random vs. non-random sampling of colonist lineages remain unclear. Here, we use a powerful common garden approach to address the potential for a role for sensitivity to nutrient limitation in determining the invasiveness of particular lineages of Potamopyrgus antipodarum, a New Zealand freshwater snail that has become globally invasive. We quantified specific growth rate (SGR), an important fitness-related trait in this species, under high phosphorus (P) vs. low-P conditions for a diverse set of native and invasive P. antipodarum.
Exploitation of shared resources often mediates the impacts of invasive species on native species... more Exploitation of shared resources often mediates the impacts of invasive species on native species. In a field experiment, we compared the ability to graze periphyton and the genera of diatoms removed by the invasive New Zealand mudsnail, Potamopyrgus antipodarum, a native caddisfly larva (Brachycentrus sp.), and a native mayfly nymph (Ephemerella sp.) over 1 week. P. antipodarum removed as much or slightly more periphyton than the native grazers, depending on whether chlorophyll a or ash-free dry mass was used to measure periphyton biomass. When we examined the diatoms in the periphyton, P. antipodarum altered the diatom assemblage more than the native grazers. Effective grazing of periphyton by P. antipodarum may impact native grazers by consuming shared algal resources. In particular, because Ephemerella sp. were also effective grazers, these mayflies may compete for periphyton with P. antipodarum in the western United States. Taken together, these results suggest that ability to procure food resources may contribute to the invasion success of P. antipodarum.
Whether or not organisms become infected by parasites is likely to be a complex interplay between... more Whether or not organisms become infected by parasites is likely to be a complex interplay between host and parasite genotypes, as well as the physiological condition of both species. Details of this interplay are very important because physiology‐driven susceptibility has the potential to confound genetic coevolutionary responses. Here we concentrate on how physiological aspects of infection may interfere with genetic‐based infectivity in a snail–trematode (Potamopyrgus antipodarum/Microphallus sp.) interaction by asking: (1) how does host condition affect susceptibility to infection? and (2) how does host condition affect the survival of infected individuals? We manipulated host condition by experimentally varying resources. Contrary to our expectation, host condition did not affect susceptibility to infection, suggesting that genetics are more important than physiology in this regard. However, hosts in poor condition had higher parasite‐induced mortality than hosts in good condition. Taken together, these results suggest that coevolutionary interactions with parasites may depend on host condition, not by altering susceptibility, but rather by affecting the likelihood of parasite transmission.
Local adaptation-typically recognized as higher values of fitness-related traits for native vs. n... more Local adaptation-typically recognized as higher values of fitness-related traits for native vs. non-native individuals when measured in the native environment-is common in natural populations because of pervasive spatial variation in the intensity and type of natural selection. Although local adaptation has been primarily studied in the context of biotic interactions, widespread variation in abiotic characteristics of environments suggests that local adaptation in response to abiotic factors should also be common. Potamopyrgus antipodarum, a freshwater New Zealand snail that is an important model system for invasion biology and the maintenance of sexual reproduction, exhibits local adaptation to parasites and rate of water flow. As an initial step to determining whether P. antipodarum are also locally adapted to phosphorus availability, we examined whether populations differ in their responses to phosphorus limitation. We found that fieldcollected juvenile P. antipodarum grew at a lower rate and reached an important size threshold more slowly when fed a relatively low vs. a relatively high-phosphorus diet. We also detected significant across-population variation in individual growth rate. A marginally significant population-by-dietary phosphorus interaction along with a twofold difference across populations in the extent of suppression of growth by low phosphorus suggests that populations of P. antipodarum may differ in their response to phosphorus limitation. Local adaptation may explain this variation, with the implication that snails from lakes with relatively low phosphorus availability should be less severely affected by phosphorus limitation than snails from lakes with higher phosphorus availability.
The predominance of sexual reproduction despite its costs indicates that sex provides substantial... more The predominance of sexual reproduction despite its costs indicates that sex provides substantial benefits, which are usually thought to derive from the direct genetic consequences of recombination and syngamy. While genetic benefits of sex are certainly important, sexual and asexual individuals, lineages, or populations may also differ in physiological and life history traits that could influence outcomes of competition between sexuals and asexuals across environmental gradients. Here, we address possible phenotypic costs of a very common correlate of asexuality, polyploidy. We suggest that polyploidy could confer resource costs related to the dietary phosphorus demands of nucleic acid production; such costs could facilitate the persistence of sex in situations where asexual taxa are of higher ploidy level and phosphorus availability limits important traits like growth and reproduction. We outline predictions regarding the distribution of diploid sexual and polyploid asexual taxa across biogeochemical gradients and provide suggestions for study systems and empirical approaches for testing elements of our hypothesis.
When species are introduced to novel environments, abiotic conditions must be suitable for specie... more When species are introduced to novel environments, abiotic conditions must be suitable for species to become invasive. For example, water chemistry must be acceptable for aquatic non-natives to colonize and persist. In two laboratory experiments, we measured growth and survival of Potamopyrgus antipodarum, a worldwide invasive snail from New Zealand, and two co-occurring native snails [Pyrgulopsis robusta and Galba (Bakerilymnaea) bulimoides group] to contrast the relative sensitivity of the three species to aspects of water chemistry (specific conductivity and concentration of multiple cations). Low conductivity reduced growth and survival of Potamopyrgus but did not affect growth of native snails and only reduced survival of one native species, Pyrgulopsis, at extremely low conductivity. In contrast, neither specific cations nor concentration affected growth and survival of Potamopyrgus, but both affected native snails; Pyrgulopsis, grew more at higher concentrations of cations, and Galba grew nine times faster with added potassium than with added magnesium and had higher survival in concentrated than in diluted solutions. Thus, the invasive and native snails differed in their sensitivity to water chemistry: the invasive snail is more sensitive to conductivity, and the native snails are more sensitive to the concentration of specific cations. Our conclusions are consistent with previous studies and with the distribution of Potamopyrgus in the western USA, and parts of Europe, where density of the invasive snail increases with conductivity. Thus, native snails may be able to escape negative effects of the invasive snails by inhabiting areas with low conductivity, when ion concentrations are sufficient.
Understanding the mechanisms that species use to succeed in new environments is vital to predicti... more Understanding the mechanisms that species use to succeed in new environments is vital to predicting the extent of invasive species impacts. Food quality is potentially important because it can affect population dynamics by affecting life history traits. The New Zealand mudsnail, Potamopyrgus antipodarum, is a worldwide invader. We examined how mudsnail growth rate and fecundity responded to the C:P ratio of algal food in laboratory conditions. Mudsnails fed low-P algae (C:P 1,119) grew more slowly, matured later, produced smaller offspring, and grew to a smaller adult size than snails reared on algae with high levels of P. A relatively small increase in algal C:P (203-270) significantly increased mudsnail age at maturity. We suggest that the relatively high body P requirements of mudsnails make them susceptible to allocation trade-offs between growth and reproduction under P-limited conditions. The elemental composition of algae varies greatly in nature, and over half of the rock biofilms in streams surveyed within the introduced range of mudsnails in the Greater Yellowstone Area had C:P ratios above which could potentially pose P limitation of life history traits. High growth rate and fecundity are common traits of many species that become invasive and are also associated with high-P demands. Therefore, fast-growing consumers with high P demands, such as mudsnails, are potentially more sensitive to P limitation suggesting that limitation of growth and reproduction by food quality is an important factor in understanding the resource demands of invasive species.
Uploads
Papers by Amy Krist