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Tabo Z, Luboobi L, Kraft P, Breuer L, Albrecht C. Control of schistosomiasis by the selective competitive and predatory intervention of intermediate hosts: A mathematical modeling approach. Math Biosci 2024:109263. [PMID: 39089572 DOI: 10.1016/j.mbs.2024.109263] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2023] [Revised: 06/24/2024] [Accepted: 07/24/2024] [Indexed: 08/04/2024]
Abstract
Schistosomiasis, a freshwater-borne neglected tropical disease, disproportionately affects impoverished communities mainly in the tropical regions. Transmission involves humans and intermediate host (IH) snails. This manuscript introduces a mathematical model to probe schistosomiasis dynamics and the role of non-host snail competitors and predators as biological control agents for IH snails. The numerical analyses include investigations into steady-state conditions and reproduction numbers associated with uncontrolled scenarios, as well as scenarios involving non-host snail competitors and/or predators. Sensitivity analysis reveals that increasing snail mortality rates is a key to reducing the IH snail population and control of the transmission. Results show that specific snail competitors and/or predators with strong competition/predation abilities reduce IH snails and the subsequent infectious cercaria populations, reduce the transmission, and possibly eradicate the disease, while those with weaker abilities allow disease persistence. Hence our findings advocate for the effectiveness of snail competitors with suitable competitive pressures and/or predators with appropriate predatory abilities as nature-based solutions for combating schistosomiasis, all while preserving IH snail biodiversity. However, if these strategies are implemented at insignificant levels, IH snails can dominate, and disease persistence may pose challenges. Thus, experimental screening of potential (native) snail competitors and/or predators is crucial to assess the likely behavior of biological agents and determine the optimal biological control measures for IH snails.
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Affiliation(s)
- Zadoki Tabo
- Department of Animal Ecology and Systematics, Justus Liebig University Giessen, Heinrich-Buff-Ring 26 (iFZ), 35392, Giessen, Germany; Department of Landscape Ecology and Resource Management, Justus Liebig University Giessen, Heinrich-Buff-Ring 26 (iFZ), 35392, Giessen, Germany.
| | - Livingstone Luboobi
- Independent Researcher, C/O Department of Mathematics, Makerere University, Kampala, Uganda
| | - Philipp Kraft
- Department of Landscape Ecology and Resource Management, Justus Liebig University Giessen, Heinrich-Buff-Ring 26 (iFZ), 35392, Giessen, Germany
| | - Lutz Breuer
- Department of Landscape Ecology and Resource Management, Justus Liebig University Giessen, Heinrich-Buff-Ring 26 (iFZ), 35392, Giessen, Germany; Centre for International Development and Environmental Research (ZEU), Justus Liebig University Giessen, Senckenbergstrasse 3, 35390, Giessen, Germany
| | - Christian Albrecht
- Department of Animal Ecology and Systematics, Justus Liebig University Giessen, Heinrich-Buff-Ring 26 (iFZ), 35392, Giessen, Germany
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Faiad SM, Williams MA, Goodman M, Sokolow S, Olden JD, Mitchell K, Andriantsoa R, Gordon Jones JP, Andriamaro L, Ravoniarimbinina P, Rasamy J, Ravelomanana T, Ravelotafita S, Ravo R, Rabinowitz P, De Leo GA, Wood CL. Temperature affects predation of schistosome-competent snails by a novel invader, the marbled crayfish Procambarus virginalis. PLoS One 2023; 18:e0290615. [PMID: 37703262 PMCID: PMC10499222 DOI: 10.1371/journal.pone.0290615] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2022] [Accepted: 08/12/2023] [Indexed: 09/15/2023] Open
Abstract
The human burden of environmentally transmitted infectious diseases can depend strongly on ecological factors, including the presence or absence of natural enemies. The marbled crayfish (Procambarus virginalis) is a novel invasive species that can tolerate a wide range of ecological conditions and colonize diverse habitats. Marbled crayfish first appeared in Madagascar in 2005 and quickly spread across the country, overlapping with the distribution of freshwater snails that serve as the intermediate host of schistosomiasis-a parasitic disease of poverty with human prevalence ranging up to 94% in Madagascar. It has been hypothesized that the marbled crayfish may serve as a predator of schistosome-competent snails in areas where native predators cannot and yet no systematic study to date has been conducted to estimate its predation rate on snails. Here, we experimentally assessed marbled crayfish consumption of uninfected and infected schistosome-competent snails (Biomphalaria glabrata and Bulinus truncatus) across a range of temperatures, reflective of the habitat range of the marbled crayfish in Madagascar. We found that the relationship between crayfish consumption and temperature is unimodal with a peak at ~27.5°C. Per-capita consumption increased with body size and was not affected either by snail species or their infectious status. We detected a possible satiation effect, i.e., a small but significant reduction in per-capita consumption rate over the 72-hour duration of the predation experiment. Our results suggest that ecological parameters, such as temperature and crayfish weight, influence rates of consumption and, in turn, the potential impact of the marbled crayfish invasion on snail host populations.
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Affiliation(s)
- Sara M. Faiad
- School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA, United States of America
| | - Maureen A. Williams
- School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA, United States of America
- Department of Biology, McDaniel College, Westminster, MD, United States of America
| | - Maurice Goodman
- Hopkins Marine Station, Dept. of Oceans and of Earth System Science, Doerr School of Sustainability, Stanford University, Stanford, CA, United States of America
| | - Susanne Sokolow
- Hopkins Marine Station, Dept. of Oceans and of Earth System Science, Doerr School of Sustainability, Stanford University, Stanford, CA, United States of America
- Marine Science Institute, University of California, Santa Barbara, Santa Barbara, CA, United States of America
| | - Julian D. Olden
- School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA, United States of America
| | - Kaitlyn Mitchell
- Hopkins Marine Station, Dept. of Oceans and of Earth System Science, Doerr School of Sustainability, Stanford University, Stanford, CA, United States of America
| | - Ranja Andriantsoa
- Réseau International Schistosomiase Environnement Aménagement et Lutte (RISEAL) Madagascar, Madagascar
| | | | - Luciano Andriamaro
- Réseau International Schistosomiase Environnement Aménagement et Lutte (RISEAL) Madagascar, Madagascar
| | | | - Jeanne Rasamy
- Réseau International Schistosomiase Environnement Aménagement et Lutte (RISEAL) Madagascar, Madagascar
- Department of Zoology and Animal Biodiversity, University of Antananarivo, Antananarivo, Madagascar
| | - Tsilavina Ravelomanana
- Réseau International Schistosomiase Environnement Aménagement et Lutte (RISEAL) Madagascar, Madagascar
- Department of Zoology and Animal Biodiversity, University of Antananarivo, Antananarivo, Madagascar
| | - Salohy Ravelotafita
- Department of Zoology and Animal Biodiversity, University of Antananarivo, Antananarivo, Madagascar
| | - Ranaivosolo Ravo
- Department of Zoology and Animal Biodiversity, University of Antananarivo, Antananarivo, Madagascar
| | - Peter Rabinowitz
- Department of Environmental/Occupational Health Sciences, Global Health, University of Washington, Seattle, WA, United States of America
- Center for One Health Research (COHR), University of Washington, Seattle, WA, United States of America
| | - Giulio A. De Leo
- Hopkins Marine Station, Dept. of Oceans and of Earth System Science, Doerr School of Sustainability, Stanford University, Stanford, CA, United States of America
- Woods Institute for the Environment, Stanford University, Stanford, CA, United States of America
| | - Chelsea L. Wood
- School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA, United States of America
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Szydlowski DK, Elgin AK, Lodge DM, Tiemann JS, Larson ER. Long-term macrophyte and snail community responses to population declines of invasive rusty crayfish (Faxonius rusticus). ECOLOGICAL APPLICATIONS : A PUBLICATION OF THE ECOLOGICAL SOCIETY OF AMERICA 2023; 33:e2818. [PMID: 36772970 DOI: 10.1002/eap.2818] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2022] [Revised: 01/04/2023] [Accepted: 01/12/2023] [Indexed: 06/18/2023]
Abstract
A central focus of invasive species research has been on human efforts to eradicate invaders or reduce their abundance to mitigate the worst of their impacts. In some cases, however, populations of invasive species decline without human intervention, which may inform management responses to these invaders. Such is the case of the invasive rusty crayfish (Faxonius rusticus) in northern Wisconsin, USA, where systematic population monitoring since 1975 has revealed population declines in approximately half of the lakes surveyed. Population declines of invasive species without human intervention remain understudied, but there is even less research on how communities respond following such declines. Using 10 lakes in Vilas County, Wisconsin, we investigated community recovery of habitat (macrophytes) and prey (freshwater snails) of F. rusticus following up to 33 years of declines of this invader in some lakes using a dataset with a rare, long-term span over which consistent data were collected (1987, 2002, 2011, and 2020). We compared community responses in lakes where F. rusticus populations reached a peak and subsequently declined (boom-bust lakes) and lakes where our dataset only captured the decline of F. rusticus (bust lakes) to reference lakes with consistently high or low crayfish abundance over time. We found partial recovery of macrophytes and snails in the bust and boom-bust lakes where F. rusticus has declined, with recovery of macrophyte abundance and richness in the boom-bust lakes achieving levels observed in the low-crayfish reference lakes. Snail abundance and richness increased after declines of F. rusticus, though not to the level of the low-crayfish reference lakes, suggesting that snail recovery may lag macrophyte recovery because snails are dependent on macrophytes and associated periphyton for habitat. The recovery we document potentially represents long-term ecosystem resilience of lakes to biological invasions. Our results suggest that lake communities may recover without active restoration interventions after invasive crayfish population declines, although identifying which lakes experience these natural declines remains a priority for future research and management.
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Affiliation(s)
- Daniel K Szydlowski
- Department of Natural Resources and Environmental Sciences, University of Illinois Urbana-Champaign, Champaign, Illinois, USA
| | - Ashley K Elgin
- National Oceanic and Atmospheric Administration, Great Lakes Environmental Research Laboratory, Muskegon, Michigan, USA
| | - David M Lodge
- Cornell Atkinson Center for Sustainability, and Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York, USA
| | - Jeremy S Tiemann
- Illinois Natural History Survey, Prairie Research Institute, University of Illinois Urbana-Champaign, Champaign, Illinois, USA
| | - Eric R Larson
- Department of Natural Resources and Environmental Sciences, University of Illinois Urbana-Champaign, Champaign, Illinois, USA
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Liukkonen M, Kronholm I, Ketola T. Evolutionary rescue at different rates of environmental change is affected by trade-offs between short-term performance and long-term survival. J Evol Biol 2021; 34:1177-1184. [PMID: 33963623 DOI: 10.1111/jeb.13797] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Accepted: 04/20/2021] [Indexed: 11/29/2022]
Abstract
As climate change accelerates and habitats free from anthropogenic impacts diminish, populations are forced to migrate or to adapt quickly. Evolutionary rescue (ER) is a phenomenon, in which a population is able to avoid extinction through adaptation. ER is considered to be more likely at slower rates of environmental change. However, the effects of correlated characters on evolutionary rescue are seldom explored yet correlated characters could play a major role in ER. We tested how evolutionary background in different fluctuating environments and the rate of environmental change affect the probability of ER by exposing populations of the bacteria Serratia marcescens to two different rates of steady temperature increase. As suggested by theory, slower environmental change allowed populations to grow more effectively even at extreme temperatures, but at the expense of long-term survival at extreme conditions due to correlated selection. Our results indicate important gap of knowledge on the effects of correlated selection during the environmental change and on evolutionary rescue at differently changing environments.
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Affiliation(s)
- Martta Liukkonen
- Department of Biological and Environmental Sciences, University of Jyväskylä, Jyväskylä, Finland
| | - Ilkka Kronholm
- Department of Biological and Environmental Sciences, University of Jyväskylä, Jyväskylä, Finland
| | - Tarmo Ketola
- Department of Biological and Environmental Sciences, University of Jyväskylä, Jyväskylä, Finland
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Pequeno PACL, Franklin E, Venticinque EM, Acioli ANS. Linking functional trade-offs, population limitation and size structure: Termites under soil heterogeneity. Basic Appl Ecol 2015. [DOI: 10.1016/j.baae.2015.03.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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6
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Patterns of spatio-temporal variation in the survival rates of a viviparous lizard: the interacting effects of sex, reproductive trade-offs, aridity, and human-induced disturbance. POPUL ECOL 2014. [DOI: 10.1007/s10144-014-0447-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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7
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Slow growth improves compensation ability: examining growth rate and starvation endurance in pit-building antlions from semi-arid and hyper-arid regions. Evol Ecol 2013. [DOI: 10.1007/s10682-013-9644-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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8
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Preisser EL, Orrock JL. The allometry of fear: interspecific relationships between body size and response to predation risk. Ecosphere 2012. [DOI: 10.1890/es12-00084.1] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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9
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Consumptive effects of fish reduce wetland crayfish recruitment and drive species turnover. Oecologia 2011; 168:1111-21. [DOI: 10.1007/s00442-011-2162-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2011] [Accepted: 09/30/2011] [Indexed: 10/16/2022]
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10
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Sura SA, Mahon HK. Effects of Competition and Predation on the Feeding Rate of the Freshwater Snail, Helisoma trivolvis. AMERICAN MIDLAND NATURALIST 2011. [DOI: 10.1674/0003-0031-166.2.358] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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11
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Competitive interactions between co-occurring invaders: identifying asymmetries between two invasive crayfish species. Biol Invasions 2011. [DOI: 10.1007/s10530-010-9933-2] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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12
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Hood J, Sterner R. Diet Mixing: Do Animals Integrate Growth or Resources across Temporal Heterogeneity? Am Nat 2010; 176:651-63. [DOI: 10.1086/656489] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
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13
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Scharf I, Filin I, Ovadia O. A trade-off between growth and starvation endurance in a pit-building antlion. Oecologia 2009; 160:453-60. [DOI: 10.1007/s00442-009-1316-y] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2008] [Accepted: 02/04/2009] [Indexed: 10/21/2022]
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14
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Field observations of the alarm response to crushed conspecifics in the freshwater snail Pomacea canaliculata: effects of habitat, vegetation, and body size. J ETHOL 2008. [DOI: 10.1007/s10164-008-0103-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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15
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Flinders CA, Magoulick DD. Effects of depth and crayfish size on predation risk and foraging profitability of a lotic crayfish. ACTA ACUST UNITED AC 2007. [DOI: 10.1899/06-103.1] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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16
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Turner AM, Chislock MF. Dragonfly predators influence biomass and density of pond snails. Oecologia 2007; 153:407-15. [PMID: 17457617 DOI: 10.1007/s00442-007-0736-9] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2006] [Accepted: 03/20/2007] [Indexed: 11/24/2022]
Abstract
Studies in lakes show that fish and crayfish predators play an important role in determining the abundance of freshwater snails. In contrast, there are few studies of snails and their predators in shallow ponds and marshes. Ponds often lack fish and crayfish but have abundant insect populations. Here we present the results of field surveys, laboratory foraging trials, and an outdoor mesocosm experiment, testing the hypothesis that insects are important predators of pulmonate snails. In laboratory foraging trials, conducted with ten species of insects, most insect taxa consumed snails, and larval dragonflies were especially effective predators. The field surveys showed that dragonflies constitute the majority of the insect biomass in fishless ponds. More focused foraging trials evaluated the ability of the dragonflies Anax junius and Pantala hymenaea to prey upon different sizes and species of pulmonate snails (Helisoma trivolvis, Physa acuta, and Stagnicola elodes). Anax junius consumed all three species up to the maximum size tested. Pantala hymenaea consumed snails with a shell height of 3 mm and smaller, but did not kill larger snails. P. acuta were more vulnerable to predators than were H. trivolvis or S. elodes. In the mesocosm experiment, conducted with predator treatments of A. junius, P. hymenaea, and the hemipteran Belostoma flumineum, insect predators had a pronounced negative effect on snail biomass and density. A. junius and B. flumineum reduced biomass and density to a similar degree, and both reduced biomass more than did P. hymenaea. Predators did not have a strong effect on species composition. A model suggested that A. junius and P. hymenaea have the largest effects on snail biomass in the field. Given that both pulmonate snails and dragonfly nymphs are widespread and abundant in marshes and ponds, snail assemblages in these water bodies are likely regulated in large part by odonate predation.
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Affiliation(s)
- Andrew M Turner
- Department of Biology, Clarion University, Clarion, PA 16214, USA.
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Burks RL, Mulderij G, Gross E, Jones I, Jacobsen L, Jeppesen E, Van Donk E. Center Stage: The Crucial Role of Macrophytes in Regulating Trophic Interactions in Shallow Lake Wetlands. WETLANDS: FUNCTIONING, BIODIVERSITY CONSERVATION, AND RESTORATION 2006. [DOI: 10.1007/978-3-540-33189-6_3] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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Watson G, Hamilton K, Tuffnail W. Chemical alarm signalling in the polychaete Nereis (Neanthes) virens (Sars) (Annelida: Polychaeta). Anim Behav 2005. [DOI: 10.1016/j.anbehav.2005.03.011] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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19
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Landscape-scale Variation in Taxonomic Diversity in Four Groups of Aquatic Organisms: The Influence of Physical, Chemical, and Biological Properties. Ecosystems 2005. [DOI: 10.1007/s10021-002-0270-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Sears MW. Geographic variation in the life history of the sagebrush lizard: the role of thermal constraints on activity. Oecologia 2004; 143:25-36. [PMID: 15742218 DOI: 10.1007/s00442-004-1767-0] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2003] [Accepted: 10/21/2004] [Indexed: 11/26/2022]
Abstract
Thermal constraints on the time available for activity have been proposed as a proximate mechanism to explain variation in suites of life history traits. The longer that an ectotherm can maintain activity, the more time it has to forage and the greater chance that it will encounter a predator and be eaten. Thus, the thermal environment may produce a trade off between growth and survival when variation in the environment favors increased activity. I used mark-recapture data from a demographic study of three natural populations of the sagebrush lizard (Sceloporus graciosus) and estimates of thermal opportunity for each population to evaluate whether variation in the thermal environment can explain patterns of growth and survival that occur over an elevational gradient. Lizards from the highest elevation population exhibited higher individual growth rates than those of lizards from lower elevation, while mortality rates increased with elevation for these populations. The covariation of fast growth and high mortality with increased thermal opportunity is the opposite trend expected if the thermal environment alone is to explain patterns of life history in these lizards. Additional factors including thermal heterogeneity in the distribution of microhabitats of lizards, adaptation to local environmental conditions, and a potential trade-off between resource acquisition and predation risk need to be addressed to obtain a satisfactory explanation of the causative mechanisms producing life history variation.
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Affiliation(s)
- Michael W Sears
- Department of Biology, University of Pennsylvania, Philadelphia, PA 19104-6018, USA.
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Peacor SD, Werner EE. HOW DEPENDENT ARE SPECIES-PAIR INTERACTION STRENGTHS ON OTHER SPECIES IN THE FOOD WEB? Ecology 2004. [DOI: 10.1890/03-0662] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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22
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Sandland GJ, Minchella DJ. Life-history plasticity in hosts (Lymnaea elodes) exposed to differing resources and parasitism. CAN J ZOOL 2004. [DOI: 10.1139/z04-143] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Assessing phenotypic expression across environments is essential for understanding the evolution of life histories, yet relatively few studies have empirically determined the role that multiple environmental factors play in altering animal phenotypes. We used a multifactorial approach to investigate the effects of both infection of Echinostoma revolutum (Frölich, 1802) and nutrient availability on phenotypic expressions in lines of the snail Lymnaea elodes (Say, 1821). Lines were initially established via selfing events followed by breeding (within lines) over the next four generations. Juveniles from each line were then size-matched and randomly exposed to parasite (exposed / sham-exposed) and diet (high protein / low protein) treatments, generating a 2 (line) × 2 (diet) × 2 (exposure) factorial design. Snail growth, reproduction, and survival were monitored over 5 weeks. Analyses revealed an interactive effect of host line and infection status on host growth. Main effects of both snail line and diet also significantly influenced host growth. Reproductive patterns differed between lines, with snails from one line producing egg masses and eggs in all treatments, and snails from the second line producing minimal eggs in only a single treatment. Snail survival remained similar between snail lines. Results from this study suggest that snail life-history traits can vary dramatically as a result of host genetics, the environment, and the interaction between these factors. Reasons for the occurrence and maintenance of this variability in life-history traits are discussed.
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