Environmental predictors of schistosome parasite production in Michigan lakes

Thomas R. Raffel, Ph.D.Madelyn Messner

Department of Biological SciencesOakland University

Rochester, MI

Raffel Lab Approach:• Spatial & temporal surveys• Experiments at large & small scales• Pollution effects on parasite communities• Temperature & parasitism

• Statistical & predictive models

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Pollution & trematodes example: (2008 Study with Jason Rohr Univ. S Florida)

+Snails

+Cercariae

Eutrophication

Cattle tank experiment:

• Trematode biology is temperature-dependent̶5 Snail growth & reproductive rates̶5 Trematode development rate̶5 Cercaria production rate**

• BUT most studies ignore:

Temperature & trematodes: (Ongoing collaboration with Piet Johnson’s lab Univ. Colorado)

Nonlinearities Variability

Day

Temperature & trematodes: (Ongoing collaboration with Piet Johnson’s lab Univ. Colorado)

• Thermal Stress Hypothesis– Depletion of host energy reserves at stressful temperatures Lower cercaria production following excessively warm periods

• Temperature-shift experiment: Predictions: Observations:

Temperature & trematodes: (Ongoing collaboration with Piet Johnson’s lab Univ. Colorado)

• Predictive model:̶5 Based on metabolic theory & dynamic energy budget theory̶5 Parameterized by measuring temperature-dependence of

host food assimilation & respiration

13°C Acclimation22°C Acclimation28°C Acclimation

Temperature & trematodes: (Ongoing collaboration with Piet Johnson’s lab Univ. Colorado)

• Predictive model:̶5 Based on metabolic theory & dynamic energy budget theory̶5 Parameterized by measuring temperature-dependence of

host food assimilation & respiration

Swimmer’s Itch Research Needs• Better monitoring & detection methods

– Filtration + microscopy; Slide samplers (short-term)– Quantitative PCR (DNA detection; medium-term)– Electronic biosensors? (longer-term)

• Control measure effectiveness & impact– Track & model population-level impacts of snail/bird removal– Test ecosystem-level impacts of copper sulfate & alternative

molluscicides (surveys/mesocosms, medium-term)• Improve predictive models for snail density, trematode

prevalence, and cercaria production– Spatial & temporal surveys (short-term)– Lab & Mesocosm experiments (medium-term)– Predictive modeling (medium-term)

DEVELOPMENT OF ALERT SYSTEMS (long-term)

Swimmer’s itch• Trematode infection (avian

schistosomes)• 2-host life cycle (SNAILS)• Discourages recreational water

use (economic impact)• Difficult to manage• Limited research literature• Limited funding opportunities

What determines swimmer’s itch exposure?

Snail population density

Percent snails infected

Cercariae produced per snail

Bird infection

Temperature variation

Nutrient loading (Eutrophication)

Cercariaein water

SWIMMER’S ITCH!

Potential Management Strategies• Snail control– Copper sulfate– Mechanical removal

• Bird control– Hunt, relocate, treat

• Pollution control• Protective skin creams• Public education• Predictive modeling

Management decisionsReal-time alerts

2015 Summer Research Aims:1. Temporal surveys: Obtain field data that can be used to validate models predicting short term fluctuations in swimmer’s itch exposure

2. Spatial Survey: Collaborate with volunteers to obtain data from 8 lakes to determine predictors of schistosome cercariae abundance across a region.

1. Temporal survey What are the best predictors of daily abundance of avian schistosome cercariae?

‒ Core hypothesis– cercaria production is driven by the thermal biology and dynamic energy budgets of the snail host

‒ Alternative predictors– water temperature, wind direction/speed, snail population dynamics, algal growth (food)

Temperature Wind speed AlgaeSnail population

Snail densitiesNutrients Land Use

2. Spatial surveyWhat determines patterns of schistosome cercariae production across a broad landscape?Potential predictors: ‒ lake size/depth/hydrology‒ Land use & soil/rock types‒ Climate (temp, precipitation, wind)‒ Snail & invertebrate densities‒ Pollutants (pesticides & nutrients)‒ Algae/vegetation growth‒ Bird visitation

MethodsLake Volunteers

• Sample from water surface using 1 liter, 35 µm mesh filters

• 50 filter scoops along shore one sample

• Rinse filters with ethanol to preserve cercariae

• Sample between sunrise and noon each day

• Store samples in cool, dark place

MethodsRaffel Lab

• Survey snail populations - Pipe-sampling

• PCR methods- qPCR to quantify schistosome DNA in water- Regular PCR & sequencing to identify species

• ELISA kits to detect pollutants Herbicides: triazines & metabolites, glyphosates Insecticides: organophosphates and carbamates

• Periphyton growth- Ceramic tiles chlorophyll extraction

• Land use characterization- GIS software and datasets

• Water temperature, wind velocity, precipitation- HOBO loggers and weather databases

Quantitative/Real-time PCR

Raffel Lab commitments:• Organize survey• Provide training and sampling materials• Survey snail & invertebrate populations • Measure environmental variables• Process cercaria DNA & water chemistry samples• Statistical analysis, reports, and presentations

Lake Association participation:• Recruit at least 1 volunteer to collect daily filter

samples for 2-4 weeks during July/August• Provide financial support to analyze cercaria DNA

and water chemistry samples ($500 per site)• Help select sampling sites

Spatial survey 2015:

TimetableMonth Goals

April Sampling schedule, refine methods, identify study sites

May/June Monthly visits to sites to survey and collect data

July/August Daily cercaria sampling from lakes known to harbor swimmer’s itch

September Process samples, compile data

Oct/Nov/Dec Follow-up experiments & analysis