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Community Ecology Natural Enemies Parasites

1. How do parasites impact their host populations?

3. Are parasites responsible for the recent increase

in amphibian deformities?

2. How does aquatic ecology relate to issues

of human health?

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Parasitism an interaction in

which one organism gains

resources at the expense of

the other.

ParasiteAn organism

which gains resources at the

expense of its host.

Sea lamprey (Petromyzon marinus) attached to a laketrout (Salvelinus namaycush)

Daphnia dentiferawith bacterial parasite

Host The organism necessary

for the development of a parasite

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Endoparasite a parasite that

lives inside its host

Ectoparasitea parasite that

lives on the outside of its host.

Sea lamprey (Petromyzon marinus) attached to a laketrout (Salvelinus namaycush)

Daphnia dentiferawith bacterial parasite

Vector an organism that

transmits the parasite from host

to host

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1. Find a host. This processcan be active or passive.

3. Overcome host defenses.

Invertebrates do not have a

well-developed immune

system

General life-cycle of parasites:

2. Attach to or enter the host.This process can also be active

or passive.

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4. Gain resources from the

host.

6. Disperse young to new hosts.

General life-cycle of parasites:

5. Reproduce.

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We know that parasites

are everywhere....

...but for many

systems we do not

understand the role ofthese parasites in

population and

community ecology.

Questions of interest for both

limnology and human health.

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Human health and aquatic ecology

Mosquitoes are vectors for at least30 human diseases

West Nile Virus

Encephalitis

Yellow FeverMalaria

Many other human diseases

have an aquatic phase

Schistosomiasis

Cholera

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Deformities in Pennsylvania

wood frogs (Rana sylvatica)Deformed American toads (Bufo americanus)

Since mid 1990s, increased reports of amphibian

deformities

3 main hypotheses: UV, parasites, chemicals

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Johnson et al.

(2002) found a

clearcorrelation

between

parasite

occurrenceand the

frequency of

abnormalities

Also

conducted

experiments

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Life cycle of

tremadodes

(flukes,

flatworms)

http://limnology.wisc.edu/personnel/pieter/Hidden%20Stuff/Amphibian%2

0Deformities%20Research.htm

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Trematode

cercariae, the

infective stagethat attacks

frogs

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Kiesecker (2002) wanted to simultaneously test the role of

parasites and chemicals

Used 6 naturally occurring ponds:

3 with high agricultural runoff (+ chemicals)

3 without agricultural runoff (- chemicals)

Built 6 cages in each pond:

3 that allowed parasites (+ parasites)

3 that did not allow parasites ( - parasites)

+ parasite - parasite

+ chemicals

- chemicals

+P, +C

+P, -C

-P, +C

-P, -C

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Ponds 1-3

Ponds 4-6

High agricultural runoff

Atrazine

Malathion

Low agricultural

runoffNo Atrazine

or Malathion

detected

6 natural ponds

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6 cages per pond

Add tadpoles to the cages

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6 cages per pond

In each pond:

3 cages allowed the parasitein (exposed)

3 cages kept the parasite out

(protected/unexposed)

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Percentage of deformities in adult

frogs:

Pond Exposed Protected

1 23% 0%2 34% 0%

3 27% 0%

4 3% 0%

5 7% 0%6 4% 0%

Green = + chemicals

Blue = - chemicals

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Why do pesticides increase occurrence of

developmental deformities when tadpoles are exposed

to parasites?

Do chemicalsweaken the

immune system

and the

tadpoles abilityto fight off

infection?

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Laboratory experiment:

Atrazine

(weed control on

crops)

Malathion

(mosquitoes and

insect control oncrops)

Esfenvalerate

(insect control

on crops)

Control

(no chemicals)

Exposeto2parasit

es

Measure

infectio

nand

immune

system

respons

e

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Summary of

laboratory results

Atrazine

Malathion

Esfenvalerate

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Concepts to know

What do we know about parasites in aquaticsystems? What is left to learn?

Are parasites the only cause of

deformities in frogs?

What are the characteristics of parasite life cycles?

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Practice Question

Recently, Kagami et al. (2004) suggested a

complex interaction between Daphnia,

Asterionella(diatom) and a fungal parasite ofthe diatom (Zygorhizidium).

The life-cycle of this parasite includes a free-

living fungal zoospore that is the same size and

shape as small, edible algal cells. When a free

zoospore encounters a diatom cell, it attaches

to it.

The key to this complex interaction between

Daphnia, the diatom and the diatoms parasiteis the relationship depicted in Figure 1.

Please explain the nature of this complex relationship. A complete answer will consider the

typical interaction between a Daphniaand a diatom, the typical interaction between a diatomand its parasite, and how the presence ofDaphniamay alter the host-parasite interaction.