Examples of parasites altering host behavior

Polymorphus paradoxus

 

Phylum:  Acanthocephala

Strategy:  Alter behavior of intermediate host to make it more susceptible to predation. 

 

Life cycle:

·        Adults reside in ducks

Anterior region of adult Polymorphus sp., from
 
http://www.nhc.ed.ac.uk/index.php?page=24.25.333.372

 

http://www.nhc.ed.ac.uk/images/collections/invertebrates/parasitic/LgPolymorphus.jpg

 

·        Invertebrate stages reside in Gammarus lacustris, about 5-10 mm in length, a small crustacean that feeds in ponds and rivers.

 

http://sites.google.com/site/fiskeprosjekt/_/rsrc/1232553576838/naeringsemne/marflo.jpg

 

·        Uninfected gammarids are negatively phototactic and positively geotactic, but infected ones are positively phototactic and negatively geotactic, and engage in a “skimming” behavior at the surface of the water.  Furthermore, they will find a rock or plant on the surface, and latch on.  Hence, they become easy prey to ducks, which are the definitive host. 

 

The evidence for selective predation of infected individuals?:

 

Comparative vulnerability of uninfected Gammarus lacustris and ones infected with Polymorphus paradoxus. (Adapted from Table 1 of Bethel and Holmes [1977], Increased vulnerability of amphipods to predation owing to altered behavior induced by larval acanthocephalans. Canadian Journal of Zoology 55(1):110-115.

 

 

 

Gammarids eaten/No. available

 

 

 

Test No.

 

Duration

(min)

 

 

No. predators

 

 

Uninfected

Infected with Polymorphus paradoxus

 

 

P*

1

7

2

6/25

16/25

<0.01

2

5

2

13/50

35/50

<0.001

3

5

2

12/50

42/50

<0.001

4

5

1

8/50

18/50

<0.05

5

10

1

0/75

48/75

<0.001

6

15

1

24/75

63/75

<0.001

TOTAL

 

 

63/325

222/325

<0.001

 *P = probability, by chi-square contingency tests

·        What is the mechanism?  It is thought that when Gammarus lacustris is infected with a thorny-headed worm, the parasite causes serotonin  
Serotonin is a monoamine neurotransmitter synthesized in serotonergic neurons in the central nervous system and enterochromaffin cells in the gastrointestinal tract of animals including humans....
 to be massively expressed. Serotonin is a neurotransmitter involved in emotions and mood. Researchers have found that during mating Gammarus lacustris expresses high levels of serotonin. Also during mating, the male Gammarus lacustris clamps down on the female and holds on for days. Researchers have additionally found that blocking serotonin releases clamping. Another experiment found that serotonin also reduces the photophobic behavior in Gammarus lacustris. Thus, it is thought that the thorny-headed worm physiologically changes the behavior of the Gammarus lacustris in order to enter its final host, the bird.

 

Sacculina sp.

Phylum Arthropoda

Strategy:  Parasitic castration, leading to behaviors of infected hosts to care for brood pouches as if they were their own.

 

Definitive hosts are crabs

 

Larval cypris form, which looks equivalent to other barnacle larvae, attaches onto host.  The following 3 images are from:
http://www.mesa.edu.au/friends/seashores/crab_parasitism.html

http://www.mesa.edu.au/friends/seashores/images/sacculina_attaches.gif

 

Graphic of parasitic barnacle changing into a kentrogen larvae

 

·        Female injects kentrogen larva into body of suitable host first.

http://www.mesa.edu.au/friends/seashores/images/sacculina_ingrowth.gif

 

 

·        Two males inject their kentrogen larvae into suitable pore of female

·        Female and accompanying females grow tumorlike, especially in gonads of host crab, castrating it.

 

Suitable hosts are found in waters near Hong Kong and Japan.

Males acquire physical characteristics of females, and both infected males and females “fan” and care for the egg pouch as if it were an authentic brood pouch.

 

 

 

Sacculina brood pouch

 
http://www.seanbluestone.com/images/animals/parasite_sacculina.jpg

 

Hymenolepis diminuta

Phylum Platyhelminthes

 

Strategies:

1.   Alter “fragrance” of food source for intermediate hosts, making it more likely for intermediate hosts to feed on food sources infected with ova.

2.   Parasitic castration of the intermediate host, to provide more nutrition for the parasite, rather than allocating it to gamete production.

 

Adults normally reside in rodents, especially rats (about 18-30 cm in length)

http://www.stanford.edu/group/parasites/ParaSites2005/Hymenolepis/Pictures/hymenol0.jpg

 

Ova are passed in the feces

http://pathmicro.med.sc.edu/parasitology/hym2.jpg

Cysticercoid larvae are found in beetles, which have ingested ova in feces from infected rat.

 

Cysticercoid larvae, ~0.1 mm in length

Tenebrio beetles, about 1 cm long, which are the beetles frequently used in laboratory experiments.

http://www.umanitoba.ca/science/zoology/faculty/dick/z346/images/hymen6.jpg

http://www.zin.ru/ANIMALIA/COLEOPTERA/images/tenebmx1.jpg

 

 

 

http://www.stanford.edu/group/parasites/ParaSites2005/Hymenolepis/Pictures/H_diminuta_LifeCycle.gif

 

·        “Beetles are lured to egg-laden droppings by an aroma that’s apparently irresistible to the insects.”

o   Source of “fragrance” could be the eggs themselves, something produced by the adult worms, or perhaps something secreted by the infected hosts.

o   Difference in droppings increases likelihood that beetles will feed on sources of tapeworm larvae.