The Devil’s Dance: Snail-host-seeking Behavior by Larval Trematodes

1. The Devil’s Dance: Snail-host-seeking Behavior by Larval Trematodes Cheyenne Conrad

2. Trematode life cycles require snail intermediate hosts SchistomsomaEchinostoma

3. Contradictory Results • 4 different small molecules were identified as the exclusive stimuli attracting miracidia • Only 2 studies controlled pH • Miracidia were exposed to artificially high concentrations of ‘attractants’ (Snail conditioned water) • Some miracidial responses to snail attractants could have been induced by toxic effects, rather than being examples of seeking behavior

4. The Reinvestigation: Experiment #1 • This study addressed two main questions: • What mechanism of chemo-orientation do miracidia and cercariae use to respond to snail cues? • What kind of molecules • are they responding to?

5. The Reinvestigation: Experiment #1 • Chemo-orientation: the phenomenon in which organisms direct their movements in in response to chemical cues • 3 possible responses: • Chemotaxis: Directional movement • Chemokinesis: Increase of turning (Increasing gradient) • Turnback Swimming (decreasing gradient)

6. The Reinvestigation: Experiment #1 The Choice-chambers: Miracidia and cercariae were exposed to concentration gradients of chemical compounds Their chemo-orientation response was observed

7. The Reinvestigation: Experiment #1 Results:

8. The Reinvestigation: Experiment #1 • Results: Miracidia show 2 types of orientation mechanism Cercariae show only 1 type of orientation mechanism Snail host cues are macromolecules

9. The Reinvestigation: Experiment #2 • Specificity in miracidial host-finding? Results: • S. mansoni(Egyptian strain) was significantly more attracted to snail conditioned water of their compatible host snail species • Miracidia of two Brazilian S. mansonistrains did not show such preference

10. The Reinvestigation: Experiment #3 • Specificity in miracidial host-finding? Results: • S. japonicummiracidia could not distinguish between their host snail O. hupensisand B. glabrataduring chemo-orientation • S. japonicumonly attached to O. hupensis

11. The Reinvestigation: Conclusions • Different Schistosome strains may achieve different levels of host specificity during chemo-orientation of miracidia • The macromolecule cues may be snail-strain specific • Higher levels of specificity may be attained during miracidial attachment and penetration

12. What about Cercariae? Employ different chemo-orientation mechanisms than miracidia They respond to small molecules

13. Why not just chemotaxis? The swimming movements of miracidia and cercariae may make chemotactic behavior difficult

14. Summary • Miracidia are attracted to snail macromolecules, and are able to employ 2 different types of chemo-orientation • Cercariae are attracted to small molecules, and are only capable of one type of chemo-orientation mechanism • Miracidia are the better host finders • Miracida-snail relationships are phylogenetically older • Some degree of specificity during host-finding, but specificity is also determined by attachment and penetration stages

15. References Haas, W, B. Haberl, M. Kalbe, M. Körner. 1995. Snail-host-finding by Miracidia and Cercariae: Chemical Host Cues. Parasitology Today 11: 468-472

16. Questions?