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SUMMARY:Mechanism of phototaxis in Platynereis larvae and the origin of vi
 sual eyes - Gáspár Jékely (Max Planck Institute for Developmental Biolo
 gy)
DTSTART:20131120T130000Z
DTEND:20131120T140000Z
UID:TALK48168@talks.cam.ac.uk
CONTACT:Jeremy Solly
DESCRIPTION:Phototaxis is widespread among planktonic organisms\, and can 
 be found in the larval stages of sponges\, cnidarians\, protostomes and de
 uterostomes. The ability of zooplankton to find their preferred water dept
 h depends on varying daily light conditions and developmental stage. Plank
 tonic larvae often undergo a behavioral change\, switching from positive p
 hototaxis\, characteristic of the post-hatching stages\, to negative photo
 taxis\, characteristic of later larval stages before settlement and metamo
 rphosis. The marine annelid Platynereis dumerilii is an excellent laborato
 ry model to study the mechanisms of larval phototaxis. Platynereis has a b
 entho-pelagic-life cycle with a pelagic larva that shows early positive an
 d late negative phototaxis. The neuronal circuit and mechanism of early la
 rval phototaxis is well understood: the larval eyespots\, consisting of a 
 shading pigment cell and a rhabdomeric photoreceptor cell\, mediate this r
 esponse. The eyespot photoreceptor directly innervates the ciliary band (p
 rototroch). The mechanism and neural circuitry underlying negative photota
 xis is unknown. To study the mechanism of negative phototaxis in Platynere
 is larvae we combined behavioral experiments\, laser ablation\, and transm
 ission electron microscopy. Late Platynereis larvae have six eyes\, the tw
 o eyespots and four additional dorsal eyes\, precursors of the adult eyes.
  We characterized the role of these eyes in larval phototaxis\, using lase
 r ablations. Our electron microscopic reconstructions revealed how the eye
 s regulate motor output during phototactic turning. The Platynereis eye ci
 rcuit shows the hallmarks of a simple visual system\, including spatial li
 ght detection and contrast modulation\, illustrating how image-forming eye
 s may have evolved via intermediate stages capable to contrast only a ligh
 t and a dark pixel during phototaxis.
LOCATION:Part II Lecture Theatre\, Department of Zoology
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