Evolution of Pharyngeal Feeding Behaviors in Free-Living Soil Nematodes

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Title: Evolution of Pharyngeal Feeding Behaviors in Free-Living Soil Nematodes
Author: Chiang, Jing-Tzyh Alan
Abstract: To explore using nematodes as a model for studying behavioral evolution , I examined pharyngeal behaviors in free -living soil nematodes related to Caenorhabditis elegans . The nematode pharynx is divided into three regions : corpus , isthmus , and terminal bulb . Pharyngeal behaviors consist of stereotyped patterns of two motions : pumping and peristalses . I observed pharyngeal behaviors in multiple species , and constructed the following evolutionary model . In the ancestor of free -living soil nematodes , the pharynx had corpus pumping , isthmus peristalses , and terminal bulb pumping , each of which occurred independently . In the Rhabditidae family , the anterior isthmus switched to pumping , and anterior isthmus and terminal bulb pumping became coupled to corpus pumping . In the Diplogasteridae family , the terminal bulb switched to peristalses . In the Cephalobidae family , isthmus peristalses and terminal bulb pumping became coupled . And in the Panagrolaimidae family , the posterior isthmus switched to pumping . The above changes in isthmus and TB behaviors suggested corresponding changes in their neuronal regulation . Using laser ablations , I found that M4's function evolved significantly : M4 stimulated posterior isthmus peristalsis (Rhabditidae ) , isthmus /terminal bulb peristalsis (Diplogasteridae ) , isthmus peristalsis and terminal bulb pumping (Cephalobidae ) , and posterior isthmus /terminal bulb pumping (Panagrolaimidae ) . Yet , increased food activated M4 activity in all families . Thus , M4 appeared to be a general "food sensor" neuron , which was co -opted during evolution to perform different downstream functions . Additionally , M2 stimulated anterior isthmus peristalsis in the Panagrolaimidae . Using Caenorhabditis elegans , I investigated possible molecular /genetic causes for the above changes . Why is the terminal bulb unaffected by M4 in Caenorhabditis elegans and the Rhabditidae ? I found that mutating slo -1 activated M4 -terminal bulb stimulations , suggesting that alterations in synaptic transmission silenced M4 -terminal bulb synapses . Also , why does M2 stimulate peristalses in the Panagrolaimidae , and M4 in the other families ? I found ceh -28 important for M4 to stimulate peristalsis in Caenorhabditis elegans , but M2 also had the potential for ceh -28 expression . This suggested a genetic /molecular link between the two neurons , and ceh -28 related mechanisms may determine which neuron stimulates peristalsis . Overall , I characterized how pharyngeal behaviors evolved at the behavioral , neuronal , and genetic levels . These results suggested the utility of nematodes for studying behavioral evolution .
URI: http : / /hdl .handle .net /2152 .5 /368
Date: 2007-05-22


Evolution of Pharyngeal Feeding Behaviors in Free-Living Soil Nematodes. Graduate School of Biomedical Sciences. Available electronically from http : / /hdl .handle .net /2152 .5 /368 .

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Cephalobidae_DWF1301_100x.mpg 2.595Mb video/mpeg View/Open
Cephalobidae_DWF1301_63x.mpg 2.536Mb video/mpeg View/Open
ChiangJian-Tzyh.pdf 859.5Kb application/pdf View/Open
Diplogasteridae_PS312_100x.mpg 2.864Mb video/mpeg View/Open
Diplogasteridae_PS312_63x.mpg 2.988Mb video/mpeg View/Open
Panagrolaimidae_PS1159_100x.mpg 5.472Mb video/mpeg View/Open
Panagrolaimidae_PS1159_63x.mpg 2.596Mb video/mpeg View/Open
Rhabditidae_DF5017_100x.mpg 3.739Mb video/mpeg View/Open
Rhabditidae_DF5017_63x.mpg 2.488Mb video/mpeg View/Open
Rhabditidae_N2_100x.mpg 2.490Mb video/mpeg View/Open
Rhabditidae_N2_63x.mpg 2.488Mb video/mpeg View/Open
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