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encysting cercariae

Omar O. Barriga barriga.2 at osu.edu
Thu Jul 17 01:23:17 EST 1997

>> Are folks comfortable with the idea that cercariae that
>> encyst "on" something are in general ancestral to those that encyst
>> "in" a next intermediate host?  Is there a nice, neat evolutionary
>> trend from encysting on a plant to encysting on an animal to
>> encysting 'in' an animal?  Any discussion (to the group or to me) is
>> welcome.

>        Hrmmm, well, just to play Devil's advocate, why could it not be that
>cercariae that encyst on something were derived from cercariae that
>encyst in another host?  Thus, it would seem that there are 2

>1)  cercariae that encyst on something gave rise to cercariae that need
>another host


>2) cercariae that encyst in another host gave rise to those that encyst
>on something.

(there is more)
>Mark Rigby

Also to play Devil's advocate:

It seems to me that the signals to start encystment *in* a host must be more
foreign to a cercaria than the signals *on* a host. After all, the environment 
*on* a host is largely the same as for the free cercaria. As a biological 
event, I would expect that responding to the signals *in* a host is a more 
complicated physiological procedure than responding to the signals *on*
a host. Therefore, I would expect that the *ecto* encystment is ancestral
to the *endo* encystment.


			Omar O. Barriga 

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