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Author Topic:   Non-mendelian genetics/ non-darwinian evolution
EZscience
Member (Idle past 5471 days)
Posts: 961
From: A wheatfield in Kansas
Joined: 04-14-2005


Message 54 of 56 (315136)
05-25-2006 1:57 PM
Reply to: Message 53 by Wounded King
05-25-2006 12:17 PM


Inheritance of symbionts
Most aphid species carry obligate symbionts in the form of various strains of the bacterium Buchnera aphidicola. The bacteria cannot survive outside the aphid and the aphid relies on them to synthesize various amino acids (usually trypotophan) that it cannot produce for itself. The bacteria are housed in a special cellular organelle, a bacteriocyte, and are inherited vertically - every developing aphid embryo receives symbionts through special processes growing from neighboring maternal bacteriocytes.
Things got more interesting with the discovery of a series of 'secondary' aphid sympbiotes belonging to various other bacterial genera. These are not completely essential for aphid survival, but some provide the aphid with interesting and unique phenotypic abilities (new host range, change in thermal tolerance, etc.). Cytological studies have revealed these bacteria 'piggy-backing' on the bacteriocytes of the primary symbionts to ensure their inheritance, although they are not actually housed within them (yet?) and their inheritance is not as consistent (usually less than 100%).
So my question is, would you consider the vertical inheritance of such symbionts to constitute a valid form of epigenetic inheritance, at least relative to the genome of the aphid ?
I guess we first have to decide whether the symbionts still deserve status as separate organisms, or whether the aphid+symbionte can be considered 'all one organism' at this point, in which case I guess the answer would be 'yes'.

This message is a reply to:
 Message 53 by Wounded King, posted 05-25-2006 12:17 PM Wounded King has replied

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 Message 55 by Wounded King, posted 05-26-2006 7:00 AM EZscience has replied

  
EZscience
Member (Idle past 5471 days)
Posts: 961
From: A wheatfield in Kansas
Joined: 04-14-2005


Message 56 of 56 (315257)
05-26-2006 8:42 AM
Reply to: Message 55 by Wounded King
05-26-2006 7:00 AM


Re: Inheritance of symbionts
WK writes:
the bacteriocytes are actually specialised cells
Yes, my incorrect terminology. The Buchnera are fully enclosed by special cells.
I think it's fascinating that these secondary endosymbiontes are now jockeying for position (competing?) with the more ancient Buchnera for a position within the aphids. Organisms can be viewed as composite micro-ecosystems.
Incidentally, the genetic phyllogeny of the Buchnera complex has a wonderful congruency with the genetic phylogeny of the Aphididae and various novel acquisition events can be inferred in different aphid lineages.

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 Message 55 by Wounded King, posted 05-26-2006 7:00 AM Wounded King has not replied

  
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