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I can tell you what I know. First note, though, that mitochondria and chloroplasts are unusual among prokaryotic endosymbionts for being so specialized - most are simply bacteria that can live inside or outside the host. The only analagous eukaryotic endosymbionts I can think of are the chloroplasts of the cryptomonads, which actually contain a reduced nucleus (nucleomorph) in addition to the green prokaryote proper. For single-celled hosts, zooxanthellae also come to mind. These are tiny green dinoflagellates that live within the frothy outer parts of some amoeboids, and I think in some anenomes. In this case the cells stay in a palmelloid stage - that is they do not have their flagella or their shells - but are otherwise fully intact, and will regenerate if removed from the host. The amoeba I gather receives some energy from them. A similar thing happens with the algae found inside lichens. Animals have a whole host of bacteria and protozoa in their gut. Of special note here I suppose are the protists that live in the gut of termites and digest cellulose for them. These aren't reduced in any way except possibly in that they lack mitochondria, but it is generally supposed that they branched off before mitochondria were developed, and they contain bacterial endosymbionts instead, which do the digesting for them. And remember that symbionts don't have to be helpful, so trypanosomes and sporozoans as well as larger things like tapeworms and roundworms would count as endosymbionts as well. I don't think any prokaryotes have endosymbionts, and they certainly don't have any eukaryotic ones - the difference in size of the cells is simply too great. I suppose one might consider viri something of this sort, but generally the requirement is that endosymbionts have to be removeable from the host in some way. Hmm, thinking about it this may invalidate some of the examples above. Well, I hope that was some help, or at least interesting. --Josh Grosse :) |
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