Question

I've been reading through Paulsson (2002) and I am not sure whathe means by "lineage selection" in the second to last section. Thepaper deals with plasmid replication, and mostly concentrates onthe contrasting pressures from two levels of selection:

1. intracell selection - competition between plasmids ina single cell. A plasmid can undergo a cis-mutation andover-replicate, resulting in a higher intracell fitness than thefocal plasmid. The plasmids reproduce.
2. intercell selection - competition between cells. Cellswith a heavier load of plasmids will take longer to reproduce, andplasmids that produce a heavy load will have lower intercellfitness. The cells containing plasmids reproduce.

In this context, what does the third level of selection-- lineage selection -- mean? What reproduces? How do thelineages split or interact?

My guess

Does lineage selection simply mean group-selection on separatecolonies of cells? In that case, how are new lineages formed? Iwould expect this group level to select for zero levels of plasmids(since they place no loads on the cells and thus these groups ofcells will grow the fastest), but Paulsson (2002) suggests theopposite:

lineage selection could favor plasmid traits that help thepopulation of plasmid-containing cells to fight plasmid-freecells.

Is there a more detailed discussions of this available than theone section in Paulsson (2002)? Neither the unit of selection noreither the evolutionary or genetic lineage Wikipedia articlesaddress my question. The first only mentions lineage in passing,and the second two don't discuss models of selection.