Buchnera

Buchnera are endosymbiotic bacteria living within aphid cells that synthesize amino acids aphids cannot produce from plant sap. They are transmitted vertically - passed from mother to offspring within eggs. Their only path to the next generation runs through their host's reproduction.

When the aphid reproduces successfully, Buchnera reproduce. When the aphid dies without offspring, Buchnera's lineage ends. This vertical transmission creates perfect alignment of evolutionary interests - selection favors Buchnera that enhance aphid reproduction. Buchnera genomes have become highly reduced, losing genes unnecessary within the host.