Scientists have recently sequenced and analyzed genomes in the bacteria of anglerfish bulbs. The anglerfish used for sampling were taken from the Gulf of Mexico. The mutually beneficial relationship that the fish and bacteria have formed has caused some of the genes that are a necessary part of living freely to be lost. This is because the bacteria create light for the fish, and the fish supplies the bacteria with nutrients. Researchers found this to be intriguing because the fish came to be about 100 million years ago. The bacteria are an example of a third type of symbiosis. The data suggests that the bacteria are continuously evolving and are not stuck with their host (fish).
It is particularly interesting to me that even though these fish evolved some 100 million years ago, their critical bacteria are continuing to evolve. I also find it interesting that the genomes are reduced during evolution.