Many insects rely on heritable bacterial endosymbionts for essential nutrients that they cannot get through their diet. A new study, published in Nature Communications, indicates that the genomes of these symbiotic bacteria often shrink over time. Some of these bacteria, which live inside certain insect cells, have lost so many genes that they have broken the record for the tiniest genome ever found—almost blurring the lines between organelle and bacteria.
Endosymbiotic relationships are common in many insects, and in sap-sucking insects, like planthoppers and cicadas, they are essential for the insect’s survival. Because the sap of plants does not typically contain certain amino acids or vitamins, the insect must get them another way. Over hundreds of millions of years, these insects have co-evolved with bacteria that provide these additional nutrients.
Sulcia and Vidania are two examples of bacterial endosymbionts, which have co-evolved with planthoppers for more than 260 million years. These bacteria live in specialized cells within the planthopper abdomen. The new study has found that, along with their hosts, these endosymbionts have evolved—or devolved—in some unexpected ways.