Gene loss in herbivores and carnivores
Throughout evolution, mammals repeatedly adapted to specialized diets, including plant-based diets for herbivores and meat-based diets for carnivores. Apart from consuming diets with different nutritional compositions, herbivores and carnivores differ in many aspects such as the time spent feeding, regularity of pancreatic juice secretion, exposure to toxic plant-derived compounds and gut microbiome diversity. Many of these specializations evolved independently in mammals, raising the question of whether herbivory or carnivory evolved through similar genetic changes in independent lineages.
Michael Hiller from the MPI-CBG, the Center for Systems Biology Dresden, and the MPI for the Physics of Complex Systems systematically searched with colleagues for the loss of genes that preferentially occurred in mammals with a strict herbivorous or carnivorous diet. This search revealed striking cases of convergent gene losses. In herbivores, the researchers found the repeated loss of a gene that inhibits the digestion of fatty acids, suggesting evolution towards an increased triglyceride digestion efficiency in herbivores. Herbivores also convergently lost a gene that is required for efficient pancreatic enzyme secretion, which is likely connected to the continuous secretion of pancreatic juice in herbivores that continuously feed many hours a day. For carnivores, the researchers found repeatedly-lost genes that have a role in regulating appetite and glucose production. Reflecting the reduced need to metabolize toxic plant-derived compounds, carnivores lost key genes required for detoxification. Finally, carnivores repeatedly lost a gene that plays a role in antimicrobial immune response in the gut, which is likely related to a reduced gut microbiome diversity in carnivores.
In summary, convergent losses of important genes highlight that similar genetic changes are involved in the repeated adaptation of different mammals to specialized diets.
Nikolai Hecker, Virag Sharma, and Michael Hiller. Convergent gene losses illuminate metabolic and physiological changes in herbivores and carnivores. Proceedings of the National Academy of Sciences Feb 2019, 201818504; DOI: 10.1073/pnas.1818504116