An article published in the journal “PLOS Biology” reports an analysis of the information available on the relationships among mammal species that aims to build an evolutionary family tree of this group of animals. Nathan Upham and Walter Jetz of Yale University together with Jacob Esselstyn of Louisiana State University used data on fossils and genomics to try to analyze at phylogenetic level the evolution of the various branches within the mammal taxonomic class. Understanding their relationships offers information on their history and biodiversity, a crucial step for environmental conservation.
The crucial problem for the scientists who study mammals is that of the approximately 6,000 species existing in this class today, 42% are rodents and 24% bats, while other groups such as cows, pigs, sheep, cats and others consist of a few species each. Using the tree comparison, it’s as if the mammal tree had two huge branches which in turn have various twigs and other small twigs. To understand why that tree is made this way first of all it’s necessary to clearly define the number of species of existing mammals. Nathan Upham had already participated in a research with this goal, and its results were published in February 2018 in the journal “Journal of Mammalogy”.
The Mammal Diversity Database (MDD) includes 6,495 recognized species of mammals, of which 96 were declared extinct in recent times. There’s an increase of over a thousand species in about 13 years. In recent decades, the great advances in genetic techniques led to a leap forward in the taxonomic study of organisms, in this case of mammals’ relationships. Genomics, a branch of molecular biology based on bioinformatics that deals with the study of the genome, and phylogenetics, the study of the various ramifications of a group of organisms, allowed to resolve controversies and to better reconstruct the history of mammals. However, there’s still a lot of work to be done and the studies published in “Journal of Mammalogy” and “PLOS Biology” seek to offer answers.
To try to build a mammal tree, Nathan Upham, Walter Jetz and Jacob Esselstyn used an approach in which they divided the analysis into two levels: the first focused on the divergences between the major mammal groups such as orders and families and the second, which concerns the various groups in detail to be connected to the tree with the main differences.
The image (courtesy Nathan S. Upham, Jacob A. Esselstyn, Walter Jetz. All rights reserved) shows a reconstruction of the relationships and tempo of mammal diversification over time. According to the researchers, the distribution of species is so uneven in the various branches due to the geographical isolation among mammalian populations, which can lead to higher levels of formation of new species and their extinction.
At a time when there’s a new wave of extinctions, also among mammals, it’s important to better understand the characteristics of the various species and their relationships in the evaluation of conservation policies. In cases where a species is crucial to the health of an ecosystem, such as elephants, the survival of an animal population is closely linked to that of their ecosystem.
