What inversion lengths can tell us about their evolution.

Genome structural differences, such as inversions, are extremely common between species and within populations. Theoretical models of how and why such inversions evolve have affirmed that they are able to evolve under both adaptive and nonadaptive scenarios (reviewed in Kirkpatrick, 2010). What has remained difficult, however, is distinguishing these scenarios from each other. In this issue of Molecular Ecology, Connallon and Olito (2022) present a model that examines how adaptive and nonadaptive scenarios lead to different distributions of inversion sizes. The authors present several important predictions including an expectation that larger inversions should evolve under local adaptation scenarios and much smaller inversions should evolve when they are either underdominant or directly beneficial. Finally, the authors ask how the presence of deleterious mutations within populations affects the probability of fixing inversions of different types. The study is therefore an important step in synthesizing decades of inversion theory.