Neo-sex chromosomes are not correlated with ecology or environment in eutherian mammals

The XX/XY chromosome system is highly conserved in therian mammals. Despite this evolutionary persistence, multiple variant sex chromosome systems exist in mammals. The potential contribution of genomic conflict to the evolution of neo-sex chromosomes has been studied extensively, while the influence of climate and ecology on the emergence and persistence of neo-sex chromosomes is less well understood. Building on previous literature that suggests ecoclimatic factors can influence intralocus sexual conflict and other forms of genome evolution, we tested whether neo-sex chromosomes in mammals are associated with these factors. We conducted a phylogenetic logistic regression in three representative mammal families using a dataset of variant mammalian sex chromosomes and a database of tetrapod traits and environmental preferences based on biogeographical data. We also incorporated a dataset of mammal species karyotypes to test for potential signatures of meiotic drive. When using a single phylogeny, none of the seven ecoclimatic variables tested nor chromosome morphology were significantly correlated with neo-sex chromosomes. However, we observed that correlations between neo-sex chromosomes and both range size and mean annual temperature were sensitive to differences in tree topology, demonstrating the importance of accounting for alternative evolutionary hypotheses in comparative methods.