Data from: Estimating tempo and mode of Y chromosome turnover: explaining Y chromosome loss with the fragile Y hypothesis

Chromosomal sex determination is phylogenetically widespread, having
arisen independently in many lineages. Decades of theoretical work provide
predictions about sex chromosome differentiation that are well supported
by observations in both XY and ZW systems. However, the phylogenetic scope
of previous work gives us a limited understanding of the pace of sex
chromosome gain and loss and why Y or W chromosomes are more often lost in
some lineages than others, creating XO or ZO systems. To gain phylogenetic
breadth we therefore assembled a database of 4724 beetle species’
karyotypes and found substantial variation in sex chromosome systems. We
used the data to estimate rates of Y chromosome gain and loss across a
phylogeny of 1126 taxa estimated from seven genes. Contrary to our initial
expectations, we find that highly degenerated Y chromosomes of many
members of the suborder Polyphaga are rarely lost, and that cases of Y
chromosome loss are strongly associated with chiasmatic segregation during
male meiosis. We propose the “fragile Y” hypothesis, that recurrent
selection to reduce recombination between the X and Y chromosome leads to
the evolution of a small pseudoautosomal region (PAR), which, in taxa that
require XY chiasmata for proper segregation during meiosis, increases the
probability of aneuploid gamete production, with Y chromosome loss. This
hypothesis predicts that taxa that evolve achiasmatic segregation during
male meiosis will rarely lose the Y chromosome. We discuss data from
mammals, which are consistent with our prediction.