Table 1.

List of the main genetic mechanisms proposed to involve sex-linked genes and supergenes in reproductive isolation, and whether they should or not apply in amphibians.

theory	description	requirement	evidence in animals	expectations in amphibians
pre-zygotic isolation
sex-antagonistic genes	build up of genes and supergenes involved in sexual isolation	sex-linked reproductive traits and no recombination	weak	not expected
intrinsic post-zygotic isolation
faster X-/Z-effect	faster divergence of X- or Z-linked loci	differentiated sex chromosomes	strong	not expected
dominance	hemizygosity of X- or Z-linked recessive incompatibilities in the heterogametic sex	differentiated sex chromosomes	strong	not expected
dosage compensation	disruption of dosage compensation	differentiated sex chromosomes	some	not expected
faster heterogametic sex	X-Y/Z-W interactions necessary for meiotic segregation and development of the heterogametic sex	—	some	potentially
meiotic drive	incompatibilities between sex-linked selfish distorters and their autosomal restorers	—	some	potentially
faster male	incompatibilities at fast-evolving male traits (notably spermatogenesis)	sex-linked male reproductive traits	some but not sex-linked	potentially, but not expected to be sex-linked
conflicts between sex-determining systems	incompatibilities (or sex ratio biases) caused by distinct sex-determining systems	turnover of sex-determining systems	rare	potentially, although the role in reproductive isolation is unclear
reinforcement
co-adapted gene complexes	evolution of supergenes for species recognition to avoid the costs of hybridization	linkage between sex-linked hybrid incompatibilities, male traits and female preferences	some	not expected