Molecular sexing applicable in 4000 species of lizards and snakes? From dream to real possibility

1. While the stability of sex chromosomes is widely accepted in viviparous mammals and birds, ectothermic vertebrates are still largely viewed as having frequent turnovers in sex-determining systems. Frequent changes in sex-determining systems in ectotherms could be problematic for field ecological studies as well as for breeding programs, as molecular sexing across a phylogenetically widespread spectrum of ectothermic vertebrates would not be possible. However, we recently documented that sex-determining systems in three important reptile lineages (caenophidian snakes, iguanas and lacertid lizards) are in fact highly conserved. 2. We applied a new molecular procedure to identify sex within each of these three lineages (encompassing altogether around 4000 species, i.e. nearly 50% of the recent species of reptiles). This technique uses quantitative PCR (qPCR) to compare copy numbers of genes specific for their respective Z (in caenophidian snakes and lacertids) and X (in iguanas) chromosomes between male and female genomes. The DNA samples required can be collected relatively non-invasively. Unlike molecular sexing based on repetitive elements, this technique can be easily applied to previously unstudied species of these lineages, as the number of copies of protein-coding genes linked to thedifferentiated sex chromosomes is evolutionarily highly conserved in each. 3. We suggest that qPCR-based molecular sexing using the comparison of gene copy number is a practical choice for non-model species of caenophidian snakes, iguanas and lacertids. Moreover, it should also soon be available for other reptile lineages with differentiated sex chromosomes.