Abstract
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. 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. 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.