Genetic evidence for co-occurrence of chromosomal and thermal sex-determining systems in a lizard.
An individual's sex depends upon its genes (genotypic sex determination or GSD) in birds and mammals, but reptiles are more complex: some species have GSD whereas in others, nest temperatures determine offspring sex (temperature-dependent sex determination). Previous studies suggested that montane scincid lizards (Bassiana duperreyi, Scincidae) possess both of these systems simultaneously: offspring sex is determined by heteromorphic sex chromosomes (XX-XY system) in most natural nests, but sex ratio shifts suggest that temperatures override chromosomal sex in cool nests to generate phenotypically male offspring even from XX eggs. We now provide direct evidence that incubation temperatures can sex-reverse genotypically female offspring, using a DNA sex marker. Application of exogenous hormone to eggs also can sex-reverse offspring (oestradiol application produces XY as well as XX females). In conjunction with recent work on a distantly related lizard taxon, our study challenges the notion of a fundamental dichotomy between genetic and thermally determined sex determination, and hence the validity of current classification schemes for sex-determining systems in reptiles.
Radder
Rajkumar S
RS
School of Biological Sciences A08, University of Sydney, New South Wales 2006, Australia.
Quinn
Alexander E
AE
Georges
Arthur
A
Sarre
Stephen D
SD
Shine
Richard
R
D000818:Animals; D001483:Base Sequence; D005260:Female; D012739:Gonadal Steroid Hormones / Q000032:analysis; D006358:Hot Temperature; D008116:Lizards / Q000235:genetics*; D008297:Male; D008969:Molecular Sequence Data; D010063:Ovum / Q000737:chemistry; D017422:Sequence Analysis, DNA; D012730:Sex Chromosomes / Q000235:genetics*; D019849:Sex Determination Processes; D012744:Sex Ratio
D012739:Gonadal Steroid Hormones