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Abstract
Amniotes possess variability in sex determining mechanisms, however, this diversity is still only partially known throughout the clade and sex determining systems still remain unknown even in such a popular and distinctive lineage as chameleons (Squamata: Acrodonta: Chamaeleonidae). Here, we present evidence for female heterogamety in this group. The Malagasy giant chameleon (Furcifer oustaleti) (chromosome number 2n = 22) possesses heteromorphic Z and W sex chromosomes with heterochromatic W. The panther chameleon (Furcifer pardalis) (2n = 22 in males, 21 in females), the second most popular chameleon species in the world pet trade, exhibits a rather rare Z1Z1Z2Z2/Z1Z2W system of multiple sex chromosomes, which most likely evolved from W-autosome fusion. Notably, its neo-W chromosome is partially heterochromatic and its female-specific genetic content has expanded into the previously autosomal region. Showing clear evidence for genotypic sex determination in the panther chameleon, we resolve the long-standing question of whether or not environmental sex determination exists in this species. Together with recent findings in other reptile lineages, our work demonstrates that female heterogamety is widespread among amniotes, adding another important piece to the mosaic of knowledge on sex determination in amniotes needed to understand the evolution of this important trait.
Highlights
Despite the popularity of chameleons among herpetologists, private breeders and hobbyists, their sex determination has remained largely unstudied
The only known exception has come from Gordon who suggested the existence of a female heterogametic system in Bradypodion ventrale, in response to the observation of the different chromosomal number existing between males (2n = 3 4) and females (2n = 3 5)
The haplotype analysis of our dataset in DnaSP v5.10.1 revealed five haplotypes for F. pardalis and two for F. oustaleti, none of which previously reported in the GenBank (Table 1)
Summary
Despite the popularity of chameleons among herpetologists, private breeders and hobbyists, their sex determination has remained largely unstudied. Chameleons are relatively poorly studied cytogenetically and karyotypes are known for only 50 out of about 200 extant species They possess karyotypes with chromosomal numbers varying from 2n = 2 0 to 2n = 3 6 Though, to our knowledge, neither karyotypes of this species, nor any other additional information which would enable the testing of sex-linkage of the polymorphism in chromosomal numbers, has been published This lack of comprehensive data prompted us to apply both classical (Giemsa staining, C-banding) and molecular (comparative genomic hybridization [CGH], fluorescence in situ hybridization [FISH]) cytogenetic approaches to reveal the karyotype and the sex chromosomes of two species of chameleons from the genus Furcifer. Due to their variegated colouration, relatively easy care and reproduction in captivity they are very popular pets in North America and Europe with large numbers being bred commercially[16,22]
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