Abstract
Dragon lizards (Squamata: Agamidae) comprise about 520 species in six subfamilies distributed across Asia, Australasia and Africa. Only five species are known to have sex chromosomes. All of them possess ZZ/ZW sex chromosomes, which are microchromosomes in four species from the subfamily Amphibolurinae, but much larger in Phrynocephalus vlangalii from the subfamily Agaminae. In most previous studies of these sex chromosomes, the focus has been on Australian species from the subfamily Amphibolurinae, but only the sex chromosomes of the Australian central bearded dragon (Pogona vitticeps) are well-characterized cytogenetically. To determine the level of synteny of the sex chromosomes of P. vitticeps across agamid subfamilies, we performed cross-species two-colour FISH using two bacterial artificial chromosome (BAC) clones from the pseudo-autosomal regions of P. vitticeps. We mapped these two BACs across representative species from all six subfamilies as well as two species of chameleons, the sister group to agamids. We found that one of these BAC sequences is conserved in macrochromosomes and the other in microchromosomes across the agamid lineages. However, within the Amphibolurinae, there is evidence of multiple chromosomal rearrangements with one of the BACs mapping to the second-largest chromosome pair and to the microchromosomes in multiple species including the sex chromosomes of P. vitticeps. Intriguingly, no hybridization signal was observed in chameleons for either of these BACs, suggesting a likely agamid origin of these sequences. Our study shows lineage-specific evolution of sequences/syntenic blocks and successive rearrangements and reveals a complex history of sequences leading to their association with important biological processes such as the evolution of sex chromosomes and sex determination.
Highlights
IntroductionReptiles are well known for their diverse modes of sex determination and sex chromosomes [1,2]
Reptiles are well known for their diverse modes of sex determination and sex chromosomes [1,2].They exhibit large variability in the degree of differentiation of sex chromosomes ranging from homomorphic to heteromorphic in structure [2,3,4,5]
W chromosomes as well as onto the telomeric region of the long arms of the chromosome pair 2 in P. vitticeps (Figure 2a). This bacterial artificial chromosome (BAC) probe hybridized onto the telomeric region of the long arms of the chromosome pair 2 in all species under the subfamilies Amphibolurinae (P. vitticeps, T. lineata and R. diemensis; Figure 2a–c), Uromastycinae (S. loricata; Figure 2d) and Leiolepidinae (L. reevesii rubritaeniata and L. cf. ngovantrii; Figure 2e,f)
Summary
Reptiles are well known for their diverse modes of sex determination and sex chromosomes [1,2] They exhibit large variability in the degree of differentiation of sex chromosomes ranging from homomorphic to heteromorphic in structure [2,3,4,5]. Known for their diverse modes sexgenome determination sex chromosomes [1,2] They large variability in in the different degree of differentiation sex chromosomes ranging found to play the role ofexhibit sex chromosomes vertebrateoftaxa [5,8,9,10,11]. Squamate reptiles (lizards, snakes and has been observed between birds to a relative degree of chromosomal amphisbaenians) are the and most squamate diverse reptilereptiles group in owing terms of species diversity low and mode of sex [1,6]. Nondetermination (GSD), and GSD with temperature influences between relatively closely related species homologous sex chromosomes have been reported even among relatively closely related species
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