Pattern of chromosomal changes in ‘beta’ Anolis (Norops group) (Squamata: Polychrotidae) depicted by an ancestral state analysis

Abstract

Background: Neotropical lizards, genus Anolis (Polychrotidae), with nearly 380 species, are members of one of the most diversified genera among amniotes. Herein, we present an overview of chromosomal evolution in 'beta' Anolis (Norops group) as a baseline for future studies of the karyotypic evolution of anoles. We evaluated all available information concerning karyotypes of Norops, including original data on a recently described species, Anolis unilobatus. We used the phylogeny of Norops based on DNA sequence data to infer the main pattern of chromosomal evolution by means of an ancestral state analysis (ASR). Results: We identified 11 different karyotypes, of which 9 in the species had so far been used in molecular studies. The ASR indicated that a change in the number of microchromosomes was the first evolutionary step, followed by an increase in chromosome numbers, likely due to centric fissions of macrochromosomes. The ASR also showed that in nine species, heteromorphic sex chromosomes most probably originated from six independent events. Conclusions: We observed an overall good correspondence of some characteristics of karyotypes and species relationships. Moreover, the clade seems prone to sex chromosome diversification, and the origins of five of these heteromorphic sex chromosome variants seem to be recent as they appear at the tip nodes in the ancestral character reconstruction. Karyotypic diversification in Norops provides an opportunity to test the chromosomal speciation models and is expected to be useful in studying relationships among anole species and in identifying cryptic taxa.

Detection of cryptic diversity in lizards (Squamata) from two Biosphere Reserves in Mesoamerica

“…The ancestral karyotype of "beta" Anolis (Norops) consists of 2n = 28 or 2n = 30 chromosomes subdivided in 14 macro-and 14 or 16 microchromosomes without evident sex chromosome heteromorphism (Castiglia et al 2013b). Another frequently observed chromosome complement in this group has 2n = 40 (24M+16m), which is considered to have been derived from the previous complement through fission events on macrochromosomes (Castiglia et al 2013b).…”

“…The lack of description of chromosome morphology in Gorman's study (Gorman 1973) did not allow detailed comparison among the 2n = 40 chromosomal complements. Thus, Anolis capito occurs within a group of species with 2n = 40 (Castiglia et al 2013b) and its additional chromosomal pair is probably due to a fission event. It has already been hypothesized that chromosomal fission is a characteristic trait of Norops chromosome evolution (Castiglia et al 2013b; Gamble et al 2014).…”

Detection of cryptic diversity in lizards (Squamata) from two Biosphere Reserves in Mesoamerica

“…The ancestral karyotype of "beta" Anolis (Norops) consists of 2n = 28 or 2n = 30 chromosomes subdivided in 14 macro-and 14 or 16 microchromosomes without evident sex chromosome heteromorphism (Castiglia et al 2013b). Another frequently observed chromosome complement in this group has 2n = 40 (24M+16m), which is considered to have been derived from the previous complement through fission events on macrochromosomes (Castiglia et al 2013b). The presence of heteromorphic sex chromosomes has been repeatedly reported in Norops.…”

“…The presence of heteromorphic sex chromosomes has been repeatedly reported in Norops. Moreover, it might have occurred independently in different lineages (Castiglia et al 2013b, Gamble et al 2014. Among "beta" Anolis, heteromorphic XY chromosomes have been reported in eight species (Castiglia et al 2013b;Giovannotti et al 2016).…”

Genome Complexity Reduction High-Throughput Genome Sequencing of Green Iguana (Iguana iguana) Reveal a Paradigm Shift in Understanding Sex-Chromosomal Linkages on Homomorphic X and Y Sex Chromosomes

“…In addition to gecko lizards and skinks, multiple variants of sex chromosome systems have been identified in iguanian lizards, including male heterogamety (XX/XY) in the majority of iguanid lizards and female heterogamety (ZZ/ZW) in many agamid lizards (Ezaz et al, 2009a,b;Gamble, 2010;Alföldi et al, 2011;Rovatsos et al, 2014a;Altmanová et al, 2017;Matsubara et al, 2019;Srikulnath et al, 2019;Singchat et al, 2020b). The study of sex-determination systems and sex chromosomes in iguanian lizards has been difficult because many have homomorphic sex chromosomes that cannot be identified easily using conventional karyotyping (Brandley et al, 2006;Castiglia et al, 2013;Singchat et al, 2020b). The green anole (Anolis carolinensis, ACA), is a highly diversified lizard in the superfamily Iguanoidea.…”