Abstract
BackgroundNeotropical 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).ResultsWe 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.ConclusionsWe 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.
Highlights
Neotropical lizards, genus Anolis (Polychrotidae), with nearly 380 species, are members of one of the most diversified genera among amniotes
All samples showed 2n = 40 with 24 macrochromosomes and 6 microchromosomes, so they are designated because they markedly differed in size (Figure 1)
A literature survey of Norops karyotypes We found 11 different karyotypes, of which 9 were from species previously used in molecular studies
Summary
Neotropical lizards, genus Anolis (Polychrotidae), with nearly 380 species, are members of one of the most diversified genera among amniotes. We present an overview of chromosomal evolution in ‘beta’ Anolis (Norops group) as a baseline for future studies of the karyotypic evolution of anoles. Anolis was recently the subject of a systematic revision that resulted in it being split into eight different genera (Nicholson et al 2012) This systematic arrangement has been vigorously criticized (e.g., Poe 2013), and in this paper, we adopted the classical view that considers anole lizards as being comprised of a single genus (Losos 2009; Uetz 2013). Anoles exhibit remarkable inter- and intraspecific variations in chromosome number and morphology as well as in the presence/absence of heteromorphic sex chromosomes For this reason, investigating speciation of anoles as driven by chromosomal changes remains challenging. Chromosomal variability is expected to be useful in studying relationships among anole species and in identifying cryptic taxa
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