New Insights on Chromosome Diversification in Malagasy Chameleons
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Department of Biology, Ecology and Earth Science, University of Calabria, Via P. Bucci 4/B, 87036 Rende, Italy
2
Independent Researcher, Via Michelangelo 123, 81031 Aversa, Italy
*
Author to whom correspondence should be addressed.
Animals 2024, 14(19), 2818; https://doi.org/10.3390/ani14192818
Submission received: 2 September 2024
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Revised: 27 September 2024
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Accepted: 28 September 2024
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Published: 30 September 2024
(This article belongs to the Section Herpetology)
Simple Summary
Chromosome diversification represents a fundamental driver of biological evolution. Here we present and discuss the results of a comparative chromosome analysis on different species of the Malagasy chameleons of the genera Brookesia and Furcifer. We show that the study species are characterized by different karyotypes in terms of chromosome number (2n = 36–22), ratio of micro- and macrochromosomes, and the variable presence of differentiated sex chromosomes. Considering our new data together with those from previous studies, we describe a chromosome evolutionary scenario in the studied taxa. Specifically, while genus Brookesia has a fixed chromosome number (2n = 36) and no differentiated sex chromosomes, which corresponds to the hypothesized ancestral chameleon karyotype, Furcifer shows a high diversity in chromosome number (2n = 20–34), morphology, and the independent raising of simple and multiple sex chromosomes with female heterogamety. The karyotypes in Furcifer with a relatively low chromosome count likely evolved from a chromosome complement similar to that of F. balteatus (2n = 34), mostly via a progressive number of chromosome fusions involving distinct micro- and macrochromosome pairs. Similarly, the diversification of simple and multiple sex chromosome systems occurred in Furcifer via independent (non-homologous) sex chromosome-autosome fusions and heterochromatinization.
Abstract
In this work, we performed a preliminary molecular analysis and a comparative cytogenetic study on 5 different species of Malagasy chameleons of the genus Brookesia (B. superciliaris) and Furcifer (F. balteautus, F. petteri, F. major and F. minor). A DNA barcoding analysis was first carried out on the study samples using a fragment of the mitochondrial gene coding for the cytochrome oxidase subunit 1 (COI) in order to assess the taxonomic identity of the available biological material. Subsequently, we performed on the studied individuals a chromosome analysis with standard karyotyping (5% Giemsa solution at pH 7) and sequential C-banding + Giemsa, + CMA3, and + DAPI. The results obtained indicate that the studied species are characterized by a different chromosome number and a variable heterochromatin content and distribution, with or without differentiated sex chromosomes. In particular, B. superciliaris (2n = 36) and F. balteatus (2n = 34) showed a similar karyotype with 6 macro- and 12–11 microchromosome pairs, without differentiated sex chromosomes. In turn, F. petteri, F. major, and F. minor showed a karyotype with a reduced chromosome number (2n = 22–24) and a differentiated sex chromosome system with female heterogamety (ZZ/ZW). Adding our newly generated data to those available from the literature, we highlight that the remarkable chromosomal diversification of the genus Furcifer was likely driven by non-homologous chromosome fusions, including autosome–autosome, Z–autosome, and W–autosome fusions. The results of this process resulted in a progressive reduction in the chromosome number and partially homologous sex chromosomes of different shapes and sizes.
Keywords:
cytogenetics; evolution; karyotype; Madagascar; reptiles
