Karyograms of five Malagasy chameleons described

Karyograms of five Malagasy chameleons described

by Alex Negro Science

It has been known for many years that the sex of chameleons is genetically determined. However, the karyograms of many species, i.e. the chromosome characteristics, are not yet known for all species. Italian scientists have now analysed the karyograms of five Madagascan chameleon species.

Existing, preserved chameleons were used for the study. One female each of the species Furcifer balteatus, Furcifer petteri, Furcifer major and Furcifer minor were sampled. One male and one female Brookesia superciliaris were also used for the study. All samples were subjected to DNA barcoding analysis using the mitochondrial gene fragment COI as a marker. The extracted DNA was amplified by PCR and then sequenced to create a karyogram for each animal.

The karyogram of Brookesia superciliaris is 2 n = 34 for both sexes. Of the 34 chromosomes, six are macrochromosome pairs and eleven are microchromosome pairs. All macrochromosomes are metacentric. Morphologically, the chromosomes do not differ from each other, so that it remains unclear which could be the sex chromosomes.

Furcifer balteatus has a very special karyogram, which actually fits better with those of the genera Brookesia and Palleon than with the genus Furcifer. The karyogram is 2n = 34, which is the highest number of chromosomes among the chameleons. Of the 34 chromosomes, six are macrochromosome pairs and eleven are microchromosome pairs. The former are all metacentric. There are no morphological differences between the chromosome pairs, so that the sex chromosome has not yet been determined.

The karyogram of Furcifer major is 2n = 24. Nine of the chromosome pairs are macrochromosome pairs and three are microchromosome pairs. Seven of the macrochromosome pairs are metacentric, only pairs two and three are submetacentric. The eleventh chromosome pair, a microchromosome pair, codes for the sex chromosome W.

Furcifer minor has a karyogram of 2n = 22 chromosomes. Of these, eight pairs are macrochromosome pairs and three are microchromosome pairs. Among the macrochromosomes, the first five pairs are metacentric, while the remaining three pairs are acrocentric. A portion of the sixth pair of chromosomes was almost completely heterochromatic and probably represents the sex chromosome W.

The karyogram of Furcifer petteri is also 2n = 22, of which eight pairs of chromosomes are macrochromosomes and three microchromosomes. Seven pairs of macrochromosomes are metacentric, only the fifth pair is submetacentric. The sex chromosome W is part of the seventh pair of macrochromosomes.

All newly described karyograms are deposited in GenBank under the number PQ272538-4. In this study, the genus Furcifer was also found to have the highest diversity in the karyograms. It also appears to be the only genus among all vertebrates that shows all variants of sex chromosome diversification.

New insights on Chromosome Diversification in Malagasy Chameleons
Marcello Mezzasalma, Gaetano Odierna, Rachele Macirella, Elvira Brunelli
Animals 2024, 14: 2818
DOI: 10.3390/ani14192818

Graphic: Karyograms of Brookesia superciliaris and Furcifer balteatus from the above-mentioned study

Karyotypes in chameleons

Karyotypes in chameleons

by Alex Negro Science

Scientists from Great Britain and Italy have now studied the chromosomes of different chameleon species. They examined the karyotype of a total of 83 different chameleon species. Among them were 57 Madagascan chameleon species, of which 32 karyotypes were described for the first time ever. For Calumma brevicorne, Calumma fallax, Calumma parsonii and Furcifer verrucosus, there were even several animals each available for examination. The scientists found out that presumably the fusion of chromosomes has reduced the total number of chromosomes in the course of evolution in chameleons. Presumably, it was mainly microchromosomes (particularly small chromosomes) that fused.

Microchromosome fusions underpin convergent evolution of chameleon karyotypes
Marcello Mezzasalma, Jeffrey W Streicher, Fabio M Guarino, Marc E H Jones, Simon P Loader, Gaetano Odierna, Natalie Cooper
Evolution, Juni 2023
DOI: 10.1093/evolut/qpad097

 

Genetics: Karyotype in the Veiled Chameleon

Genetics: Karyotype in the Veiled Chameleon

by Alex Negro Science

It has been known for some time that the sex of the Veiled chameleon (Chamaeleo calyptratus) is genetically determined. The species has an XX/XY system. Scientists from Russia, Great Britain, Italy, and Thailand have now studied the karyotype of the species, i.e. the characteristics of the chromosomes.

The probably most original karyotype of all chameleons is 2n= 36. This “primal chameleon” had six pairs of metacentric macrochromosomes and twelve pairs of microchromosomes, particularly small chromosomes. The Veiled chameleon, on the other hand, has a smaller number of chromosomes, namely only 2n=24. Using various genetic investigation methods, the researchers in the present study found that this karyotype probably arose through fusions. Microchromosomes apparently fused with each other twice, and micro- and macrochromosomes fused no less than four times. The latter, the so-called heterogeneous fusion between chromosomes of different sizes, is unusual for vertebrates. Normally, macro- and microchromosomes are located at different locations in the cell nucleus and are transcribed and replicated at different rates. However, this phenomenon is already known from alligators and turtles – for chameleons it is new.

Until now, it was also unclear which pair of chromosomes in the Veiled chameleon is actually responsible for the sex. In Chamaeleo chamaeleon, the second largest chromosome pair codes for sex. However, initial speculation suggests that in the Veiled chameleon the fifth chromosome pair (CCA5) may instead be the sex chromosome pair. The conjecture still needs to be validated by further research. It is also still up for discussion which gene is actually predominantly responsible for the development of the sex organs in the embryo – the researchers identified at least three possible genes on CCA5.

Identification of Iguania ancestral syntenic blocks and putative sex chromosomes in the Veiled Chameleon (Chamaeleo calyptratus, Chamaeleonidae, Iguania)
Katerina V. Tishakova, Dmitry Yu. Prokopov, Guzel I. Davletshina, Alexander V. Rumyantsev, Patricia C. M. O’Brien, Malcolm A. Ferguson-Smith, Massimo Giovannotti, Artem P. Lisachov, Vladimir A. Trifonov
International Journal of Molecular Sciences 23, December 2022
DOI: 10.3390/ijms232415838