Gaetano Odierna

Evolution of sex-chromosomes in lacertid lizards

The occurrence and form of sex chromosomes were investigated with the aid of C-banding and 4′-6-diamidino-2-phenylindole (DAPI) staining in 13 species of lacertid lizards. The results obtained show the presence in five species of a female heterogamety in which the two sex chromosomes have the same shape and size, but the W differs from the Z in being almost entirely heterochromatic. This condition is clearly similar to that found in some snakes and considered to be an early stage of differentiation of sex chromosomes by Singh et al. (1976, 1980). A more evolved condition may be that found in three other species in which the W is distinctly smaller than the Z. A third situation is that found in all Podarcis species which, even though they are considered to be among the more evolved species in the family, possess two sex chromosomes that are indistinguishable. In general, the situation in lacertids may be compatible with the hypothesis of sex chromosome evolution put forward by Singh et al. (1976, 1980). However a differentiation mechanism of this kind does not seem to be well established in lacertids, and is probably not the only mechanism that is in operation in this family.

C-band variability and phylogeny of Lacertidae

The karyology of various species from the family Lacertidae (Reptilia, Sauria) has been studied with conventional and C-banding techniques.The study shows that this family is not so conservative from a karyological viewpoint as considered till now. In fact a higher diploid number than that generally observed in most species of Lacertidae and supernumerary chromosomes have been observed in three of the species investigated. Moreover an evident interand intraspecific variability has been found in the C-banding pattern of the various species studied. The situation found in Podarcis sicula is particularly remarkable. Different C-banding patterns have been observed in three different subspecies and in two populations of the same subspecies. These variations do not show a well defined trend and their role in the evolution of lacertid lizards is discussed.The C-banding analysis evidences also the existence in two of the species studied of a female sex heteromorphism, in which the W chromosome has the same shape and size as the Z, but differs from it in being completely heterochromatic. This situation reminds that observed in some snakes and suggests that in lacertid lizards the evolution of sex chromosomes might have followed the same steps previously hypothesized for ophidians.

Ancient tetraploidy and slow molecular evolution in Scaphiophryne: ecological correlates of speciation mode in Malagasy relict amphibians

Karyotypes of three microhylid frog species of the Malagasy relict genus Scaphiophryne were studied: Scaphiophryne gottlebei, S. madagascariensis and S. spinosa. The latter two showed a plesiomorphic ranoid karyotype of 2n = 26. In contrast, tetraploidy was demonstrated in S. gottlebei, which constitutes an exceptional state among Malagasy amphibians. A combination of different banding techniques and of rDNA-FISH provided evidence for allopolyploidy in the species and for a completed subsequent functional and structural diploidization. Phylogenetic analysis of mitochondrial 16S rDNA sequences revealed a significant deceleration of nucleotide substitution rates in Scaphiophryne. The tetraploidy of S. gottlebei probably occurred early in their radiation. Ecological and behavioural patterns of Scaphiophryne probably favoured intraspecific gene flow and hybridization events, thereby leading to slow molecular substitution rates and to allopolyploid chromosome speciation in S. gottlebei.

Consistent sex ratio bias of individual female dragon lizards

Sex ratio evolution relies on genetic variation in either the phenotypic traits that influence sex ratios or sex-determining mechanisms. However, consistent variation among females in offspring sex ratio is rarely investigated. Here, we show that female painted dragons (Ctenophorus pictus) have highly repeatable sex ratios among clutches within years. A consistent effect of female identity could represent stable phenotypic differences among females or genetic variation in sex-determining mechanisms. Sex ratios were not correlated with female size, body condition or coloration. Furthermore, sex ratios were not influenced by incubation temperature. However, the variation among females resulted in female-biased mean population sex ratios at hatching both within and among years.

Different genomic evolutionary rates in the various reptile lineages

Although Reptiles occupy a strategic position among terrestrial vertebrates, studies of the composition and evolution of their genome are scarce. The cytogenetic analysis of nearly 1400 species evidenced different karyotypical evolutionary rates and different G-banding structures in turtles and crocodiles on the one hand and squamates on the other. A similar dichotomy was also identified through the study of the quantitative and compositional characteristics of the genome. The different evolutionary rates of chromosome morphology and genome size and composition and the diversification of coding and non-coding sequences bear an interesting relationship to the number of extant species and the extinction rates of the reptilian orders and suborders studied, suggesting a large role for such different evolutionary rates in the phylogenesis of this class. The different molecular and structural organisation of chromosomes could be an important, though by no means the sole, factor affecting the genomes evolutionary rate.

Further data on sex chromosomes of Lacertidae and a hypothesis on their evolutionary trend

Sex chromosomes were studied in eight species of lacertid lizards using C-banding, G-banding and restriction enzyme treatment. All of the species showed female heterogamety. The W chromosome was a microchromosome in Lacerta graeca and Ophisops elegans. Two types of W were found in Lacerta vivipara; in specimens from The Netherlands it was metacentric, whereas in specimens from Russia it was acrocentric or subtelocentric. The W chromosome was homomorphic or nearly homomorphic but completely C-banded and heterochromatic in Lacerta agilis, Podarcis hispanica, Algyroides moreoticus and A. nigropunctatus. In was only possible to find sex chromosomes using the G-banding method in Podarcis sicula. The results obtained, together with data in the literature, suggest that sex chromosomes are likely to be present in all Lacertidae and that their differentiation took place repeatedly and independently in different taxa within the family. A model for sex chromosome evolution in the family, in which the starting point was the heterochromatization of the W chromosome, is proposed.

Repetitive DNA and polyploidy in selachians

1. The DNA reassociation kinetics have been studied in 6 selachian species: Raja asterias, Raja montagui, Dasyatis violacea, Torpedo marmorata, Torpedo ocellata and Oxynotus centrina. 2. The results obtained show that the genomes of the two Torpedo, Dasyatis and Oxynotus are polyploid if compared with those of the two rays, though this finds no correspondence in the diploid chromosome number. 3. The phenomena of polyploidization would often be followed by wide chromosome rearrangements and by a progressive divergence of the various repetitive DNA sequences. 4. The existence of polyploidy in almost all the main superorders of living Selachians suggests that this mechanism of genomic evolution may have played an important role in the phylogeny of this class.

Karyology of the primitive slamanders, family hynobiidae

Karyotypes have been studied in 3 species ofHynobius and in 1 species each of the remaining genera of Hynobiids (Ranodon, Batrachuperus, Salamandrella andOnychodactylus). All species have large diploid numbers, between 56 and 66, and asymmetrical and bimodal karyotypes. DNA contents (2C) were found to vary between 33 and 51 pg. Determination was not possible inOnychodactylus where higher values may be suspected. Some of the karyotypes investigated are similar to those of Cryptobranchids. Phylogenetic implications are discussed.

Detection of DNA in Ancient Bones Using Histochemical Methods

We describe histochemical techniques for detecting DNA within the osteocytic lacunae of ancient bones. The bones examined were fragments of femurs from two human individuals found in the Pompeian C. I. Polybius house and fragments of metacarpals from two horses (Equus sp.) found in the Pompeian “Casti Amanti” house. Both buildings were buried by the 79 A. D. Vesuvius eruption. Fragments of femurs from a modern horse, a modern swine and a modern amphibian also were studied as controls. Some bone sections were stained with two different DNA-specific fluorochromes, 4′ -′ 6-diamidino-2-phenylindole (DAPI) and chromomycin A3 (CMA), while others were stained by the Feulgen reaction. All of the techniques gave a positive reaction within the osteocytic lacunae. Histological analysis of the undecalcified, ground and unstained sections agreed well with results of bone sections stained with either the fluorochromes or the Feulgen reaction. Bones showing good histology also were positive by our DNA-specific stain. Histochemical and histological analyses correlated well with the success of DNA extraction and amplification. Using conventional DNA-specific histochemical techniques in conjunction with histological analysis can be useful in the study of DNA extracted from ancient bone remains while reducing both the amount of time and cost.

Chromosomal and molecular analysis of some repeated families in Discoglossus Otth, 1837 (Anura, Discoglossidae): Taxonomic and phylogenetic implications

Abstract We conducted a cytogenetic and molecular analysis in six out of the eight Discoglossus taxa CD. pictus pictus, D. p. auritus, D. sardus, D. montalentii, D. galganoi galganoi and D. g. jean‐neae) All the taxa possessed 2n = 28 biarmed chromosomes, except D. pictus pictus where the 13th pair was acrocentric, and the NORs were located on the short arm of the 7th pair in all the taxa but D. galganoi, where they were on the short arm of the 13th pair. Heterochromatin was detected by banding methods (C‐band‐ing, base‐specific fluorochromes, replication patterns and digestions with restriction enzymes). The techniques used were able to discriminate among all the Discoglussus taxa studied, identifying several heterochromatin families with marked differences in chromosome location and/or in the behaviour of the banding techniques used. The differentiation of these heterochromatin families can have either a phylogenetic (as is the case with A+T rich cen‐tromeric heterochromatin) or an adaptive (G+C rich in...