Reptiles: a group of transition in the evolution of genome size and of the nucleotypic effect

Abstract

A comparison between genome size and some phenotypic parameters, such as developmental length and metabolic rate, showed in reptiles a nucleotypic correlation similar to the one observed in birds and mammals. Indeed, like homeotherms, reptiles exhibit a highly significant, inverse correlation of genome size with metabolic rate but unlike amphibians, no relationship with developmental length. Several lines of evidence suggest that these nucleotypic correlations are influenced by body temperature, which also affects the guanine + cytosine nuclear percentage, and that they play an important role in the adaptation of these amniotes. However, the reptilian suborders exhibit differences in the quantitative and compositional characters of the genome that do not completely correspond to differences in the phenotypic parameters commonly involved in the nucleotypic effect. Thus, additional factors could have influenced genome size in this class. These data could be explained with the model of Hartl and Petrov, who observed an inverse correlation between genome size, non-coding portion of the genome and rate of DNA loss and hypothesized a strong role for different spectra of spontaneous insertions and deletions (indels) in the variations of genome size. It is thus reasonable to surmise that variations in the reptilian genome were initially influenced by different indels spectra typical of the diverse lineages, possibly related to different chromosome compartmentalizations. The consequent size increases or decreases would have influenced various morphological and functional cell parameters, and through these some phenotypic characteristics of the whole organism, especially the metabolic rate, very important for environmental adaptation and thus subject to natural selection. Through this “nucleotypic” bond, natural selection would also have controlled genome size variations.

Transposable Elements in Reptilian and Avian (Sauropsida) Genomes

“…Given the observed differences in sauropsid genome sizes [Olmo, 2003], elevated recombination rates [International Chicken Genome Sequencing Consortium, 2004], highly divergent TE repertoires, differences in the activities and copy numbers of TEs [Novick et al, 2009;Piskurek et al, 2009], accumulations of lineage-specific SINEs [Piskurek et al, 2009], and differences in the amounts of highly and moderately repetitive DNA fractions in diverse sauropsid lineages [Olmo et al, 1981[Olmo et al, , 1985[Olmo et al, , 1988, it will be important to acquire direct experimental evidence that will show how the activity of TEs has shaped diverse sauropsid genomes.…”

Genome size and metabolic intensity in tetrapods: a tale of two lines

“…The redundant non-coding DNA is supposed to serve for adjustment of metabolic rate mediated by a change in general cellular parameters (such as nuclear size, chromatin condensation, nucleocytoplasmic ratio), which in multicellulars can be independent of body size (Szarski 1983;Cavalier-Smith 1985;Vinogradov 1995Vinogradov , 1997Vinogradov , 1998aGregory 2002;Kozlowski et al 2003;Olmo 2003;Vinogradov & Anatskaya 2004;Vinogradov 2005a). The link between genome size and metabolic rate can be considered as an example of the symmorphosis, a general principle of evolutionary biology defined as a quantitative match of structural design and functional demand (Weibel et al 1991;Diamond & Hammond 1992;Weibel 2000).…”

“…The latter trait is of special interest because it might have a clear adaptive significance: the more economical physiology should allow a species to occupy a niche with a low energy supply (Szarski 1983;Vinogradov 1998aVinogradov , 2005a. However, the link between metabolic rate and genome size was demonstrated only in amniotes (in reptiles, on a limited dataset; Vinogradov 1995Vinogradov , 1997Gregory 2002;Waltari & Edwards 2002;Olmo 2003;Vinogradov & Anatskaya 2004). The studies of anamniotes were inconclusive, notwithstanding a much broader range of genome sizes (Licht & Lowcock 1991;Waltari & Edwards 2002;Gregory 2003).…”

The First Cytogenetic Map of the Tuatara, <i>Sphenodon punctatus</i>

“…Tuatara also have unusual thermal biology, remaining active at extremely low temperatures ( ϳ 5 ° C), and exhibiting the lowest optimal body temperature range of any reptile (16-21 ° C) [Werner and Whitaker, 1978;Thompson and Daugherty, 1998;Besson, 2009]. In accordance with this, they have a low metabolic rate [Thompson and Daugherty, 1998] and one of the largest reptilian genomes, with a C-value of 5.0 [Olmo, 1981[Olmo, , 2003Vinogradov and Anatskaya, 2006].…”