Meeting Abstract

S1-1.6  Thursday, Jan. 3  Rate of chromosome changes and speciation in reptiles OLMO, Ettore; Universita Politecnica delle Marche. e.olmo@univpm.it

The chromosome changing rate was studied in 1329 species of reptiles in order to evaluate the karyological evolutionary trend and a possible correlation between chromosome mutations and some aspects of the evolution of the class. The results highlight the existence of a general direct correlation between chromosome changing rate and number of living species, though different trend was observed in the different orders and suborders. In turtles, the separation of pleurodires from cryptodires was accompanied by a considerable karyological diversification. Similarly there is no correlation between changing rate and species number in crocodiles. Chromosome variability was greater in squamates. In lizards chromosomes variations accompanied the separation of the infraorders and the evolution of most of the families and of some genera. The origin of snakes has also been accompanied by marked karyological diversification while the subsequent evolution of the infraorders and families has entailed a high level of mutations only in colubrids. The karyological evolution in reptiles generally showed a progressive reduction in chomosome changing rate and this trend seems to be consistent with the �canalization model� as originally proposed by Bickham and Baker (1979). However, several inconsistencies have been found excluding that in this class the ultimate goal of chromosome variations was the achievement of a so-called �optimum karyotype�. Other mechanisms could underpin chromosome variability in reptiles. Among them a genomic composition more or less favourable to promoting chromosome rearrangements and factors favouring the fixation of a mutant karyotype in condition of homozygosis.