BAG. Journal of basic and applied genetics
versión On-line ISSN 1852-6233
IPUCHA, María Claudia; GOMES SANTOS, Cinthya; DA CUNHA LANA, Paulo y SBALQUEIRO, Ives José. Cytogenetic characterization of seven South American species of nereididae (annelida: polychaeta): implications for the karyotypic evolution. BAG, J. basic appl. genet. [online]. 2007, vol.18, n.2, pp. 27-38. ISSN 1852-6233.
This paper describes, for the first time, the cytogenetic characteristics of some South Atlantic nereidid polychaetes, collected in Paranaguá Bay, southeast Brazil. Mitotic chromosomes were obtained from regenerative tissue after amputation of the posterior tips of the animals. Seven species, of five genera, were analyzed: 1) Platynereis dumerilii (2n=28; FN=56), which is considered cosmopolitan but is suspected to be a species-complex. Karyotypic divergences were detected when comparing chromosome morphology and NOR distribution from Paraná and North American populations (2n=28; FN=56), 2) Perinereis vancaurica (2n=28; FN=56), P. anderssoni (2n=28; FN=56) and P. ponteni (2n=28; FN=54). Karyotypes and NOR distribution allowed us to relate P. anderssoni (Paraná, Brazil) to P. macropus (Italy), the former showing a derived karyotype. The remaining karyotypes of species of Perinereis showed independent divergences; 3) Pseudonereis palpata (2n=28; FN=56), known from the south and south-east coast of Brazil; 4) Nereis oligohalina (2n=28; FN=50), occurring in the South Atlantic. The last two species share the conservative chromosome number of the family; and 5) Laeonereis culveri, occurring in both the South and North Atlantic, has the highest chromosome number in the family (2n=38). We discuss the important role of karyotypic evolution in the origin of modern families of polychaetes, when the current chromosomal diversity (2n=6 to 2n=64) was developed, followed by a period of chromosomal stability of nereidid polychaetes during the dispersion which followed the Pangea breakup, with the predominance of divergences of neutral chromosomal changes, involving mainly pericentric inversions and NOR amplifications.