Karyology of the Antarctic chiton Nuttallochiton mirandus (Thiele, 1906) (Mollusca: Polyplacophora) with some considerations on chromosome evolution in chitons.
We describe the karyotype, location of nucleolus-organizing regions (NORs) and heterochromatin distribution and composition in the Antarctic chiton Nuttallochiton mirandus. Specimens had a karyotype of 2n = 32 chromosomes, of which two were microchromosomes. Among macrochromosomes, the elements of the first and fourth pair were bi-armed, the others were telocentric. At least six NOR sites were detected with NOR-FISH, but only four were Ag-NOR-banding-positive. The two microchromosomes were essentially euchromatic, while all macrochromosomes exhibited clear pericentromeric C bands that were found to be AT-rich (being quinacrine- and DAPI-positive) and resistant to digestion with AluI and HaeIII. N. mirandus has the largest number of chromosomes (2n = 32) and telocentric elements (26) of all the chiton species studied to date. The karyological results of our study agree with previous molecular data indicating N. mirandus as a sister taxon of Acanthochitona crinita. The karyotypes of the two species could be related as a result of Robertsonian rearrangements. According to the more parsimonious hypothesis, the former would be the primitive karyotype, although other evolutionary events cannot be ruled out.
Odierna
Gaetano
G
Dipartimento di Biologia Strutturale e Funzionale, Università di Napoli 'Federico II', Via Cinthia, 80126, Napoli, Italy.
Aprea
Gennaro
G
Barucca
Marco
M
Biscotti
Maria Assunta
MA
Canapa
Adriana
A
Capriglione
Teresa
T
Olmo
Ettore
E
D000818:Animals; D000864:Antarctic Regions; D002875:Chromosomes / Q000235:genetics*; D019143:Evolution, Molecular; D007621:Karyotyping; D008297:Male; D008677:Metaphase; D010802:Phylogeny; D049916:Polyplacophora / Q000235:genetics*; D013093:Spermatogonia / Q000166:cytology