Karyotypes of operculate land snails of the genus<i>Cyclophorus</i>(Prosobranchia: Cyclophoridae) in Thailand

Abstract

Summary Although earliest known records of the Cyclophoridae are from the European Mesozoic, Cyclophorus is a genus of dioecious terrestrial prosobranchs that currently ranges from South Asia to the Western Pacific region. Karyotypes of ten species of Cyclophorus have been examined from Thailand. Haploid and diploid chromosome numbers were invariant (n = 14, 2n = 28, FN = 56), but the karyotypes varied along a continuum with 14 metacentric chromosomes in C. volvulus while the remaining species contain unique representatives of every summed combination of metacentric and submetacentric types from 13m + 1sm to 6m + 8sm. The two larger species, C. aurantiacus and C. malayanus, exhibit the same karyotypes of 7m + 7sm. Karyotypes among populations of C. fulguratus showed variation between the central (12m + 2sm) and northeastern regions (13m + 1sm) of Thailand. Among the species with unique karyotypes, northern species possess a higher metacentric number relative to southern species. The ZZ-ZW sex-determining chromosomes were observed in C. fulguratus from Phuwiang, C. malayanus from Sramorakot and C. volvulus from Wang Kanlueang. Taxonomic and evolutionary implications of the present findings are discussed.