Journal Article

Hybrid Origin of Polyploidy in Freshwater Snails of the Genus Bulinus (Mollusca: Planorbidae)

Chrisman, C. Larry, LoVerde, Philip T., Goldman, Michael A.

1983

Overview

G-banded karyotypes of the diploid freshwater snail, Bulinus tropicus, and of the tetraploid, B. truncatus, were studied in order to determine whether the tetraploid had arisen through hybridization of karyotypically distinct taxa or through simple doubling of the genome, and to infer cytological characteristics of the diploid taxa involved in the origin of the tetraploid. Most of the homologous chromosomes of the two species were indistinguishable within the limits of resolution of our techniques, and most chromosomes of the tetraploid were found in groups of four, suggesting an origin through simple genome doubling. However, the occurrence of four marker chromosomes-two satellited pairs, one subtelocentric pair, and one pair with a lightly-staining arm-in pairs rather than in sets of four in B. truncatus implies that the tetraploid arose through hybridization. Only the pair with the lightly staining arm occurs also in B. tropicus, suggesting that at least one other diploid population was involved in the founding of the tetraploids. In contrast to the situation in plants, polyploidy is rare in animals. Many of the barriers to polyploidy which have been suggested to explain its rarity in animals are surmounted in Bulinus, due to its facultatively selfing hermaphroditic breeding system. The physiological disadvantages of polyploidy, which we discuss briefly in light of the limited data available for Bulinus, may be overcome by the advantages of the hybrid condition.

• Publisher: Society for the Study of Evolution
• Subject: Animals / Bulinus tropicus / Bulinus truncatus / Chromosomes / Diploidy / Fresh water / Freshwater / Genomes / Hybridity / Karyotype / Polyploidy / Snails / Tetraploidy