Evidence for parthenogenesis and natural imposex in the Patagonian freshwater snail Heleobia hatcheri (Gastropoda : Hydrobiidae)

摘要

The genus Heleobia Stimpson, 1865 is the most species-rich, widespread and ecologically diverse genus among Neotropical Hydrobiidae. It includes marine, brackish water and freshwater species, which are generally assumed to be dioecious and oviparous (hatching as free-swimming veligers or at a crawling stage). Heleobia hatched (Pilsbry, 1911) is one of the southernmost freshwater hydrobiids in the world, most aspects of its biology being unknown because of its distribution, mainly restricted to rivers in Patagonia. Gaillard and Gaillard & Castellanos described for the first time the penis of H. hatched and Heleobia simplex (Pilsbry 1911) and placed the latter in synonymy, on the basis of their sympatry, morphological shell overlap, and specially for sharing a diminutive penis, reduced to a small nuchal papilla. Cazzaniga4 observed this character also in Heleobia kuested (Strobel, 1874) and established the genus Strobeliella for those species of Heleobia with a papilliform penis, highly reduced in relation to other species within the genus and the family. Hershler & Thompson1 placed Strobeliella under synonymy with Heleobia, considering that it '...was based on gerontic specimens having degenerate penis ...'. Here, I report that the organ that has been previously regarded as being a penis is not a male organ functional in insemination and that reproduction is parthenogenetic in H. hatched.