Studies on the ecological genetics of the land snail sitala jenynsi (PFR)

The shell-banding polymorphism of the arboreal snail S. jenynsi (Pfr.) was used for micro-evolutionary studies in Central Coastal Tanzania. This urocyclid pulmonate has a 12-month life-span), sperm transfer is reciprocated by the two partners and breeding soon follows before the parental die out. Growth rates and the shell’s ultimate metrics depend on the population in question. A knowledge of parameters like numbers, density, rates of survival, loss and dilution introduced the setting of the snail, population. In dimorphic populations (Main Campus, University of Dar es Salaam) morph-ratio distribution was spatially homogeneous, temporally stable and specific for a locally. The distribution was also locally-specific in trimorphic populations (Wazo) but was usually beterogeneous in space and the frequencies of non-predominant morphs fluctuated in time. Basing on clinal distribution of morph ratios, shell-size and weight, it is held that whole or sections of parapatrically differentiated subpopulations were reduced to founder stocks which are presently evolving under mainly unstable environments. Indications of the possible involvement of climatic selection and mating non-randommess in the maintenance of the polymorphism are presented: selective predation does not appear to operate.