| Popis: |
Size-related and inter-population morphological variation were analyzed for Chilina parchappii (d’Orbigny, 1835) in the Naposta Grande stream, Southern Pampas, Argentina. Shell changes during growth are gradual and subtle: the spire becomes relatively wider and the outer lip less prominent. The apertural area grows more slowly than the somatic biomass, probably diminishing the relative gas exchange area. The total weight grows faster than the aperture area (and foot area) presumably without lessening locomotive capacity, since locomotion depends on muscular power. The shell is three times heavier than the body but grows more slowly. A morphological overlap exists in the C. parchappii populations inhabiting different parts of the course of the Naposta Grande stream, but mean shell shapes are significantly different. A genetic basis cannot be discarded but the spatial variation in the incidence of repaired shell breakage could affect the morphology of the populations inhabiting sites with different slope an... |
