Life cycle of Pomacea americanista, a poorly known apple snail endemic to the Iguazú and Alto Paraná Rivers, southern South America

Abstract

The Ampullariidae (apple snails) are freshwater snails of tropical and subtropical regions. Recent research has concentrated on a few species that are invasive or potential biocontrol agents, but the basic life history traits of most species remain unknown. One such poorly known species is Pomacea americanista, endemic to the Alto Paraná and Iguazú Rivers in southern South America, which may be vulnerable to environmental degradation. We studied the growth, survivorship, maturation and reproductive activity of P. americanista to help evaluate its resilience under different scenarios of environmental change. Fifty snails that hatched in the laboratory from two egg masses collected in San Francisco Stream (Misiones Province, Argentina) were reared under controlled conditions until their natural death. Shell growth was almost linear up to the 20th week of life, subsequently decreasing smoothly. Growth rate, asymptotic sizes, time to reach asymptotic size and age at maturity were greater for females than males. Mortality patterns were similar for both sexes, with no deaths up to 38 weeks and steady mortality thereafter, the maximum longevity being 143 weeks. The fecundity of P. americanista is lower than that of other apple snails under similar conditions. Under laboratory conditions males and females underwent a single extended reproductive period, but under the seasonal climate in their natural habitats their life cycle would probably extend for more than 3 years, with two or more reproductive periods. The low fecundity and the late maturity of P. americanista indicate slow population growth and low resilience relative to invasive apple snails. These traits, combined with a restricted geographical range and an association with hard substrates in swiftly flowing waters, suggest that P. americanista could be vulnerable.