Stress tolerance in neonates of two <i>Pomacea</i> apple snails with contrasting invasive histories

ABSTRACT Several species of Pomacea apple snails have become invasive, causing severe ecological, economic and sanitary impacts worldwide. Understanding the relationship between bioecological traits and invasiveness helps to predict, retard and prevent invasions. Environmental stressors act as a main barrier against invasions, so the tolerance to them could be a good predictor of invasiveness. Pomacea canaliculata and Pomacea scalaris were transported from South America to Taiwan for aquaculture around 1980. Pomacea canaliculata established in Taiwan and dispersed rapidly through Asia, but P. scalaris established itself only in a few locations and never reached other countries. Hence, these species appear appropriate to elucidate the traits that make successful invaders within the genus Pomacea. The tolerance of neonates to stressors is probably critical for establishment and persistence, because they must cope with many environmental challenges with a minimum of resources and experience. We postulate that the tolerance to stressors of neonates of Pomacea contributes to their invasiveness. For both these species of apple snails, we tested for 60 days the tolerance of 3.5-day-old neonates to starvation, desiccation, high and low temperatures (5 and 35 °C), high and low salinities (2.615 and 0.062 g/l), and urban and rural waters. We recorded periodically the survival and the initial and final shell size. Overall, the neonates of the invasive P. canaliculata have significantly higher survival times than those of the noninvasive P. scalaris, especially under harsh stresses (starvation, desiccation and high and low temperatures and salinities). Instead, the specific growth rates were not generally greater for the invasive apple snail. The much higher tolerance of P. canaliculata neonates, especially to starvation and desiccation, may be related to their bigger size and their functional lung. Our results indicate that neonate tolerances would aid in predicting the relative invasiveness and vulnerability of different Pomacea species.