Control of the Seasonal Arrest of Copulation and Spawning in the Apple Snail Pomacea canaliculata (Prosobranchia: Ampullariidae): Differential Effects of Food Availability, Water Temperature, and Day Length

Two laboratory experiments were carried out on summer (active) pairs of Pomacea canaliculata (Lamarck, 1822), to study the influence of food availability (ad libitum feeding and restriction to 25% of the ad libitum requirements), and to determine the effects of water temperature (25 degree C and 18 degree C) and day length (14 hr light/day and 10 hr light/day) on the frequencies of copulation and spawning, and on some spawn measurements such as egg number and volume, and percentage of fertile eggs (i.e., those containing developing embryos). In all groups, the animals were first observed during 14 days in "acclimation" conditions (i.e., ad libitum feeding, 25 degree C, and 14 hr light/day), and then changed to one of the different "treatments." Both food restriction and low water temperatures induced a decrease in the frequencies of both copulation and spawning, without altering the spawn measurements. Short day length was without effect on these behaviors. We conclude that low food availability and cool water are important cues for the seasonal arrest of copulation and spawning in P. canaliculata. We conclude that both food restriction and low water temperatures are responsible for the seasonal arrest of copulatory and spawning behaviors in Pomacea canaliculata, although autumn decreasing temperature seems to be the critical factor in the field. Shortening of the photoperiod may be of little or no importance in determining the seasonal reproductive arrest.