A quantitative study of environmental factors influencing the seasonal onset of reproductive behaviour in the South American apple-snail Pomacea canaliculata (Gastropoda: Ampullariidae).

摘要

Two laboratory experiments were carried out on winter (inactive) pairs of Pomacea canaliculata. In the first experiment, the effects of water temperature (18 or 25deg C, corresponding to late winter and summer temperatures in Mendoza, Argentina, respectively) and daylength (LD 10:14 or 14:10, corresponding to the shortest and the longest day of the year in Mendoza, respectively), were determined on the frequency of copulation and spawning, on spawn measurements (number and volume of eggs, and spawn volume), and on an index of the reproductive effort. In the 2nd experiment, the effects of food availability (ad libitum feeding vs. restriction to 25% of the ad libitum requirements) were determined. Low water temperatures induced a lesser and later activation of copulation and spawning than warm temperatures. Daylength did not effect behaviour. Both the frequency of spawning and the reproductive effort index decreased under restricted feeding, without altering the spawn measurements. The latency periodsfor both copulatory and spawning behaviours were similar in both ad libitum and restrictedly fed groups. It is concluded that water temperature may be the critical factor that causes the seasonal onset of copulatory and spawning behaviour. However, foodavailability may also be a determining factor, mainly to trigger spawning activity. It is suggested that the factors that control the seasonal onset of the sexual activities in Pomacea canaliculata are similar to those that control the seasonal arrest,thereby establishing the annual pattern of reproduction in this species.