Investigação experimental sobre a ecologia de gastrópodes do gênero Pomacea, PERRY 1810 (Gastropoda, Ampullariidae) da Região Amazônica

Abstract

Gastropods from the Ampullariidae family are divided among nine genera being the most famous the Pomacea genera. There is about 20 species of Pomacea that lives in the Amazon ecosystem which has influence of flood pulses of the rivers. So this study evaluated the daily activity and the influence of the flood pulse in the apple snails behavior using Pomacea bridgesii as a model and also evaluated the desiccation resistance of the apple snails comparing the resistance between Pomacea amazonica and P. bridgesii. The gastropods were sampled between May 2012 and June 2013 in the city of Itacoatiara, Amazonas, Brazil. The daily activity, substratum selection and flood pulse simulation were made under natural light and temperature. The behaviors were registered on an ethogram and the daily activity was observed for 48 hours and the flood pulse simulation observations were made during 70 days. In the desiccation resistance experiment, the animals were put in plastics recipients and weighted with 24 hours interval until the death of the animals, after that the animals were dried on a 60ºC kiln to obtain the dry weight. Pomacea bridgesii had more activity during the night where up to 80% of the animals were exploring the tank and during the day up to 80% were immobile. The most used substratum was the pebble. When comparing day with night the part of the usage of pebble during the day shifted to the smooth surface significantly (X²=26.51; DF=3; P<0.05). The behavior of P. bridgesii related to the simulated flood pulse had significant difference between flood peak and dry period but there was no significant difference between the rising water period and the draining period. As for the desiccation resistance, P. amazonica survived a maximum of 314 days and P. bridgesii 157. There was neither difference between the sexes of both species nor difference between species. The size comparison was different for P. amazonica which the small individuals (5--|30 mm) survived less than the medium sized ones (30--|55 mm; H=13.33; DF=2; Z=2.78; P<0.05) and large ones (≥55 mm; H=13.33; DF=2; Z=3.11; P<0.05), and for P. bridgesii the large animals (≥36 mm) survived more time than small individuals (12--|25 mm; H=14.40; DF=2; Z=3.42; P<0.05) and medium ones (25--|36 mm; H=14.40; GL=2; Z=2.90; P<0.05). The species showed similar survival tendency and water loss although the maximum survival time was different. So we can conclude that P. bridgesii displays more activity during the night and had more usage of the pebble substratum during the day, but part of this usage shifted to the smooth surface relating to their nocturnal activity. This species also displayed adaptations to the complex Amazon ecosystem interrupting the activities and closing their operculum to survive the long drought period. And both Pomacea amazonica and P. bridgesii have high desiccation resistance as a part of their adaptations for the ecosystem which allows them to survive the drought period of the Amazon basin and even longer drought periods which may happen.