Threshold temperatures and degree-day estimates for embryonic development of the invasive apple snail Pomacea canaliculata (Caenogastropoda: Ampullariidae)

SEUFFERT, M. E., SAVEANU, L & MARTÍN, P. R.

MALACOLOGIA

INST MALACOL

Lugar: Philadelphia; Año: 2012 vol. 55 p. 209 - 217

0076-2997

Pomacea canaliculata is a freshwater snail native to subtropical-temperate South America that invaded different types of freshwater systems around the world. Temperature is probably one of the main limitations to the expansion of this and other apple snails to higher latitudes in invaded regions. Embryonic development occurs within calcareous egg capsules and hatching usually occurs two weeks after oviposition but this period varies greatly due to the inverse relationship of air temperature and development rate. The aims of this work are to compare different methods for determining lower temperature thresholds for the embryonic development of P. canaliculata and to estimate the degree-days required for the completion of the development. Egg mass were incubated in a laboratory room without temperature control and were checked daily to record the appearance of hatchlings; air temperature was recorded hourly with a data-logger. The duration of development was calculated as the number of days elapsed between egg laying and the date of first hatching. The lower temperature threshold for embryonic development was estimated with four different methods and two sets of temperature data: hourly temperature data and a daily means calculated averaging the records of maximum and minimum temperatures of each day. The cumulative degree-days for embryonic development were calculated using the hourly records of temperature and the daily mean of temperature calculated according to the single triangle and the single sine methods. The lower temperature thresholds estimated for the embryonic development of P. canaliculata fluctuated between 15.8 and 18.3 °C. The mean cumulative DD estimations ranged between 88.8 and 133.8 °C.d according to the different methods. The estimations obtained with the single triangle and the single sine methods were exactly the same. The values estimated from the hourly temperature records were 4.72 to 7.65% lower than both cumulative degree-days obtained from the daily mean of maximum and minimum records. The range of temperature thresholds for embryonic development reported here is up to two degrees higher than those reported for nonindigenous populations of this species. The reported cumulative degree days for Pomacea are more variable than those of temperature thresholds and our values (119.2 133.8 °C.d) lay well within the range reported previously using other methods. The durations of embryonic development reported for egg masses under constant temperatures in their natural range only differed from our predictions in two days at most. In contrast, estimates obtained under constant temperatures with populations in the invaded range were generally lower than predicted, from 2 to 13 days shorter at 32 and 21 °C, respectively. The estimation of lower thresholds and cumulative degree-days for embryonic development on the basis of hourly or daily records of fluctuating temperatures provided results comparable to those already available for Pomacea spp. and computed on the basis of development duration at different constant temperatures. Additionally, our general approach is more economical as it does not involve special equipment (temperature controlled rearing chambers), instead it only requires a max min thermometer (or a thermograph or data-logger if available) and it can also be applied in the field. This would permit the development of specific degree-day models at a local scale even if apple snails are not correctly identified.