Terminating dormancy: hatching phenology of sympatric large branchiopods in Siangtian Pond, a temporary wetland in Taiwan

Abstract

Large branchiopods adapt to stochastic temporary wetlands by means of rapid development and production of dormant eggs. Unhatched eggs build the egg bank that bridges the frequent unfavorable periods. Dormancy termination is complex not only in appropriate hatching times, but also in hatching fractions. We investigated the parameters of hatching phenology including the initial hatching time, hatching duration, hatching rate, and cumulative hatching rate of two sympatric large branchiopods, Branchinella kugenumaensis (Ishikawa, 1895) and Eulimnadia braueriana Ishikawa, 1895, in Siangtian Pond in northern Taiwan, to explore the hatching strategies. In the laboratory studies, substrate samples with quantified egg numbers were inundated and dehydrated periodically and repetitively until no further hatching occurred, and the according parameters were recorded and calculated. We found that for both species, the hatching time was focused early in the hydroperiod. Most larvae hatched in the early hydroperiods. Overall, E. braueriana had a higher hatching rate through hydroperiods, and a higher cumulative hatching rate (82.9%) than B. kugenuaensis (47.5%). Early and concentrated hatching in a given hydroperiod could be adaptive, leading individuals to mature before the end of hydroperiod and reducing the frequency of abortive hatching. Since the hydroperiods of Siangtian Pond were synchronous with torrential rains, to incline the hatchings toward early hydroperiods is more preferable than to spread over several hydroperiods under the predictable hydroregime. Generally, the hatching phenology of E. braueriana, i.e., the longer the hatching duration and higher hatching rate, the better the adaptation to the hydroregime of Siangtian Pond.