Estágios dormentes do zooplâncton: variação morfológica entre espécies e influência do tempo de dessecação na eclosão

Abstract

The presence of dormant stages is a key feature in the life cycle of zooplanktonic organisms. The presence of resting eggs and the existence of eggs banks in the sediment are considered as a temporal refuge against adverse conditions, enabling the reestablishment of communities after favorable conditions resume in the environment. This study is divided into two approaches described in two chapters, both using egg banks from permanent lakes. In the first one, a quantitative comparison was performed on the morphology of cladoceran resting eggs (and their ephippia), sampled from 4 different lakes, and looking for similarities and metrics that may help in the identification of the species. This morphometric approach found that ephippia descriptors such as height, width and area of the ephippia can be summarized in just one measurement, as these descriptors are highly correlated. However, it is important to considerif the use of morphology for species identification outweighs the hatching of resting eggs, due to technological costs and available time. The results presented here also created a photographic catalog with eggs from different species, for greater readiness in identifying the egg bank community. In the second approach, the effect of desiccation of sediment on hatchling communities was experimentally evaluated, seeking to assess how communities recover after atypical drought events in permanent lakes. It was expected that longer desiccation durations would result in lower abundance and species richness of hatchlings. For the response variables abundance, composition and species richness in different communities, sediment samples were taken in 4 different lakes. A complementary experiment was aimed to recognize the effects of desiccation at the population level, so replicates were taken from a single lake. At the population level, only one calanoid copepod, Notodiaptomus iheringi, was found in high numbers. This species showed more hatchlings in longer desiccated sediments. Desiccation increased the number of hatchlings in both experiments when compared to humid sediments, implying that resting eggs of some species are able to survive desiccation for at least 9 months, so desiccation can be considered as one of the possible cues to stimulate hatching. Climate change models predict an increase in drought cycles for many regions of the world, so future studies are desirable in order to determine which species eventually benefit or are vulnerable to drought periods.