Bet-hedgers commit to the hedge: Zooplankton in ephemeral semiarid wetlands of tropical Brazil that widely spread risk.

Bet-hedging is an ecological risk-aversion strategy in which a population does not commit all its effort toward a single reproductive event or specific environmental condition, and instead spreads the risk to include multiple reproductive events or conditions. For aquatic invertebrates in dry wetlands, this often takes the form of some propagules hatching in the first available flood, while remaining propagules hatch in subsequent floods (the "hedge"); this better ensures that a subset of propagules will hatch in a flood of sufficient duration to successfully complete development. Harsh environmental conditions are believed to promote an increased reliance on bet-hedging. Bet-hedging studies have typically been restricted to single sites or single populations. Community-level assessments may provide more robust support for the range of hatching strategies that exist in nature. Here, we tested whether freshwater zooplankton assemblages inhabiting ephemeral and unpredictable wetlands of a semiarid zone of tropical Brazil employ hatching strategies suggestive of bet-hedging; few efforts have addressed bet-hedging in the tropics where the unique conditions may influence the strategy. We collected dry sediments from six ephemeral wetlands, and flooded them across a sequence of three hydrations under similar laboratory conditions to assess whether hatching patterns conform to some of the predictions of the bet-hedging theory. We found that taxa showing hatching patterns akin to bet-hedging associated with delayed hatching numerically dominated the assemblages that emerged from dry sediments, although there was large heterogeneity in the hatching rate among sites and across taxa. While some populations distributed their hatching across all three floods and committed most of their hatching fraction to the first hydration, others committed as much or more effort to the second hydration (the "hedge") or the third hydration (another substantial "hedge"). Thus, in the harsh study wetlands, hatching patterns akin to bet-hedging associated with delayed hatching were common and occurred at multiple temporal scales. Our community assessment found that a commitment to the "hedge" was greater than the current theory would predict. Our findings have broader implications; bet-hedger taxa seem especially well equipped to tolerate stress if conditions become harsher as environments change.

Invertebrate Richness and Hatching Decrease with Sediment Depth in Neotropical Intermittent Ponds.

Some groups of invertebrates from intermittent wetlands produce dormant stages in response to environmental fluctuations. Dormancy is a strategy to survive such fluctuations and to persist in extreme aquatic habitats, such as temporary habitats. We investigated the hatching responses of invertebrate dormant stages across different depths of sediment in intermittent ponds. Our hypotheses were: (1) the richness and abundance of invertebrate hatchlings decrease as the depth of the sediment column increases, and (2) the composition of invertebrate hatchlings varies over the wetland sediment depth. Four intermittent ponds were sampled in southern Brazil. One sediment column of 30 cm depth was collected in each pond and stratified into 1 cm thick slices for analysis of the dormant stages. A total of 1,931 hatchlings distributed among 31 taxa were collected from the sediment columns over the experiment. The total richness and abundance of hatchlings (after bdelloid taxa exclusion) were negatively related with the sediment depth. The composition of aquatic invertebrates varied among the different strata over the sediment depth. As intermittent wetlands are ecosystems extremely susceptible to climate variations, the results help to understand the resilience of aquatic resistant communities from different sediment strata after drought events. Supplementary Information: The online version contains supplementary material available at 10.1007/s13157-023-01675-6.