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We compared dispersal rates and patterns using both spatial genetic structure as well as direct measures of dispersal in Branchipodopsis wolfi, a freshwater anostracan inhabiting clusters of spatially fragmented and temporally unpredictable ephemeral rock pools in southeastern Botswana. For a total of 29 populations from three rock pool sites, the active population component was subjected to allozyme analysis for four loci and gene flow between populations was estimated. For a subset of the pools, we quantified the number of viable floating dormant eggs and larvae dispersing into overflow traps during flood events. Genetic and geographic distances were significantly correlated within each site. Gene flow estimates indicated from 0.6 to 227 migrants per generation. This relatively high effective dispersal rate corresponds with our direct observation of peak dispersal between pools during floods. Up to 784 viable dormant eggs and 301 larvae were trapped at one overflow during one single rainfall event. We determined that a distance of 50 m is already an effective barrier to gene flow for this species. There is ample effective genetic communication between different populations within each rock pool site, but this communication is limited by distance.

The anostracan Phallocryptus spinosa has an almost exclusively palearctic distribution. The Makgadikgadi Pans area in Botswana represents the only distribution record south of the Sahara. In this ephemeral wetland, it is an important food item in the diet of migrating birds. By studying egg bank characteristics (such as depth and density) and hatching requirements, we investigated the persistence of this sub-Saharan population. At localities in the middle and north basin of Sua Pan, sediment cores were taken along a transect, and dormant eggs were isolated. Densities of the active dormant egg bank ranged from 833 to 31449 dormant eggs m )2 , indicating that this species is well established. Most of the dormant eggs were found in the top 4 cm of the sediments, and densities decreased to zero at a depth of 13 cm. Considering the expected low sedimentation rate, the presence of dormant eggs down to 13 cm indicates long-time occurrence of P. spinosa in the Makgadikgadi Pans area. We observed high hatching fractions (up to 85%) at a temperature of 22°C and a salinity of 5 ppt. A second anostracan species, Branchinella ornata, co-occurred with P. spinosa in our study site. This population also had a large active dormant egg bank (ranging from 6634 to 50557 dormant eggs m )2 ) with dormant eggs present until a depth of about 11 cm. This pattern indicates a long-time co-occurrence of P. spinosa and B. ornata.

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