Patterns of genetic differentiation in resting egg banks of a rotifer species complex in Spain

Here we present the first population study on the genetic diversity of a ro tifer species complex (Brachionus plicatilis) in a geographic area (Eastern Spain), which includes inland and coastal habitats. A novel approach was u sed by hatching resting eggs from sediment samples rather than sampling rot ifers from the water column. Hatchlings from resting eggs sampled at 22 sit es resulted in 434 clones which were screened using four polymorphic allozy me loci. A high level of genetic diversity was found consisting of 43 multi locus genotypes which were clustered into six well differentiated groups, o ften found in sympatry, with few or no hybrids between them. Mating experim ents revealed preferences that supported the observed pattern of genetic di fferentiation. Some groups had restricted geographical distributions, and s howed a preference for habitat type. Our results confirm patterns found in other zoo-planktonic organisms and suggest that classical taxonomy has unde restimated biological diversity in rotifers. The presence of additional cry ptic sibling species in this complex seems very probable. Our study demonst rates the feasibility of using sediment sampling to explore genetic differe ntiation between species and populations, and shows the role of the resting egg bank in maintaining genetic diversity.