ECOLOGICAL FACTORS AFFECTING GENE FLOW IN THE BRACHIONUS-PLICATILIS COMPLEX (ROTIFERA)

We investigated how adaptation to salinity and temperature acts as rep roductive barriers in three sympatric species from the Brachionus plic atilis species complex. These species co-occur in a salt marsh in Spai n, and a previous electrophoretic study of variation revealed Ilo hybr ids between them. A factorial experiment was designed to test for diff erences in population growth rates and patterns of bisexual reproducti on. The design combined representative strains from each species in di fferent salinity and temperature conditions, representing the range ov er which these rotifers are found in their natural environment. We fou nd differences is the growth response of the three species to both fac tors and in the pattern of bisexual reproduction. These differences he lp to explain patterns of succession observed in the field. We conclud e that these ecological factors. together with mate recognition system s, account for the absence of gene flow in these sympatric species.