Ref ID : 7066
Manuel Serra, Africa Gomez, and Maria Jose Carmona; Ecological genetics of Brachionus sympatric sibling species. Hydrobiologia 387/388:373-384, 1998
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In this paper we review previous studies on sympatric Brachionus populations in Torreblanca Marsh as a model of evolutionary and ecological relationships between closely related species. The marsh is a wetland on the Mediterranean coast of Spain with high spatial and temporal heterogeneity. Allozyme and morphometric analysis showed that Brachionus group plicatilis (formerly, Brachionus plicatilis and currently split into B. plicatilis and B. rotundiformis) was composed of three groups of genotypes with no evidence of gene flow between them (B. plicatilis, B. rotundiformis SM and B. rotundiformis SS). Correlations between seasonal and spatial distributions, on one hand, and temperature and salinity, on the other hand, were consistent with the results of experimental studies on population dynamics. Accordingly, B. plicatilis is a euryhaline, low temperature group; B. rotundiformis SM is adapted to high temperature and low salinity conditions; and B. rotundiformis SS is adapted to high temperature and high salinity conditions. The groups had different mictic responses to density, salinity and temperature, which can be explained to some extent as an adaptive escape response, given their different ecological preferences. These differences imply a partial ecological barrier to male-female encounter between groups. Mating experiments showed that most copulations occurred within a group. B. plicatilis has a mating recognition system different from those of either B. rotundiformis SM or SS, whereas the two B. rotundiformis groups had partially differentiated mating preferences. Cross-mating experiments performed in the laboratory failed to produce any detectable hybrids. We conclude that three sympatric sibling species inhabit Torreblanca Marsh. The remarkable association between genetic differences among clonal groups and their ecological preferences, mixis response and mating behavior is hypothesized to play a role in stabilizing sympatry, and gives insight into the evolution of genetic divergence and speciation in rotifers.