Molecular, ecophysiological and morphological data suggest that Navicula phyllepta is a species complex K. Sabbe, B. Vanelslander, V. Chepurnov, W. Vyverman Protistology and Aquatic Ecology, Department of Biology, Ghent University, Belgium and V. Creach, A. Ernst, L. Stal Centre for Estuarine and Marine Ecology, Netherlands Institute of Ecology, Yerseke, The Netherlands Diatom diversity ohas been underestimated Sellaphora, Diploneis, Pseudo-nitzschia, Ditylum, etc. cryptic diversity microdiversity oat different evolutionary scales from populations to species complexes ocomplex spatial and temporal patterns, often coexistence owhat are the evolutionary, ecological, neutral or random processes and mechanisms creating this diversity and regulating the coexistence of microdiverse clusters ? Navicula phyllepta Ktzing 1844 Krammer & Lange-Bertalot (1986) 10 m Witkowski (1994) Sabbe (1997) Kuylenstierna (1991) Sabbe et al. (2003) : Flemish-Dutch Cooperation project Diversity-Productivity Relationships in Microphytobenthos biodiversity of benthic diatom communities: morphological, molecular, physiological (growth ~ salinity) multi-method approach Navicula phyllepta dominant member of communities along estuarine gradient (5-30 psu) about 20 strains isolated from 3 stations in the Schelde estuary (The Netherlands)(marine to brackish), 1 strain from Colne estuary (UK), 1 strain from Ems-Dollard (The Netherlands) oecophysiology: salinity ~ growth experiments omolecular analyses SSU and ITS 1 omorphology oreproductive features (crossing experiments) ecophysiological data growth rate vs salinity no survival < 5 psu survival at 2 psu growth > 0 psu 0.512 molecular data - ITS 1 Global (Gapcost:0%) its PA Ems-Dollard (Nl) BI PA BA (*) AP AP AP AP BI BA BA BA (*) Colne-estuary (UK)(*) BA (*) BA BA (*) BA-04-01 molecular data - ITS 1 Global (Gapcost:0%) its PA Ems-Dollard (Nl) BI PA BA (*) AP AP AP AP BI BA BA BA (*) Colne-estuary (UK)(*) BA (*) BA BA (*) BA ITS 1 30 bases difference, 9 indels SSU rDNA 2 base difference morphological data BI (*) BA-04-01BA BA AP BA PA (*) morphological data same form (PA-03-01) 4 months time span morphological data same form (PA-03-01) 4 months time span taxonomy natural populations from Schelde estuary: 2 forms congruence between morphological, molecular and ecophysiological data good congruence between morphological, molecular and ecophysiological data: two distinct morphological forms are present, these can also be distinguished on the basis of their salinity tolerance, and ITS 1 and SSU rDNA sequences. some strains appear to be intermediate with respect to salinity tolerance, but not with respect to morphology and ITS 1 sequence. It is as yet not clear how this should be interpreted. reproductive isolation sexual reproduction in N. phyllepta has not yet been observed. Diversity not truly cryptic, but cryptic diversity may yet be present. Which of these two is true Navicula phyllepta? lectotype BM (Ktzing 1471) taxonomy lectotype BM (Ktzing 1471) taxonomy conclusions Navicula phyllepta s.l. is heterogeneous reproductive isolation? intermediate ecophysiological types? variation in ITS 1 - more closely related than e.g. Sellaphora pupula species and Pseudo-nitzschia delicatissima divergence in ITS does not necessarily correlate well with morphological dissimilarity coexistence of closely related (cryptic) species at least partly niche- related? provenance of strains polyhaline oligohaline Westerschelde estuary, The Netherlands 5 km