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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

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Molecular, ecophysiological and morphological data suggest that

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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

    • has been underestimated

      • Sellaphora, Diploneis, Pseudo-nitzschia, Ditylum, etc.

      • crypticdiversity

      • microdiversity

    • at different evolutionary scales – from populations to species complexes

    • complex spatial and temporal patterns, often coexistence

    • what are the evolutionary, ecological, neutral or random processes and mechanisms creating this diversity and regulating the coexistence of microdiverse clusters ?


Navicula phyllepta Kützing 1844

Witkowski

(1994)

Sabbe (1997)

Sabbe et al. (2003)

10 µm

Krammer &

Lange-Bertalot

(1986)

Kuylenstierna

(1991)


  • 2002-2006 : 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)

    • ecophysiology: salinity ~ growth experiments

    • molecular analyses – SSU and ITS 1

    • morphology

    • reproductive features (crossing experiments)


ecophysiological data – growth rate vs salinity

no survival < 5 psu

survival at 2 psu

growth > 0 psu

0.5

1

2


molecular data - ITS 1

Global (Gapcost:0%)

its1

100

96

90

91

92

93

94

95

97

98

99

PA-02-02

Ems-Dollard (Nl)

BI-02-02

PA-02-01

BA-04-06 (*)

AP-02-02

AP-02-03

AP-02-01

AP-03-01

BI-02-03

BA-04-04

BA-04-05

BA-04-08 (*)

Colne-estuary (UK)(*)

BA-04-07 (*)

BA-04-02

BA-04-09 (*)

BA-04-01


molecular data - ITS 1

Global (Gapcost:0%)

its1

100

96

90

91

92

93

94

95

97

98

99

PA-02-02

Ems-Dollard (Nl)

BI-02-02

PA-02-01

ITS 1 – 30 bases difference, 9 indels

SSU rDNA – 2 base difference

BA-04-06 (*)

AP-02-02

AP-02-03

AP-02-01

AP-03-01

BI-02-03

BA-04-04

BA-04-05

BA-04-08 (*)

Colne-estuary (UK)(*)

BA-04-07 (*)

BA-04-02

BA-04-09 (*)

BA-04-01


morphological data


morphological data

AP-03-01

PA-03-01 (*)

BI-02-01 (*)

BA-04-05

PA-03-01 (*)

BA-04-01

BA-04-02

BA-04-04


morphological data


morphological data

same form (PA-03-01) 4 months time span


morphological data


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?


taxonomy

‘lectotype’ BM 18874

(Kützing 1471)


taxonomy

‘lectotype’ BM 18874

(Kützing 1471)


  • 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?


oligohaline

polyhaline

Westerschelde estuary, The Netherlands

provenance of strains

5 km


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