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

o has been underestimated

Sellaphora, Diploneis, Pseudo-nitzschia, Ditylum, etc. cryptic diversity microdiversity

o at different evolutionary scales – from populations to species complexes

o complex spatial and temporal patterns, often coexistence

o 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

Krammer & Lange-Bertalot (1986)

10 µ

m

Witkowski(1994)

Sabbe (1997)

Kuylenstierna(1991)

Sabbe et al. (2003)

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)

o ecophysiology: salinity ~ growth experimentso molecular analyses – SSU and ITS 1o morphologyo reproductive features (crossing experiments)

ecophysiological data – growth rate vs salinity

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0 5 10 15 20 25 30

salinity (psu)

gro

wth

rat

e (d

ivis

ion

s d

ay-1

)

PA-03-01 AP-03-01 BI-02-01 AP-02-01 BI-02-02 PA-02-01

PA-02-02 BA-04-01 BA-04-02 BA-04-03 BA-04-04 BA-04-05

no survival < 5 psu

survival at 2 psu

growth > 0 psu

0.5 1 2

molecular data - ITS 1

Global (Gapcost:0%)its1

100

99989796959493929190

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

99989796959493929190

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

ITS 1 – 30 bases difference, 9 indels

SSU rDNA – 2 base difference

morphological data

morphological data

BI-02-01 (*)

BA-04-01 BA-04-02

BA-04-05

AP-03-01

BA-04-04

PA-03-01 (*)

PA-03-01 (*)

morphological data

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

5 10 15 20 25 30 35

valve length (µm)

va

lve

wid

th (

µm

)

morphological data

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

5 10 15 20 25 30 35

valve length (µm)

va

lve

wid

th (

µm

)

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

morphological data

14

15

16

17

18

19

20

21

22

23

24

4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0

valve width (µm)

str

ia d

en

sit

y (

n°

in 1

0 µ

m)

morphological data

14

15

16

17

18

19

20

21

22

23

24

4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0

valve width (µm)

str

ia d

en

sit

y (

n°

in 1

0 µ

m)

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

taxonomy

14

15

16

17

18

19

20

21

22

23

24

4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0

valve width (µm)

stri

a d

ensi

ty (

n°

in 1

0 µm

)

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?

14

15

16

17

18

19

20

21

22

23

24

4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0

valve width (µm)

stri

a d

ensi

ty (

n°

in 1

0 µm

)

‘lectotype’ BM 18874(Kützing 1471)

taxonomy

14

15

16

17

18

19

20

21

22

23

24

4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0

valve width (µm)

stri

a d

ensi

ty (

n°

in 1

0 µm

)

‘lectotype’ BM 18874(Kützing 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 Netherlands5 km