Lake Pavin History, geology, biogeochemistry, and sedimentology of a deep meromictic maar lake

325

size fraction from public database. These sequences were
obtained by the traditional cloning-sequencing method from
11 worldwide lakes (Fig. 19.5 ). Although with this approach
the sampling is far from exhaustive and many more taxa
(especially rare) might be present at the sampling sites, sta-
tistical analysis (UniFrac analysis; Lozupone and Knight
2005 ) showed 18S rRNA gene OTUs compositions signifi -
cantly different among most of lakes, and this difference
does not seem to be related to the trophic status at any spatial
scales. Such results were expected because the effect of dis-
persal limitation would occur at the largest geographic scales
(across continents) rather than at regional scales where envi-
ronment selection could theoretically be predominant
(Martiny et al. 2006 ). At the global scale, a signifi cant linear
relationship with lake areas is obtained but only when using
the smaller lake areas (lower than 114 km^2 corresponding the
lakes Bourget and George; Fig. 19.5 ) (Lepère et al. 2013 ).

19.5 Concluding Remarks

19.5.1 Including Picoeukaryotes
in the Debates on Biodiversity
and Ecosystem Functioning: Issues
of Scale and Trophic Complexity

A central goal in ecology is to understand the patterns and
processes of biodiversity. As aquatic microbial ecologists,
we still lack a solid understanding of the characteristic scales
of variation in aquatic eukaryotic community composition,
and this hampers our ability to develop theories about how
the stability of the functions (eukaryotes-mediated func-
tions) are maintained across space and time in lakes.The
effects of the main drivers (local and global pressures) affect-
ing biodiversity involve changes in species at different tro-

phic level. Evaluating how ecosystem processes are likely to

change following species rearrangements (or loss) at multi-

ple trophic levels is important to advance knowledge on bio-

diversity–ecosystem functioning links.The eukaryotic

microbes have certainly to be included in such research

work, due to the variety of eukaryotic functional groups

involved in trophic network functioning.

Research on the relationship between biodiversity and

ecosystem functioning is entering a new phase with the

application of DNA/RNA tools used to reveal the huge diver-

sity of microbial communities. The taxa recently revealed

within the picoeukaryotic fraction have undoubtedly to be

included in the studies aiming at identifying the effects of the

main drivers on aquatic biodiversity and the resulting

changes in ecosystemic functioning.

Acknowledgments The authors thank, very sincerely, Tom Richards

for his review and the quality of its evaluation on this chapter.

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Netherlands (in Dutch)

1.6

1.2

0.8

0.4

0

-2 -1 012345

Pavin

Villerest

Bourget

George

Baikal

Xuanwu Tanganyika

Log(Area)

Aydat

Sep

Log(Dmg) Godivelle

Zixia

0

1.2

Pavin

Fig. 19.5 Relationship between
lake areas and richness expressed by
a diversity index (Margalef:Dmg)
calculated from cloning–sequencing
method (six French lakes + fi ve
worldwide lakes = Baikal (sequence
accesion numbers:
JN547261-JN547327), George
(AY919677-AY919829),
Tanganyika
(GU290066-GU290116), Zixia
(FJ939033-FJ939124), Xuanwu
(FJ939033-FJ939124))

19 Diversity and Biogeography of Lacustrine Picoeukaryotes

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