Biology Reference
In-Depth Information
abundance and activity during the winter in the Antarctic Peninsula
(
Grzymski et al., 2012; Williams et al., 2012
). Similarly, bacterial clades
within the Rhodobacteraceae, uncultivated
g
-Proteobacteria and
Bacteriodetes show large seasonal variations between samples from summer
and winter from both the Antarctic Peninsula and the sub-Antarctic Kergue-
len Islands (
Ghiglione & Murray, 2012
). On top of these oscillations, over
shorter time and spatial scales, Flavobacteria can become dominant in
response to algal blooms (
Ghiglione & Murray, 2012; Grzymski et al.,
2012; Williams et al., 2013
).
The composition of the sea-ice microbiota is also unique as a result of its
seasonal nature and physicochemical environment (
Bowman et al., 2012;
Brown & Bowman, 2001
). It has an important role in providing the “seed
populations” for the productive springtime microbial communities. It is still
unclear whether the selective pressure within the winter sea ice generates sig-
nificant genetic bottlenecks on different microbial species (
Connelly,
Tilburg, &Yager, 2006; Junge, Imhoff, Staley, &Deming, 2002
).What is clear
is that, when compared to surrounding sea water, the species richness in sea ice
is lower than in surrounding waters (
Bowman et al., 2012
), which in turn has
been shown to decrease when moving from lower to higher latitudes (
Sul,
Oliver, Ducklow, Amaral-Zettler, & Sogin, 2013
). This lower richness might
not provide enough resilience in case of future climatic changes.
Compared to the heterotrophic community, the latitudinal distribution
and temporal variation of primary producers are even more extreme. Cyano-
bacteria, for example,
Synechococcus
sp. and
Prochlorococcus
sp., are fundamental
in carbon fixation and responsible for more than half of primary production in
oligotrophic ocean waters (
Liu et al., 1998; Liu, Nolla, & Campbell, 1997
).
Aconsistent trend is the progressive disappearance of
Prochlorococcus
populations
south of the Polar Front and the appearance of specific clades of
Synechococcus
which dominate at higher latitudes (
Scanlan et al., 2009
). This trend holds true
at both poles. In fact, bipolar distribution of organisms is the rule rather than the
exception amongst microbial taxa (
Suletal.,2013
). In microeukaryotes, the
observation of pheromone cross signalling amongst Arctic andAntarctic strains
of the polar protozoan ciliate
Euplotes nobilii
suggests mechanisms for recent
genetic exchange (
Di Giuseppe et al., 2011
). If associatedwith the strong bipo-
lar biogeographical patterns, this could be true for all classes of organisms living
at lowReynolds numbers, with the caveat that deep-sea currents, in particular
those associated with thermohaline circulation, are allowing an ongoing
genetic exchange between the poles
(
Lauro, Chastain, Blankenship,
Yayanos, & Bartlett, 2007
).
