of these lakes (Felip et al. 1999), and the environmental heterogeneity at the local
scale is larger than expected (Catalan et al. 1992, 2006). In addition, mountain
lakes have been traditionally studied by limnologists with a background of ecology
and phyto- and zooplankton biology (e.g. Catalan et al. 2006 and references
therein, Tolotti et al. 2009) rather than by microbial ecologists with a background
in microbiology and genetics. Consequently, the genetic diversity, taxonomic
identity and ecological distribution of the unseen majority in genuinely high
mountain systems have remained mostly unknown. A few investigations in the past
years are however helping to fill this gap, primarily in the Alps (Pernthaler et al.
1998; Pérez and Sommaruga 2011), the Himalayas (Liu et al. 2006; Sommaruga
and Casamayor 2009; Kammerlander et al. 2015), the high mountains of west USA
(Nelson 2009; Hayden and Beman 2016) and, specially, in the Central Pyrenees
within and around the Aiguestortes i Estany de Sant Maurici National Park
(Catalan et al. 2006). Meteorologic variability, catchment inputs, and warming are
key factors structuring microbial communities (Nelson 2009). These lakes are very
sensitive to detect an excess of reactive N of human origin circulating through the
atmosphere (Camarero and Catalan 2012). Some of these lakes are glacier-fed
ecosystems and hold specific physical conditions, biodiversity and ecological
functioning (Edwards et al. 2013; Peter and Sommaruga 2016). High mountain
lakes formed by glaciers erosion are very comparable worldwide ecosystems, and
the new lakes that are currently appearing after the glacial retreat in mountain areas
offer great opportunities for ecological and limnological studies (Catalan and
Rondon 2016). Microbial diversity in high-altitude aquatic ecosystems from
highlands such as Tibetan lakes (Zhang et al. 2013) and Andean lakes (Ordoñez
et al. 2009) are not considered here because of the consistent limnological,
physicochemical and environmental differences mostly characteristic from the
relatively flat terrain of plateau areas.
Probably, one of the most intensive and extensive limnological studies of alpine
lakes to date have been carried out in the Central Pyrenees (Catalan et al. 2006).
Extensive studies on microscopically conspicuous organisms have been already
done (Catalan et al. 2015; Felip et al. 1999; Pla et al. 2003) and will be obviated
here. Using environmental ribosomal RNA genes sequencing, a sample set representative of the lacustrine Pyrenean landscape heterogeneity has been studied in
detail for bacteria, archaea and mostly inconspicuous microbial eukaryotes biodiversity, as will be presented further in this chapter. This alpine area contains the
main freshwater lake district of south-west Europe, and constitutes a mosaic of
highly diverse water bodies mimicking the geological diversity of the catchments
(Catalan et al. 1992) that usually remain ice-covered for 4–7 months every year
(typically from December to April). Very low concentrations of nutrients and salts
(i.e. ultraoligotrophic and hypotonic waters), persistent extreme conditions (high
UV exposure and water transparency, and low temperatures), and isolation might
promote an adapted microbiota with a large number of specialist populations
(Catalan et al. 2006). Although, lakes located at high altitudes efficiently integrate
160
E.O. Casamayor
scale is larger than expected (Catalan et al. 1992, 2006). In addition, mountain
lakes have been traditionally studied by limnologists with a background of ecology
and phyto- and zooplankton biology (e.g. Catalan et al. 2006 and references
therein, Tolotti et al. 2009) rather than by microbial ecologists with a background
in microbiology and genetics. Consequently, the genetic diversity, taxonomic
identity and ecological distribution of the unseen majority in genuinely high
mountain systems have remained mostly unknown. A few investigations in the past
years are however helping to fill this gap, primarily in the Alps (Pernthaler et al.
1998; Pérez and Sommaruga 2011), the Himalayas (Liu et al. 2006; Sommaruga
and Casamayor 2009; Kammerlander et al. 2015), the high mountains of west USA
(Nelson 2009; Hayden and Beman 2016) and, specially, in the Central Pyrenees
within and around the Aiguestortes i Estany de Sant Maurici National Park
(Catalan et al. 2006). Meteorologic variability, catchment inputs, and warming are
key factors structuring microbial communities (Nelson 2009). These lakes are very
sensitive to detect an excess of reactive N of human origin circulating through the
atmosphere (Camarero and Catalan 2012). Some of these lakes are glacier-fed
ecosystems and hold specific physical conditions, biodiversity and ecological
functioning (Edwards et al. 2013; Peter and Sommaruga 2016). High mountain
lakes formed by glaciers erosion are very comparable worldwide ecosystems, and
the new lakes that are currently appearing after the glacial retreat in mountain areas
offer great opportunities for ecological and limnological studies (Catalan and
Rondon 2016). Microbial diversity in high-altitude aquatic ecosystems from
highlands such as Tibetan lakes (Zhang et al. 2013) and Andean lakes (Ordoñez
et al. 2009) are not considered here because of the consistent limnological,
physicochemical and environmental differences mostly characteristic from the
relatively flat terrain of plateau areas.
Probably, one of the most intensive and extensive limnological studies of alpine
lakes to date have been carried out in the Central Pyrenees (Catalan et al. 2006).
Extensive studies on microscopically conspicuous organisms have been already
done (Catalan et al. 2015; Felip et al. 1999; Pla et al. 2003) and will be obviated
here. Using environmental ribosomal RNA genes sequencing, a sample set representative of the lacustrine Pyrenean landscape heterogeneity has been studied in
detail for bacteria, archaea and mostly inconspicuous microbial eukaryotes biodiversity, as will be presented further in this chapter. This alpine area contains the
main freshwater lake district of south-west Europe, and constitutes a mosaic of
highly diverse water bodies mimicking the geological diversity of the catchments
(Catalan et al. 1992) that usually remain ice-covered for 4–7 months every year
(typically from December to April). Very low concentrations of nutrients and salts
(i.e. ultraoligotrophic and hypotonic waters), persistent extreme conditions (high
UV exposure and water transparency, and low temperatures), and isolation might
promote an adapted microbiota with a large number of specialist populations
(Catalan et al. 2006). Although, lakes located at high altitudes efficiently integrate
160
E.O. Casamayor