Combined stress effect of pH and temperature narrows the niche width of flagellates in acid mining lakes

Abstract

Strains of the green alga Chlamydomonas acidophila and two chrysomonads, Ochromonas spp., isolated from each of two similar acid mining lakes (AMLs) with extremely low pH (∼2.6) were investigated to consider a possible synergistic stress effect of low pH and unfavourable temperature. We measured flagellate growth rates over a combination of four pH (2.5, 3.5, 5.0 and 7.0) and three temperatures (10, 17.5 and 25°C) in the laboratory. Our hypothesis was that, under highly acidic conditions (pH <3), an obligate acidophil species (C. acidophila) would be less sensitive to the combined stress of pH and temperature than acidotolerant species (Ochromonas spp.). We expected that the difference of the fundamental vs. realized pH niche would be greater in the latter. Another chrysomonad, Poterioochromonas malhamensis strain DS, served as a reference for a closely related neutrophil species. Surprisingly, C. acidophila did not survive temperatures >27°C. The lowest temperature tested reduced growth rates of all three chrysomonad strains significantly. Since all chrysomonads were tolerant to high temperature, growth rate of one Ochromonas spp. strain was measured exemplarily at 35°C. Only at this high temperature was the realized pH niche significantly narrowed. We also recorded significant intraspecific differences within the C. acidophila strains from the two AML, illustrating that the niche width of a species is broader than that of individual clones.

Multiple environmental stressors confine the ecological niche of the rotifer Cephalodella acidophila

“…Algal stock cultures were maintained as batch cultures in 50‐mL culture tissue flasks with modified Woods Hole Medium (MWC) at a continuous light intensity of 90–100 mmol m −2 s −1 and 17.5 °C. pH ranged from 2.8 to 3.0 to mimic the natural situation (Moser & Weisse, 2011b). Rotifers were kept in identical flasks and the same medium with Chlamydomonas as food, but at 15 °C.…”

“…Subcultures of the algae and rotifers (100 mL volume each) were gradually acclimated to the respective experimental conditions using a similar procedure as applied earlier in our laboratory with protists (Weisse & Stadler, 2006; Moser & Weisse, 2011a). The longest adaptation period (∼2 weeks) was used for the lowest temperature and pH investigated.…”

“…, 2010; Moser & Weisse, 2011b). The present investigation is part of a larger project investigating whether the pelagial of acidic mining lakes is primarily colonised by pH specialists or generalists (Moser & Weisse, 2011a,c; Weisse et al. , 2011) and to determine what factors control these plankton communities.…”

Significant habitat effects influence protist fitness: evidence for local adaptation from acidic mining lakes

“…This view dates back to the 'everything is everywhere' hypothesis formulated by the Dutch microbiologist Baas Becking in the early 20th century (see short reviews by Quispel 1998, Whitfield 2005. However, recent studies provide evidence for limited dispersal and local adaptation among wide-spread freshwater ciliates (Nanney 2005, Barth et al 2006, Gächter and Weisse 2006, Moser and Weisse 2011a) and flagellates (Kim et al 2004, Koch and Ekelund 2005, Boenigk et al 2007, Logares et al 2009, Aleya et al 2011. Intraspecific, clonal differences in ecophysiological key features such as growth and grazing rates were reported for marine and freshwater protists (Lowe et al 2005, Gächter and Weisse 2006, Weisse and Rammer 2006.…”

“…Oxytricha is the only ciliate genus encountered in all our study lakes (T. Weisse et al, unpublished manuscript). Both Ochromonas and one of the Oxytricha species are acid tolerant, i.e., they survive at low pH (,3) but perform better at higher pH (Moser and Weisse 2011a;T. Weisse et al, unpublished manuscript); accordingly, they served as model for generalist species in AML.…”