Vol. 54, 2015
Thicker filaments of Aphanizomenon gracile are more harmful to Daphnia than thinner Cylindrospermopsis raciborskii
Lukasz Wejnerowski*, Slawek Cerbin and Marcin Krzysztof Dziuba
Department of Hydrobiology, Faculty of Biology, Adam Mickiewicz University, Umultowska 89, 61-614 Poznań, Poland
cyanobacteria are known to negatively affect the life history of
planktonic herbivores through mechanical interference with filtering
apparatus. Here, we hypothesise that not only the length but alsothe
thickness of cyanobacterial filaments is an important factor shaping
the life history of Daphnia.
Results: To test our hypothesis, we cultured Daphnia magna with non-toxin-producing strains of either Aphanizomenon gracile or Cylindrospermopsis raciborskii. The former possesses wide filaments, whereas the latter has thinner filaments. The strain of A. gracile has two morphological forms differing in filament widths. The exposure to the thicker A. gracile
filaments caused a stronger body-length reduction in females at
maturity and a greater decrease in offspring number than exposure
to the thinner C. raciborskii
filaments. The width of filaments, however, did not significantly
affect the length of newborns. The analysis of mixed thick and thin A. gracile filament width distribution revealed that D. magna
reduces the number of thinner filaments, while the proportion of
thicker ones increases. Also, the effects of cyanobacterial exudates
alone were examined to determine whether the changes in D. magna
life history were indeed caused directly by the physical presence of
morphologically different filaments and not by confounding effects from
metabolite exudation. This experiment demonstrated no negative effects
ofboth A. gracile and C. raciborskii exudates.
our knowledge, this is the first study that demonstrates that the
thickness of a cyanobacterial filament might be an important factor in
shaping D. magna’s life history. At a given biomass, thicker filaments of A. gracile were more detrimental to D. magna than thinner ones of C. raciborskii.
There was also a strong interaction between species of the
cyanobacterium and filament biomass, where species with thicker
filaments and at higher biomass had the strongest negative impact on D. magna life history.
Key words: Filter-feeding; Cyanobacterial exudates; Mechanical interference; Daphnia magna filamentous cyanobacteria; Aphanizomenon gracile; Cylindrospermopsis raciborskii; Filament morphology.
*Correspondence: E-mail: email@example.com