Investigation of defence mechanisms against grazing in the green alga Microglena globulifera
(2022) BION02 20221Degree Projects in Biology
- Abstract
- Algae exhibit different strategies to avoid predation by zooplankton. In green algae, which are generally not known for being toxic, colony formation or a protective mucilage cover can be such defence mechanisms. This study investigates the predation defence of Microglena globulifera (Chlamydomonadales), a unicellular freshwater green alga, against the rotifer Brachionus calyciflorus. Rotifers grown with M. globulifera strains from the two Swedish lakes Älgarydssjön and Lillesjön had an almost two to three times higher mortality than when grown with edible algae. The rotifer mortality with M. globulifera from Lillesjön was similar to starvation. Further experiments looking at potential toxicity of M. globulifera and the feeding of the... (More)
- Algae exhibit different strategies to avoid predation by zooplankton. In green algae, which are generally not known for being toxic, colony formation or a protective mucilage cover can be such defence mechanisms. This study investigates the predation defence of Microglena globulifera (Chlamydomonadales), a unicellular freshwater green alga, against the rotifer Brachionus calyciflorus. Rotifers grown with M. globulifera strains from the two Swedish lakes Älgarydssjön and Lillesjön had an almost two to three times higher mortality than when grown with edible algae. The rotifer mortality with M. globulifera from Lillesjön was similar to starvation. Further experiments looking at potential toxicity of M. globulifera and the feeding of the rotifers, showed that B. calyciflorus does not feed on M. globulifera or other algae in the presence of M. globulifera and that rotifer mortality due to M. globulifera temporarily exceeded starvation. This leads to the conclusion that M. globulifera has a predation defence against its grazers differs in intensity depending on the origin of the algae. The defence prohibits the rotifers from feeding and still has a stronger negative effect on their survival than just starvation. This is more in line with toxic defences than mechanical avoidance of ingestion and digestion like colony formation and mucilage. No allelopathy of M. globulifera on other algae could be detected. (Less)
- Popular Abstract
- Nina Ariane Ahlers
A toxic green alga? – Grazer defence in Microglena globulifera
In aquatic ecosystems most of the primary production (photosynthesis) is done by phytoplankton. Therefore, phytoplankton is often referred to as the base of the aquatic food web and one could argue that it is the fate of phytoplankton to be eaten by zooplankton which keeps the aquatic ecosystem running. However, if you have a closer look, things turn out to be much more complex. Phytoplankton has a variety of defence strategies against their zooplankton grazers (or predators, depending on the definition). Phytoplankton can change size via spines or colony formation to get out of the size range the zooplankton can eat. Among diatoms, dinoflagellates or... (More) - Nina Ariane Ahlers
A toxic green alga? – Grazer defence in Microglena globulifera
In aquatic ecosystems most of the primary production (photosynthesis) is done by phytoplankton. Therefore, phytoplankton is often referred to as the base of the aquatic food web and one could argue that it is the fate of phytoplankton to be eaten by zooplankton which keeps the aquatic ecosystem running. However, if you have a closer look, things turn out to be much more complex. Phytoplankton has a variety of defence strategies against their zooplankton grazers (or predators, depending on the definition). Phytoplankton can change size via spines or colony formation to get out of the size range the zooplankton can eat. Among diatoms, dinoflagellates or cyanobacteria are phytoplankton species that can produce toxins to harm or kill their grazers. Green algae (Chlorophyta) are not known to be toxic and typical defences mechanisms are avoiding being ingested by increasing the size, e.g., colony formation, or avoiding being digested by a mucilage cover protecting the cells.
In this study, the grazer defence of the green alga Microglena globulifera was investigated. This unicellular alga does not form colonies nor does it seem to have protective mucilage covers. Still, grazing rotifers (Brachionus calyciflorus) died if they had to feed on M. globulifera. Different M. globulifera strains, meaning clones of different genetic individuals, were compared regarding their negative effect on the rotifers. This was done by microscopic observations to assess the rotifers’ mortality under various conditions and a feeding experiment where the difference in algal cell concentrations was used to calculate the ingestion rate of the rotifers.
The mortality of the rotifers was increased if their only food source was M. globulifera. The extent of this higher mortality depended on the origin of the M. globulifera strains and the mortalities could be similar to starvation of the rotifers. Furthermore, the rotifers died earlier if grown with M. globulifera than when grown without any food at all. Investigations on the origin of the harmful effects revealed that grazers were only negatively affected if intact cells of M. globulifera were present. Experiments investigating the feeding behaviour of the rotifers showed that the rotifer B. calyciflorus did not feed on M. globulifera although it has a similar shape as, for example, the edible green alga Chlamydomonas reinhardtii. Besides, rotifers seemed to stop feeding completely even on edible algae in presence of M. globulifera. These observations cannot be explained by rotifers not ingesting or not digesting M. globulifera cells and is more similar to responses of predators subjected to toxin producing algae. A negative effect of M. globulifera harming other algae, so called allelopathy, could not be observed. In fact, the exposed alga Rhodomonas lacustris did better with M. globulifera. In this case, M. globulifera would not only protect itself from grazers, but also other algae.
What exactly lies behind the harmful effect of M. globulifera remains unclear, but it certainly prevents the grazers from feeding, leads to a higher mortality in the grazer population, and only has an effect when live M. globulifera cells are present.
Master’s Degree Project in Aquatic Ecology, 45 credits, 2022, Department of Biology, Lunds University
Advisors: Maria Svensson Coelho, Evolutionary Ecology, and Hannah Blossom, Aquatic Ecology, Lunds University (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9113462
- author
- Ahlers, Nina Ariane
- supervisor
- organization
- course
- BION02 20221
- year
- 2022
- type
- H2 - Master's Degree (Two Years)
- subject
- language
- English
- id
- 9113462
- date added to LUP
- 2023-04-14 11:24:03
- date last changed
- 2023-04-14 11:24:03
@misc{9113462,
abstract = {{Algae exhibit different strategies to avoid predation by zooplankton. In green algae, which are generally not known for being toxic, colony formation or a protective mucilage cover can be such defence mechanisms. This study investigates the predation defence of Microglena globulifera (Chlamydomonadales), a unicellular freshwater green alga, against the rotifer Brachionus calyciflorus. Rotifers grown with M. globulifera strains from the two Swedish lakes Älgarydssjön and Lillesjön had an almost two to three times higher mortality than when grown with edible algae. The rotifer mortality with M. globulifera from Lillesjön was similar to starvation. Further experiments looking at potential toxicity of M. globulifera and the feeding of the rotifers, showed that B. calyciflorus does not feed on M. globulifera or other algae in the presence of M. globulifera and that rotifer mortality due to M. globulifera temporarily exceeded starvation. This leads to the conclusion that M. globulifera has a predation defence against its grazers differs in intensity depending on the origin of the algae. The defence prohibits the rotifers from feeding and still has a stronger negative effect on their survival than just starvation. This is more in line with toxic defences than mechanical avoidance of ingestion and digestion like colony formation and mucilage. No allelopathy of M. globulifera on other algae could be detected.}},
author = {{Ahlers, Nina Ariane}},
language = {{eng}},
note = {{Student Paper}},
title = {{Investigation of defence mechanisms against grazing in the green alga Microglena globulifera}},
year = {{2022}},
}