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Cyanobacterial lichen symbiosis: the fungal partner as an optimal harvester

Hyvärinen, M; Härdling, Roger LU and Tuomi, J (2002) In Oikos 98(3). p.498-504
Abstract
Lichen symbiosis has been traditionally treated as a model case of mutualism in which both partners, the fungus and the photobiont. gain benefits reciprocally. Some recent evidence, however, supports an alternative view that lichen symbiosis may represent an association largely controlled by the commensal or even parasitic fungal partner. The latter gains photosynthates from the photobiont (algae and/or cyanobacteria) which may not always substantially benefit from the symbiosis. We analyze from this perspective how a lichen fungus may maximize photosynthetic gains in bipartite and tripartite associations. We treat the frequency of nitrogen-fixing cells called heterocysts in cyanobacteria and the relative proportion of green algal cells... (More)
Lichen symbiosis has been traditionally treated as a model case of mutualism in which both partners, the fungus and the photobiont. gain benefits reciprocally. Some recent evidence, however, supports an alternative view that lichen symbiosis may represent an association largely controlled by the commensal or even parasitic fungal partner. The latter gains photosynthates from the photobiont (algae and/or cyanobacteria) which may not always substantially benefit from the symbiosis. We analyze from this perspective how a lichen fungus may maximize photosynthetic gains in bipartite and tripartite associations. We treat the frequency of nitrogen-fixing cells called heterocysts in cyanobacteria and the relative proportion of green algal cells vs. that of cyanobacteria per unit fungus as the variables to be manipulated for maximal carbon gain. The model predicts that even with a negligible cost of cephalodia (compartments containing cyanobacteria) it is in the interest of the tripartite lichen, first, to increase the heterocyst frequency, and second, keep the relative number of cyanobacteria considerably lower than that of green algae. Hence, the lichen fungus achieves higher fitness by making the cyanobacterial partner to specialize on N fixation. The available empirical data support these predictions as the reported heterocyst frequencies in bipartite lichens range from 2 to 8%, and in tripartite lichens between 10 and 55%. It is concluded that interaction asymmetry (i.e. commensalism or parasitism rather than mutualism) provides a sound basis to understand the high phenotypic plasticity expressed by fungi-forming bipartite and tripartite associations with cyanobacteria and green algae. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Oikos
volume
98
issue
3
pages
498 - 504
publisher
Wiley-Blackwell
external identifiers
  • wos:000178440000014
  • scopus:0036745295
ISSN
1600-0706
DOI
10.1034/j.1600-0706.2002.980314.x
language
English
LU publication?
yes
id
1279c382-5f17-487f-b94a-ff4c1b0c5b31 (old id 147627)
date added to LUP
2007-07-03 12:01:11
date last changed
2017-10-22 03:51:10
@article{1279c382-5f17-487f-b94a-ff4c1b0c5b31,
  abstract     = {Lichen symbiosis has been traditionally treated as a model case of mutualism in which both partners, the fungus and the photobiont. gain benefits reciprocally. Some recent evidence, however, supports an alternative view that lichen symbiosis may represent an association largely controlled by the commensal or even parasitic fungal partner. The latter gains photosynthates from the photobiont (algae and/or cyanobacteria) which may not always substantially benefit from the symbiosis. We analyze from this perspective how a lichen fungus may maximize photosynthetic gains in bipartite and tripartite associations. We treat the frequency of nitrogen-fixing cells called heterocysts in cyanobacteria and the relative proportion of green algal cells vs. that of cyanobacteria per unit fungus as the variables to be manipulated for maximal carbon gain. The model predicts that even with a negligible cost of cephalodia (compartments containing cyanobacteria) it is in the interest of the tripartite lichen, first, to increase the heterocyst frequency, and second, keep the relative number of cyanobacteria considerably lower than that of green algae. Hence, the lichen fungus achieves higher fitness by making the cyanobacterial partner to specialize on N fixation. The available empirical data support these predictions as the reported heterocyst frequencies in bipartite lichens range from 2 to 8%, and in tripartite lichens between 10 and 55%. It is concluded that interaction asymmetry (i.e. commensalism or parasitism rather than mutualism) provides a sound basis to understand the high phenotypic plasticity expressed by fungi-forming bipartite and tripartite associations with cyanobacteria and green algae.},
  author       = {Hyvärinen, M and Härdling, Roger and Tuomi, J},
  issn         = {1600-0706},
  language     = {eng},
  number       = {3},
  pages        = {498--504},
  publisher    = {Wiley-Blackwell},
  series       = {Oikos},
  title        = {Cyanobacterial lichen symbiosis: the fungal partner as an optimal harvester},
  url          = {http://dx.doi.org/10.1034/j.1600-0706.2002.980314.x},
  volume       = {98},
  year         = {2002},
}