Transcript Document

Influence of temperature on the host-parasite interaction
in the diatom Asterionella formosa and its parasite Zygorhizidium planktonicum
A.Gsell, L. de Senerpont Domis, S. Wiezer, E. Van Donk, B. Ibelings
[email protected]
Aquatic Food Web Studies, Center for Limnology, Netherlands Institute for Ecology, KNAW
Introduction
Experimental set up
The A. formosa population in Lake Maarsseveen (NL)
typically blooms twice a year1, and the spring bloom
often is tracked by a chytrid (Z. planktonicum)
epidemic. The host population shows a surprisingly
high genetic diversity2 considering the lack of gene
flow or documented sexual reproduction.
Parasite mediated, frequency dependent selection
and / or seasonal temperature changes may maintain
this high diversity of genotypes in the lake. To
disentangle differential selection of host genotypes
(GH) by temperature (ET) from parasite genotype(GP)
interactions, we conducted two experiments.
Seven monoclonal A. formosa genotypes isolated
from the same spring bloom in Lake Maarsseveen
were acclimatised for two weeks to their experimental
temperature at 1,6,11,16 or 21°C.
Six replicates per genotype and temperature were set
at 10 000 cells ml-1 and grown for 15 days at saturating
light and nutrient conditions. Growth rates and surface
to volume ratios were analysed for GHxE interactions.
A. formosa colonies showing the
extent of cell size differences
Z. planktonicum asexual life cycle
The same set up was repeated and infected with one
monoclonal parasite strain. Parasite and host growth
rate were analysed for GHxGPxE interactions.
Parasite
(GP)
temperature controlled water baths
Host
(GH)
Environment
(ET)
Conclusions GHxET experiment
Conclusions GHxGPxET experiment
Adaptation to different temperatures comes at differential costs
for the tested host strains, thus changing temperatures can
select for different genotypes and thereby maintain genetic
variability in the host population.
Temperature influences the overall level as well as the
rank order of susceptibility of host strains to fungal infection,
thus it may select for both strength and direction of the
host parasite interaction.
Results GHxET experiment
Preliminary results GHxGPxET experiment
Mean growth rates of all strains across
five temperatures
1) Mean growth rate per day
Growth rate d-1
0.5
0.4
0.3
S24
S26
S37
S38
S43
S49
S53
0.2
Error bars:  standard error
0.1
1
6
11
16
21
Temperature in °C
SA/V of all strains across five
temperatures
1.7
Growth rate d-1
1.5
1.3
1.2
Error bars:  standard error
1
6
11
16
21
p < 0.001 
p < 0.001 
p < 0.001 
2
1
0
S24
S26
S37
S38
S43
S49
S53
-1
-2
-3
1
6
11
16
21
Temperature in °C
4) Rank order changes
per genotype and temperature.
SA/V is a proxy for nutrient uptake
capacity, a low ratio means less
uptake opportunities.
The significant GHxE interaction
suggests that adaptation to different
temperatures is costly and not uniform
for all genotypes.
Two way ANOVA
Genotype (GH )
Temperature (E)
GH x ET
p < 0.001 
p < 0.001 
p = 0.002 
1°C
6°C
11°C
16°C
21°C
1
S24
3
1
1
7
2
2
S26
4
2
3
3
4
3
S37
1
4
6
1
5
4
S38
2
3
5
5
1
5
S43
5
5
7
4
3
6
S49
6
7
2
2
6
7
S53
7
6
4
6
7
Temperature in °C
1
BW Ibelings, A De Bruin, M Kagami, M Rijkeboer, M Brehm & E Van Donk. 2004.
HOST PARASITE INTERACTIONS BETWEEN FRESHWATER PHYTOPLANKTON AND CHYTRID FUNGI (Chytridiomycota)
J. Phycol. 40:3 pp 437–53.
2
of sporangia numbers per ml per host
genotype and temperature.
Fungal growth rates are host strain
dependent and increase with rising
temperature, but drop rapidly at 21°C.
This suggests that temperature can
select for the strength of the host
parasite outcome. Further, the crossing
reaction norms suggest potential for a
GHxGPxET interaction.
2) Surface:volume ratio SA/V
1.4
1.1
Two way ANOVA
Genotype (GH)
Temperature (E)
GH x ET
3
3)Sporangia growth rate
sporangia ml-1: rank order
S24
S26
S37
S38
S43
S49
S53
1.6
per genotype and temperature.
Generally, each genotype expresses
a singular phenotype, and growth
rates
increase
with
rising
temperature.
The significant GHxE interaction is reflected in crossing reaction norm
lines and suggests that both level
and direction of the genotype effect
is dependent on the level of the
temperature.
Growth rate d-1
0.6
growth rate of sporangia ml-1 d-1 on all
host strains across five temperatures
A De Bruin, BW Ibelings, M Rijkeboer, M Brehm & E van Donk. 2004.
GENETIC VARIATION IN ASTERIONELLA FORMOSA (BACILLARIOPHYCEAE): IS IT LINKED TO FREQUENT EPIDEMICS OF HOST-SPECIFIC PARASITIC FUNGI?
J. Phycol. 40:5 pp 823-830.
in sporangia growth rate per host
genotype and temperature.
Rank order for the most infected strain
(1) to the least infected host (7)
changes for each temperature. This
suggests that temperature may also
select for the direction of the host
parasite interaction.