The effects of temperature on Corophium volutator and its flatworm

The effects of temperature on Corophium volutator
and its flatworm parasite: experimental studies
Will Shim
Department of Biology
Carleton University
Gynaecotyla adunca and Corophium volutator:
• Life cycle of G. adunca:
Shorebird (flatworm
matures)
C. volutator (digenean
encysts to become
metacercaria)
cercaria
Ilyanassa obsoleta
Past works:
Meißner and Bick, 1999
Mouritsen and Jensen, 1997
Higher number of Parasites = Corophium die faster!
• According to models for the Baltic Sea region:
3.8oC increase = C. volutator population crash due to increase
digenean parasitism.
Maximum levels of infection intensity
Mouritsen et al., 2005.
Minimum population sizes
In the Bay of Fundy, G. adunca can:
• Affect the reproductive synchrony and output of C. volutator
and
• Increases the crustacean’s probability of being predated by
shorebirds
(McCurdy et al., 1999)
In the Bay of Fundy, G. adunca can:
• Affect the reproductive synchrony and output of C. volutator
and
• Increases the crustacean’s probability of being predated by
shorebirds
(McCurdy et al., 1999)
However, little was known about the role of
temperature on the exit patterns of G. adunca
larvae from I. obsoleta snails and the effects of the
parasite in the amphipod in warmer conditions.
Experimental Questions:
Temperature
?
EXIT
First host
SURVIVORSHIP
?
?
SWIMMING
Free-living parasite
?
?
INFECTION
MORTALITY
Second host
A note on experimental parameters:
Three temperatures was chosen for the experiments:
~12oC is the average water temperatures in the summer months (July &
August) in the Upper Bay of Fundy according to Fisheries and Oceans
Canada
~17oC is the average maximum water temperatures in the summer
months in the Upper Bay of Fundy according to Oceans and Fisheries
Canada
22oC is 5oC above 17oC
Summer months’ temperatures were chosen because this is the time when
mud snail presence is highest in the intertidal zone
Most experimental specimens collected from Peck’s Cove
Experimental
Results
1) Exit of Parasites from snail hosts:
paired t-tests on ln (datum+1)-transformed data
Replicate one:
Replicate two:
17oC vs. 12oC: t= 3.18, df= 19, P= 0.005, N=20,
significantly different;
17oC vs. 12oC: t= -3.37, df= 6, P= 0.015, N= 7,
significantly different;
17oC vs. 22oC: t= -5.79, df= 16, P <0.001,
N=17, significantly different.
17oC vs. 22oC: t= -3.095, df= 6, P= 0.021, N=7,
significantly different.
Significantly more parasites exit from snails at higher temperatures
2) Parasite survivorship:
Replicate 1
Log Rank test: X2= 70.39, df=1, P<0.001
significantly different
Replicate 2
Log Rank test: X2= 57.4, df=1, P<0.001
significantly different
Parasites at lower temperature survived significantly longer
2) Parasite survivorship:
3) Parasite swimming: Seems more parasites remain swimming at lower temperatures
4) Infections (number of parasites inside Corophium)
Replicate 1
Replicate 2
Mann-Whitney U test: Z= 0.078;
P= 0.938
Mann-Whitney U test: Z=-0.291;
P= 0.771
Not Significant
Not Significant
There was no significant difference in infections at both temperatures
5) Mortality of infected second hosts:
P value = 0.017,
significant!
P value = 0.269
P value = 0.233
Yes
Note: Logistic regression was used =
Infected Corophium mortality
was only significantly different
from non-infected controls at
12oC
Infected
No
Days alive
Experimental Questions:
Temperature
?
EXIT
First host
SURVIVORSHIP
?
?
SWIMMING
Free-living parasite
?
?
INFECTION
MORTALITY
Second host
Experimental Questions:
Temperature
EXIT
SURVIVORSHIP
T >> t
T << t
First host
SWIMMING
T<t
Free-living parasite
INFECTION
MORTALITY
T=t
Affected
only at low
Temp.
Second host
Note: “T” = higher temperature; “t” = lower temperature; “>>” “<<“ = significantly less and more
Experimental Questions:
Temperature
Past works have shown high mortality of hosts due to
higher number of parasites penetrating host
EXIT
SURVIVORSHIP
T >> t
T << t
First host
SWIMMING
T<t
Free-living parasite
INFECTION
MORTALITY
T=t
Affected
only at low
Temp.
Second host
Note: “T” = higher temperature; “t” = lower temperature; “>>” “<<“ = significantly less and more
Experimental Questions:
Temperature
Past works have shown high mortality of hosts due to
higher number of parasites penetrating host
Thus, mortality of Corophium in global warming scenarios might be
due only to increased presence of parasites trying to infect it
EXIT
SURVIVORSHIP
T >> t
T << t
First host
SWIMMING
T<t
Free-living parasite
INFECTION
MORTALITY
T=t
Affected
only at low
Temp.
Second host
Note: “T” = higher temperature; “t” = lower temperature; “>>” “<<“ = significantly less and more
Thank You!
From here on are graphs of other results
in case questions about them come up
Field Results
4 sites sampled in May and July
Grande Anse
(NB)
Peck’s Cove
(NB)
Starr’s Point
(NS)
Moose Cove
(NS)
Prevalence of infected snails varies with months and sites:
Prevalence of infected snails varies with months and sites:
Number of infected Corophium higher in July:
Data for Peck’s Cove, NB
However, few has looked at the effects of
higher temperatures on the “parasite
factories” (i.e. snail first hosts)
Will they be around when temperature is high?
Next set of experiments:
1. Long term shedding pattern of parasites from snails
2. “Health” of snails after long exposure to above average
temperatures:
For “health”, I measured the time the snails took to flip
over from upside down position.
=> Quicker = more active = healthier
17oC vs. 22oC and infected vs. uninfected (control)
Long term shedding patterns of parasites from snail:
After the first days, number of parasites from snails remains low (lower at
22oC)
Time for snails to flip after exposure to different temperatures:
Time to flip (min.) full factorial
analysis:
Temperature (17oC vs. 22oC): F1,3=25.2,
P<0.001, significant difference
Snail state (infected vs. uninfected):
F1,3=4.54, P=0.035, significant difference
Temperature*Snail state :
F1,3=0.025, P=0.875, not significant
difference
The snails at 22oC were quicker/more active (therefore healthier) than
those at 17oC
Conclusion: at 22oC, the snails will be happier than ever!
Summary:
1. Parasites do not exit in high numbers once the snails
are used to be living at 22oC
2. Even the infected snails won’t have problems living at 22oC
Data from all my experiments indicate that the
trematode G. adunca will likely not have an impact
on the populations of Corophium in a warmer future