EFFECT OF LIGHT REGIME ON THE SEASONAL CYCLE OF … · Carapax length Thorax ! Gender and sexual...
Transcript of EFFECT OF LIGHT REGIME ON THE SEASONAL CYCLE OF … · Carapax length Thorax ! Gender and sexual...
EFFECT OF LIGHT REGIME ON THE SEASONAL CYCLE
OF ANTARCTIC KRILL Flavia Höring Mathias Teschke, Fabio Piccolin, Lavinia Suberg, Felix Müller, So Kawaguchi, Bettina Meyer
3rd International Symposium on Krill, St. Andrews, Scotland Ecosystems: why are krill so successful? 14 June 2017
Why are krill so successful?
The Southern Ocean – a strongly seasonal habitat
Sea ice extent Primary production Photoperiod
Meyer 2012 Meyer et al. 2010 NASA Earth Observatory maps by Joshua Stevens, using AMSR2 data supplied by GCOM-W1/JAXA.
Spring Summer Seasonal and interannual variability
Autumn 2004 Autumn 2005 Autumn 2006
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Seasonal rhythms in E. superba
Lipid dynamics
Maturation cycle
Respiration Meyer 2012
Meyer 2012
Latitudinal differences: Ø Lower lipid stores and
higher feeding activities observed at lower latitudes in winter
Kawaguchi et al. 2006
How are these rhythms modulated?
3
r
al
n
m
XII
VI
IIIIX
Biological timing in E. superba
What do we know? • Photoperiod has an impact on: > Maturity
> Body composition > Respiration rate > Gene expression
• Clock genes and an endogenous timing system in Antarctic krill
INPUT OUTPUT
Light
Food
Rhythms
The concept of biological clocks
Internal Oscillator
Short-term studies only
4
Aim of the study
Research objectives:
Ø Investigation of the effect of different latitudinal light regimes on the phenology of E. superba
1) Growth 2) Maturity 3) Lipid metabolism 4) Gene expression
Ø Long-term lab experiments over 2 years with constant food supply
Hypotheses: I. Light regime triggers seasonal
rhythms in Antarctic krill.
II. Seasonal rhythms are maintained by an endogenous timing system.
5
0 2 4 6 8 10 12
05
1015
20
Simulated light regimes
Month
Hou
rs o
f lig
ht
52°S
62°S
66°S
DD
Long-term lab experiments
Light regime 52°S
Light regime 62°S
Light regime 66°S
Constant darkness
(DD)
Australian Antarctic Division, Kingston, Tasmania
Experimental set-up Recorded data
Ø Carapax length Ø Gender and sexual maturity
stage
Thorax
Thelycum (female)
Petasma (male)
Photos: Fabio Piccolin
Hypothesis I: Light regime triggers seasonal rhythms in Antarctic krill.
Hypothesis II: Seasonal rhythms are maintained by an endogenous timing system.
6
Growth Generalized additive mixed model (GAMM):
Carapax length ~ General trend + Seasonal trend
General trend
5 10 15 20
−11
3
Treatment 52°S
Experimental duration[months]
5 10 15 20
−11
3
Treatment 62°S
Experimental duration[months]
5 10 15 20−1
13
Treatment 66°S
Experimental duration[months]
5 10 15 20
−11
3
Treatment DD
Experimental duration[months]
Car
apax
leng
th *** p<0.001 *** p<0.001 *** p<0.001 *** p<0.001
Similar trend in all treatments:
Ø Shrinkage in beginning of experiment – related to experimental conditions
0 2 4 6 8 10 12
05
1015
20
Simulated light regimes
Month
Hou
rs o
f lig
ht
52°S
62°S
66°S
DD
7
Seasonal trend
2 4 6 8 10 12
−11
3
Treatment 52°S
Month
Car
apax
leng
th
2 4 6 8 10 12
−11
3
Treatment 62°S
Month
2 4 6 8 10 12−1
13
Treatment 66°S
Month
2 4 6 8 10 12
−11
3
Treatment DD
Month
0 2 4 6 8 10 12
05
1015
20
Simulated light regimes
Month
Hou
rs o
f lig
ht
52°S
62°S
66°S
DD
Growth
*** p<0.001 *** p<0.001 *** p<0.001 p=0.0533
Generalized additive mixed model (GAMM):
Carapax length ~ General trend + Seasonal trend
Similar trend in all treatments:
Ø Seasonal trend observed in all treatments – influenced by light regime
Ø Rhythmic pattern under constant darkness – Indication for an endogenous seasonal timing system
summer autumn winter spring summer autumn winter spring summer autumn winter spring summer autumn winter spring
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Maturity analysis
5 10 15 20
Males
Hours of light
Mat
urity
sco
re
23
45
5 10 15 20
Females
Hours of light
Mat
urity
sco
re
23
45
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Relationship between maturity and photoperiod:
Ø Different pattern in females and males
Ø Further maturity analysis carried out with females only
Differences between females and males
2 4 6 8 10 12
−0.2
0.0
0.2
Treatment 52°S
Month
Mat
uri
ty s
core
2 4 6 8 10 12
−0.2
0.0
0.2
Treatment 62°S
Month
2 4 6 8 10 12−0
.20.
00.
2
Treatment 66°S
Month
2 4 6 8 10 12
−0.2
0.0
0.2
Treatment DD
Month
Generalized additive model (GAM):
Maturity score ~ Seasonal trend
Maturity analysis
** p<0.01 *** p<0.001 ns p=0.085 ns
10
Seasonal trend 0 2 4 6 8 10 12
05
1015
20
Simulated light regimes
Month
Hou
rs o
f lig
ht
52°S
62°S
66°S
DD
summer autumn winter spring summer autumn winter spring summer autumn winter spring summer autumn winter spring
Ø Seasonal pattern observed under light regimes 52°S, 62°S and 66°S
Ø No seasonality under constant darkness
Maturity analysis
Maturity under constant darkness
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Ø Sexual regression in beginning of experiment
Ø Indication for an endogenous timing system
5 10 15 20
3.0
3.5
4.0
4.5
5.0
Treatment DDM
atur
ity s
core
Experimental duration [months]
*
0 2 4 6 8 10 12
05
1015
20
Simulated light regimes
Month
Hou
rs o
f lig
ht
52°S
62°S
66°S
Maturity analysis
12
Binomial model:
Probability of maturity score 5 ~ Hours of light
Probability to be sexually mature
Data
Maturity score 5?
yes
no
0 5 10 15 20
0.0
0.2
0.4
0.6
0.8
1.0
Binomial model
Hours of light
Prob
abilit
y of
mat
urity
sco
re 5
52°S62°S66°S
Ø Probability of sexual
maturity higher with
longer photoperiod
Are the critical photoperiods different between treatments?
Critical photoperiod (CPP):
= Photoperiod for 50% sexual maturity
Maturity analysis
13
0 5 10 15 20
0.0
0.2
0.4
0.6
0.8
1.0
Binomial model
Hours of light
Prob
abilit
y of
mat
urity
sco
re 5
52°S66°S
Ø Critical photoperiods (CPPs) are different
between treatment 52°S and 66°S
Ø CPP is longer in higher latitude light regime
CPP 52°S: 12.56±0.68 CPP 66°S: 14.80±1.48
Analysis of critical photoperiods
Binomial model:
Probability of maturity score 5 ~ Hours of light
0 2 4 6 8 10 12
05
1015
20
Simulated light regimes
MonthH
ours
of l
ight
52°S
62°S
66°S
CPP 52°S CPP 66°S
What is the advantage of different critical photoperiods?
Ø Longer CPPs − an adaptation to the light
regime at higher latitudes
Ø Krill is able to start sexual regression and
maturation at the right time
Conclusions 1) Growth
• Seasonal growth patterns are influenced by light regime • Growth patterns are modulated by an endogenous timing system
2) Maturity
• The maturity cycle is light-dependent • The observation of sexual regression under constant darkness
suggests an endogenous timing system in krill • Krill under the high latitude light regime have a longer critical
photoperiod (an adaptation to more extreme light conditions)
Take-home message
Seasonal cycles of growth and maturity in E. superba are triggered by different latitudinal light regimes and governed by an
endogenous timing system.
INPUT OUTPUT
Rhythms Internal Oscillator
Growth & Maturity E. superba Light regime
Acknowledgments
Literature • Brown, M., Kawaguchi, S., King, R., Virtue, P., Nicol, S. (2011). Flexible adaptation of the seasonal krill
maturity cycle in the laboratory. J. Plankton Res. 33, 821–826. • Brown, M., Kawaguchi, S., Candy, S., Yoshida, T., Virtue, P., and Nicol, S. (2013). Long-Term Effect of
Photoperiod, Temperature and Feeding Regimes on the Respiration Rates of Antarctic Krill (Euphausia superba). Open J. Mar. Sci. 03, 40–51.
• Mazzotta, G.M., De Pittà, C., Benna, C., Tosatto, S.C.E., Lanfranchi, G., Bertolucci, C., and Costa, R. (2010). A cry from the krill. Chronobiol. Int. 27, 425–445.
• Kawaguchi, S., Yoshida, T., Finley, L., Cramp, P., and Nicol,S. (2006). The krill maturity cycle: a conceptural model of the seasonal cycle in Antarctic krill. Polar Biol. 30, 689-698.
• Meyer, B. (2012). The overwintering of Antarctic krill, Euphausia superba, from an ecophysiological perspective. Polar Biol. 35, 15–37.
• Meyer, B., Auerswald, L., Siegel, V., Spahić, S., Pape, C., Fach, B.A., Teschke, M., Lopata, A., and Fuentes, V. (2010). Seasonal variation in body composition, metabolic activity, feeding, and growth of adult krill Euphausia superba in the Lazarev Sea. Mar. Ecol. Prog. Ser. 398, 1–18.
• Schmidt, K., Atkinson, A., Pond, D.W., and Ireland, L.C. (2014). Feeding and overwintering of Antarctic krill across its major habitats: The role of sea ice cover, water depth, and phytoplankton abundance. Limnol. Oceanogr. 59, 17–36.
• Seear, P., Tarling, G.A., Teschke, M., Meyer, B., Thorne, M.A., Clark, M.S., Gaten, E., and Rosato, E. (2009). Effects of simulated light regimes on gene expression in Antarctic krill (< i> Euphausia superba</i> Dana). J. Exp. Mar. Biol. Ecol. 381, 57–64.
• Teschke, M., Kawaguchi, S., and Meyer, B. (2007). Simulated light regimes affect feeding and metabolism of Antarctic krill, Euphausia superba. Limnol. Oceanogr. 52, 1046–1054.
• Teschke, M., Kawaguchi, S., and Meyer, B. (2008). Effects of simulated light regimes on maturity and body composition of Antarctic krill, Euphausia superba. Mar. Biol. 154, 315–324.
• Teschke, M., Wendt, S., Kawaguchi, S., Kramer, A., and Meyer, B. (2011). A Circadian Clock in Antarctic Krill: An Endogenous Timing System Governs Metabolic Output Rhythms in the Euphausid Species Euphausia superba. PLoS ONE 6, e26090–e26090.