trade-off egg size vs. number in nematodes
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Phenotypic trade-offs between number and size of eggs: Are parasites different from free-
living organisms?
V. Herreras, F. E. Montero, D. J. Marcogliese, J. A. Raga and J. A. Balbuena
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Limited energy to allocate between egg size & egg
number
Egg number
Egg
siz
e
r < 0
A classical problem in ecology
Phenotypic trade-off expected
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But often not observed!
1. Trade-off masked by other variables
2. No trade-offEgg number
Egg
siz
e
r ≥ 0 ! Two explanations
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Egg number
Egg
siz
e
r ≥ 0 !Female size
The role of female quality (size)
r < 0
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Seldom tested in parasite populations
• Copepod Lernanthropus cynoscicola on Cynoscion guatucupa (Timi et al. 2005)
• Nematode Graphidioides subterraneus in Ctenomys talarum (Rossin et al. 2005)
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r ≥ 0 after female-size correction
A universal rule for parasites?
Egg number
Egg
siz
e
No trade-off? • Host resources are very high
• No conflict in allocation
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Our objectives
• Study the egg size vs. egg # relationship in 3 populations of anisakid nematodes
• Identify factors determining the nature of this relationship
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Source of specimens
• Anisakis simplex
• Pseudoterranova decipiens
• Contracaecum osculatum
9 harbour porpoises,
22 grey seals, Gulf of St. Lawrence
Hej!
Bonjour!
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Overview of data analysis
jth species: 50 females
Egg numbe
r
Egg volume
Proxy of
female size
• Partial correlations(classical approach)
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• Body volume
• Uterine volume
Our proxies of female size
→ female investment in growth
→ physical space for the clutch
Highly correlated but...
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Size estimated from digitized outlines
Body volume
jth speciesith female
Imag
e an
alys
is p
rogr
amUterine volume
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Egg parameters
Egg numbe
r
Egg volume
Uterus dissected
Coulter
10× egg diam. Average of volumes
jth speciesith female
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Results: some metrics first
9 k160 – 34 k
64 k(5 k – 243 k)
402 k(110 k – 1.2 M)
Egg number
226(186 – 301)
41(32 – 55)
42 (27 – 60)
Egg volume (pl)
4(1 –14)
14(1 – 91)
46(10 – 162)
Uterine volume (µl)
40 (26 – 66)
60(46 – 77)
84(51 – 125)
Body length (mm)
C. osculatumP. decipiensA. simplex
> >
>>
<
>>
=
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Results: some metrics first
9 k160 – 34 k
64 k(5 k – 243 k)
402 k(110 k – 1.2 M)
Egg number
226(186 – 301)
41(32 – 55)
42 (27 – 60)
Egg volume (pl)
4(1 –14)
14(1 – 91)
46(10 – 162)
Uterine volume (µl)
40 (26 – 66)
60(46 – 77)
84(51 – 125)
Body length (mm)
C. osculatumP. decipiensA. simplex
> >
>>
<
>>
=
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Trade-off in A. simplex only
Egg number
Egg volume
-0.32 **
-0.24 *Body
volume
Uterine volume
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Trade-off in A. simplex only
Egg number
Egg volume
-0.32 **
-0.24 *Body
volume
Uterine volumeFirst time detected in a
parasite population!
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Only in A. simplex egg volume varied significantly with size
Egg volume
Body volume
Uterine volume
0.42 **
n.s.
0.55 **
0.39 **
Uterine size explains more variation in egg volume than body size
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The trade-off seems structural
• Extreme semelparity in A. simplex:uterine size might be limiting
Even if host resources are plentiful the trade-off can still occur
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No trade-off observed in the other 2 species
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No trade-off observed in the other 2 species
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In C. osculatum and P. decipiens…
Variation in egg volume is small:
C. osculatumP. decipiensA. simplex
11.712.019.3Coef. Variation (%) > =
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In C. osculatum and P. decipiens…
Trade-off absent because one of the 2 life-history traits (egg size) is fixed
Response to optimal allocation rules?
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Time to summarize
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“Before” and “After” scenarios
• Host resources in excess of parasite needs
Before• Structural
trade-offs do occur
• Egg size fixed: optimization
After
Adopt a pluralistic approach!
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Thank you very much!¡Muchas Gracias!