trade-off egg size vs. number in nematodes

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

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

But often not observed!

1. Trade-off masked by other variables

2. No trade-offEgg number

Egg

siz

e

r ≥ 0 ! Two explanations

Egg number

Egg

siz

e

r ≥ 0 !Female size

The role of female quality (size)

r < 0

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)

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

Our objectives

• Study the egg size vs. egg # relationship in 3 populations of anisakid nematodes

• Identify factors determining the nature of this relationship

Source of specimens

• Anisakis simplex

• Pseudoterranova decipiens

• Contracaecum osculatum

9 harbour porpoises,

22 grey seals, Gulf of St. Lawrence

Hej!

Bonjour!

Overview of data analysis

jth species: 50 females

Egg numbe

r

Egg volume

Proxy of

female size

• Partial correlations(classical approach)

• Body volume

• Uterine volume

Our proxies of female size

→ female investment in growth

→ physical space for the clutch

Highly correlated but...

Size estimated from digitized outlines

Body volume

jth speciesith female

Imag

e an

alys

is p

rogr

amUterine volume

Egg parameters

Egg numbe

r

Egg volume

Uterus dissected

Coulter

10× egg diam. Average of volumes

jth speciesith female

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

> >

>>

<

>>

=

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

> >

>>

<

>>

=

Trade-off in A. simplex only

Egg number

Egg volume

-0.32 **

-0.24 *Body

volume

Uterine volume

Trade-off in A. simplex only

Egg number

Egg volume

-0.32 **

-0.24 *Body

volume

Uterine volumeFirst time detected in a

parasite population!

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

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

No trade-off observed in the other 2 species

No trade-off observed in the other 2 species

In C. osculatum and P. decipiens…

Variation in egg volume is small:

C. osculatumP. decipiensA. simplex

11.712.019.3Coef. Variation (%) > =

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?

Time to summarize

“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!

Need + Info?• Ask me now

• [email protected]

• Herreras et al. Oikos (in press)

Thank you very much!¡Muchas Gracias!