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Table 2 Summary of the scenarios tested

From: Adaptation of gastrointestinal nematode parasites to host genotype: single locus simulation models

Scenario

Number of worm generations or yearsa

s h (%)

s p (%)

p 0

x

Model typeb

Mechanism to reduce sheep WECc

Evaluation of the genotype-by-genotype interaction

1

80 gen

20

0

0.001, 0.01,

1.0

reduced

-

0.1, 0.3

2

80 gen

0 to 30

0 to 30

0.3

0.2, 0.5, 0.8

reduced

-

Evaluation of the host-parasite interaction properties

3

1 yr

-

-

0

0

full

-

4

1 yr

25

10

0.5d

0.5

full

E, M, F

Testing hypotheses 1 and 2

5

20 yr

25

10

0.3

0.0 to 1.0

reduced, full

E, M, F

  1. a the reduced model is defined by worm generations and the full model is defined by years of simulation; results show that there are 2.2 worm generations per year of simulation; s h = survival advantage of the B allele in sheep; s p = survival trade-off on pasture for the B allele; p 0 = initial frequency of the B allele in worms; x = frequency of the low WEC A allele in sheep; b see text for details of the full model, which includes complexities of the host-parasite relationship, and the reduced model, which explicitly excludes these factors; c postulated mechanisms to reduce WEC in sheep through the ‘resistance’ A allele: E = reduced worm establishment, M = increased worm mortality, and F = reduced female worm fecundity; d to evaluate the effect of the low WEC allele for each mechanism of the sheep ‘resistance’ A allele, the worm allele frequency was fixed (p = 0.5) during the transition stages of the worm lifecycle.