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Cost of Resistance: tradeoff between increased resistance and reduced fertility

Cost of Resistance: tradeoff between increased resistance and reduced fertility. Snail-Schistosome host-parasite system. Eric Stock Bio. 4800. Outline. Review Purpose Methods Experiments 1 & 2 Results Experiments 1 & 2 Conclusion. Snail- Schistosome. Snail ( Biomphalaria glabrata)

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Cost of Resistance: tradeoff between increased resistance and reduced fertility

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  1. Cost of Resistance: tradeoff between increased resistance and reduced fertility Snail-Schistosome host-parasite system Eric Stock Bio. 4800

  2. Outline • Review • Purpose • Methods • Experiments 1 & 2 • Results • Experiments 1 & 2 • Conclusion

  3. Snail-Schistosome • Snail (Biomphalaria glabrata) • Schistosome (Schistosoma mansoni) • Remember: • Miracidia infect mollusc – snail • Cercariae infects mammal - human

  4. AIM? • Investigate cost of resistance to snail • Artificially breed snails • Resistance (R) and Susceptible (S) to schisto. • Snail fertility (reproductive performance) • # offspring produced • Snail fecundity (potential reproductive capacity) • # of eggs and embryos formed

  5. Methods – Experiment #1 • Snails housed in tanks with Styrofoam sheets to lay eggs on • 6 tanks – 60 sexually mature snails • 4 tanks – exposed each snail to 5 miracidia • 5 miracidia = infection rate of 50% snail population • 2 tanks – controls – no parasites

  6. Methods • After 4-7 weeks screened for cercariae • Screening: Post 48hr dark period – placed in light for 2hr – looked for shedding of cercariae • Week 7: divided tanks • separated resistant (R) from susceptible (S) & control (C) • 10 tanks: 4 R, 4 S, 2 C • Bred for 15 weeks

  7. Experiment #1 Parameters • 1) # breeding adults remaining (mortality) • 2) Total # of egg masses in tank • 3) Mean # of eggs/egg mass • embryo within egg visible • 4) # malformed egg masses • 5) # offspring/tank

  8. Experiment #2 • F6 exposed to 5 miracidia & screened • To determine if reproductive success was demonstrated in absence of parasite • Differences are due to genotype (R & S) not phenotype (Individual) • If Phenotypic response: • Parasitized snail offspring more susceptible • Unparasitized offspring more resistant • If Genotypic response: • F6 snails identical between groupings

  9. Experiment 1

  10. Experiment 2

  11. Results • Resistance and susceptibility to schistosome infection was heritable • Significant difference between S & R & C fertility • F1 and all subsequent generations • No R snail shed after 7 weeks = Resistant • F6 – no significant difference between R & S • Therefore genotype not phenotype

  12. Experiment #1 • Significant difference in fertility & mortality • S higher offspring than C and R (lowest) • S higher mortality than C and R (lowest) Experiment #2 • Significant difference in fertility • S higher offspring than C and R (lowest)

  13. Week + (exposed-infected) - (unexposed-uninfected)

  14. Conclusion • Resistant snails produced fewer offspring • = lower fertility • Wasn’t due to phenotype of snail – genotype • Suggest cost of resistance in absence of parasite

  15. References • Webster, J.P., Woolhouse, M.E.J. (1999) Cost of resistance : relationship between reduced fertility and increased resistance in a snail-dchidtosome host-parasite system. The Royal Society. 266: 391-39.6

  16. Questions?

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