Drivers of population-level effects of parasite virulence

1. Drivers of population-level effects of parasite virulence Life-history meets meta-analysis Maggie J. Watson Charles Sturt University, Australia

2. A central goal of population ecology is to identify factors controlling population dynamics.

3. Parasites—the focus of MANY experimental studies Do parasites affect individuals?

4. Parasites—the focus of MANY experimental studies Do parasites regulate populations?

5. Population regulation by parasites has been identified in Red Grouse Lagopuslagopusscoticus Hudson et al. 1998

6. Svalbard Reindeer Rangifertarandusplatyrhnchus Albon et al. 2002

7. and Soay Sheep Ovisaries Gulland 1992

9. ...but, they are all managed populations

13. Thus, the question still remains—are parasites significant drivers of population-level effects and what host life-history traits drive observed parasite virulence?

14. Identify a common measure of EFFECT SIZE resulting in a weighted average • Estimate, with great power, the TRUE EFFECT SIZE What is a meta-analysis?

15. A meta-analysis of 38 experimental studies (31 avian, 6 mammalian, 1 fish) of the costs of parasites to population-level measures of natural, free-ranging hosts revealed an overall effect size,d =0.49 % breeding succ., # young produced, survival, clutch size, hatching succ.

16. d =0.49 This is HUGE!

17. But, a very small pool… • 1 Perciformes • 2 Galliformes • 1 Columbiformes • 1 Ciconiiformes • 1 Pelicaniformes • 2 Charadriiformes • 1 Apodiformes • 23 Passeriformes • 2Lagomorpha • 3 Rodentia • 1 Artiodactyla

18. But, a very small pool… • 1 Perciformes • 2 Galliformes • 1 Columbiformes • 1 Ciconiiformes • 1 Pelicaniformes • 2 Charadriiformes • 1 Apodiformes • 23 Passeriformes • 2Lagomorpha • 3 Rodentia • 1 Artiodactyla

19. Not everything is a passerine…

20. So where to now? What host traits influence parasite virulence?

21. Some predictions… Expect greater effects in: • Cavity nesters • Colonial species • Tropical species • Species with high mortality rates Møller et al. 2009 A meta-analysis of parasite virulence in nestling birds. Biol. Rev. 84: 567-588 Nidelet et al. 2009. Effects of shortened host life span on the evolution of parasite life history and virulence in a microbial host-parasite system. BMC Evolutionary Biology 9:65.

22. …cavity nesters? Z*=-0.34 p-value=0.97 Open Nest Cavity Nest

23. …coloniality? Z*=0.36 p-value=0.72 Not Colonial Highly Colonial

24. …latitude? Z*=-1.30 p-value=0.19

25. …host lifespan (maximum)? Z*=-1.44 p-value=0.15

26. …host lifespan (average)? Z*=-1.93 p-value=0.05

27. …which species?

28. Some results… Found greater effects in: • Cavity nesters  • Colonial species • Tropical species • Species with lower average lifespans

29. Conclusions • Yes, parasites do have population level effects, but are they biologically relevant to all species? • What life-history attributes determine virulence? • Future areas of inquiry—lifespan of host organism, ideally study (truly) long-lived organisms and species other than tits and swallows and martins!

30. An aside about data reporting… • Means • SD or SE • Sample sizes • …and make sure there are comparable categories to other studies

31. Now for a parasite removal experiment! …and lots of pretty pictures!

32. Host species • Crested Tern (Thalasseusbergiicristata , Stephens 1826) • Colonial • Abundant (IUCN Least Concern) • Ubiquitous (Africa to Australia) • Naturally heavily parasitised • And VERY long lived…

33. Parasite Species • Lice • Austromenoponatrofulvum • Quadracepssellatus • Saemundssonialaticaudata • …and maybe more! • Ticks • Ornithodoroscapensis • Ixodes kohlsi

34. Methods • Morphometric changes • Bill + Head • Mass • Sex specific growth • Haematological changes • Haematocrit • Immunological changes • Total WBC counts • Heterophil/Eosinophil Ratio • Survival • Metabolic (?) changes • Ptilochronology • Fluctuating Asymmetry Medication experiment: Sample size: 388; 178 recaptured Ivomec vs. Control

35. Pthilochronology: growth bars 1 2 3

36. Results • Medication reduced parasite numbers (p=0.00051) • High vs. Low Parasites • Weight gain p=0.23 • Bill + Head p=0.51 • Males vs. Females • Weight gain p=0.35 • Bill + Head p=0.39 • Haematocrit • NS

37. Results: Immunological (Total WBC Counts)

38. Results: Immunological (H/E Ratio)

39. 2009-10 good food supplies Results: Ptilochronology 2008-9 poor food supplies Growth bars (mm) Number of Parasites (Rank Order)

40. Results: Fluctuating Asymmetry N=26

41. What do the non-significant results mean? • Morphometric changes obfuscated by food supply • Haematocrit and age • Ptilochronology and food supply • Ptilochronology and “quality” • Long-lived species and survival

42. What do the significant results mean? • The benefits of parasites • Immunological “costs” • Metabolic “costs” and effects on long-term “quality

43. Conclusions In highly evolved natural systems, parasites may not affect hosts except during extreme stochastic events. Long-lived species are not as affected by their parasites as short-lived species.

44. Acknowledgements Trusty fieldworkers: Dave, Douglas, Jack and Charlie Watson, Andrew, and the other Maggie The notoriously unphotographable advisor: Shane Raidal Funded by ILWS CSU Scholarship and Holsworth Foundation Grants