The effects of bot fly parasitism on aggressive behavior in Peromyscus leucopus
- 1. The Effects of Bot Fly Parasitism on Aggression in White-footed Mice ( Peromyscus leucopus) Michael J. Cramer and Guy Cameron Department of Biological Sciences University of Cincinnati
- 2. Sexual Selection Selection to maximize number of matings Mechanisms Competition for mates (intrasexual) Mate selection (intersexual) Strength dependent on mating system
- 3. Mating System in Peromyscus Ranges from promiscuity to facultative monogamy Males home ranges that overlap with several females Dominance hierarchy determines number of matings Some evidence of multiply mated females
- 4. Aggression in Peromyscus Aggression limited to breeding season Sex differences in home range and territory Male home range large, territory used mainly for access to females Female home range small, territory used mainly for nesting and rearing young Intrasexual aggression greater for males than females Dominance site-specfic
- 5. Parasitism Potential effect on population ecology of both host and parasite species Has been studied in the context of sexual selection (parasite-mediated sexual selection)
- 6. Peromyscus Bot Fly Life Cycle Females lay eggs in host habitat. Hosts pick up newly hatched larvae . Larvae migrate to inguinal region and develop warble. After 3 rd instar, larvae exit host and burrow underground to pupate. Flies emerge and mate at aggregation sites. 5 days 21 days P. Meyer C. N. Shiffer M. J. Cramer
- 7. Reproductive Cost of Bot Fly Parasitism ? May disrupt pregnancy or lactation No evidence of castration No evidence of disruption of gonad function (sperm and egg development) Gonad weight lower for infected animals May affect reproductively important behaviors Competition for mates Mate choice
- 8. Objective Determine effects of bot fly parasitism on aggressive behavior Test hypothesis that animals infected with bot flies are less aggressive than uninfected animals If infected animals are less aggressive, then they may not mate as often as uninfected animals
- 9. Animal Subjects Trapped on four 6 x 6 grids in beech-maple forest in southwestern Ohio Individuals given unique marks Animals tested during summer Peak density, reproduction and infection
- 10. Intrasexual Aggression Trials Individuals from different grids tested in neutral arena at night in field 10 minute trials (2 minutes acclimation time) videotaped Tapes of each trial viewed in lab Score behaviors Measure locomotion time
- 11. Avoid contact with opponent Avoidance/Retreat Up on hind legs, front paws forward; may hit opponent Defense/Retaliation Turn on side, ears flat, eyes half-closed Submissive Posture Quick move towards opponent Lunge Paws on opponent’s back Climb-on Bites, hits, or kicks opponent Attack Groom opponent on face or back Aggressive Groom Description Behavior
- 12. Climb-on Aggressive Groom Submissive Posture Retaliation
- 13. Statistical Analysis Analyze sexes separately Index of aggression: factor loadings of principal components analysis of behaviors Paired t-test: response of one individual dependent on behavior of the other H o (null): aggression index similar regardless of infection status H A (alternate): infected animal less aggressive relative to uninfected animal
- 14. PCA Loadings: Males Aggressive Submissive
- 15. PCA Loadings: Females Aggressive Submissive
- 16. Test of Aggression for Males Aggression higher for uninfected males. Aggressive Submissive
- 17. Test of Aggression for Females Aggression similar for uninfected and infected females. Aggressive Submissive
- 18. Conclusion Males uninfected more aggressive Females aggression similar Interpretation of index may be compromised by loading of attack behavior on PC1
- 19. Why Sex Differences Differences between sexes may be explained by mating system Male aggression may be subject to stronger sexual selection: competition for matings Female aggression may operate in different context: nest defense Trials were not conducted on females who were pregnant or lactating
- 20. Further Study Increase sample size for males Investigate other mechanism of sexual selection: mate choice Do females avoid mating with infected males?
- 21. Acknowledgements Field Work Diane McCubbin Theresa Pfarr Kelly Roberts Ashley Mattingly Ohio Department of Natural Resources, Division of Wildlife Randy Morgan Todd Haynes Funding: UC Department of Biological Sciences Wieman Summer Research Grant Analysis/Discussion Craig Wilmhoff Andrew Osterberg Matt Hopton J. Andrew Roberts Phil Taylor Jerry Hinn Research Advisory Committee George Uetz Ken Petren Nancy Solomon Michal Polak Tom Kane