Do parasites matter? Assessing the fitness consequences of haemogregarine infection in snakes

G. P. Brown, C. M. Shilton, R. Shine*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

45 Citations (Scopus)


Although much research in evolutionary ecology is based upon the premise that high levels of parasitism impair the host's functioning, the assumed link between parasitism and fitness has been assessed for relatively few kinds of animals. At our study site in tropical Australia, keelback snakes (Tropidonophis mairii (Gray, 1841), Colubridae) are heavily infected with haemogregarine blood parasites: 90% of snakes that we tested carried the parasite, with the proportion of erythrocytes containing haemogregarines averaging 15% and ranging up to a remarkable 64%. Prevalence increased with snake body size, but intensity decreased with age. Unlike lizards studied previously, the snakes did not respond to haemogregarine infection by releasing immature erythrocytes into the circulation. In striking contrast to results from a recent study on a sympatric snake species, we did not find any empirical links between parasite numbers and several measures of host fitness (body condition, growth rate, feeding rate, antipredator behaviour, locomotor performance, reproductive status, reproductive output, and recapture rate). The association between this parasite and its host thus appears to be surprisingly benign, suggesting that host-parasite interactions sometimes may have only trivial consequences for host fitness in natural populations. Plausibly, host-parasite coevolution weakens or eliminates fitness costs of parasitism.

Original languageEnglish
Pages (from-to)668-676
Number of pages9
JournalCanadian Journal of Zoology
Issue number5
Publication statusPublished - May 2006
Externally publishedYes


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