The impact of nematode parasites on the behaviour of an Australian lizard, the gidgee skink Egernia stokesii

Abstract The Australian scincid lizard Egernia stokesii lives in social groups and is infected with two nematode species: Pharyngodon tiliquae and Thelandros trachysauri . This study asked whether those nematodes affected levels of lizard activity in field populations. In a laboratory colony, application of a combination of ivermectin and fenbendazole reduced nematode egg count in lizard scats after 12 weeks. In the field, the same doses of those antihelminthic drugs were applied to lizards in six social groups across three populations, and a saline control was given to lizards in six adjacent groups. Observations showed significant changes in behaviour between the two groups developing over 2 months. Drug‐treated lizards spent more time basking and moved about for longer times during observation sessions. The results suggest that nematode infection altered host behaviour and reduced fitness. No influence of social group size was detected on the impact of parasitic nematodes.