Host-parasite system
Cane toads were introduced to Australia in 1935, and carried with them the lung nematode Rhabdias pseudosphaerocephala that now occurs throughout most of the toad’s Australian range (Barton 1998; Phillipset al. 2010). Hermaphroditic adult nematodes live inside the toad’s lungs, where they release eggs that hatch into first-stage male and female free-living forms within the host’s alimentary tract and are defecated. These larvae mate to produce infective third-stage larvae (L3), which develop for 4-10 days (L2 stage) before breaking out of their mother’s body and entering the soil (Baker 1979). When an L3 locates a host, it pierces the epidermis and migrates through tissue to reach the lungs of the toad where it matures and feeds on blood from capillary beds (Kelehear et al. 2012). The entire life cycle takes 5-36 days (Kelehear et al. 2012). Infection prevalence of lungworms varies seasonally and climatically within Australian cane toads (Barton 1998; Pizzatto et al. 2013), but low host densities mean that the parasites do not occur at the forefront of the toad invasion (Phillips et al. 2010).