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).