Do skin secretions affect the entry and establishment of parasite
larvae into the host?
On average, 17.4 L3 (± 2.3 SD) entered the toad. Toad SUL, toad origin,
L3 origin, and treatment were uninformative in explaining the number of
L3 entering the toad, which was best explained by the intercept-only
model (Table S1). Infection prevalence was 92.4% (73 of 79 toads had
nematodes in their lungs). The proportion of L3 establishing in the
lungs was best explained by toad SUL, toad origin and L3 origin (Table
S1), being higher in toads from the range-core versus the
invasion-front, higher for toads infected with L3 from invasion-frontversus range-core populations, and higher in larger toads (Table
S2, Fig. S1). When we analyzed the data separately for range-core and
invasion-front toads, we found that the number of L3 establishing in the
lungs was increased by intact skin secretions for range-core L3 but
reduced by intact skin secretions for invasion-front L3 (Table S1, S2,
Fig. 2). This effect was stronger in toads from the invasion-front
compared to the range-core (Fig. 2).
Fifteen days post-infection, toads had between 0 and 19 nematodes in
their lungs (mean ± SD: 7.5 ± 4.3), and generally there were more
nematodes in the lungs of larger toads, in range-core toads, and when
infected with invasion-front L3 (Table S1, S2). Range-core toads had
more nematodes in their lungs when the L3 originated from the
invasion-front, but the interaction of treatment and L3 origin was
uninformative (Fig. 2, Table S2). In invasion-front toads, reduced skin
secretions led to a lower number of nematodes in the lungs when the L3
originated from the range-core, but this effect was absent when infected
with invasion-front L3 (Fig. 2).