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).