Results
After filtering, the final ASV table encompassed 3923 unique ASVs,
included in a total of 39 bacteria phyla. The most abundant phyla among
the species studied were Firmicutes, Bacteroidota, Actinobacteroidota,
Proteobacteroidota and Campylobacterota.
Gut bacterial diversity, measured through alpha-diversity indices, was
significantly different between localities considering the number of
Observed ASVs and PD indices (F-statistics > 39.74; p
< 0.02), with species from Lisbon showing consistently higher
alpha-diversity indices than the ones from Moledo, (Fig. 2). No
differences between localities were found with the Shannon index
(F-statistics = 8.33; p = 0.07). Moreover, neither species or sex had a
significant effect on microbial alpha-diversity (F < 1.95; p
> 0.11), but P. siculus had higher diversity than
the native P. virescens . Microbial structure, measured through
beta-diversity indices, was significantly different between localities
(R2 > 0.03; p < 0.04) and
species (R2 > 0.08; p < 0.03)
(Fig. 3). In general, pairwise differences in beta-diversity between
species were found in species collected from Lisbon (Table 1), while no
differences were found between sexes. In samples collected in Moledo, no
differences were found in beta-diversity between species or sexes.
Although no differences were found in the proportion of the most
abundant phyla between species or sexes, among the most abundant genera
some differences were observed (Fig. 4). In the case of species in
Moledo, sex influenced the proportion of the genusCorynebacterium (F-statistics = 4.46, p = 0.02) (Table 2).
Differences in the proportion of the most abundant taxa between P.
siculus and P. virescens were found for an unidentified genus
belonging to the orderCorynebacterium(F-statistics = 6.66, p = 0.003) and forOdoribacter (F-statistics = 10.10, p = 0.0002) (Table 2).
Pearson correlation test only showed significantly positive correlations
between SVL and bacterial alpha-diversity (for Shannon index) for males
of the invasive species P. siculus (Fig. 5).
Results from FEAST software indicated that the level of bacterial
transmission between sympatric species in both populations (Parque das
Nações and Moledo) was high. Nevertheless, while bacterial transmission
was balanced in both directions between the syntopic P.
lusitanicus and P. bocagei (estimated transmission from P.
bocagei towards P. lusitanicus was ~ 71% on
average, and from P. lusitanicus towards P. bocagei was
~ 69% on average), between the two sympatric species in
Lisbon there was a more biased transmission, with P. virescensseemingly having a higher contribution towards P. siculus gut
microbiota (transmission estimates from P. virescens towardsP. siculus was ~ 72% on average, and fromP. siculus towards P. virescens it was about 55% on
average).