Fig 1.
Effect of S. invicta invasion on biodiversity of resident ant species (Independent sample t test, mean±SE, n = 3 biological replicates).
Asterisks indicate significant differences (***P < 0.001). C: Simpson dominance index; H’: Shannon-Wiener index; E: the Pielou evenness index.
Fig 2.
Individual and group behavior of workers of T. melanocephalum from either invaded or non-invaded areas when attacked by S. invicta workers.
(A) Attack level (No significant difference of attack levels was found between invaded and non-invaded areas except Level II; Level III: t = 0.044, df = 2, P = 0.178; Level II: t = 4.612, df = 2, P = 0.044; Level III: t = 0.143, df = 2, P = 0.899; Level IV: t = -1.0, df = 2, P = 0.423) and (B) aggressiveness index (Independent sample t test, mean ± SE, n = 3 biological replicates) between S. invicta and T. melanocephalum from S. invicta invaded and non-invaded areas. (C) Group mortality (Independent sample t test, mean ± SE, n = 15 biological replicates) of T. melanocephalum under attack by S. invicta workers in S. invicta invaded and non-invaded areas. (D) Aggressiveness index (One-Way ANOVA, mean ± SE, bars with same letters indicate no significant difference (P > 0.05)) for T. melanocephalum from the non-invaded area at different times following contact with S. invicta. CK: T. melanocephalum without previous contact with S. invicta; Asterisks indicate significant differences (*P < 0.05, **P < 0.01, ***P < 0.001).
Fig 3.
Stable isotope content (δN) (Independent sample t test, mean ± SE, 3 biological replicates were both collected from 3 separate invaded sites and 3 separate non-invaded sites) of T. melanocephalum workers from S. invicta invaded and non-invaded areas.
Asterisks indicate significant differences (***P < 0.001).
Fig 4.
Functional analysis of bacterial symbionts from T. melanocephalum workers from S. invicta invaded and non-invaded areas.
(A) According to PICRUSt analysis, the most enriched metabolic pathways for symbionts in T. melanocephalum workers represented as mean number of KO (KEGG orthology) ± SE for energy metabolism, metabolism of cofactors and vitamins, amino acid metabolism and nucleotide metabolism, Independent sample t test, n = 3 biological replicates, P values in the chart were adjusted by a False Discovery Rate (FDR) correction to account for multiple testing [88]). (B) Bacterial groups that differ between T. melanocephalum workers from S. invicta invaded and non-invaded areas based on LEfSe analysis. T.m.I: T. melanocephalum in S. invicta invaded areas; T.m.NI: T. melanocephalum in S. invicta non-invaded areas. (C) V3+V4 areas of the 16S rRNA gene phylogeny of Wolbachia from workers of T. melanocephalum (441 aligned nucleotide sites). Host insect names are in brackets. Bootstrap values (500 replicates) greater than 50% are indicated at the nodes. Sequences of Wolbachia collected from T. melanocephalum workers are in red font. Asterisks indicate significant differences (*P < 0.05).
Fig 5.
Relative abundances of Wolbachia, Lactobacillales and Enterobacteriaceae and vitamin B concentration in workers of T. melanocephalum.
(A) A shift in abundances of Wolbachia, Lactobacillales and Enterobacteriaceae in T. melanocephalum workers from invaded versus non-invaded areas occurs when dietary composition is shifted to sugar (carbohydrate) or locusts (protein) respectively. (B) No shift in abundances of Wolbachia, Lactobacillales and Enterobacteriaceae in T. melanocephalum workers from invaded versus non-invaded areas occurs when diet is not changed in protein or sugar content, respectively. (C) Vitamin B concentration in T. melanocephalum workers from S. invicta invaded and non-invaded areas after supplying with sugar and locusts as food, respectively. (D) Vitamin B concentration in T. melanocephalum workers supplied with complementary food (e.g. peptone or sugar for ants from S. invicta invaded areas and non-invaded areas, respectively) (as follow-up experiment to (C)). ‘LG’ (on the y-axis) stands for logarithm to the base of 10.
Fig 6.
Stable isotope content δN and abundances of Wolbachia, Lactobacillales and Enterobacteriaceae in more wild populations of T. melanocephalum.
(A) Comparison for the δN values (Independent sample t test, mean ± SE) and (B) abundances of Wolbachia, Lactobacillales and Enterobacteriaceae (Independent sample t test, mean ± SE) in T. melanocephalum from another three non-invaded and four invaded sites. (C) Comparison for the δN values (Paired sample t test, mean ± SE, n = 3 biological replicates) and (D) abundances of Wolbachia, Lactobacillales and Enterobacteriaceae (Paired sample t test, mean ± SE, n = 3 biological replicates) in T. melanocephalum after rearing with or without S. invicta for one month. ‘LG’ (on the y-axis) stands for logarithm to the base of 10. Asterisks indicate significant differences (*P < 0.05, **P < 0.01, ***P < 0.001).