Ecological and sanitary impacts of bacterial communities associated to biological invasions in African commensal rodent communities

Abstract

Changes in host-parasite ecological interactions during biological invasion events may affect both the outcome of invasions and the dynamics of exotic and/or endemic infections. We tested these hypotheses, by investigating ongoing house mouse (Mus musculus domesticus) and black rat (Rattus rattus) invasions in Senegal (West Africa). We used a 16S gene rRNA amplicon sequencing approach to study potentially zoonotic bacterial communities in invasive and native rodents sampled along two well-defined independent invasion routes. We found that individual host factors (body mass and sex) were important drivers of these bacterial infections in rodents. We observed that the bacterial communities varied along invasion routes and differed between invasive and native rodents, with native rodents displaying higher overall bacterial diversity than invasive rodents. Differences in prevalence levels for some bacterial Operational Taxonomic Units (OTUs) provided support for ecological processes connecting parasitism and invasion success. Finally, our results indicated that rodent invasions may lead to the introduction of exotic bacterial genera and/or to changes in the prevalence of endemic ones. This study illustrates the difficulty of predicting the relationship between biodiversity and disease risks, and advocate for public health prevention strategies based on global pathogen surveillance followed by accurate characterization of potential zoonotic agents.

Differential immune gene expression associated with contemporary range expansion of two invasive rodents in Senegal

“…The difference of Aere Lao among recently-invaded sites was already noticeable in some of the effectors (complement; haptoglobin) previously measured by immune challenges 32 . This pattern may not be related to parasitological data, because endemic parasites were found at high levels of prevalence in this site 33,34 . On the contrary, it may reflect a more ancient invasion history of the house mouse in this locality than in the neighbouring ones, for which we have historical data 30 .…”

“…These immune variations could be considered as responses to novel parasite pressures encountered in recently invaded areas. Surveys of bacterial communities in Senegal seemed to corroborate this prediction 33 as both quantitative and qualitative changes in bacterial composition were observed along the house mouse and black rat routes of invasion. However, this pattern could not be generalised to any 'parasite' pressure.…”

“…Indeed, we observed changes in bacterial communities between anciently and recently invaded sites. In particular, we detected introduction of exotic bacterial genera and/or changes in the prevalence of endemic ones, see 33 . Similar rapid changes in immunity have been observed in other invading organisms, but these studies revealed a wide array of patterns that did not enable to conclude on the potential genericity / specificity of the EICA hypotheses 16 .…”

“…We used some of the spleen samples of M. m. domesticus and R. rattus that were previously analysed for the bacterial metabarcoding study previously described 33 . Briefly, for both invasive species, rodent trapping was performed in four anciently invaded (more than 100 years) and four recently invaded (less than 30 years) sites defined according to historical and longitudinal surveys 30 .…”

“…On the other hand, under the EICA-refined hypothesis, we expected lower levels of expression for genes encoding for energetically costly immune pathways (e.g., inflammation) and higher levels of expression for genes encoding for cost-effective immune pathways (e.g., antibody mediated responses), in recently invaded sites. Enemy release of macroparasites and changes in the composition of bacterial communities in recently invaded sites could mediate such trade-offs between energetically costly and cost-effective immune pathways 33,34 .…”