Parasites and invasions: changes in gastrointestinal helminth assemblages in invasive and native rodents in senegal

Abstract

Postal address: CBGP, 755 avenue du campus Agropolis, 34988 Montferrier-sur-Lez.Telephone: + 33(0)4 99 62 33 08 / Fax : + 33(0)4 99 62 33 45 Abstract Understanding why some exotic species become widespread and abundant in their colonized range is a fundamental issue that still needs to be addressed. Among many hypotheses, newly established host populations may benefit from a "parasite release" through impoverishment of their original parasite communities or reduced infection levels. Moreover, the fitness of competing native hosts may be affected by the acquisition of exotic taxa from invaders ("parasite spill-over") and/or by an increased transmission risk of native parasites due to their amplification by invaders ("parasite spill-back"). We focused on gastrointestinal helminth (GIH) communities to determine whether these predictions could explain the ongoing invasion success of the commensal house mouse (Mus musculus domesticus) and black rat (Rattus rattus), as well as the associated drop of native Mastomys species, in Senegal. A decrease of overall prevalence and individual species richness of GIH were observed along the invasion gradients as well as lower specific prevalence/abundance (Aspiculuris tetraptera in M. m. domesticus, Hymenolepis diminuta in R. rattus) on the invasion front. Conversely, we did not find any strong evidence of GIH spill-over or spill-back in invasion fronts, where native and invasive rodents co-occurred. For both invasive species, our results were consistent with the predictions of the parasite release hypothesis. Further experimental research is needed to determine whether and how the loss of GIH and reduced infection levels along invasion routes may result in any advantageous effects on invader fitness and competitive advantage.

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

“…However it did not support the EICA or EICA refined hypotheses 14 . Despite the enemy release patterns detected for mouse helminths in Senegal, from anciently invaded sites to recently invaded ones (decrease of specific richness and of overall prevalence, see 34 ), we did not find any evidence of a global dampening of immune related gene expression in recently invaded sites (the pattern expected according to the EICA hypothesis). We neither observed changes in immune related gene expression that would depend on the relative energetic costs of immune pathways (the pattern expected according to the EICA refined hypothesis).…”

“…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 .…”

“…However, this pattern could not be generalised to any 'parasite' pressure. A decrease of the overall prevalence in gastrointestinal helminths was also observed in recently invaded sites compared with anciently invaded ones, suggesting enemy release for these macroparasites 34 from introduction areas to invasion fronts. We therefore developed a whole RNA sequencing (i.e., RNAseq) approach to assess without any a priori differential gene expression patterns between populations from anciently and recently invaded sites.…”

“…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 .…”

Biological invasions in rodent communities: from ecological interactions to zoonotic bacterial infection issues

“…The role of parasites in successful colonization events of the house mouse and black rat has previously been documented, mainly with regard to insular ecosystems (Harris 2009; Wyatt, et al 2008). More recently, (Diagne, et al 2016) have revealed an association between the loss of gastrointestinal helminths and the range expansion of these rodents in Senegal. Because invasive and African rodent species studied here are known to carry a large array of zoonotic agents (Meerburg, et al 2009), it is also likely that the risks of zoonotic diseases for human may change along the mouse and rat invasion routes.…”