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

Abstract

Understanding why some exotic species become widespread and abundant in their colonised range is a fundamental issue that still needs to be addressed. Among many hypotheses, newly established host populations may benefit from a parasite loss ("enemy release" hypothesis) through impoverishment of their original parasite communities or reduced infection levels. Moreover, the fitness of competing native hosts may be negatively affected by the acquisition of exotic taxa from invaders ("parasite spillover") and/or by an increased transmission risk of native parasites due to their amplification by invaders ("parasite spillback"). We focused on gastrointestinal helminth 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 decrease in native Mastomys spp., in Senegal. For both invasive species, our results were consistent with the predictions of the enemy release hypothesis. A decrease in overall gastrointestinal helminth prevalence and infracommunity species richness was observed along the invasion gradients as well as lower specific prevalence/abundance (Aspiculuris tetraptera in Mus musculus domesticus, Hymenolepis diminuta in Rattus rattus) on the invasion fronts. Conversely, we did not find strong evidence of GIH spillover or spillback in invasion fronts, where native and invasive rodents co-occurred. Further experimental research is needed to determine whether and how the loss of gastrointestinal helminths and reduced infection levels along invasion routes may result in any advantageous effects on invader fitness and competitive advantage.

Rodents as Hosts of Pathogens and Related Zoonotic Disease Risk

“…Third, our results were in line with the expectation of lower parasitism highly documented in invading populations during their geographical spread (enemy release hypothesis; [82][83][84]); details and potential mechanisms are presented and discussed elsewhere (e.g., [21,[85][86][87]). Our findings were consistent with previous ones obtained for the house mouse in Senegal (e.g., [21]), and might provide the first empirical evidence for either low infection rates and/or potential parasite reduction experienced by the Nigerian gerbil during its geographical spread in West Africa. However, to conclude on this point requires a robust biogeographical comparison between well-defined source and currently invading populations of this rodent species.…”

“…In the frame of various projects on rodents and their bacterial pathogens in Northern Senegal (http://ohmi-tessekere.in2p3.fr/projets; http://projetcerise-ird-frb.fr), we had the opportunity to sample different rodent communities within human settlements from several villages (indoor sites) and natural wild habitats (outdoor sites) in the Ferlo region. This area represents a colonization front for two invasive rodent species: (i) The house mouse (Mus musculus), a major invasive species worldwide [2] that was introduced to Senegal in the colonial period, and which tends to replace native rodent communities (mainly Mastomys erythroleucus and Arvicanthis niloticus) with various consequences in disease risk and ecological interactions within invaded communities [20][21][22]; (ii) the Nigerian gerbil (Gerbillus nigeriae) that recently colonized North Senegal thanks to climatic and environmental changes experienced by the Sahelian bioclimatic zone during the last three decades, where it now represents the dominant species in outdoor rodent assemblages [23].…”

Rodents as Hosts of Pathogens and Related Zoonotic Disease Risk

“…Our findings were consistent with previous ones obtained for the house mouse in Senegal (e.g. [21]) and might provide a first empirical evidence for either low infection rates and/or potential parasite reduction experienced by the Nigerian gerbil during its geographical spread in West Africa. However, concluding on this point requires a robust biogeographical comparison between well-defined source and currently invading populations of this rodent species.…”

“…Third, our results were in line with the expectation of lower parasitism highly documented in invading populations during their geographical spread (enemy release hypothesis; [77][78][79]) ; details and potential mechanisms are presented and discussed elsewhere (e.g. [21,[80][81][82]). Our findings were consistent with previous ones obtained for the house mouse in Senegal (e.g.…”

Molecular characterization of cosmopolitan and potentially co-invasive helminths of commensal, murid rodents in Gauteng Province, South Africa

“…Several studies worldwide have investigated the parasites of introduced Rattus spp. (Abu-Madi et al 2005;Chaisiri et al 2010;Panti-May et al 2013;Shimalov 2016) in isolation, while few have simultaneously assessed the parasites of introduced and native rodents to be able to identify potential coinvaders where parasite spill over has occurred (Morand et al 2015;Diagne et al 2016).…”