We define co-introduced parasites as those which have been transported with an alien host to a new locality, outside of their natural range, and co-invading parasites as those which have been ...co-introduced and then spread to new, native hosts. Of 98 published studies of co-introductions, over 50% of hosts were freshwater fishes and 49% of parasites were helminths. Although we would expect parasites with simple, direct life cycles to be much more likely to be introduced and establish in a new locality, a substantial proportion (36%) of co-introductions were of parasites with an indirect life cycle. Seventy-eight per cent of co-introduced parasites were found in native host species and can therefore be classed as co-invaders. Host switching was equally common among parasites with direct and indirect life cycles. The magnitude of the threat posed to native species by co-invaders will depend, among other things, on parasite virulence. In 16 cases where co-introduced parasites have switched to native hosts and information was available on relative virulence, 14 (85%) were more virulent in native hosts than in the co-introduced alien host. We argue that this does not necessarily support the naïve host theory that co-invading parasites will have greater pathogenic effects in native hosts with which they have no coevolutionary history, but may instead be a consequence of the greater likelihood for parasites with lower virulence in their natural host to be co-introduced.
Diphyllobothriosis is a reemerging zoonotic disease because of global trade and increased popularity of eating raw fish. We present molecular evidence of host switching of a human-infecting broad ...fish tapeworm, Dibothriocephalus latus, and use of salmonids as intermediate or paratenic hosts and thus a source of human infection in South America.
Host–parasite systems, including social parasites that exploit resources of the host colonies, are fascinating objects for evolutionary biologists mainly due to the dynamic and often rapid ...host–parasite coevolution. Host‐switching events are believed to induce rapid speciation of parasitic species. The socially parasitic ant lineage Myrmoxenus, which corresponds to the monophyletic Temnothorax corsicus group, counts in total a dozen species. Most Myrmoxenus species utilize a single host species, but a few others, like Myrmoxenus ravouxi (André, 1896) and M. gordiagini Ruzsky, 1902, are known to use multiple host taxa. Myrmoxenus zaleskyi (Sadil, 1953) was described as a putative congener of M. ravouxi based on its distinct host selection. In this paper, we investigate the diversity of the widely distributed European lineages M. ravouxi and M. zaleskyi from multiple and complementary perspectives to understand whether the host preference exhibited by these two forms implies speciation. We integrated evidence from molecular genetics using mitochondrial CO I/CO II genes, including the tLeu‐region, and multivariate analyses of morphometric data collected from workers and female sexuals (gynes). Although there is substantial regional host species specificity, results suggest that host switching did not result in phylogenetic or morphological divergence and that the central European M. zaleskyi can be considered the junior synonym of M. ravouxi. As the lineage Myrmoxenus has been the subject of considerable evolutionary research, these results are essential to achieve a more accurate picture of host–parasite systems in the future and further strengthen the justification of an integrative approach in studying similarly complex systems. We advise against describing new parasitic species based on host preference unless coupled with marked heritable phenotypic adaptations.
Host‐switching events are believed to induce rapid speciation of parasitic species. In our study, we integrated evidence from molecular genetics using mitochondrial CO I/CO II genes, including the tLeu‐region, and multivariate analyses of morphometric data collected from Myrmoxenus zaleskyi and M. ravouxi workers and female sexuals (gynes) to understand whether the host preference exhibited by these two forms implies speciation. Although there is substantial regional host species specificity, results suggest that host switching did not result in phylogenetic or morphological divergence and that the central European M. zaleskyi can be considered the junior synonym of M. ravouxi.
Aim
We test the predictions of the Stockholm Paradigm, a synthesis of eco‐evolutionary theory explaining the nature of faunal assembly, host range and parasite diversification. Faunal diversification ...and assembly, manifested in patterns of host colonization, co‐adaptation and parasite speciation, are predicted to emerge as a consequence of alternating episodes of ecological disruption and stability. Specifically, for a diverse cestode genus (Arostrilepis), we evaluate the number and direction of Pleistocene dispersal events across Beringia, the number and relative timing of host colonization events and the relationship between host and parasite biogeographic histories and associations through time.
Location
Beringia and adjacent temperate to arctic biomes in North America and Eurasia.
Taxon
Arostrilepis (Cyclophyllidea: Hymenolepididae) and its rodent hosts.
Methods
Multi‐locus phylogenetic reconstruction and biogeographic ancestral range estimation.
Results
Arostrilepis lineages crossed Beringia eastward into North America a minimum of four times and westward into Asia twice in association with temporally disjunct geographic expansions of three major tribes of cricetid rodents (Arvicolini, Myodini, Lemmini). Inferences of ancestral host associations support at least nine instances of host colonization involving shifts from one rodent tribe or family to another. Several previously unrecognized lineages of Arostrilepis are revealed.
Main conclusions
Consistent with expectations of the Stockholm Paradigm, episodes of intercontinental dispersal were both frequent in the history of Arostrilepis and preceded a majority of inferred host‐colonization events. Events of historical geographic expansion created numerous opportunities for development of novel host–parasite associations through ecological fitting, as parasites tracked historically conserved resources available across diverse host taxa. Beringia played a major role in shaping rodent/parasite assemblages by mediating dispersal between the northern continents during glacial episodes of the Pleistocene, rather than by serving as a zone of refugial isolation.
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•Monogeneans are co-introduced with invasive Nile tilapia in sub-Saharan Africa.•DNA barcoding is applied to genetically detect parasite transmissions.•Parasite transmissions occur ...between invasive Nile tilapia and native tilapias.•A broad host range and environmental tolerance may promote parasite transmission.•Continuous monitoring is important to understand long-term parasitological impact.
Invasive Nile tilapias negatively impact native tilapia species through hybridisation and competition. However, the co-introduction of parasites with Nile tilapia, and subsequent changes in parasite communities, are scarcely documented. Monogeneans are known pathogens of cultured Nile tilapia, although little is known about their fate once Nile tilapias establish in new ecosystems. We investigate the parasitological consequences of Nile tilapia introduction on native tilapias in basins in Cameroon, the Democratic Republic of the Congo (DRC), and Zimbabwe, focusing on ectoparasitic dactylogyrids (Monogenea). Using the mitochondrial cytochrome oxidase c subunit I (COI) and nuclear 18S-internal transcribed spacer 1 (18S-ITS1) rDNA region of 128 and 166 worms, respectively, we evaluated transmission of several dactylogyrid species. Parasite spillover from Nile tilapia was detected for Cichlidogyrus tilapiae to Coptodon guineensis in Cameroon, Cichlidogyrus thurstonae to Oreochromis macrochir in the DRC, and Cichlidogyrus halli and C. tilapiae to Coptodon rendalli in Zimbabwe. Parasite spillback to Nile tilapia was detected for Cichlidogyrus papernastrema and Scutogyrus gravivaginus from Tilapia sparrmanii and Cichlidogyrus dossoui from C. rendalli or T. sparrmanii in the DRC, and Cichlidogyrus chloeae from Oreochromis cf. mortimeri and S. gravivaginus from O. macrochir in Zimbabwe. ‘Hidden’ transmissions (i.e. transmission of certain parasite lineages of species that are naturally present on both alien and native hosts) were detected for C. tilapiae and Scutogyrus longicornis between Nile tilapia and Oreochromis aureus and C. tilapiae between Nile tilapia and Oreochromis mweruensis in the DRC, and Cichlidogyrus sclerosus and C. tilapiae between Nile tilapia and O. cf. mortimeri in Zimbabwe. A high density of Nile tilapia occurring together with native tilapias, and the broad host range and/or environmental tolerance of the transmitted parasites, are proposed as factors behind parasite transmission through ecological fitting. However, continuous monitoring and the inclusion of environmental variables are necessary to understand the long-term consequences of these transmissions on native tilapias and to elucidate other underlying factors influencing these transmissions.
Experimental evidence is accumulating that endosymbionts of phytophagous insects may transmit horizontally via plants. Intracellular symbionts known for manipulating insect reproduction and altering ...fitness (
, and bacterial parasite of the leafhopper
) have been found to travel from infected insects into plants. Other insects, either of the same or different species can acquire the symbiont from the plant through feeding, and in some cases transfer it to their progeny. These reports prompt many questions regarding how intracellular insect symbionts are delivered to plants and how they affect them. Are symbionts passively transported along the insect-plant-insect path, or do they actively participate in the process? How widespread are these interactions? How does symbiont presence influence the plant? And what conditions are required for the new infection to establish in an insect? From an ecological, evolutionary, and applied perspective, this mode of horizontal transmission could have profound implications if occurring frequently enough or if new stable symbiont infections are established. Transmission of symbionts through plants likely represents an underappreciated means of infection, both in terms of symbiont epidemiology and the movement of symbionts to new host species.
Aim
Mutualisms are often disrupted for plants introduced to new ranges, yet many of these plants have managed to obtain effective mutualistic associations in their new ranges. There are two potential ...pathways for non‐native plants to reassemble mutualisms: cointroduction (i.e. familiar associations with cointroduced mutualists) or ecological fitting (i.e. forming or adapting novel associations with resident native mutualists). We assessed the importance of each pathway for mutualist reassembly in four Australian Acacia species (A. baileyana, A. dealbata, A. decurrens and A. melanoxylon) and their associated nitrogen‐fixing rhizobial symbionts in two non‐native locations.
Location
Native ranges of acacias in south‐eastern Australia and two non‐native ranges in New Zealand and South Africa.
Methods
Rhizobia associated with each acacia species in each country were isolated and identified based on DNA sequencing of the housekeeping recA gene and the symbiotic nodA gene. Separate phylogenies were reconstructed for each gene region to infer biogeographic histories of acacia‐associated rhizobia. Selected rhizobial strains for each acacia species by country combination were used as inocula in a glasshouse experiment and early growth kinetics and nitrogen fixation efficiency of acacia seedlings were compared between inoculum treatments to determine symbiotic effectiveness.
Results
All isolated rhizobial strains belonged to the genus Bradyrhizobium. Phylogenetic analyses revealed almost no country‐ or species‐specific clusters of these strains for either gene region and indicated that most acacia‐associated bradyrhizobia in New Zealand and South Africa were cointroduced from Australia. These results were supported by little variation in the growth performances of acacia seedlings, irrespective of inoculum treatment.
Main conclusions
This study revealed that cointroduction of Australian acacias and their rhizobia may be more prevalent than previously thought. Additionally, a single rhizobium cointroduction event may be sufficient to facilitate the establishment of effective mutualisms in numerous Acacia species, potentially leading to an invasion meltdown.
To integrate ecological fitting, the oscillation hypothesis and the taxon pulse hypothesis into a coherent null model for the evolution of complex host-parasite associations. Global. This paper ...reviews and synthesizes literature that focuses on phylogenetic analyses and reciprocal mapping of a model system of hosts and their parasites to determine patterns of host-parasite associations and geographical distributions through time. Host-switching and geographical dispersal of parasites are common phenomena, occurring on many temporal and spatial scales. Diversification involving both co-evolution and colonization explains complex host-parasite associations. Across the expanse of Earth history, the major radiations in host-parasite assemblages have been preceded by ecological disruption, ecological breakdown and host-switching in a context that can be defined by the concept of ecological fitting. This cyclical process sets the stage for co-diversification during periods of relative stability, punctuated by host-switching during episodes of regional to global environmental disruption and climatological change. Most observed host-parasite associations can be explained by an historical interaction between ecological fitting, oscillation (episodes of increasing host range alternating with isolation on particular hosts) and taxon pulses (cyclical episodes of expansion and isolation in geographical range). Major episodes of environmental change appear to be the main drivers for both the persistence and diversification of host-parasite systems, creating opportunities for host-switching during periods of geographical expansion and allowing for co-evolution and co-speciation during periods of geographical isolation.
Free‐living organisms are often host to multiple lineages of closely related parasites. Different lineages of obligate parasites living on the same hosts might potentially be expected to display ...similar cophylogenetic patterns. However, there are also reasons why these lineages might have different evolutionary histories (e.g. host switching, host geography). In the present study, we use mitochondrial and nuclear DNA sequence data to evaluate the cophylogenetic patterns between doves and their wing and body lice. Previous studies have found that the wing and body lice of doves have different levels of congruence between their phylogenetic histories. However, these studies are limited in scope, either taxonomically or geographically. We used both new and existing data to generate a worldwide and taxonomically diverse data set for doves and two independent groups of lice: wing and body lice. Using event and topology‐based methods, we found that cophylogenetic patterns were not correlated between wing and body lice, even though both groups showed evidence of cospeciation with their hosts. These results indicate that external factors vary in their impact on different groups of parasites and also that broad sampling is critical for identifying patterns in cophylogenetic analyses.
•Hantaviruses and their reservoir hosts are co-evolving.•Hantaviruses are ancient viruses that have co-existed with their hosts for more than 100MYR.•Hantaviruses may have evolved from insect-borne ...pre-bunyaviruses.
The most recent (9th) Report of the International Committee on Taxonomy of Viruses (ICTV) lists 23 established and 30 provisional species in the genus Hantavirus (family Bunyaviridae) (Plyusnin et al., 2012). These virus species are harbored by altogether 51 species of rodents, shrews and moles and thus in most cases it is a relationship of “one hantavirus-one host”. Such a tight bond between the two, in combination with the observed association between whole groups of hantaviruses and (sub)families of rodents, helped to develop the widely accepted view of a long-term co-evolution (co-speciation) of these viruses with their hosts. Accumulating evidence of host-switching events, both recent and ancient, however challenged some of the earlier views on hantavirus evolution. In this paper we discuss the concept of hantavirus-host co-speciation and propose a scenario of hantavirus evolution based on the currently available genetic information. This scenario is based on the hypothesis that hantaviruses are very ancient viruses which already existed at the estimated diversification point of major placental clades, of which one includes the ancestors of the order Rodentia and another the ancestors of both orders Eulipotyphla and Chiroptera; the diversification occurred approximately at 90–100MYA. We also speculate that the evolutionary history of hantaviruses extents even deeper in the past, beyond this time-point, and included the transmission of a (pre)bunyavirus from an insect host to a mammal host.
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