Dual transcriptomics reveals co-evolutionary mechanisms of intestinal parasite infections in blue mussels Mytilus edulis

On theoretical grounds, antagonistic co-evolution between hosts and their parasites should be a widespread phenomenon but only received little empirical support sofar. Consequently, the underlying molecular mechanisms and evolutionary stepsremain elusive, especially in nonmodel systems. Here, we utilized the natural history of invasive parasites to document the molecular underpinnings of co-evolutionary trajectories. We applied a dual-species transcriptomics approach to experimental cross-infections of blue mussel <i>Mytilus edulis</i> hosts and their invasive parasitic copepods <i>Mytilicola intestinalis</i> from two invasion fronts in the Wadden Sea. We identified differentially regulated genes from an experimental infection contrast for hosts (infected vs. control) and a sympatry contrast (sympatric vs. allopatric combinations)for both hosts and parasites. The damage incurred by <i>Mytilicola</i> infection and the following immune response of the host were mainly reflected in cell division processes,wound healing, apoptosis and the production of reactive oxygen species(ROS). Furthermore, the functional coupling of host and parasite sympatry contrasts revealed the concerted regulation of chitin digestion by a Chitotriosidase 1 homologin hosts with several cuticle proteins in the parasite. Together with the coupled regulation of ROS producers and antagonists, these genes represent candidates that mediate the different evolutionary trajectories within the parasite’s invasion. The host–parasite combination-specific coupling of these effector mechanisms suggests that underlying recognition mechanisms create specificity and local adaptation. In this way, our study demonstrates the use of invasive species’ natural history to elucidate molecular mechanisms of host–parasite co-evolution in the wild

Biological invasions and host–parasite coevolution: different coevolutionary trajectories along separate parasite invasion fronts

Host–parasite coevolution has rarely been observed in natural systems. Its study often relies on microparasitic infections introducing a potential bias in the estimation of the evolutionary change of host and parasite traits. Using biological invasions as a tool to study host–parasite coevolution in nature can overcome these biases. We demonstrate this with a cross-infection experiment in the invasive macroparasite <i>Mytilicola intestinalis</i> and its bivalve host, the blue mussel <i>Mytilus edulis</i>. The invasion history of the parasite is well known for the southeastern North Sea and is characterised by two separate invasion fronts that reached opposite ends of the Wadden Sea (i.e. Texel, The Netherlands and Sylt, Germany) in a similar time frame. The species’ natural history thus makes this invasion an ideal natural experiment to study host–parasite coevolution in nature. We infected hosts from Texel, Sylt and Kiel (Baltic Sea, where the parasite is absent) with parasites from Texel and Sylt, to form sympatric, allopatric and naïve infestation combinations, respectively. We measured infection rate, host condition and parasite growth to show that sympatric host–parasite combinations diverged in terms of pre- and post-infection traits within <100 generations since their introduction. Texel parasites were more infective and more efficient at exploiting the host’s resources. Hosts on Texel, on the other hand, evolved resistance to infection, whereas hosts on Sylt may have evolved tolerance. This illustrates that different coevolutionary trajectories can evolve along separate invasion fronts of the parasite, highlighting the use of biological invasions in studies of host–parasite coevolution in nature

Invading the Occupied Niche: How a Parasitic Copepod of Introduced Oysters Can Expel a Congener From Native Mussels

In species introductions, non-native species are often confronted with new niches occupied by more specialized natives, and for introduced parasites this conflict can be amplified because they also face novel hosts. Despite these obstacles, invasions of introduced parasites occur frequently, but the mechanisms that facilitate parasite invasion success are only rarely explored. Here, we investigated how the parasitic copepod Mytilicola orientalis, that recently spilled over from its principal host - the Pacific oyster Crassostrea gigas, managed to invade the niche of blue mussel Mytilus edulis intestines, which is densely occupied by its specialist congener, Mytilicola intestinalis. From field observations demonstrating invasion dynamics in nature, we designed a series of experiments addressing potential mechanisms facilitating a successful occupation of the new niche. As expected the specialist M. intestinalis can only infect mussel hosts, but displayed higher infection success there than M. orientalis in both principal host species combined. In the absence of direct competitive interactions M. orientalis compensated its lower infection success (1) by recurrent spill-over from its high-fitness reservoir oyster host, and (2) by active aggregation interference enhancing its own mating success while limiting that of M. intestinalis. The introduced parasite could thus avoid direct competition by changing its own epidemiology and indirectly decreasing the reproductive success of its competitor in the new host. Such mechanisms outside of direct competition have seldom been considered, but are crucial to understand invasion success, parasite host range and community assembly in the context of species introductions

Publisher correction:Resource landscapes explain contrasting patterns of aggregation and site fidelity by red knots at two wintering sites

[This corrects the article DOI: 10.1186/s40462-018-0142-4.].</p

Coinvasion and Coinfection: Evolution and adaptation of two invasive parasites infecting blue mussels

Biological invasions of parasites offer ideal opportunities to study coevolution in nature - especially when hosts are faced with repeated invasions of parasites. Such coinvasions not only lead to selection on the host but also to selection on parasites arising from direct competition. Here, we present data from a crossed coinfection experiment using two closely related copepod parasites that have invaded the Eastern Atlantic, infecting mussels. One is the specialist Mytilicola intestinalis, that invaded from the Mediterranean Sea in the 1930s and the other one is the generalist Mytilicola orientalis that invaded from Japan in the 1990ies. This system thus offers the opportunity to study host-parasite interactions along a gradient of different coevolutionary timescales and host specificity. Here we report the first results of this experiment on the phenotypic level focussing on the balance and trade-offs between host and parasite traits, i.e. infectivity - virulence for the parasites and virulence-tolerance for the hosts. We find different interactions along these trade-offs between both interactions. We also find that the generalist invader is outcompeting the old invader

Publisher Correction: Resource landscapes explain contrasting patterns of aggregation and site fidelity by red knots at two wintering sites

In the original publication of this article [1], the majorit

Global invasion genetics of two parasitic copepods infecting marine bivalves

Invasive species, and especially invasive parasites, represent excellent models to study ecological and evolutionary mechanisms in the wild. To understand these processes, it is crucial to obtain more knowledge on the native range, invasion routes and invasion history of invasive parasites. We investigated the consecutive invasions of two parasitic copepods (Mytilicola intestinalis and Mytilicola orientalis) by combining an extensive literature survey covering the reported putative native regions and the present-day invaded regions with a global phylogeography of both species. The population genetic analyses based on partial COI sequences revealed significant population differentiation for M. orientalis within the native region in Japan, while introduced populations in North America and Europe could not be distinguished from the native ones. Thus, M. orientalis' invasion history resembles the genetic structure and recent spread of its principal host, the Pacific oyster, Crassostrea gigas, while M. intestinalis lacks population genetic structure and has an overall low genetic diversity. Therefore, the native origin of M. intestinalis remains unclear. With this study, we demonstrate that even highly related and biologically similar invasive species can differ in their invasion genetics. From this, we conclude that extrapolating invasion genetics dynamics from related invasive taxa may not always be possible

Coping with poachers in European stalked barnacle fisheries: Insights from a stakeholder workshop

In January 2020, a stakeholder workshop was organized as a knowledge sharing strategy among European stalked barnacle fisheries. Management of this fishery differs greatly among regions and ranges from less organized and governed at large scales (>100 km, coasts of SW Portugal and Brittany in France) to highly participatory systems which are co-managed at small spatial scales (10′s km and less, Galicia and Asturias). Discussions revealed that poaching is ubiquitous, hard to eradicate, and adapts to all types of management. The stakeholders identified some key management initiatives in the fight against poaching: granting professional harvesters with exclusive access to the resource, increasing social capital among harvesters through tenure systems (e.g. Territorial Use Rights in Fisheries) that empower them as stewards of their resource and intensification of surveillance with the active participation of the harvesters. Furthermore, increased cooperation between fishers associations and regional fisheries authorities, improved legal frameworks, adoption of new technologies and the implementation of market-based solutions can also help coping with this systemic problemAgencia Estatal de Investigación | Ref. PCIN-2016-120Agencia Estatal de Investigación | Ref. PCIN-2016-063Fundação para a Ciência e a Tecnologia | Ref. BIODIVERSA / 0005/2015Fundação para a Ciência e a Tecnologia | Ref. BIODIVERSA / 0006/2015Agence Nationale de la Recherche | Ref. ANR-16-EBI3-0006-01Agence Nationale de la Recherche | Ref. ANR-16-EBI3-0006-02 a ANFundação para a Ciência e a Tecnologia | Ref. UIDB / 04292/2020Fundação para a Ciência e a Tecnologia | Ref. UIDP / 50017 / 2020Fundação para a Ciência e a Tecnologia | Ref. UIDB / 50017/2020Principado de Asturias | Ref. PA-18-PF-BP17-184Ministerio de Ciencia, Innovación y Universidades | Ref. FPU2016- 04258Principado de Asturias | Ref. FC-Grupin-IDI-2018- 000201Xunta de Galicia | Ref. ED481A-2020/199Fundação para a Ciência e a Tecnologia | Ref. SFRH / BD / 135872/2018Ministerio de Economía y Competitividad |Ref. CTM2014-51935-