Component Endoparasite Communities Mirror Life-History Specialization in Syntopic Reed Frogs (Hyperolius spp.)

Most of our knowledge on the processes structuring parasite communities in amphibians originate from temperate-zone taxa, whereas Afrotropical communities have been neglected so far. We found evidence that ecological fitting of the hosts and, probably, differential immune response may influence the variation in parasite species richness, prevalence, and infestation intensity of East African frogs Hyperolius kivuensis and H. viridiflavus. The most closely related host species share the same macrohabitat (that implies the same pool of potential parasites), but differ in microhabitat preference, so that a comparative analyses of syntopic and allopatric populations is expedient to reveal ecological fitting. We detected 11 parasite species (one annelid, four nematodes, five trematodes, one cestode) and two endocommensal species (protozoans). The component parasite communities included 4–5 helminth species in H. kivuensis and 6–8 in the more aquatic H. viridiflavus, supporting the hypothesis that trematode diversity increases with the amount of time spent in water. Five parasite species (Orneoascaris chrysanthemoides, Clinostomum chabaudi, an undetermined echinostomatid) and two protozoans (Nyctotheroides sp., and Protoopalina sp.) are shared among the syntopic amphibian populations. This finding indicates a similar susceptibility of these amphibians to infestation from the local parasite pool. Yet, the low prevalence of single- and multi-species infestations in H. kivuensis indicates that parasite clearing by its immune response is probably more effective and prominent than in H. viridiflavus. Therefore, H. viridiflavus suffered from significantly reduced short-term survival due to the infection. Thus, we conclude that the processes structuring component parasite communities in amphibians do not differ generally between temperate-zone and Afrotropical host species, but they do in the magnitude of ecological fitting.

The role of phylogeny and ecological opportunity in host-parasite interactions: network metrics, host repertoire, and network link prediction.

Hosts and parasites have often intimate associations. Therefore, the evolution of their interactions is crucial for understanding species-rich host-parasite communities. Yet relatively few studies investigate eco-evolutionary feedbacks in these systems as large datasets remain scarce. Here, we explore African cichlid fishes and their flatworm gill parasites (Cichlidogyrus spp.) including 9901 reported infections and 473 different host-parasite combinations collected through a survey of peer-reviewed literature. We apply network metrics, estimate host repertoires, and use network link prediction (NLP) algorithms to investigate meta-community structures and their predictors including evolutionary, ecological, and morphological parameters. Host repertoire was mostly determined by the hosts’ evolutionary history. Both ecological and evolutionary parameters predicted host parasite associations but many interactions remain undetected according to NLP. We conclude that ecological opportunity paired with ecological fitting has shaped interactions. The cichlid-Cichlidogyrus network is a suitable study system for eco-evolutionary feedbacks but taxonomic research remains key to finding undetected interactions.

A highly invasive malaria parasite has expanded its range to non-migratory birds in North America

Parasite range expansions are a direct consequence of globalization and are an increasing threat to biodiversity. Here, we report a recent range expansion of the SGS1 strain of a highly invasive parasite, Plasmodium relictum , to two non-migratory passerines in North America . Plasmodium relictum is considered one of the world's most invasive parasites and causes the disease avian malaria: this is the first reported case of SGS1 in wild non-migratory birds on the continent. Using a long-term database where researchers report avian malaria parasite infections, we summarized our current understanding of the geographical range of SGS1 and its known hosts. We also identified the most likely geographical region of this introduction event using the MSP1 allele. We hypothesize that this introduction resulted from movements of captive birds and subsequent spillover to native bird populations, via the presence of competent vectors and ecological fitting. Further work should be conducted to determine the extent to which SGS1 has spread following its introduction in North America.

“Accidents waiting to happen” – insights from a simple model on the emergence of infectious agents in new hosts.

Summary: This study evaluates through modeling the possible individual and combined effect of three populational parameters of pathogens (reproduction rate; rate of novelty emergence; and propagule size) on the colonization of new host species – putatively the most fundamental process leading to the emergence of new infectious diseases. The results are analyzed under the theoretical framework of the Stockholm Paradigm using IBM simulations to better understand the evolutionary dynamics of the pathogen population and the possible role of Ecological Fitting. The simulations suggest that all three parameters positively influence the success of colonization of new hosts by a novel parasite population but contrary to the prevailing belief, the rate of novelty emergence (e.g. mutations) is the least important factor. Maximization of all parameters result in a synergetic facilitation of the colonization and emulates the expected scenario for pathogenic microorganisms. The simulations also provide theoretical support for the retention of the capacity of fast-evolving lineages to retro-colonize their previous host species/lineage by ecological fitting. Capacity is, thus, much larger than we can anticipate. Hence, the results support the empirical observations that opportunity of encounter (i.e. the breakdown in mechanisms for ecological isolation) is a fundamental determinant to the emergence of new associations – especially Emergent Infectious Diseases - and the dynamics of host exploration, as observed in SARS-CoV-2. Insights on the dynamics of Emergent Infectious Diseases derived from the simulations and from the Stockholm Paradigm are discussed.

“Accidents waiting to happen” – insights from a simple model on the emergence of infectious agents in new hosts.

This study evaluates through modeling the possible individual and combined effect of three populational parameters of pathogens (reproduction rate; rate of novelty emergence; and propagule size) on the colonization of new host species – putatively the most fundamental process leading to the emergence of new infectious diseases. The results are analyzed under the theoretical framework of the Stockholm Paradigm using IBM simulations to better understand the evolutionary dynamics of the pathogen population and the possible role of Ecological Fitting. The simulations suggest that all three parameters positively influence the success of colonization of new hosts by a novel parasite population but contrary to the prevailing belief, the rate of novelty emergence (e.g. mutations) is the least important factor. Maximization of all parameters result in a synergetic facilitation of the colonization and emulates the expected scenario for pathogenic microorganisms. The simulations also provide theoretical support for the retention of the capacity of fast-evolving lineages to retro-colonize their previous host species/lineage by ecological fitting. Capacity is, thus, much larger than we can anticipate. Hence, the results support the empirical observations that opportunity of encounter (i.e. the breakdown in mechanisms for ecological isolation) is an fundamental determinant to the emergence of new associations - in special of Emergent Infectious Diseases - and the dynamics of host exploration, as observed in SARS-CoV-2. Insights on the dynamics of Emergent Infectious Diseases derived from the simulations and from the Stockholm Paradigm are discussed.

Diversity of Tetrabothriidae (Eucestoda) among Holarctic Alcidae (Charadriiformes): Resolution of the Tetrabothrius jagerskioeldi Cryptic Species Complex— Cestodes of Alcinae—Provides Insights on the Dynamic Nature of Tapeworm and Marine Bird Faunas under the Stockholm Paradigm

We begin resolution of the Tetrabothrius jagerskioeldi–species complex with descriptions of Tetrabothrius alcae n. sp. based on numerous specimens, primarily in murres (species of Uria), from the greater North Pacific basin and Tetrabothrius sinistralis n. sp. based on cestodes in guillemots (species of Cepphus) from the central Bering Sea and West Greenland. These tetrabothriids are characterized, among 44 species of Tetrabothrius in avian hosts, by attributes of the scolex, male and female organ systems, structure and dimensions of the vitelline gland, numbers of testes, configuration of the genital atrium, genital papillae and the male and female atrial canals, position of the genital ducts relative to the poral osmoregulatory canals, structure, dimensions and position of the vaginal seminal receptacle, and dimensions of the embryophore and oncosphere, in addition to a broader array of characters. Remarkably, T. alcae, T. sinistralis, and a cryptic complex had remained unrecognized for the past century, given that these species are unequivocally differentiated by multiple suites of unique structural attributes relative to T. jagerskioeldi. Alcids and cestodes of the T. jagerskioeldi–complex are restricted to cold marine systems of advection and upwelling along coastal margins adjacent to the continental shelf or are associated with archipelagos (especially the Aleutian Arc), isolated islands and rocky headlands of the Bering Sea, Chukchi Sea, Gulf of Alaska, Sea of Okhotsk, and Sea of Japan. Tetrabothrius alcae, T. jagerskioeldi, and T. sinistralis may occur in sympatry but with minimal overlap in the faunas associated with murres (Alcini) and guillemots (Cepphini). Transmission for cestodes and persistence of this fauna is expected to be associated with pelagic and neritic systems adjacent to colony sites in zones where critical prey species are concentrated or secondarily dispersed downstream by predictable advective and upwelling processes and become available to foraging birds. Faunal assembly represents the outcomes of oscillating climate, shifting ranges (breakdown in isolation, ecological fitting, and exploration modes for cestodes) and the changing interfaces for resource availability maintained by trophic and habitat overlaps. Dynamics at these ecotones constitute the nexus of opportunity and capacity for infection by species of Tetrabothrius among avian hosts where capacity appears broad and opportunity is ecologically restricted in space and prevatime. Life history pathways for cestodes are tied to trophic associations and dynamics at mesoscales across marine domains and provinces. Resilience and connectivity through ecological fitting strongly suggest the influence of multiple trophic pathways for transmission and persistence of this complex fauna through differing assemblages of zooplankters, fishes, and cephalopods depending on locality, oceanographic conditions, and temporal variability. Changing conditions, especially ecological perturbations driven by climate oscillations, directly determine production cycles and distributions of micro- and macro-zooplankton, forage fishes, cephalopods, and trophic structure in high-latitude marine ecosystems. Expanding regimes of accelerating change emphasize the critical importance of field collections, archives, and baselines to assess biological outcomes across temporal and spatial scales. Parasite assemblages reveal macro- to meso-scale connectivity serving as adjuncts and proxies in recognizing and understanding outcomes for episodes of environmental oscillation and directional atmospheric and oceanic warming in marine ecosystems.

The role of biotic interactions in invasion ecology: theories and hypotheses.

Changes in biotic interactions in the native and invaded range can enable a non-native species to establish and spread in novel environments. Invasive non-native species can in turn generate impacts in recipient systems partly through the changes they impose on biotic interactions; these interactions can lead to altered ecosystem processes in the recipient systems. This chapter reviews models, theories and hypotheses on how invasion performance and impact of introduced species in recipient ecosystems can be conjectured according to biotic interactions between native and non-native species. It starts by exploring the nature of biotic interactions as ensembles of ecological and evolutionary games between individuals of both the same and different groups. This allows us to categorize biotic interactions as direct and indirect (i.e. those involving more than two species) that emerge from both coevolution and ecological fitting during community assembly and invasion. We then introduce conceptual models that can reveal the ecological and evolutionary dynamics between interacting non-native and resident species in ecological networks and communities. Moving from such theoretical grounding, we review 20 hypotheses that have been proposed in invasion ecology to explain the invasion performance of a single non-native species, and seven hypotheses relating to the creation and function of assemblages of non-native species within recipient ecosystems. We argue that, although biotic interactions are ubiquitous and quintessential to the assessment of invasion performance, they are nonetheless difficult to detect and measure due to strength dependency on sampling scales and population densities, as well as the non-equilibrium transient dynamics of ecological communities and networks. We therefore call for coordinated efforts in invasion science and beyond, to devise and review approaches that can rapidly map out the entire web of dynamic interactions in a recipient ecosystem.