Search

This study explores the utilisation of European freshwater mussels as hosts by the European bitterling (Rhodeus amarus) at their current sympatric occurrence range. Our study confirms Pseudanodonta complanata as a suitable, occasional host for bitterling. The spawning relationship of R. amarus with freshwater mussels has physiological costs for the hosts, leading to resource competition and potential negative effects on host fertility. Further research is needed to assess the dynamics of host-parasite interactions, mussel adaptations to prevent parasitism, and the consequences of the bitterling recent and possible future expansion in Europe for mussel populations.

The coevolutionary dynamic of host–parasite associations varies from strictly local adaptations to diffuse guild coevolution. How innate and acquired immune responses modulate host resistance to parasitism and how host specificity and geographic scaling affect the efficacy of host response have consequences for range dynamics and biological invasions.Using reciprocal transplant experiments, we tested whether local or diffuse coevolution shapes host response to parasitism in the host–parasite association between bitterling fishes and larval stages (glochidia) of freshwater mussels from Europe and East Asia.We found that glochidia initially indiscriminately attached to all study host species, but immune responses elicited significant differences in host responses within 24 h of infection, which intensified during glochidial development. European bitterlings were more resistant to European glochidia and Asian bitterlings to Asian glochidia, with the strongest geographic bias in resistance in the Asian bitterling hosts.This finding suggests a strong effect of local adaptation but also indicates the non‐negligible role of coevolutionary hotspots. Low natural glochidia load on bitterling species overall hence arise from competent immune response rather than glochidia avoidance behaviour. Bitterling immune response is primarily innate and not acquired.Overall, our data demonstrate the complex outcome of parasite pressure on the evolution of host resistance, and important role of geographically structured coevolution in shaping host response. [ABSTRACT FROM AUTHOR]

Synodontis catfishes in Lake Tanganyika have undergone a modest radiation, with differences among species in reproductive strategies, including one species that has evolved to be an obligate brood parasite. Here, we provide insights into the reproductive traits and histology of male and female reproductive organs of five Lake Tanganyika Synodontis species (S. irsacae, S. melanostictus, S. multipunctatus, S. petricola and S. polli). We describe the structures employed in oogenesis, spermiogenesis and spermiation. We show that the shape and size of the urogenital papilla is a valuable trait for sex determination in all species except S. polli, where the imprecision reached > 20 %. From a histological perspective, the inter-specific structural differences associated with the type of reproductive strategy were not found in the ovaries. However, testicular histology indicated variations in spermiation structures among species, namely in S. multipunctatus and S. irsacae. The differences identified may be related to variation in reproductive strategies among species. In particular, weaker eosinophily of testicular secretions was found in S. multipunctatus than in other species, suggesting the possibility of a different composition. Experimental manipulation of environmental and hormonal stimuli represents a promising direction for further research into the structural and functional diversity of male gonads in Synodontis species from Lake Tanganyika. [ABSTRACT FROM AUTHOR]

Embryonic development is often considered shielded from the effects of natural selection, being selected primarily for reliable development. However, embryos sometimes represent virulent parasites, triggering a coevolutionary "arms race" with their host. We have examined embryonic adaptations to a parasitic lifestyle in the bitterling fish. Bitterlings are brood parasites that lay their eggs in the gill chamber of host mussels. Bitterling eggs and embryos have adaptations to resist being flushed out by the mussel. These include a pair of projections from the yolk sac that act as an anchor. Furthermore, bitterling eggs all adopt a head-down position in the mussel gills which further increases their chances of survival. To examine these adaptations in detail, we have studied development in the rosy bitterling (Rhodeus ocellatus) using molecular markers, X-ray tomography, and time-lapse imaging. We describe a suite of developmental adaptations to brood parasitism in this species. We show that the mechanism underlying these adaptions is a modified pattern of blastokinesis--a process unique, among fish, to bitterlings. Tissue movements during blastokinesis cause the embryo to do an extraordinary "front-flip" on the yolk. We suggest that this movement determines the spatial orientation of the other developmental adaptations to parasitism, ensuring that they are optimally positioned to help resist the ejection of the embryo from the mussel. Our study supports the notion that natural selection can drive the evolution of a suite of adaptations, both embryonic and extra-embryonic, via modifications in early development. [ABSTRACT FROM AUTHOR]

Host–parasite dynamics involve coevolutionary arms races, which may lead to host specialization and ensuing diversification. Our general understanding of the evolution of host specialization in brood parasites is compromised by a restricted focus on bird and insect lineages. The cuckoo catfish (Synodontis multipunctatus) is an obligate parasite of parental care of mouthbrooding cichlids in Lake Tanganyika. Given the ecological and taxonomic diversity of mouthbrooding cichlids in the lake, we hypothesized the existence of sympatric host‐specific lineages in the cuckoo catfish. In a sample of 779 broods from 20 cichlid species, we found four species parasitized by cuckoo catfish (with prevalence of parasitism of 2%–18%). All parasitized cichlids were from the tribe Tropheini, maternal mouthbrooders that spawn over a substrate (rather than in open water). Phylogenetic analysis based on genomic (ddRAD sequencing) and mitochondrial (Dloop) data from cuckoo catfish embryos showed an absence of host‐specific lineages. This was corroborated by analyses of genetic structure and co‐ancestry matrix. Within host species, parasitism was not associated with any individual characteristic we recorded (parent size, water depth), but was costly as parasitized parents carried smaller clutches of their own offspring. We conclude that the cuckoo catfish is an intermediate generalist and discuss costs, benefits and constraints of host specialization in this species and brood parasites in general. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Public Law / Zeitschrift für Öffentliches Recht is the property of Verlag Oesterreich GmbH and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)