Parasitism and invasive species : an ecological study of mussel populations

The Mediterranean mussel Mytilus galloprovincialis, was introduced accidentally to South Africa and has since become invasive. One possible explanation for the success of this species is that it has been released from the effects of parasites which affect the indigenous species of mussels. The aim of this work was to examine the parasitic load of different mussel populations along the southern African coast and to assess the effects of parasites on their hosts. A survey was done to quantify the levels of parasitism in indigenous populations of Perna perna from Southern Africa and of Mytilus galloprovincialis from South Africa (where it is exotic) and Spain (where it is indigenous). This survey was carried out at three different geographic scales: small scale (metres), studying the incidence of parasites within a mussel bed; medium scale (kilometres to tens of kilometres), comparing prevalences of infection among different localities; and large scale (hundreds to thousands of kilometres), examining infection rates along the Southern African coast, as well as the coast of the Basque Country (North Spain). During this survey metazoan parasites other than trematodes were rare. Four species of trematodes were commonly found infecting the indigenous mussel Perna perna. These were metacercariae of the genus Proctoeces, bucephalid sporocysts, encysted metacercariae on the labial palps and gelatinous cysts with metacercariae inside. A detailed description of Proctoeces is given; the other parasites are described elsewhere. No parasites were found in M. galloprovincialis either in South Africa or in Spain. This thesis concentrates on the study of prevalences of Proctoeces and bucephalid sporocysts and their effects on Perna perna. Infection rates with Proctoeces are highly dependent on the sex of the host, with more females than males being infected, and are also size dependent, though only for females. Identification of the sex of mussels infected with bucephalid sporocysts is often not possible since the sporocysts spread over the gonad and replace it. Prevalence of infection with this parasite also increases with the size of the host. To study the influence of Proctoeces and bucephalid sporocysts on the ecological fitness of Perna perna, their effects on survival and competitive ability were tested. The results showed significant negative effects. Both parasites significantly depressed condition but only after spawning, when the mussels were already stressed. In order to check for effects on host survival, the effects of both parasites on mortality rates, gaping behaviour and water loss of mussels exposed to air were also examined. Neither parasite affected mortality rate or gaping behaviour of Perna perna. Proctoeces did not affect the amount of water lost by mussels, but the bucephalid sporocysts did. Mussels infected with sporocysts lost significantly more water than non-infected individuals. This increase in water loss was not related to the gaping behaviour, but a test of the strength of the adductor muscles showed that less force was needed to open mussels with bucephalid sporocysts than non-infected mussels. This was not the case for mussels infected by Proctoeces. Weaker mussels will fail to seal the valves properly, resulting in an increase of water loss on exposure to air by evaporation. Another factor that will have an obvious effect on a population is the reproductive output of the animals. Histological sections of the gonad of infected and non-infected females were cut to study the effects of both parasites on reproduction. Statistical tests comparing the numbers and sizes of oocytes in females infected with Proctoeces and non-infected females showed no significant differences. However, bucephalid sporocysts have a dramatic effect on reproduction by castrating the host, leaving no trace of sex products. One of the major factors shaping the composition of a mussel bed is competition for space and food, with smaller mussels being at a competitive disadvantage. Thus, in order to examine effects of both parasites on the competitive ability of Perna perna, summer and winter growth rates were compared for infected and non-infected mussels. Proctoeces reduced growth both in summer and in winter whilst bucephalid sporocysts had no significant effect. Both growth and reproduction are important components of the energy budget of an animal, and each is affected by either Proctoeces or the bucephalid sporocysts. In an attempt to test if Perna perna compensates energetically for these negative effects, filtration rates and oxygen consumption of mussels with and without parasites were measured. Neither parasite had a significant effect on filtration rates or oxygen consumption of the host. All these results indicate that both Proctoeces and the bucephalid sporocysts have a detrimental effect on their host, and that the mussels do not compensate for these negative effects. There is neither an increase in filtration, nor a decrease in respiration to balance the energy lost to the parasite. The two parasites studied affect the host in different but complementary ways. The effects of both parasites are concentrated on those size classes of mussel which channel most energy into the portion of the energy budget affected by the parasite. Proctoeces affects growth only in the smaller individuals, which under normal conditions would put most energy into growth; and the bucephalid sporocysts castrate the bigger mussels, which would expend most energy on reproduction. By reducing growth rates of small mussels or castrating large mussels, these parasites effectively remove them from the breeding population and reduce their competitive abilities. These negative effects, together with the high prevalence of both parasites in Perna perna along the South African coast and their absence in Mytilus galloprovincialis, suggest that parasites may be an important reason for the success of Mytilus

Parasitism, host behavior, and invasive species

Animal behavior and parasitism are inextricable linked. In many cases, host behavior can affect what parasites are encountered. In other cases, parasites can manipulate the behavior of the host in an attempt to maximize their own transmission. These long-standing interactions are now further complicated by species movement around the globe. The list of introduced species that have become invasive includes parasites that have adapted to new hosts in areas of introduction, as well as invasive hosts that alter the association between existing parasite–host assemblages. Researchers have documented differences in rates of parasitism and in the consequences of parasite infection between invasive and native hosts, and sometimes these differences are a result of behavioral differences, either pre-existing host behaviors or host behaviors that are altered as a consequence of infection. Parasites have been shown to mediate interactions between native and invasive hosts; occasionally, these parasites determine the outcome of invasions. The effects on native species can be severe, and to that end, interactions between invasive species, parasites, and behavior have ramifications for conservation biology

Effects of Endolithic Parasitism on Invasive and Indigenous Mussels in a Variable Physical Environment

Biotic stress may operate in concert with physical environmental conditions to limit or facilitate invasion processes while altering competitive interactions between invaders and native species. Here, we examine how endolithic parasitism of an invasive and an indigenous mussel species acts in synergy with abiotic conditions of the habitat. Our results show that the invasive Mytilus galloprovincialis is more infested than the native Perna perna and this difference is probably due to the greater thickness of the protective outer-layer of the shell of the indigenous species. Higher abrasion due to waves on the open coast could account for dissimilarities in degree of infestation between bays and the more wave-exposed open coast. Also micro-scale variations of light affected the level of endolithic parasitism, which was more intense at non-shaded sites. The higher levels of endolithic parasitism in Mytilus mirrored greater mortality rates attributed to parasitism in this species. Condition index, attachment strength and shell strength of both species were negatively affected by the parasites suggesting an energy trade-off between the need to repair the damaged shell and the other physiological parameters. We suggest that, because it has a lower attachment strength and a thinner shell, the invasiveness of M. galloprovincialis will be limited at sun and wave exposed locations where endolithic activity, shell scouring and risk of dislodgement are high. These results underline the crucial role of physical environment in regulating biotic stress, and how these physical-biological interactions may explain site-to-site variability of competitive balances between invasive and indigenous species

Systematic Collaborative Reanalysis of Genomic Data Improves Diagnostic Yield in Neurologic Rare Diseases

Altres ajuts: Generalitat de Catalunya, Departament de Salut; Generalitat de Catalunya, Departament d'Empresa i Coneixement i CERCA Program; Ministerio de Ciencia e Innovación; Instituto Nacional de Bioinformática; ELIXIR Implementation Studies (CNAG-CRG); Centro de Investigaciones Biomédicas en Red de Enfermedades Raras; Centro de Excelencia Severo Ochoa; European Regional Development Fund (FEDER).Many patients experiencing a rare disease remain undiagnosed even after genomic testing. Reanalysis of existing genomic data has shown to increase diagnostic yield, although there are few systematic and comprehensive reanalysis efforts that enable collaborative interpretation and future reinterpretation. The Undiagnosed Rare Disease Program of Catalonia project collated previously inconclusive good quality genomic data (panels, exomes, and genomes) and standardized phenotypic profiles from 323 families (543 individuals) with a neurologic rare disease. The data were reanalyzed systematically to identify relatedness, runs of homozygosity, consanguinity, single-nucleotide variants, insertions and deletions, and copy number variants. Data were shared and collaboratively interpreted within the consortium through a customized Genome-Phenome Analysis Platform, which also enables future data reinterpretation. Reanalysis of existing genomic data provided a diagnosis for 20.7% of the patients, including 1.8% diagnosed after the generation of additional genomic data to identify a second pathogenic heterozygous variant. Diagnostic rate was significantly higher for family-based exome/genome reanalysis compared with singleton panels. Most new diagnoses were attributable to recent gene-disease associations (50.8%), additional or improved bioinformatic analysis (19.7%), and standardized phenotyping data integrated within the Undiagnosed Rare Disease Program of Catalonia Genome-Phenome Analysis Platform functionalities (18%)

Small-scale Fisheries in South Africa: The Uneven Road from Recognition to Governance

Small-scale fishing communities in South Africa were recognised for the first time in 1998, when the Marine Living Resources Act, aimed at redressing apartheid era inequalities, was enacted. Government's primary intervention has been to issue annual individual permits, wherein Government defined the technical parameters for the fishers to operate as subsistence or as small-scale commercial fishers, dependent on the resources they harvested. These top-down driven regulations were initially accepted by the un-empowered fishers who hoped for some financial gain from possessing a legal fishing licence. Gradually, however, resistance to the categorisation of fishers into different sectors has grown among fishing communities and associated non-governmental organisations. Fishers argue that the rights allocation criteria have excluded many from their traditional activities, and that they typically employ a range of livelihood strategies, depending on resource availability and market opportunities. Evidence is given, based on research in several coastal communities, of this apparent polarisation effect between fishing practices and regulations. Fisher protests and a court challenge forced Government to redraft its small scale fishing policies in a consultative manner, the challenge being to find the balance between an economically driven, commercial rights model and an appropriate poverty reduction strategy. Whether a long-term, people centred, developmental approach will emerge remains to be seen, but it is certain that the fishers will no longer be satisfied with anything less than a more collaborative management approach and meaningful local governance over their livelihoods, derived from the harvest of a basket of nearshore marine resources

Bridging taxonomic and disciplinary divides in infectious disease

Citation: Borer, E.T., & Antonovics, J. (2011). Bridging Taxonomic and Disciplinary Divides in Infectious Disease. EcoHealth 8, 261–267. https://doi.org/10.1007/s10393-011-0718-6Pathogens traverse disciplinary and taxonomic boundaries, yet infectious disease research occurs in many separate disciplines including plant pathology, veterinary and human medicine, and ecological and evolutionary sciences. These disciplines have different traditions, goals, and terminology, creating gaps in communication. Bridging these disciplinary and taxonomic gaps promises novel insights and important synergistic advances in control of infectious disease. An approach integrated across the plant-animal divide would advance our understanding of disease by quantifying critical processes including transmission, community interactions, pathogen evolution, and complexity at multiple spatial and temporal scales. These advances require more substantial investment in basic disease research