Trematode genetic patterns at host individual and population scales provide insights about infection mechanisms.

Multiple parasites can infect a single host, creating a dynamic environment where each parasite must compete over host resources. Such interactions can cause greater harm to the host than single infections and can also have negative consequences for the parasites themselves. In their first intermediate hosts, trematodes multiply asexually and can eventually reach up to 20% of the host's biomass. In most species, it is unclear whether this biomass results from a single infection or co-infection by 2 or more infective stages (miracidia), the latter being more likely a priori in areas where prevalence of infection is high. Using as model system the trematode Bucephalus minimus and its first intermediate host cockles, we examined the genetic diversity of the cytochrome c oxidase subunit I region in B. minimus from 3 distinct geographical areas and performed a phylogeographic study of B. minimus populations along the Northeast Atlantic coast. Within localities, the high genetic variability found across trematodes infecting different individual cockles, compared to the absence of variability within the same host, suggests that infections could be generally originating from a single miracidium. On a large spatial scale, we uncovered significant population structure of B. minimus, specifically between the north and south of Bay of Biscay. Although other explanations are possible, we suggest this pattern may be driven by the population structure of the final host.

Effect of light on the trematode Himasthla elongata: from cercarial behaviour to infection success.

The cockle Cerastoderma edule, a socioeconomically important bivalve of the northeast Atlantic, is host to several trematodes, including Himasthla elongata. In the life cycle of this trematode, cercariae (free-living stages) emerge from the first intermediate host, a snail, to infect cockles as second intermediate hosts. During their lifespan (less than 2 d), cercariae must ensure successful host-to-host transmission via the surrounding water and therefore are exposed to and impacted by different environmental conditions, including abiotic factors. Given that the light:dark cycle is one of the major drivers of behaviour in aquatic habitats, we aimed to determine the influence of light on cercariae and host behaviour based on 3 hypotheses. First, by having a benthic second intermediate host, these cercariae will display a photonegative orientation; second, and conversely, host behaviour will not be influenced by light; and third, cercariae infection success will be light-dependent. Results showed that cercariae display a photopositive orientation (first hypothesis rejected), displaying movements towards light. Host activity (evaluated by oxygen consumption) was similar among conditions, i.e. dark vs. light (second hypothesis accepted), but hosts acquired more parasites when experimentally infected in the dark (third hypothesis accepted). This light-dependent infection of the host is explained by a change of cercarial behaviour when exposed to light, decreasing their infection success. This study highlights that trematode responses to external conditions may be linked to successful life cycle completion rather than being altered by the host habitat. Light influence on cercarial behaviour resulted in increased infection success that may affect trematode population dynamics and their distributional range.

Latitudinal influence on gametogenesis and host-parasite ecology in a marine bivalve model.

Reproduction and parasites have significant impacts on marine animal populations globally. This study aimed to investigate the associative effects of host reproduction and a host-parasite interplay on a marine bivalve, along a geographic gradient of latitude. Cockles Cerastoderma edule were sampled from five European sites (54°N to 40°N), between April 2018 and October 2019. A histological survey provided data on trematode (metacercaria and sporocyst life stages), prevalence, and cockle stage of gametogenesis to assess the influence of a latitudinal gradient on both interplays. Sex ratios at the northernmost sites were skewed toward females, and spawning size was reduced at the lower latitudes. Trematode infection did not follow a latitudinal gradient. Localized site-related drivers, namely seawater temperature, varied spatially, having an impact on cockle-trematode interactions. Spawning was related to elevated temperatures at all sites. Prolonged spawning occurred at southern latitudes, where seawater temperatures were warmer. Trematode prevalence and the impact of trematodes on gametogenesis were found to be spatially variable, but not latitudinally. Therefore, it is not possible to determine the likelihood of boom and bust events in cockles, based on the latitudinal location of a population. In terms of sublethal impacts, it appeared that energy was allocated to reproduction rather than somatic growth in southern populations, with less energy allocated to reproduction in the larger, northern cockles. The demonstrated spatial trend of energy allocation indicates the potential of a temporal trend of reduced cockle growth at northern sites, as a result of warming sea temperatures. This awareness of the spatially varying drivers of populations is crucial considering the potential for these drivers/inhibitors to be exacerbated in a changing marine environment.

Parental perspectives on negotiations over diet and physical activity: how do we involve parents in adolescent health interventions?

OBJECTIVE: To identify the ways in which parental involvement can be incorporated into interventions to support adolescent health behaviour change. DESIGN: Data from semi-structured interviews were analysed using inductive thematic analysis. SETTING: Southampton, Hampshire, UK. PARTICIPANTS: A convenience sample of twenty-four parents of adolescents. RESULTS: Parents consider themselves to play an important role in supporting their adolescents to make healthy choices. Parents saw themselves as gatekeepers of the household and as role models to their adolescents but recognised this could be both positive and negative in terms of health behaviours. Parents described the changing dynamics of the relationships they have with their adolescents because of increased adolescent autonomy. Parents stated that these changes altered their level of influence over adolescents' health behaviours. Parents considered it important to promote independence in their adolescents; however, many described this as challenging because they believed their adolescents were likely to make unhealthy decisions if not given guidance. Parents reported difficulty in supporting adolescents in a way that was not viewed as forceful or pressuring. CONCLUSIONS: When designing adolescent health interventions that include parental components, researchers need to be aware of the disconnect between public health recommendations and the everyday reality for adolescents and their parents. Parental involvement in adolescent interventions could be helpful but needs to be done in a manner that is acceptable to both adolescents and parents. The findings of this study may be useful to inform interventions which need to consider the transitions and negotiations which are common in homes containing adolescents.

Behaviour change interventions: getting in touch with individual differences, values and emotions.

Systematic reviews and meta-analyses suggest that behaviour change interventions have modest effect sizes, struggle to demonstrate effect in the long term and that there is high heterogeneity between studies. Such interventions take huge effort to design and run for relatively small returns in terms of changes to behaviour.So why do behaviour change interventions not work and how can we make them more effective? This article offers some ideas about what may underpin the failure of behaviour change interventions. We propose three main reasons that may explain why our current methods of conducting behaviour change interventions struggle to achieve the changes we expect: 1) our current model for testing the efficacy or effectiveness of interventions tends to a mean effect size. This ignores individual differences in response to interventions; 2) our interventions tend to assume that everyone values health in the way we do as health professionals; and 3) the great majority of our interventions focus on addressing cognitions as mechanisms of change. We appeal to people's logic and rationality rather than recognising that much of what we do and how we behave, including our health behaviours, is governed as much by how we feel and how engaged we are emotionally as it is with what we plan and intend to do.Drawing on our team's experience of developing multiple interventions to promote and support health behaviour change with a variety of populations in different global contexts, this article explores strategies with potential to address these issues.

Spatio-temporal variation of trematode parasites community in Cerastoderma edule cockles from Ria de Aveiro (Portugal).

Cerastoderma edule (edible cockle) is among the most exploited bivalves in Europe playing an important socio-economic role. Cockles live in estuaries and lagoons where their population is controlled by several environmental factors including parasitism. Parasites represent an important part of the world known biodiversity but are often neglected. Trematodes are the most prevalent macroparasites of cockles being able to exert an impact both at the individual and population levels. Therefore, it is of prime relevance to recognize and understand the parasite-host system dynamics in order to better predict potential conservation threats to bivalve populations and to maximize the success of stock and disease episodes management. Cockle monitoring was conducted in 2012 and 2016, in six and eight stations, respectively, at the Ria de Aveiro coastal lagoon, Portugal. Cockles were sampled in one single occasion in 2012 and seasonally in 2016. The tested hypothesis is that the trematode community in cockles was spatially and seasonally heterogeneous but stable over time. The main result showed that despite a relative homogeneity of the parasite community structure in cockles, the among-years heterogeneity of trematode communities was higher than among-stations and among-seasons heterogeneity rejecting the postulated hypothesis. Results demonstrated that trematode communities from the Ria de Aveiro are characterized by low abundance, which resulted in a spatial and seasonal trematode homogeneity (despite an overall channel difference and a slight downstream-upstream gradient). The interannual analysis showed a worrisome loss of trematode diversity and prevalence which consequently indicates an important loss of overall diversity and/or environmental conditions reflecting the negative effects of global change (mean temperature rise and overharvesting, among others). The present study highlighted the importance of trematodes in characterising their associated environment and respective biodiversity which might be helpful to assess ecosystem ecological status and to identify threatened areas.