Background Parasites can alter host and vector phenotype and thereby affect ecological processes in natural populations. Laboratory studies have suggested that Borrelia burgdorferi sensu lato, the causative agent of human Lyme borreliosis, may induce physiological and behavioural alterations in its main tick vector in Europe, Ixodes ricinus , which increase the tick’s mobility and survival under challenging conditions. These phenotypic alterations may allow I. ricinus to colonise marginal habitats (‘facilitation hypothesis’), thereby fuelling the ongoing range expansion of I. ricinus towards higher elevations and latitudes induced by climate change. To explore the potential for such an effect under natural conditions, we studied the prevalence of B. burgdorferi s.l. in questing I. ricinus and its variation with elevation in the Swiss Alps. Results We screened for B. burgdorferi s.l. infection in questing nymphs of I. ricinus (N = 411) from 15 sites between 528 and 1774 m.a.s.l to test if B. burgdorferi s.l. prevalence is higher at high elevations (i.e. in marginal habitats). Opposite of what is predicted under the facilitation hypothesis, we found that B. burgdorferi s.l. prevalence in I. ricinus nymphs decreased with increasing elevation and that Borrelia prevalence was 12.6% lower in I. ricinus nymphs collected at the range margin compared to nymphs in the core range. But there was no association between Borrelia prevalence and elevation within the core range of I. ricinus . Therefore the observed pattern was more consistent with a sudden decrease in Borrelia prevalence above a certain elevation, rather than a gradual decline with increasing elevation across the entire tick range. Conclusions In conclusion, we found no evidence that B. burgdorferi s.l.-induced alterations of I. ricinus phenotype observed in laboratory studies facilitate the colonisation of marginal habitats in the wild. Rather, ticks in marginal habitats are substantially less likely to harbour the pathogen. These findings have implications for a better understanding of eco-evolutionary processes in natural host-parasite systems, as well as the assessment of Lyme borreliosis risk in regions where I. ricinus is newly emerging.

Frequent users of emergency departments (FUEDs) (≥5 ED visits/year) represent a vulnerable population with complex needs accounting for a significant number of emergency department (ED) consultations, thus contributing to EDs overcrowding. Research exploring ED staff perceptions of FUEDs is scarce. The current study aimed to evaluate in ED staff a) the extent to which FUEDs are perceived as an issue; b) their perceived levels of knowledge and understanding of FUEDs; c) levels of perceived usefulness of case management (CM) and interest in implementing this intervention in their ED service. Head physicians of the EDs at all public hospitals in Switzerland (of various level of specialization) were sent a 19-item web-based survey, pilot tested prior to its dissemination. The head physicians were asked to forward the survey to ED staff members from different health professional backgrounds. The hospital response rate was 81% (85/106). The exploitable hospital response rate was 71% (75/106 hospitals) including 208 responding health professionals. Issues and difficulties around FUEDs were perceived as important by 64% of respondents. The perceived frequency of being confronted with FUEDs was higher among nurses in more specialized EDs. In total, 64% of respondents felt poorly informed about FUEDs, nurses feeling less informed than physicians. The understanding of FUEDs was lower in the French-Italian-speaking parts (FISP) of Switzerland than in the German-speaking part. Eighty-one percent of respondents had no precise knowledge of FUED-related interventions. The perceived usefulness of CM interventions after receiving explanations about it was high (92%). However, the overall level of interest for CM implementation was 59%. The interest in CM by physicians was low across all regions and ED categories. Nurses, on the other hand, showed more interest, especially those in EDs of high specialization. The majority of ED staff reported being confronted with FUEDs on a regular basis. Staff perceived FUEDs as a vulnerable population, yet, they felt poorly informed about how to manage the issue. The majority of ED staff thought a CM intervention would be useful for FUEDs, however there appears to be a gap in their desire or willingness to implement such interventions.

Frequent users of emergency departments (FUED; ≥ 5 ED visits/year) commonly cumulate medical, social, and substance use problems requiring complex and sustained care coordination often unavailable in ED. This study aimed to explore ED healthcare providers’ challenges related to FUED care to gain insight into the support and resources required to address FUED complex needs. An online survey was sent to all general adult emergency services within Switzerland (N = 106). Participants were asked to indicate the extent to which they perceived that FUED represented a problem and to describe the main challenges encountered. In total, 208 physicians and nurses from 75 EDs (70.7%) completed the survey. Among the 208 participants, 134 (64%) reported that FUED represented a challenge and 133 described 1 to 5 challenges encountered. A conventional content analysis yielded 4 main categories of perceived challenges. Negative consequences in the ED secondary to FUED’s presence (eg, ED overcrowding, staff helplessness, and fatigue) was the most frequently reported challenge, followed by challenges related to FUEDs’ characteristics (eg, mental health and social problems) leading to healthcare complexity. The third most frequently encountered challenge was related to the ED inappropriateness and inefficiency to address FUEDs’ needs. Finally, challenges related to the lack of FUED healthcare network were the least often mentioned. ED healthcare providers experience a wide range of challenges related to FUED care. These findings suggest that currently EDs nor their staff are equipped to address FUEDs’ complex needs.

Environmental conditions change rapidly along elevational gradients and have been found to affect community composition in macroscopic taxa, with lower diversity typically observed at higher elevations. In contrast, microbial community responses to elevation are still poorly understood. Specifically, the effects of elevation on vector-associated microbiota have not been studied to date, even though the within-vector microbial community is known to influence vector competence for a range of zoonotic pathogens. Here we characterize the structure and diversity of the bacterial microbiota in an important zoonotic disease vector, the sheep tick Ixodes ricinus, along replicated elevational gradient (630–1673 m) in the Swiss Alps. 16S rRNA sequencing of the whole within-tick bacterial microbiota of questing nymphs and adults revealed a decrease in Faith’s phylogenetic microbial alpha diversity with increasing elevation, while beta diversity analyses revealed a lower variation in microbial community composition at higher elevations. We also found a higher microbial diversity later in the season and significant differences in microbial diversity among tick life stages and sexes, with lowest microbial alpha diversity observed in adult females. No associations between tick genetic diversity and bacterial diversity were observed. Our study demonstrates systematic changes in tick bacterial microbiota diversity along elevational gradients. The observed patterns mirror diversity changes along elevational gradients typically observed in macroscopic taxa, and they highlight the key role of environmental factors in shaping within-host microbial communities in ectotherms.

(a) Objective This study aimed to identify trajectories of alcohol use (AU) and their associations with the development of alcohol use disorder (AUD) among young men with different weekly drinking patterns. (b) Method A longitudinal latent class analysis integrating several aspects of AU, such as drinking quantity and frequency on weekends vs workweek days, involving 4719 young Swiss men at ages 20, 21, and 25, and collected by the Cohort Study on Substance Use Risk Factors, was used to identify different AU trajectories over time. The development of AUD scores in these trajectories was investigated using generalized linear mixed models. (c) Results Six AU trajectory classes, similar to those described in the literature, were identified: 'abstainers-light drinkers', 'light workweek increasers', 'light decreasers', 'moderate weekend decreasers', 'moderate workweek increasers', and 'heavy drinkers'. Only 12% of participants were assigned to a trajectory class with decreasing AU associated with a decline in their AUD score. AUD scores increased in trajectory classes exhibiting increasing AU on workweek days, despite low and moderate general AU. Finally, more than 59% of participants were on an AU trajectory presenting no change in their mean AUD score over time. (d) Conclusions Maturing out of problematic AU in emerging adulthood is not the norm in Switzerland, and the AUD score developed in late adolescence remains until at least emerging adulthood. AU on workweek days is a more practical marker of potentially problematic AU. This calls for timely interventions in adolescence and concerning regular drinking on workweek days in emerging adulthood.

Background Alcohol use disorder (AUD) is known to co-occur with other addictions, as well as with mental health problems. However, the effects of other addictions co-occurring with AUD on mental health problems were rarely studied and not considering them may bias estimates of the association between AUD and mental health problems. This study investigated which role co-occurring addictions play for the cross-sectional associations between self-reported AUD and mental health problems. Method Participants were 5516 young Swiss men (73.0% of those that gave written informed consent) who completed a self-report questionnaire. Using short screening questionnaires, we assessed three substance use disorders (alcohol, cannabis and tobacco), seven behavioural addictions (internet, gaming, smartphone, internet sex, gambling, work, exercise) and four mental health problems (major depression, bipolar disorder, attention deficit hyperactivity disorder (ADHD) and social anxiety disorder). Differences in the proportions of mental health problems were tested using logistic regressions between (1) participants with no AUD and AUD, (2) participants with no AUD and AUD alone and (3) participants with no AUD and AUD plus at least one co-occurring addiction. Results Overall, (1) participants with AUD had higher proportions of major depression (Odds ratio (OR [95% confidence interval]) = 3.51 [2.73, 4.52]; ADHD (OR = 3.12 [2.41, 4.03]); bipolar disorder (OR = 4.94 [3.38, 7.21]) and social anxiety (OR = 2.21 [1.79, 2.73])) compared to participants with no AUD. Considering only participants with AUD alone compared to participants with no AUD (2), differences in proportions were no longer significant for major depression (OR = 0.83 [0.42, 1.64]), bipolar disorder (OR = 1.69 [0.67, 4.22]), social anxiety (OR = 1.15 [0.77, 1.73]) and ADHD (OR = 1.65 [1.00, 2.72]) compared to participants with no AUD. In contrast, (3) proportions of mental health problems were considerably higher for participants with AUD plus at least one other addiction when compared to participants with no AUD, with OR's ranging from 2.90 [2.27, 3.70] for social anxiety, 4.03 [3.02, 5.38] for ADHD, 5.29 [4.02, 6.97] for major depression to 6.64 [4.44, 9.94] for bipolar disorder. Conclusions AUD was associated with all four measured mental health problems. However, these associations were mainly due to the high proportions of these mental health problems in participants with AUD plus at least one co-occurring addiction and only to a lesser degree due to participants with AUD alone (i.e. without any other co-occurring addictions). Hence, estimates of the association between AUD and mental health problems that do not consider other addictions may be biased (i.e. overestimated). These findings imply that considering addictions co-occurring with AUD, including behavioural addictions, is important when investigating associations between AUD and mental health problems, and for the treatment of AUD and co-morbid disorders.

Abstract Background Frequent users of emergency department (FUEDs; ≥ 5 ED visits/ year) are often vulnerable individuals cumulating medical, social and substance use problems. FUEDs often require complex and sustained care coordination generally unavailable in ED and are commonly considered contributing to ED crowding. In view of supporting ED health-care providers through specific training and interventions tailored to FUEDs, this study aimed to explore ED healthcare providers’ perceptions of difficulties related to FUEDs. Methods Participants (N = 208) were ED healthcare providers (i.e., nurses, physicians) from 75 university and community hospitals in Switzerland (71% of all EDs) who answered a questionnaire on FUEDs. They were asked to indicate the extent to which FUEDs represent a problem in their ED. Perceived difficulties related to FUEDs were elicited by an open-ended question. Conventional content analysis was used to extract common categories and themes. Results Among the 208 participants, 134 (64%) reported that FUEDs represent a problem. Of those, 132 provided 1 to 5 answers to the open-ended question. Twenty-eight categories were identified and organized in 4 themes. First, participants reported difficulties related to FUEDs’ characteristics themselves (e.g., problem’s chronicity; behavioural difficulties) leading to healthcare complexity. Second, participants perceived negative consequences related to the presence of FUEDs in the ED (e.g., work overload, staff helplessness and fatigue). Third, ED healthcare offer was considered inappropriate and inefficient to respond to FUEDs needs and fourth collaborating with FUEDs’ existing healthcare network was perceived as difficult. Conclusions ED healthcare providers experience a wide range of difficulties related to the management of FUEDs. Providing training and implementing a case management intervention tailored to FUEDs might support ED health-care providers and contribute to address FUEDs’ complex needs. Key messages ED healthcare providers perceive FUEDs to represent a problem. Perceived difficulties might decrease through training and case management support might contribute to better address FUEDs complex needs.

Even though the idea that modes of speciation other than allopatric speciation are possible in nature is now widespread, compelling examples of ecological speciation in sympatry remain rare. We studied an undescribed radiation of haplochromine cichlids in a young crater lake in western Uganda, and in the small river that is nearby but has currently no known surface connection to the lake. We describe two different modes of speciation that occurred in this cichlid lineage within the past 1,500–10,000 years. Not constrained by gene flow, allopatric divergence between river and lake cichlids affects many different morphological traits as well as nuptial colouration—muted in the river, but intensified and polymorphic in lake cichlids—and neutral genetic differentiation. More surprisingly, we demonstrate a case for sympatric speciation within the small lake that is associated with dramatic differences in male breeding colouration (yellow with bright red-chest versus bright blue) and subtle differences in microhabitat, feeding regime and morphology. Reproductive isolation by assortative mating is suggested by significant differentiation between yellow and blue males in neutral markers of gene flow despite complete sympatry. We hypothesize speciation is mediated by divergent selection on sexual signalling between microhabitats.

OBJECTIVE:The Protective Behavioral Strategies Scale (PBSS-20) is one of the most commonly used measures of engagement in protective behavioral strategies (PBS). This research aimed to examine the psychometric properties of a French and German version of the PBSS-20 in a large sample of young males in Switzerland.METHOD:The sample included 5,017 young males (mean age = 25.44) participating in the Cohort Study on Substance Use Risk Factors in Switzerland. Measures of PBS use, total drinks per week, and alcohol-related consequences were used from a second follow-up assessment.RESULTS:Confirmatory factor analysis testing different models previously documented in the literature provided initial support for a four-factor model. Fit statistics indicated that this model adequately reflects the structure of data. Further findings also provided support for adequate internal consistency and for convergent validity of this four-factor model, whereas metric-but not scalar-measurement invariance across linguistic regions was demonstrated.CONCLUSION:Although further research testing measurement invariance across linguistic regions and gender is warranted, results of the current study suggest that the French and German PBSS-20 is reliable and that it may represent a promising research and clinical tool that can be used in both French- and German-speaking countries.

Abstract Background Frequent users of emergency departments (FUED; 5 ED visits during the preceding 12 months) account for a disproportionate part of ED visits, causing a wide range of work difficulties to ED staff potentially leading to FUED discrimination. Whereas case management (CM) tailored to FUED leads to a reduction in ED visits, CM impact on ED staff has not been explored yet. This study aimed to compare ED staff perceptions of FUED with and without dedicated CM support. Methods Participants (N = 253) were ED staff (81 physicians; 172 nurses/assistant nurses) of two Swiss university hospitals, one with CM and one without CM support. Perceptions regarding FUED (i.e., knowledge and awareness of the issue extent; related work difficulties; FUEDs’ legitimate use of ED resources) were measured with a 25-item online survey (4 to 10-level Likert scales). Multivariable regression analyses were conducted to 1) explore the associations between CM implementation and FUED perceptions, and 2) test the moderating effect of profession (physician or nurse/nurse assistant) on these associations. All analyses were adjusted by gender and years of practical experience. Results Physicians with CM considered FUED as a less important problem (=.375, R2=.11, p <.05) and rated their knowledge of FUED issue higher (=.245, R2=.077, p <.05) compared to those without CM. In contrast, nurses without CM perceived fewer FUED-related work difficulties (i.e., feeling of failure and helplessness) than nurses with CM. (=-1.01, R2=.06, p <.05) No significant difference was found regarding ED staff’s perceptions of FUEDs’ legitimate use of ED resources and frequentation, nor on nurses’ knowledge of the issue. Conclusions These results suggest that CM intervention for FUED is a potential source of support for ED physicians working with FUED. Further qualitative research is needed to explore why nurses without CM support reported feeling less failure and helplessness regarding FUED. Key messages By highlighting a different impact of CM on nurses’ perception, this study illustrates where CM intervention might be improved. This study supports CM as a promising intervention for FUED by potentially having a positive impact on ED physicians’ perception besides the one previously proved on FUEDs’ number of visits and QOL.

Background: Non-medical use of prescription drugs (NMUPD) is an increasing phenomenon associated with physical and psychological consequences. This study investigated the effects of distinct forms of stress on NMUPD. Methods: Data from 5308 young adult men from the Swiss cohort study on substance use risk factors (C-SURF) were analysed regarding NMUPD of sleeping pills, tranquilizers, opioid analgesics, psychostimulants, and antidepressants. Various forms of stress (discrete, potentially traumatic events, recent and long-lasting social-environmental stressors) during the period preceding the NMUPD assessment were measured. Backward log-binomial regression was performed and risk ratios (RR) were calculated. Results: NMUPD was significantly associated with the cumulative number of potentially traumatic events (e.g. for opioid analgesics, RR = 1.92, p < .001), with problems within the family (e.g. for sleeping pills, RR = 2.45, p < .001), and the peer group (e.g. for tranquilizer use, RR = 2.34, p < .01). Factors describing family functioning in childhood showed very few significant associations. Sexual assault by acquaintances was associated only with use of sleeping pills (RR = 2.91, p p

Parasites can alter host and vector phenotype and thereby affect ecological processes in natural populations. Laboratory studies have shown that Borrelia burgdorferi sensu lato, the causative agent of human Lyme borreliosis, induces physiological alterations in its main tick vector in Europe, Ixodes ricinus , which increase its survival under challenging conditions. We hypothesise that these phenotypic alterations may allow I. ricinus to colonise marginal habitats, thereby fuelling the ongoing range expansion of I. ricinus towards higher elevations and latitudes induced by climate change. To explore the potential for such an effect under natural conditions, we studied the prevalence of B. burgdorferi s.l. in questing I. ricinus and its variation with elevation in the Swiss Alps. We screened for B. burgdorferi s.l. infection in questing nymphs of I. ricinus (N = 411) from 15 sites between 528 and 1774 m.a.s.l to test if B. burgdorferi s.l. prevalence is higher at high elevations (i.e. in marginal habitats). We found that B. burgdorferi s.l. prevalence in I. ricinus nymphs decreased linearly with increasing elevation and that it was 12.6% lower in I. ricinus nymphs collected at high elevations compared to nymphs in the core range. Thus, we found no evidence that the B. burgdorferi s.l.-induced alterations of I. ricinus phenotype facilitate the colonisation of marginal habitats in the wild. These findings have implications for a better understanding of eco-evolutionary processes in natural host-parasite systems, as well as the assessment of Lyme borreliosis risk in regions where I. ricinus is newly emerging.

AbstractParasites can alter host and vector phenotype and thereby affect ecological processes in natural populations. Laboratory studies have shown thatBorrelia burgdorferisensu lato, the causative agent of human Lyme borreliosis, induces physiological alterations in its main tick vector in Europe,Ixodes ricinus, which increase its survival under challenging conditions. We hypothesise that these phenotypic alterations may allowI. ricinusto colonise marginal habitats, thereby fuelling the ongoing range expansion ofI. ricinustowards higher elevations and latitudes induced by climate change. To explore the potential for such an effect under natural conditions, we studied the prevalence ofB. burgdorferis.l. in questingI. ricinusand its variation with elevation in the Swiss Alps. We screened forB. burgdorferis.l. infection in questing nymphs ofI. ricinus(N = 411) from 15 sites between 528 and 1774 m.a.s.l to test ifB. burgdorferis.l. prevalence is higher at high elevations (i.e. in marginal habitats). We found thatB. burgdorferis.l. prevalence inI. ricinusnymphs decreased linearly with increasing elevation and that it was 12.6% lower inI. ricinusnymphs collected at high elevations compared to nymphs in the core range. Thus, we found no evidence that theB. burgdorferis.l.-induced alterations ofI. ricinusphenotype facilitate the colonisation of marginal habitats in the wild. These findings have implications for a better understanding of eco-evolutionary processes in natural host-parasite systems, as well as the assessment of Lyme borreliosis risk in regions whereI. ricinusis newly emerging.

Spatial variation in pathogen-mediated selection is predicted to influence the evolutionary trajectory of host populations and lead to spatial variation in their immunogenetic composition. However, to date few studies have been able to directly link small-scale spatial variation in infection risk to host immune gene evolution in natural, nonhuman populations. Here, we use a natural rodent-Borrelia system to test for associations between landscape-level spatial variation in Borrelia infection risk along replicated elevational gradients in the Swiss Alps and Toll-like receptor 2 (TLR2) evolution, a candidate gene for Borrelia resistance, across bank vole (Myodes glareolus) populations. We found that Borrelia infection risk (i.e., the product of Borrelia prevalence in questing ticks and the average tick load of voles at a sampling site) was spatially variable and significantly negatively associated with elevation. Across sampling sites, Borrelia prevalence in bank voles was significantly positively associated with Borrelia infection risk along the elevational clines. We observed a significant association between naturally occurring TLR2 polymorphisms in hosts and their Borrelia infection status. The TLR2 variant associated with a reduced likelihood of Borrelia infection was most common in rodent populations at lower elevations that face a high Borrelia infection risk, and its frequency changed in accordance with the change in Borrelia infection risk along the elevational clines. These results suggest that small-scale spatial variation in parasite-mediated selection affects the immunogenetic composition of natural host populations, providing a striking example that the microbial environment shapes the evolution of the host's immune system in the wild.

Global environmental change has negative impacts on ecological systems, impacting the stable provision of functions, goods, and services. Whereas effects of individual environmental changes (e.g. temperature change or change in resource availability) are reasonably well understood, we lack information about if and how multiple changes interact. We examined interactions among fourtypes of environmental disturbance (temperature, nutrient ratio, carbon enrichment, and light) in a fully factorial design using a microbial aquatic ecosystem and observed responses of dissolved oxygen saturation at three temporal scales (resistance, resilience, and return time). We tested whether multiple disturbances combine in a dominant, additive, or interactive fashion, and compared the predictability of dissolved oxygen across scales. Carbon enrichment and shading reduced oxygen concentration in the short term (i.e. resistance); although no other effects or interactions were statistically significant, resistance decreased as the number of disturbances increased. In the medium term, only enrichment accelerated recovery, but none of the other effects (including interactions) were significant. In the long term, enrichment and shading lengthened return times, and we found significant two-way synergistic interactions between disturbances. The best performing model (dominant, additive, or interactive) depended on the temporal scale of response. In the short term (i.e. for resistance), the dominance model predicted resistance of dissolved oxygen best, due to a large effect of carbon enrichment, whereas none of the models could predict the medium term (i.e. resilience). The long-term response was best predicted by models including interactions among disturbances. Our results indicate the importance of accounting for the temporal scale of responses when researching the effects of environmental disturbances on ecosystems.

Gene flow is usually thought to reduce genetic divergence and impede local adaptation by homogenising gene pools between populations. However, evidence for local adaptation and phenotypic differentiation in highly mobile species, experiencing high levels of gene flow, is emerging. Assessing population genetic structure at different spatial scales is thus a crucial step towards understanding mechanisms underlying intraspecific differentiation and diversification. Here, we studied the population genetic structure of a highly mobile species – the great tit Parus major – at different spatial scales. We analysed 884 individuals from 30 sites across Europe including 10 close-by sites (< 50 km), using 22 microsatellite markers. Overall we found a low but significant genetic differentiation among sites (FST = 0.008). Genetic differentiation was higher, and genetic diversity lower, in south-western Europe. These regional differences were statistically best explained by winter temperature. Overall, our results suggest that great tits form a single patchy metapopulation across Europe, in which genetic differentiation is independent of geographical distance and gene flow may be regulated by environmental factors via movements related to winter severity. This might have important implications for the evolutionary trajectories of sub-populations, especially in the context of climate change, and calls for future investigations of local differences in costs and benefits of philopatry at large scales.

Glacial phases during the Pleistocene caused remarkable changes in species range distributions, with inevitable genetic consequences. Specifically, during interglacial phases, when the ice melted and new habitats became suitable again, species could recolonize regions that were previously covered by ice, such as high latitudes and elevations. Based on theoretical models and empirical data, a decrease in genetic variation is predicted along recolonization routes as a result of the consecutive founder effects that characterize the recolonization process. In the present study, we assessed the relative importance of historical and contemporary processes in shaping genetic diversity and differentiation of bank vole (Myodes glareolus) populations at different elevations in the Swiss Alps. By contrast to expectations, we found that genetic variation increased with elevation. Estimates of recent migration rates and a contrasting pattern of genetic differentiation observed at the mitochondrial cytochrome b gene and nuclear microsatellites support the hypothesis that higher genetic diversity at high elevation results from contemporary gene flow. Although historical recolonization processes can have marked effects on the genetic structure of populations, the present study provides an example where contemporary processes along an environmental gradient can reverse predicted patterns of genetic variation.

Although rapid phenotypic evolution during range expansion associated with colonization of contrasting habitats has been documented in several taxa, the evolutionary mechanisms that underlie such phenotypic divergence have less often been investigated. A strong candidate for rapid ecotype formation within an invaded range is the three-spine stickleback in the Lake Geneva region of central Europe. Since its introduction only about 140 years ago, it has undergone a significant expansion of its range and its niche, now forming phenotypically differentiated parapatric ecotypes that occupy either the pelagic zone of the large lake or small inlet streams, respectively. By comparing museum collections from different times with contemporary population samples, we here reconstruct the evolution of parapatric phenotypic divergence through time. Using genetic data from modern samples, we infer the underlying invasion history. We find that parapatric habitat-dependent phenotypic divergence between the lake and stream was already present in the first half of the twentieth century, but the magnitude of differentiation increased through time, particularly in antipredator defence traits. This suggests that divergent selection between the habitats occurred and was stable through much of the time since colonization. Recently, increased phenotypic differentiation in antipredator defence traits likely results from habitat-dependent selection on alleles that arrived through introgression from a distantly related lineage from outside the Lake Geneva region. This illustrates how hybridization can quickly promote phenotypic divergence in a system where adaptation from standing genetic variation was constrained.

Host condition can influence both the nutritive resources available to parasites and the strength of host defences. Since these factors are likely to be correlated, it is unclear whether parasites would be more successful on hosts in good, intermediate or poor conditions. For more complex parasites, like fleas, where larvae depend on adults to extract and make available some essential host resources, host condition can act at two levels. First, it can affect the investment of females into eggs, and second, it can influence offspring growth. In a two-step experiment, we first let female hen fleas Ceratophyllus gallinae feed on nestlings of reduced, control or enlarged great tit Parus major broods and secondly used the blood from these nestlings as a food source for flea larvae reared in the laboratory. We then assessed the effect of brood size manipulation on reproductive investment and survival of female fleas, and on survival, developmental time, mass and size of pre-imago larvae and adults of the first generation. Although host condition, measured as body mass controlled for body size, was significantly influenced by brood size manipulation, it did not affect the female fleas' reproductive investment and survival. Larvae fed with blood from nestlings of reduced broods lived longer, however, than larvae fed on blood from enlarged or control broods. Additionally, F1 adults grew shorter tibiae when their mother had fed on hosts of reduced broods. The finding that brood size manipulation influenced parasite reproduction suggests that it affected nutritive resources and/or host defence, but the precise mechanism or balance between the two requires further investigation.

The Cape Verdean islands form a distinct aquatic freshwater ecoregion characterized mainly by temporal water bodies with an adapted invertebrate community. Freshwater fish were not previously recorded from the archipelago. During a non-exhaustive survey of freshwater bodies on five islands of the archipelago, the first presence of a freshwater fish was recorded. Using barcoding sequences, the species was identified as the guppy (Poecilia reticulata), a highly invasive species alien to the Cape Verdean Islands.