Life history and virulence are linked in the ectoparasitic salmon louse Lepeophtheirus salmonis.

Models of virulence evolution for horizontally transmitted parasites often assume that transmission rate (the probability that an infected host infects a susceptible host) and virulence (the increase in host mortality due to infection) are positively correlated, because higher rates of production of propagules may cause more damages to the host. However, empirical support for this assumption is scant and limited to microparasites. To fill this gap, we explored the relationships between parasite life history and virulence in the salmon louse, Lepeophtheirus salmonis, a horizontally transmitted copepod ectoparasite on Atlantic salmon Salmo salar. In the laboratory, we infected juvenile salmon hosts with equal doses of infective L. salmonis larvae and monitored parasite age at first reproduction, parasite fecundity, area of damage caused on the skin of the host, and host weight and length gain. We found that earlier onset of parasite reproduction was associated with higher parasite fecundity. Moreover, higher parasite fecundity (a proxy for transmission rate, as infection probability increases with higher numbers of parasite larvae released to the water) was associated with lower host weight gain (correlated with lower survival in juvenile salmon), supporting the presence of a virulence-transmission trade-off. Our results are relevant in the context of increasing intensive farming, where frequent anti-parasite drug use and increased host density may have selected for faster production of parasite transmission stages, via earlier reproduction and increased early fecundity. Our study highlights that salmon lice, therefore, are a good model for studying how human activity may affect the evolution of parasite virulence.

Monogenean parasites of introduced pumpkinseed Lepomis gibbosus (Centrarchidae) in the Danube River Basin.

The pumpkinseed, Lepomis gibbosus, a centrarchid fish native to eastern North America, was introduced into Europe at the end of the 19th century. Lepomis gibbosus now represents one of the most successful of introduced fish species, having spread widely throughout many European countries. In this study, we collected monogenean parasites of L. gibbosus from four sites in the Danube River Basin. We recorded four monogenean species: Gyrodactylus sp., probably acquired in the area of introduction, and Onchocleidus similis, O. dispar and Actinocleidus recurvatus, species introduced together with their host. Onchocleidus similis dominated the parasite community at all sampling sites. Actinocleidus recurvatus has only been reported from southern Europe to date and, therefore, this is the first report of A. recurvatus from Central Europe and the Danube River Basin. We observed high morphological variability in both anchor pairs of A. recurvatus. Only in O. similis was there a positive correlation observed between haptor metric traits and fish host length. Differences in metric traits between native and introduced O. similis populations may reflect a difference in fish host size, the introduced fish host achieving a smaller size than fish from native populations. A detailed analysis of microhabitat distribution indicated a preference for the second gill arch for both dominant species O. similis and A. recurvatus, with dissimilar site segregation.

Sexual selection for male dominance reduces opportunities for female mate choice in the European bitterling (Rhodeus sericeus).

Sexual selection involves two main mechanisms: intrasexual competition for mates and intersexual mate choice. We experimentally separated intrasexual (male-male interference competition) and intersexual (female choice) components of sexual selection in a freshwater fish, the European bitterling (Rhodeus sericeus). We compared the roles of multiple morphological and behavioural traits in male success in both components of sexual competition, and their relation to male reproductive success, measured as paternity of offspring. Body size was important for both female choice and male-male competition, though females also preferred males that courted more vigorously. However, dominant males often monopolized females regardless of female preference. Subordinate males were not excluded from reproduction and sired some offspring, possibly through sneaked ejaculations. Male dominance and a greater intensity of carotenoid-based red colouration in their iris were the best predictors of male reproductive success. The extent of red iris colouration and parasite load did not have significant effects on female choice, male dominance or male reproductive success. No effect of parasite load on the expression of red eye colouration was detected, though this may have been due to low parasite prevalence in males overall. In conclusion, we showed that even though larger body size was favoured in both intersexual and intrasexual selection, male-male interference competition reduced opportunities for female choice. Females, despite being choosy, had limited control over the paternity of their offspring. Our study highlights the need for reliable measures of male reproductive success in studies of sexual selection.

Seasonal occurrence and metrical variability of Gyrodactylus rhodei Zitnan 1964 (Monogenea, Gyrodactylidae).

The seasonal dynamics of Gyrodactylus rhodei, a monogenean ectoparasite of bitterling (Rhodeus sericeus), was studied from June 2000 to May 2001 in the Kyjovka River, Czech Republic. A negative relationship between prevalence and intensity of infection of G. rhodei and water temperature was found. Metrical variability of the hard parts of the parasite haptor was studied throughout the sampling season. A negative relationship between water temperature and the size of the hard parts of the G. rhodei haptor was evident in the measurements of the total length of the marginal hooks, the sickle length of marginal hooks, anchors, anchor point and root, the width of the ventral bar and the membrane processes. Sequences of the partial ITS (rDNA) of specimens collected during the cold and warm seasons were analysed. Sequences of all studied parasite specimens were identical and there was no evidence of intraspecific variability in the sequenced region.

[Basal energy expenditure in smokers and non-smokers with Crohn's disease]. / Základní energetický výdej u kuráku a nekuráku s Crohnovou chorobou.

BACKGROUND: Crohn's disease (CD) is associated with smoking and ulcerative colitis with non-smokers. The aim of study was to compare resting energy status of smokers is worse when compared with non-smokers. The aim of the study was to compare resting energy expenditure (REE) in smokers and non-smokers with CD. METHODS AND RESULTS: REE was measured in the morning in 18 fasting patients with CD (11 non-smokers, 7 smokers) using a metabolic cart (Deltatrac Datex) in a canopy system. In smokers REE was measured before and 30 minutes after having smoked one cigarette, in non-smokers before and 30 minutes after light physical activity. The results were expressed in per cent of the expected values calculated from Harris-Benedict formula (%HB). In CD REE was significantly higher in smokers when compared with non-smokers (mean +/- S.E.M.: 113.3 +/- 12.7 vs 103.1 +/- 10.2; p < 0.03; t-test). The increase of the second measurement was not significant both in smokers (115.4 +/- 9.4) and non-smokers (105.4 +/- 10.3). In 15 CD patients substrate utilization was also estimated from indirect calorimetry and urea production. There was a higher rate of glycides (mean +/- S.E.M.: 185.9 +/- 81.9 gm/min) and a lower rate of protein oxidation (22.7 +/- 15.5) in smokers when compared with non-smokers (glycides: 141.6 +/- 78.0, NS; proteins: 41.8 +/- 36.7, NS). There was no significant difference between smokers and non-smokers with CD in lipids oxidation (33.7 +/- 19.5 vs 32.9 +/- 22.3). CONCLUSIONS: A significantly higher REE was found in smokers with CD when compared with non-smokers with CD. Differences in substrate utilization were not significant. Our results support a recommendation for CD patients to be non-smokers.