Blood parasites shape extreme major histocompatibility complex diversity in a migratory passerine

Pathogens are one of the main forces driving the evolution and maintenance of the highly polymorphic genes of the vertebrate major histocompatibility complex (MHC). Although MHC proteins are crucial in pathogen recognition, it is still poorly understood how pathogen‐mediated selection promotes and maintains MHC diversity, and especially so in host species with highly duplicated MHC genes. Sedge warblers (Acrocephalus schoenobaenus) have highly duplicated MHC genes, and using data from high‐throughput MHC genotyping, we were able to investigate to what extent avian malaria parasites explain temporal MHC class I supertype fluctuations in a long‐term study population. We investigated infection status and infection intensities of two different strains of Haemoproteus, that is avian malaria parasites that are known to have significant fitness consequences in sedge warblers. We found that prevalence of avian malaria in carriers of specific MHC class I supertypes was a significant predictor of their frequency changes between years. This finding suggests that avian malaria infections partly drive the temporal fluctuations of the MHC class I supertypes. Furthermore, we found that individuals with a large number of different supertypes had higher resistance to avian malaria, but there was no evidence for an optimal MHC class I diversity. Thus, the two studied malaria parasite strains appear to select for a high MHC class I supertype diversity. Such selection may explain the maintenance of the extremely high number of MHC class I gene copies in sedge warblers and possibly also in other passerines where avian malaria is a common disease.     

Indoor mites and forensic acarology

House dust mites (HDM) have been shown to produce allergens causing atopic allergies in human beings, known in medicine as house-dust-mite allergy or atopy. Over the past 25 years (1981–2006) a survey of dust samples from different places was made in the southern part of Poland, to determine the diversity of indoor acarofauna. In total, 1,532 samples were taken from dwellings, hospitals, libraries, research laboratories, drug-stores, and offices and other workplaces. More than 30 mite species were found of which the most abundant and common were HDM, especially Dermatophagoides farinae. Highest mite densities (g^?1 dust) were noted in dwellings. This survey revealed differences in the occurrence and prevalence of various species of domestic mites between and within (dwellings in) geographical areas. This knowledge may be useful in the field of forensic medicine.     

Variation in hostplant preference and performance by the milfoil weevil, Euhrychiopsis lecontei Dietz, exposed to native and exotic watermilfoils

Exotic plants often displace native plants and thus alter the availability of native hostplants for specialist herbivorous insects. The submersed aquatic weevil Euhrychiopsis lecontei Dietz is endemic to North America, but there are now source populations on the exotic Eurasian watermilfoil (Myriophyllum spicatum L.) as well as on the weevil's ancestral host, northern watermilfoil (Myriophyllum sibiricum Komarov). This provides an opportunity to examine a host range expansion in progress. To further define the host range of the weevil and to determine how population source and rearing plant influence host plant preference and performance, we conducted a series of preference and rearing experiments with weevils from two source populations reared on northern milfoil, on Eurasian milfoil, switched late in larval development from northern to Eurasian milfoil, and vice versa. We also included two rearing treatments with milfoils on which the weevil has not been documented: the native M. verticillatum L. and the exotic M. aquaticum Verd. Preference by weevils in the switched rearing treatments was similar to preferences exhibited by weevils reared solely on the second (later) milfoil species and an increase in preference for Eurasian milfoil was induced by adult exposure to Eurasian milfoil for 2 weeks. In contrast, sizes and development times of weevils in the switched rearing treatments were similar to sizes and development times exhibited by weevils reared solely on the first (early) milfoil species. These results indicate that preference by the milfoil weevil is determined late in larval development or later and Hopkins' host selection principle is not supported. However, size and development time were most affected by hostplant quality during larval development when larvae must acquire the resources needed for pupation. Oviposition preference in the milfoil weevil was a population attribute, not a fixed individual attribute and there was no significant variation in preference among individuals reared on northern milfoil, but significant variation in preference was detected among weevils reared on Eurasian milfoil. Weevils oviposited on all four milfoil species and completed development on three of them, but did not develop beyond the larval stage on M. aquaticum. Weevils reared on Eurasian milfoil developed faster and reached larger adult sizes than weevils in any other rearing treatment. The smallest sizes and longest development times were for weevils reared on the natives, northern milfoil and M. verticillatum. The milfoil weevil oviposits on an array of milfoil species and is unable to distinguish an unsuitable host (M. aquaticum) within this genus. The influence of rearing plant and adult exposure to Eurasian milfoil on hostplant preference suggests that host range expansion to novel congeners may occur more rapidly than predicted by models which assume that genetic variation is required. Significant variation among individuals in hostplant preference suggests the potential for a host shift to a plant for which E. lecontei appears pre-adapted.     

Oviposition specificity and behavior of the watermilfoil specialist Euhrychiopsis lecontei

Eurasian watermilfoil (Myriophyllum spicatum L.) is a nuisance aquatic weed, exotic to North America. The freshwater weevil Euhrychiopsis lecontei (Dietz) is a potential control agent of Eurasian watermilfoil and is a fully submersed aquatic specialist herbivore. Its presumed original host is the native northern watermilfoil (Myriophyllum sibiricum Komarov). We conducted a set of oviposition experiments to reveal first and second oviposition preference of Euhrychiopsis lecontei when presented with seven macrophytes. We tested differences between source (lake) populations of weevils, differences in behavior between weevils reared on the exotic Eurasian watermilfoil and the native northern watermilfoil and between weevils in the presence and absence of their preferred hostplant. Oviposition assays confirmed that E. lecontei is a watermilfoil specialist. Out of the 207 females that laid eggs, only three oviposited on a non-watermilfoil plant, Megalodonta beckii. The weevils' degree of specificity was influenced by the watermilfoil species on which they were reared. Weevils reared on Eurasian watermilfoil tended to oviposit on Eurasian watermilfoil, spent more time on Eurasian watermilfoil than on other plants, and spent more time off plants and took longer to oviposit when Eurasian watermilfoil was removed. Weevils reared on northern watermilfoil did not exhibit a preference for either watermilfoil species in oviposition or in time allocation, although they oviposited on and spent significantly more time on watermilfoils than on other species. Rearing of the two populations on their complementary watermilfoil hostplant resulted in responses typical of the rearing plant, not the original host. These results show that although both weevil populations are watermilfoil specialists, Eurasian-reared weevils prefer Eurasian watermilfoil in general host attraction and oviposition, whereas northern-reared weevils do not. The results support the contention that E. lecontei may be a good biocontrol agent for Eurasian watermilfoil because of its high specificity. The results also suggest that the current host range expansion of the weevil to Eurasian watermilfoil has the potential to become a host shift due to the increased specificity. Herbivory in freshwater systems is not well studied, and the E. lecontei-M. spicatum relationship is a rare example of submersed freshwater specialist herbivore-host-plant interactions.     

Contrasting patterns in the invasions of European terrestrial and freshwater habitats by alien plants,insects and vertebrates

Aim To provide the first comparative overview on the current numbers of alien species that invade representative European terrestrial and freshwater habitats for a range of taxonomic groups. Location Europe. Methods Numbers of naturalized alien species of plants, insects, herptiles, birds and mammals occurring in 10 habitats defined according to the European Nature Information System (EUNIS) were obtained from 115 regional data sets. Only species introduced after ad 1500 were considered. Data were analysed by ANCOVA and regression trees to assess whether differences exist among taxonomic groups in terms of their habitat affinity, and whether the pattern of occurrence of alien species in European habitats interacts with macroecological factors such as insularity, latitude or area. Results The highest numbers of alien plant and insect species were found in human‐made, urban or cultivated habitats; if controlled for habitat area in the region, wetland and riparian habitats appeared to support relatively high numbers of alien plant species too. Invasions by vertebrates were more evenly distributed among habitats, with aquatic and riparian, woodland and cultivated land most invaded. Mires, bogs and fens, grassland, heathland and scrub were generally less invaded. Habitat and taxonomic group explained most variation in the proportions of alien species occurring in individual habitats related to the total number of alien species in a region, and the basic pattern determined by these factors was fine‐tuned by geographical variables, namely by the mainland–island contrast and latitude, and differed among taxonomic groups. Main conclusions There are two ecologically distinct groups of alien species (plants and insects versus vertebrates) with strikingly different habitat affinities. Invasions by these two contrasting groups are complementary in terms of habitat use, which makes an overall assessment of habitat invasions in Europe possible. Since numbers of naturalized species in habitats are correlated among taxa within these two groups, the data collected for one group of vertebrates, for example, could be used to estimate the habitat‐specific numbers of alien species for other vertebrate groups with reasonable precision, and the same holds true for insects and plants.