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Models of host-parasite coevolution predict pronounced genetic dynamics if resistance and infectivity are genotype-specific or associated with costs, and if selection is fueled by sufficient genetic variation. We addressed these assumptions in the black bean aphid, Aphis fabae, and its parasitoid Lysiphlebus fabarum. Parasitoid genotypes differed in infectivity and host clones exhibited huge variation for susceptibility. This variation occurred at two levels. Clones harboring Hamiltonella defensa, a bacterial endosymbiont known to protect pea aphids against parasitoids, enjoyed greatly reduced susceptibility, yet clones without H. defensa also exhibited significant variation. Although there was no evidence for genotype-specificity in the H. defensa-free clones' interaction with parasitoids, we found such evidence in clones containing the bacterium. This suggests that parasitoid genotypes differ in their ability to overcome H. defensa, resulting in an apparent host × parasitoid genotype interaction that may in fact be due to an underlying symbiont × parasitoid genotype interaction. Aphid susceptibility to parasitoids correlated negatively with fecundity and rate of increase, due to H. defensa-bearing clones being more fecund on average. Hence, possessing symbionts may also be favorable in the absence of parasitoids, which raises the question why H. defensa does not go to fixation and highlights the need to develop new models to understand the dynamics of endosymbiont-mediated coevolution.

BackgroundHoneybees provide economically and ecologically vital pollination services to crops and wild plants. During the last decade elevated colony losses have been documented in Europe and North America. Despite growing consensus on the involvement of multiple causal factors, the underlying interactions impacting on honeybee health and colony failure are not fully resolved. Parasites and pathogens are among the main candidates, but sublethal exposure to widespread agricultural pesticides may also affect bees.Methodology/Principal FindingsTo investigate effects of sublethal dietary neonicotinoid exposure on honeybee colony performance, a fully crossed experimental design was implemented using 24 colonies, including sister-queens from two different strains, and experimental in-hive pollen feeding with or without environmentally relevant concentrations of thiamethoxam and clothianidin. Honeybee colonies chronically exposed to both neonicotinoids over two brood cycles exhibited decreased performance in the short-term resulting in declining numbers of adult bees (−28%) and brood (−13%), as well as a reduction in honey production (−29%) and pollen collections (−19%), but colonies recovered in the medium-term and overwintered successfully. However, significantly decelerated growth of neonicotinoid-exposed colonies during the following spring was associated with queen failure, revealing previously undocumented long-term impacts of neonicotinoids: queen supersedure was observed for 60% of the neonicotinoid-exposed colonies within a one year period, but not for control colonies. Linked to this, neonicotinoid exposure was significantly associated with a reduced propensity to swarm during the next spring. Both short-term and long-term effects of neonicotinoids on colony performance were significantly influenced by the honeybees’ genetic background.Conclusions/SignificanceSublethal neonicotinoid exposure did not provoke increased winter losses. Yet, significant detrimental short and long-term impacts on colony performance and queen fate suggest that neonicotinoids may contribute to colony weakening in a complex manner. Further, we highlight the importance of the genetic basis of neonicotinoid susceptibility in honeybees which can vary substantially.

The overenrichment (eutrophication) of aquatic ecosystems with nutrients leading to algal blooms and anoxic conditions has been a persistent and widespread environmental problem. Although there are many studies on the ecological impact of elevated phosphorus (P) levels (e.g., decrease in biodiversity and water quality), little is known about the evolutionary consequences for animal species. We reconstructed the genetic architecture of a Daphnia species complex in 2 European lakes using diapausing eggs that were isolated from sediment layers covering the past 100 years. Changes in total P were clearly associated with a shift in species composition and the population structure of evolutionary lineages. Although environmental conditions were largely reestablished after peak eutrophication during the 1970s and 1980s, original species composition and the genetic architecture of species were not restored but evolved along new evolutionary trajectories. Our data demonstrate that anthropogenically induced temporal alterations of habitats are associated with long-lasting changes in communities and species via interspecific hybridization and introgression.biological archive ͉ eutrophication ͉ hybridization ͉ introgression ͉ invasiveness

1 Pollinating insects provide crucial and economically important ecosystem services to crops and wild plants, but pollinators, particularly bees, are globally declining as a result of various driving factors, including the prevalent use of pesticides for crop protection. Sublethal pesticide exposure negatively impacts numerous pollinator lifehistory traits, but its influence on reproductive success remains largely unknown. Such information is pivotal, however, to our understanding of the long-term effects on population dynamics. 2 We investigated the influence of field-realistic trace residues of the routinely used neonicotinoid insecticides thiamethoxam and clothianidin in nectar substitutes on the entire life-time fitness performance of the red mason bee Osmia bicornis. 3 We show that chronic, dietary neonicotinoid exposure has severe detrimental effects on solitary bee reproductive output. Neonicotinoids did not affect adult bee mortality; however, monitoring of fully controlled experimental populations revealed that sublethal exposure resulted in almost 50% reduced total offspring production and a significantly male-biased offspring sex ratio. 4 Our data add to the accumulating evidence indicating that sublethal neonicotinoid effects on non-Apis pollinators are expressed most strongly in a rather complex, fitness-related context. Consequently, to fully mitigate long-term impacts on pollinator population dynamics, present pesticide risk assessments need to be expanded to include whole life-cycle fitness estimates, as demonstrated in the present study using O. bicornis as a model.

Summary1. Pollinating insects provide vital ecosystem services of enormous importance for economies and biodiversity. Yet, there is a concerning global trend of pollinator declines. Parasites and pesticides are among the suspected principle drivers of these declines. However, especially in the case of key wild pollinators, there are insufficient data on the relative impact of these individual environmental stressors and whether they interact to increase detrimental effects. 2. Using a fully crossed factorial design, we investigated how laboratory exposure to neonicotinoid insecticides, thiamethoxam and clothianidin, over a 9-week period and a prevalent trypanosome gut parasite Crithidia bombi affects various crucial colony traits of the bumblebee Bombus terrestris. 3. We show that chronic dietary exposure from an early stage of colony development to doses of thiamethoxam and clothianidin that could be encountered in the field truncated worker production, reduced worker longevity and decreased overall colony reproductive success. Further, we demonstrate a significant interaction between neonicotinoid exposure and parasite infection on mother queen survival. The fate of the mother queen is intrinsically linked to colony success, and under combined pressure of parasite infection and neonicotinoid exposure, mother queen survival was lowest. This indicates increased detrimental effects of combined exposure on this crucial colony trait. Combined effects may be exacerbated in stressful natural environments where more pronounced parasite virulence is expected. 4. Synthesis and applications. Our findings reiterate that dietary exposure to neonicotinoids can impact on bumblebee colony performance and fitness. The indication of combined negative effects of ecologically relevant pressures suggests additional adverse consequences for long-term population dynamics under complex field conditions. To help safeguard pollinator health, whole life-cycle fitness assessments, particularly for non-Apis bees, stringently incorporating chronic and sublethal side effects of pesticides, as well as interactions with common natural stressors, such as prevalent parasites, should be considered in the corresponding test guidelines.

The evolutionary maintenance of sex is one of the big unresolved puzzles in biology. All else being equal, all-female asexual populations should enjoy a two-fold reproductive advantage over sexual relatives consisting of male and female individuals. However, the "all else being equal" assumption rarely holds in real organisms because asexuality tends to be confounded with altered genomic constitutions such as hybridization and polyploidization or to be associated with parthenogenesis-inducing microbes. This limits the ability to draw general conclusions from any particular system. Here we describe a new system that permits unbiased comparisons of sexual and asexual reproduction: the parasitic wasp Lysiphlebus fabarum. Crossing experiments demonstrated that asexual reproduction has a simple genetic basis in this species and is consistently inherited as a single-locus recessive trait. We further show that the asexuality-inducing allele exhibits complete linkage to a specific allele at a microsatellite marker: all asexual lines in the field were homozygous for this allele, and the allele cosegregated perfectly with asexual reproduction in our experimental crossings. This novel system of contagious asexuality allows the production of closely related individuals with different reproductive modes, as well as the monitoring of the asexuality-inducing allele in natural and experimental populations.

We present 32 polymorphic microsatellite markers for species of the European Daphnia longispina group: D. galeata, D. hyalina, D. rosea, D. cucullata and D. curvirostris. Microsatellite markers were either isolated from genomic libraries or optimized based on previously published sequence information of sister taxa. Cross‐species tests revealed that all but one of the polymorphic markers are applicable to more than one species, which allows intra‐ and interspecific genetic studies on, i.e. population structure, hybridization events and introgression.