Niche construction theory explains how organisms' niche modifications may feed back to affect their evolutionary trajectories. In theory, the evolution of other species accessing the same modified niche may also be affected. We propose that this niche construction may be a general mechanism driving the evolution of mutualisms. Drosophilid flies benefit from accessing yeast-infested fruits, but the consequences of this interaction for yeasts are unknown. We reveal high levels of variation among strains of Saccharomyces cerevisiae in their ability to modify fruits and attract Drosophila simulans. More attractive yeasts are dispersed more frequently, both in the lab and in the field, and flies associated with more attractive yeasts have higher fecundity. Although there may be multiple natural yeast and fly species interactions, our controlled assays in the lab and field provide evidence of a mutualistic interaction, facilitated by the yeast's niche modification.

Summary1. Polyandry is common in insects. Nevertheless, the evolutionary causes and consequences of this phenomenon remain contentious, in part because of a lack of information about natural mating rates and the fact that most post-copulatory processes are hidden from view within female reproductive tracts. 2. We captured wild female yellow dung flies (Scathophaga stercoraria) over the whole spring season and genotyped the sperm from their spermathecae to obtain information on sperm transfer, sperm storage and natural levels of polyandry for this model species of post-copulatory sexual selection research. 3. On average, females stored sperm from a minimum of 2AE47 males (based on the most conservative estimate). Incorporating knowledge of population allele frequencies yielded a slightly higher estimate of 3AE33 mates per female. 4. Sperm storage and therefore sperm competition intensity showed high temporal variation. The proportion of multiply mated females (i.e. females with sperm from ‡2 males within their sperm stores) and the absolute number of ejaculates detected within females increased strongly over the spring season before sharply decreasing as midsummer approached. 5. Interestingly, we detected a positive relationship between the number of stored ejaculates and females' wing injuries, suggesting that mating not only causes measurable cumulative damage to wild females but also provides a potential mechanism by which males may be able to assess the intensity of sperm competition within a female. 6. Our study found no evidence for intraejaculate sperm sorting, but importantly, the number of ejaculates in storage differed amongst the three sperm storage organs (spermathecae) of female yellow dung flies. Different sperm mixtures across the spermathecae could enable females to bias paternity towards certain males if females can selectively use sperm from a certain spermatheca at the time of fertilization.

Summary1. Natural populations are exposed to multiple stressors, including both anthropogenic challenges such as xenobiotics and natural stressors associated with exposure to parasites and predators. While there is increasing concern and interest in the combined impact of current exposure to multiple stressors, little attention has been given to how past exposure to a stressor and its evolutionary response shapes the effects of current stressors. 2. Here, we performed a life-table experiment using the water flea Daphnia magna to study combined effects of current exposure to the pesticide carbaryl, parasite spores and fish predation risk and how these effects depend upon past exposure to carbaryl using clones obtained from a previous carbaryl selection experiment. 3. The current exposure to all three treatments affected life-history traits. Exposure to fish kairomones increased intrinsic population growth rate, while carbaryl and parasite exposure decreased this fitness measure. The three treatments interacted only in a few cases: carbaryl and fish kairomone exposure interacted in shaping intrinsic population growth rate and its component individual reproductive performance, yet the latter only in the animals not exposed to carbaryl stress in the past. 4. Our data revealed not only adaptive evolution of carbaryl resistance but also associated evolutionary costs in terms of reduced resistance to parasites, corroborating results of an earlier study. Importantly, both the evolutionary benefits and costs of past exposure to carbaryl stress were conditional on current environmental conditions, exposure to predation risk and parasites, respectively. 5. The emerging pattern showed that past stress interacted with current stress in shaping life history. Such evolution-driven carry-over effects across generations have been often ignored and may complicate the prediction of effects of current exposure to single and combined stressors even long after the past stress has disappeared.

Abstract-

Interactions between organisms and their environments are central to how biological diversity arises and how natural populations and ecosystems respond to environmental change. These interactions involve processes by which phenotypes are affected by or respond to external conditions (e.g., via phenotypic plasticity or natural selection) as well as processes by which organisms reciprocally interact with the environment (e.g., via eco-evolutionary feedbacks). Organism-environment interactions can be highly dynamic and operate on different hierarchical levels, from genes and phenotypes to populations, communities, and ecosystems. Therefore, the study of organism-environment interactions requires integrative approaches and model systems that are suitable for studies across different hierarchical levels. Here, we introduce the freshwater isopod Asellus aquaticus, a keystone species and an emerging invertebrate model system, as a prime candidate to address fundamental questions in ecology and evolution, and the interfaces therein. We review relevant fields of research that have used A. aquaticus and draft a set of specific scientific questions that can be answered using this species. Specifically, we propose that studies on A. aquaticus can help understanding (i) the influence of host-microbiome interactions on organismal and ecosystem function, (ii) the relevance of biotic interactions in ecosystem processes, and (iii) how ecological conditions and evolutionary forces facilitate phenotypic diversification.

Summary 1. Environmental stressors can influence population and community structure. However, the majority of experimental work on multiple environmental stressors has been done at the individual level only. 2. In this work, we followed changes in experimental assemblages of Daphnia (waterfleas; consisting of two taxa and three clones per taxon) after exposure to the fungal parasite Metschnikowia sp. and/or the pesticide diazinon. 3. We found a significant shift in taxonomic and clonal composition under both stressors. Strikingly, in the parasite and parasite + pesticide treatments, one taxon went extinct. While the pesticide had no effect on total parasite prevalence, the taxon that was more susceptible to extinction was, at the same time, more infected when additionally exposed to the pesticide. Furthermore, the density of all adult females was significantly reduced in the parasite treatment, but not in the pesticide treatment. 4. Our results demonstrate that the dynamics of Daphnia assemblages are altered by parasites and pesticide exposure. Given the key role of Daphnia in aquatic food webs in transferring primary production into fish food, this could be of wide significance in aquatic ecosystems.

Organisms are exposed to multiple biotic and abiotic environmental stressors, which can influence the dynamics of individual populations and communities. Populations may also genetically adapt to both natural (e.g. disease) and anthropogenic (e.g. chemical pollution) stress. In the present study, we studied fitness consequences of exposure to both a parasite (i.e. biotic) and a pesticide (i.e. abiotic) for the water flea Daphnia. In addition, we investigated whether these fitness consequences change through time as a population evolves. Thus, we exposed Daphnia magna clones, hatched from dormant eggs isolated from different time layers of a natural dormant egg bank, to the parasite Pasteuria ramosa and the insecticide diazinon in a multifactorial experiment. While our experimental treatments for unknown reasons failed to induce disease symptoms in the Daphnia, we did observe a reduced survival of D. magna when simultaneously exposed to both the parasite and the pesticide. No increased mortality upon exposure to individual stressors was observed. We did not observe an evolutionary change in fitness response of the Daphnia clones hatched from different time horizons upon exposure to stressors.

Vector‐borne parasites often manipulate hosts to attract uninfected vectors. For example, parasites causing malaria alter host odor to attract mosquitoes. Here, we discuss the ecology and evolution of fruit‐colonizing yeast in a tripartite symbiosis—the so‐called “killer yeast” system. “Killer yeast” consists of Saccharomyces cerevisiae yeast hosting two double‐stranded RNA viruses (M satellite dsRNAs, L‐A dsRNA helper virus). When both dsRNA viruses occur in a yeast cell, the yeast converts to lethal toxin‑producing “killer yeast” phenotype that kills uninfected yeasts. Yeasts on ephemeral fruits attract insect vectors to colonize new habitats. As the viruses have no extracellular stage, they depend on the same insect vectors as yeast for their dispersal. Viruses also benefit from yeast dispersal as this promotes yeast to reproduce sexually, which is how viruses can transmit to uninfected yeast strains. We tested whether insect vectors are more attracted to killer yeasts than to non‑killer yeasts. In our field experiment, we found that killer yeasts were more attractive to Drosophila than non‐killer yeasts. This suggests that vectors foraging on yeast are more likely to transmit yeast with a killer phenotype, allowing the viruses to colonize those uninfected yeast strains that engage in sexual reproduction with the killer yeast. Beyond insights into the basic ecology of the killer yeast system, our results suggest that viruses could increase transmission success by manipulating the insect vectors of their host.