Abstract. Adaptations and counteradaptations are common in coevolving predatorprey systems, but little is known of the role of maternal transfer of adaptive traits in mediating species interactions. Here, we focused on tolerance against cyanobacterial toxins and asked whether this tolerance was an induced defense developed during Daphnia's lifetime, whether it was a trait that is constantly expressed, and whether such tolerance to the toxin can be transferred to the next generation through maternal effects. These questions were addressed by feeding a single clone of Daphnia magna a diet with and without algal toxin and recording changes in fitness (as intrinsic rate of population increase). Analysis of F1, F2, and F3 generations revealed that the increased tolerance to toxic Microcystis was an inducible defense developed during an individual's lifetime, and that this trait could be transferred from mother to offspring. This maternal effect was expressed in several fitness parameters, including shorter time to maturity and first reproduction, and higher numbers of offspring compared to inexperienced individuals. In some circumstances, such maternal effects may increase population production by up to 40% and may help to stabilize material and energy transfer to higher trophic levels.

1. Toxic algal blooms widely affect our use of water resources both with respect to drinking water and recreation. However, it is not only humans, but also organisms living in freshwater and marine ecosystems that may be affected by algal toxins. 2. In order to assess if cyanobacterial toxins affect the composition of natural zooplankton communities, we quantified the temporal fluctuations in microcystin concentration and zooplankton community composition in six lakes. 3. Microcystin concentrations generally showed a bimodal pattern with peaks in early summer and in autumn, and total zooplankton biomass was negatively correlated with microcystin concentrations. Separating the zooplankton assemblages into finer taxonomic groups revealed that high microcystin concentrations were negatively correlated with Daphnia and calanoid copepods, but positively correlated with small, relatively inefficient phytoplankton feeders, such as cyclopoid copepods, Bosmina and rotifers. 4. In a complementary, mechanistic laboratory experiment using the natural phytoplankton communities from the six lakes, we showed that changes in in situ levels of microcystin were coupled with reduced adult size and diminished juvenile biomass in Daphnia. 5. We argue that in eutrophic lakes, large unselective herbivores, such as Daphnia, are 'sandwiched' between high fish predation and toxic food (cyanobacteria). In combination, these two mechanisms may explain why the zooplankton community in eutrophic lakes generally comprise small forms (e.g. rotifers and Bosmina) and selective raptorial feeders, such as cyclopoid copepods, whereas large, unselective herbivores, such as Daphnia, are rare. Hence, this cyanobacterial chemical warfare against herbivores may add to our knowledge on population and community dynamics among zooplankton in eutrophic systems.

Objectives To examine the outcomes of the Elderly Persons in the Risk Zone study, which was designed to evaluate whether it is possible to delay deterioration if a health‐promoting intervention is made when an older adult (≥80) is at risk of becoming frail and whether a multiprofessional group intervention is more effective in delaying deterioration than a single preventive home visit with regard to frailty, self‐rated health, and activities of daily living (ADLs) at 3‐month follow‐up. Design Randomized, three‐armed, single‐blind, controlled trial performed between November 2007 and May 2011. Setting Two urban districts of Gothenburg, Sweden. Participants Four hundred fifty‐nine community‐living adults aged 80 and older not dependent on the municipal home help service. Intervention A preventive home visit or four weekly multiprofessional senior group meetings with one follow‐up home visit. Measurements Change in frailty, self‐rated health, and ADLs between baseline and 3‐month follow‐up. Results Both interventions delayed deterioration of self‐rated health (odds ratio (OR) = 1.99, 95% confidence interval (CI) = 1.12–3.54). Senior meetings were the most beneficial intervention for postponing dependence in ADLs (OR = 1.95, 95% CI = 1.14–3.33). No effect on frailty could be demonstrated. Conclusion Health‐promoting interventions made when older adults are at risk of becoming frail can delay deterioration in self‐rated health and ADLs in the short term. A multiprofessional group intervention such as the senior meetings described seems to have a greater effect on delaying deterioration in ADLs than a single preventive home visit. Further research is needed to examine the outcome in the long term and in different contexts.

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