Is bigger better? A possibility for adaptation of <Emphasis Type="Italic">Daphnia</Emphasis> to filamentous cyanobacteria in the face of global warming

Body size is a key determinant of fitness in Daphnia. Bigger size means higher feeding efficiency and reproduction. However, filamentous cyanobacteria have a more detrimental effect on larger daphnids. Predicted global warming is expected to reduce size of Daphnia and facilitate frequent occurrence of cyanobacteria. Therefore, we asked two questions: (i) does elevated temperature cause reduced size of daphnids, and (ii) is temperature-dependent size reduction adaptive in an environment dominated by filamentous cyanobacteria? To address these issues, we obtained 8 clones of the Daphnia longispina complex from artificially heated lakes and 8 clones from control lakes, and exposed them to a favorable food Scenedesmus obliquus and a mixture of S. obliquus and the filamentous cyanobacterium Cylindrospermopsis raciborskii in life table experiments at 16, 20, and 24°C. Individuals from heated lakes attained larger body size than those from control lakes. Moreover, exposure to the filamentous cyanobacterium led to reduced fecundity of Daphnia from the non-heated lakes and did not affect reproduction of Daphnia from the heated lakes. We conclude that Daphnia display some evolutionary adaptations to cope with filamentous cyanobacteria, linked to long-term exposition to elevated temperature. Our results violate broadly accepted assumptions that ectotherms are smaller in warmer environments.     

High predation is of key importance for dominance of small-bodied zooplankton in warm shallow lakes: evidence from lakes, fish exclosures and surface sediments

The mean body size of limnetic cladocerans decreases from cold temperate to tropical regions, in both the northern and the southern hemisphere. This size shift has been attributed to both direct (e.g. physiological) or indirect (especially increased predation) impacts. To provide further information on the role of predation, we compiled results from several studies of subtropical Uruguayan lakes using three different approaches: (i) field observations from two lakes with contrasting fish abundance, Lakes Rivera and Rodó, (ii) fish exclusion experiments conducted in in-lake mesocosms in three lakes, and (iii) analyses of the Daphnia egg bank in the surface sediment of eighteen lakes. When fish predation pressure was low due to fish kills in Lake Rivera, large-bodied Daphnia appeared. In contrast, small-sized cladocerans were abundant in Lake Rodó, which exhibited a typical high abundance of fish. Likewise, relatively large cladocerans (e.g. Daphnia and Simocephalus) appeared in fishless mesocosms after only 2 weeks, most likely hatched from resting egg banks stored in the surface sediment, but their abundance declined again after fish stocking. Moreover, field studies showed that 9 out of 18 Uruguayan shallow lakes had resting eggs of Daphnia in their surface sediment despite that this genus was only recorded in three of the lakes in summer water samples, indicating that Daphnia might be able to build up populations at low risk of predation. Our results show that medium and large-sized zooplankton can occur in subtropical lakes when fish predation is removed. The evidence provided here collectively confirms the hypothesis that predation, rather than high-temperature induced physiological constraints, is the key factor determining the dominance of small-sized zooplankton in warm lakes.     

Chronic responses of different clones of Daphnia longispina (field and ephippia) to different food levels

Resting eggs are a fundamental reproductive strategy among freshwater cladocerans. Under adverse environmental conditions, whole Daphnia populations can disappear from a lake and a new community will arise from ephippial eggs. Since these new populations are subjected to genetic variation, their responses to environmental stress or contaminants can be different from the “original” population. In the present study, life history responses (reproduction and growth) of Daphnia longispina to different food concentrations was studied. Two Daphnia populations were tested: (a) field clones and (b) ephippial clones. Food (Selenastrum capricornutum) concentration was the stressor tested (absence of food, and low to high food concentrations). The results showed that reproductive responses of D. longispina to the tested food concentrations varied among clones, independently from their origin.     

Potassium enrichment stimulates the growth and reproduction of a clone of Daphnia dentifera

Nutrient limitation commonly constrains organisms in natural ecosystems. Typically, ecologists focus on limitation by N and P. However, other nutrients can limit growth or reproduction. Here we focus on K limitation of invertebrate consumers (Daphnia dentifera) and phytoplankton in freshwater lakes. All organisms require K for several metabolic processes. In freshwater, K could limit growth because low external concentrations can increase the energetic costs of accumulating K. Furthermore, in a study linking K to disease, we previously found that K enrichment of water from one low-K lake stimulated the growth and reproduction of Daphnia. Here we test whether K could limit the production of Daphnia and phytoplankton across lakes and years. We repeated a life table experiment using water collected from a low-K lake during a different year. K again stimulated Daphnia reproduction. We also enriched water from 12 lakes with K or P and measured short-term growth of Daphnia and the resident algal community. Both nutrients increased Daphnia growth in five lakes. However, only P enhanced algal production. P stimulation of Daphnia positively correlated with algal quantity and the ratio of C to P in seston. However, K stimulation of Daphnia was not correlated with these factors or the background concentration of K. Thus, this study shows repeatable K-limited animal physiology in nature. Further, we can exclude the hypothesis that K stimulates Daphnia indirectly by enhancing algal production. These patterns call for future physiological studies to uncover the mechanistic basis of K limitation in natural systems.     

Phytoplankton composition modifies predator-driven life history evolution in Daphnia

Organisms experience competing selective pressures, which can obscure the mechanisms driving evolution. Daphnia ambigua is found in lakes where a predator, the alewife (Alosa pseudoharengus) either does (anadromous) or does not (landlocked) migrate between marine and freshwater. We previously reported an association between alewife variation and life history evolution in Daphnia. However, differences in alewife migration indirectly influence phytoplankton composition for Daphnia. In ‘anadromous lakes’, Daphnia are present in the spring and experience abundant high-quality green algae. Intense predation by young-of-the-year anadromous alewife quickly eliminates these Daphnia populations by early summer. Daphnia from ‘landlocked lakes’ and lakes without alewife (‘no alewife lakes’) are present during the spring and summer and are more likely to experience high concentrations of sub-optimal cyanobacteria during the summer. To explore links between predation, resources, and prey evolution, we reared third-generation laboratory-born Daphnia from all lake types on increasing cyanobacteria concentrations. We observed several significant ‘lake type × resource’ interactions whereby the differences among lake types depended upon cyanobacteria concentrations. Daphnia from anadromous lakes developed faster, were larger at maturation, produced more offspring, and had higher intrinsic rates of increase in the absence of cyanobacteria. Such trends disappeared or reversed as cyanobacteria concentration was increased because Daphnia from anadromous lakes were more strongly influenced by the presence of cyanobacteria. Our results argue that alewife migration and phytoplankton composition both play a role in Daphnia evolution.     

The evolution of eye size in response to increased fish predation in Daphnia

Variation in eye size is ubiquitous across taxa. Increased eye size is correlated with improved vision and increased fitness via shifts in behavior. Tests of the drivers of eye size evolution have focused on macroevolutionary studies evaluating the importance of light availability. Predator‐induced mortality has recently been identified as a potential driver of eye size variation. Here, we tested the influence of increased predation by the fish predator, the alewife (Alosa pseudoharengus) on eye size evolution in waterfleas (Daphnia ambigua) from lakes in Connecticut. We quantified the relative eye size of Daphnia from lakes with and without alewife using wild‐caught and third‐generation laboratory reared specimens. This includes comparisons between lakes where alewife are present seasonally (anadromous) or permanently (landlocked). Wild‐caught specimens did not differ in eye size across all lakes. However, third‐generation lab reared Daphnia from lakes with alewife, irrespective of the form of alewife predation, exhibited significantly larger eyes than Daphnia from lakes without alewife. This genetically based increase in eye size may enhance the ability of Daphnia to detect predators. Alternatively, such shifts in eye size may be an indirect response to Daphnia aggregating at the bottom of lakes. To test these mechanisms, we collected Daphnia as a function of depth and found that eye size differed in Daphnia found at the surface versus the bottom of the water column between anadromous alewife and no alewife lakes. However, we found no evidence of Daphnia aggregating at the bottom of lakes. Such results indicate that the evolution of a larger eye may be explained by a connection between eyes and enhanced survival. We discuss the cause of the lack of concordance in eye size variation between our phenotypic and genetic specimens and the ultimate drivers of eye size.     

Higher parasite resistance in Daphnia populations with recent epidemics

Natural populations often show genetic variation in parasite resistance, forming the basis for evolutionary response to selection imposed by parasitism. We investigated whether previous epidemics selected for higher resistance to novel parasite isolates in a Daphnia galeata–microparasite system by comparing susceptibility of host clones from populations with varying epidemic history. We manipulated resource availability to evaluate whether diet influences Daphnia susceptibility as epidemics are common in nutrient‐rich lakes. Exposing clones from 10 lakes under two food treatments to an allopatric protozoan parasite, we found that Daphnia originating from lakes (mainly nutrient rich) with previous epidemics better resist infection. Despite this result, there was a tendency of higher susceptibility in the low food treatment, suggesting that higher resistance of clones from populations with epidemic background is not directly caused by lake nutrient level. Rather, our results imply that host populations respond to parasite‐mediated selection by evolving higher parasite resistance.     

<Emphasis Type="Italic">Daphnia</Emphasis> distribution in Andean Patagonian lakes: effect of low food quality and fish predation

Food quality in terms of carbon (C):phosphorus (P) ratio can constrain the success of highly demanding P herbivores as Daphnia. North Andean Patagonian lakes are ultraoligotrophic with low nutrient concentrations and well-developed euphotic zones. We investigated the distribution of the large Daphnia commutata in relation with food quality (sestonic C:P ratio) and predation risk in these lakes. The predation risk was estimated based on the fish species present and their relative eye diameter and transparency of the lake. The C:P ratios in the lakes were high, varying from 350 to >1,200. The lakes with D. commutata had significantly lower C:P ratio than those without these daphnids. On the other hand, those lakes where Daphnia is present have the lower predation risk than those were Daphnia is absent. In addition, we carried out growth experiments with neonates and natural seston of three lakes with different C:P ratio. The growth rates were inversely related with C:P of the food. Food quality and predation risk together determined the success or failure of large Daphnia populations in these Andean clear ultraoligotrophic lakes.     

Stoichiometry in an ecological context: testing for links between <Emphasis Type="Italic">Daphnia</Emphasis> P-content,growth rate and habitat preference

We used laboratory experiments with ten Daphnia taxa to test for links between Daphnia P-content, growth rate and habitat preference. The taxa represent a wide range of body sizes and most show distinct preferences for one of three habitats: shallow lakes, deep, stratified lakes or fishless ponds. Previous studies show that taxa from shallow lakes and fishless ponds experience high predation risk and rich food resources, whereas taxa from deep lakes experience low predation risk, strong food limitation and potentially P-deficient resources. Thus, we predicted higher P-content and higher maximal growth rates in taxa from ponds and shallow lakes and lower P-content, lower maximal growth but reduced sensitivity to P-limitation in taxa preferring stratified lakes. In each of 25 experiments, a clonal Daphnia cohort was cultured for 4 days on a P-sufficient (molar C:P ratio 70) or a P-deficient (C:P 1,000) diet of a green alga at a high concentration (1 mg C l^–1). The P-content of adult Daphnia fed the P-sufficient diet ranged from 1.52 to 1.22% mass. Small-bodied taxa from shallow lakes had higher P-content than larger-bodied taxa from deep lakes or fishless ponds. However, we found a nonsignificant negative correlation between P-content and growth on the P-sufficient diet, rather than the positive relationship predicted by the growth rate hypothesis. The P-deficient diet resulted in declines in both growth rate and P-content compared with the P-sufficient controls and the extent of the declines differed between taxa. Taxa from ponds showed a marginally greater decline in growth with the P-deficient diet compared with taxa from shallow or deep lakes. However, contrary to stoichiometric theory, no relationship was found between a species P-content and growth depression on the P-deficient diet. Although we found evidence for habitat adaptations, our results show that factors other than Daphnia P-content are important in determining differences between Daphnia species in both maximal growth rate and sensitivity to P-limited growth.     

At the edge and on the top: molecular identification and ecology of Daphnia dentifera and D. longispina in high-altitude Asian lakes

The occurrence of members of the highly diverse Daphnia longispina complex in Southern and Central Asian high-mountain lakes has been recognized for more than a century. Until now, however, no molecular data have been available for these populations inhabiting the “Roof of the World.” Here, we present the first identification for D. gr. longispina from that region based on a molecular phylogeny. Our findings show that alpine lakes in the Pamir and Himalaya mountains host populations of widespread species of the complex, for which these are the highest known localities. A spineless morph from the Himalaya region, previously labeled as D. longispina var. aspina, was clustering tightly with D. dentifera, while a population from the Pamir mountain range was grouped with D. longispina. In addition, we analyzed ecological data available for lakes in the Khumbu region (Himalaya) to investigate ecological preferences of non-pigmented D. gr. longispina. The identified factors can at least partly be related to avoidance of high UV conditions by this species. We conclude that the widespread species D. dentifera and D. longispina also colonized the Asian high-mountain lakes, and identify the need for further research to trace the possible effect of rapid environmental changes in this region on the diversity and ecology of high-altitude Daphnia populations.     

Longevity of <Emphasis Type="Italic">Daphnia magna</Emphasis> males and females

In many species, males are shorter-lived than females, and, mostly anecdotally, shorter lifespan was also attributed to Daphnia males. This does not necessarily stay in accordance with the biological roles of the sexes in Daphnia. Daphnia females maximize their fitness by maximizing the number of produced offspring, which incurs costs associated with quick attainment of large body size: metabolic costs of fast growth and increased risk of predation. In contrast, Daphnia males maximize fitness by maximizing the number of fertilized females, and seem to follow the strategy that enables them to maximize the lifetime female encounter rate, which should increase with lengthening lifespan. As arguments exist both in favour and against males living longer than females, we tested for differences in physiological lifespan of Daphnia magna males and females. Although maximum observed lifespan was always equal or longer in males than in females, no statistically significant differences were found. The results indicate that Daphnia males should not be considered short-lived anymore.     

Effects of Cell-Bound Microcystins on Survival and Feeding of Daphnia spp.

The influence of cell-bound microcystins on the survival time and feeding rates of six Daphnia clones belonging to five common species was studied. To do this, the effects of the microcystin-producing Microcystis strain PCC7806 and its mutant, which has been genetically engineered to knock out microcystin synthesis, were compared. Additionally, the relationship between microcystin ingestion rate by the Daphnia clones and Daphnia survival time was analyzed. Microcystins ingested with Microcystis cells were poisonous to all Daphnia clones tested. The median survival time of the animals was closely correlated to their microcystin ingestion rate. It was therefore suggested that differences in survival among Daphnia clones were due to variations in microcystin intake rather than due to differences in susceptibility to the toxins. The correlation between median survival time and microcystin ingestion rate could be described by a reciprocal power function. Feeding experiments showed that, independent of the occurrence of microcystins, cells of wild-type PCC7806 and its mutant are able to inhibit the feeding activity of Daphnia. Both variants of PCC7806 were thus ingested at low rates. In summary, our findings strongly suggest that (i) sensitivity to the toxic effect of cell-bound microcystins is typical for Daphnia spp., (ii) Daphnia spp. and clones may have a comparable sensitivity to microcystins ingested with food particles, (iii) Daphnia spp. may be unable to distinguish between microcystin-producing and -lacking cells, and (iv) the strength of the toxic effect can be predicted from the microcystin ingestion rate of the animals.     

Lake restoration by biomanipulation using piscivore and Daphnia stocking; results of the biomanipulation in Japan

Biomanipulation has been employed in numerous locations throughout the world as a means for reducing phytoplankton biomass; however, it has not been employed very often in Japan. A common approach involves the introduction of piscivorous fish to reduce the abundance of planktivorous fish. In our study, to first apply biomanipulation, we stocked Lake Shirakaba (a high-altitude, protected area in a park) in central Japan with rainbow trout fingerlings and cladoceran Daphnia (Daphnia galeata) in 2000. A “pre-biomanipulation” data set (1997–1999) and “a post-biomanipulation” data set (2000–2006) allowed us to evaluate the lake's response to biomanipulation. After the biomanipulation, zoo-planktivorous pond smelt disappeared and a large population of Daphnia had been established, which substantially reduced the number of the previously dominant small cladocerans and rotifers. Water transparency increased from about 2 m (before biomanipulation) to more than 4 m (after biomanipulation). Reductions in algal biomass and increased transparency led to expansion of the submerged macrophyte Elodea nuttallii. Total phosphorus concentrations declined as well over this time period. Based on these results, we concluded that biomanipulation using piscivore and Daphnia stocking succeeded in improving lake water quality by reducing algal abundance and providing favorable conditions for the establishment of rooted plants.     

Behavioural and physiological mechanisms behind extreme longevity in Daphnia

The combined effect of external environment and energy allocation strategy of the organism on longevity can be exceptional. In a cold oligotrophic fishless habitat, individual Daphnia can live for over a year, several times the usual Daphnia lifespan. This extreme lifespan is in part a consequence of the overwintering strategy which includes storing resources and delaying reproduction until another spring. Yet, contrasting strategies may be applied by Daphnia, resulting in over twofold differences in lifespan within a single habitat. We identify physiological mechanisms mediating such differences in longevity in closely related Daphnia of two lineages coexisting within a high altitude lake, testing the predictions that long-lived animals stay in colder waters and have lower metabolic rates, irrespective of temperature. Vertical distribution of the animals was assessed during three summer stratification seasons, and metabolic activity was measured as oxygen consumption and RNA:DNA ratio. The results not only support our predictions but also reveal that habitat choice is dependent on reproductive status rather than genotype. The young individuals of the overwintering lineage may delay reproduction in part by staying in colder waters than the reproducing adults, which together with low intrinsic metabolic rates may underlie the longevity of Daphnia of this lineage.     

Clonal integration facilitates invasiveness of the alien aquatic plant Myriophyllum aquaticum L. under heterogeneous water availability

The avoidance of visually feeding fish has long been considered as the primary driver of diel vertical migration of zooplankton. The diurnal vertical distribution of Cyclops gr. abyssorum, Arctodiaptomus alpinus, and Daphnia gr. longispina from 13 alpine lakes with fish (Salvelinus fontinalis) and without, was compared in order to understand whether fish in transparent lakes reduce the presence of large zooplankton from the irradiated zone. We used the light level at each sampling depth and the size of each specimen as proxies of predation risk, and we tested two predictions: (P1) the relative abundance of zooplankton in the well-lit surface waters vs. the darker waters will be greater in fishless lakes; (P2) the size of zooplankton in the well-lit surface waters vs. the deeper, darker waters will be greater in fishless lakes. We did not find any evidence of the validity of P1, but we confirmed P2 for Arctodiaptomus alpinus. These results support with new field data the Transparency Regulator Hypothesis, which argues that in transparent lakes, fish predation is less important for the vertical distribution of zooplankton than ultraviolet radiation, and further suggest that zooplankton size rather than vertical distribution may be more effective against visual predators in transparent lakes.     

Predator-induced plasticity does not alter the pathway from evolution to ecology among locally adapted populations of <Emphasis Type="Italic">Daphnia</Emphasis>

In the growing field of eco-evolutionary dynamics, evidence for an influence of rapid shifts in phenotype on ecological processes is accumulating, yet, the contributions of phenotypic plasticity versus genetic change to these observed ecological changes are unclear. In one of the best studied ecosystems in terms of eco-evolutionary dynamics, landlocked versus anadromous alewife (Alosa pseudoharengus) have caused strong evolutionary divergence in their key zooplankton prey (Daphnia ambigua). We previously showed that such evolutionary differences have cascading ecological effects on consumer-resource dynamics and primary production. Yet, these locally adapted populations of Daphnia also differ in trait plasticity, which may, in turn, modify the pathway from evolution to ecology. Here we compared Daphnia from lakes with landlocked versus anadromous alewife for differences in rates of population growth in the presence and absence of predator cues over the course of a 39-day experiment. We predicted that predator-induced shifts in life history traits would facilitate faster rates of population growth. Contrary to our expectations, predator cue exposure did not alter rates of population growth. We instead found that Daphnia from lakes with landlocked alewife ultimately attained higher population densities (and exhibited faster population growth) when compared with Daphnia from lakes with anadromous alewife. Based on our previous work, these population level responses were unexpected, as Daphnia from lakes with landlocked alewife exhibit slower rates of somatic growth and delayed maturation. We discuss our results in lieu of the known differences in plasticity and how the population growth patterns may be influenced by resource limitation.     

Are they still viable? Physical conditions and abundance of <Emphasis Type="Italic">Daphnia pulicaria</Emphasis> resting eggs in sediment cores from lakes in the Tatra Mountains

All species of Daphnia (Cladocera) produce, at some stage in their life cycle, diapausing eggs, which can remain viable for decades or centuries forming a “seed bank” in lake sediments. Because of their often good preservation in lake sediment, they are useful in paleolimnology and microevolutionary studies. The focus of this study was the analysis of cladoceran resting eggs stored in the sediment in order to examine the ephippial eggs bank of Daphnia pulicaria Forbes in six mountain lakes in the High Tatra Mountains, the Western Carpathians (northern Slovakia and southern Poland). Firstly, we analyzed distribution, abundance and physical condition of resting eggs in the sediment for their later used in historical reconstruction of Daphnia populations by genetic methods. To assess changes in the genetic composition of the population through time, we used two microsatellite markers. Although DNA from resting eggs preserved in the High Tatra Mountain lake sediments was extracted by various protocols modified for small amounts of ancient DNA, DNA from eggs was not of sufficient quality for microsatellite analyses. Distribution curves of resting eggs from sediment cores correspond to the environmental changes that have occurred in the High Tatra Mountains area during last two centuries (atmospheric acid deposition, fish introduction) and demonstrate their influence on natural populations. Evaluation of ephippia physical condition (the most common category was empty ephippial covers) suggests that the majority of resting eggs hatched to produce a new generation of Daphnia or may be due to failed deposition of resting eggs by Daphnia to the chitinous case. In conclusion, age, low quantity and poor physical condition of resting eggs from these Tatra lake sediments proved to be unsuitable not just for use in genetic analyses, but also the possibilities of autogenous restoration of Daphnia populations from the resting egg banks in the Tatra sediments are negligible.     

DNA extraction and amplification methods for ephippial cases of Daphnia resting eggs in lake sediments: a novel approach for reconstructing zooplankton population structure from the past

This study describes a method of DNA extraction and amplification for ephippial cases of Daphnia resting eggs from lake sediment. Recent studies have reconstructed succession records of Daphnia species by genetically analyzing Daphnia resting eggs stored in lake sediments and revealed changes in dominant Daphnia species that correspond well with environmental changes. However, this approach is not applicable to lakes where most of the resting eggs in the sediment have already hatched out. We modified conventional methods for DNA extraction and amplification to enable genetic analyses of the ephippial case that envelops and protects the resting eggs, and we compared the performance of the modified method to the conventional one. We confirmed that we could efficiently analyze the sequences of the ephippial cases collected in a sediment core using our modified method. It enables us to reconstruct changes in genetic structure of Daphnia populations regardless of hatching rates of the resting eggs.     

Uniform Temperature Dependency in the Phenology of a Keystone Herbivore in Lakes of the Northern Hemisphere

Spring phenologies are advancing in many ecosystems associated with climate warming causing unpredictable changes in ecosystem functioning. Here we establish a phenological model for Daphnia, an aquatic keystone herbivore based on decadal data on water temperatures and the timing of Daphnia population maxima from Lake Constance, a large European lake. We tested this model with long-term time-series data from two lakes (Müggelsee, Germany; Lake Washington, USA), and with observations from a diverse set of 49 lakes/sites distributed widely across the Northern Hemisphere (NH). The model successfully captured the observed temporal variation of Daphnia phenology in the two case study sites (r² = 0.25 and 0.39 for Müggelsee and Lake Washington, respectively) and large-scale spatial variation in the NH (R² = 0.57). These results suggest that Daphnia phenology follows a uniform temperature dependency in NH lakes. Our approach – based on temperature phenologies – has large potential to study and predict phenologies of animal and plant populations across large latitudinal gradients in other ecosystems.     

Zooplankton (Cladocera) species turnover and long-term decline of Daphnia in two high mountain lakes in the Austrian Alps

We investigated long-term succession of sedimentary cladoceran assemblages in two morphologically divergent mountain lakes by utilizing sediment traps and previously available sediment data. We aimed to detect lake-specific changes in pelagic communities potentially attributable to climate warming under the presumption that lakes and biotic communities may respond individually to the same regional climatic forcing. Both lakes showed a similar community turnover, as Daphnia was first replaced by Chydorus cf. sphaericus and during the twentieth century by the latest colonizer Bosmina. The community succession was similar among the lakes and consistent with the regional temperature increase, although the timing of community shift, the magnitude of change, and taxa in question differed. Decline of Daphnia mismatched with historical fish stockings, but the eventual extirpation of Daphnia in one of the lakes corresponded to the start of fish introductions. We propose that the observed shifts were mainly governed by increasing temperatures and its limnoecological consequences (e.g., deeper mixing). We suggest that Bosmina distribution may be extending to lakes at higher altitudes as a response to climate warming, and that it may replace Daphnia as the key component of pelagic alpine food webs by coping in interspecific resource competition under changed limnological regimes.