Daphnia Pulicaria Research Articles

Invasive species triggers a massive loss of ecosystem services through a trophic cascade

Despite growing recognition of the importance of ecosystem services and the economic and ecological harm caused by invasive species, linkages between invasions, changes in ecosystem functioning, and in turn, provisioning of ecosystem services remain poorly documented and poorly understood. We evaluate the economic impacts of an invasion that cascaded through a food web to cause substantial declines in water clarity, a valued ecosystem service. The predatory zooplankton, the spiny water flea (Bythotrephes longimanus), invaded the Laurentian Great Lakes in the 1980s and has subsequently undergone secondary spread to inland lakes, including Lake Mendota (Wisconsin), in 2009. In Lake Mendota, Bythotrephes has reached unparalleled densities compared with in other lakes, decreasing biomass of the grazer Daphnia pulicaria and causing a decline in water clarity of nearly 1 m. Time series modeling revealed that the loss in water clarity, valued at US$140 million (US$640 per household), could be reversed by a 71% reduction in phosphorus loading. A phosphorus reduction of this magnitude is estimated to cost between US$86.5 million and US$163 million (US$430-US$810 per household). Estimates of the economic effects of Great Lakes invasive species may increase considerably if cases of secondary invasions into inland lakes, such as Lake Mendota, are included. Furthermore, such extreme cases of economic damages call for increased investment in the prevention and control of invasive species to better maximize the economic benefits of such programs. Our results highlight the need to more fully incorporate ecosystem services into our analysis of invasive species impacts, management, and public policy.

Competition‐mediated feedbacks in experimental multispecies epizootics

Competition structures ecological communities and alters host-pathogen interactions. In environmentally transmitted pathogens, an infection-resistant competitor may influence infection dynamics in a susceptible species through the negative impacts of competition (e.g., by reducing host density or causing nutritional stress that increases susceptibility to infection) and/or the positive impacts of reducing transmission efficiency (e.g., by removing environmental pathogen stages). Thus, a non-susceptible competitor may enhance, reduce, or have no net effect on susceptible host density and infection prevalence. Here, we couple an epidemiological model with experimental epidemics to test how resource competition with a non-susceptible competitor (Daphnia pulicaria) influences fungal microparasite (Metschnikowia bicuspidata) infection dynamics in a susceptible host species (D. dentifera). Our model and experiments suggest that competitor density can mediate the direction and magnitude of the effect of competition on infection dynamics, with a peak in infection prevalence occurring at intermediate competitor densities. At low densities, the non-susceptible competitor D. pulicaria may reduce infection prevalence in the susceptible host by removing fungal spores from the environment through feeding. However, when competitor density is increased and resources become limiting, D. pulicaria negatively impacts the susceptible host by increasing susceptible host feeding rates, and therefore fungal spore intake, and further by reducing susceptible host population size as it is driven toward competitive exclusion. In conclusion, these results show that a tradeoff between the competitor as a consumer of pathogen, which serves to reduce epidemic size, and as a modifier of susceptible host foraging ecology, which influences infection rates, may alternately enhance or dampen the magnitude of local epidemics.

Molecular diversity of some species belonging to the genus Daphnia O. F. Müller, 1785 (Crustacea: Cladocera) in Turkey

Daphnia is a freshwater zooplankton species with controversial taxonomy due to its high morphological variation linked to environmental factors and inter-specific hybridization and polyploidy in some groups. The aim of the present study is to examine molecular diversity of some Daphnia species in Turkey and to establish DNA barcodes of Turkish Daphnia species. Sequence analysis was performed using 540 bp region of cytochrome oxidase subunit I gene of mitochondrial DNA. A total of 34 haplotypes have been identified for Turkey. Daphnia pulex complex was divided into two clades with 16.1% sequence divergence according to molecular taxonomy based on Kimura 2-parameter. The clade which was molecularly diverged from Daphnia pulex with 16.1% sequence divergence was found to show 99% similarity with Daphnia cf. pulicaria (sensu Alonso 1996) instead of Daphnia pulicaria Forbes, 1893. Furthermore, this study has contributed to Turkish zoogeography by demonstrating the distribution of Daphnia species in Turkey.

Variation in copper effects on kairomone-mediated responses in Daphnia pulicaria

Chemical signals play an integral role in many predator–prey relationships but their effectiveness can be altered by environmental conditions. Prey species can detect predator kairomones, which induce anti-predator defenses. An example of this predator–prey relationship exists between Daphnia spp. and Chaoborus spp.; however, when living in water contaminated with low concentrations of copper (Cu) Daphnia can fail to respond to Chaoborus kairomone and, in turn, become more susceptible to predation. This has implications for Daphnia living in regions with Cu contamination, such as areas where mining activity has resulted in increased levels of metals in the surrounding lakes. We examined kairomone-mediated responses of multiple Daphnia pulicaria clones obtained from 8 lakes in Ontario, Canada, in the absence and presence of environmentally-relevant Cu concentrations. Life history traits and morphological anti-predator defenses were assessed using neonates collected from mothers that were exposed to kairomone and Cu treatments.We found that kairomone-mediated responses and Cu-tolerance varied among D. pulicaria clones. Clones exposed to kairomone, in the absence of Cu additions, had diverse responses, including larger neonates, delayed reproduction, or altered brood size relative to no-kairomone controls. These kairomone-induced responses act as antipredator defense strategies against Chaoborus by preventing predation or stabilizing population growth. When exposed to Cu, two clones were able to respond to kairomone, while four clones no longer induced a response to kairomone. This variation in non-lethal effects of Cu on aquatic organisms suggests that toxicity tests should incorporate multiple genotypes and include predator–prey interactions.

A review of the effects ofBythotrephes longimanusand calcium decline on zooplankton communities — can interactive effects be predicted?

Anthropogenic stressors including acid deposition, invasive species, and calcium (Ca) decline have produced widespread damage to Canadian Shield lakes, especially to their zooplankton communities. Here, we review current knowledge on the individual effects on zooplankton by the non-indigenous predator Bythotrephes longimanus and Ca decline; we identify knowledge gaps in this literature and examine the likely interactive impacts of Bythotrephes invasions and Ca decline on zooplankton. The negative impacts of Bythotrephes longimanus on zooplankton communities are well known, whereas current understanding of the effects of declining Ca on zooplankton is restricted to Daphnia spp.; hence, there is a large knowledge gap on how declining Ca may affect zooplankton communities in general. The co-occurring impacts of Bythotrephes and declining Ca have rarely been studied at the species level, and we expect daphniids, particularly Daphnia retrocurva and Daphnia pulicaria, to be the most sensitive to both stressors. We also expect a synergistic negative interaction on cladocerans in lakes with both stressors, leaving a community dominated by Holopedium glacialis and (or) copepods. Our predictions form testable hypotheses but since species and ecosystem response to multiple stressors are difficult to predict, we may actually see ecological surprises in Canadian Shield lakes as Bythotrephes continues to spread and Ca levels continue to fall.

Statistical Mechanics of Zooplankton.

Statistical mechanics provides the link between microscopic properties of many-particle systems and macroscopic properties such as pressure and temperature. Observations of similar “microscopic” quantities exist for the motion of zooplankton, as well as many species of other social animals. Herein, we propose to take average squared velocities as the definition of the “ecological temperature” of a population under different conditions on nutrients, light, oxygen and others. We test the usefulness of this definition on observations of the crustacean zooplankton Daphnia pulicaria. In one set of experiments, D. pulicaria is infested with the pathogen Vibrio cholerae, the causative agent of cholera. We find that infested D. pulicaria under light exposure have a significantly greater ecological temperature, which puts them at a greater risk of detection by visual predators. In a second set of experiments, we observe D. pulicaria in cold and warm water, and in darkness and under light exposure. Overall, our ecological temperature is a good discriminator of the crustacean’s swimming behavior.

The stable isotopic composition of <i>Daphnia</i> ephippia reflects changes in δ<sup>13</sup>C and δ<sup>18</sup>O values of food and water

Abstract. The stable isotopic composition of fossil resting eggs (ephippia) of Daphnia spp. is being used to reconstruct past environmental conditions in lake ecosystems. However, the underlying assumption that the stable isotopic composition of the ephippia reflects the stable isotopic composition of the parent Daphnia, of their diet and of the environmental water have yet to be confirmed in a controlled experimental setting. We performed experiments with Daphnia pulicaria cultures, which included a control treatment conducted at 12 °C in filtered lake water and with a diet of fresh algae and three treatments in which we manipulated the stable carbon isotopic composition (δ13C value) of the algae, stable oxygen isotopic composition (δ18O value) of the water and the water temperature, respectively. The stable nitrogen isotopic composition (δ15N value) of the algae was similar for all treatments. At 12 °C, differences in algal δ13C values and in δ18O values of water were reflected in those of Daphnia. The differences between ephippia and Daphnia stable isotope ratios were similar in the different treatments (δ13C: +0.2 ± 0.4 ‰ (standard deviation); δ15N: −1.6 ± 0.4 ‰; δ18O: −0.9 ± 0.4 ‰), indicating that changes in dietary δ13C values and in δ18O values of water are passed on to these fossilizing structures. A higher water temperature (20 °C) resulted in lower δ13C values in Daphnia and ephippia than in the other treatments with the same food source and in a minor change in the difference between δ13C values of ephippia and Daphnia (to −1.3 ± 0.3 ‰). This may have been due to microbial processes or increased algal respiration rates in the experimental containers, which may not affect Daphnia in natural environments. There was no significant difference in the offset between δ18O and δ15N values of ephippia and Daphnia between the 12 and 20 °C treatments, but the δ18O values of Daphnia and ephippia were on average 1.2 ‰ lower at 20 °C than at 12 °C. We conclude that the stable isotopic composition of Daphnia ephippia provides information on that of the parent Daphnia and of the food and water they were exposed to, with small offsets between Daphnia and ephippia relative to variations in Daphnia stable isotopic composition reported from downcore studies. However, our experiments also indicate that temperature may have a minor influence on the δ13C, δ15N and δ18O values of Daphnia body tissue and ephippia. This aspect deserves attention in further controlled experiments.

The stable isotopic composition of Daphnia ephippia reflects changes in delta C-13 and delta O-18 values of food and water

The stable isotopic composition of fossil resting eggs (ephippia) of Daphnia spp. is being used to reconstruct past environmental conditions in lake ecosystems. However, the underlying assumption that the stable isotopic composition of the ephippia reflects the stable isotopic composition of the parent Daphnia, of their diet and of the environmental water have yet to be confirmed in a controlled experimental setting. We performed experiments with Daphnia pulicaria cultures, which included a control treatment conducted at 12 A degrees C in filtered lake water and with a diet of fresh algae and three treatments in which we manipulated the stable carbon isotopic composition (delta C-13 value) of the algae, stable oxygen isotopic composition (delta O-18 value) of the water and the water temperature, respectively. The stable nitrogen isotopic composition (delta N-15 value) of the algae was similar for all treatments. At 12 A degrees C, differences in algal delta C-13 values and in delta O-18 values of water were reflected in those of Daphnia. The differences between ephippia and Daphnia stable isotope ratios were similar in the different treatments (delta C-13: +0.2 +/- 0.4 parts per thousand (standard deviation); delta N-15: -1.6 +/- 0.4 parts per thousand; delta O-18: -0.9 +/- 0.4 parts per thousand), indicating that changes in dietary delta C-13 values and in delta O-18 values of water are passed on to these fossilizing structures. A higher water temperature (20 A degrees C) resulted in lower delta C-13 values in Daphnia and ephippia than in the other treatments with the same food source and in a minor change in the difference between delta C-13 values of ephippia and Daphnia (to -1.3 +/- 0.3 parts per thousand). This may have been due to microbial processes or increased algal respiration rates in the experimental containers, which may not affect Daphnia in natural environments. There was no significant difference in the offset between delta O-18 and delta N-15 values of ephippia and Daphnia between the 12 and 20 A degrees C treatments, but the delta O-18 values of Daphnia and ephippia were on average 1.2 parts per thousand lower at 20 A degrees C than at 12 A degrees C. We conclude that the stable isotopic composition of Daphnia ephippia provides information on that of the parent Daphnia and of the food and water they were exposed to, with small offsets between Daphnia and ephippia relative to variations in Daphnia stable isotopic composition reported from downcore studies. However, our experiments also indicate that temperature may have a minor influence on the delta C-13, delta N-15 and delta O-18 values of Daphnia body tissue and ephippia. This aspect deserves attention in further controlled experiments.

The variation of stygofauna along a gradient of salinization in a coastal aquifer

We examined the variation of stygofauna composition collected in wells, along a gradient in groundwater salinity/conductivity in a coastal aquifer from southern Portugal. The studied coastal aquifer is considered vulnerable to salinization due to seawater intrusion, caused by overexploitation of the aquifer. Knowing the response of the stygofauna species to present levels of groundwater salinity makes it possible to understand and measure the effects of saltwater intrusion on stygofauna, rendering them potential bioindicators of this environmental pressure. Biotic and abiotic sampling was conducted in six shallow wells located in the fresh–saltwater interface of the Arade estuary along the salinity gradient established in the groundwater from the estuary to inland locations (microSiemens/cm). Groundwater salinity was highly correlated with taxa distribution. The stygobites Eucyclops hadjebensis and Acanthocyclops sensitivus, the cosmopolitan Megacyclops viridis and Cypria ophtalmica were particularly associated with low-salinity conditions, whereas Eucyclops graeteri, Megacyclops brachypus and Daphnia pulicaria were related to high-salinity waters. Multivariate analyses indicated that stygofauna assemblages varied significantly with location. We suggest that stygofauna composition and structure can be a useful complementing tool for monitoring seawater intrusion into coastal aquifers, where reduction or deterioration in groundwater resources is predicted.

Invasion and molecular evolution of Daphnia pulex in Japan

AbstractWe examined Daphnia pulex in Japan to clarify if they were representative of indigenous populations or colonized recently. Phylogenetic analysis of mtDNA suggests that Japanese lineages of D. pulex are immigrants from North America, and are hybrids formed with Daphnia pulicaria prior to this immigration. Based on the mtDNA sequences, the D. pulex individuals aggregated into four distinct genetic groups (JPN 1‐4) comprising a total of 21 haplotypes. Surprisingly, microsatellite analysis with 12 loci revealed only a single multilocus genotype per genetic group, suggesting that D. pulex populations in Japan are comprised of asexual individuals, derived from only four clones. According to the reported mutation rate of mtDNA, JPN 1 and 2, now widely distributed across Japan, were estimated to have invaded between 680 yr and 3400 yr ago, while JPN 3 and 4 colonized much more recently. Results also indicated that the invasion of some clones could not be attributed to recent human activities and most likely occurred by rare natural events. Since the evolutional longevity of asexual clones is thought to be limited, genetic diversity of D. pulex in Japan has the possibility of decreasing in the near future without addition of novel gene flow.

Zooplankton community changes confound the biodilution theory of methylmercury accumulation in a recovering mercury-contaminated lake.

In this study, the biodilution hypothesis of methylmercury (MeHg) accumulation was examined in a Hg-contaminated ecosystem that has undergone concurrent changes in nutrient loading and zooplankton community composition. Using a long-term record of 17 years (between 1980 and 2009), we demonstrate that zooplankton MeHg concentrations in Onondaga Lake, NY, are strongly driven by changes in the zooplankton community and body size. MeHg concentrations in zooplankton increased with an increase in body size and biomass. The highest concentrations of MeHg were observed under eutrophic and hypereutrophic conditions when large-bodied Daphnia species, Daphnia pulicaria and Daphnia galeata mendotae, were present. Bioconcentration rather than biodilution was governing the accumulation of MeHg in zooplankton without apparent growth dilution or zooplankton biomass dilution. Algal-bloom dilution controlled the variability in the MeHg concentration only under hypereutrophic conditions when Ceriodaphnia predominated the cladoceran population. Our study demonstrates that changes in zooplankton community composition confound the biodilution theory in Onondaga Lake and that the presence of large-bodied zooplankton species drives elevated MeHg concentrations.

Out with the old, in with the new? Younger Daphnia clones are competitively superior over centuries-old ancestors

A laboratory microcosm experiment was conducted to examine the roles of food quantity and food quality on the competitive abilities of clones of the keystone aquatic zooplankter, Daphnia pulicaria. Using methods of resurrection ecology, clones were established by hatching dormant eggs from sediment layers of a lake (South Center, MN, U.S.A) that were separated by centuries of environmental change (nutrient enrichment). Two sets of paired clones (“modern” vs. “ancient”) were competed against each other in a 2 × 2 factorial design of high/low food quantity and high/low food quality. Experimental carbon:phosphorus (C:P) ratios were designed to mimic food quantity and food quality parameters respective to each of the two time periods from which the clones were extracted to test whether clones are competitively superior under conditions representative of the time period in which they existed. Contrary to predictions, we found that “modern” clones were able to outcompete “ancient” clones under all food treatments. We discuss potential mechanisms (i.e., mutational input, viability of long-dormant eggs, differences in phenotypic plasticity) that may have differentially impacted the performance of experimental clones. Our results should aid in deciphering microevolutionary dynamics observed in resurrection ecology studies, a powerful tool that can illuminate adaptive dynamics of organisms to environmental changes on long-term (centuries-long) temporal scales.

Variation in toxicity of a current-use insecticide among resurrected Daphnia pulicaria genotypes.

This study examined how genotypes of Daphnia pulicaria from a single population, separated by thousands of generations of evolution in the wild, differ in their sensitivity to a novel anthropogenic stressor. These genotypes were resurrected from preserved resting eggs isolated from sediments belonging to three time periods: 2002-2008, 1967-1977, and 1301-1646 A.D. Toxicity of the organophosphate insecticide chlorpyrifos was determined through a series of acute toxicity tests. There was a significant dose-response effect in all genotypes studied. Moreover, significant variation in toxicity among genotypes within each time period was detected. Importantly, a significant effect of time period on sensitivity to chlorpyrifos was found. Analysis of the median effect concentrations (EC50s) for genotypes within each time period indicated that the 1301-1646 genotypes were 2.7 times more sensitive than the 1967-1977 genotypes. This trend may be partially explained by microevolutionary shifts in response to cultural eutrophication.

Do the presence of filamentous cyanobacteria and an elevated temperature favor small-bodied Daphnia in interspecific competitive interactions?

According to the Size-Efficiency Hypothesis, when the intensity of fish predation is low, large-bodied zooplankton species are competitively superior as they are more efficient filter feeders than small-bodied species and they have relatively reduced metabolic demands per unit mass. The presence of filamentous cyanobacteria can reduce the competitive superiority of large-bodied cladocerans, because they are less resistant than small-bodied ones to interference with food collection by filaments. The viscosity of water decreases with increasing temperature which may alter the filtering mechanisms of cladocerans, making the large-bodied species even more susceptible to interference by cyanobacterial filaments. The aims of this study were (1) to test if the presence of the filamen- tous non-toxic cyanobacterium Cylindrospermopsis raciborskii shifts competitive dominance from a large-bodied cladoceran species towards a small-bodied one and (2) to determine whether the competitive superiority of a small- bodied species in the presence of cyanobacterial filaments is temperature-dependent. A laboratory competition experiment was conducted with large-bodied Daphnia pulicaria and small-bodied D. longispina, in the presence or absence of cyanobacteria in two different thermal regimes -18 and 25 °C. Unexpectedly, D. pulicaria was dominant over D. longispina, irrespective of the food and thermal treatments applied. The large-bodied Daphnia species was competitively superior even in the presence of filamentous cyanobacteria and at an elevated temperature.

Gene expression variation in duplicate lactate dehydrogenase genes: do ecological species show distinct responses?

Lactate dehydrogenase (LDH) has been shown to play an important role in adaptation of several aquatic species to different habitats. The genomes of Daphnia pulex, a pond species, and Daphnia pulicaria, a lake inhabitant, encode two L-LDH enzymes, LDHA and LDHB. We estimated relative levels of Ldh gene expression in these two closely related species and their hybrids in four environmental settings, each characterized by one of two temperatures (10°C or 20°C), and one of two concentrations of dissolved oxygen (DO; 6.5–7 mg/l or 2–3 mg/l). We found that levels of LdhA expression were 4 to 48 times higher than LdhB expression (p<0.005) in all three groups (the two parental species and hybrids). Moreover, levels of LdhB expression differed significantly (p<0.05) between D. pulex and D. pulicaria, but neither species differed from the hybrid. Consistently higher expression of LdhA relative to LdhB in both species and the hybrid suggests that the two isozymes could be performing different functions. No significant differences in levels of gene expression were observed among the four combinations of temperature and dissolved oxygen (p>0.1). Given that Daphnia dwell in environments characterized by fluctuating conditions with long periods of low dissolved oxygen concentration, we suggest that these species could employ regulated metabolic depression to survive in such environments.

A dark shell hiding great variability: a molecular insight into the evolution and conservation of melanicDaphniapopulations in the Alps

Zooplanktonic microcrustaceans of the Daphnia pulex group appear highly differentiated at high altitudes as a result of alternative colonizations and quick local adaptation to harsh environments. In particular, the occurrence of deeply differentiated mountain lineages of European Daphnia pulicaria (EuPC) is highly related to glacial advances and retreats during the Pleistocene. Nowadays, one single ancient EuPC lineage survives in the Pyrenees, with another inhabiting the High Tatra Mountains. Much less is known about populations inhabiting the Alps, where EuPC populations are extremely rare. Recently, four new melanic populations have been discovered in lakes in the Western Italian Alps, offering the opportunity to study their origin and adaptations. We inferred phylogenetic relationships of melanic high-mountain populations in order to disentangle their history and clarify the colonization patterns of alpine populations. Molecular data suggest that dark populations originated from at least two ancestors, one genetically close to boreal haplotypes, the other apparently related to refugial populations that survived in southern Europe. Therefore, dark pigmentation and obligate parthenogenesis evolved independently within both lineages inhabiting the studied lakes as extreme local adaptations to the alpine environment. Finally, since impacts of human-related activities and climate changes on mountain species are known to be dramatic, we pose strong issues for the conservation of these extremely localized endemisms. © 2014 The Linnean Society of London

Relationship between heat shock protein 70 expression and life span in Daphnia

The longevity of an organism is directly related to its ability to effectively cope with cellular stress. Heat shock response (HSR) protects the cells against accumulation of damaged proteins after exposure to elevated temperatures and also in aging cells. To understand the role of Hsp70 in regulating life span of Daphnia, we examined the expression of Hsp70 in two ecotypes that exhibit strikingly different life spans. Daphnia pulicaria, the long lived ecotype, showed a robust Hsp70 induction as compared to the shorter lived Daphnia pulex. Interestingly, the short-lived D. pulex isolates showed no induction of Hsp70 at the mid point in their life span. In contrast to this, the long-lived D. pulicaria continued to induce Hsp70 expression at an equivalent age. We further show that the Hsp70 expression was induced at transcriptional level in response to heat shock. The transcription factor responsible for Hsp70 induction, heat shock factor-1 (HSF-1), although present in aged organisms did not exhibit DNA-binding capability. Thus, the decline of Hsp70 induction in old organisms could be attributed to a decline in HSF-1's DNA-binding activity. These results for the first time, present a molecular analysis of the relationship between HSR and life span in Daphnia.

Tail probabilities of extinction time in a large number of experimental populations.

Determining the distribution of population extinction times is a fundamental problem in theoretical population biology. In particular, the tail properties, patterns in the probability of long-term persistence, have not been studied. Further, until now there have been no experimental or observational data sets with which to empirically test the "rare event" predictions of the standard stochastic theory of extinction, which holds that extinction times should be exponentially distributed. I performed an experimental study of extinction in a large number of replicate (n = 1076) laboratory populations of the waterflea Daphnia pulicaria. Observed extinction time ranged from 1 to 1239 days. Statistical models supported the hypothesis of a power-law distribution over the exponential distribution and other alternatives. This pattern contradicts the notion that population extinction time has an exponential tail, questioning its ubiquitous use in theoretical ecology. It is also a rare instance of a data set that exhibits power-law scaling under appropriate statistical criteria.

A millennial‐scale chronicle of evolutionary responses to cultural eutrophication in Daphnia

For an accurate assessment of the anthropogenic impacts on evolutionary change in natural populations, we need long-term environmental, genetic and phenotypic data that predate human disturbances. Analysis of c. 1600years of history chronicled in the sediments of South Center Lake, Minnesota, USA, revealed major environmental changes beginning c. 120years ago coinciding with the initiation of industrialised agriculture in the catchment area. Population genetic structure, analysed using DNA from dormant eggs of the keystone aquatic herbivore, Daphnia pulicaria, suggested no change for c. 1500years prior to striking shifts associated with anthropogenic environmental alterations. Furthermore, phenotypic assays on the oldest resurrected metazoan genotypes (potentially as old as c. 700years) indicate significant shifts in phosphorus utilisation rates compared to younger genotypes. Younger genotypes show steeper reaction norms with high growth under high phosphorus (P), and low growth under low P, while 'ancient' genotypes show flat reaction norms, yet higher growth efficiency under low P. Using this resurrection ecology approach, environmental, genetic and phenotypic data spanning pre- and post-industrialised agricultural eras clearly reveal the evolutionary consequences of anthropogenic environmental change.

Large effects of consumer offense on ecosystem structure and function

Study of the role of within-species adaptation in ecological dynamics has focused largely on prey adaptations that reduce consumption risk (prey defense). Few, if any, studies have examined how consumer adaptations to overcome prey defenses (consumer offense) affect ecosystem structure and function. We manipulated two sets of genotypes of a planktonic herbivore (Daphnia pulicaria) in a highly productive ecosystem with abundant toxic prey (cyanobacteria). The two sets of consumer genotypes varied widely in their tolerance of toxic cyanobacteria in the diet (i.e., sensitive vs. tolerant). We found a large effect of tolerant D. pulicaria on phytoplankton biomass and gross primary productivity but no effect of sensitive genotypes, this result stemming from genotype-specific differences in population growth in the presence of toxic prey. The former effect was as large as effects seen in previous Daphnia manipulations at similar productivity levels. Thus, we demonstrated that the effect of consumer genotypes with contrasting offensive adaptations was as large as the effect of consumer presence/absence.