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Teresa J. Crease - One of the best experts on this subject based on the ideXlab platform.
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Copy Number of the Transposon, Pokey, in rDNA Is Positively Correlated with rDNA Copy Number in Daphnia obtusa
PloS one, 2014Co-Authors: Kaitlynn Leriche, Shannon H. C. Eagle, Teresa J. CreaseAbstract:Pokey is a class II DNA transposon that inserts into 28S ribosomal RNA (rRNA) genes and other genomic regions of species in the subgenus, Daphnia. Two divergent lineages, PokeyA and PokeyB have been identified. Recombination between misaligned rRNA genes changes their number and the number of Pokey elements. We used quantitative PCR (qPCR) to estimate rRNA gene and Pokey number in isolates from natural populations of Daphnia obtusa, and in clonally-propagated mutation accumulation lines (MAL) initiated from a single D. obtusa female. The change in direction and magnitude of Pokey and rRNA gene number did not show a consistent pattern across ∼87 generations in the MAL; however, Pokey and rRNA gene number changed in concert. PokeyA and 28S gene number were positively correlated in the isolates from both natural populations and the MAL. PokeyB number was much lower than PokeyA in both MAL and natural population isolates, and showed no correlation with 28S gene number. Preliminary analysis did not detect PokeyB outside rDNA in any isolates and detected only 0 to 4 copies of PokeyA outside rDNA indicating that Pokey may be primarily an rDNA element in D. obtusa. The recombination rate in this species is high and the average size of the rDNA locus is about twice as large as that in other Daphnia species such as D. pulicaria and D. pulex, which may have facilitated expansion of PokeyA to much higher numbers in D. obtusa rDNA than these other species.
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Haploid number of Pokey and rRNA genes in isolates of Daphnia obtusa.
2014Co-Authors: Kaitlynn Leriche, Shannon H. C. Eagle, Teresa J. CreaseAbstract:Haploid number of Pokey and rRNA genes in isolates of Daphnia obtusa.
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Correlation between the number of rRNA genes and Pokey elements in isolates of Daphnia obtusa.
2014Co-Authors: Kaitlynn Leriche, Shannon H. C. Eagle, Teresa J. CreaseAbstract:Correlation between the number of rRNA genes and Pokey elements in isolates of Daphnia obtusa.
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Evolution of a transposon in Daphnia hybrid genomes
Mobile DNA, 2013Co-Authors: Roland Vergilino, Teresa J. Crease, Tyler A Elliott, Philippe Desjardins-proulx, France DufresneAbstract:Background Transposable elements play a major role in genome evolution. Their capacity to move and/or multiply in the genome of their host may have profound impacts on phenotypes, and may have dramatic consequences on genome structure. Hybrid and polyploid clones have arisen multiple times in the Daphnia pulex complex and are thought to reproduce by obligate parthenogenesis. Our study examines the evolution of a DNA transposable element named Pokey in the D. pulex complex. Results Portions of Pokey elements inserted in the 28S rRNA genes from various Daphnia hybrids (diploids and polyploids) were sequenced and compared to sequences from a previous study to understand the evolutionary history of the elements. Pokey sequences show a complex phylogenetic pattern. We found evidence of recombination events in numerous Pokey alleles from diploid and polyploid hybrids and also from non-hybrid diploids. The recombination rate in Pokey elements is comparable to recombination rates previously estimated for 28S rRNA genes in the congener, Daphnia obtusa. Some recombinant Pokey alleles were encountered in Daphnia isolates from multiple locations and habitats. Conclusions Phylogenetic and recombination analyses showed that recombination is a major force that shapes Pokey evolution. Based on Pokey phylogenies, reticulation has played and still plays an important role in shaping the diversity of the D. pulex complex. Horizontal transfer of Pokey seems to be rare and hybrids often possess Pokey elements derived from recombination among alleles encountered in the putative parental species. The insertion of Pokey in hotspots of recombination may have important impacts on the diversity and fitness of this transposable element.
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Consensus Bayesian phylogeny of the Daphnia pulex species complex based on the mitochondrial ND5 gene.
2012Co-Authors: Teresa J. Crease, Angela R. Omilian, Katie S. Costanzo, Derek J. TaylorAbstract:The alignment contains 398 sequences of length 496 nt with 241 polymorphic nt positions of which 204 are phylogenetically informative (excluding the outgroup). Posterior probabilities are indicated on the nodes of the tree and are not shown if less than 0.80. The tree is rooted using an ND5 sequence from Daphnia obtusa. Triangles represent clusters that are collapsed to save space and the number of individuals included is shown in parentheses. The large letters indicate the three major groups within the D. pulex species complex: A = tenebrosa; B = pulicaria; C = pulex. The two or three-letter code names of some individuals correspond to sampling locations as follows: ARG = Argentina, BOL = Bolivia, CHI = Chile, CT = Connecticut, USA. The expanded version of this tree showing all individuals is available in Figure S1.
Seanna J. Mctaggart - One of the best experts on this subject based on the ideXlab platform.
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Length Variation in 18S rRNA Expansion Segment 43/e4 of Daphnia obtusa: Ancient or Recurring Polymorphism?
Journal of Molecular Evolution, 2009Co-Authors: Seanna J. Mctaggart, Teresa J. CreaseAbstract:Expansion segments in ribosomal DNA (rDNA) can show length variation at the level of the individual, yet our understanding of the evolutionary forces shaping this variation is incomplete. Previous studies of expansion segment 43/e4 of the 18S rRNA gene in Daphnia obtusa have examined this variation in six individuals; however, it is not known if the variation documented at this locus is representative of variation across the species’ geographic range. Furthermore, it is unclear whether length variants found in multiple individuals share common ancestry, or were generated de novo through recombination. We quantified expansion segment length variant frequencies in 134 individual D. obtusa from 33 populations at 15 sites across the species range in the US, and used a phylogeographic approach to determine whether recombination continues to add to the standing crop of variation at this locus. We identified seven length variants across the sampling range, which spans almost 3000 km. Based on the phylogeographic distribution of length variants in the expansion segment, we conclude that they are shared ancient polymorphisms that have persisted despite the operation of molecular mechanisms that cause the concerted evolution of multigene families such as rDNA.
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length variation in 18s rrna expansion segment 43 e4 of Daphnia obtusa ancient or recurring polymorphism
Journal of Molecular Evolution, 2009Co-Authors: Seanna J. Mctaggart, Teresa J. CreaseAbstract:Expansion segments in ribosomal DNA (rDNA) can show length variation at the level of the individual, yet our understanding of the evolutionary forces shaping this variation is incomplete. Previous studies of expansion segment 43/e4 of the 18S rRNA gene in Daphnia obtusa have examined this variation in six individuals; however, it is not known if the variation documented at this locus is representative of variation across the species’ geographic range. Furthermore, it is unclear whether length variants found in multiple individuals share common ancestry, or were generated de novo through recombination. We quantified expansion segment length variant frequencies in 134 individual D. obtusa from 33 populations at 15 sites across the species range in the US, and used a phylogeographic approach to determine whether recombination continues to add to the standing crop of variation at this locus. We identified seven length variants across the sampling range, which spans almost 3000 km. Based on the phylogeographic distribution of length variants in the expansion segment, we conclude that they are shared ancient polymorphisms that have persisted despite the operation of molecular mechanisms that cause the concerted evolution of multigene families such as rDNA.
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Rates of Recombination in the Ribosomal DNA of Apomictically Propagated Daphnia obtusa Lines
Genetics, 2006Co-Authors: Seanna J. Mctaggart, Jeffry L. Dudycha, Angela Omilian, Teresa J. CreaseAbstract:Ribosomal (r)DNA undergoes concerted evolution, the mechanisms of which are unequal crossing over and gene conversion. Despite the fundamental importance of these mechanisms to the evolution of rDNA, their rates have been estimated only in a few model species. We estimated recombination rate in rDNA by quantifying the relative frequency of intraindividual length variants in an expansion segment of the 18S rRNA gene of the cladoceran crustacean, Daphnia obtusa, in four apomictically propagated lines. We also used quantitative PCR to estimate rDNA copy number. The apomictic lines were sampled every 5 generations for 90 generations, and we considered each significant change in the frequency distribution of length variants between time intervals to be the result of a recombination event. Using this method, we calculated the recombination rate for this region to be 0.02–0.06 events/generation on the basis of three different estimates of rDNA copy number. In addition, we observed substantial changes in rDNA copy number within and between lines. Estimates of haploid copy number varied from 53 to 233, with a mean of 150. We also measured the relative frequency of length variants in 30 lines at generations 5, 50, and 90. Although length variant frequencies changed significantly within and between lines, the overall average frequency of each length variant did not change significantly between the three generations sampled, suggesting that there is little or no bias in the direction of change due to recombination.
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Selection on the Structural Stability of a Ribosomal RNA Expansion Segment in Daphnia obtusa
Molecular biology and evolution, 2005Co-Authors: Seanna J. Mctaggart, Teresa J. CreaseAbstract:The high rate of sequence divergence in nuclear ribosomal RNA (rRNA) expansion segments offers a unique opportunity to study the importance of natural selection in their evolution. To this end, we polymerase chain reaction amplified and cloned a 589-nt fragment of the 18S rRNA gene containing expansion segments 43/e1 and 43/e4 from six individual Daphnia obtusa from four populations. We screened 2,588 clones using single-stranded conformation polymorphism analysis and identified 103 unique haplotype sequences. We detected two pairs of indel sites in segment 43/e4 that complement each other when the secondary structure of the linear sequence is formed. Seven of the 12 observed combinations of length variants at these four sites (haplotypes) are shared between individuals from different populations, which may suggest that some of the length variation was present in their common ancestor. Haplotypes with uncompensated indels were only observed at low frequencies, while compensated indel haplotypes were found at a wide range of frequencies, supporting the hypothesis that the energetic stability of expansion segments is a trait under natural selection. In addition, there was strong linkage disequilibrium between the four complementary indel sites, particularly those that pair with one another in the secondary structure. Despite selection against unpaired bulges at these four indel sites, some nucleotides that form unpaired bulges are highly conserved in segment 43/e4, indicating that they are under a different selective constraint, possibly due to their role in higher level structural interactions.
Nestor Mazzeo - One of the best experts on this subject based on the ideXlab platform.
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trophic cascade effects of hoplias malabaricus characiformes erythrinidae in subtropical lakes food webs a mesocosm approach
Hydrobiologia, 2010Co-Authors: Nestor Mazzeo, Franco Teixeirade Mello, Ana Borthagaray, Claudia Fosalba, Roberto Ballabio, Diego Larrea, Jovana Vilches, Soledad Garcia, Carlos Iglesias, Juan Pablo PachecoAbstract:While the cascading effect of piscivorous fish on the pelagic food-web has been well studied in north temperate lakes, little is known about the role of native piscivores in warm lakes. Here, the fish communities are typically characterized by high abundances of small, omnivorous fish exerting a high predation pressure on the zooplankton. We conducted a 1-month replicated mesocosm experiment at subtropical conditions to test the effects of piscivorous (Hoplias malabaricus) fish on phytoplankton biomass and water transparency. Our experimental design comprised two (phytoplankton + zooplankton), three (phytoplankton + zooplankton + planktivores) and four (phytoplankton + zooplankton + planktivores + piscivores) trophic levels. We designed two different four trophic level treatments, one with juveniles of H. malabaricus ( 30 cm), to evaluate the strength of the effects of juveniles and adults. A major trophic cascade response was observed. In the planktivores treatment, chlorophyll a (Chl a) and turbidity significantly increased, while total zooplankton abundance (especially Daphnia obtusa) and water transparency decreased. In both H. malabaricus treatments and in the two trophic levels control, the opposite pattern was observed; thus, Chl a and turbidity decreased, while zooplankton abundance and water transparency increased. The differences observed reflected the strong control on the planktivore Jenynsia multidentata by both sizes of H. malabaricus, propagating down through the trophic web. Hoplias malabaricus is widely distributed in South America and may, therefore, be a good candidate for restoration by biomanipulation in eutrophic lakes of subtropical and tropical regions. However, detailed investigations at whole-lake scale are needed to determine its potential.
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field and experimental evidence of the effect of jenynsia multidentata a small omnivorous planktivorous fish on the size distribution of zooplankton in subtropical lakes
Freshwater Biology, 2008Co-Authors: Carlos Iglesias, Nestor Mazzeo, Claudia Fosalba, Soledad Garcia, Guillermo Goyenola, Franco Teixeira De Mello, Erik JeppesenAbstract:SUMMARY 1. Small cladocerans, copepod nauplii and rotifers often dominate the zooplankton community in tropical and subtropical lakes. This is probably because of high predation pressure by small omnivorous–planktivorous fish, but experimental evidence is scarce. 2. This study used two approaches to test the effect of the small omnivorous–planktivorous fish species Jenynsia multidentata, which is frequently abundant in (sub)tropical eutrophic lakes in South America, on the size distribution of zooplankton. In Lake Blanca (Uruguay), which lacks any piscivores, we sampled seasonally for both fish and zooplankton. We also conducted an outdoor mesocosm experiment with treatments containing or lacking J. multidentata. 3. Together, the empirical and experimental data suggest that J. multidentata predation plays an important role in modulating the size structure of the zooplankton community in subtropical lakes. In the absence of J. multidentata, stocked large-sized zooplankters like Daphnia obtusa were abundant in the experiments, while small-sized zooplankton dominated in the presence of fish, as they did in the lake itself from spring to the end of the season.
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An experimental study of habitat choice by Daphnia: plants signal danger more than refuge in subtropical lakes
Freshwater Biology, 2006Co-Authors: Mariana Meerhoff, Nestor Mazzeo, Claudia Fosalba, Carla Bruzzone, Willemijn Noordoven, Erik JeppesenAbstract:SUMMARY 1. In shallow temperate lakes, submerged plants often provide refuge for pelagic zooplankton against fish predation, a mechanism with potential strong cascading effects on water transparency and on the entire ecosystem. In (sub)tropical lakes, however, the interaction between aquatic plants and predation may be more complex, particularly because fish density is high within the plant beds in such systems. 2. Using laboratory ‘habitat choice’ experiments, we determined the effects of three (sub)tropical free-floating plants, Eichhornia crassipes, Pistia stratiotes and Salvinia auriculata and the cosmopolitan submerged Ceratophyllum demersum, on horizontal movement by the water flea Daphnia obtusa. We tested for avoidance of plants in the absence and presence of alarm signals from crushed conspecifics and chemical cues from the fish Cnesterodon decemmaculatus, the fish have been subjected to different feeding regimes. 3. In the absence of other stimuli, D. obtusa strongly avoided the plants and the crushed conspecifics, as expected. However, the response to fish was insignificant regardless of their previous feeding regime. The avoidance of free-floating plants was more pronounced than that of the submerged plant. Contrary to predictions based on research in temperate lakes, Daphnia did not take refuge among the plants but rather swam away from them when exposed simultaneously to plants and alarm signals. 4. We hypothesise that the avoidance of plants by D. obtusa may ultimately be attributable to an expectedly higher predation risk within the plants than in the pelagic, because of a high density of associated zooplanktivorous fish in the former. In the (sub)tropics, therefore, aquatic plants and particularly the free-floating ones, may not promote cascading effects via Daphnia grazing on phytoplankton as seen in temperate eutrophic lakes.
M. Beltrami - One of the best experts on this subject based on the ideXlab platform.
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2001. In situ toxicity testing of Lake Orta sediments
2016Co-Authors: Renato Baudo, D. Rossi, M. BeltramiAbstract:The use of in situ assays, which was initially proposed by Nebeker et al. (1984), is presently recognised as an effective tool to study the effects of contaminated sediments (Burton 1992). The placement of caged organisms to study short-term effects of exposure to contaminated environments has been employed for a number of aquatic species, both fish and invertebrate. This paper describes the application of this techniques to study the toxicity of Lake Orta sediments using both resident (Daphnia obtusa, D. longispina) and non-resident (D. magna, Echinogammarus stammeri) invertebrate species. In each of the selected stations, a group of four chambers, each containing 10 individuals, were deployed by scuba divers at 10 m depth and collected after 48 h. For each chamber, the surviving animals were counted, transferred to the laboratory and kept in Lake Orta water until their death. The number of neo-nates produced by each female in the laboratory was recorded daily in order to determine if the short exposure period could affect the reproductive behaviour of the animals. The technique and results reported here indicate the utility of in situ testing and suggest that, under certain conditions, this method of testing may yield results which are more representative of actual environmental condi-tions by avoiding the sample manipulation required for traditional laboratory toxicity tests
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In situ toxicity testing of Lake Orta sediments
Journal of Limnology, 2001Co-Authors: Renato Baudo, D. Rossi, M. BeltramiAbstract:The use of in situ assays, which was initially proposed by Nebeker et al. (1984), is presently recognised as an effective tool to study the effects of contaminated sediments (Burton 1992). The placement of caged organisms to study short-term effects of exposure to contaminated environments has been employed for a number of aquatic species, both fish and invertebrate. This paper describes the application of this techniques to study the toxicity of Lake Orta sediments using both resident (Daphnia obtusa, D. longispina) and non-resident (D. magna, Echinogammarus stammeri) invertebrate species. In each of the selected stations, a group of four chambers, each containing 10 individuals, were deployed by scuba divers at 10 m depth and collected after 48 h. For each chamber, the surviving animals were counted, transferred to the laboratory and kept in Lake Orta water until their death. The number of neonates produced by each female in the laboratory was recorded daily in order to determine if the short exposure period could affect the reproductive behaviour of the animals. The technique and results reported here indicate the utility of in situ testing and suggest that, under certain conditions, this method of testing may yield results which are more representative of actual environmental conditions by avoiding the sample manipulation required for traditional laboratory toxicity tests.
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Sediment ecological risk assessment: In situ and laboratory toxicity testing of Lake Orta sediments
Chemosphere, 1998Co-Authors: D. Rossi, M. BeltramiAbstract:Abstract Specifically designed benthic chambers have been used to test whether the exposure for 48 hrs to polluted Lake Orta sediments could affect survival and reproduction behaviour of Daphnia obtusa and Echinogammarus stammeri . In situ results have been coupled to lab testing with Microtox, seed germination and root elongation ( Lactuca sativa, Cucunris sativus, Lepidium sativum ), and invertebrates ( Daphnia obtusa, D. magna, E,. stammeri ) acute toxicity tests. The technique and results here reported indicate the utility of in situ testing and suggest that under certain conditions this kind of test may be more realistic (avoiding sample manipulation in the lab) than traditional laboratory toxicity tests.
Claudia Fosalba - One of the best experts on this subject based on the ideXlab platform.
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trophic cascade effects of hoplias malabaricus characiformes erythrinidae in subtropical lakes food webs a mesocosm approach
Hydrobiologia, 2010Co-Authors: Nestor Mazzeo, Franco Teixeirade Mello, Ana Borthagaray, Claudia Fosalba, Roberto Ballabio, Diego Larrea, Jovana Vilches, Soledad Garcia, Carlos Iglesias, Juan Pablo PachecoAbstract:While the cascading effect of piscivorous fish on the pelagic food-web has been well studied in north temperate lakes, little is known about the role of native piscivores in warm lakes. Here, the fish communities are typically characterized by high abundances of small, omnivorous fish exerting a high predation pressure on the zooplankton. We conducted a 1-month replicated mesocosm experiment at subtropical conditions to test the effects of piscivorous (Hoplias malabaricus) fish on phytoplankton biomass and water transparency. Our experimental design comprised two (phytoplankton + zooplankton), three (phytoplankton + zooplankton + planktivores) and four (phytoplankton + zooplankton + planktivores + piscivores) trophic levels. We designed two different four trophic level treatments, one with juveniles of H. malabaricus ( 30 cm), to evaluate the strength of the effects of juveniles and adults. A major trophic cascade response was observed. In the planktivores treatment, chlorophyll a (Chl a) and turbidity significantly increased, while total zooplankton abundance (especially Daphnia obtusa) and water transparency decreased. In both H. malabaricus treatments and in the two trophic levels control, the opposite pattern was observed; thus, Chl a and turbidity decreased, while zooplankton abundance and water transparency increased. The differences observed reflected the strong control on the planktivore Jenynsia multidentata by both sizes of H. malabaricus, propagating down through the trophic web. Hoplias malabaricus is widely distributed in South America and may, therefore, be a good candidate for restoration by biomanipulation in eutrophic lakes of subtropical and tropical regions. However, detailed investigations at whole-lake scale are needed to determine its potential.
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field and experimental evidence of the effect of jenynsia multidentata a small omnivorous planktivorous fish on the size distribution of zooplankton in subtropical lakes
Freshwater Biology, 2008Co-Authors: Carlos Iglesias, Nestor Mazzeo, Claudia Fosalba, Soledad Garcia, Guillermo Goyenola, Franco Teixeira De Mello, Erik JeppesenAbstract:SUMMARY 1. Small cladocerans, copepod nauplii and rotifers often dominate the zooplankton community in tropical and subtropical lakes. This is probably because of high predation pressure by small omnivorous–planktivorous fish, but experimental evidence is scarce. 2. This study used two approaches to test the effect of the small omnivorous–planktivorous fish species Jenynsia multidentata, which is frequently abundant in (sub)tropical eutrophic lakes in South America, on the size distribution of zooplankton. In Lake Blanca (Uruguay), which lacks any piscivores, we sampled seasonally for both fish and zooplankton. We also conducted an outdoor mesocosm experiment with treatments containing or lacking J. multidentata. 3. Together, the empirical and experimental data suggest that J. multidentata predation plays an important role in modulating the size structure of the zooplankton community in subtropical lakes. In the absence of J. multidentata, stocked large-sized zooplankters like Daphnia obtusa were abundant in the experiments, while small-sized zooplankton dominated in the presence of fish, as they did in the lake itself from spring to the end of the season.
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An experimental study of habitat choice by Daphnia: plants signal danger more than refuge in subtropical lakes
Freshwater Biology, 2006Co-Authors: Mariana Meerhoff, Nestor Mazzeo, Claudia Fosalba, Carla Bruzzone, Willemijn Noordoven, Erik JeppesenAbstract:SUMMARY 1. In shallow temperate lakes, submerged plants often provide refuge for pelagic zooplankton against fish predation, a mechanism with potential strong cascading effects on water transparency and on the entire ecosystem. In (sub)tropical lakes, however, the interaction between aquatic plants and predation may be more complex, particularly because fish density is high within the plant beds in such systems. 2. Using laboratory ‘habitat choice’ experiments, we determined the effects of three (sub)tropical free-floating plants, Eichhornia crassipes, Pistia stratiotes and Salvinia auriculata and the cosmopolitan submerged Ceratophyllum demersum, on horizontal movement by the water flea Daphnia obtusa. We tested for avoidance of plants in the absence and presence of alarm signals from crushed conspecifics and chemical cues from the fish Cnesterodon decemmaculatus, the fish have been subjected to different feeding regimes. 3. In the absence of other stimuli, D. obtusa strongly avoided the plants and the crushed conspecifics, as expected. However, the response to fish was insignificant regardless of their previous feeding regime. The avoidance of free-floating plants was more pronounced than that of the submerged plant. Contrary to predictions based on research in temperate lakes, Daphnia did not take refuge among the plants but rather swam away from them when exposed simultaneously to plants and alarm signals. 4. We hypothesise that the avoidance of plants by D. obtusa may ultimately be attributable to an expectedly higher predation risk within the plants than in the pelagic, because of a high density of associated zooplanktivorous fish in the former. In the (sub)tropics, therefore, aquatic plants and particularly the free-floating ones, may not promote cascading effects via Daphnia grazing on phytoplankton as seen in temperate eutrophic lakes.
