A fast and inexpensive genotyping system for the simultaneous analysis of human and Aedes albopictus short tandem repeats.

BACKGROUND: Determination of the interactions between hematophagous mosquitoes and their human hosts is of great importance for better understanding the transmission dynamics of mosquito-borne arboviruses and developing effective strategies to mitigate risk. Genetic analysis of human and mosquito DNA can play a key role in this, but commercial kits for human short tandem repeat (STR) genotyping are expensive and do not allow for the simultaneous STR analysis of host and vector DNA. Here, we present an inexpensive and straightforward STR-loci multiplex system capable of simultaneously amplifying Aedes albopictus and human STRs from blood-fed mosquitoes. Additionally, we examine the effect of storage methods and post-feeding time on the integrity of host DNA. METHODS: Thirty-five STRs (16 human and 19 Ae. albopictus STRs) subdivided in three multiplexes were tested for amplification and scoring reliability. Under laboratory conditions we compared the efficacy of two preservation methods (absolute ethanol vs lysis buffer) on the integrity of host DNA in Ae. albopictus blood meals. We also evaluated the effect of post-feeding time by sacrificing blood-fed mosquitoes at different time intervals after feeding, and we assessed our ability to detect multiple feedings. To determine if the system can be employed successfully under field conditions, we carried out a preliminary study using field-collected Ae. albopictus. RESULTS: All 35 STRs amplified consistently in the laboratory. Lysis buffer performed better than absolute ethanol in terms of allele peak height and clarity of electropherograms. Complete human DNA profiles could be obtained up to 48 h following the blood meal. Analysis of multiple feedings confirmed that peak heights can be used as a proxy to determine post-feeding time and thus derive the number of different people bitten by a mosquito. In the field trial, amplification was successful for 32 STRs. We found human DNA signal in 38 of the 61 field-collected mosquitoes (62%), of which 34 (89%) had ingested a single blood meal, while four (11%) contained double meals. CONCLUSIONS: Our new genotyping system allows fast and reliable screening of both host and vector species, and can be further adapted to other mosquito species living in close contact with humans.

New insights on patterns of genetic admixture and phylogeographic history in Iberian high mountain populations of midwife toads.

Multiple Quaternary glacial refugia in the Iberian Peninsula, commonly known as "refugia within refugia", allowed diverging populations to come into contact and admix, potentially boosting substantial mito-nuclear discordances. In this study, we employ a comprehensive set of mitochondrial and nuclear markers to shed light onto the drivers of geographical differentiation in Iberian high mountain populations of the midwife toads Alytes obstetricans and A. almogavarii from the Pyrenees, Picos de Europa and Guadarrama Mountains. In the three analysed mountain regions, we detected evidence of extensive mito-nuclear discordances and/or admixture between taxa. Clustering analyses identified three major divergent lineages in the Pyrenees (corresponding to the eastern, central and central-western Pyrenees), which possibly recurrently expanded and admixed during the succession of glacial-interglacial periods that characterised the Late Pleistocene, and that currently follow a ring-shaped diversification pattern. On the other hand, populations from the Picos de Europa mountains (NW Iberian Peninsula) showed a mitochondrial affinity to central-western Pyrenean populations and a nuclear affinity to populations from the central Iberian Peninsula, suggesting a likely admixed origin for Picos de Europa populations. Finally, populations from the Guadarrama Mountain Range (central Iberian Peninsula) were depleted of genetic diversity, possibly as a consequence of a recent epidemic of chytridiomycosis. This work highlights the complex evolutionary history that shaped the current genetic composition of high mountain populations, and underscores the importance of using a multilocus approach to better infer the dynamics of population divergence.

Multiple invasions, Wolbachia and human-aided transport drive the genetic variability of Aedes albopictus in the Iberian Peninsula.

The Asian tiger mosquito, Aedes albopictus, is one of the most invasive species in the world. Native to the tropical forests of Southeast Asia, over the past 30 years it has rapidly spread throughout tropical and temperate regions of the world. Its dramatic expansion has resulted in public health concerns as a consequence of its vector competence for at least 16 viruses. Previous studies showed that Ae. albopictus spread has been facilitated by human-mediated transportation, but much remains unknown about how this has affected its genetic attributes. Here we examined the factors that contributed to shaping the current genetic constitution of Ae. albopictus in the Iberian Peninsula, where the species was first found in 2004, by combining population genetics and Bayesian modelling. We found that both mitochondrial and nuclear DNA markers showed a lack of genetic structure and the presence of worldwide dominant haplotypes, suggesting regular introductions from abroad. Mitochondrial DNA showed little genetic diversity compared to nuclear DNA, likely explained by infection with maternally transmitted bacteria of the genus Wolbachia. Multilevel models revealed that greater mosquito fluxes (estimated from commuting patterns and tiger mosquito population distribution) and spatial proximity between sampling sites were associated with lower nuclear genetic distance, suggesting that rapid short- and medium-distance dispersal is facilitated by humans through vehicular traffic. This study highlights the significant role of human transportation in shaping the genetic attributes of Ae. albopictus and promoting regional gene flow, and underscores the need for a territorially integrated surveillance across scales of this disease-carrying mosquito.

A new fairy shrimp, Branchinecta piurae sp. nov. (Branchiopoda: Anostraca), from Peru.

South American species of Branchinecta that inhabit high altitude biotopes are so far represented by B. brushi and B. papillata. Here we describe a new species inhabiting these extreme habitats, B. piurae sp. nov., whose closest species is B. papillata. Differential characters of B. piurae are the lack, in males, of proximal and distal anteromedial bulges with spines at the second antenna basal antennomere which are conversely present in males of B. papillata; instead, the males of B. piurae have scattered, triangular spines over the anterior and medial surfaces at the distal half of the basal antennomere. In females of B. piurae, the dorsal surface of thoracic segments are provided with well-marked rough protuberances mainly on segments 3 to 10, features that are not observed in B. papillata. As far as is known, Branchinecta piurae sp. nov. is endemic to the Peruvian and Ecuadorian Andes, appearing at altitudes around 3,7003,800 m a.s.l, and latitudes from 247 to 504 S. The results of the genetic analyses based both on mitochondrial and nuclear markers provide a clear support for the morphological description of B. piurae as a new species. We also provide genetic sequences of B. papillata, B. ferox from Spain and B. orientalis from Spain and Mongolia, and show that Palaearctic Branchinecta species are not directly related to B. piurae and B. papillata. In the phylogeny derived from COI, the last two species form a sister clade to the American Branchinecta clade, including several North American species, or in the 16S phylogeny, only B. papillata is at the base. Our results suggest a different history about the genus in America than previous hypotheses. New molecular studies are needed that include additional South American species in order to better explore the diversity and biogeographical patterns of the genus Branchinecta.

Factors of surface thermal variation in high-mountain lakes of the Pyrenees.

Thermal variables are crucial drivers of biological processes in lakes and ponds. In the current context of climate change, determining which factors better constrain their variation within lake districts become of paramount importance for understanding species distribution and their conservation. In this study, we describe the regional and short-term interannual variability in surface water temperature of high mountain lakes and ponds of the Pyrenees. And, we use mixed regression models to identify key environmental factors and to infer mean and maximum summer temperature, accumulated degree-days, diel temperature ranges and three-days' oscillation. The study is based on 59 lake-temperature series measured from 2001 to 2014. We found that altitude was the primary explicative factor for accumulated degree-days and mean and maximum temperature. In contrast, lake area showed the most relevant effect on the diel temperature range and temperature oscillations, although diel temperature range was also found to decline with altitude. Furthermore, the morphology of the catchment significantly affected accumulated degree-days and maximum and mean water temperatures. The statistical models developed here were applied to upscale spatially the current thermic conditions across the whole set of lakes and ponds of the Pyrenees.

Ceriodaphnia smirnovi (Crustacea: Cladocera), a new species from the Mediterranean Region, and a phylogenetic analysis of the commonest species.

Species of the genus Ceriodaphnia Dana, 1853 (Crustacea: Cladocera: Daphniidae) are present in the plankton of many freshwater bodies all around the World. However, the taxonomy of the genus is still poorly developed. Most species have been described in the nineteenth century and data on their morphology and distribution should be revised according to current standards. Currently, due to lack of reliable morphological and genetic data, almost all nominal species of Ceriodaphnia are considered as species groups rather than separate biological species, complicating the detection and description of new species of the genus. Here, we redescribe the morphology of Ceriodaphnia quadrangula (O.F. Müller, 1785) based on material close to the type locality in Denmark, and describe a new species of Ceriodaphnia from the Mediterranean region. Also, we provide a phylogenetic analysis using existing and novel sequences of mitochondrial DNA of the commonest species of the genus. Ceriodaphnia smirnovi sp. nov. can be easily distinguished from C. quadrangula via presence of the head pore and the structure of the second thoracic limb, the postabdomen and the ephippium. From other species of Ceriodaphnia known to date C. smirnovi sp. nov. can also be separated on ephippium structure and some other fine morphological features. Although distribution range of C. smirnovi sp. nov. must be clarified in the future based on analysis of more sampling points, most likely, it is restricted to the Mediterranean region. The phylogenetic analyses showed high divergence among 16 different clades (mean clade separation of 13±2.3 % (mean ± SD) and 20.7±2.1% for 16S and COI respectively). These clades belonged to 11 described species and 5 undescribed. The high intraspecific variability of some species indicates the possible existence of more undescribed species within present species groups.

Design of Negative and Positive Allosteric Modulators of the Cannabinoid CB2 Receptor Derived from the Natural Product Cannabidiol.

Cannabidiol (CBD), the second most abundant of the active compounds found in the Cannabis sativa plant, is of increasing interest because it is approved for human use and is neither euphorizing nor addictive. Here, we design and synthesize novel compounds taking into account that CBD is both a partial agonist, when it binds to the orthosteric site, and a negative allosteric modulator, when it binds to the allosteric site of the cannabinoid CB2 receptor. Molecular dynamic simulations and site-directed mutagenesis studies have identified the allosteric site near the receptor entrance. This knowledge has permitted to perform structure-guided design of negative and positive allosteric modulators of the CB2 receptor with potential therapeutic utility.

Multiple glacial refugia and contemporary dispersal shape the genetic structure of an endemic amphibian from the Pyrenees.

Historical factors (colonization scenarios, demographic oscillations) and contemporary processes (population connectivity, current population size) largely contribute to shaping species' present-day genetic diversity and structure. In this study, we use a combination of mitochondrial and nuclear DNA markers to understand the role of Quaternary climatic oscillations and present-day gene flow dynamics in determining the genetic diversity and structure of the newt Calotriton asper (Al. Dugès, 1852), endemic to the Pyrenees. Mitochondrial DNA did not show a clear phylogeographic pattern and presented low levels of variation. In contrast, microsatellites revealed five major genetic lineages with admixture patterns at their boundaries. Approximate Bayesian computation analyses and linear models indicated that the five lineages likely underwent separate evolutionary histories and can be tracked back to distinct glacial refugia. Lineage differentiation started around the Last Glacial Maximum at three focal areas (western, central and eastern Pyrenees) and extended through the end of the Last Glacial Period in the central Pyrenees, where it led to the formation of two more lineages. Our data revealed no evidence of recent dispersal between lineages, whereas borders likely represent zones of secondary contact following expansion from multiple refugia. Finally, we did not find genetic evidence of sex-biased dispersal. This work highlights the importance of integrating past evolutionary processes and present-day gene flow and dispersal dynamics, together with multilocus approaches, to gain insights into what shaped the current genetic attributes of amphibians living in montane habitats.

Responses of fish assemblage structure to large-scale weir construction in riverine ecosystems.

Worldwide, increasing amounts of dams and weirs have been established in rivers in recent decades, often with drastic effects on their ecosystems. Between late 2009 and 2011, 16 large-scale dams were built in the main channels of the four largest rivers in South Korea, eight of these along the main channel of Nakdong River (300 km, 520 km in total). We studied the effect of these constructions on the fish community in the riparian zone based on intensive fish field surveys conducted in the littoral zone during 2007-2017, analysis of fishermen's catch data and molecular analysis of the diet of the keystone species, largemouth bass (Micropterus salmoides). Our results, based on RDA and GLM analyses, showed that environmental characteristics and fish species composition changed significantly with dam construction. Total fish abundance and biomass decreased after the start of the weir construction and fish richness decreased with time. The abundance and biomass of exotic fish decreased during construction but recovered afterwards, leading to higher proportions of exotics. Dominance and Shannon indices did not change significantly from before to after construction, while the Evenness index showed a significant decreasing trend. A comparison of the diet composition of largemouth bass showed decreasing genetic variation after construction. The changes in Functional Feeding Group (FFG) of the benthic communities at the study sites did not coincide with FFG changes in the prey items of largemouth bass, indicating a transition in feeding mode from before to after construction. In conclusion, the endemic and native fish species were most sensitive and showed lower resilience to disturbance by the large-scale dam construction than the translocated and exotic species, and the lake-like ecosystems after construction markedly improved the competitive capacity of these exotic fish over the native and endemic species in the riparian zone of the river.

Non-native Minnows Threaten Quillwort Populations in High Mountain Shallow Lakes.

Submersed aquatic plants are a key component of shallow, clear water lakes contributing to primary production and water quality. High mountain lakes are naturally fishless although invasive trout and most recently minnows have been introduced causing a major impact on fauna richness. The Pyrenean high mountain range has preserved soft-water oligotrophic boreal isoetids in their southern limit of distribution but the recent fish introduction is a potential factor of stress that needs to be addressed. We here work under the hypothesis that due to contrasting ecological features, trout will not be heavily affecting quillwort populations while minnows will have a stronger effect on zooplankton and zoobenthos that will promote algal growth and reduce light availability for the underwater meadows. Ten Pyrenean shallow lakes representative of three scenarios -fishless, with trout and with minnows-, were sampled for meadow structure, water column and benthic environment characterization in mid-summer 2015 and 2016. Quillwort biomass allocation (above vs. belowground), epiphytic load, and composition of the algal community (abundant cyanobacteria) differed in the presence of minnows. In trout lakes biomass allocation and epiphytic load were average and the algal community composed by chlorophytes and diatoms as in fishless lakes. Biomass ratio was close to thresholds of negative buoyancy in minnow lakes indicating that meadows were at risk of uprooting and consequent de-vegetation. Total and soluble carbohydrates were lower and the sporangia contained significantly less reserves to constrain growth and expansion in the presence of minnows. Lake scenarios were coupled to physicochemical differences with low light, high phosphorus and Chl-a (mesotrophia) in minnow lakes, while trout and fishless lakes remained oligotrophic. This is the first study assessing the impact of non-native fish on soft-water isoetids from mountain lakes and shows that minnows are a major threat to quillworts. The impaired light environment (from epiphytic algal overgrow and water column Chl-a) entails consequent regression (i.e., no recruitment) and de-vegetation (uprooting) of the meadows. Since soft-water oligotrophic mountain lakes are protected under the Habitats Directive, some action needs to be urgently implemented not only to preserve quillworts but to the overall ecological integrity of the lakes.

The dominant detritus-feeding invertebrate in Arctic peat soils derives its essential amino acids from gut symbionts.

Supplementation of nutrients by symbionts enables consumers to thrive on resources that might otherwise be insufficient to meet nutritional demands. Such nutritional subsidies by intracellular symbionts have been well studied; however, supplementation of de novo synthesized nutrients to hosts by extracellular gut symbionts is poorly documented, especially for generalists with relatively undifferentiated intestinal tracts. Although gut symbionts facilitate degradation of resources that would otherwise remain inaccessible to the host, such digestive actions alone cannot make up for dietary insufficiencies of macronutrients such as essential amino acids (EAA). Documenting whether gut symbionts also function as partners for symbiotic EAA supplementation is important because the question of how some detritivores are able to subsist on nutritionally insufficient diets has remained unresolved. To answer this poorly understood nutritional aspect of symbiont-host interactions, we studied the enchytraeid worm, a bulk soil feeder that thrives in Arctic peatlands. In a combined field and laboratory study, we employed stable isotope fingerprinting of amino acids to identify the biosynthetic origins of amino acids to bacteria, fungi and plants in enchytraeids. Enchytraeids collected from Arctic peatlands derived more than 80% of their EAA from bacteria. In a controlled feeding study with the enchytraeid Enchytraeus crypticus, EAA derived almost exclusively from gut bacteria when the worms fed on higher fibre diets, whereas most of the enchytraeids' EAA derived from dietary sources when fed on lower fibre diets. Our gene sequencing results of gut microbiota showed that the worms harbour several taxa in their gut lumen absent from their diets and substrates. Almost all gut taxa are candidates for EAA supplementation because almost all belong to clades capable of biosynthesizing EAA. Our study provides the first evidence of extensive symbiotic supplementation of EAA by microbial gut symbionts and demonstrates that symbiotic bacteria in the gut lumen appear to function as partners both for symbiotic EAA supplementation and for digestion of insoluble plant fibres.

Discovering hidden biodiversity: the use of complementary monitoring of fish diet based on DNA barcoding in freshwater ecosystems.

Ecological monitoring contributes to the understanding of complex ecosystem functions. The diets of fish reflect the surrounding environment and habitats and may, therefore, act as useful integrating indicators of environmental status. It is, however, often difficult to visually identify items in gut contents to species level due to digestion of soft-bodied prey beyond visual recognition, but new tools rendering this possible are now becoming available. We used a molecular approach to determine the species identities of consumed diet items of an introduced generalist feeder, brown trout (Salmo trutta), in 10 Tasmanian lakes and compared the results with those obtained from visual quantification of stomach contents. We obtained 44 unique taxa (OTUs) belonging to five phyla, including seven classes, using the barcode of life approach from cytochrome oxidase I (COI). Compared with visual quantification, DNA analysis showed greater accuracy, yielding a 1.4-fold higher number of OTUs. Rarefaction curve analysis showed saturation of visually inspected taxa, while the curves from the DNA barcode did not saturate. The OTUs with the highest proportions of haplotypes were the families of terrestrial insects Formicidae, Chrysomelidae, and Torbidae and the freshwater Chironomidae. Haplotype occurrence per lake was negatively correlated with lake depth and transparency. Nearly all haplotypes were only found in one fish gut from a single lake. Our results indicate that DNA barcoding of fish diets is a useful and complementary method for discovering hidden biodiversity.

Environmental factors prevail over dispersal constraints in determining the distribution and assembly of Trichoptera species in mountain lakes.

Aiming to elucidate whether large-scale dispersal factors or environmental species sorting prevail in determining patterns of Trichoptera species composition in mountain lakes, we analyzed the distribution and assembly of the most common Trichoptera (Plectrocnemia laetabilis, Polycentropus flavomaculatus, Drusus rectus, Annitella pyrenaea, and Mystacides azurea) in the mountain lakes of the Pyrenees (Spain, France, Andorra) based on a survey of 82 lakes covering the geographical and environmental extremes of the lake district. Spatial autocorrelation in species composition was determined using Moran's eigenvector maps (MEM). Redundancy analysis (RDA) was applied to explore the influence of MEM variables and in-lake, and catchment environmental variables on Trichoptera assemblages. Variance partitioning analysis (partial RDA) revealed the fraction of species composition variation that could be attributed uniquely to either environmental variability or MEM variables. Finally, the distribution of individual species was analyzed in relation to specific environmental factors using binomial generalized linear models (GLM). Trichoptera assemblages showed spatial structure. However, the most relevant environmental variables in the RDA (i.e., temperature and woody vegetation in-lake catchments) were also related with spatial variables (i.e., altitude and longitude). Partial RDA revealed that the fraction of variation in species composition that was uniquely explained by environmental variability was larger than that uniquely explained by MEM variables. GLM results showed that the distribution of species with longitudinal bias is related to specific environmental factors with geographical trend. The environmental dependence found agrees with the particular traits of each species. We conclude that Trichoptera species distribution and composition in the lakes of the Pyrenees are governed predominantly by local environmental factors, rather than by dispersal constraints. For boreal lakes, with similar environmental conditions, a strong role of dispersal capacity has been suggested. Further investigation should address the role of spatial scaling, namely absolute geographical distances constraining dispersal and steepness of environmental gradients at short distances.

Tracing carbon sources through aquatic and terrestrial food webs using amino acid stable isotope fingerprinting.

Tracing the origin of nutrients is a fundamental goal of food web research but methodological issues associated with current research techniques such as using stable isotope ratios of bulk tissue can lead to confounding results. We investigated whether naturally occurring δ(13)C patterns among amino acids (δ(13)CAA) could distinguish between multiple aquatic and terrestrial primary production sources. We found that δ(13)CAA patterns in contrast to bulk δ(13)C values distinguished between carbon derived from algae, seagrass, terrestrial plants, bacteria and fungi. Furthermore, we showed for two aquatic producers that their δ(13)CAA patterns were largely unaffected by different environmental conditions despite substantial shifts in bulk δ(13)C values. The potential of assessing the major carbon sources at the base of the food web was demonstrated for freshwater, pelagic, and estuarine consumers; consumer δ(13)C patterns of essential amino acids largely matched those of the dominant primary producers in each system. Since amino acids make up about half of organismal carbon, source diagnostic isotope fingerprints can be used as a new complementary approach to overcome some of the limitations of variable source bulk isotope values commonly encountered in estuarine areas and other complex environments with mixed aquatic and terrestrial inputs.

A new fairy shrimp Phallocryptus tserensodnomi (Branchiopoda: Anostraca) from Mongolia.

A new species of Phallocryptus Biraben 1951 (Branchiopoda, Anostraca) from Mongolia is described. Phallocryptus tserensodnomi sp. nov. is close to P. spinosa (Milne-Edwards 1840), but both morphological and molecular analyses (Cytochrome Oxidase I, COI) indicate that they represent separate species. Most relevant differential features of the new species include: (1) frontal appendage provided with small ventral conical outgrowths; (2) second antennamere evenly curved, sickle-shaped; (3) distal fleshy process on labrum evenly curved forwards and tapering; (4) short stout acute spine-like projections present at each side of basal portion of gonopods; (5) female second antennae shorter and wider than in P. spinosa, tapering. Based on morphological comparisons the new species appears to be a Mongolian endemic, although some genotypes of presumed P spinosa from Africa are similar to the new species, suggesting P. tserensodnomi might have a wider distribution.

Diversity in the reproductive modes of European Daphnia pulicaria deviates from the geographical parthenogenesis.

BACKGROUND: Multiple transitions to obligate parthenogenesis have occurred in the Daphnia pulex complex in North America. These newly formed asexual lineages are differentially distributed being found predominantly at high latitudes. This conforms to the rule of geographical parthenogenesis postulating prevalence of asexuals at high latitudes and altitudes. While the reproductive mode of high-latitude populations is relatively well studied, little is known about the reproduction mode in high altitudes. This study aimed to assess the reproductive mode of Daphnia pulicaria, a species of the D. pulex complex, from high altitude lakes in Europe. METHODOLOGY/PRINCIPAL FINDINGS: Variation at eight microsatellite loci revealed that D. pulicaria from the High Tatra Mountains (HTM) had low genotype richness and showed excess of heterozygotes and significant deviations from Hardy-Weinberg expectations, and was thus congruent with reproduction by obligate parthenogenesis. By contrast, populations from the Pyrenees (Pyr) were generally in Hardy-Weinberg equilibrium and had higher genotypic richness, suggesting that they are cyclic parthenogens. Four lakes from lowland areas (LLaP) had populations with an uncertain or mixed breeding mode. All D. pulicaria had mtDNA ND5 haplotypes of the European D. pulicaria lineage. Pyr were distinct from LLaP and HTM at the ND5 gene. By contrast, HTM shared two haplotypes with LLaP and one with Pyr. Principal Coordinate Analysis of the microsatellite data revealed clear genetic differentiation into three groups. HTM isolates were intermediate to Pyr and LLaP, congruent with a hybrid origin. CONCLUSION/SIGNIFICANCE: Inferred transitions to obligate parthenogenesis have occurred only in HTM, most likely as a result of hybridizations. In contrast to North American populations, these transitions do not appear to involve meiosis suppressor genes and have not been accompanied by polyploidy. The absence of obligate parthenogenesis in Pyr, an environment highly similar to the HTM, may be due to the lack of opportunities for hybridization.

Reticulate evolution of the Daphnia pulex complex as revealed by nuclear markers.

The study of species complexes is of particular interest to understand how evolutionary young species maintain genomic integrity. The Daphnia pulex complex has been intensively studied as it includes species that dominate freshwater environments in the Northern hemisphere and as it is the sole North American complex that shows transitions to obligate parthenogenesis. Past studies using mitochondrial markers have revealed the presence of 10 distinct lineages in the complex. This study is the first to examine genetic relationships among seven species of the complex at nuclear markers (nine microsatellite loci and one protein-coding gene). Clones belonging to the seven species of the Daphnia pulex complex were characterized at the mitochondrial NADH dehydrogenase (ND5) gene and at the Lactate dehydrogenase (LDH) locus. K-means, principal coordinate analyses and phylogenetic network analyses on the microsatellite data all separated European D. pulicaria, D. tenebrosa, North American D. pulex, D. pulicaria and their hybrids into distinct clusters. The hybrid cluster was composed of diploid and polyploid hybrids with D. pulex mitochondria and some clones with D. pulicaria mitochondria. By contrast, the phylogeny of the D. pulex complex using Rab4 was not well resolved but still showed clusters consisting mostly of D. pulex alleles and others of D. pulicaria alleles. Incomplete lineage sorting and hybridization may obscure genetic relationships at this locus. This study shows that hybridization and introgression have played an important role in the evolution of this complex.

Do phosphorus requirements for RNA limit genome size in crustacean zooplankton?

As for most other organisms, genome size in zooplankton differs widely. This may have a range of consequences for growth rate, development, and life history strategies, yet the causes of this pronounced variability are not settled. Here we propose that small genome size may be an evolutionary consequence of phosphorus (P) allocation from DNA to RNA under P deficiency. To test this hypothesis we have compared the two major groups of zooplankton, copepods and cladocerans, that have overlapping niches and body size. Relative to the cladocerans, copepods have a more complex life history and a lower mass-specific P content, while cladocerans tend to have higher P and RNA contents and higher specific growth rates and frequently experience P-limited growth, likely due to a shortage of P for ribosome synthesis. Cladocerans also generally have smaller genomes than copepods (1C = 0.17-0.63 pg DNA.cell(-1) vs. 1C = 0.10-10 pg DNA.cell(-1)). Furthermore, cladocerans have a higher slope of the relationship of body size with DNA content (1.5 vs. 0.28 in copepods) and present almost 15-fold higher RNA:DNA ratios (24.8 in cladocerans vs. 1.6 in copepods). Hence, small genome size in cladocerans could reflect an evolutionary pressure towards "efficient" genomes to conserve a key element needed to maximize growth rate. We do not claim that this is a universal cause of genome size variability, but propose that streamlining of genomes could be related to P conservation rather than energy conservation. This could be relevant for a range of organisms that may suffer P-limited growth rates.

Distribution of polycyclic aromatic hydrocarbons in the food web of a high mountain lake, Pyrenees, Catalonia, Spain.

We investigated the contents of polycyclic aromatic hydrocarbons (PAHs) in the food web organisms included in the diet of brown trout from a remote mountain lake. The preferential habitat and trophic level of the component species have been assessed from the signature of stable isotopes (delta13C and delta15N). Subsequently, the patterns of accumulation and transformation of these hydrocarbons in the food chain have been elucidated. Most of the food web organisms exhibit PAH distributions largely dominated by phenanthrene, which agrees with its predominance in atmospheric deposition, water, and suspended particles. Total PAH levels are higher in the organisms from the littoral habitat than from the deep sediments or the pelagic water column. However, organisms from deep sediments exhibit higher proportions of higher molecular weight PAH than those in other lake areas. Distinct organisms exhibit specific features in their relative PAH composition that point to different capacities for uptake and metabolic degradation. Brown trout show an elevated capacity for metabolic degradation because they have lower PAH concentrations than food and they are enriched strongly in lower molecular weight compounds. The PAH levels in trout highly depend on organisms living in the littoral areas. Fish exposure to PAH, therefore, may vary from lake to lake according to the relative contribution of littoral organisms to their diet.

The roles of food and water in the bioaccumulation of organochlorine compounds in high mountain lake fish.

An integrated study encompassing the distribution of organochlorine compounds (OC) in water, food web (chironomids, terrestrial insects, cladocerans, mollusks, and cyanobacteria), and fish (brown trout) from a high mountain lake (Redon, Pyrenees) is reported. OC distributions in these compartments have been determined to assess theirtransport routes into fish. Food diets have been estimated by analysis of fish stomach content and food web stable isotopes (delta13C and delta15N). OCs with octanol--water partition coefficient (Kow) higher than 10(6) showed lower concentrations in food than expected from theoretical octanol--water partition, indicating thatthe distribution of these compounds does not reach equilibrium within the life span of the food web organisms (ca. 1 year). On the other hand, the degree of biomagnification in fish increased with Kow, except in the case of the largest compound analyzed (seven chlorine substituents, PCB #180). OC exchange at fish gill and gut has been evaluated using a fugacity model based on the water, food, and fish concentrations. All compounds exhibited a net gill loss and a net gut uptake. A pseudostationary state was only achieved for compounds with log(Kow) < 6. Calculation of fish average residence times for the compounds in apparent steady state gave values of days to a few weeks for HCHs, 1 year for HCB and 4,4'-DDE, and 2-3 years for 4,4'-DDT and PCB#28 and PCB#52. Residence times longer than one decade were found for the more chlorinated PCB.