Speciation leads to divergent methylmercury accumulation in sympatric whitefish

Central European lake whitefish (Coregonus spp.) colonized Swiss lakes following the last glacial retreat and have undergone rapid speciation and adaptive radiation. Up to six species have been shown to coexist in some lakes, and individual species occupy specific ecological niches and have distinct feeding and reproductive ecologies. We studied methylmercury (MeHg) accumulation in sympatric whitefish species from seven Swiss lakes to determine if ecological divergence has led to different rates of MeHg bioaccumulation. In four of seven lakes, sympatric species had distinctly different MeHg levels, which varied by up to a factor of two between species. Generally, species with greater MeHg levels were smaller in body size and planktivorous, and species with lower MeHg were larger and benthivorous. While modest disparities in trophic position between species might be expected a priori to explain the divergence in MeHg, δ15N of bulk tissue did not correlate with fish MeHg in five of seven lakes. Results of a nested ANCOVA analysis across all lakes indicated that only two factors (species, lake) explained substantial portions of the variance, with species accounting for more variance (52%) than inter-lake differences (32%). We suggest that differences in MeHg accumulation were likely caused by diverging metabolic traits between species, such as differences in energy partitioning between anabolism and catabolism, potentially interacting with species-specific prey resource utilization. These results indicate substantial variability in MeHg accumulation between closely related fish species, illustrating that ecological speciation in fish can lead to divergent MeHg accumulation pattern

Population structure, inbreeding and local adaptation within an endangered riverine specialist: the nase ( Chondrostoma nasus )

Chondrostoma nasus is a cyprinid fish with highly specialized, ecologically and geographically distinct, ontogenetic trophic niches. Nase population numbers across their Swiss range have shown massive declines and many localized extinctions. In this study, we integrate genetic data (AFLP, microsatellite, mtDNA sequence) with phenotypic and demographic analyses to survey patterns of neutral and adaptive genetic diversity in all extant (and one extinct) Swiss nase populations, with the aim to delineate intraspecific conservation units (CUs) and to inform future population management strategies. We discovered two major genetically and geographically distinct population groupings. The first population grouping comprises nase inhabiting rivers flowing into Lake Constance; the second comprises nase populations from Rhine drainages below Lake Constance. Within these clusters there is generally limited genetic differentiation among populations. Genomic outlier scans based on 256 to 377 polymorphic AFLP loci revealed little evidence of local adaptation both within and among population clusters, with the exception of one candidate locus identified in scans involving the low genetic diversity Schanzengraben population. However, significant phenotypic differentiation in body shape between certain populations suggests a need for more intensive future studies of local adaptation. Our data strongly suggests that the two major population groups should be treated as distinct CUs, with any supplemental stocking and reintroductions sourced only from within the range of the CU concerned

A Stable Polyaniline-Benzoquinone-Hydroquinone Supercapacitor

A Polyaniline‐Supercapacitor with quinone electrolytes remains stable over 50 000 galvanostatic charge‐discharge cycles. The quinones provide superior stability by preventing the conversion of porous polyaniline to a highly reactive state. Our work shows that highly stable polymer‐supercapacitors can be engineered by combining electrochemically active polymers and redox‐active electrolytes with concerted electrochemical properties

A Stable Polyaniline-Benzoquinone-Hydroquinone Supercapacitor

A Polyaniline‐Supercapacitor with quinone electrolytes remains stable over 50 000 galvanostatic charge‐discharge cycles. The quinones provide superior stability by preventing the conversion of porous polyaniline to a highly reactive state. Our work shows that highly stable polymer‐supercapacitors can be engineered by combining electrochemically active polymers and redox‐active electrolytes with concerted electrochemical properties

Nanooptics of molecular-shunted plasmonic nanojunctions.

Gold nanoparticles are separated above a planar gold film by 1.1 nm thick self-assembled molecular monolayers of different conductivities. Incremental replacement of the nonconductive molecules with a chemically equivalent conductive version differing by only one atom produces a strong 50 nm blue-shift of the coupled plasmon. With modeling this gives a conductance of 0.17G(0) per biphenyl-4,4'-dithiol molecule and a total conductance across the plasmonic junction of 30G(0). Our approach provides a reliable tool quantifying the number of molecules in each plasmonic hotspot, here <200.We acknowledge financial support from EPSRC grant EP/ G060649/1, EP/I012060/1, EP/L027151/1, EP/K028510/1, ERC grant LINASS 320503. F.B. acknowledges support from the Winton Programme for the Physics of Sustainability. C.T. and J.A. acknowledge financial support from Project FIS2013- 41184-P from MINECO, ETORTEK 2014-15 of the Basque Department of Industry and IT756-13 from the Basque consolidated groups.This paper was originally published in Nano Letters under a CC-BY licence (F Benz, C Tserkezis, LO Herrmann, B de Nijs, A Sanders, DO Sigle, L Pukenas, SD Evans, J Aizpurua, JJ Baumberg, Nano Letters 2015, 15, 669−674

Population structure, inbreeding and local adaptation within an endangered riverine specialist: the nase (Chondrostoma nasus)

Chondrostoma nasus is a cyprinid fish with highly specialized, ecologically and geographically distinct, ontogenetic trophic niches. Nase population numbers across their Swiss range have shown massive declines and many localized extinctions. Here we integrate data from different genetic markers with phenotypic and demographic data to survey patterns of neutral and adaptive genetic diversity in all extant (and one extinct) Swiss nase populations, with the aim to delineate intraspecific conservation units (CUs) and to inform future population management strategies. We discovered two major genetically and geographically distinct population groupings. The first population grouping comprises nase inhabiting rivers flowing into Lake Constance; the second comprises nase populations from Rhine drainages below Lake Constance. Within these clusters there is generally limited genetic differentiation among populations. Genomic outlier scans based on 256–377 polymorphic AFLP loci revealed little evidence of local adaptation both within and among population clusters, with the exception of one candidate locus identified in scans involving the inbred Schanzengraben population. However, significant phenotypic differentiation in body shape between certain populations suggests a need for more intensive future studies of local adaptation. Our data strongly suggests that the two major population groups should be treated as distinct CUs, with any supplemental stocking and reintroductions sourced only from within the range of the CU concerned

Genomic signatures of relaxed disruptive selection associated with speciation reversal in whitefish

Background: Speciation reversal: the erosion of species differentiation via an increase in introgressive hybridization due to the weakening of previously divergent selection regimes, is thought to be an important, yet poorly understood, driver of biodiversity loss. Our study system, the Alpine whitefish (Coregonus spp.) species complex is a classic example of a recent postglacial adaptive radiation: forming an array of endemic lake flocks, with the independent origination of similar ecotypes among flocks. However, many of the lakes of the Alpine radiation have been seriously impacted by anthropogenic nutrient enrichment, resulting in a collapse in neutral genetic and phenotypic differentiation within the most polluted lakes. Here we investigate the effects of eutrophication on the selective forces that have shaped this radiation, using population genomics. We studied eight sympatric species assemblages belonging to five independent parallel adaptive radiations, and one species pair in secondary contact. We used AFLP markers, and applied F-ST outlier (BAYESCAN, DFDIST) and logistic regression analyses (MATSAM), to identify candidate regions for disruptive selection in the genome and their associations with adaptive traits within each lake flock. The number of outlier and adaptive trait associated loci identified per lake were then regressed against two variables (historical phosphorus concentration and contemporary oxygen concentration) representing the strength of eutrophication. Results: Whilst we identify disruptive selection candidate regions in all lake flocks, we find similar trends, across analysis methods, towards fewer disruptive selection candidate regions and fewer adaptive trait/candidate loci associations in the more polluted lakes. Conclusions: Weakened disruptive selection and a concomitant breakdown in reproductive isolating mechanisms in more polluted lakes has lead to increased gene flow between coexisting Alpine whitefish species. We hypothesize that the resulting higher rates of interspecific recombination reduce either the number or extent of genomic islands of divergence surrounding loci evolving under disruptive natural selection. This produces the negative trend seen in the number of selection candidate loci recovered during genome scans of whitefish species flocks, with increasing levels of anthropogenic eutrophication: as the likelihood decreases that AFLP restriction sites will fall within regions of heightened genomic divergence and therefore be classified as F-ST outlier loci. This study explores for the first time the potential effects of human-mediated relaxation of disruptive selection on heterogeneous genomic divergence between coexisting species