A taxonomic revision of the whitefish of lakes Brienz and Thun, Switzerland, with descriptions of four new species (Teleostei, Coregonidae)

The alpha taxonomy of the endemic whitefish of lakes Brienz and Thun, Switzerland, is revised. We evaluate the status of seven known species: Coregonus steinmanni sp. nov., Coregonus profundussp. nov.and Coregonus acrinasussp. nov.are endemic to Lake Thun; Coregonusbrienzii sp. nov. is endemic to Lake Brienz; and C. alpinus, C. albellus, and C. fatioi from lakes Brienz and Thun are redescribed. One of these species, C. alpinus, is revised, since the lectotype for this species is incongruent with the species descrip-tion given by Kottelat (1997) and Kottelat and Freyhof (2007). The name C. alpinus is thus retained for the lectotype designated by Kottelat (1997) and a new description of this taxon provided. For the species otherwise described by Kottelat (1997) and Kottelat and Freyhof (2007) as C.alpinus the new name C. profundus is designated. Coregonusacrinasus is genetically partially of allochthonous origin, closely related to the radiation of Lake Constance, and we therefore compare it to all recognized species of Lake Constance, C. wartmanni, C.macrophthalmus, C. arenicolus,and C. gutturosus

Allopatric and sympatric diversification within roach (Rutilus rutilus) of large prealpine lakes

Intraspecific differentiation in response to divergent natural selection between environments is a common phenomenon in some lineages of northern freshwater fishes, especially salmonids and stickleback. Understanding why these taxa diversify and undergo adaptive radiations while most other fish species in the same environments do not, remains an open question. The possibility for intraspecific diversification has rarely been evaluated for most northern freshwater fish species. Here, we assess the potential for intraspecific differentiation between and within lake populations of roach (Rutilus rutilus) – a widespread and abundant cyprinid species - in lakes in which salmonids have evolved endemic adaptive radiations. Based on more than 3,000 polymorphic RADseq markers, we detected low but significant genetic differentiation between roach populations of two ultraoligotrophic lakes and between these and populations from other lakes. This, together with differentiation in head morphology and stable isotope signatures, suggests evolutionary and ecological differentiation among some of our studied populations. Next, we tested for intralacustrine diversification of roach within Lake Brienz, the most pristine lake surveyed in this study. We found significant phenotypic evidence for ecological intralacustrine differentiation between roach caught over a muddy substrate and those caught over a rocky substrate. However, evidence for intralacustrine genetic differentiation is at best subtle and phenotypic changes may therefore be mostly plastic. Overall, our findings suggest roach can differ between ecologically distinct lakes, but the extent of intralacustrine ecological differentiation is weak, which contrasts with the strong differentiation among endemic species of whitefish in the same lakes

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

Assessment of fish health status in four Swiss rivers showing a decline of brown trout catches

Abstract.: A pronounced decline in catch of brown trout (Salmo trutta L.) over the last 10-20 years has been reported for many rivers in Switzerland. Impaired health status of the fishes has been suggested as one possible cause of the decline. The present study investigated the health status of juvenile brown trout from four Swiss rivers which experienced reductions of brown trout catches during the last two decades: Emme, Liechtensteiner Binnenkanal (LBK), Necker and Venoge. A gradient approach was applied, studying at each river a headwater (HW), midstream (D1) and downstream site (D2). Fish health was assessed by the following indices: hepatic 7-ethoxyresorufin-O-deethylase (EROD) activity, organ (liver, kidney) histopathology, and gross biometric indices (condition factor, hepatosomatic index). Hepatic EROD activities were generally low without showing significant within- or between-stream differences. Histopathological alterations of the liver displayed a moderate downstream increase in the Emme, LBK and Necker, but not in the Venoge. Between-stream differences of liver pathology were small. Kidney histopathology was not different between upstream and downstream sites, except for Emme and Venoge, where fishes at the downstream sites were infected with the parasite Tetracapsuloides bryosalmonae, the cause of the proliferative kidney disease (PKD). The findings from this study point to an association of within-stream gradients in water quality, PKD prevalence, fish health and brown trout biomass, whereas between-stream differences of actual fish health status reflecting the different levels of catch declines observed in the four rivers during the last two decades are not eviden

Comparisons of day-time and night-time hydroacoustic surveys in temperate lakes

In recent years, due to an increased need for non-intrusive sampling techniques, hydroacoustics has attracted attention in fishery science and management. Efforts to promote standardisation are increasing the accuracy, efficiency, and comparability of this method. The European Water Framework Directive and the Standard Operating Procedures for Fisheries Hydroacoustic Surveys in North American Great Lakes has recommended that surveys be conducted at night. At night, fish usually disperse in the water column, thus allowing for single echo detection and subsequent accurate fish size estimation, while day-time schooling behaviour hampers the estimation of fish size. However, sampling during the day would often be safer and cheaper. This study analyses how fisheries hydroacoustic results differ between day-time and night-time surveys, using data from 14 natural temperate lakes of various size. Data collected during the day and night at two depth layers linked to thermal stratification were compared in terms of acoustic scattering strength, target strength, and biomass estimates. The results showed a significant correlation between day-time and night-time estimates, though biomass in the upper layer was biased for day-time surveys, mainly due to incorrect fish size estimates resulting from rare single echo detections and schooling behaviour. Biomass estimates for the lower depth layer did not significantly differ between the two diel periods. Thus, this study confirms that hydroacoustic sampling in temperate lakes should be performed at night for accurate fish stock biomass estimates

Standardisierte Befischung - Methode zur Erhebung des Fischbestands in stehenden Gewässern

Für den Erhalt und die Förderung von Ökosystemen müssen deren Zustand und die möglichen Ursachen von Beeinträchtigungen bekannt sein. Um den Zustand der Gewässer zu ermitteln, dienen Fische als Bioindikatoren. Eine neu entwickelte, standardisierte Befischungsmethode für Stehgewässer ermöglicht es, Fischbestände im Verlauf der Zeit besser zu überwachen und diese mit denen anderer Gewässer zu vergleichen

Does eutrophication-driven evolution change aquatic ecosystems?

Eutrophication increases primary production and changes the relative abundance, taxonomic composition and spatial distribution of primary producers within an aquatic ecosystem. The changes in composition and location of resources alter the distribution and flow of energy and biomass throughout the food web. Changes in productivity also alter the physico-chemical environment, which has further effects on the biota. Such ecological changes influence the direction and strength of natural and sexual selection experienced by populations. Besides altering selection, they can also erode the habitat gradients and/or behavioural mechanisms that maintain ecological separation and reproductive isolation among species. Consequently, eutrophication of lakes commonly results in reduced ecological specialization as well as genetic and phenotypic homogenization among lakes and among niches within lakes. We argue that the associated loss in functional diversity and niche differentiation may lead to decreased carrying capacity and lower resource-use efficiency by consumers. We show that in central European whitefish species radiations, the functional diversity affected by eutrophication-induced speciation reversal correlates with community-wide trophic transfer efficiency (fisheries yield per unit phosphorus). We take this as an example of how evolutionary dynamics driven by anthropogenic environmental change can have lasting effects on biodiversity and ecosystem functioning. This article is part of the themed issue ‘Human influences on evolution, and the ecological and societal consequences’