Lipid biomarkers in Holocene and glacial sediments from ancient Lake Ohrid (Macedonia, Albania)

Abstract. Organic matter preserved in Lake Ohrid sediments originates from aquatic and terrestrial sources. Its variable composition reflects climate-controlled changes in the lake basin’s hydrology and related organic matter export, i.e. changes in primary productivity, terrestrial plant matter input and soil erosion. Here, we present first results from lipid biomarker investigations of Lake Ohrid sediments from two near-shore settings: site Lz1120 near the southern shore, with low-lying lands nearby and probably influenced by river discharge, and site Co1202 which is close to the steep eastern slopes. Variable proportions of terrestrial n-alkanoic acids and n-alkanols as well as compositional changes of !- hydroxy acids document differences in soil organic matter supply between the sites and during different climate stages (glacial, Holocene, 8.2 ka cooling event). Changes in the vegetation cover are suggested by changes in the dominant chain length of terrestrial n-alkanols. Effective microbial degradation of labile organic matter and in situ contribution of organic matter derived from the microbes themselves are both evident in the sediments. We found evidence for anoxic conditions within the photic zone by detecting epicholestanol and tetrahymanol from sulphur-oxidising phototrophic bacteria and bacterivorous ciliates and for the influence of a settled human community from the occurrence of coprostanol, a biomarker for human and animal faeces (pigs, sheep, goats), in an early Holocene sample. This study illustrates the potential of lipid biomarkers for future environmental reconstructions using one of Europe’s oldest continental climate archives, Lake Ohrid.

Sedimentary evolution and environmental history of Lake Van (Turkey) over the past 600,000 years

The lithostratigraphic framework of Lake Van, eastern Turkey, has been systematically analysed to document the sedimentary evolution and the environmental history of the lake during the past ca 600,000 years. The lithostratigraphy and chemostratigraphy of a 219 m long drill core from Lake Van serves to separate global climate oscillations from local factors caused by tectonic and volcanic activity. An age model was established based on the climatostratigraphic alignment of chemical and lithological signatures, validated by 40Ar/39Ar ages. The drilled sequence consists of ca 76% lacustrine carbonaceous clayey silt, ca 2% fluvial deposits, ca 17% volcaniclastic deposits and 5% gaps. Six lacustrine lithotypes were separated from the fluvial and event deposits, such as volcaniclastics (ca 300 layers) and graded beds (ca 375 layers), and their depositional environments are documented. These lithotypes are: (i) graded beds frequently intercalated with varved clayey silts reflect rising lake-levels during the terminations; (ii) varved clayey silts reflect strong seasonality and an intralake oxic–anoxic boundary, for example, lake-level highstands during interglacials/interstadials; (iii) CaCO3-rich banded sediments are representative of a lowering of the oxic-anoxic boundary, for example, lake-level decreases during glacial inceptions; (iv) CaCO3-poor banded and mottled clayey silts reflect an oxic–anoxic boundary close to the sediment-water interface, for example, lake-level low-stands during glacials/stadials; (v) diatomaceous muds were deposited during the early beginning of the lake as a fresh water system; and (vi) fluvial sands and gravels indicate the initial flooding of the lake basin. The recurrence of lithologies (i) to (iv) follows the past five glacial/interglacial cycles. A 20 m thick disturbed unit reflects an interval of major tectonic activity in Lake Van at ca 414 ka BP.

The history of subaquatic volcanism recorded in the sediments of Lake Kivu

Subaquatic volcanic activity has been ongoing in Lake Kivu since the early Holocene and has a dynamic effect on the biological productivity in the surface water, and the preservation of carbonate in the deep anoxic water. Groundwater discharge into the lake’s deepwater propels the upward advection of the water column that ultimately supplies nutrients to the surface water for biological production. The amount of nutrients supplied from the deepwater can be increased suddenly by (1) a cold meteorological event that drives deep seasonal mixing resulting in increased nutrients from below and oxygen from above, or (2) subaquatic volcanic activity that induces a buoyant hydrothermal plume, which entrains nutrients from the deepwater and results in anoxia or suboxic conditions in the surface water. Previous sedimentological studies in Lake Kivu have hypothesized that regional climatic changes are responsible for sudden changes in the preservation of carbonates in the Main Basin. Here we reveal that sublacustrine volcanic events most likely induce the abrupt changes to the geochemistry in the sediment in Lake Kivu. An unprecedented look into the sediment stratigraphy and geochemistry from high-resolution seismic-reflection, and 15N-isotope analyses was conducted in the Main Basin. The results reveal that buoyant hydrothermal plumes caused by subaquatic volcanic activity are a possible trigger for increased biological productivity and organic matter preservation, and that ongoing hydrothermal activity increases the alkalinity in the deepwater, leading to carbonate preservation. The onset of carbonate preservation since the 1970s that is currently observed in the sediment could indicate that hydrothermal discharge has recently increased in the lake.

The sediment record of the past 200 years in a Swiss high-alpine lake: Hagelseewli (2339 ma.s.l.)

Sediment cores spanning the last two centuries were taken in Hagelseewli, a high-elevation lake in the Swiss Alps. Contiguous 0.5 cm samples were analysed for biological remains, including diatoms, chironomids, cladocera, chrysophyte cysts, and fossil pigments. In addition, sedimentological and geochemical variables such as loss-on-ignition, total carbon, nitrogen, sulphur, grain-size and magnetic mineralogy were determined. The results of these analyses were compared to a long instrumental air temperature record that was adapted to the elevation of Hagelseewli by applying mean monthly lapse rates. During much of the time, the lake is in the shadow of a high cliff to the south, so that the lake is ice-covered during much of the year and thus decoupled from climatic forcing. Lake biology is therefore influenced more by the duration of ice-cover than by direct temperature effects during the short open-water season. Long periods of ice-cover result in anoxic water conditions and dissolution of authigenic calcites, leading to carbonate-free sediments. The diversity of chironomid and cladoceran assemblages is extremely low, whereas that of diatom and chrysophyte cyst assemblages is much higher. Weak correlations were observed between the diatom and chrysophyte cyst assemblages on the one hand and summer or autumn air temperatures on the other, but the proportion of variance explained is low, so that air temperature alone cannot account for the degree of variation observed in the paleolimnological record. Analyses of mineral magnetic parameters, spheroidal carbonaceous particles and lead suggest that atmospheric pollution has had a significant effect on the sediments of Hagelseewli, but little effect on the water quality as reflected in the lake biota.

Human–climate interactions in the central Mediterranean region during the last millennia: The laminated record of Lake Butrint (Albania)

Lake Butrint (39°47 N, 20°1 E) is a ca. 21 m deep, coastal lagoon located in SW Albania where finely-laminated sediments have been continuously deposited during the last millennia. The multi-proxy analysis (sedimentology, high-resolution elemental geochemistry and pollen) of a 12 m long sediment core, supported by seven AMS radiocarbon dates and 137Cs dating, enable a precise reconstruction of the environmental change that occurred in the central Mediterranean region during the last ∼4.5 cal kyrs BP. Sediments consist of triplets of authigenic carbonates, organic matter and clayey laminae. Fluctuations in the thickness and/or presence of these different types of seasonal laminae indicate variations in water salinity, organic productivity and runoff in the lake's catchment, as a result of the complex interplay of tectonics, anthropogenic forcing and climate variability. The progradation of the Pavllo river delta, favoured by variable human activity from the nearby ancient city of Butrint, led to the progressive isolation of this hydrological system from the Ionian Sea. The system evolved from an open bay to a restricted lagoon, which is consistent with archaeological data. An abrupt increase in mass-wasting activity between 1515 and 1450 BC, likely caused by nearby seismic activity, led to the accumulation of 24 homogenites, up to 17 cm thick. They have been deposited during the onset of finely laminated sedimentation, which indicates restricted, anoxic bottom water conditions and higher salinity. Periods of maximum water salinity, biological productivity, and carbonate precipitation coincide with warmer intervals, such as the early Roman Warm Period (RWP) (500 BC–0 AD), the Medieval Climate Anomaly (MCA) (800–1400 AD) and recent times (after 1800 AD). Conversely, lower salinity and more oxic conditions, with higher clastic input were recorded during 1400–500 BC, the Late Roman and the Early Medieval periods (0–800 AD) and during the Little Ice Age (1400–1800 AD). Hydrological fluctuations recorded in Butrint are in phase with most central and western Mediterranean records and correlate with NAO variability. In contrast, opposite hydrological patterns have been recorded in the Eastern Balkans and the Levant during the last millennium, emphasizing a complex spatial variability in the region. Phases of maximum settlement intensity in Butrint (Roman-Late Antique) coincide with warmer and/or stable climate periods (0–800 AD and MCA, respectively), indicating a long-term influence of climatic conditions on human activities. The Late Holocene sedimentary record of Lake Butrint demonstrates the complex interplay of climate variability, tectonics and human impact in the recent evolution of coastal Mediterranean regions.

Analysis of llicit and illicit drugs in waste, surface and lake water samples using large volume direct injection high performance liquid chromatography – Electrospray tandem mass spectrometry (HPLC–MS/MS)

http://www.sciencedirect.com/science/article/pii/S0045653510008891

Patterns of morphological changes and hybridization between sympatric whitefish morphs (Coregonus spp.) in a Swiss lake: a role for eutrophication?

Whitefish, genus Coregonus, show exceptional levels of phenotypic diversity with sympatric morphs occurring in numerous postglacial lakes in the northern hemisphere. Here, we studied the effects of human-induced eutrophication on sympatric whitefish morphs in the Swiss lake, Lake Thun. In particular, we addressed the questions whether eutrophication (i) induced hybridization between two ecologically divergent summer-spawning morphs through a loss of environmental heterogeneity, and (ii) induced rapid adaptive morphological changes through changes in the food web structure. Genetic analysis based on 11 microsatellite loci of 282 spawners revealed that the pelagic and the benthic morph represent highly distinct gene pools occurring at different relative proportions on all seven known spawning sites. Gill raker counts, a highly heritable trait, showed nearly discrete distributions for the two morphs. Multilocus genotypes characteristic of the pelagic morph had more gill rakers than genotypes characteristic of benthic morph. Using Bayesian methods, we found indications of recent but limited introgressive hybridization. Comparisons with historical gill raker data yielded median evolutionary rates of 0.24 haldanes and median selection intensities of 0.27 for this trait in both morphs for 1948-2004 suggesting rapid evolution through directional selection at this trait. However, phenotypic plasticity as an alternative explanation for this phenotypic change cannot be discarded. We hypothesize that both the temporal shifts in mean gill raker counts and the recent hybridization reflect responses to changes in the trophic state of the lake induced by pollution in the 1960s, which created novel selection pressures with respect to feeding niches and spawning site preferences.

Female mating preferences and male coloration covary with water transparency in a Lake Victoria cichlid fish

Rapid speciation in Lake Victoria cichlid fish of the genus Pundamilia may be facilitated by sexual selection: female mate choice exerts sexual selection on male nuptial coloration within species and maintains reproductive isolation between species. However, declining water transparency coincides with increasingly dull coloration and increasing hybridization. In the present study, we investigated the mechanism underlying this pattern in Pundamilia nyererei, a species that interbreeds with a sister species in turbid but not in clear water. We compared measures of intraspecific sexual selection between two populations from locations that differ in water transparency. First, in laboratory mate-choice experiments, conducted in clear water and under broad-spectrum illumination, we found that females originating from turbid water have significantly weaker preferences for male coloration than females originating from clear water. Second, both the hue and body coverage of male coloration differ between populations, which is consistent with adaptation to different photic habitats. These findings suggest that the observed relationship between male coloration and water transparency is not mediated by environmental variation alone. Rather, female mating preferences are indicated to have changed in response to this variation, constituting the first evidence for intraspecific preference-trait co-evolution in cichlid fish. (C) 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99, 398-406.

Sympatric colour polymorphisms associated with nonrandom gene flow in cichlid fish of Lake Victoria

Colour polymorphisms have fascinated evolutionary ecologists for a long time. Yet, knowledge on the mechanisms that allow their persistence is restricted to a handful of well-studied cases. We studied two species of Lake Victoria cichlid fish, Neochromis omnicaeruleus and Neochromis greenwoodi, exhibiting very similar sex-linked colour polymorphisms. The ecology and behaviour of one of these species is well studied, with colour-based mating and aggression preferences. Here, we ask whether the selection potentially resulting from female and male mating preferences and aggression biases reduces gene flow between the colour morphs and permits differentiation in traits other than colour. Over the past 14 years, the frequencies of colour morphs have somewhat oscillated, but there is no evidence for directional change, suggesting the colour polymorphism is persistent on an ecological timescale. We find limited evidence of ecomorphological differentiation between sympatric ancestral (plain) and derived (blotched) colour morphs. We also find significantly nonrandom genotypic assignment and an excess of linkage disequilibrium in the plain morph, which together with previous information on mating preferences suggests nonrandom mating between colour morphs. This, together with negative frequency-dependent sexual selection, found in previous studies, may facilitate maintenance of these polymorphisms in sympatry

Genetics of male nuptial colour divergence between sympatric sister species of a Lake Victoria cichlid fish

The hypothesis of sympatric speciation by sexual selection has been contentious. Several recent theoretical models of sympatric speciation by disruptive sexual selection were tailored to apply to African cichlids. Most of this work concludes that the genetic architecture of female preference and male trait is a key determinant of the likelihood of disruptive sexual selection to result in speciation. We investigated the genetic architecture controlling male nuptial colouration in a sympatric sibling species pair of cichlid fish from Lake Victoria, which differ conspicuously in male colouration and female mating preferences for these. We estimated that the difference between the species in male nuptial red colouration is controlled by a minimum number of two to four genes with significant epistasis and dominance effects. Yellow colouration appears to be controlled by one gene with complete dominance. The two colours appear to be epistatically linked. Knowledge on how male colouration segregates in hybrid generations and on the number of genes controlling differences between species can help us assess whether assumptions made in simulation models of sympatric speciation by sexual selection are realistic. In the particular case of the two sister species that we studied a small number of genes causing major differences in male colouration may have facilitated the divergence in male colouration associated with speciation.

No evidence for a genetic association between female mating preference and male secondary sexual trait in a Lake Victoria cichlid fish

Sexual selection by female mating preference for male nuptial coloration has been suggested as a driving force in the rapid speciation of Lake Victoria cichlid fish. This process could have been facilitated or accelerated by genetic associations between female preference loci and male coloration loci. Preferences, as well as coloration, are heritable traits and are probably determined by more than one gene. However, little is known about potential genetic associations between these traits. In turbid water, we found a population that is variable in male nuptial coloration from blue to yellow to red. Males at the extreme ends of the phenotype distribution resemble a reproductively isolated species pair in clear water that has diverged into one species with blue-grey mates and one species with bright red males. Females of the turbid water population vary in mating preference coinciding with the male phenotype distribution. For the current study, these females were mated to blue males. We measured the coloration of the sires and male offspring. Parents-offspring regression showed that the sires did not affect male offspring coloration, which confirms earlier findings that the blue species breeds true. In contrast, male offspring coloration was determined by the identity of the dams, which suggests that there is heritable variation in male color genes between females. However, we found that mating preferences of the dams were not correlated with male offspring coloration. Thus, there is no evidence for strong genetic linkage between mating preference and the preferred trait in this population [Current Zoology 56 (1): 57-64 2010].