962 resultados para ALPINE LAKE
Resumo:
Divergent selection acting on several different traits that cause multidimensional shifts are supposed to promote speciation, but the outcome of this process is highly dependent on the balance between the strength of selection vs. gene flow. Here, we studied a pair of sister species of Lake Victoria cichlids at a location where they hybridize and tested the hypothesis that divergent selection acting on several traits can maintain phenotypic differentiation despite gene flow. To explore the possible role of selection we tested for correlations between phenotypes and environment and compared phenotypic divergence (P-ST) with that based on neutral markers (F-ST). We found indications for disruptive selection acting on male breeding colour and divergent selection acting on several morphological traits. By performing common garden experiments we also separated the environmental and heritable components of divergence and found evidence for phenotypic plasticity in some morphological traits contributing to species differences.
Resumo:
More than 500 endemic haplochromine cichlid species inhabit Lake Victoria. This striking species diversity is a classical example of recent explosive adaptive radiation thought to have happened within the last similar to 15,000 years. In this study, we examined the population structure and historical demography of 3 pelagic haplochromine cichlid species that resemble in morphology and have similar niche, Haplochromis (Yssichromis) laparogramma, Haplochromis (Y.) pyrrhocephalus, and Haplochromis (Y.) sp. "glaucocephalus". We investigated the sequences of the mitochondrial DNA control region and the insertion patterns of short interspersed elements (SINEs) of 759 individuals. We show that sympatric forms are genetically differentiated in 4 of 6 cases, but we also found apparent weakening of the genetic differentiation in areas with turbid water. We estimated the timings of population expansion and species divergence to coincide with the refilling of the lake at the Pleistocene/Holocene boundary. We also found that estimates can be altered significantly by the choice of the shape of the molecular clock. If we employ the nonlinear clock model of evolutionary rates in which the rates are higher towards the recent, the population expansion was dated at around the event of desiccation of the lake ca. 17,000 YBP. Thus, we succeeded in clarifying the species and population structure of closely related Lake Victoria cichlids and in showing the importance of applying appropriate clock calibrations in elucidating recent evolutionary events. (C) 2009 Elsevier B.V. All rights reserved.
Resumo:
Mycoplasma conjunctivae is considered the major cause of infectious keratoconjunctivitis (IKC) in Alpine ibex (Capra i. ibex) and chamois (Rupicapra r. rupicapra). While it is known that domestic sheep can act as healthy carriers for M. conjunctivae, this question has not been addressed in wild ungulates so far. In this study, bacteriological investigations and field observations were performed to assess whether free-ranging Alpine ibex can be healthy carriers of M. conjunctivae. Among 136 ibex without clinical signs of IKC, M. conjunctivae was identified 26 times (19.1%) by TaqMan PCR. To assess the potential pathogenicity of M. conjunctivae strains isolated from asymptomatic eyes, strains from three healthy ibex and from 15 IKC-ibex and IKC-chamois were analysed genetically by DNA sequence analysis of the variable part of the lppS gene. No significant differences were observed between strains from asymptomatic and clinically affected animals, reflecting the assumption that healthy ibex may act as carriers for M. conjunctivae strains that may be pathogenic for other individuals. Our results further indicate that development of IKC is associated with M. conjunctivae load in the eyes. In addition, a questionnaire survey revealed that IKC is generally less common in ibex than chamois and that infection in wild ungulates is not necessarily linked to the presence of sheep. These data support the hypothesis that apparently healthy ibex may be important in the epizootiology of IKC and indicate that host predilection may play a role in IKC development.
Resumo:
Five cases of fatal babesiosis in free-ranging chamois (Rupicapra r. rupicapra) attributed to infections with Babesia capreoli were recently recorded in two regions of the Swiss Alps. To investigate the ecologic factors that possibly lead to those fatal B. capreoli infections in chamois, blood, ticks, and demographic data of 46 roe deer (Capreolus c. capreolus), 48 chamois, and nine red deer (Cervus elaphus) were collected in 2006 and 2007 in both affected regions. Whereas no parasitic inclusions were found by microscopical examination of blood smears, B. capreoli was identified by polymerase chain reaction/sequencing in blood of 12 roe deer (26%, 95% confidence interval [CI]: 14.3-41.1), one chamois (2%, CI: 0-6.1), and one red deer (11%, CI: 0.3-48.2). Prevalence of B. capreoli was significantly higher in roe deer compared with chamois (P<0.001). All 214 ticks were identified as Ixodes ricinus, and significantly more roe deer (63%, CI: 47.5-76.8) were infested compared with chamois (21%, CI: 10.5-35.0, P<0.001). Overall, prevalences of both tick infestation and Babesia infection increased significantly (P<0.001) with decreasing altitude, and Babesia-positive samples were detected significantly more often from animals with tick infestation compared with animals without ticks (P = 0.040). Our results indicate that roe deer may play an important reservoir role for B. capreoli. It is hypothesized that the expansion of the presumed vector I. ricinus to higher elevations and its increased abundance in overlapping habitats of roe deer and chamois may favor the spillover of B. capreoli from roe deer to chamois.
Resumo:
Since 2000, a surprisingly high number of macroscopical gonad alterations has been reported in whitefish (Coregonus spp.) from Lake Thun, Switzerland. This unique phenomenon is still unexplained and has received much public attention. As one possible trigger for these effects, the presence of persistent, bioaccumulative and toxic compounds acting as endocrine disruptors in the lake has been discussed. In this study, concentrations of selected persistent organic pollutants were examined in two morphs of whitefish from Lake Thun and their link to the observed abnormalities was investigated. Analyzed compound classes included polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins and dibenzofurans, polychlorinated naphthalenes, polybrominated diphenyl ethers and hexabromocyclododecanes. The target substances were identified in all samples and concentrations of the analyzed compounds were highly correlated among each other. These correlations show that the analyzed substances have the same distribution pattern throughout the lake and that uptake, accumulation and elimination processes are similar. Significant differences in contaminant levels within the samples existed between the two analyzed morphs of whitefish, most likely due to different age, food patterns and growth rate. No difference in contaminant levels was observed between fish with abnormal gonads and fish with normal gonads, suggesting no causal link between the investigated lipophilic organohalogen compounds present in fish and the observed gonad abnormalities in whitefish from Lake Thun. A comparison to existing data shows that concentrations in Lake Thun whitefish are at the lower bound of contaminant levels in whitefish from Swiss lakes or from European waters.
Resumo:
A high prevalence of gonad morphological variations has been observed in whitefish Coregonus lavaretus from Lake Thun (Switzerland). To clarify the role of endocrine disruption as a possible cause of the gonad alterations, whitefish were reared in a long-term laboratory experiment under exposure to 17 beta-estradiol (E2). Fish were fed from first-feeding until 3 yr of age at a daily rate of 0 (control), 0.5 or 50 microg E2 kg(-1) fish. E2 exposure resulted in a time- and concentration-dependent increase of prevalence and intensity of intersex gonads, i.e. gonads that macroscopically appeared as either testis or ovary but microscopically contained both male and female germ cells. Four types of intersex could be distinguished: Types 1 and 2 were composed of mainly male tissue, with Type 1 containing single oocytes and Type 2 displaying an ovary-like lamellar structure of the tissue. In Type 3, an increased percentage of the tissue was occupied by female germ cells, while in Type 4, the majority of the gonad tissue consisted of female germ cells. Chronic E2 exposure additionally resulted in a concentration-dependent shift of the sex ratio towards females, a reduced condition factor, retarded gonad growth together with delayed maturation of germ cells, and elevated levels of hepatic vitellogenin mRNA. However, Lake Thun-typical alterations of gonad morphology were not induced by chronic E2 exposure. The results provide evidence that estrogen-active compounds unlikely play a role in the etiology of gonad malformations in Lake Thun whitefish.
Resumo:
Understanding past methane dynamics in arctic wetlands and lakes is crucial for estimating future methane release. Methane fluxes from lake ecosystems have increasingly been studied, yet only few reconstructions of past methane emissions from lakes are available. In this study, we develop an approach to assess changes in methane availability in lakes based on δ13C of chitinous invertebrate remains and apply this to a sediment record from a Siberian thermokarst lake. Diffusive methane fluxes from the surface of ten newly sampled Siberian lakes and seven previously studied Swedish lakes were compared to taxon-specific δ13C values of invertebrate remains from lake surface sediments to investigate whether these invertebrates assimilated 13C-depleted carbon typical for methane. Remains of chironomid larvae of the tribe Orthocladiinae that, in the study lakes, mainly assimilate plant-derived carbon had higher δ13C than other invertebrate groups. δ13C of other invertebrates such as several chironomid groups (Chironomus, Chironomini, Tanytarsini, and Tanypodinae), cladocerans (Daphnia), and ostracods were generally lower. δ13C of Chironomini and Daphnia, and to a lesser extent Tanytarsini was variable in the lakes and lower at sites with higher diffusive methane fluxes. δ13C of Chironomini, Tanytarsini, and Daphnia were correlated significantly with diffusive methane flux in the combined Siberian and Swedish dataset (r = −0.72, p = 0.001, r = −0.53, p = 0.03, and r = −0.81, p < 0.001, respectively), suggesting that δ13C in these invertebrates was affected by methane availability. In a second step, we measured δ13C of invertebrate remains from a sediment record of Lake S1, a shallow thermokarst lake in northeast Siberia. In this record, covering the past ca 1000 years, δ13C of taxa most sensitive to methane availability (Chironomini, Tanytarsini, and Daphnia) was lowest in sediments deposited from ca AD 1250 to ca AD 1500, and after AD 1970, coinciding with warmer climate as indicated by an independent local temperature record. As a consequence the offset in δ13C between methane-sensitive taxa and bulk organic matter was higher in these sections than in other parts of the core. In contrast, δ13C of other invertebrate taxa did not show this trend. Our results suggest higher methane availability in the study lake during warmer periods and that thermokarst lakes can respond dynamically in their methane output to changing environmental conditions.
Resumo:
Accumulation and delta O-18 data from Alpine ice cores provide information on past temperature and precipitation. However, their correlation with seasonal or annual mean temperature and precipitation at nearby sites is often low. This is partly due to the irregular sampling of the atmosphere by the ice core (i.e. ice cores almost only record precipitation events and not dry periods) and the possible incongruity between annual layers and calendar years. Using daily meteorological data from a nearby station and reanalyses, we replicate the ice core from the Grenzgletscher (Switzerland, 4200m a.s.l.) on a sample-by-sample basis by calculating precipitation-weighted temperature (PWT) over short intervals. Over the last 15 yr of the ice core record, accumulation and delta O-18 variations can be well reproduced on a sub-seasonal scale. This allows a wiggle-matching approach for defining quasi-annual layers, resulting in high correlations between measured quasi-annual delta O-18 and PWT. Further back in time, the agreement deteriorates. Nevertheless, we find significant correlations over the entire length of the record (1938-1993) of ice core delta O-18 with PWT, but not with annual mean temperature. This is due to the low correlations between PWT and annual mean temperature, a characteristic which in ERA-Interim reanalysis is also found for many other continental mid-to-high-latitude regions. The fact that meteorologically very different years can lead to similar combinations of PWT and accumulation poses limitations to the use of delta O-18 from Alpine ice cores for temperature reconstructions. Rather than for reconstructing annual mean temperature, delta O-18 from Alpine ice cores should be used to reconstruct PWT over quasi-annual periods. This variable is reproducible in reanalysis or climate model data and could thus be assimilated into conventional climate models.
Resumo:
Lake-effect snow is an important constraint on ecological and socio-economic systems near the North American Great Lakes. Little is known about the Holocene history of lake-effect snowbelts, and it is difficult to decipher how lake-effect snowfall abundance affected ecosystem development. We conducted oxygen-isotope analysis of calcite in lake-sediment cores from northern Lower Michigan to infer Holocene climatic variation and assess snowbelt development. The two lakes experience the same synoptic-scale climatic systems, but only one of them (Huffman Lake) receives a significant amount of lake-effect snow. A 177-cm difference in annual snowfall causes groundwater inflow at Huffman Lake to be 18O-depleted by 2.3‰ relative to O'Brien Lake. To assess when the lake-effect snowbelt became established, we compared calcite-δ18O profiles of the last 11,500 years from these two sites. The chronologies are based on accelerator-mass-spectrometry 14C ages of 11 and 17 terrestrial-plant samples from Huffman and O'Brien lakes, respectively. The values of δ18O are low at both sites from 11,500 to 9500 cal yr BP when the Laurentide Ice Sheet (LIS) exerted a dominant control over the regional climate and provided periodic pulses of meltwater to the Great Lakes basin. Carbonate δ18O increases by 2.6‰ at O'Brien Lake and by 1.4‰ at Huffman Lake between 9500 and 7000 cal yr BP, suggesting a regional decline in the proportion of runoff derived from winter precipitation. The Great Lakes snowbelt probably developed between 9500 and 5500 cal yr BP as inferred from the progressive 18O-depletion at Huffman Lake relative to O'Brien Lake, with the largest increase of lake-effect snow around 7000 cal yr BP. Lake-effect snow became possible at this time because of increasing contact between the Great Lakes and frigid arctic air. These changes resulted from enhanced westerly flow over the Great Lakes as the LIS collapsed, and from rapidly rising Great Lakes levels during the Nipissing Transgression. The δ18O difference between Huffman and O'Brien lakes declines after 5500 cal yr BP, probably because of a northward shift of the polar vortex that brought increasing winter precipitation to the entire region. However, δ18O remains depleted at Huffman Lake relative to O'Brien Lake because of the continued production of lake-effect snow.
Resumo:
Continental evaporation is a significant and dynamic flux within the atmospheric water budget, but few methods provide robust observational constraints on the large-scale hydroclimatological and hydroecological impacts of this ‘recycled-water' flux. We demonstrate a geospatial analysis that provides such information, using stable isotope data to map the distribution of recycled water in shallow aquifers downwind from Lake Michigan. The δ2H and δ18O values of groundwater in the study region decrease from south to north, as expected based on meridional gradients in climate and precipitation isotope ratios. In contrast, deuterium excess (d = δ2H − 8 × δ18O) values exhibit a significant zonal gradient and finer-scale spatially patterned variation. Local d maxima occur in the northwest and southwest corners of the Lower Peninsula of Michigan, where ‘lake-effect' precipitation events are abundant. We apply a published model that describes the effect of recycling from lakes on atmospheric vapor d values to estimate that up to 32% of recharge into individual aquifers may be derived from recycled Lake Michigan water. Applying the model to geostatistical surfaces representing mean d values, we estimate that between 10% and 18% of the vapor evaporated from Lake Michigan is re-precipitated within downwind areas of the Lake Michigan drainage basin. Our approach provides previously unavailable observational constraints on regional land-atmosphere water fluxes in the Great Lakes Basin and elucidates patterns in recycled-water fluxes that may influence the biogeography of the region. As new instruments and networks facilitate enhanced spatial monitoring of environmental water isotopes, similar analyses can be widely applied to calibrate and validate water cycle models and improve projections of regional hydroecological change involving the coupled lake-atmosphere-land system. Read More: http://www.esajournals.org/doi/abs/10.1890/ES12-00062.1
Resumo:
The mean transit time (MTT) of water in a catchment gives information about storage, flow paths, sources of water and thus also about retention and release of solutes in a catchment. To our knowledge there are only a few catchment studies on the influence of vegetation cover changes on base flow MTTs. The main changes in vegetation cover in the Swiss Alps are massive shrub encroachment and forest expansion into formerly open habitats. Four small and relatively steep headwater catchments in the Swiss Alps (Ursern Valley) were investigated to relate different vegetation cover to water transit times. Time series of water stable isotopes were used to calculate MTTs. The high temporal variation of the stable isotope signals in precipitation was strongly dampened in stream base flow samples. MTTs of the four catchments were 70 to 102 weeks. The strong dampening of the stable isotope input signal as well as stream water geochemistry points to deeper flow paths and mixing of waters of different ages at the catchments' outlets. MTTs were neither related to topographic indices nor vegetation cover. The major part of the quickly infiltrating precipitation likely percolates through fractured and partially karstified deeper rock zones, which increases the control of bedrock flow paths on MTT. Snow accumulation and the timing of its melt play an important role for stable isotope dynamics during spring and early summer. We conclude that, in mountainous headwater catchments with relatively shallow soil layers, the hydrogeological and geochemical patterns (i.e. geochemistry, porosity and hydraulic conductivity of rocks) and snow dynamics influence storage, mixing and release of water in a stronger way than vegetation cover or topography do.