Publications by authors named "Nils Andersen"

15 Publications

  • Page 1 of 1

Higher sea surface temperature in the Indian Ocean during the Last Interglacial weakened the South Asian monsoon.

Proc Natl Acad Sci U S A 2022 03 1;119(10):e2107720119. Epub 2022 Mar 1.

Leibniz Laboratory for Radiometric Dating and Stable Isotope Research, Kiel University, 24118 Kiel, Germany.

SignificanceUnderstanding the drivers of South Asian monsoon intensity is pivotal for improving climate forecasting under global warming scenarios. Solar insolation is assumed to be the dominant driver of monsoon variability in warm climate regimes, but this has not been verified by proxy data. We report a South Asian monsoon rainfall record spanning the last ∼130 kyr in the Ganges-Brahmaputra-Meghna river catchment. Our multiproxy data reveal that the South Asian monsoon was weaker during the Last Interglacial (130 to 115 ka)-despite higher insolation-than during the Holocene (11.6 ka to present), thus questioning the widely accepted model assumption. Our work implies that Indian Ocean warming may increase the occurrence of severe monsoon failures in South Asia.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1073/pnas.2107720119DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8915836PMC
March 2022

Fossil leaf wax hydrogen isotopes reveal variability of Atlantic and Mediterranean climate forcing on the southeast Iberian Peninsula between 6000 to 3000 cal. BP.

PLoS One 2020 23;15(12):e0243662. Epub 2020 Dec 23.

CRC1266, Christian-Albrechts University, Kiel, Germany.

Many recently published papers have investigated the spatial and temporal manifestation of the 4.2 ka BP climate event at regional and global scales. However, questions with regard to the potential drivers of the associated climate change remain open. Here, we investigate the interaction between Atlantic and Mediterranean climate forcing on the south-eastern Iberian Peninsula during the mid- to late Holocene using compound-specific hydrogen isotopes from fossil leaf waxes preserved in marine sediments. Variability of hydrogen isotope values in the study area is primarily related to changes in the precipitation source and indicates three phases of increased Mediterranean sourced precipitation from 5450 to 5350 cal. BP, from 5150 to 4300 cal. BP including a short-term interruption around 4800 cal. BP, and from 3400 to 3000 cal. BP interrupted around 3200 cal. BP. These phases are in good agreement with times of prevailing positive modes of the North Atlantic Oscillation (NAO) and reduced storm activity in the Western Mediterranean suggesting that the NAO was the dominant modulator of relative variability in precipitation sources. However, as previously suggested other modes such as the Western Mediterranean Oscillation (WeMO) may have altered this overall relationship. In this regard, a decrease in Mediterranean moisture source coincident with a rapid reduction in warm season precipitation during the 4.2 ka BP event at the south-eastern Iberian Peninsula might have been related to negative WeMO conditions.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0243662PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7757796PMC
February 2021

Alterations of the bile microbiome in primary sclerosing cholangitis.

Gut 2020 04 26;69(4):665-672. Epub 2019 Jun 26.

1st Department of Medicine, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.

Background: Patients with primary sclerosing cholangitis (PSC) display an altered colonic microbiome compared with healthy controls. However, little is known on the bile duct microbiome and its interplay with bile acid metabolism in PSC.

Methods: Patients with PSC (n=43) and controls without sclerosing cholangitis (n=22) requiring endoscopic retrograde cholangiography were included prospectively. Leading indications in controls were sporadic choledocholithiasis and papillary adenoma. A total of 260 biospecimens were collected from the oral cavity, duodenal fluid and mucosa and ductal bile. Microbiomes of the upper alimentary tract and ductal bile were profiled by sequencing the 16S-rRNA-encoding gene (V1-V2). Bile fluid bile acid composition was measured by high-performance liquid chromatography mass spectrometry and validated in an external cohort (n=20).

Results: The bile fluid harboured a diverse microbiome that was distinct from the oral cavity, the duodenal fluid and duodenal mucosa communities. The upper alimentary tract microbiome differed between PSC patients and controls. However, the strongest differences between PSC patients and controls were observed in the ductal bile fluid, including reduced biodiversity (Shannon entropy, p=0.0127) and increase of pathogen (FDR=4.18×10) in PSC. abundance in ductal bile was strongly correlated with concentration of the noxious secondary bile acid taurolithocholic acid (r=0.60, p=0.0021).

Conclusion: PSC is characterised by an altered microbiome of the upper alimentary tract and bile ducts. Biliary dysbiosis is linked with increased concentrations of the proinflammatory and potentially cancerogenic agent taurolithocholic acid.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1136/gutjnl-2019-318416DOI Listing
April 2020

Labrador Sea freshening at 8.5 ka BP caused by Hudson Bay Ice Saddle collapse.

Nat Commun 2019 02 4;10(1):586. Epub 2019 Feb 4.

Institute of Geosciences, Kiel University, Ludewig-Meyn-Straße 10, 24118, Kiel, Germany.

A significant reduction in the Atlantic Meridional Overturning Circulation and rapid northern Hemisphere cooling 8200 years ago have been linked to the final melting of the Laurentide Ice Sheet. Although many studies associated this cold event with the drainage of Lake Agassiz-Ojibway, recent model simulations have shown that the Hudson Bay Ice Saddle collapse would have had much larger effects on the Atlantic Meridional Overturning Circulation than the lake outburst itself. Based on a combination of Mg/Ca and oxygen isotope ratios of benthic foraminifera, this study presents the first direct evidence of a major Labrador shelfwater freshening at 8.5 ka BP, which we associate with the Hudson Bay Ice Saddle collapse. The freshening is preceded by a subsurface warming of the western Labrador Sea, which we link to the strengthening of the West Greenland Current that could concurrently have accelerated the ice saddle collapse in Hudson Bay.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-019-08408-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6362222PMC
February 2019

Late Miocene climate cooling and intensification of southeast Asian winter monsoon.

Nat Commun 2018 04 20;9(1):1584. Epub 2018 Apr 20.

Leibniz Laboratory for Radiometric Dating and Stable Isotope Research, Christian-Albrechts-University, Kiel, D-24118, Germany.

The late Miocene offers the opportunity to assess the sensitivity of the Earth's climate to orbital forcing and to changing boundary conditions, such as ice volume and greenhouse gas concentrations, on a warmer-than-modern Earth. Here we investigate the relationships between low- and high-latitude climate variability in an extended succession from the subtropical northwestern Pacific Ocean. Our high-resolution benthic isotope record in combination with paired mixed layer isotope and Mg/Ca-derived temperature data reveal that a long-term cooling trend was synchronous with intensification of the Asian winter monsoon and strengthening of the biological pump from ~7 Ma until ~5.5 Ma. The climate shift occurred at the end of a global δC decrease, suggesting that changes in the carbon cycle involving the terrestrial and deep ocean carbon reservoirs were instrumental in driving late Miocene climate cooling. The inception of cooler climate conditions culminated with ephemeral Northern Hemisphere glaciations between 6.0 and 5.5 Ma.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-018-03950-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5910391PMC
April 2018

Know your fish: A novel compound-specific isotope approach for tracing wild and farmed salmon.

Food Chem 2018 Aug 19;256:380-389. Epub 2018 Feb 19.

Leibniz-Laboratory for Radiometric Dating and Stable Isotope Research, Christian-Albrechts University of Kiel, Max-Eyth-Str. 11-13, 24118 Kiel, Germany.

The rapid expansion of the aquaculture industry with carnivorous fish such as salmon has been accompanied by an equally rapid development in alternative feed ingredients. This has outpaced the ability of prevailing authentication method to trace the diet and origins of salmon products at the retail end. To close this gap, we developed a new profiling tool based on amino acid δC fingerprints. With this tool, we discriminated with high-accuracy among wild-caught, organically, and conventionally farmed salmon groups, as well as salmon fed alternative diets such as insects and macroalgae. Substitution of fishmeal with macroalgae was detected at 5% difference level. The δC fingerprints of essential amino acids appear particularly well suited for tracing protein sources, and the non-essentials for tracing lipid origins (terrestrial vs. aquatic). In an industry constantly developing new feed proteins and functional additives, our method is a promising tool for tracing salmon and other seafood products.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.foodchem.2018.02.095DOI Listing
August 2018

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

J Anim Ecol 2016 Sep 21;85(5):1275-85. Epub 2016 Jul 21.

Institute of Arctic Biology and Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, AK, 99775-7000, USA.

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.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/1365-2656.12563DOI Listing
September 2016

Feedback on Measured Dust Concentrations Reduces Exposure Levels Among Farmers.

Ann Occup Hyg 2016 Aug 31;60(7):812-24. Epub 2016 May 31.

1.Department of Public Health, Section for Environment, Occupation and Health, Danish Ramazzini Center, Aarhus University, Bartholins Allé 2, bg 1260, 8000 Aarhus C, Denmark; 5.National Research Center for the Working Environment, Lersø Parkallé 105, 2100 Copenhagen Ø, Denmark.

Background: The high burden of exposure to organic dust among livestock farmers warrants the establishment of effective preventive and exposure control strategies for these workers. The number of intervention studies exploring the effectiveness of exposure reduction strategies through the use of objective measurements has been limited.

Objective: To examine whether dust exposure can be reduced by providing feedback to the farmers concerning measurements of the exposure to dust in their farm.

Methods: The personal dust levels of farmers in 54 pig and 26 dairy cattle farms were evaluated in two measurement series performed approximately 6 months apart. Detailed information on work tasks and farm characteristics during the measurements were registered. Participating farms were randomized a priori to a control (n = 40) and an intervention group (n = 40). Shortly after the first visit, owners of intervention farms only received a letter with information on the measured dust concentrations in the farm together with some general advises on exposure reduction strategies (e.g. use of respirators during certain tasks). Relationships between measured dust concentrations and intervention status were quantified by means of linear mixed effect analysis with farm and worker id as random effects. Season, type of farming, and work tasks were treated as fixed effects. Changes in exposure over time were explored primarily at a farm level in models combined, as well as separate for pig and cattle farmers.

Results: After adjustment for fixed effects, an overall reduction of 23% in personal dust exposures was estimated as a result of the intervention (P = 0.02). Exposure reductions attributable to the intervention were similar across pig and cattle farmers, but statistically significant only for pig farmers. Intervention effects among pig farmers did not depend on the individuals' information status; but among cattle farmers a significant 48% reduction in exposure was found only among individuals that reported to have been informed. No systematic differences in changes over time considering the use of respiratory protection between the intervention and control groups were observed.

Conclusion: The results of the present study suggest reductions between 20 and 30% in personal exposure to inhalable dust to be feasible through simple information provided to the farm owners regarding actual levels of exposure together with instructions on basic measures of prevention. The exact reasons for these effects are unclear, but likely they involve changes in behavior and working practices among intervention farmers.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/annhyg/mew032DOI Listing
August 2016

Exposure-affecting factors of dairy farmers' exposure to inhalable dust and endotoxin.

Ann Occup Hyg 2014 Jul 18;58(6):707-23. Epub 2014 Apr 18.

1.Department of Public Health, Section for Environment, Occupation and Health, Danish Ramazzini Center, Aarhus University, Bartholins Allé 2, bg 1260, 8000 Aarhus C, Denmark 6.Department of Occupational Medicine, Danish Ramazzini Center, Aarhus University Hospital, Nørrebrogade 44, 8000 Aarhus C, Denmark.

Introduction: Studies on determinants of dairy farmers' exposure to dust and endotoxin have been sparse and so far none has addressed the combined effect of tasks and farm characteristics.

Objective: To study whether and how work tasks and specific stable characteristics influence the level of dairy farmers' personal exposure to inhalable dust and endotoxin.

Methods: We applied an observational design involving full-shift repeated personal measurements of inhalable dust and endotoxin exposure among 77 subjects (owners and farm workers) from 26 dairy farms. Performed tasks were self-registered in activity diaries, and information on stable characteristics was collected through personal interviews and walk-through surveys. Associations between exposure, tasks, and stable characteristics were examined in linear mixed-effect models with individual and farm treated as random effects. Separate as well as combined models for tasks and stable characteristics were elaborated.

Results: The 124 personal samples collected had a geometric mean level (geometric standard deviation) of 360 EU m(-3) (3.8) for endotoxin exposure and of 1.0mg m(-3) (2.7) for dust exposure. Identified factors that increased endotoxin exposure included a lower outdoor temperature and use of slope-based or back-flushed slurry systems along with milking, distribution of bedding, and handling of feed and seeds in barns. For dust, exposure was higher when fully automatic (robotic) milking was used and during re-penning of animals, handling of feed and seeds, handling of silos and when distributing bedding. Dust exposure increased also as a result of use of rail feed dispensers in a model without fully automatic milking.

Conclusions: The current exposure to dust and in particular endotoxin among Danish dairy farmers demand effective strategies to reduce their exposure. The present findings suggest that future interventions should focus on feeding and manure handling systems. Use of respirators during handling of feed and distribution of bedding should be advised until adequate risk management measures have been established. The expected increased use of fully automatic milking in the future might increase dust exposure of dairy farmers.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/annhyg/meu024DOI Listing
July 2014

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

PLoS One 2013 17;8(9):e73441. Epub 2013 Sep 17.

Leibniz-Laboratory for Radiometric Dating and Stable Isotope Research, Christian-Albrechts Universität zu Kiel, Kiel, Germany ; Biogeodynamics and Biodiversity Group, Centre for Advanced Studies of Blanes, Spanish Research Council (CEAB-CSIC), Blanes, Catalonia, Spain.

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.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0073441PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3775739PMC
April 2014

Middle to Late Eocene paleoenvironmental changes in a marine transgressive sequence from the northern Tethyan margin (Adelholzen, Germany).

Austrian J Earth Sci 2013;106(2):45-72

Geologische Bundesanstalt, Neulinggasse 38, A-1030 Wien, Austria ; Universität Wien, Institut für Paläontologie, Althanstraße 14, A-1090 Wien, Austria.

The northern Tethyan margin is a key region for determining environmental changes associated with the collision of continental and oceanic tectonic plates and Alpine orogeny. Herein we investigated Middle to Late Eocene neritic to bathyal sediments deposited during an interval of unstable climatic conditions. In order to quantify paleoenvironmental changes, we developed a detailed age model based on biozonations of planktic foraminifera, calcareous nannoplankton, and larger benthic foraminifera. The section at Adelholzen covers the almost complete Lutetian Stage (calcareous nannoplankton zones NP15a-16, planktic foraminifera zones E8-11, shallow benthic (foraminifera) zones SBZ13-15) and large parts of the Priabonian Stage (NP18-20, E14/15), while the intermediate Bartonian Stage (NP17) is completely missing. Foraminiferal, calcareous nannoplankton, and macrofossil assemblages were analyzed for changes in paleo-water depth, mixing and stratification, paleo-primary productivity (pPP), food supply, and bottom water oxygenation. Paleo-water depth estimates range from 50 m (middle neritic, early Lutetian) to nearly 500 m (upper bathyal, late Priabonian). The combination of assemblage composition, planktic and benthic foraminiferal accumulation rates, and derived parameters (carbon-flux to sea floor, pPP) enabled us to identify a series of distinct paleoceanographic events of at least regional significance. Such events are characterized by considerable changes in primary productivity or reduced bottom water ventilation. Calculated pPP-values indicate oligotrophic conditions throughout.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4558959PMC
January 2013

Exposure to inhalable dust and endotoxin among Danish livestock farmers: results from the SUS cohort study.

J Environ Monit 2012 Feb 9;14(2):604-14. Epub 2011 Dec 9.

Department of Environmental & Occupational Medicine, School of Public Health, Aarhus University, Bartholins Allé 2, bg 1260, 8000 Aarhus C, Denmark.

Studies on personal dust and endotoxin concentrations among animal farmers have been either small or limited to a few sectors in their investigations. The present study aimed to provide comparable information on the levels and variability of exposure to personal dust and endotoxin in different types of animal farmers. 507 personal inhalable dust samples were collected from 327 farmers employed in 54 pig, 26 dairy, 3 poultry, and 3 mink farms in Denmark. Measurements in pig and dairy farmers were full-shift and performed during summer and winter, while poultry and mink farmers were monitored during 4 well-defined production stages. The collected samples were measured for dust gravimetrically and analyzed for endotoxin by the Limulus amebocyte lysate assay. Simple statistics and random-effect analysis were used to describe the levels and the variability in measured dust and endotoxin exposure concentrations. Measured inhalable dust levels had an overall geometric mean of 2.5 mg m(-3) (range
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c1em10576kDOI Listing
February 2012

155,000 years of West African monsoon and ocean thermal evolution.

Science 2007 Jun;316(5829):1303-7

Department of Earth Science and Marine Science Institute, University of California, Santa Barbara, CA 93106-9630, USA.

A detailed reconstruction of West African monsoon hydrology over the past 155,000 years suggests a close linkage to northern high-latitude climate oscillations. Ba/Ca ratio and oxygen isotope composition of planktonic foraminifera in a marine sediment core from the Gulf of Guinea, in the eastern equatorial Atlantic (EEA), reveal centennial-scale variations of riverine freshwater input that are synchronous with northern high-latitude stadials and interstadials of the penultimate interglacial and the last deglaciation. EEA Mg/Ca-based sea surface temperatures (SSTs) were decoupled from northern high-latitude millennial-scale fluctuation and primarily responded to changes in atmospheric greenhouse gases and low-latitude solar insolation. The onset of enhanced monsoon precipitation lags behind the changes in EEA SSTs by up to 7000 years during glacial-interglacial transitions. This study demonstrates that the stadial-interstadial and deglacial climate instability of the northern high latitudes exerts dominant control on the West African monsoon dynamics through an atmospheric linkage.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1126/science.1140461DOI Listing
June 2007

Influence of the growth substrate on ester-linked phospho- and glycolipid fatty acids of PAH-degrading Mycobacterium sp. LB501T.

Environ Microbiol 2003 Aug;5(8):672-80

Swiss Federal Institute of Technology Lausanne (EPFL), ENAC/ISTE-Laboratory of Soil Science, CH-1015 Lausanne, Switzerland.

The influences of poorly water-soluble anthracene on ester-linked phospholipid fatty acid (PLFA) and glycolipid fatty acid (GLFA) profiles of Mycobacterium sp. LB501T were studied. Bacteria were cultivated on either anthracene or glucose (one culture with successively amended small doses of this substrate and one with excess concentrations) to distinguish between influences of the chemical structure and the bioavailability of the growth substrate. Results revealed that GLFA and PLFA profiles of M. sp. LB501T depended on the availability and the structure of the carbon source. Fatty acid profiles obtained with anthracene differed from those obtained with excess glucose. They were interpreted as a specific adaptation to this poorly bioavailable polycyclic aromatic hydrocarbon (PAH). In contrast, profiles obtained with low glucose concentrations showed clear signs of starvation stress. Stable carbon isotopic ratios (delta13C) of GLFA and PLFA of M. sp. LB501T were analysed to characterize the 13C-fractionation during the biosynthesis of individual fatty acids and to evaluate their value as markers for substrate usage. Although the delta13C values of PLFA and GLFA showed differential isotope fractionation during anthracene- and glucose-degradation, they were sufficiently distinct to be used as signatures of bacterial substrate usage.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1046/j.1462-2920.2003.00455.xDOI Listing
August 2003

CLADISTIC INFERENCE AND EVOLUTIONARY SCENARIOS: LOCOMOTORY STRUCTURE, FUNCTION, AND PERFORMANCE IN WATER STRIDERS.

Cladistics 1995 Sep 19;11(3):279-295. Epub 2005 Jul 19.

Zoological Museum, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, Denmark.

A research methodology that aims to reveal how historical changes in environmental conditions (or selective regimes) have shaped the adaptive evolution of clades is applied to the adaptive evolution of water striders and their allies (Hemiptera-Heteroptera, Gerromorpha), a group of semiaquatic insects which includes species that are conspicuously adapted to life on the surface film of water. Based upon reconstructed phylogenies for the higher gerromorphan taxa, the hypothesis that the hygropetric zone is the ancestral one is confirmed for the Mesoveliidae, Hebridae and the clade comprising the Paraphrynoveliidae, Macroveliidae and Hydrometridae, but not for the Hermatobatidae and Veliidae. There is no support for the hypothesis that the intersection zone was a sort of transitional zone during the ecological evolution of pleustonic bugs. It is shown that the unique morphological and behavioural traits of the most derived members of this group evolved after inferred historical changes in environmental conditions and therefore qualify as adaptations in the sense ofGould and Vrba (1982),Coddington (1988) andBaum and Larson (1991). Other predictions about the adaptive evolution of gerromorphan bugs do not pass the cladistic test. The study illustrates that cladistic inference is a valuable tool in clarifying and sharpening retrospective explanations of complex evolutionary scenarios.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/j.1096-0031.1995.tb00090.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7162302PMC
September 1995
-->