Bimodal transparency as an indicator for alternative states in South American lakes

1. The alternative state theory claims that shallow lakes may have either clear water, and be dominated by submerged macrophytes, or turbid water and be dominated by phytoplankton. Most evidence for this theory comes from studies in temperate or boreal regions of Europe. Because of differences in the strength of trophic interactions, such as in the pressure of zooplankton grazing on phytoplankton, this influential theory might not apply elsewhere. 2. Here, we test the theory for South American lakes, combining field data and Landsat satellite data. We studied the frequency distribution of primary producers and water transparency, looking for potential bimodality separating clear and turbid lakes. A bimodal distribution might be observed if there are indeed alternative states, although would not itself be sufficient evidence for the theory. Possible shifts between alternative states were analysed by comparing satellite data from 1987 to 2005. 3. In our field data, there was a bimodal pattern in phytoplankton abundance and possibly in the abundance of submerged macrophytes, but not in water transparency. Analyses of the larger satellite data set revealed bimodality in lake transparency in 2005, but less so in 1987. In 1987, the lakes were generally clearer, and the transition to higher turbidity was more gradual than in 2005. The stronger bimodality in the more recent data, and the overall lower transparency, could have been caused by an increase in fertiliser use and subsequent eutrophication but also by differences in hydrology. Further, 1987 was much wetter than 2005, which could have caused dilution of suspended particles, leading to clearer water. 4. While a bimodal distribution in the abundance of primary producers and water clarity is not decisive evidence for or against the theory of alternative states, our data clearly fail to refute it.     

Redescription and palaeobiology of Palaeoscorpius devonicus Lehmann, 1944 from the Lower Devonian Hunsrück Slate of Germany

Abstract: Palaeoscorpius devonicus Lehmann, 1944 is known from only a single specimen, found in the Eschenbach Pit near Bundenbach in the Lower Devonian Hunsrück Slate of Germany. It is a key fossil, having been interpreted both as the most basal member of the Scorpiones and as one of the order’s most likely candidates for an aquatic mode of life. Prepared both ventrally and dorsally, some aspects of its morphology remain problematic. Here, with the aid of new techniques, including computed tomography, we present a re‐investigation of this scorpion’s anatomy and a new reconstruction, with a particular focus on the species’ original habitat. On the basis of the environmental interpretation of the Hunsrück Slate and the completeness of the specimen, previous authors concluded that P. devonicus was marine, but none offered convincing morphological evidence. Recent studies of the deposit’s environment suggest that the Hunsrück Sea was part of an intrashelf basin, relatively close to the coastline, and fossils of land plants show that terrestrial wash‐in occasionally occurred. Our revised interpretation of the fossil’s morphology demonstrates that the scorpion was most probably terrestrial. Internal mesosomal organs are interpreted as book lungs, but other terrestrial adaptations are lacking. The absence of both coxapophyses and gnathobases makes determining the scorpion’s feeding mechanism difficult. Interpreting the scorpion’s character states within a phylogenetic framework, especially the possible presence of book lungs, implies either that the plesiomorphic position of P. devonicus is no longer supported or that the development of book lungs had already taken place early in the scorpion lineage.     

Frequency of fault bars in feathers of birds and susceptibility to predation

Fault bars are transparent bands in the feathers of birds produced under stressful and adverse conditions. The frequency of feathers with fault bars is highly heterogeneous among species. We predicted that prey had a higher frequency of fault bars than individuals from the general population, and that a high susceptibility to predation would be associated with a low frequency of fault bars among species of birds because such species would suffer particularly high costs of producing fault bars. The frequency of fault bars in prey was almost three-fold higher than in the general population, based on a database on the frequency of fault bars and susceptibility to predation by the goshawk Accipiter gentilis L., implying intense natural selection against fault bars. A high susceptibility to predation by the sparrowhawk Accipiter nisus L. and the goshawk, relative to what would be expected from their abundance, was associated with a low frequency of fault bars across species, with long distance migration also being negatively associated with frequency of fault bars. Feathers with fault bars were more likely to break than feathers without fault bars, thereby potentially affecting the flight ability of individuals. These findings are consistent with the hypothesis that susceptibility to factors that cause production of fault bars can be modified by natural selection, as illustrated by the impact of predation on the frequency of fault bars.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 334–345.     

Population‐specificity of heat stress gene induction in northern and southern eelgrass Zostera marina populations under simulated global warming

Summer heat waves have already resulted in mortality of coastal communities, including ecologically important seagrass meadows. Gene expression studies from controlled experiments can provide important insight as to how species/genotypes react to extreme events that will increase under global warming. In a common stress garden, we exposed three populations of eelgrass, Zostera marina, to extreme sea surface temperatures, simulating the 2003‐European heat wave. Populations came from locations widely differing in their thermal regime, two northern European locations [Ebeltoft (Kattegat), Doverodde (Limfjord, Baltic Sea)], and one southern population from Gabicce Mare (Adriatic Sea), allowing to test for population specificity in the response to a realistic heat stress event. Eelgrass survival and growth as well as the expression of 12 stress associated candidate genes were assessed during and after the heat wave. Contrary to expectations, all populations suffered equally from 3 weeks of heat stress in terms of shoot loss. In contrast, populations markedly differed in multivariate measures of gene expression. While the gene expression profiles converged to pre‐stress values directly after the heat wave, stress correlated genes were upregulated again 4 weeks later, in line with the observed delay in shoot loss. Target genes had to be selected based on functional knowledge in terrestrial plants, nevertheless, 10/12 genes were induced relative to the control treatment at least once during the heat wave in the fully marine plant Z. marina. This study underlines the importance of realistic stress and recovery scenarios in studying the impact of predicted climate change.     

The Occurrence and Ape-to-Ape Transmission of the Entodiniomorphid Ciliate Troglodytella abrassarti in Captive Gorillas

ABSTRACT. Entodiniomorphid ciliates are often present in the colons of wild apes. In captive apes the infection tends to gradually disappear, with the exception of Troglodytella abrassarti . We used fecal examinations to screen the gorillas ( Gorilla gorilla gorilla ) in European (Czech Republic, UK) and Australian Zoos to explore the ape-to-ape transmission pattern of T. abrassarti . Gorillas from two out of three European Zoos were positive for T. abrassarti , while gorillas from the Australian Zoo were negative. We documented a horizontal transmission of T. abrassarti to a non-infected adult gorilla introduced into a Troglodytella -positive group in the Prague Zoo and traced the origin of the ciliate infection to the Paignton Zoo (UK) using serial fecal examinations. During this study, two infant gorillas born in the Prague Zoo (CZ) first became positive for T. abrassarti at the age of 9 mo. Ciliate morphology and the sequencing of the small subunit rRNA gene and the internal transcribed spacer rDNA spacer region revealed that T. abrassarti affects both captive gorillas and chimpanzees. We conclude that zoo transport plays a major role in the distribution of T. abrassarti among captive gorillas.     

Disentangling stocking introgression and natural migration in brown trout: survival success and recruitment failure in populations with semi‐supportive breeding

1. Introgression into natural salmonid populations from stocked conspecifics has been widely studied. Outcomes vary from no effect even after decades of stocking, to population replacement after only a couple of generations. Potential introgression caused by semi‐supportive breeding (i.e. using a mixture of local strains as brood stock) is, however, less well studied. 2. We investigated population structure of brown trout (Salmo trutta) in a regulated alpine lake with three natural, environmentally contrasting tributaries used as spawning and rearing habitat. Massive semi‐supportive breeding of admixed local strains has been implemented for decades. Stocked trout represented c. 17% of the total lake population, and a substantial post‐release survival reflects a considerable potential for introgression. However, the mark‐recapture studies indicate no spawning runs of stocked fish. 3. Using 13 polymorphic microsatellite loci, we found natural straying and non‐native reproduction, especially among wild populations inhabiting environmentally unstable habitat. Retained genetic structure across tributaries indicated low reproductive success of wild‐born non‐natives. Moreover, the genetic structure among tributaries has probably not been influenced by semi‐supportive breeding, because of recruitment failure of stocked trout.     

Biogeochemical interactions between iron and sulphate in freshwater wetlands and their implications for interspecific competition between aquatic macrophytes

1. Wetlands are threatened by desiccation, eutrophication and changing water quality, generally leading to greatly altered biogeochemical processes. Sulphate pollution can lead to severe eutrophication and sulphide toxicity, but may also interact with the availability of iron and other metals. 2. In the present study, we examined the biogeochemical interactions between sulphate and iron availability, and their effects on aquatic macrophytes, in a field experiment with enclosures. The natural iron supply by groundwater was mimicked by adding iron to the sediment, and the effect of increased sulphate concentrations in the surface water was also studied. The enclosure experiment was performed in a mesotrophic, anaerobic ditch in a peat meadow reserve in the Netherlands. In all enclosures, three Stratiotes aloides plants were introduced to serve as indicator species. 3. Addition of sulphate led to the mobilisation of phosphate, whereas addition of iron or both iron and sulphate did not affect P mobilisation. Growth of S. aloides was decreased by both iron addition and sulphate addition (sulphide toxicity). Addition of iron under sulphidic conditions, however, led to mutual detoxification of both toxicants (iron and sulphide) and did not decrease S. aloides growth. The uptake of metals was highest in the treatment involving sulphate addition, probably as a result of increased mineralisation of the peat soil. 4. Growth of Elodea nuttallii, which grew naturally in the enclosures, was stimulated by iron or iron plus sulphate addition. It did not, however, grow in the enclosures with sulphate addition, as a result of sulphide toxicity or sulphide‐induced iron deficiency. Under iron‐rich conditions, E. nuttallii appeared to be a better competitor than S. aloides and depressed the growth of the latter species. 5. We propose that the growth of S. aloides is directly regulated by interactions between sulphide and iron and indirectly by the effects of both compounds on the competitive strength of E. nuttallii. In general, we conclude that biogeochemical interactions between sulphate and iron can have a strong influence on plant species composition in freshwater wetlands, because of direct effects or changes in the competitive strength of plant species related to differential sensitivity to either iron or sulphide.     

Short‐term temperature change may impact freshwater carbon flux: a microbial perspective

Small freshwater bodies are abundant and economically and ecologically important on a global scale. Within these, protozoa play an important role in structuring planktonic food webs and sequestering CO₂. We hypothesized that short‐term (～20 days) fluctuations, of 2–10 °C, will significantly alter carbon flux associated with predator–prey interactions within the microbial planktonic food web. We examined the model ciliate, Urotricha farcta, which is abundant and common; it was fed the autotrophic flagellate Cryptomonas sp., which is also common. Laboratory experiments were conducted over relevant ranges: 8–24 °C; 0–2 × 10⁵ prey mL^?1. Mechanistic‐phenomenological multiple regressions were developed and fit to the data to obtain relationships for (1) growth rate and volume changes of the flagellate vs. temperature and (2) growth rates, grazing, and cell volume change of the ciliate vs. temperature and prey concentration. Responses revealed interaction between temperature and prey levels on all ciliate parameters, indicating it is inappropriate to apply simple temperature corrections (e.g. Q₁₀) to such functions. The potential impact of such temperature changes on carbon flux was illustrated using a simple ciliate–flagellate predator–prey model, with and without the top grazer, Daphnia, added. The model indicated that predator–prey pulses occurred over 20 days, with the ciliate controlling the prey population. For ciliates and prey, carbon production peaked at 20 °C and rapidly decreased above and below this maximum; differences between minimum and maximum were approximately fourfold, for both prey and ciliate, with low levels at 25–30 °C and 10–15 °C. Including literature data to parameterize, the influence of the grazer Daphnia did not alter the prediction that the ciliate may control short‐term flagellate pulses and temperature will influence these in a nonintuitive fashion.