Effects of phytoplankton-induced turbidity on predation success of piscivorous Eurasian perch (Perca fluviatilis): possible implications for fish community structure in lakes

Turbidity can strongly influence predation success of visually oriented fish, especially piscivores such as adult Eurasian perch (Perca fluviatilis). This purely carnivorous species usually becomes a facultative piscivore after two discrete food niche shifts. Perch biomass has been observed to decrease in lakes along the productivity gradient, and then be replaced by cyprinids in non-manipulated eutrophic systems. Until now, this change has been mainly attributed to the competitive superiority of cyprinids for zooplankton prey during the juvenile phase of perch, while the piscivorous phase—as a possible factor influencing the recruitment success of perch—has been neglected. As the abundance of suitably sized prey fish should not be limiting in highly productive systems, we hypothesise that the switch from benthivorous feeding to preying on fish is inhibited by the reduced visibility in eutrophic lakes. We tested this hypothesis in laboratory experiments, where perch were fed two size classes of juvenile cyprinids at different phytoplankton- and bentonite-induced turbidity levels. Predation success was significantly influenced by turbidity level and turbidity source, but not by prey size. These experimental results suggest for the first time that piscivory of Eurasian perch is negatively influenced by different sources of turbidity, and hence low visibility might delay the onset of the food niche shift to fish prey.     

Unsuspected functional disparity in Devonian fishes revealed by tooth morphometrics?

The shape of features involved in key biological functions, such as teeth in nutrition, can provide insights into ecological processes even in ancient time, by linking the occupation of the morphological space (disparity) to the occupation of the ecological space. Investigating disparity in radiating groups may provide insights into the ecological diversification underlying evolution of morphological diversity. Actinopterygian fishes initiated their radiation in the Devonian, a period characterized by the diversification of marine ecosystem. Although a former morpho-functional analysis of jaw shape concluded to conservative and poorly diversified morphologies in this early part of their history, fish tooth disparity evidenced here an unsuspected diversity of possible functional significance in the pivotal period of the Late Devonian (Famennian). All teeth being caniniforms, some were stocky and robust, in agreement with expectations for active generalist predators. More surprisingly, elongated teeth also occurred at the beginning of Famennian. Their needle-like shape challenges morpho-functional interpretations by making them fragile in response to bending or torsion. The occurrence of both types of fish teeth during the beginning of the Famennian points to a discrete but real increase in disparity, thus testifying a first burst of feeding specialization despite overall conservative jaw morphology. The disappearance of these needle-like teeth in the Late Famennian might have been related to a relay in dental diversity with abundant co-occurring groups, namely conodonts and chondrichthyans (sharks).     

Chicken-sized oviraptorid dinosaurs from central China and their ontogenetic implications

Oviraptorids are a group of specialized non-avian theropod dinosaurs that were generally one to 8 m in body length. New specimens of baby oviraptorids from the Late Cretaceous of Henan Province are some of the smallest individuals known. They include diagnostic characters such as the relative position of the antorbital fenestra and the external naris, distinct opening in the premaxilla anteroventral to the external naris, antorbital fossa partly bordered by premaxilla posterodorsally, lacrimal process of premaxilla does not contact the anterodorsal process of the lacrimal, parietal almost as long as frontal; in dorsal view, posterior margin forms a straight line between the postzygapophyses in each of the fourth and fifth cervicals; femur longer than ilium. They also elucidate the ontogenetic processes of oviraptorids, including fusion of cranial elements and changes in relative body proportions. Hind limb proportions are constant in oviraptorids, regardless of absolute body size or ontogenetic stage. This suggests a sedentary lifestyle that did not involve the pursuit of similar-sized prey. The functional implications for bite force and therefore dietary preferences are better understood through the study of such small animals. The comparison of the measurements of 115 skeletons indicates that oviraptorids maintain their hind limb proportions regardless of ontogenetic stage or absolute size, which is a pattern seen more commonly in herbivores than in carnivores. This may weakly support the hypothesis that oviraptorids are herbivores rather than active carnivores.     

Contaminant geochemistry—a new perspective

To date, the field of contaminant geochemistry—which deals with the study of chemical interactions in soil and aquifer environments—has focused mainly on pollutant toxicity, retention, persistence, and transport and/or on remediation of contaminated sites. Alteration of subsurface physicochemical properties by anthropogenic chemicals, which reach the land surface as a result of human activity, has been essentially neglected. Contaminant-induced changes in subsurface properties are usually considered as deviations from a normal geological environment, which will disappear under natural attenuation or following remediation procedures. However, contaminants may in many cases cause irreversible changes in both structure and properties of the soil–subsurface geosystem between the land surface and groundwater. The time scales associated with these changes are on a “human time scale”, far shorter than geological scales relevant for geochemical processes. In this review, we draw attention to a new perspective of contaminant geochemistry, namely, irreversible changes in the subsurface as a result of anthropogenic chemical pollution. We begin by briefly reviewing processes governing contaminant–subsurface interactions. We then survey how chemical contamination causes irreversible changes in subsurface structure and properties. The magnitude of the anthropogenic impact on the soil and subsurface is linked directly to the amounts of chemical contaminants applied and/or disposed of on the land surface. This particular aspect is of major importance when examining the effects of humans on global environmental changes. Consideration of these phenomena opens new perspectives for the field of contaminant geochemistry and for research of human impacts on the soil and subsurface regimes.     

Habitat selection by breeding waterbirds at ponds with size-structured fish populations

Fish may significantly affect habitat use by birds, either as their prey or as competitors. Fish communities are often distinctly size-structured, but the consequences for waterbird assemblages remain poorly understood. We examined the effects of size structure of common carp (Cyprinus carpio) cohorts together with other biotic and abiotic pond characteristics on the distribution of breeding waterbirds in a seminatural system of monocultured ponds, where three fish age classes were separately stocked. Fish age corresponded to a distinct fish size gradient. Fish age and total biomass, macroinvertebrate and amphibian abundance, and emergent vegetation best explained the differences in bird density between ponds. Abundance of animal prey other than fish (aquatic macroinvertebrates and larval amphibians) decreased with increasing carp age in the ponds. Densities of ducks and smaller grebes were strongly negatively associated with fish age/size gradient. The largest of the grebes, the piscivorous great crested grebe (Podiceps cristatus), was the only species that preferred ponds with medium-sized fish and was positively associated with total fish biomass. Habitat selection by bitterns and most rallids was instead strongly influenced by the relative amount of emergent vegetation cover in the ponds. Our results show that fish size structure may be an important cue for breeding habitat choice and a factor affording an opportunity for niche diversification in avian communities.     

Development of the lateral line mechanoreceptors in the catfish Silurus glanis

In fish the neuromasts of the lateral line develop as follows: a “migrating primordium” (MP) migrates from the postotic placode along the future posterior lateral line canal to the tail fin. Its placodal cells are assumed to be the basis for the development of the neuromasts. However, an MP was not found in all fish, e.g., in catfish. In the present study, a search was made for the MP in the larvae of the catfish Silurus glanis. Using light and electron microscopy, an MP was found to migrate along the ventral rim of the tail. It precedes the formation of a ventral row of free neuromasts. An MP preceding the main lateral row of the future canal neuromasts was not found. The necessity of the MP for the ventral-free neuromast development is shown by making incisions which block its migration. The result: caudal to the incision site neuromasts do not develop. On the other hand, the same incision procedure applied to the assumed migration route of a—hypothetical—lateral MP does not block the development of the lateral neuromasts. It is concluded that in this case an MP is not necessary for the development of the canal neuromasts.     

Contribution of anadromous fish to the diet of European catfish in a large river system

Many anadromous fish species, when migrating from the sea to spawn in fresh waters, can potentially be a valuable prey for larger predatory fish, thereby efficiently linking these two ecosystems. Here, we assess the contribution of anadromous fish to the diet of European catfish (Silurus glanis) in a large river system (Garonne, southwestern France) using stable isotope analysis and allis shad (Alosa alosa) as an example of anadromous fish. Allis shad caught in the Garonne had a very distinct marine δ¹³C value, over 8‰ higher after lipid extraction compared to the mean δ¹³C value of all other potential freshwater prey fish. The δ¹³C values of European catfish varied considerably between these two extremes and some individuals were clearly specializing on freshwater prey, whereas others specialized on anadromous fish. The mean contribution of anadromous fish to the entire European catfish population was estimated to be between 53% and 65%, depending on the fractionation factor used for δ¹³C.     

Restricted gene flow and fine-scale population structuring in tool using New Caledonian crows

New Caledonian crows Corvus moneduloides are the most prolific avian tool users. It has been suggested that some aspects of their complex tool use behaviour are under the influence of cultural processes, involving the social transmission—and perhaps even progressive refinement—of tool designs. Using microsatellite and mt-haplotype profiling of crows from three distinct habitats (dry forest, farmland and beachside habitat), we show that New Caledonian crow populations can exhibit significant fine-scale genetic structuring. Our finding that some sites of <10 km apart were highly differentiated demonstrates considerable potential for genetic and/or cultural isolation of crow groups. Restricted movement of birds between local populations at such small spatial scales, especially across habitat boundaries, illustrates how specific tool designs could be preserved over time, and how tool technologies of different crow groups could diverge due to drift and local selection pressures. Young New Caledonian crows have an unusually long juvenile dependency period, during which they acquire complex tool-related foraging skills. We suggest that the resulting delayed natal dispersal drives population-divergence patterns in this species. Our work provides essential context for future studies that examine the genetic makeup of crow populations across larger geographic areas, including localities with suspected cultural differences in crow tool technologies.     

应用稳定同位素技术对海州湾拖网渔获物营养级的研究

应用碳、氮稳定稳定同位素技术，对2014年夏季海州湾海洋牧场海域拖网渔获物营养级进行了初步分析，建立了海州湾海洋牧场区域主要拖网渔获物的营养结构。结果表明:海州湾拖网渔获物中鱼类氮稳定同位素比值主要集中在9.6‰～13.9‰，碳稳定同位素比值分布范围为-16.2‰～-23.3‰；计算得到的鱼类的营养级最大值和最小值分别为3.9和1.9；其中，中国花鲈和孔虎鱼所处营养级最高，为食物网中的顶级捕食者，螠蛏和中国毛虾营养级相对较低，位于食物网下层；中国花鲈个体大小与其氮稳定同位素比值存在显著正相关关系（R2=0.90，P < 0.01）；碳稳定同位素比值分布结果显示海州湾海洋牧场海域各生物类群存在明显的生态位重叠现象。     

Wind and sky as compass cues in desert ant navigation

While integrating their foraging and homing paths, desert ants, Cataglyphis fortis, depend on external compass cues. Whereas recent research in bees and ants has focused nearly exclusively on the polarization compass, two other compass systems—the sun compass and the wind (anemo) compass—as well as the mutual interactions of all these compass systems have received little attention. In this study, we show that of the two visual compass systems, it is only the polarization compass that invariably outcompetes the wind compass, while the sun compass does so only under certain conditions. If the ants are experimentally deprived of their polarization compass system, but have access simultaneously to both their sun compass and their wind compass, they steer intermediate courses. The intermediate courses shift the more towards the wind compass course, the higher the elevation of the sun is in the sky.     

Larval salivary glands are a source of primer and releaser pheromone in honey bee (Apis mellifera L.)

A brood pheromone identified in honeybee larvae has primer and releaser pheromone effects on adult bees. Using gas chromatography–mass spectrometry (GC–MS) to evaluate fatty acid esters—the pheromonal compounds—in different parts of the larvae, we have localized the source of the esters as the larval salivary glands. A histochemical study describes the glands and confirms the presence of lipids in the glands. Epithelial cells of the gland likely secrete the fatty acids into the lumen of the gland. These results demonstrate the salivary glands to be a reservoir of esters, components of brood pheromone, in honeybee larvae.     

Microspectrophotometric evidence for cone monochromacy in sharks

Sharks are apex predators, and their evolutionary success is in part due to an impressive array of sensory systems, including vision. The eyes of sharks are well developed and function over a wide range of light levels. However, whilst close relatives of the sharks—the rays and chimaeras—are known to have the potential for colour vision, an evolutionary trait thought to provide distinct survival advantages, evidence for colour vision in sharks remains equivocal. Using single-receptor microspectrophotometry, we measured the absorbance spectra of visual pigments located in the retinal photoreceptors of 17 species of shark. We show that, while the spectral tuning of the rod (wavelength of maximum absorbance, λ_max 484–518 nm) and cone (λ_max 532–561 nm) visual pigments varies between species, each shark has only a single long-wavelength-sensitive cone type. This suggests that sharks may be cone monochromats and, therefore, potentially colour blind. Whilst cone monochromacy on land is rare, it may be a common strategy in the marine environment: many aquatic mammals (whales, dolphins and seals) also possess only a single, green-sensitive cone type. It appears that both sharks and marine mammals may have arrived at the same visual design by convergent evolution. The spectral tuning of the rod and cone pigments of sharks is also discussed in relation to their visual ecology.     

Characterisation of black carbon-rich samples by <Superscript>13</Superscript>C solid-state nuclear magnetic resonance

There are difficulties in quantifying and characterising the organic matter (OM) in soils that contain significant amounts of partially oxidised char or charcoal materials. The anthropogenic black carbon (BC), such as that found in the Terra Preta de índio soils of the Amazon region, is a good example of the OM that is difficult to analyse in such soils. ¹³C direct polarisation/magic angle spinning (DP/MAS) at high MAS frequency, ¹H-¹³C cross polarisation (CP)/MAS with total suppression of spinning sidebands (TOSS), and chemical shift anisotropy (CSA) filter nuclear magnetic resonance techniques have been applied successfully for quantifying the different components of OM. However, because pyrogenic materials present strong local magnetic susceptibility heterogeneities, the use of CSA-filter and TOSS make the pulse sequences very sensitive to imperfections in the π pulses. In this study, the DP/MAS pulse sequence was replaced by a CP with a radio frequency ramp—variable amplitude CP (VACP)—VACP/MAS pulse sequence, and composite π pulses were used in the CSA-filter and TOSS pulse sequences. In that way, the component functionalities in a humic acid from a BC soil were successfully determined. The spectrometer time needed was greatly decreased by employing this VACP/MAS technique. This development provides an accurate method for characterising BC-rich samples from different origins.     

“Winter” aggregations, colony cycle, and seasonal phenotypic change in the paper wasp Polistes versicolor in subtropical Brazil

Social wasps from temperate zones have clear annual colony cycles, and the young queens hibernate during winter. In the subtropics, the only previously reported evidence for the existence of “hibernation” is the facultative winter aggregations of females during harsh climate conditions. As in temperate-zone species analyzed so far, we show in this study that in the paper wasp, Polistes versicolor, a subtropical species, body size increases as an unfavorable season approaches. Our morphological studies indicate that larger females come from winter aggregations—that is, they are new queens. Multivariate analyses indicate that size is the only variable analyzed that shows a relationship to the differences. Given the absence of a harsh climate, we suggest that the occurrence of winter aggregations in tropical P. versicolor functions to allow some females to wait for better environmental conditions to start a new nest, rather than all being obliged to start a new nest as soon as they emerge.     

First complete sauropod dinosaur skull from the Cretaceous of the Americas and the evolution of sauropod dentition

Sauropod dinosaur bones are common in Mesozoic terrestrial sediments, but sauropod skulls are exceedingly rare—cranial materials are known for less than one third of sauropod genera and even fewer are known from complete skulls. Here we describe the first complete sauropod skull from the Cretaceous of the Americas, Abydosaurus mcintoshi, n. gen., n. sp., known from 104.46 ± 0.95 Ma (megannum) sediments from Dinosaur National Monument, USA. Abydosaurus shares close ancestry with Brachiosaurus, which appeared in the fossil record ca. 45 million years earlier and had substantially broader teeth. A survey of tooth shape in sauropodomorphs demonstrates that sauropods evolved broad crowns during the Early Jurassic but did not evolve narrow crowns until the Late Jurassic, when they occupied their greatest range of crown breadths. During the Cretaceous, brachiosaurids and other lineages independently underwent a marked diminution in tooth breadth, and before the latest Cretaceous broad-crowned sauropods were extinct on all continental landmasses. Differential survival and diversification of narrow-crowned sauropods in the Late Cretaceous appears to be a directed trend that was not correlated with changes in plant diversity or abundance, but may signal a shift towards elevated tooth replacement rates and high-wear dentition. Sauropods lacked many of the complex herbivorous adaptations present within contemporaneous ornithischian herbivores, such as beaks, cheeks, kinesis, and heterodonty. The spartan design of sauropod skulls may be related to their remarkably small size—sauropod skulls account for only 1/200th of total body volume compared to 1/30th body volume in ornithopod dinosaurs.     

Managing dependencies in forest offset projects: toward a more complete evaluation of reversal risk

Although forest carbon offsets can play an important role in the implementation of comprehensive climate policy, they also face an inherent risk of reversal. If such risks are positively correlated across projects, it can affect the integrity of larger project portfolios and potentially the entire offsets program. Here, we discuss three types of risks that could affect forest offsets—fat tails, micro-correlation, and tail dependence—and provide examples of how they could present themselves in a forest offset context. Given these potential dependencies, we suggest several new risk management approaches that take into account dependencies in reversal risk across projects and which could help guard the climate integrity of an offsets program. We also argue that data collection be included as an integral part of any offsets program so that disturbance-related dependencies may be identified and managed as early and to the greatest extent possible.     

<Emphasis Type="Italic">Bonitasaura salgadoi</Emphasis> gen. et sp. nov.: a beaked sauropod from the Late Cretaceous of Patagonia

Ornithischian and theropod dinosaurs were morphologically diverse during the Cretaceous. In contrast, sauropods were relatively more conservative. The anatomy of Bonitasaura salgadoi, a new 9-m titanosaurian sauropod from Upper Cretaceous beds of Patagonia, suggests that sauropod anatomical diversity would have included unexpected items. Its unusual, rectangular lower jaw possesses narrow, anteriorly restricted teeth and shows evidence of a sharp keratinous sheath over the non-dentigerous region that probably worked to guillotine plant material. This discovery definitely demonstrates that titanosaurs acquired a mandibular configuration similar to that of some basal diplodocoids, as had already been suggested by the lower jaw of the controversial genus Antarctosaurus. This oral configuration, plus the beak-like structure and the skull shape, resemble some traits more commonly seen in Laurasian ornithischians, mostly unexpressed in southern continents. A high sauropod morphological diversity seems to be in agreement with the poorly represented ornithischian clades of the southern hemisphere.Communicated by G. Mayr     

Morphological change and phenotypic plasticity in native and non-native pumpkinseed sunfish in response to competition

Non-indigenous species are oftentimes exposed to ecosystems with unfamiliar species, and organisms that exhibit a high degree of phenotypic plasticity may be better able to contend with the novel competitors that they may encounter during range expansion. In this study, differences in morphological plasticity were investigated using young-of-year pumpkinseed sunfish (Lepomis gibbosus) from native North American and non-native European populations. Two Canadian populations, isolated from bluegill sunfish (L. macrochirus) since the last glaciation, and two Spanish populations, isolated from bluegill since their introduction in Europe, were reared in a common environment using artificial enclosures. Fish were subjected to allopatric (without bluegill) or sympatric (with bluegill) conditions, and differences in plasticity were tested through a MANOVA of discriminant function scores. All pumpkinseed populations exhibited dietary shifts towards more benthivorous prey when held with bluegill. Differences between North American and European populations were observed in body dimensions, gill raker length and pelvic fin position. Sympatric treatments induced an increase in body width and a decrease in caudal peduncle length in native fish; non-native fish exhibited longer caudal peduncle lengths when held in sympatry with bluegill. Overall, phenotypic plasticity influenced morphological divergence less than genetic factors, regardless of population. Contrary to predictions, pumpkinseeds from Europe exhibited lower levels of phenotypic plasticity than Canadian populations, suggesting that European pumpkinseeds are more canalized than their North American counterparts.     

Temperature and parasitism by <Emphasis Type="BoldItalic">Asobara tabida</Emphasis> (Hymenoptera: Braconidae) influence larval pupation behaviour in two <Emphasis Type="BoldItalic">Drosophila</Emphasis> species

In holometabolous insects, pupation site selection behaviour has large consequences for survival. Here, we investigated the combined effects of temperature and parasitism by the parasitoid Asobara tabida on larval pupation behaviour in two of its main Drosophila sp. hosts differing in their climate origin. We found that larvae of Drosophila melanogaster—a species with a (sub)tropical origin—placed at 25°C pupated higher in rearing jars than those placed at 15°C. The opposite pattern was observed for Drosophila subobscura larvae—a species from temperate regions—which pupated lower, i.e. on or near the substrate at 25°C, than those placed at 15°C. When placed at 25°C, parasitized larvae of both species pupated closer to the substrate than unparasitized ones. Moreover, the Drosophila larvae that had been exposed and probably stung by A. tabida, but were not parasitized, pupated lower than the control unparasitized larvae. These results provide new insights of host behaviour manipulation by A. tabida larvae.     

Fish survival on fine mesh traveling screens

The survival of fish impinged on 1-mm mesh Ristroph-type traveling screens was evaluated at Somerset Station, a 625-MW coal-fired electric generating station located on the south shore of Lake Ontario. Somerset Station was designed and built with an offshore intake, discharge and fish return system. Survival testing was conducted over a 4-year period that included all four seasons. Test fish were diverted from the fish return and held for 96 h for observation. Following observation, a specially constructed screening table was used to differentiate test fish that typically would have been impinged on a standard 9.5-mm mesh screen from smaller individuals that typically would be entrained. Twenty-eight species were tested, and collections were dominated by five species: alewife, emerald shiner, gizzard shad, rainbow smelt, and spottail shiner. Survival rates commonly approached or exceeded 80%, and were influenced by species, fish size or life stage, season and fish condition. Results are interpreted in terms of survival rates demonstrated elsewhere for entrained fish and fish impinged on alternative traveling screen technologies.