A possible mechanism for the formation of annual growth lines in bivalve shells

We report a unique shell margin that differed from the usual shell structure of Pinctada fucata. We observed empty organic envelopes in the prismatic layer and the formation of the nacreous layer in the shell margin. All the characteristics of the growing margin indicated that the shell was growing rapidly. To explain this anomaly, we propose the concept of “jumping development”. During jumping development, the center of growth in the bivalve shell jumps forward over a short time interval when the position of the mantle changes. Jumping development explains the unusual structure of the anomalous shell and the development of annual growth lines in typical shells. Annual growth lines are the result of a discontinuity in the shell microstructure induced by jumping development.     

Variation of the physiological energetics of the bivalve Spisula subtruncata (da Costa, 1778) within an annual cycle

Spisula subtruncata is an infaunal filter-feeding bivalve, which lives in shallow sandy bottoms (2-20 m depth) from Norway to the Atlantic coasts of Morocco, including the Mediterranean Sea. Considering that fisheries of this species have become an important economic resource in some European countries (e.g. The Netherlands), it is of great interest to know the seasonal variation in its physiological energetics. For this purpose, individuals of S. subtruncata were collected and maintained under ambient temperature and seawater conditions of Dutch coastal waters. Physiological processes related to the acquisition and utilisation of energy (e.g. clearance rate [CR], absorption and oxygen uptake) were measured under ambient conditions of the period March 1999 to February 2000. Mean annual clearance and respiration rates (RR) were 0.99 l h⁻¹ and 0.23 ml O₂ h⁻¹ for a standard individual of 250 mg. Values for both clearance and respiration rate were high during spring and summer and low during autumn and winter. Stepwise multiple regression analyses indicated a significant relationship of the clearance rate with temperature and particulate organic matter (POM), whereas respiration rate was significantly related to temperature, absorption rate (AR) of the animals and their reproductive condition. Absorption efficiency (AE) of the food was significantly related to food quality. Scope for growth (SFG) of S. subtruncata, as well as flesh weight of the animals, was high in summer and low in winter.     

Occurrence of Perkinsus olseni in the Venus clam Protothaca jedoensis in Korean waters

This is the first report of the occurrence of Perkinsus olseni in the Venus clam Protothaca jedoensis off the western and southern coasts of South Korea. Histological observations revealed Perkinsus-like organisms in the mantle, gills, digestive tubules, and gonad. Haemocytic infiltration and tissue necrosis were also observed in heavily infected clams. Hypnospore formation of the Perkinsus-like organism was confirmed with Ray's fluid thioglycollate medium assay (RFTM). When incubated in filtered and aerated seawater, the hypnospore gave rise to cell division and subsequently discharged hundreds of motile zoospores. Genus- and species-specific polymerase chain reaction (PCR) assays and the DNA sequences of the internal transcribed spacer region (ITS) of the Perkinsus sp. isolated from the Venus clam were identical to those of P. olseni reported from the Manila clam Venerupis (=Ruditapes)philippinarum. Based on the DNA sequences and microscopic data, the Perkinsus-like pathogen isolated from P. jedoensis was identified as P. olseni, which parasitizes the Manila clam in European and Asian waters and Haliotis rubra (abalone) in Australian waters. The prevalence and infection intensity of a clam population collected from Yosu, Korea, was determined using RFTM and Choi's 2M NaOH digestion technique. The intensities averaged 10,768 and 7438 Perkinsus cells per gram tissue in 2003 and 2004, and the prevalence ranged from 37.0 to 53.9%, respectively.     

Age and growth rate determinations of an intertidal bivalve, Phacosoma japonicum, using internal shell increments

A venerid bivalve Phacosoma japonicum (Reeve) occurring commonly in the Japanese coastal area preserves periodic growth lines in the shell cross-section. Long-term shell growth patterns of this species have been traced for many individuals on the intertidal flat of the Seto Inland Sea, west Japan. Sclerochronological analysis of these individuals and specimens collected monthly shows that several growth cessation marks within their shells are formed during the winter of each year prior to spawning. Hence the marks were used for age and growth rate determinations. As large individuals showed little shell growth for more than two years after the formation of 7 or 8 annual increments, this species probably has a lifespan of more than ten years. Shell growth patterns of this species based on annual increments can be accurately approximated by a von Bertalanffy curve. The number of microgrowth increments formed during a year tends to decrease with age, although it varies markedly among specimens of the same age. Furthermore, even in summer during rapid shell growth, the microgrowth increments do not represent daily and/or sub-daily tidal rhythms in many specimens. The results of this study and those by several authors strongly suggest that the annual increments are the key for age and growth rate determinations of both living and fossil bivalve species.     

Introduction of the European minnow into a subalpine lake: habitat use and long-term changes in population dynamics

Minnows Phoxinus phoxinus , studied 30 years after the first record of the species in the subalpine Lake Øvre Heimdalsvatn, Norway, ≥55 mm L _T, were estimated to have densities of c . 4.7 kg ha⁻¹ (120 000 fish) in June 1999 and 2.1 kg ha⁻¹ (63 000 fish) in June 2000. The population was characterized by low individual growth, delayed age of maturity and lived longer when compared to values reported in a previous study in the early phase of its establishment, and other values reported in the literature. Most minnows reached sexual maturity at 4–5 years and >55 mm L _T. Although the estimated annual survival of minnows >55 mm was low ( S =0.2), ages up to 13 years were recorded. Despite a moderate increase in the population size during the last 20 years, the present reduction in individual growth, followed by delayed age of maturity, suggested the existence of density-dependent effects on the population dynamics of the minnows. The minnows were restricted to the littoral zone and near bottom areas. A vertical or horizontal expansion in habitat use was probably prevented by the presence of piscivorous brown trout Salmo trutta .     

Length-dependent deactivation of ventricular trabeculae in the bivalve, Spisula solidissima

Shortening-deactivation has been identified and characterized in ventricular trabeculae of the bivalve, Spisula solidissima (Heterodonta, Mactridae). This muscle had ultrastructural similarities to vertebrate smooth muscle. Deactivation was defined as the fraction of maximal force lost during a contraction when a muscle is shortened rapidly (by a quick-release, QR) to a known length, relative to a control isometric contraction at that same length. The magnitude of deactivation was dependent on the size of the release and the point at which the release was applied during the cycle of contraction. QR/quick-stretch (QS) perturbations at the same point during the contraction resulted in negligible deactivation. The magnitude of deactivation was independent of shortening rate. Deactivation was attenuated by applying caffeine (100 μM) and blocked with high extracellular Ca²⁺ (56 mM). The Ca²⁺ ionophore, A23187 (10 μM), augmented deactivation as did the positive inotrope serotonin (100 nM). Treatment with ryanodine (5 μM) had no significant effect on deactivation. These results suggest that a reduction in Ca²⁺ at the contractile element and/or sequestration of Ca²⁺ may occur during shortening. Deactivation may minimize the magnitude of work done during active shortening of bivalve cardiac muscle, particularly against the low afterload exhibited in the bivalve peripheral circulatory system. Intracellular Ca²⁺ fluxes during sudden length perturbations may explain the effect of stretch on action potential duration in the bivalve heart, as shown previously.     

Enhanced growth and feeding rate in Atlantic salmon parr occupying a lacustrine habitat in the River Utsjoki, northern Scandinavia

The length, weight and stomach fullness index of salmon parr from a lake were higher than in a fluvial habitat on the same river in northern Finland, but no differences in diet composition were detected between the habitats in August. The most important food items of the parr in both habitats were insect pupae and adults. Some lake parr also fed on fish.     

Interpretation of the temperature dependence of rate constants in biosensor studies

A comparison is made between Arrhenius and transition-state analyses of the temperature dependence of rate constants reported in four published biosensor studies. Although the Eyring transition-state theory seemingly affords a more definitive solution to the problem of characterizing the activation energetics, the analysis is equivocal because of inherent assumptions about reaction mechanism and the magnitude of the transmission coefficient. In view of those uncertainties it is suggested that a preferable course of action entails reversion to the empirical Arrhenius analysis with regard to the energy of activation and a preexponential factor. The former is essentially equivalent to the enthalpy of activation, whereas the magnitude of the latter indicates directly the extent of disparity between the frequency of product formation and the universal frequency factor (temperature multiplied by the ratio of the Boltzmann and Planck constants) and hence the likelihood of a more complicated kinetic mechanism than that encompassed by the Eyring transition-state theory.     

A novel role for dpp in the shaping of bivalve shells revealed in a conserved molluscan developmental program

During the molluscan evolution leading to the bivalves, the single dorsal shell was doubled. To elucidate the molecular developmental basis underlying this prominent morphological transition, we described the cell cleavage and expression patterns of three genes, brachyury, engrailed, and dpp in the Japanese spiny oyster Saccostrea kegaki, and examined the function of dpp in this species. The cleavage pattern of the S. kegaki embryo was nearly the same as the previously described pattern of other bivalve species, suggesting that the pattern itself is highly important for the establishment or the maintenance of the bivalve body plan. The expression pattern of a brachyury homolog in S. kegaki (SkBra) was similar to the pattern in gastopods even at the single cell level despite the deep divergence of gastropods and bivalves. Engrailed and dpp were previously found to be expressed around the shell anlagen in gastropods. Like that of gastropods, an engrailed homolog in S. kegaki (SkEn) was found to be expressed around the shell anlagen. However, the dpp homolog in S. kegaki (SkDpp) was expressed only in the cells along the dorsal midline. ZfBMP4 treatment experiments revealed the importance of dpp in establishing the characteristic shape of the bivalve shell anlagen.     

Larval habitat segregation between the molecular forms of the mosquito Anopheles gambiae in a rice field area of Burkina Faso, West Africa

In West Africa, lineage splitting between the M and S molecular forms of the major Afro-tropical malaria mosquito, Anopheles gambiae (Diptera: Culicidae), is thought to be driven by ecological divergence, occurring mainly at the larval stage. Here, we present evidence for habitat segregation between the two molecular forms in and around irrigated rice fields located within the humid savannahs of western Burkina Faso. Longitudinal sampling of adult mosquitoes emerging from a range of breeding sites distributed along a transect extending from the heart of the rice field area into the surrounding savannah was conducted from June to November 2009. Analysis revealed that the two molecular forms and their sibling species Anopheles arabiensis are not randomly distributed in the area. A major ecological gradient was extracted in relation to the perimeter of the rice fields. The M form was associated with larger breeding sites mostly consisting of rice paddies, whereas the S form and An. arabiensis were found to depend upon temporary, rain-filled breeding sites. These results support hypotheses about larval habitat segregation and confirm the suggestion that the forms have different larval habitat requirements. Segregation appears to be clearly linked to anthropogenic permanent habitats and the community structure they support.     

Mechanisms of density dependence in fluctuating vole populations: deducing annual density dependence from seasonal processes

Based on recent advances in time-series analyses of ecological dynamics using statistical and mathematical models, we summarise our recent results on the seasonal processes in the annual population dynamics of the grey-sided vole Clethrionomys rufocanus (Sundevall, 1846) in Hokkaido, Japan, and report additional analyses on annual and seasonal density dependence. Annual direct density dependence was strong in almost all populations. In contrast, delayed density dependence was generally weak, although clear delayed density dependence was detected in some of the studied populations. Although seasonal density dependence was observed both in winter and summer, direct density dependence was much more profound during winter; thus, winter density dependence contributed most to the overall annual direct density dependence. We found no correlation between the seasonal components of annual direct density dependence; however, the corresponding seasonal components for annual delayed density dependence were positively correlated. We conclude that winter conditions influence the strength of annual direct density dependence most profoundly. Moreover, we conclude that direct density dependence during summer and winter may be generated by different mechanisms, whereas delayed density dependence seems to be generated by a common mechanism. Candidate mechanisms are discussed in relation to general knowledge of northern rodent populations and to specific insights provided by earlier studies of grey-sided voles in Hokkaido.     

Latitudinally structured variation in the temperature dependence of damselfly growth rates

The Metabolic Theory of Ecology predicts that the slope of the rate–temperature relationship, E, remains consistent across traits and organisms, acting as a major determinant of large‐scale ecological patterns. Although E has recently been shown to vary systematically, we have a poor understanding of its ecological significance. To address this question, we conducted a common‐garden experiment involving six damselfly species differing in distribution, estimating E at the level of full‐sib families. Each species was sampled throughout its latitudinal range, allowing us to characterise variation in E along a latitudinal gradient spanning 3600 km. We show that E differs among populations and increases with latitude. E was right‐skewness across species, but this was largely an artefact of the latitudinal trend. Increased seasonality towards higher latitude may contribute to the latitudinal trend in E. We conclude that E should be seen as a trait involved in local adaptation.     

Ontogenetic variation in density‐dependent growth of brown trout through habitat competition

1. Density‐dependent growth has been widely reported in freshwater fishes, but the ontogenetic evolution of competition and its subsequent effects on growth through a life span remains unclear. 2. Patterns of competition can be described by integrating population abundance data with habitat‐modelling results. Weighted usable area (WUA; m² WUA ha^?1) curves are obtained for each flow value and are then coupled with demographic data to obtain the occupancy rates (trout m^?2 WUA, the density of a given age class related to its suitable habitat) of the WUA for every age class, year and site. 3. We examined a long‐term data series searching for temporal variation in the influence of habitat occupancy rate on the growth of brown trout Salmo trutta. We tested whether (i) mean cohort mass (mean mass of the cohort during the first 3 years of life) is affected by the occupancy rate experienced across a life span; and (ii) the occupancy rate experienced at different ages influenced mean body size. 4. We observed a consistent negative power relationship between average cohort mass and mean occupancy rate through a life span, indicating that stronger cohorts were related to a reduced growth, with likely consequences for individual fitness. 5. The effects of occupancy rate on size‐at‐age were mainly detected in the size attained at the second year of life, but they were because of the competition at different times. Thus, the level of competition varied through ontogeny, in some of the rivers affecting growth since the first year of life, whereas in most of the rivers the main effects on body size resulted from the competition during the second year of life. 6. Occupancy rate appears more appropriate than density for assessing the occurrence of habitat competition in freshwater fishes, since it encompasses the differences in quantity and quality of suitable habitat for each age class. 7. Our study highlights the importance of density‐dependent growth as a key process in the dynamics of brown trout populations, its temporal variation depending on the temporal changes of density and the variation of competition associated with the habitat capacity for each life stage.     

Effects of annual rainfall and habitat types on the body mass of impala (Aepyceros melampus) in the Zambezi Valley, Zimbabwe

Body mass is often considered as a good indicator of body condition of individuals in ungulates, hence of their fitness, and thus, may be used as an index to monitor the status of populations subject to harvesting schemes. Here, we report the influence of annual rainfall (a proxy for primary production) and habitat on the body mass of impala in a population cropped for meat in a communal area of Zimbabwe. We analyzed the data from 2 contrasted years for rainfall, in two different habitats. In the good year (i.e. high annual rainfall) impala were heavier than in the poor year, and adult females seemed to be less affected than males by variation in primary production. We show that adult males were suffering from a seasonal decrease in body mass, supposedly linked to the rut, particularly in good habitat. Overall, the habitat effect appeared to be dominated by the rainfall effect, and this may be due to the very high animal densities in the good habitat, i.e. fast resource depletion. Our results also suggest that males (juvenile and adult) are more susceptible to changes in food resource abundance and quality than females, which supports previous studies on sexually dimorphic and polygynous species.     

Metabolism of polyamines in NaCl-resistant cell lines from Nicotiana sylvestris

The polyamine titers in three cell lines of Nicotiana sylvestris were compared: Type 1, rapidly adapting to NaCl; Type 2, constantly resistant to NaCl; Type 3, a saltsensitive wild strain. During short-term cultivation in MS medium in the presence of 170 mM NaCl (1 passage, 14 d) the changes in polyamine titer in cell suspensions of type 1 (in a slightly adapted state) and non-adapted wild strain (type 3) showed a considerable increase in spermidine and spermine and a decrease in putrescine. After prolonged adaptation to NaCl (20 passages) the putrescine content in the cells of type 1 and of type 2 was increased at the expense of the polyamines. This suggests that the pattern of polyamine titer varies under short- and long-term adaptation to NaCl. The inverse ratio between growth processes and changes in polyamine and proline level indicates that polyamines fulfil primarily a protective and osmorepulatory function in plant cells under NaCl stress.     

Adult survival and reproductive rate are linked to habitat preference in territorial,year‐round resident Song Sparrows Melospiza melodia

Individual animal fitness can be strongly influenced by the ability to recognize habitat features which may be beneficial. Many studies focus on the effects of habitat on annual reproductive rate, even though adult survival is typically a greater influence on fitness and population growth in vertebrate species with intermediate to long lifespans. Understanding the effects of preferred habitat on individuals over the annual cycle is therefore necessary to predict its influences on individual fitness. This is particularly true in species that are resident and territorial year‐round in the temperate zone, which may face potential trade‐offs between habitat that maximizes reproduction and that which maximizes non‐breeding season (‘over‐winter’) survival. We used a 37‐year study of Song Sparrows Melospiza melodia residing territorially year‐round on a small island to examine what habitat features influenced adult over‐winter survival, how site‐specific variation in adult survival vs. annual reproductive rate influenced long‐term habitat preference, and if preferred sites on average conferred higher individual fitness. Habitat features such as area of shrub cover and exposure to intertidal coastline predicted adult over‐winter survival independent of individual age or sex, population size, or winter weather. Long‐term habitat preference (measured as occupation rate) was better predicted by site‐specific annual reproductive rate than by expected over‐winter survival, but preferred sites maximized fitness on average over the entire annual cycle,. Although adult over‐winter survival had a greater influence on population growth (λ) than did reproductive rate, the influence of reproductive rate on λ increased in preferred sites because site‐specific variation in reproductive rate was higher than variation in expected over‐winter survival. Because preferred habitats tended to have higher mean site‐specific reproductive and adult survival rates, territorial birds in this population do not appear to experience seasonal trade‐offs in preferred habitat but are predicted to incur substantial fitness costs of settling in less‐preferred sites.     

Potential for redistribution of post-moult habitat for Eudyptes penguins in the Southern Ocean under future climate conditions

Anthropogenic climate change is resulting in spatial redistributions of many species. We assessed the potential effects of climate change on an abundant and widely distributed group of diving birds, Eudyptes penguins, which are the main avian consumers in the Southern Ocean in terms of biomass consumption. Despite their abundance, several of these species have undergone population declines over the past century, potentially due to changing oceanography and prey availability over the important winter months. We used light-based geolocation tracking data for 485 individuals deployed between 2006 and 2020 across 10 of the major breeding locations for five taxa of Eudyptes penguins. We used boosted regression tree modelling to quantify post-moult habitat preference for southern rockhopper (E. chrysocome), eastern rockhopper (E. filholi), northern rockhopper (E. moseleyi) and macaroni/royal (E. chrysolophus and E. schlegeli) penguins. We then modelled their redistribution under two climate change scenarios, representative concentration pathways RCP4.5 and RCP8.5 (for the end of the century, 2071–2100). As climate forcings differ regionally, we quantified redistribution in the Atlantic, Central Indian, East Indian, West Pacific and East Pacific regions. We found sea surface temperature and sea surface height to be the most important predictors of current habitat for these penguins; physical features that are changing rapidly in the Southern Ocean. Our results indicated that the less severe RCP4.5 would lead to less habitat loss than the more severe RCP8.5. The five taxa of penguin may experience a general poleward redistribution of their preferred habitat, but with contrasting effects in the (i) change in total area of preferred habitat under climate change (ii) according to geographic region and (iii) the species (macaroni/royal vs. rockhopper populations). Our results provide further understanding on the regional impacts and vulnerability of species to climate change.     

Growth and morphology of neuronal cell lines cultured in perfusion

Summary To optimize culture conditions and gain a more reliable culturing system for studies of metabolic properties of neuronal cells, a simplified perfusion chamber was developed. It consists of two parts: a perfusion block and a standard plastic culture dish. To confirm the suitability of this chamber for continuous culturing of anchorage-dependent cells, the growth and morphology of the four neuronal cell lines glioma C6 and glioma 138MG, neuroblastoma C1300, clones N1E115 and N18 were followed for 4 d using both traditional and perfusion techniques. A marked increase in growth and a decrease in the degree of morphological differentiation were obtained with the latter technique compared to the former. This work was supported by grants from the National Swedish Board for Technical Development (Grant 81-5009), the Swedish Work Environmental Foundation (Grant 76-53), and Ollie and Elof Ericssons Foundation for Scientific Research.     

Evaluating the dependence of opportunistic Yellow-legged Gulls (Larus michahellis) on marine habitat and fishing discards

Several bird species benefit from anthropogenic food subsidies, such as landfills and fishing discards, that are being reduced owing to introduced legislation. For instance, since 2019, Europe has passed legislation to reduce dramatically the amount of fisheries discards through the Landing Obligation (LO), which states that all fish species under Total Allowable Catch (TAC) should not be discarded at sea. This European discard ban is expected to impact some gulls, as several gull populations have been observed to be heavily reliant on this resource. In this work, GPS tracking data from adult Yellow-legged Gulls Larus michahellis and Vessel Monitoring System (VMS) data (i.e. detailed data of the spatial distribution of fishing vessels) are used to determine the utilization of the marine habitat and the level of interaction of gulls with fishing activity offshore and discards in the south-eastern part of the Bay of Biscay. We found that these gulls had a low use of the marine habitat (ca. 15%) compared with terrestrial habitats, in contrast to the ca. 40% of the diet of this population which comprises marine prey. Furthermore, we detected that most of the gull tracking positions at sea did not interact with the fishing vessels (an overlap of 21.5% between gulls and VMS data). Conversely, other gull populations of the Iberian Peninsula were found to depend much more strongly on fishing activity. Therefore, the Yellow-legged Gull population of the SE Bay of Biscay did not obtain most of its fish prey from interactions with offshore fishing activity but most possibly by taking fish remains in harbours and by feeding themselves. Consequently, we expect a minimal effect of the European policies oriented to ban fishing discards offshore on this population, which would be more affected by policies directed towards the reduction of food availability in landfills or fish landing management in harbours.