Suspension feeding in the brittle-star Ophiothrix fragilis : efficiency of particle retention and implications for the use of encounter-rate models

Dense beds of the suspension-feeding brittle-star Ophiothrix fragilis are common in European waters. Their potential importance in benthic–pelagic coupling has been highlighted, but little is known about the feeding dynamics of this species. Encounter-rate models provide a potential mechanism for the estimation of feeding rates on suspended material of varying sizes. This work investigates factors essential to the application of such models. Particle-retention efficiency (RE) converts encounter rate into capture, or clearance rate. Laboratory studies demonstrated that RE varied with the interactive effects of flow velocity and particle size. RE was lowest for large particles, particularly at high flow velocity where RE as low as 59% was observed. This indicates that if RE is not accounted for in encounter-rate models, significant overestimates of feeding rates on large particles may occur. Flow around feeding arms and tube feet was characterised by intermediate Reynolds numbers, precluding application of the most simple encounter-rate models. Complex secondary-flow patterns were observed, which carried particles along the downstream side of the feeding arms, but these did not appear to increase the area available for particle capture. Previously reported particle capture by arm spines was not observed. Evidence of active rejection of large particles by tube feet was recorded. Difficulties in the application of encounter-rate models for prediction of seston-removal rates are highlighted by these results. Predicted encounter rate may deviate from actual clearance rate due to the effects of retention dynamics, localised flow patterns and differential particle handling. Other methods of estimation of seston-removal rates are equally problematic however, so that encounter-rate models are likely to remain a useful tool for such estimates. Received: 23 January 1998 / Accepted: 24 June 1998     

Variation in male sailfin molly, preference for female size: does sympatry with sexual parasites, drive preference for smaller conspecifics?

Male sailfin mollies (Poecilia latipinna) are sexually parasitized by gynogenetic Amazon mollies (Poecilia formosa). In areas of sympatry, Amazon mollies are frequently larger than female sailfin mollies. In sympatry, selection may favor males that prefer smaller conspecific mates (avoid mismating with Amazon mollies), or selection may favor males that prefer larger conspecific mates (higher fecundity). To explore this potential species and mate-quality recognition conflict, we examined male preference variation across populations. Males from one sympatric population showed stabilizing preference functions, whereas in another sympatric population, males showed directional preference functions. Variation across sympatric populations may be related to the length of time of co-evolution with Amazon mollies. In the allopatric populations, we found flat preference functions. Variation in male preferences could have important ramifications for the maintenance of Amazon mollies, as well as for the evolution of female size.     

Predator–prey models: an application for the plankton dynamics of lake Geneva

In this paper we present a hierarchical Bayesian analysis for a predator–prey model applied to ecology considering the use of Markov Chain Monte Carlo methods. We consider the introduction of a random effect in the model and the presence of a covariate vector. An application to ecology is considered using a data set related to the plankton dynamics of lake Geneva for the year 1990. We also discuss some aspects of discrimination of the proposed models.     

Sexual selection on mature male parr of masu salmon (Oncorhynchus masou): does sneaking behavior favor small body size and less-developed sexual characters?

In many salmonid species, males exhibit morphological dimorphism associated with alternative mating behaviors. ”Precocious males” have a small body size with little or no development of sexual characters and adopt sneaking to gain access to females, while ”migratory males” of large body size and well-developed secondary sexual characters fight. We quantified selection on precocious male parr of masu salmon (Oncorhynchus masou) under simulated natural conditions to examine the contribution of morphology to sneaking success. In contrast to the prediction that sneaking behavior favors small body size, we detected selection favoring relatively large body size for sneaking success. This selection pressure was caused by the dominance hierarchy within parr and may have been facilitated by indifference of dominant migratory males to parr. Unlike the secondary sexual characters exhibited by migratory male salmon, such as the hooked snout and humped back, no morphological characters other than body size contributed to the reproductive success of masu salmon parr. This non-contribution may have been responsible for the lack of development of sexual characters in precocious males. Received: 15 November 1999 / Accepted: 20 May 2000     

Light and carbon balance in the seagrass Thalassia testudinum : evaluation of current production models

The production dynamics and carbon balance of Thalassia testudinum in the lower Laguna Madre, Texas, USA, were examined during the 1995 summer period based on in situ photosynthesis vs irradiance (PI) measurements and continuous measurements of underwater photon-flux density (PFD). The validity of applying the H _sat model, used to calculate production for Zostera marina as the product of the maximum rate of photosynthesis (P _max) and daily hours of saturating irradiance (H _sat) was assessed for T. testudinum by comparison with integrated production estimates derived through numerical integration. Gross integrated production values were combined with dark-respiration measurements of photosynthetic (PS) and non-photosynthetic (NPS) tissues and areal biomass to generate daily whole-plant carbon balance. Production and whole-plant carbon balance are discussed in relation to surface and underwater PFD measurements, biomass and other physical and chemical parameters collected during a 1 yr period from January to December 1995. The H _sat model significantly underestimated production during all summer months, averaging 70% of integrated production over the entire study period. Gross integrated production ranged between 11.5 mg C g⁻¹ leaf dry wt d⁻¹ in June (during a period of unseasonably low PFDs caused by a drift-alga mat covering the seagrass bed) to 26.7 mg C g⁻¹ leaf dry wt d⁻¹ in July. Modeled net carbon gain was highest in July at 454 mg C m⁻² d⁻¹ (1.4 g dry wt m⁻² d⁻¹), sufficient to account for measured rates of leaf production in the study area and representative of T. testudinum populations of low productivity. During part of the summer period, however, the population was in negative carbon balance. The relatively low productivity of this population and the periods of negative carbon balance are attributed to low net photosynthesis:dark respiration (P _net:R _d) ratios, sporadic low-light periods, the small fraction of PS tissue relative to whole-plant biomass (5 to 13%) and nutrient limitation. Production models are sensitive to both light availability and the proportion of PS tissue supporting NPS biomass as reflected in whole-plant P _net:R _d ratios. Received: 13 August 1997 / Accepted: 6 March 1998     

Chelipeds are the real weapon: cheliped size is a more effective determinant than body size in male–male competition for mates in a hermit crab

To understand the evolution of weapons, we must understand both their functions and relative importance compared to body size in determining fighting success. Many decapod crustaceans develop disproportionately large chelipeds for their body size and use them as a weapon in agonistic interaction. There are, however, examples where weapons are merely signals of resource holding potential (RHP) and the RHP is actually determined by body size. We investigated the function and relative efficacy of body size and major cheliped size in male–male contests for females in the hermit crab Diogenes nitidimanus. Contests over females took two forms: (1) males preemptively guarded females and opponents did not fight with the guarding male. Cheliped size contributed significantly to the settlement of these contests and probably functioned as a visual signal for the opponents. (2) Guarding males engaged in physical combat with an opponent. In these cases, both body and cheliped sizes affected contest outcomes. The effect size for cheliped size was as strong, or stronger, than that for body size. These results suggest that large chelipeds have evolved as a true weapon and are effective in escalated fights for resources. Therefore they are also efficient visual signals for settling contests with only display. Our results are a rare example that clearly demonstrate that weapons are a more important determinant of fights than body size when both body and weapon size affect resource acquisition.     

The recent 500th anniversary of Leonardo da Vinci’s death: a reminder of his contribution in the field of fluid mechanics

Environmental Fluid Mechanics - In this work, a summary of Leonardo da Vinci’s contribution in the field of fluid mechanics is reported. Some theoretical laws or fluid flows analyzed or drawn...     

A dynamic size-structured population model: does disturbance control size structure of a population of the massive coral Gardineroseris planulata in the Eastern Pacific?

Using a long-term data set of Gardineroseris planulata (Dana) on Uva Island reef, Panamá, we developed a simulation model that relates size-specific schedules of growth and partial mortality to predation by Acanthaster planci (Linnaeus) and El Niño–Southern Oscillation (ENSO)-related elevation of water temperature. We compared the model predictions to field observations for both the subpopulation of colonies that was used for model development and for the entire population. No statistically significant differences in the size-frequency distributions of the real and modeled coral populations were found for the subpopulation during any of 9 yr or for the entire population during 4 yr. These results suggested that the model relationships were reflecting field conditions. Longer-term (100 yr) simulations were conducted to assess the relative importance of predation and ENSO-related colony losses in determining the size structure of the coral population. Predation by A. planci was of overwhelming importance due to both stronger effects of predation (larger transitions) and the frequency of predation (yearly) compared to ENSO (episodically). Even the least-frequent predation scenario skewed the distribution toward smaller colonies, while simulations where populations were subjected to frequent ENSO events (≥3 yr) still maintained colonies in the largest size class. The model results suggested that sea star predators may not have been in the present abundance on this reef prior to the last 30 yr; with predators present, the model predicts that the distribution would be skewed toward smaller colonies.     

The scent of alarm: ontogenetic and genetic variation in the osmeterial gland chemistry of Papilio glaucus (Papilionidae) caterpillars

Within a species, ontogenetic and genetic variation in defensive chemistry can provide the basis for natural selection from different predator types. The osmeterial chemistry of fifth (last) instar Papilio glaucus caterpillars is known to differ qualitatively from the composition of early instar caterpillars. However, the osmeterial chemistry of early instar caterpillars has not been thoroughly characterized and may change as the caterpillars undergo their first three molts. We have used GC/MS to identify a suite of about 50 different terpene compounds in the osmeterial secretions of P. glaucus caterpillars, and found the relative amounts of these compounds changed significantly with each molt. These quantitative changes preceded the more dramatic qualitative switch to the production of 2-methylbutyric and isobutyric acids after the molt to the fifth instar. We also examined the effects of diet and genetic background on the relative quantities of 15 terpenes present in the secretions of third instar caterpillars. Parentage was found to affect the percentages of many more of the individual components than did diet, although both exerted an effect. The ontogenetic and genetic variations in the composition of the osmeterial secretions appear to have an effect on would-be predators. In the laboratory, terpene secretion was found to discourage attack by ants, whereas the switch from terpene to acid production rendered the caterpillars less palatable to a larger predator, the green anole. In the field, the presence of functional osmeteria did not seem to dramatically increase survival in a field study, and only a small, non-significant advantage was seen. Similarly, field data was suggestive that parentage might affect the likelihood of survival in a natural setting, but the stage of the caterpillar and the field site significantly affected survivorship. Further studies with greater replicates will be needed to determine whether and to what extent chemical differences in osmeterial components as well as behavior contribute to differences in outcomes in the field.     

Signal variation and call preferences for whine frequency in the túngara frog, Physalaemus pustulosus

Properties of sexual signals can differ in the amount of within-male variability. In several species of anurans, females exert stabilizing or weakly directional preferences on less variable call properties, and highly directional preferences on more variable ones. Preferences of female túngara frogs, Physalaemus pustulosus, were examined for two call characteristics: a less variable spectral character, dominant frequency of the whine, and a more variable temporal character, inter-call interval. Eight phonotaxis experiments using synthetic calls were conducted with gravid females. Stimuli presented for both characters were based on the mean and standard deviation (SD) of those characters in the study population. For each character, we used four intervals of variation (1, 2, 3, and 4 SD) between stimuli in four different experiments. As has been found in some other anuran species, preference was stronger for the more variable temporal character, increasing in proportion to the difference between stimuli. Preference for the less variable spectral character was not significant until the difference between stimuli was substantial. The strength of female preference, estimated as latency to choose, the number of speakers visited, and the number of females showing phonotaxis, increased in proportion to the increase in the difference between stimuli. All these measures of strength of preference were greater in response to the more variable temporal character compared to responses to the less variable spectral character. Received: 20 September 2000 / Accepted: 7 October 2000     

WINDA—a system of models for assessing the probability of wind damage to forest stands within a landscape

An integrated system of models, WINDA, is presented for calculating the stand-wise probabilities of wind damage, uprooting and breakage of trees within a landscape. The calculations are made point-wise at exposed stand edges. WINDA integrates a modified version of the dose/response model HWIND [Can. J. For. Res. 29 (1999) 647], the airflow model WASP [Wind Atlas Analysis and Application Program (WASP), Risø National Laboratory, Roskilde, Denmark], and a component for calculating the zero-plane displacement and surface roughness and uses a GIS for geographical computations. The likelihood of damage is calculated using extreme value theory. WINDA was able to predict damage that compared well with observed extensive damage within 6.7 km² large landscape in southern Sweden. Output from the system of models was most sensitive to modifications in the input variables tree height and diameter at breast height and to the internal parameter critical friction velocity. The mechanistic modelling approach makes WINDA useful for evaluating effects on the probability of wind damage of silvicultural treatments and forestry activities as well as of a changed climate.     

Seasonal and interannual variation of soil respiration in four vegetation types in the loess hilly region北大核心CSCD

Soit carbon (C) stock is the largest C pool in terrestrial ecosystems, and the emission of CO2 through soil respiration contributes to the majority of soil C expenditure and atmospheric C. Soil respiration is also one of the major processes controlling the C budget of terrestrial ecosystems. A slight change in soil CO2 emission might cause drastic variations in global C balance. Therefore, it is of great significance to investigate the characteristics of soil respiration of soils growing different types of vegetation over a long period, and determine its relationship with variables such as soil temperature and moisture. The rate of soil respiration was measured each month in the growing seasons (from April to October) of 2011, 2013, and 2014 using the Li-8100 CO2 flux measurement system in the central Loess Plateau. Four types of vegetation (Quercus liaotungensis, Platycladus orientalis, Robinia pseudoacacia, and a natural shrub) were chosen for the periodical measurements. A permanent sample plot was established for each type of vegetation, and five polyvinyl chloride (PVC) collars were placed in each plot for the measurements. The temperature and water content of the soil in the upper 12 cm near the collar were measured using a digital soil temperature probe and a TDR 200 soil moisture meter at the same time when the soil respiration was measured. The soil respiration rates were fitted to the soil temperature and moisture with an exponential function, power function, linear function, and an equation combining the two variables. The results showed that: (1) the seasonal variation in the rates of soil respiration in the soils growing the four types of vegetation were almost the same, and were lower in the earlier period and then increased to high levels in the middle and later periods; (2) the rates of soil respiration in the same month varied with the type of vegetation grown, and were in the descending order: Q. liaotungensis > P. orientalis > shrub > R. pseudoacacia; (3) the average values of the rates of soil respiration in 2011, 2013, and 2014 were 2.77, 3.48, and 5.08 μmol m-2 s-1, respectively. The variation in soil respiration was higher across the three years than the variation for the types of vegetation grown; and (4) the rate of soil respiration was positively correlated to soil temperature and moisture for all the types of vegetation. A better fit was obtained by using the equation that included both the variables, soil temperature and moisture, than by an equation that included a single factor. Our results suggested that both seasonal and inter-annual variations of soil respiration occurred in the soils growing the four types of vegetation in the region. The temperature and water content of soils are the major regulating factors, and soil respiration in the Loess Plateau is more greatly affected by environment factors than by the type of vegetation. © 2018 Science Press. All rights reserved.     

Species-specific variation in cuttlebone δ13C and δ18O for three species of Mediterranean cuttlefish

Stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotopes in cuttlebones of three species of Mediterranean cuttlefish (Sepia elegans, S. officinalis, and S. orbignyana) with different life histories were contrasted. Cuttlebone δ¹³C and δ¹⁸O were quantified at both the core and edge (representing early life and recent deposition, respectively) for all three species sampled from the southern Adriatic Sea in 2010 (n = 28). For S. officinalis, cuttlebone δ¹³C and δ¹⁸O values were both lower relative to S. elegans and S. orbignyana at the core by approximately 1.0–2.0 and 3.0 ‰, respectively. Differences between core and edge in cuttlebone δ¹³C and δ¹⁸O were also observed for S. officinalis with observed values at the cuttlebone edge (recent) exceeding core (early life) values by 2.5 ‰ for δ¹³C and 1.4 ‰ for δ¹⁸O. Differences in isotopic composition across S. officinalis cuttlebones are possibly reflective of ontogenetic migrations from nearshore nurseries (lower seawater δ¹³C and δ¹⁸O values) to offshore overwintering habitats (higher seawater δ¹³C and δ¹⁸O values). Overall, results from this study suggest that cuttlebone δ¹³C and δ¹⁸O hold promise as natural tags for determining the degree of spatial connectivity between nearshore and offshore environments used by cuttlefish.     

Sexual selection in the zebra finch Taeniopygia guttata : condition, sex traits and immune capacity

The aim of this study was to test two hypotheses: (1) that condition-dependent secondary sexual traits reflect an individual's immune capacity and (2) that immune capacity and secondary sexual traits covary with primary sex traits, specifically ejaculate quality. We used the zebra finch Taeniopygia guttata as a study species, since the traits that females find attractive in males of this species, song rate and beak colour, are well established. A paired experimental design comprising 31 pairs of brothers was used; for each pair, one male was assigned to a control group provided with ad libitum food and no additional exercise, and the other male was assigned to an experimental group which experienced additional exercise and a reduced rate of food intake. After 11 weeks, the experimental group differed significantly from the control group in a range of variables, including body mass, haematocrit, granulocyte:lymphocyte (G:L) ratio and several primary sex traits, indicating that condition in this group was reduced. Birds in the experimental group showed a differential response to the treatment. We used the rank order in which birds could be captured by an experimenter as an index of condition. Birds easily caught were assumed to be in poorer condition than those which were more difficult to capture. Rank capture order was repeatable and was significantly correlated with the G:L ratio in the experimental group, but not in the control group. In the experimental group, rank capture order was correlated significantly with both secondary sex traits: birds in better condition had redder beaks and a higher song rate. However, beak colour and song rate did not covary significantly, suggesting that these two traits provide different types of information. Secondary sex traits did not covary with primary sex traits or any sperm features. Thus, there was no evidence for Trivers' sexual-competence hypothesis or the phenotype-linked fertility hypothesis. We used four assays of immune capacity, two general (G:L ratio and spleen mass) and two specific [antibody titres to sheep red blood cells (SRBCs) and Brucella abortus (BA)]. The G:L ratio was significantly higher in the experimental group, spleen mass (absolute and relative) did not differ between the groups, anti-SRBC antibody titres were significantly higher in the control group (contrary to expectation), and anti-BA antibody titres were close to being significantly lower in the experimental group. Within the experimental group, there was no evidence that antibody titres covaried with secondary sex traits. Although we demonstrated that beak colour and song rate were condition dependent, our experiment provided no evidence that either of these traits covaried with immune capacity or sperm features. Received: 9 February 1998 / Accepted after revision: 5 September 1998     

Visions for the future of transport: Approaching consensus?

Many cities and national authorities have made substantial progress in developing transport strategies to reconcile environmental pressures with the increasing demand for travel. However, there is still some doubt as to what are the key ingredients of a successful strategy and progress in implementing such changes has been slow. Research is needed to better understand what are the essential ingredients to a balanced transport policy, the constraints, which are preventing these from being implemented, and the acceptability of such changes. This paper reports on the outcomes of a project funded under the Rees Jeffreys Road Fund research programme 'From Realism to Reality', which aims to identify the elements necessary for a successful transport policy in the UK into the 21st century, The project seeks to develop a vision for the transport system of the future through an understanding of the extent of the current problems in the transport sector and an examination of the range and effectiveness of options and instruments available to resolve them. The paper examines a range of visions that are currently in the public domain. Results show that there is a degree of consistency in the general aims and objectives of such visions, but that there is rather less consensus in the means proposed to achieve those aims.     

An approach for particle sinking velocity measurements in the 3–400?μm size range and considerations on the effect of temperature on sinking rates

The flux of organic particles below the mixed layer is one major pathway of carbon from the surface into the deep ocean. The magnitude of this export flux depends on two major processes—remineralization rates and sinking velocities. Here, we present an efficient method to measure sinking velocities of particles in the size range from approximately 3–400?μm by means of video microscopy (FlowCAM^?). The method allows rapid measurement and automated analysis of mixed samples and was tested with polystyrene beads, different phytoplankton species, and sediment trap material. Sinking velocities of polystyrene beads were close to theoretical values calculated from Stokes’ Law. Sinking velocities of the investigated phytoplankton species were in reasonable agreement with published literature values and sinking velocities of material collected in sediment trap increased with particle size. Temperature had a strong effect on sinking velocities due to its influence on seawater viscosity and density. An increase in 9?°C led to a measured increase in sinking velocities of ~40?%. According to this temperature effect, an average temperature increase in 2?°C as projected for the sea surface by the end of this century could increase sinking velocities by about 6?% which might have feedbacks on carbon export into the deep ocean.     

Regional-scale variation in the distribution and abundance of farming damselfishes on Australia’s Great Barrier Reef

Territorial damselfishes that manipulate (“farm”) the algae in their territories can have a marked effect on benthic community structure and may influence coral recovery following disturbances. Despite the numerical dominance of farming species on many reefs, the importance of their grazing activities is often overlooked, with most studies only examining their roles over restricted spatial and temporal scales. We used the results of field surveys covering 9.5° of latitude of the Great Barrier Reef to describe the distribution, abundance and temporal dynamics of farmer communities. Redundancy analysis revealed unique subregional assemblages of farming species that were shaped by the combined effects of shelf position and, to a lesser extent, by latitude. These spatial patterns were largely stable through time, except when major disturbances altered the benthic community. Such disturbances affected the functional guilds of farmers in different ways. Since different guilds of farmers modify benthic community structure and affect survival of juvenile corals in different ways, these results have important implications for coral recovery following disturbances.     

Cell cycle of symbiotic dinoflagellates: variation in G1 phase-duration with anemone nutritional status and macronutrient supply in the Aiptasia pulchella–Symbiodinium pulchrorum symbiosis

The metabolite exchange in alga–invertebrate symbioses has been the subject of extensive research. A central question is how the biomass of the algal endosymbionts is maintained within defined limits under a given set of environmental conditions despite their tremendous growth potential. Whether algal growth is actively regulated by the animal cells is still an open question. We experimentally evaluated the effect of inorganic nutrient supply and host-animal nutritional status on the biomass composition, growth and cell-cycle kinetics of the endosymbiotic dinoflagellate Symbiodinium pulchrorum (Trench) in the sea anemone Aiptasia pulchella. Dinoflagellates in anemones starved for 14?d exhibited lower growth rates, chlorophyll content and higher C:N ratios than in anemones fed Artemia sp. (San Francisco brand #65034) nauplii every 2 d, indicating N-limitation of the algae during starvation of the host animal. Manipulation of the dissolved inorganic nutrient supply through ammonium and phosphate additions induced a rapid recovery (half time, t _½～ 2?d) in the C:N ratio of the dinoflagellate cells to levels characteristic of N-sufficient cells. The mitotic index and population growth rate of the dinoflagellate symbionts subjected to this enrichment did not recover to the levels exhibited in fed associations. Flow cytometric analysis of dinoflagellate cell size and DNA content revealed that the duration of the G₁ phase (first peak of DNA content: 70 to 100 relative fluorescence units, rfu) of their cell cycle lengthened dramatically in the symbiotic state, and that the majority of algal biomass increase occurred during this phase. Covariate analysis of dinoflagellate cell size and DNA-content distributions indicated that the symbiotic state is associated with a nutrient-independent constraint on cell progression from G₁ through the S phase (intermediate DNA content: 101 to 139?rfu). This analysis suggests that the host-cell environment may set the upper limit on the rate of dinoflagellate cell-cycle progression and thereby coordinate the relative growth rates of the autotrophic and heterotrophic partners in this symbiotic association.     

Use of biomarkers in zooplankton for assessment of the ‘health status’ of marine and brackish environments: a short overview

The biomarker approach has been used for 25 years to study the environmental quality of marine, brackish and freshwater ecosystems. Biomarkers may indicate health status and can be applied to organisms of all zoological phyla by destructive or non destructive methods. For 5 years we have been using this approach in zooplankton to detect ecotoxicological alterations at low levels of the food chain due to contaminants. Here we review our approach to validate and apply biomarker techniques in zooplankton. We discuss advantages, limitations, some results and future research. We indicate that biomarkers in zooplankton can be used as new indices of trophic status and ecological integrity of Italian marine coastal and lagoon environments, to be included among the tools specified by Italian law D.Lgs. 152/2006.