Feeding and bacteriolytic responses of the deposit-feeder Abarenicola pacifica (Polychaeta: Arenicolidae) to changes in temperature and sediment food concentration

Deposit-feeders can respond to seasonal fluctuations in food concentration both functionally (e.g. by adjusting feeding rates) and physiologically (e.g. by changing the concentration of bacteriolytic agents in gut fluids). Laboratory feeding experiments were carried out (11 to 21 July 1997) with the arenicolid polychaete worm Abarenicola pacifica (Healy and Wells). Objectives were to test for separate and interactive effects of sediment food concentration and temperature (6, 11, and 16 °C) on deposit-feeder functional (feeding rates) and physiological (bacteriolytic activity of gut fluids) responses. Food concentration was varied experimentally using sieved (1 mm) natural sediments (Md φ=2.00; 0.6% organic) mixed with combusted (500 °C, 8 h) sediments for final concentrations of 25, 50, and 100% natural sediment. Sediment food quality was measured as: (1) bioavailable amino acids (EHAA), (2) chlorophyll a (chl a), and (3) bacterial abundance. Feeding rates were inferred from egestion rates (ER, g h⁻¹) and analyzed with respect to worm size. Bacteriolytic activity of midgut fluids was assayed turbidimetrically against two bacterial isolates, after worms had fed on experimental sediments for 15 d. Temperature and food concentration both significantly affected feeding rates, with maxima occurring at 50 and 100% natural sediment mixtures, and at high (16 °C) temperature. ER was positively, but not significantly correlated with EHAA and chl a; a positive, significant correlation was detected between ER and sediment bacterial abundance. Overall, functional responses agreed with earlier compensatory intake models for deposit-feeders. However, the size and direction of these responses was temperature-sensitive, suggesting that these models need to be adjusted for changes in absorption rates. No effects of ambient temperature or food concentration on bacteriolytic rates were observed, possibly due to compensatory mechanisms or the presence of multiple bacteriolytic agents in gut fluids. Received: 28 June 1999 / Accepted: 14 March 2000     

Lipid content of some Caribbean corals in relation to depth and light

Three procedures for the extraction of coral lipids were compared and a rapid and effective method for future use is suggested. This method was used to measure the lipid content of the branching coral Porites porites (Pallas) and the massive corals Montastrea annularis (Ellis and Solander) and Siderastrea siderea (Ellis and Solander) during July and August 1991. P. porites and M. annularis were sampled on two fringing reefs, each characterised by different water quality affecting light transmission, and at depths of down to 30 m on a barrier reef on the west coast of the island. m. annularis contained, on average, 29% of dry weight as lipid, and there were no significant differences in lipid levels between corals sampled on either fringing reef at 3 and 6 m, or between fringing reefs and the barrier reef at 13, 20 or 30 m depth. Five samples were also taken from a single massive colony of S. siderea at 3 m on a fringing reef and at 13, 20 and 30 m depth on the barrier reef. Values for lipid ranged from 26 to 35% of dry tissue weight. P. porites from 3 and 6 m depth on both fringing reefs contained the same amount of lipid (11% of dry tissue weight). However, at 13 m depth on the barrier reef this coral contained significantly less lipid (8.5% of dry tissue weight). This difference may be attributable to a higher nutritional intake by P. porites on the fringing reefs.     

沙罗竹人工林生长与立地条件的关系研究

对广东省罗定市泗纶镇沙罗竹人工林生长与地形因子和土壤理化性质之间的关系进行了分析研究。结果表明,地形部位、坡型、坡向、土壤质地、立竹密度等对沙罗竹平均胸径有显著影响;沙罗竹平均胸径与土壤水分、有机质、全氮、速效氮、速效磷、有效硅质量分数呈显著正相关关系。回归分析结果表明,土壤有机质、速效氮、速效磷、有效镁质量分数及其组合是影响沙罗竹生长的主要养分因子。研究结果对沙罗竹林地选择和制定营林管理措施具有科学指导意义。     

Rapid changes in growth,condition, size and age of small pelagic fish in the Mediterranean

Since 2007, the ecosystem of the Gulf of Lions has shifted to a different regime, characterised by a low anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) biomass and a remarkably high sprat (Sprattus sprattus) biomass. Surprisingly, the abundance and recruitment of anchovy and sardine remained high. To understand which processes (bottom-up or top-down control, etc.) could have caused this shift, we studied the changes in body condition, growth and size and age of anchovy, sardine and sprat over 1984–1985 and 1992–2012, using data from scientific surveys. The annual age structure of anchovy and sardine was estimated using Bayesian mixture models based on size frequency data with priors on the age–length relationship derived from independent otolith readings. The results indicated periods during which anchovy and sardine were in an average (1992–2004), good (2005–2007) or poor (2008–2012) overall state of condition. For sardine, the shift towards smaller fish observed during these past 4 years was explained by a combination of slower growth and the disappearance of older individuals (ages 2+). Despite the increase in biomass of sprat since 2008, indications were found that sprat was also smaller than in the past. As growth and condition decreased and overexploitation has not been documented or suspected for those three species in this area, we propose that the current decline in sardine and anchovy biomass could be due to qualitative and/or quantitative modifications in the planktonic production (i.e. a bottom-up control) or mass mortalities of adults due to an epidemic disease.     

Recruitment,growth, and diel vertical migration of Euphausia pacifica in a temperate fjord

The pelagic crustacean Euphausia pacifica Hansen was sampled with a multiple-sample 1.0 m² Tucker trawl and a multiple-sample 1.0 m² vertical net in Dabob Bay, Washington on 17 dates between May 1985 and October 1987. Size (stage) structure and abundance of the population were determined for each date, while vertical distribution and diel migration were determined for 13 dates. Although internannual variability in both timing and magnitude of events occurred, consistent patterns were discernable. The population produced a large pulse of larvae (2 to 5 mm) in late spring of each year, apparently in response to the vernal phytoplankton bloom. Much lower abundances of larvae occurred during summer and autumn of each year, and larvae were completely absent during winter. Recruitment to the juvenile (6 to 9 mm) and adult (10 mm) stages was strongest during the summer, with abundances of these individuals peaking in summer and autumn. Individual growth rates, determined by modal progression analysis, were calculated for E. pacifica. Rates ranged from zero for some adult cohorts during the winter to 0.12 mm d^-1 for larvae during spring. The latter are among the highest ever reported for this species in the field. The vertical distributions and diel vertical migrations (DVM) of E. pacifica varied seasonally and between size (stage) classes. At night, all size classes were distributed in the surface layer (upper 25 m) irrespective of season or year. During the day, the larger/older stages were always distributed at middepths (50 to 125 m). In contrast, the daytime distribution of the larvae was more variable, being concentrated at the surface during spring and early summer of 1985, and at increasing depths later in the summer and autumn of 1985 and again in spring of 1986. This resulted in invariant DVM in the juveniles and adults, but variable DVM in the larvae, the latter of which is hypothesized to be a response to variable abundances of zooplanktivorous fish.     

In situ variation in heart rate of the shore crab Carcinus maenas in relation to environmental factors and physiological condition

Heart rate of Carcinus maenas was recorded continuously for two days in situ, together with water temperature, salinity, depth and light intensity. Of each sex, 25 crabs were used and assigned to groups on the basis of size and colour (the carapace changes colour with prolongation of the intermoult phase). Wet weight:dry weight ratios of midgut gland, muscle, gonads and whole body were examined together with midgut gland lipid content and haemolymph protein concentration. Heart rates and wet wt:dry wt ratios for all the tissues examined were higher in early intermoult than in late intermoult stages of the adult C. maenas (P<0.05). Heart rate, lipid content and haemolymph protein concentrations were higher and wet wt:dry wt ratios of midgut gland, gonads and whole body were lower in juvenile crabs than in adults (P<0.05). The relationship between heart rate and wet wt:dry wt of whole body differed among C. maenas in early and late intermoutl. Heart rate was positively correlated with midgut gland lipid content (a Darwinian fitness parameter) in crabs that were in late intermoult. Physico-chemical environmental parameters, sex and colour accounted for 12% of the variation in heart rate of C. maenas recorded in situ. Temperature and prolonged intermoult were the most important factors influencing heart rate. The findings are discussed in relation to laboratory studies of cardiac activity and observed behaviour of C. maenas in the field.     

Seasonal changes in the physiology,reproductive condition and carbohydrate content of the cockle Cardium (=Cerastoderma) edule (Bivalvia: Cardiidae)

Pronounced seasonal cycles in the rates of oxygen consumption and feeding were found for Cardium (=Cerastoderma) edule L. measured in the field under ambient conditions. The cockles had a maximum rate of oxygen consumption (0.89 ml O₂ g^-1 h^-1) in April which declined to a minimum of 0.35 ml O₂ g^-1 h^-1 in March. Their feeding rate was variable but had a maximum value (3.91 l g^-1 h^-1) in April and a minimum value (0.73 l g^-1 h^-1) in October. There was no apparent seasonal variation in absorption efficiency, with a mean value of 67.6%. Gametogenesis was initiated in January and the population reached a peak in reproductive condition in April/May, followed by a 3 month spawning period. Carbohydrate reserves were synthesised during spawning, and were then utilised during the winter and early spring. An adaptive function for a reduction in time spent feeding is postulated, and correlations between the rates of certain physiological processes and some exogenous and endogenous variables are discussed.     

Relationships between the movements,growth, age structures,and reproductive biology of the teleosts Sillago burrus and S. vittata in temperate marine waters

Sillago burrus and S. vittata both use sheltered, nearshore shallow waters ( 1.5 m) as nursery areas. However, the juveniles of the former species remain there for only a few months, before migrating into deeper waters (5 to 15 m) as they increase in size, whereas some juvenile S. vittata do not undergo a similar migration until considerably later. S. burrus rarely exceeded 2 yr of age and was never found beyond 4 yr of age. Although only a small number of S. vittata exceeded 2 yr of age, a few individuals of this species were caught between 4 and 7 yr old. The maximum and asymptotic lengths of S. burrus (251 and 180 mm, respectively) were far lower than those of S. vittata (325 and 320 mm, respectively), whereas the growth coefficients (K) were much higher for the former species, i.e. 2.4 vs 0.4. Virtually all S. burrus, and also those S. vittata that moved into deeper waters early in life, spawned at the end of their first year of life. Since relatively few S. burrus reached 2 yr of age, the attainment of almost full size by the end of their first year of life enables a relatively large number of eggs to be produced by fish at the end of their first year-for many, their only spawning period. Those individuals of S. vittata that remained in their shallow nursery areas until the end of their first year of life, did not reach maturity until the end of their second year of life. The proportions of mature gonads and the numbers of yolk-vesicle and yolk-granule oocytes and post-ovulatory follicles in ovaries were far higher in both S. burrus and S. vittata during December to February than in any other month, demonstrating that these two species spawn largely in these summer months. During this period, the ovaries of individual S. burrus and S. vittata often contained post-ovulatory follicles, as well as yolkvesicle and yolk-granule oocytes that ranged widely in size, strongly suggesting that both species are multiple spawners. During the spawning period of S. burrus, the ovaries possessed large numbers of hydrated oocytes and no post-ovulatory follicles or the reverse situation, and the oocytes tended to form several relatively discrete size groups. This indicates that S. burrus produces eggs in batches and that the spawning of the members of this species is synchronised. The presence of large numbers of yolk-granule oocytes with migrating nuclei in the ovaries of many S. vittata at certain times suggests that this species is also a batch- and synchronised spawner. Comparisons between the results of the present study and past work emphasise that the relationships between the timing of offshore movements and the sizes and ages at first maturity vary considerably amongst whiting species.     

Migratory orientation of red-eyed vireos,Vireo olivaceus,in relation to energetic condition and ecological context

How and when migrants integrate directional information from different sources may depend not only on the bird’s internal state, including fat stores, but also on the ecological context during passage. We designed experiments to (1) examine the influence of stored fat on the decision to migrate and on the choice of migratory direction and (2) investigate how the integration of orientation cue information is tied to energetic status in relation to migration across an ecological barrier. Migratory orientation of red-eyed vireos (Vireo olivaceus) at twilight was recorded using two different techniques, orientation cage experiments and free-flight release tests, during both fall and spring migration. During fall migration, the amount of stored fat proved decisive for directional selections of the vireos. Fat birds chose directions in accordance with migration across the Gulf of Mexico. Lean birds oriented either parallel to the coast line (cage tests) or moved inland (free-flight releases). Whereas only fat birds showed significant responses to experimental deflections of the geomagnetic field, lean birds displayed a tendency to shift their activity in the expected direction, making it difficult to evaluate the prediction that use of the magnetic compass is context dependent. Fat loads also had a significant effect on the decision to migrate, i.e., fat individuals were more likely to embark on migration than were lean birds (true for both cage and release experiments). During spring migration, a majority of experimental subjects were classified as lean, following their arrival after crossing the Gulf of Mexico, and oriented in seasonally appropriate directions. The vireos also showed significant responses to experimental deflections of the geomagnetic field regardless of their energetic status. Free-flight release experiments during spring migration revealed a significant difference in mean directions between clear sky and overcast tests. The difference may indicate a compensatory response to wind drift or possibly a need for celestial cues to calibrate the magnetic compass. Finally, this is the first demonstration of magnetic compass orientation in a North American vireo. Received: 15 December 1995/Accepted after revision: 24 March 1996     

生长介质中CaCO3质量分数及水分状况与HCO3-的关系

探讨生长介质中CaCO3质量分数(g/kg)与HCO3^-质量摩尔浓度(mmol／kg)之间的定量关系，以及HCO3^-产生过程中水分条件所起的作用。培养试验结果表明，生长介质中CaCO3质量分数一旦达到较高水平，将对作物生长产生明显的不利影响。介质中CaCO3质量分数与HCO3^-质量摩尔浓度之间未表现出显著的正相关关系；但HCO3^-质量摩尔浓度随着水分含量增加而显著增加，尤其是过饱和的水分条件能使HCO3。质量摩尔浓度大幅度增加。随CaCO3含量增加，培养介质的pH值并未产生明显变化，水分状况对介质pH值的影响也不显著。供试条件下CaCO3在介质中的淋溶量随着供水量的增加而增加。     

Egg composition in relation to social environment and maternal physiological condition in the collared flycatcher

Offspring survival can be influenced by resources allocated to eggs, which in turn may be affected by the environmental factors the mother experiences during egg formation. In this study, we investigated whether experimentally elevated social interactions and number of neighbouring pairs influence yolk composition of collared flycatchers (Ficedula albicollis). Social challenge was simulated by presentation of a conspecific female. Experimental females spent more time near the cage and produced eggs with higher androgen concentration, but local breeding density did not affect yolk androgen level. Moreover, we found that females exposed to more intra-specific interactions and those that bred at higher density produced eggs with smaller yolk. These females may be more constrained in foraging time due to more frequent social encounters, and there might be increased competition for food at areas of higher density. In contrast, the present study did not reveal any evidence for the effect of social environment on yolk antioxidant and immunoglobulin levels. However, we found that yolk lutein and immunoglobulin concentrations were related to the female’s H/L ratio. Also, yolk lutein and α-tocopherol levels showed a seasonal increase and were positively related to the female’s plasma carotenoid level. Mothers may incur significant costs by transferring these compounds into the eggs, thus only females in good physiological condition and those that lay eggs later, when food is probably more abundant, could allocate higher amounts to the eggs without compromising their defence mechanisms. Our results suggest that environmental circumstances during egg formation can influence conditions for embryonic development.     

Relationship between reproductive biology and age composition and growth in Urolophus lobatus (Batoidea: Urolophidae)

The aim of the present study was to use samples, collected by trawling throughout the year along the lower west coast of Australia, to determine the reproductive biology, size and age compositions, and growth rate of Urolophus lobatus, a member of a speciose elasmobranch family (Urolophidae) for which there was previously only a small amount of such data. U. lobatus copulates about 3 months prior to the time when females ovulate, which implies that sperm is stored in the oviducal gland of the female in the intervening period. Gestation lasts for 10 months, which is relatively long for a species that does not grow to a large size. This feature is reflected in the fact that the mean disc width at parturition (105 mm) is equivalent to as much as 44% and 52% of the asymptotic disc widths of the females and males of this species, respectively. The trends exhibited by the marginal increments on vertebral centra demonstrated that each of the translucent zones in these centra is laid down annually and that their numbers can thus be used to age this species. Maturity was attained by about 70% of females and 50% of males at the end of the 4th and 3rd years after conception, respectively, or at just over 3 and 2 years after birth, respectively. Females and males typically first reach maturity at ˜200 and ∼160 mm, respectively, and attained maximal disc widths of 277 and 237 mm, respectively. Females reached maximum ages of 15 years from conception and 14 years from birth, with the corresponding values for males being 13 and 12 years, respectively. Since such a large amount of growth occurs during gestation, von Bertalanffy growth curves were constructed using the date of conception, that is, the fertilisation date, as age 0, as is usually the case with teleosts, as well as employing the birth date as age 0, as is typically the case with elasmobranchs. The growth curves drawn through the points for the disc width-at-age of the older female and male fish gave a slightly better fit when using, as age 0, the parturition date rather than the conception date. However, the asymptotic disc widths derived for females and males using the conception date, that is, 241.3 and 202.9 mm, were each still only 7.6 mm less than those derived using the birth date. Moreover, the fit of the line drawn through the points for the disc width-at-age of fish during gestation was better using the conception date as age 0 than would be achieved by a backwards extrapolation of the growth curve using the birth date as age 0. Received: 6 January 2000 / Accepted: 17 June 2000     

Male reproductive investment relative to age and flight behaviour in the monandrous butterfly Pararge aegeria

Male reproductive investment may signify a considerable cost to male insects that produce sperm packages or spermatophores. Male butterflies allocate much of their active time budget to mate location, and they may adopt different behavioural strategies to do so. In the speckled wood butterfly (Pararge aegeria L.), males adopt either a territorial wait-and-fight strategy (territorial perching) or a fly-and-search strategy in wider areas (patrolling). In this study, we analysed the impact of male age, male size and male behaviour (i.e. behavioural strategies and levels of activity) on spermatophore investment (i.e. spermatophore mass, number of eupyrene sperm bundles). As predicted, reproductive investment increased with male age and size. Nevertheless, the increase of spermatophore mass with age and the number of eupyrene sperm bundles (i.e. fertile sperm) was stronger in low-activity males compared to active flying males. This suggests that flight activity has a negative impact on male reproductive investment. However, males that were forced to fly in the laboratory produced more eupyrene sperm bundles than resting males. We discuss the potential effects of male–male competition and predation risk on current versus future male reproduction. Males adopting different mate-locating strategies (perching and patrolling) in outdoor cages did not differ in spermatophore traits as was predicted from their very different flight performances. Copulations of territorial perching males took somewhat longer than copulations with non-perching males. There was a significant family effect of spermatophore size and of the expression of male mate-locating strategies suggesting heritable variation. Female traits (i.e. age and size) did not strongly affect spermatophore production. We discuss the results relative to both ultimate and proximate explanations of the complex relationships between butterfly activity, behavioural strategies, age and spermatophore production.     

Correlations between age, phenotype, and individual contribution to population growth in common terns

There have been numerous reports of changes in phenology, which are frequently attributed to environmental change. Age-dependent change in phenotypic traits, fledgling production, and the timing of events in the life cycle is also widespread. This means that changes in the age structure of a population could generate changes in phenology, which may be incorrectly attributed to environmental change or microevolution. Here, estimates of selection for arrival date, arrival mass, and laying date are compared when age is and is not corrected for. This is achieved using long-term individual-based data collected from a breeding colony of Common Terns (Sterna hirundo) and a novel fitness measure: individual contributions to population growth. The failure to correct for age generated deceptive estimates of selection in eight out of nine comparisons. In six out of nine comparisons, the direction of selection differed between age-corrected and uncorrected estimates. Persistent individual differences were detected: individuals remained within the same part of the phenotype distribution throughout life. The age-corrected estimates of selection were weak and explained little variation in fitness, suggesting that arrival date, arrival mass, and laying date are not under intense selection in this population. These results also demonstrate the importance of correcting for age when identifying factors associated with changes in seabird phenology.     

Threshold to maturity in a long-lived reptile: interactions of age, size, and growth

Thresholds to sexual maturity—either age or size—are critical life history parameters. Usually investigated in short-lived organisms, these thresholds and interactions among age, size, and growth are poorly known for long-lived species. A 34-year study of captive green turtles (Chelonia mydas) that followed individuals from hatching to beyond maturity provided an opportunity to evaluate these parameters in a long-lived species with late maturity. Age and size at maturity are best predicted by linear growth rate and mass growth rate, respectively. At maturity, resource allocation shifts from growth to reproductive output, regardless of nutrient availability or size at maturity. Although captive turtles reach maturity at younger ages than wild turtles, the extensive variation in captive turtles under similar conditions provides important insights into the variation that would exist in wild populations experiencing stochastic conditions. Variation in age/size at maturity should be incorporated into population models for conservation and management planning.     

Relation of habitat to glycogen concentration and glycogen synthetase in polychaetes

The glycogen content of whole body or muscle of 14 species of polychaetes was determined, and the activity, co-factor requirements, and substrate affinity of glycogen synthetase from muscles of 4 of the species were measured. Species average glycogen concentrations were positively correlated with the risk of anoxia each species faced in the field. Total activity of glycogen synthetase was not correlated with glycogen concentration in muscle, but polychaetes most likely to experience anoxia had the highest proportion of the enzyme in the active (co-factor independent = I) form; moreover, in such species, the glycogen synthetase had the highest affinity for substrate. It was concluded that evolutionary adaptation to oxygen-poor habitats occurs through qualitative changes in enzyme properties rather than through quantitative changes in enzyme production.     

Nectar-receiver behavior in relation to the reward rate experienced by foraging honeybees

Since forager honeybees change their food-unloading behavior according to nectar-source profitability, an experiment was performed in order to analyze whether food-receivers modify their within-hive tasks related to different reward conditions. We offered individual foragers two reward conditions at a rate feeder while an additional feeder offered a constant reward and was of free access to the rest of the hive. Both feeders were the only food sources exploited by the colony during the assays since a flight chamber was used. After receiving nectar, hive bees performed processing cycles that involved several behaviors and concluded when they returned to the delivery area to receive a new food sample. During these cycles, receivers mainly performed oral contacts offering food, or inspected cells, and often both. In the latter case, both behaviors occurred simultaneously and at the same distance from the hive entrance. When they performed a single task, either the occurrence of cell inspections increased or contact offerings decreased for the highest reward rate offered to the donor-forager. Receivers also begged for food more often after interacting with low-profit foragers. Thus, the profitability of the food source exploited by nectar-forager honeybees could affect receiver behaviors within the hives based on individual-to-individual interactions.Communicated by R.F.A. Moritz     

Otolith ring deposition in relation to growth rate in herring (Clupea harengus) and turbot (Scophthalmus maximus) larvae

Larvae of Clyde spring-spawning Clupea harengus L. and hatchery-produced Scophthalmus maximus (L.) were reared from hatching through metamorphosis in 1980 and 1981 in laboratory tanks and in large enclosures under various light, temperature, and feeding regimes in order to study otolith ring deposition and growth under different conditions. Ring deposition and growth rates were significantly affected by rearing conditions in both species. The ring deposition rates observed under the conditions tested ranged from 0.34 to 0.92 rings d^-1 in herring larvae, and from 0.07 to 1.0 rings d^-1 in turbot larvae. Growth rates ranged from 0.11 to 0.42 mm d^-1 in herring and from 0.05 to 0.27 mm d^-1 in turbot. The number of otolith rings was dependent on the growth rate of the individual larva. At the population level, higher ring deposition rates were observed in faster growing populations. In herring larvae, the relationship between average growth rate and average ring deposition rate was logarthmic, reaching an asymptote at 1 ring d^-1 for growth rates approaching 0.40 mm d^-1. The relationship was linear for turbot larvae for the range of growth rates observed.