Scaling of Cardiovascular Physiology in Snakes

The elongate body form of snakes and the wide diversity of habitatsinto which they have radiated have affected the form and functionof the cardiovascular system. Heart position is strongly correlatedwith habitat. The heart is located 15–25% of the bodylength from the head in terrestrial and arboreal species, but25–45% in totally aquatic species. Semi-aquatic and fossorialspecies are intermediate. The viperids are exceptional, withgenerally more posterior hearts but arboreal species have heartscloser to the head. An anterior heartis favored when snakesclimb because it reduces the hydrostatic pressure of the bloodcolumn above the heart and tends to stabilize cephalic bloodpressure. In water, where hydrostatic bloodpressure is not aproblem, a more centrally located heart is favored because theheart does less work perfusing the body. In terrestrial species,head-heart distance increases linearly with body length andthe increased hydrostatic pressure is matched by higher restingarterial blood pressure in longer animals. Unlike mammals andbirds, snakes have blood pressures that increasewith body mass.The added stress on the ventricle wall in larger snakes is correlatedwith ventricles that are larger than predicted by other reptiles.Heart mass scales with body mass to the 0.95 power in snakesbut only 0.77–0.91 in other reptiles that are not as subjectto the hydrostatic effects of gravity. The spongy hearts ofreptiles do not conform well to the Principle of Laplace.     

Why are there about 5000 species of phytoplankton in the sea?

The relative abundances of phytoplankton taxa conform approximatelyto a finite geometric series in which there are 20–25species per decade of ranked abundance. Such series can contain160–400 species between the commonest (10²²–10²⁶cells) and the rarest (10¹⁰–10¹⁴ cells). Thus, between12 and 31 such series are needed to explain the observed diversity,5x10³ species, of marine phytoplankton. The number of seriesis similar to the number (20–25) of upper-ocean watermasses defined by dilution time scale of order 10¹–10²years. Interpretations of this coincidence are discussed.     

Seasonal occurrence and vertical distribution of appendicularians in Toyama Bay, southern Japan Sea

To investigate seasonal variation in the community structureof appendicularians, vertical hauls (0–500 m) with a Norpacnet were made at an offshore station in Toyama Bay at intervalsof 2–4 weeks from February 1990 to January 1991. Additionalsamples were collected with MTD nets at 12–17 differentdepth layers between the surface and a depth of 600–700m at the same position in June, September and December 1986,and March 1992, to examine the vertical distribution of appendicularians.Twenty-one species (including two unidentified species) belongingto five genera were found, and the dominant species were dividedinto three groups by their occurrence period. Oikopleura longicauda,Fritillaria borealis f. typica and F. borealis f. sargassi occurredthroughout most of the year. Fritillaria pellucida, O. fusiformisand O. rufescens were found in summer and autumn. Oikopleuradioica was found in spring and winter. Oikopleura longicaudawas overwhelmingly the most abundant species throughout theyear. This species was always distributed in the upper 100 mdepth, with a peak at a depth of 0–50 m that correspondedto the peak of chlorophyll a concentration during the day andnight in all seasons. The day–night vertical distributionpatterns of F. borealis f. typica, F. pellucida, O. fusiformisand O. rufescens were similar to that of O. longicauda. Seasonalvariations in abundance of appendicularians are considered tobe the result of biological factors rather than physical factorssuch as temperature and salinity. In particular, O. dioica seemsto be affected by food availability.     

Midwater macroplankton of British Columbia studied by submersible PISCES IV

Data are reported from 30 dives during winter and spring 1980–83at sites in the Strait of Georgia and inlets running off it,and in inlets on the west coast of Vancouver Island. Observationswere made from the surface to the bottom (maximum 733 m) butmost attention was given to the midwater plankton community.The vertical distribution and abundance of hydromedusae, siphonophores,ctenophores, euphausiids, pelagic worms and molluscs were recordedsystematically, along with data for one copepod species (Neocalanusplumchrus). The midwater environment was found to be stablein terms of species composition and depth ranges, which permittedthe data for several years and many locations to be pooled.Four categories of plankton are recognized: (a) epipelagic (concentratedin the top 50 m); (b) mesopelagic (50–175 m); (c) bathypelagic(below 175 m); and (d) meso-bathypelagic (forms living in bothmeso- and bathypelagic zones). Species in this last categorybehave like mesopelagic forms at the upper end of their ranges,migrating to the surface at night. Deeper-lying members of thesame species do not migrate. For six such species, the cut-offpoint between migratory and non-migratory components was foundto lie at a mean depth of 175 m. This depth is therefore takenas the demarcation point between the meso- and bathypelagiczones. Taking account of published data on light penetration,it is estimated that, for the whole region, daytime light intensityat 175 m, and hence the effective limit for phototaxis of thespecies in question, lies in the range 10^–8–10^–9µW cm^–2.     

The vertical and horizontal distribution of four species of the genus Gnathophausia (Crustacea: Mysidacea) in the eastern North Atlantic Ocean

The occurrence of four species of the genus Gnathophausia takenin several series of vertically discrete hauls in the easternNorth Atlantic is discussed. The five sets of samples describedhere were taken at the following positions: (i) six stationsbetween 11 and 60°N, close to the 20°W meridian; (ii)three other stations between 42 and 55°N; (iii) stationsin the North West African upwelling area; (iv) five stationsacross the Azores Front at 30–35 30–34°W; (v)three stations close to an area of weak hydrographic frontsbetween 39–40°N 15°W and 45–46 14°W.Distribution of species above 1500–2000 m are describedand, where possible, correlated with the hydrographic regime.     

The Role of Carbonic Anhydrase in Blood Ion and Acid-Base Regulation

The role of carbonic anhydrase (CA) in ion transport processesof aquatic and terrestrial arthropod species is reviewed. Inboth insects and crustaceans CA is found in a variety of iontransporting tissues. The bulk of CA activity in crustaceansis concentrated in the posterior gills, which are morphologicallyand biochemically adapted for ion transport. The enzyme canbe specifically localized to gill lamellae which contain largepopulations of salt transporting chloride cells. Enzyme activityin the posterior gills of species having the ability to regulateblood ion concentrations increases when these organisms areacclimated to environmental salinities in which they ion regulate.In stenohaline, ion conforming species branchial CA activityis uniformly low, being only 5–10% that in regulatingspecies. Studies on the blue crab, Callinectes sapidus, usingthe specific CA inhibitor acetazolamide have shown that theenzyme is indeed important in blood ion regulation. Blood Na^$and Cl^– concentrations are both severely lowered in drug-treatedanimals acclimated to low salinity, while they remain virtuallyunaffected in animals acclimated to high salinity, in whichthe animal is an ion conformer. High salinity acclimated crabstreated with acetazolamide do not survive transfer to low salinity,and mortality is related to a breakdown in the ion regulatorymechanism. Branchial CA most likely functions in the hydrationof respiratory CO₂ to H^$ and HCO₃^–, which serve as counterionsfor the active uptake of Na^$ and Cl^–, respectively. Interrestrial species the role of CA is unclear and merits furtherinvestigation.     

闽北闽粤栲天然林林隙物种数量特征及更新规律分析

以福建省顺昌县的闽粤栲〔Castanopsis fissa(Champ.ex Benth.)Rehd.et Wils.〕天然林为研究对象,根据林隙面积(A)划定4个等级(A<50 m2、50 m2≤A<100 m2、100 m2≤A<150 m2和150 m2≤A<200 m2)的样地,并以非林隙样地为对照,对林隙和非林隙的乔木层、灌木层和灌草层中的物种分布、组成及生长状况进行调查和统计;在此基础上,对林隙和非林隙中主要物种的数量特征和更新响应规律进行比较分析.结果表明:闽粤栲天然林林隙和非林隙的乔木层分别有54和35种植物,共有种28种;灌木层分别有61和37种植物,共有种29种;灌草层分别有72和49种植物,共有种37种.从乔木层和灌木层各种类的重要值及灌草层各种类的密度看,林隙和非林隙中的优势种类均为闽粤栲和木荷(Schima superba Gardn.et Champ.)等,且林隙和非林隙间各优势种类的重要值差异不明显,其中,闽粤栲的重要值和密度均位居第一.从林隙和非林隙间各优势种类的重要值差值看,林隙的主要优势种类(如闽粤栲和木荷等)对林隙更新响应不明显,而其他种类对林隙则有强烈或中等的正、负更新响应,且在不同林层间有差异.从平均更新密度看,林隙面积对各优势树种的更新有一定影响,其中,林隙面积在150~200 m2时闽粤栲和丝栗栲(Castanopsis fargesii Franch.)的平均更新密度最大,林隙面积在100~150 m2时米槠〔Castanopsis carlesii(Hemsl.)Hay.〕、木荷、青冈〔Cyclobalanopsis glauca(Thunb.)Oerst.〕和黄毛润楠(Machilus chrysotricha H.W.Li)的平均更新密度最大,但在不同面积林隙间各树种的平均更新密度无显著差异(P=0.867).研究结果说明:在闽粤栲天然林中,对林隙更新响应不明显的种类较易成为林分的优势种或建群种,但林隙面积对树种的更新密度没有明显影响;从林隙到林冠的发育过程中,闽粤栲始终处于该林分的优势地位.     

Water and Seed Survival

Between about –350 and –14 MPa the rate of lossof viability in orthodox seeds is a positive function of waterpotential. The relative effect of water potential has been analysedin an oily seed (lettuce) and a non-oily seed (barley) and foundto be more or less identical. The lower limit for the relationin various species coincides with a seed moisture content (wetbasis) between about 2 and 6%. Below this level there is littleor no improvement in longevity with reduction in moisture content.The upper limit coincides with moisture contents of between15 and 28%, depending on whether the seeds are oily or non-oily.A water potential of about –14 MPa is the threshold forrespiration which increases more-or-less linearly with increasein water potential above this level. Above this threshold, andproviding oxygen is available to sustain respiration, seed longevityincreases with increase in water potential except that, unlessthe seeds are dormant, germination may be initiated at a waterpotential of about –1·5 to –0·5 MPa.In the absence of oxygen there may be a slight further declinein longevity with increase in water potential above –14MPa before longevity reaches a minimum value Since they cannot be dried very much without immediate lossof viability, recalcitrant seeds survive longest in the presenceof oxygen at maximum water potential commensurate with preventinggermination. The threshold water potential for immediate lossof viability has not been determined for most species but itis probable that it is close to the water potential typicalof the permanent wilting point in these plants, say –2MPa Lactuca saliva L., lettuce, Hordeum oulgare L., barley, seed storage, moisture content, relative humidity, water potential, temperature, oxygen     

Small-scale distribution of a cnidarian population in the western Mediterranean

The neritic area of the coast of Catalonia (north–westMediterranean) has a continental shelf narrower in the northernhalf and broader in the southern half. This area is crossedfrom north to south by a coastal current whose intensity decreasesto the south. Both conditions, together with other local geographicaland hydrographical features, are thought to be the key factorsin determining the distribution of planktonic cnidarian assemblages,along two main variational axes: a north-south axis and a coast-opensea axis. Aiming to find support to this hypothesis, the planktoniccnidarians collected in two seasons of the year 1983 have beenstudied. The first season (April–May) corresponds to thehighest abundance and heterogeneity, and the second (September–October),to the epoch when the cnidarian population is lower, but constant,along the coastal area. In a global principal component analysisthe factor that best explains the group distribution in thearea is the coastal character, as given by the bottom depthof the sampling station. The number of individuals is greaternear the coast (due to the dominance of a euryhaline species,Muggiaea atlantica), but the species number increases towardsthe open sea (due to the addition of more oceanic species, suchas Narcomedusae and Trachymedusae and the effect of a permanenthydrographic front at the shelf-slope boundary). The secondfactor is the latitudinal axis. The northern half of the coastis under the influence of waters favouring a greater numberof species and individuals. On the contrary, the southern halfshows a less marked influence of the north–south current,their cnidarian assemblages being more constant over time. Althoughthe global cnidarian population follows this general pattern,the most abundant and frequent species (M.atlantica and Aglaurahemistoma) show a broad distribution over all the studied areabecause they are rather insensitive to hydrographical variations.     

An intermediate polymer in the assembly of clathrin baskets

Clathrin (8 S) is known to polymerize into two varieties of basket structures (150 S or 300 S) under the normal buffer conditions [100 mM 2-(N-morpholino)ethanesulfonic acid (Mes), pH 5.9-6.7] used for the isolation of coated vesicles. However, it is now observed that under very low salt conditions (2 mM Mes, pH 5.9), it forms a homogeneous species with a sedimentation coefficient of 27 S. Increasing the salt concentration to 50 mM Mes completely converts all the 27S species into 150S baskets. Sedimentation equilibrium data show that this 27S species has a molecular weight that is 6 times that of the clathrin protomer and is the result of highly cooperative reversible self-association of the 8S protomer. Light-scattering studies show that the stabilities of 27S species and baskets (150 S or 300 S) are comparable. Fluorescent labeling of sulfhydryl groups with N-(1-anilinonaphthalenyl)maleimide indicates that the conformation of clathrin in 27S species and baskets (150 S or 300 S) is similar. Trypsin digestion reveals that in the 27S species clathrin has a conformation differing from that in both the 8S species and baskets.     

Distribution and species-specific egg production of Pseudocalanus in the Gulf of Alaska

Pseudocalanus species are important contributors to the secondaryproduction of the northern hemisphere mid- to high-latitudeoceans. In the coastal Gulf of Alaska, Pseudocalanus are presentyear round and are represented by three species. In 2001, Pseudocalanusmimus was the dominant Pseudocalanus species on the shelf duringspring and summer, comprising 30–100% of the total, whilePseudocalanus newmani dominated in Prince William Sound (10–90%).Pseudocalanus minutus were only abundant in Prince William Soundduring early spring. Egg production (by number and volume) wasa function of female prosome length and decreased from springto summer; however, significant variability was attributableto regional influences that were independent of size. For thesame sized female, P. newmani produced more eggs per clutchthan P. mimus. Pseudocalanus mimus, however, tended to havea larger mean egg size than P. newmani. Consequently, clutchvolumes of the two species were indistinguishable. Pseudocalanusegg production rates (EPRs) (eggs female^–1 day^–1)were lower in July and August (ca. 2–4) than April andMay (ca. 1–9), but total egg production by the population(eggs day^–1) was nearly equivalent for the two time periodsdue to higher female concentrations in summer.     

Larval fish assemblages and geostrophic circulation in Bahia de La Paz and the surrounding southwestern region of the Gulf of California

We analyze spatial–temporal relationship between larvalfish assemblages and geostrophic surface flow in Bahíade La Paz and the neighboring Gulf of California (May, Julyand October 2001 and February 2002). The analysis of fish larvaedistribution in relation to geostrophic circulation and hydrographyis an innovative interdisciplinary approach for the understandingof fish larvae ecology. The Bray–Curtis Index definedtwo larval fish assemblages with spatial–temporal variations:coastal assemblage dominated by epipelagic coastal species (e.g.Sardinops caeruleus) and oceanic assemblages—oceanic andtransitional oceanic assemblages both dominated by mesopelagicspecies (e.g. Vinciguerria lucetia and Benthosema panamense)but with different larval abundance. The assemblage variationsappear to be related to water exchange between the bay and theGulf through the North Mouth. During July–October, thegeostrophic flow through the entrance is strong, and the oceanicassemblages spread in the whole bay, whereas during February–Maywhen the geostrophic transport is weak, the coastal assemblageis distributed over the whole bay. The strong summer–autumnwater interchange between bay and gulf is in agreement withthe annual evolution of the surface water properties insidethe bay, from high-salinity Gulf of California Water duringwinter–spring to fresher Tropical Surface Water duringsummer–autumn, when the highest species number was recorded.     

Estuarine diversity of tintinnids (planktonic ciliates)

In Chesapeake Bay, a large eutrophic and partially stratifiedestuary, we investigated diversity among tintinnids (Ciliophora,suborder Tintinninia) in September 1999. In contrast with thetypical estuarine pattern, tintinnid diversity was high andincreased with decreasing salinity from the mouth of the bayto the mid-bay region. Peak species numbers and diversity values[20–25 species, H' (ln) = 2.4–2.5] were found instations in the mesohaline (14–17     

Taxonomic studies on some cram negative polarly flagellated “hydrogen bacteria” and related species

Summary The properties of several named and unnamed strains of polarly flagellated hydrogen bacteria are described and compared with those of related autotrophic and non-autotrophic species. Two new species ofPseudomonas are described: one, a yellow-pigmented hydrogen bacterium,P. palleronii Davis; the other, a non-autotrophic, non-pigmented species,P. delafieldii Davis.     

What is the upper size limit for cosmopolitan distribution in free‐living microorganisms?

A comparison of testate amoebae assemblages from the Arctic and Antarctic (areas of similar habitat a maximum distance apart) is used to try and answer the question ‘What is the upper size limit for cosmopolitan distribution in free‐living microbes?’ Species restricted to either the Arctic or Antarctic exhibited sizes up to 230 μm while the largest cosmopolitan species was 135 μm in size. Comparison of the testate assemblages using a multivariate classificatory technique (TWINSPAN ) also suggested more restricted distribution for the larger species. There was a negative relationship between species size and number of sites at which it was recorded (r_s=?0.261, P < 0.05), with all the more widespread species having a size of below 100 μm. It is suggested that for testate amoebae cosmopolitan distributions become common below 100–150 μm. This suggests that most species of testate (indeed most free‐living microbes) have low species richness because of lack of opportunities for allopatric speciation as most are below 100 μm and so geographical isolation is unlikely. It is suggested that if this is correct, only the largest free‐living microbes (> 150 μm) are likely to be of conservation concern because of their smaller ranges. However, I point out that currently different studies are giving very different answers to the question, how ubiquitous and species rich are free‐living microbes? The subject requires further work to try and reconcile these different results.     

Separation of marine seston and density determination of marine diatoms by density gradient centrifugation

An attempt has been made to separate constituents of marineseston samples: inorganic material, detritus and the algal species,by density gradient centrifugation, without affecting the physiologicalstate of the algae. A relatively inert gradient material, consistingof Percoll, salt and sucrose, was composed. Since the densitiesof detritus and algae as well as those of different algal speciesoften overlapped, only 10 of the 100 samples processed in thecourse of the year showed a reasonable separation. However,an enrichment with respect to one or more species was oftenachieved. Densities of eleven species of marine diatoms andof one dinoflagellate have been determined at different timesof the year. For eight diatom species and for the dinoflagellatethe following specific density ranges were established: Bidduiphiaaurita: 1.18–1.23 g cm^–3, Biddulphia sinensis: 1.03–1.08g cm^–3, Cerataulina bergonii: 1.03–1.06 g cm^–3,Ditylum brightwellii: 1.07–1.13 g cm^–3, Rhizosoleniadelicatula: 1.04–1.09 g cm^–3, Skeletonema costatum:1.12–1.17 g cm^–3, Streptotheca thamensis: 1.04–1.10g cm^–3 , Thalassiosira rotula: 1.05–1.10 g cm^–3,Peridinium sp.: 1.08–1.12 g cm^–3. No seasonal variationin density was demonstrated. Gradients of different compositiondid not influence density measurements.     

LIFE HISTORIES, DENSITY AND BIOMASS IN A WOODLAND SNAIL COMMUNITY

Data, based on 8 monthly sets of random samples, are presentedon the life histories, densities and biomass of snail populationsin a mixed deciduous wood with moderately rich soil. Discus rotundatus, Oxychilus helveticus, O. cellarius and Trichiahispida have approximately annual life cycles, with rather littlepost-reproductive survival. Aegopinella nitiduta and Cochlodinalaminata take two years to reach maturity, and adults of thelatter may survive for several years. Breeding seasons are prolonged,but annual species peak in the autumn. Density does not vary much with season. Mean annual densityof all species combined (37.m^–2) is much lower than thoserecorded for similar woods elsewhere, but the estimate of meanannual standing crop (175 mg ashfree dry weight m^–2) doesnot show the same discrepancy. Comparisons reveal that the maincause of low density is the absence or rarity of several verysmall litter-dwelling species which have little effect on overallbiomass, and reasons for this are discussed. (Received 27 January 1981;     

Carbon flux by seasonal vertical migrant copepods is a small number

The abundant species of Calanus that dominate the mesozooplanktonof high North Atlantic latitudes overwinter at depths >500m, when the population loses 70–80% of its biomass bypredation and physiological stress. This represents an annualflux of carbon, obtained in the photic zone, into the interiorof the ocean of 274.5 mg C m^–2 year^–1, or 0.0018Gt C year^–1 for the North Atlantic. This is a small valuecompared with the flux of respiratory carbon by diel migrantsin warmer oceans and, when extrapolated to a global flux (0.012–0.018Gt C year^–1 over areas where winter migrations are importantis also small compared with computations of the global sinkingflux of particles through 200 m (1.6–3.8 Gt C year^–1or other relevant global carbon fluxes in the oceans.     

Annual Variation of Environmental Variables, Phytoplankton Species Composition and Photosynthetic Parameters in a Coastal Lagoon

Physical–chemical variables, phytoplankton biomass, speciescomposition and photosynthesis–irradiance (P-I) parameterswere analysed during 1 year in the Santo André Lagoon,SouthwestPortugal – a land-locked coastal ecosystem withtemporary connections with the sea. When the lagoon stayed closedthe observed phytoplankton blooms were mainly caused by Prorocentrumminimum, a potentially toxic dinoflagellate. It was dominantduring most of the year but the seawater inflow to the lagoontriggered a decrease in phytoplankton biomass and an abruptshift in species composition. The maximum photosynthetic rate(P_max) ranged from 2.0 to 22.5 mg C (mg chlorophyll a)^–1h^–1 and the light saturation index (I_k), ranged from 5.2to 335.0 µE m^–2 s^–1, with winter minima andsummer maxima. P_max and I_k were both positively correlated totemperature. Abundance ofP. minimum was associated with highnitrate concentrations whereas diatoms appear when ammonium,salinity and wind velocity are high. A mathematical model todescribe photosynthetic rate as a function of irradiance andtemperature [P (I, t)] was applied to the samples in which P.minimum was the dominant species