A 91-year record of seasonal and interannual variability of diatoms from laminated sediments in Saanich Inlet, British Columbia

Diatom seasonal succession and interannual variability werestudied using laminated sediments from Saanich Inlet, BritishColumbia, for the years 1900–1991. Frozen sediment coresallowed fine-scale sampling of laminae for each year. Thus,three ‘seasons’ for each year were identified basedon species composition. Thalassiosira species were indicatorsof spring deposition. Skeletonema costatum was abundant in samplesfollowing Thalassiosira, probably deposited in late spring andsummer. Rhizosolenia sp. was most abundant in fall/winter samples.Diatom stratigraphies were related to sea surface temperature,salinity, sea level and the Pacific North American Index (PNA)using canonical correspondence analysis (CCA). CCA showed thatspecies of a particular season generally had optima for temperatureand salinity characteristic of that time. Interannual changesin diatom species composition and abundance were most prevalentin the decades 1920–1940, with the exception of S.costatumwhich showed cyclic changes in abundance. Skeletonema was moreabundant during periods of cool temperatures, while littoraldiatoms were more abundant during times of heavy winter rains.Sea level was an important variable in CCA and while its relationshipto diatoms is not clear, it may be related to variations innutrient supply to diatoms in surface waters.     

Observations on the Biology of Fomes annosus, with Particular Reference to East Anglian Pine Plantations: II. Spore Production, Stump Infection, and Saprophytic Activity in Stumps

F. annosus produces conidia abundantly in culture but rarelyunder natural conditions. Sporophorea are formed on stumps anddying trees throughout the year provided that the humidity issufficiently high. Spore discharge in the plantations may occurat any time of year, but slowa down or ceases during very dryweather. It takes place at low temperatures, ceasing only whensporophores freeze. In the laboratory, F. annosus basidiospores germinate in relativehumidity exceeding 92 per cent. on freshly cut, unsterilizedpine wood. Viability is lost rapidly in light at temperaturesabove 15°C. Under humid conditions F. annosus spores will infect freshlycut pine stumps. There is evidence that spores of F. annosus washed down intosoil remain viable for at least a short period and that stumpscovered with soil are infected from this source. F. annosusspores can infect stumps for only a few weeks after felling,colonization after a longer interval probably beingprevdntedby competing fungi. In stumps inoculated with a mixed suspensionof F. annosus and Peniophora gigantea spores, Fomes at firstcolonized the wood but was soon replaced by P. gigantea. Otheraspects of competition are discussed. The incidence of natural infection in stumps and the factorsaffecting it are discussed Growth rates of F. annosus on malt agar and in lengths of pineroot are given. The fungus grows in stump roots at about 1 m.per year, and so closely approaches adjacent trees within ayear of thinning the plantation: In large stumps, F. annosusmay survive 15 or even 30 years after felling. Data are givenwhich suggest that the infective capacity of stumps containingF. annosus is greater in alkaline than in acid mils, while replacementby other fungi is slower. Competition of F. annosus with other fungi during colonizationof stumps is discussed. The parasite can grow along roots alreadyoccupied by certain fungi but not along roots containing others.The probable course of succession in stumps rotted by F. annousis described.     

Dispersion characteristics of two planktonic diatoms

Not all phyloplankton behave as ideal water tracers. Longitudinaldispersion experiments were conducted in a large flume withseawater of constant depth and velocity. The transport of thepassive, fluorescent tracer, Rhodamine B dye, was compared withunialgal cultures of a large, fast-sinking diatom (Odontellachinensis) and a small, slow-sinking diatom (Skeletonema costatum).Horizontal dispersion rates, proportional to variance per distance,were linear for the dye and Skeletonema but nonlinear for Odontella.Results are explained by the interaction of Odontella sinkingand advection. Longitudinal dispersion coefficients for thedye and Skeletonema were between 60–80 cm² s^–1 andas high as 280 cm² s^–1 for Odontella. This may have implicationsfor nutrient uptake in natural phytoplankton populations.     

Corbicula (Bivalvia: Sphaeriacea) vs. Indigenous Mussels (Bivalvia: Unionacea) in U.S. Rivers: A Hard Case for Interspecific Competition?

At a time when populations of indigenous river mussels havebeen dwindling and/or disappearing, the introduced Asian clam,Corbicula, has spread through many U.S. rivers from Californiato Florida. In the Arkansas River Navigation System, a heavilymanaged waterway, Corbicula presently has a different "competitive"presence than it does in the relatively unmanaged Buffalo Riverin Arkansas. Comparative studies of both Corbicula and indigenousbivalved mollusks reveal biological bases for the contrastingkinds of benthic faunal change. There are ecologically relevant,distinctive differences between the two kinds of animals: inmantle/shell and mantle/gill apparatus, in the reproductivecomplex and neuroanatomy, and in spawning and locomotor behaviors.It is argued that the conservative molluscan characteristicsof Corbicula enable it to function in an exclusive, "contradictory"role with indigenous bivalves in a heavily managed waterway,and in a "contrary" competitive role elsewhere. Rationale ispresented for incorporating organismic evaluation into studiesof competition between distantly related taxa.     

Size-fractionated phytoplankton carboxylase activities in the Indian sector of the Southern Ocean

During the ANTARES 3 cruise in the Indian sector of the SouthernOcean in October–November 1995, the surface waters ofKerguelen Islands plume, and the surface and deeper waters (30–60m) along a transect on 62°E from 48°36'S to the iceedge (58°50'S), were sampled. The phytoplankton communitywas size-fractionated (2 µm) and cell numbers, chlorophyllbiomass and carbon assimilation, through Rubisco and ß-carboxylaseactivities, were characterized. The highest contribution of<2 µm cells to total biomass and total Rubisco activitywas reported in the waters of the Permanent Open Ocean Zone(POOZ) located between 52°S and 55°S along 62°E.In this zone, the picophytoplankton contributed from 26 to 50%of the total chlorophyll (a + b + c) with an average of 0.09± 0.02 µg Chl l^–1 for <2 µm cells.Picophytoplankton also contributed 36 to 64% of the total Rubiscoactivity, with an average of 0.80 ± 0.30 mg C mg Chla^–1 h^–1 for <2 µm cells. The picophytoplanktoncells had a higher ß-carboxylase activity than largercells >2 µm. The mixotrophic capacity of these smallcells is proposed. From sampling stations of the Kerguelen plume,a relationship was observed between the Rubisco activity perpicophytoplankton cell and apparent cell size, which variedwith the sampled water masses. Moreover, a depth-dependent photoperiodicityof Rubisco activity per cell for <2 µm phytoplanktonwas observed during the day/night cycle in the POOZ. In thenear ice zone, a physiological change in picophytoplankton cellsfavouring phosphoenolpyruvate carboxykinase (PEPCK) activitywas reported. A species succession, or an adaptation to unfavourableenvironmental conditions such as low temperature and/or availableirradiance levels, may have provoked this change. The high contributionof picophytoplankton to the total biomass, and its high CO₂fixation capacity via autotrophy and mixotrophy, emphasize thestrong regeneration of organic materials in the euphotic layerin the Southern Ocean.     

Selection and control of Deborah numbers in plankton ecology

The Deborah number (De) is widely used to characterize processestaking place in deforming continua. De=(the time scale of aprocess)/(the time scale of deformation). When De >>lthe process thus takes place in a functionally fluid medium,but when De <<1 the regime is functionally solid. De hasbeen used to refine concepts in three pelagic processes. Dispersionof dividing cells may be characterized by De, and may be regulatedby means of secretions. Dispersion of microzones by diffusionand shear is characterized. The characteristic time of microzonesis shown to depend on the concentration. Because microzonessmear Out along the shear, to prevent nutrient-seekers and predatorsusing them as scent trails, organisms may convolute their microzonesby swimming, particularly across the shear. In a predator-preymodel, it has been shown that when De, (shear rate) (time takento swim radius of detection sphere), >2.6, not all the perceivedprey is accessible. More economical hunting strategies and thoseallowing access to more of the perceived prey, require bettersensory and navigational abilities. When De >2.6, the predatorwill perceive a greater flux of accessible prey when it swimsacross the shear than when it swims in the other two dimensions.De may help to understand many more biological processes indeforming media.     

Structure and Function of Transfer Cells in the Sporophyte Haustorium of Funaria hygrometrica Hedw: III. TRANSLOCATION OF ASSIMILATE INTO THE ATTACHED SPOROPHYTE AND ALONG THE SETA OF ATTACHED AND EXCISED SPOROPHYTES

Translocation of products of photosynthesis from gametophyteto sporophyte was examined in the moss Funaria hygrometricaHedw., as an adjunct to companion studies on the ultrastructureof the sporophyte haustorium and its capacity for absorptionof sugars in vitro. Labelled products derived from gametophyticphotosynthesis are transported to the sporophyte at an approximatelylinear rate for up to 12 h after a pulse treatment with ¹⁴CO₂.Large sporophytes receive label at a greater rate than smallerones. Transport is inhibited under conditions of water stress,and by lack of light, though darkening the sporophyte alonehas no effect. Movement of label from the haustorium along theseta occurs at a velocity of 1–3 mm h^–1, and issimilar to the onward movement of label derived from [³H]glucosesupplied to the haustorium in vitro.     

Immunological Studies on the Tuber-bearing Solanums: II. Relationships of the North American Species

Investigations using the Ouchtlerlony double-diffusion techniqueand immuno-electrophoretic analysis showed a much greater numberand diversity of antigens amongst the North American speciesof Solomon than had been found previously amongst the SouthAmerican ones. Double diffusion against antisera to S. tuberosum,S. acaule, S. iopetalum, S. bulbocastanum, and S. cardiophyllumsubsp. ehrenbergii, showed a difference between the speciesin series Bulbocastana and Pinnati-secta, and those in seriesLongipedicellata and Demissa. This technique did not providemuch information on the similarities or differences betweenthe species within these two groups. However, immuno-electrophoreticanalysis of the same species with the antisera to S. bulbocastanumand to S. iopetalum gave results which were easier to analyse,and provided much greater resolution of the individual species. At least one identical antigen was found in all the speciesstudied. Some antigens were consistently present in all speciesin certain series, while others had no apparent significancein their occurrence. Three fast-moving antigens were found tohave different, but characteristic, relative mobilities in differentspecies in the series Bulbocastana and Pinnatisecta. The relativemobilities of these three components were similar in the twosubspecies of S. cardiopkyllum and in S. sam-budnum which isconsidered to be a hybrid of subsp. ehrenbergii with S. pinnatisectum. A separate study on S. moreUiforme and S. clarum emphasizedthe distinctness of S. moreUiforme from all other potatoes,but indicated that S. clarum was more closely related to S.bulbocastanum and subsp. ehrenbergii than to S. tuberosum. With antisera to S. tuberosum and S. iopetalum on the one hand,and to S. bulbocastanum on the other, extracts of S. polyadeniumwere found to react more strongly than the species in seriesBulbocastana and Pinnatisecta with the first two antisera, andmore strongly than those in Longipedicellata and Demissa withthe other antiserum. This indicated that S. polyadenium hadsome of the group-specific antigens from both groups, and therefore,that it may be in some intermediate position between these twomajor groups of species. Problems of evolutionary relationship between Mexican speciesand series are discussed in the light of serological, morphological,arid cytogenetical evidence.     

Abundance, breeding and temporal size distribution of the chaetognath Sagitta setosa in the Kattegat

During a hydrographical survey in the northern Kattegat, 1975to 1977, vertical plankton hauls were taken monthly at fourstations between Göteborg and Frederikshavn. Hydrographicalparameters were measured at 10 stations along the transect.Sagitta setosa J. Mailer was by far the most dominant chaetognath(99% of individuals). Sagitta elegans Verrill and Eukrohniahamata Möbius occurred simultaneously with inflowing highsaline water during autumn and winter. The transport of S. setosaby currents was an important factor influencing the abundancesand the breeding period in the Kattegat. The abundance peakin 1977 was only one fifth of that found in 1975. The startand the duration of the breeding period (defined as presenceof stage 1 individuals <3 mm) varied between the three years.Breeding occurred between the middle of July and December witha peak in August and September. Changes in size distributionwere small during winter and spring, possibly due to low temperatures.S. setosa has probably a life span of one year in the Kattegat.Some earlier results regarding the number of breeding periodsof S. setosa per year are questioned. It is proposed that thenumber of generations per year of S. setosa and the start andthe duration of the breeding period(s) in western European watersshould be regarded as an open question until further informationis available.     

The Influence of the Rht1 and Rht2 Alleles on the Growth of Wheat Stems and Ears

A field experiment was carried out with a set of near-isogenicspring wheat lines (cv. Triple Dirk) to determine the influenceof the Rht₁ and Rht₂ alleles on the partitioning of dry matterbetween the developing stem and the ear. Each line was sampledtwice weekly and dissected into its component above-ground parts.The rate of change of the dry mass of the individual plant organswas expressed as a proportion of the rate of change of the totalplant dry mass. This ratio was used to assess the relative sinkstrengths of the stem and ear during crop growth. The Rht₁ andRht₂ alleles reduced plant height, but increased grain yield.The greater yield was achieved through a greater grain numberper ear in the Rhtl line, a greater ear number per plant inthe Rht₂ line, and a greater allocation of assimilate to thedeveloping ear than to the developing stem in both Rht lines,particularly at the time of maximum stem growth (17 d beforeanthesis). From the earliest stages of detectable ear growthuntil anthesis, the ear masses per unit area of the Rht₁ andRht₂ lines exceeded that of Triple Dirk (Rht). It was not possibleto determine whether the Rht₁ and Rht₂ alleles were directlyresponsible for increasing grain number per ear and ear numberper plant, respectively, since the increase in these componentsof yield could equally be explained by a greater partitioningof assimilate to developing ears and tillers caused simply bya reduction in plant height. Triticum aestivum L., wheat Rht genes, stem and ear development, dry matter partitioning, allocation ratio     

Variation in hatching success and egg production of Eurytemora affinis (Calanoida, Copepoda) from the Gulf of Bothnia, Baltic Sea, in relation to abundance and clonal differences of diatoms

We monitored the hatching frequencies and clutch sizes of Eurytemoraaffinis, and environmental variables in the Gulf of Bothnia,between May and October 2003. We tested the hypothesis thatthe hatching frequency of the copepod would be negatively affectedduring time periods with high diatom concentrations. Resultsfrom two stations showed significant differences between thedifferent sampling occasions, with the lowest observed hatchingfrequency during the spring diatom bloom. The reverse was truefor clutch size, with the highest average egg number duringthe diatom bloom. These results were not correlated to ambienttemperature, salinity or chlorophyll a (Chl a). In a separatelaboratory experiment, nine different local clones of the diatomSkeletonema costatum were used as food for adult E. affinisfemales, in order to screen for possible differences in toxicitywithin the Skeletonema community. The resulting average copepodhatching frequency varied between 5 and 75% for the differentclones, indicating that there can be large within-species variationin the toxic properties of diatoms. The significance of suchvariations in natural communities remains to be tested in futurestudies.     

Utility of mitochondrial‐encoded cytochrome c oxidase I gene for phylogenetic analysis and species identification of the planktonic diatom genus Skeletonema

Small subunit (SSU) and large subunit (LSU) rDNA sequences have been commonly used to delineate the taxonomy and biogeography of the planktonic diatom genus Skeletonema, but the genes occur as multiple copies and are therefore not suitable for barcoding purposes. Here, we analyzed phylogenetic relationships of Skeletonema using the mitochondrial‐encoded cytochrome c oxidase I gene (cox1), as well as partial LSU rDNA (D1–D3) and SSU rDNA, to identify the factors that define species and to evaluate the utility of these three markers for this taxon. Twelve Skeletonema species were divided into six clades, I–VI, each of which comprised the same species by the three markers: clades I (S. japonicum, S. grethae, S. pseudocostatum, and S. tropicum), II (S. menzelii), III (S. dohrnii and S. marinoi), IV (S. costatum, S. potamos, and S. subsalsum), V (S. grevillei), and VI (S. ardens). However, the branching order among these clades was incongruent among the markers. In clade III, six S. marinoi strains had identical cox1 sequences. These S. marinoi strains branched along with S. dohrnii, except for strains from the Gulf of Naples, with high support in cox1. Species delimitation between S. dohrnii and S. marinoi was therefore not supported. In clade IV, S. costatum and S. subsalsum were robustly clustered, with S. potamos as a sister clade in the cox1 tree, not in the LSU and SSU trees. In clade II, cox1 also confirmed that S. menzelii includes three subclades potentially distinguishable from each other by morphological features. Cox1 proved to be the most useful marker for the identification of Skeletonema species because it gave a tree with highly supported clades, has sufficient variation within and among species, encodes a protein in a single copy, and requires relatively few primers.     

Vegetative Anatomy of Uncinia (Cyperaceae)

The vegetative anatomy of 18 (19) Uncinia spp. (Cyperaceae-Cariceae)including representatives of most taxonomic subdivisions wasstudied to determine the range of variation in certain anatomicaland morphological characters of the vegetative organs withinthe genus. The two South American species U. erinacea and U. kingii differfrom all others, the former in having a closed cylinder of sclerenchymain the culm, and the latter a grooved culm. The three tall SouthAmerican spp., U. brevicaulis, U. hamata, and U. phleoides var.trichocarpa, are characterized by adaxial intercostal fibrestrands in the leaves, and in this respect show affinities withtall New Zealand species, U. sinclairii and U. uncinata. Thelast species does not have the intercostal strands. The muchsmaller U. tenuis from S. America resembles, in the size andshape of transverse sections of leaf and culm, a group of speciesfrom New Zealand comprising U. angustifolia, U. egmontiana,and U. rupestris. To these could be added U. banksii, U. hookeri,and perhaps also U. tenella, although the last two spp. exhibitsome distinctive characters in the transverse section of theleaf and also in the leaf epidermis in surface view. No exactcounterpart to the Australian and New Zealand spp. U. divaricata,U. riparia, U. rubra and U. scabra was found amongst the S.American material. This group of spp. is distinctive, for example,because of the triangular or irregularly triangular shape oftransverse sections of the culm and the large amount of sclerenchymain transverse sections of the leaf. The range of structural variation appears to be particularlywide in the S. American spp., which represent two extreme typesin the shape of the leaf in transverse section. The other talland small species have their respective counterparts in eacharea, although they are more profusely represented in New Zealandthan in America, and therefore show a correspondingly greaterrange of structure.     

A Method of Raising Clones of the Hydroid Phialidium gregarium (A. Agassiz, 1862) in the Laboratory

The hydroid Phialidium gregarium can be successfully culturedto sexual maturity at any time of the year and maintained foryears in a closed system marine aquarium. Artificial sea waterwas used in place of natural sea water and was renewed by one-quarterof its volume each 4 weeks, Freshly hatched Artemia naupliiwere used as the sole food source. Methods for obtaining coloniesof a single genotype from planulae are described. Subculturingpieces from parental stock is accomplished by a new method.A new technique for removing hydroid colonies from their substratefor histological study is described.     

PHOSPHOGLUCOMUTASE ALLOZYME EVIDENCE FOR AN OUTCROSSING MODE OF REPRODUCTION IN THE HERMAPHRODITIC BROODING BIVALVE MYSELLA TUMIDA (GALEOMMATACEA)

Allozyme variation of a Mysella tumida population in PatriciaBay, B.C., Canada was investigated at the phosphoglucomutase(PGM) locus. Seven alleles were detected. The observed frequencyof allelic combinations did not differ significantly from randommating expectations (0.25 < P < 0.50), however, heterozygositylevels were slightly greater than expected (Selander's D = 0.022).These results, together with previous work on the M. tumidareproductive cycle, indicate that natural populations of thisbivalve rarely, if ever, self-fertilize. ^*Present Address: Friday Harbor Laboratories, University ofWashington, Friday Harbor, WA 98250, U.S.A. ^**Present Address: Museum of Zoology, University of Michigan,Ann Arbor, M1 48109, U.S.A. (Received 30 December 1986;     

Analysis of Growth and Yield of Winter and Spring Wheats

In a field experiment to investigate the physiological causesof variation in yield between autumn- and spring-sown wheatand between old and new varieties, the grain yields of the winterwheats were 3-15 per cent, greater than of the spring ones andthe new varieties Cappelle-Desprez and Jufy I yielded 40-70per cent, more than Squarehead's Master and Atle. Nitrogen fertilizerincreased the yields of Cappelle-Desprez and Jufy I more thanof Atle, and decreased the yield of Squarehead's Master by makingit lodge. Until ear emergence the winter varieties had greater leaf-areaindices (L) and dry weights, but smaller net assimilation rates(E), than the spring varieties. Square-head's Master had greaterL but smaller E, and similar dry weight to Cappelle-Desprez.Jufy I had similar E to Atlc, but greater L and dry weight.Nitrogen increased L and dry weight, but decreased E. All thedifferences in E between varieties and nitrogen treatments couldbe explained by the opposite effects on L, that is to say, thedifferences in E were caused by variation in mutual shadingarising from the differences in L and not by changes in leafphysiology. L of winter wheat reached its maximum at the end of May, butL of spring wheat continued to increase until ear emergence.Afterwards Ldecreased more rapidly for winter than for springwheat, so that eventually spring wheat had the greater L. Thesedifferences in the time changes of L partially compensated forthe shorter growth period of spring wheat, and tended to equalizethe grain yield from winter and spring sowings. After ear emergence total dry weight of winter varieties continuedto be greater than of spring ones, but the difference in dryweight of ears was much smaller because ear: shoot dry-weightratio was greater for the spring varieties. Total dry weight,ear dry weight and ear: shoot ratio were all greater in thenew than in the old varieties. Leaf area duration (D) afterear emergence was slightly greater for the winter than for thespring varieties and similar for old and new. The apparent efficiencyof this leaf area in grain production, measured by the grainleaf ratio (ratio of grain dry weight to D), was similar forwinter and spring varieties but greater for new than for old.This suggests that Cappelle-Desprez and Jufy I have higher grainyields because their ears photosynthesize more than do the earsof Squarehead's Master and Atle. Before ear emergence winter varieties had more shoots than springones, and old varieties more than new. After ear emergence therewere only small differences in numbers of ears; percentage survivalwas greater for spring than for winter and for new than forold varieties. Differences in dry weight between varieties were not causedby differences in nitrogen uptake.     

The role of thermal stratification on the population dynamics of Sagitta elegans Verrill in the western Irish Sea

Temperature and prey availability have a marked effect on thedevelopment and growth of Sagitta elegans. This study addressesthe effects of thermal stratification on the growth and sizeof adult S.elegans in the western Irish Sea. It shows that instratified waters, bottom water temperature had a greater effecton the development of mature adults than surface water temperature.Whilst the length of mature individuals caught in 1992 and 1994decreased with increasing temperature, they did not conformto the models of McLaren (1963) and Sameoto (1971), as the animalswere larger than predicted. The long breeding period found inthe stratified region, suggests that previous reports of oneor two generations per year in the western Irish Sea do notaccount for the likely mix of generations that occur from Februarythrough to September.     

Change in Size and Cell Number during the Development of Lateral Root Primordia in Zea mays L.

Increase in cell number, anlage volume and length have beeninvestigated during the overall period of lateral root primordiumdevelopment in excised primaries and in attached roots of Zeamays L. Each of these aspects of anlage growth was found toincrease more or less exponentially during the interval betweenprimordium initiation and subsequent emergence as a lateralin both batches of roots. Values were then determined for celldoubling time (Td), the size of the proliferative fraction (Pf),and for anlage volume (Tv) and length (Tt) doubling times duringthe overall period of primordium development and at intervalsduring this period in both the excised and attached roots. Thepattern of change which took place in Td, Tv, Tl and Pf duringlateral primordium development was found to be similar in bothbatches of roots. However, the overall period of anlage developmentwas shorter in the excised roots than in the attached ones.Moreover, when laterals grew out of the excised roots they didso with fewer cells than comparable laterals emerging from theattached roots. Zea mays L., maize, root primordia, lateral emergence, cell doubling time     

The Movement of Zinc through Excised Stems of Seedlings of Pinus radiata D. Don.

Radioactive Zn solns were drawn through 10 cm stem sectionsexcised from seedlings of P. radiata to determine the locationand quantity of ⁶⁵Zn remaining in the stems and the concn of⁶⁵Zn in the exudate. Zinc was removed from solns passing through the excised stemsby processes which appeared to be non-metabolic because coolingthe inflow solns did not decrease the proportion of Zn removedand non-specific because Ca competed with Zn for ‘exchangesites’. The formation of anionic or uncharged complexes between Zn andEDTA, or citrate resulted in more Zn passing through the excisedstems. Consistent with the greater stability of Zn-EDTA complexesmore Zn passed through stems treated with EDTA than with citrate.Decreasing the pH of solns containing Zn, Ca and potassium citrateincreased the amount of Zn deposited in the basal (inflow) endof the stems, probably by decreasing the amount of Zn boundto citrate. Increasing the conen of Zn in test solns containingZn, Ca and potassium citrate did not change the distributionof ⁶⁵Zn in the stems as the capacity of the stems to removeZn from soln was large enough to remove all the free Zn in allthe solns Pinus radiata D. Don, pine, zinc, movement, stems     

Some Thermal Requirements of Fiddler Crabs of the Temperate and Tropical Zones and Their Influence on Geographic Distribution

Thermal stress is one environmental parameter that has greatlyinfluenced the migration of crustaceans from the sea to land.Since a greater number of species of terrestrial crabs are foundin the tropics than in the temperate zone, comparative studiesof the influence of temperature on latitudinally separated populationswere undertaken. Two tropical species, U. rapax and U. thayeri,may occur as far north as St. Augustine, Florida, or, followinga severe winter, may be rare north of Cape Kennedy. The lethaleffect of the low temperatures recorded during one severe winter(1957–58) is supported by laboratory studies in whichLD₅₀, deaths occurred in 4.5 days at 10°C for U. rapax acclimatedto 18°C. The experiment demonstrates that U. rapax cannotacclimate to and survive low temperatures. This contrasts markedlywith the situation in semi-terrestrial crabs of the temperatezone, which are able to acclimate to cold. The distribution of Uca around Cape Cod Bay correlates wellwith the coastal hydrographic thermal gradient and supportsPassano's suggestion that temperatures below 20° may belimiting as they inhibit proecdysis in U. pugnax. Such an inhibitionis found experimentally in U. pugilator and in the tropicalspecies, U. rapax. It is hypothesized that a shift in the thermodynamicsof the processes underlying molting has not occurred in Ucaof the temperate zone. The paucity of semi-terrestrial Brachyurain the temperate zone may be due to the failure of many speciesto evolve capacity-adaptations to carry out all requisite lifeprocesses at temperatures below 20°, or the resistance-adaptationsnecessary to survive the low temperatures of winter.