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  • 1
    Electronic Resource
    Electronic Resource
    Coexistence, size overlap and population regulation in tidal vs. non-tidal Palaemon prawns (1982)
    Springer
    Oecologia 54 (1982), S. 1-7 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The effect of increased habitat heterogeneity in tidal areas on coexistence between Palaemon prawns was studied at eight sites along the European Atlantic coast. Two species which are sympatric in non-tidal areas, Palaemon adspersus Rathke and P. squilla (L.) are largely allopatric in tidal areas, and the sympatric size difference decreases in allopatry. In tidal areas the smaller species, P. squilla, is restricted to brown algal belts and rockpools. A third species, P. serratus (Pennant), larger than the others, occurs under oceanic salinities in subtidal brown algal belts and there has forced P. squilla to restrict its habitat distribution to adjacent intertidal rockpools. At estuarine salinities, however, P. squilla also inhabits the brown algal belts. A larger diel variation in stomach fullness index in P. squilla than in P. adspersus persists in non-tidal areas. Abiotic factors probably restrict the two largest species, viz. P. adspersus and P. serratus, to subtidal environments; these species are sensitive to the extremes in salinity, temperature or O2 levels characteristic of the intertidal zone. Competition and/or predation probably relegates P. squilla to the intertidal zone. In non-tidal areas, where this zone is reduced, P. squilla increases its niche width and coexists with P. adspersus, and the size differentiation associated with sympatry may reduce interspecific competition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00541099
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  • 2
    Electronic Resource
    Electronic Resource
    Biotic and abiotic factors determining the distribution of two prawn species: Palaemon adspersus and P. squilla (1981)
    Springer
    Oecologia 49 (1981), S. 300-304 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The reasons behind the absence of the prawn Palaemon adspersus and the presence of P. squilla in rockpools and on bare sand bottoms were studied. Some maximal abundances in different habitats are given. Introduction experiments into natural and artificial rockpools and measurements of tolerance towards low oxygen levels showed that nocturnal hypoxia excluded P. adspersus which was significantly more sensitive to oxygen depletion. Respiration rates measured by the closed-bottle method showed no interspecific difference. On bare sand bottoms P. aspersus was probably excluded by predators, since predator exclusion experiments in cages and predator inclusion experiments in containers showed that P. adaspersus was more vulnerable to predation than P. squilla. The costs for being able to cope with a wide array of habitat in P. squilla are probably balanced by the benefits of access to habitats such as intertidal rockpools, very shallow bottoms and deeper sand bottoms. Tolerance towards abiotic factors extends its habitat range upwards into shallower waters, and tolerance towards biotic factors, i.e. predation, extends it downwards.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00347589
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  • 3
    Electronic Resource
    Electronic Resource
    Reproductive ecology of five pipefish species in one eelgrass meadow (1995)
    Springer
    Environmental biology of fishes 44 (1995), S. 347-361 
    Details
    ISSN: 1573-5133
    Keywords: Syngnathidae ; Sex differences ; Entelurus aequoreus ; Nerophis ophidion ; Syngnathus ; Pisces
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Synopsis Synopsis Pipefishes have rarely been watched in the wild and have never before been followed in their common seagrass habitats. This study explores the reproductive ecology of five species of pipefishes living in a Swedish eelgrass meadow during parts of four breeding seasons, tagging four of the species. Pipefish are remarkable for their specialised paternal care: only males aerate, osmoregulate and nourish the developing embryos. Two of the species (Entelurus aequoreus andNerophis ophidion) have simple ventral gluing of eggs on the trunk while three species (Syngnathus acus, S. rostellatus andS. typhle) have fully enclosed brood pouches on their tails. Males of the former species receive eggs from one female while males of the genusSyngnathus receive partial clutches from several females. Sex ratios of adults on the site differed from equal to male-biased to female-biased, according to species.S. typhle were most numerous and were resighted most often. They were present throughout the breeding season whereas there were temporal shifts in the presence of the other species on the meadow and in some sex ratios. Most species occurred in the deeper, denser part of the meadow but there was some habitat separation by species and sex. All species tended to stay low in the eelgrass, primarily coming up above the eelgrass to display and mate. No species showed site fidelity either to a home range or to the meadow, withE. aequoreus adults spending least time on the meadow. Sexual size dimorphism differed: males were larger inS. rostellatus, the same size inS acus and smaller in the other species. Although the species overlap in habitat requirements and breeding season, the only observed interspecific interactions were abortive courtships betweenSyngnathus species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00008250
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  • 4
    Electronic Resource
    Electronic Resource
    Alignment of flexible molecules at their receptor site using 3D descriptors and Hi-PCA (1997)
    Springer
    Journal of computer aided molecular design 11 (1997), S. 601-612 
    Details
    ISSN: 1573-4951
    Keywords: Molecular alignment ; Flexible alignment ; Grid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Three categories of molecular flexibility are defined. A novel method ofaligning partly flexible molecules with each other is described. The bindingmode of one of these molecules to its receptor site was already well knownfrom previous crystallographic studies, and this known binding mode was usedto predict the binding mode of the other molecules at their receptor. Thepredictions were checked by comparison with previous observations, and werecorrect. Two novel methods were combined in this research. It was necessaryto take account of the conformational changes which occur when each ligandmolecule binds to the protein, and a new release of programme Grid was usedfor this. It was also necessary to analyse the Grid results in order todistinguish the role of each chemical group at the receptor site. This wasdone by applying hierarchical principal component analysis (Hi-PCA) methodsto the descriptors obtained from Grid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007983320854
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  • 5
    Electronic Resource
    Electronic Resource
    Interactive variable selection (IVS) for PLS. Part II: Chemical applications (1995)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 331-342 
    Details
    ISSN: 0886-9383
    Keywords: partial least squares (PLS) ; variable selection ; IVS-PLS ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: With the aim of developing PLS models with improved predictive properties, an interactive variable selection (IVS) approach for PLS regression was introduced in Part I of this series. IVS-PLS is based on a dimension-wise selective removal of single elements in the PLS weight vector w. IVS uses cross-validation (CV) as a guiding tool. The present paper illustrates the use of IVS-PLS on both simulated data and real examples from chemistry. In the first example, spectrophotometric data were simulated according to an experimental design. The objective was to see how IVS-PLS was influenced by different levels of noise in X and Y and by the number of predictor variables (K). The results of the modelling are shown as response surfaces. In addition, four real examples were modelled by the IVS-PLS technique. The real data sets were chosen to reflect different types of data from chemistry. For each example a comparison of ‘prediction error sum of squares’ (PRESS) between IVS-PLS and classical PLS is madeFor most of the examples containing many predictor variables IVS-PLS shows an improvement in predictive properties over classical PLS. Also, improvements for IVS-PLS2 (modelling of more than one y-variable) models were found. For data sets with a moderate number of variables the influence of the IVS method becomes less pronounced.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180090502
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  • 6
    Electronic Resource
    Electronic Resource
    To change or not to change sex: A comparison between twoOphryotrocha species (Polychaeta) (1991)
    Springer
    Evolutionary ecology 5 (1991), S. 128-135 
    Details
    ISSN: 1573-8477
    Keywords: Sex change ; sequential hermaphrodition ; size-advantage ; hypothesis ; gonochorism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The polychaeteOphryotrocha puerilis is a male-to-female sex-changer, whereasO. labronica has separate sexes throughout life. In other respects the two species are remarkably similar: they occur in the same habitat, they look the same, they eat the same things, and in someO. labronica populations sex-changers can actually be found. The size-advantage hypothesis predicts that inO. puerilis males should not benefit reproductively from a size increase as much as males inO. labronica: henceO. puerilis but notO. labronica males should change to the female sex at a certain size. I experimentally compared reproductive success at different body sizes between the two species. In isolated male-female pairs reproductive rate increased significantly with female body size but not with male body size, and this pattern was the same in both species. Hence male fecundityper se cannot account for the difference in reproductive type between the two species. In other experiments I investigated if larger males gained access to more females because they were superior competitors for mates or were preferred by females, compared to small males. InO. puerilis the combined effect of these two factors conferred no size advantage to the males, whereas inO. labronica larger males acquired more females than did smaller males. Hence interactions among males and females, in accordance with the size-advantage hypothesis, can explain why sex change is maintained inO. puerilis, and why separate sexes are maintained inO. labronica.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02270829
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  • 7
    Electronic Resource
    Electronic Resource
    Selective males and ardent females in pipefishes (1993)
    Springer
    Behavioral ecology and sociobiology 32 (1993), S. 331-336 
    Details
    ISSN: 1432-0762
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In the pipefishes Syngnathus typhle and Nerophis ophidion, males have been shown to limit female reproductive rate, and females to compete for access to males. Hence, these species fit the criteria for sex-role reversal. Males brood the eggs and provide the offspring with nutrients, oxygen and an osmoregulated environment. Moreover, in S. typhle both sexes prefer a larger mate when given a choice. Sexual selection theory predicts that males should be more “choosy” than females, and that was experimentally demonstrated in this study. We predicted that S. typhle males should be less eager to copulate than S. typhle females with an unattractive (i.e. small) mate. We measured eagerness as the time from the start of the experiment until copulation occurred. Males with unattractive partners took significantly longer to copulate than females with unattractive partners. Moreover, females invariably initiated the courtship dance, and resumed it quicker after copulation than did the males, again suggesting “reproductive hesitation” in males. Neither male nor female size per se was correlated with time until copulation. In N. ophidion, where we have previously shown that males prefer larger to smaller females, we found that females did not select males with regard to size. Our results are consistent both with earlier findings (males limit female reproduction and females compete for males) and with operational sex ratios in nature: in seven annual field samples in June, the numbers of S. typhle females with ripe eggs always significantly exceeded numbers of receptive males. Hence, the potential cost of being choosy in terms of lost matings is much higher in females than in males. In conclusion, S. typhle females were somewhat choosy, but less so than males, whereas N. ophidion females were not choosy at all.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00183788
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  • 8
    Electronic Resource
    Electronic Resource
    Operational sex ratios and behavioural sex differences in a pipefish population (1994)
    Springer
    Behavioral ecology and sociobiology 34 (1994), S. 142-435 
    Details
    ISSN: 1432-0762
    Keywords: Operational sex ratios ; Behavioural sex differences ; Pipefish ; Syngnathidae ; Sex role reversal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In the pipefish Syngnathus typhle, only males brood embryos in specially developed brood pouches, supplying oxygen and nutrients. Laboratory studies have shown that this elaborate paternal care has led to sex-role reversal in this species: males limit female reproductive rate, females are the primary competitors for mates and males exercise greater selectivity in accepting mates. In the first field study of this pipefish, we describe mating behaviour in the wild and test the hypothesis that temporal variations in the operational sex ratio (OSR) determine sex differences in mating behaviour. Our study comprised two reproductive seasons of two sequential mating periods each, the latter separated by a lengthy interval of male brooding. During mating periods, females displayed to all males without wandering and males moved about searching for females, without reacting to all females. The OSR was least female-biased (or even male-biased) at the onset of the breeding season, when most pipefish were simultaneously available to mate, but became strikingly female-biased as males' pouches were filled. The OSR remained substantially female-biased during the second mating period, because few males became available to remate at any one time. As hypothesised, female-biased OSRs resulted in more female-female meetings. As well, females were above the eelgrass more often than brooding males, thus exposing themselves to conspecifics and/ or predators. In the second year, males arrived earlier than females on the breeding site and male pregnancies were shorter, because of higher water temperatures, so rematings occurred earlier. Males met more often during that year than the previous one, but male competitive interactions were still not observed. The field results support laboratory studies and demonstrate that behaviours associated with female-female competition are more prominent when the OSR is more female-biased.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00167335
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  • 9
    Electronic Resource
    Electronic Resource
    Male limitation of female reproductive success in a pipefish: effects of body-size differences (1990)
    Springer
    Behavioral ecology and sociobiology 27 (1990), S. 129-133 
    Details
    ISSN: 1432-0762
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In the pipefish Syngnathus typhle, a species with exclusive male parental care, males limit female reproductive success because of their limited brood pouch space and long pregnancy. Sexual size dimorphism is absent in these 1-year-old animals but increases with age so that older females are larger than similarly aged males. Because fecundity is related to size in both sexes and increases more rapidly with body size in females than in males, the difference in growth increases female fecundity more, relative to male fecundity, as the fish get older. We therefore predicted that male limitation of female reproductive success is even more severe when all age classes are considered. To measure a female's maximum reproductive rate, she was provided with three males. Small 1-year-old females produced as many eggs, or produced eggs at the same rate, as a male of similar size could care for. Small females filled on average 1.06 males within the time span of one male pregnancy and actually produced on average 10 eggs fewer than needed to fill a similarly sized male. Large 2-year-old females, in contrast, produced on average a surplus of 149 eggs and filled 2.7 similarly sized males within the course of one pregnancy. The difference between females of the two size classes was highly significant. Males prefer to mate with larger females if given a choice. In nature sex ratios are equal, and males limit female reproductive success in the whole population. Therefore, small females are more severely constrained by mate availability than are larger females because males choose to mate with larger females.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00168456
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  • 10
    Electronic Resource
    Electronic Resource
    Operational sex ratios and behavioural sex differences in a pipefish population (1994)
    Springer
    Behavioral ecology and sociobiology 34 (1994), S. 435-442 
    Details
    ISSN: 1432-0762
    Keywords: Key words: Operational sex ratios ; Behavioural sex differences ; Pipefish ; Syngnathidae ; Sex role reversal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. In the pipefish Syngnathus typhle, only males brood embryos in specially developed brood pouches, supplying oxygen and nutrients. Laboratory studies have shown that this elaborate paternal care has led to sex-role reversal in this species: males limit female reproductive rate, females are the primary competitors for mates and males exercise greater selectivity in accepting mates. In the first field study of this pipefish, we describe mating behaviour in the wild and test the hypothesis that temporal variations in the operational sex ratio (OSR) determine sex differences in mating behaviour. Our study comprised two reproductive seasons of two sequential mating periods each, the latter separated by a lengthy interval of male brooding. During mating periods, females displayed to all males without wandering and males moved about searching for females, without reacting to all females. The OSR was least female-biased (or even male-biased) at the onset of the breeding season, when most pipefish were simultaneously available to mate, but became strikingly female-biased as males' pouches were filled. The OSR remained substantially female-biased during the second mating period, because few males became available to remate at any one time. As hypothesised, female-biased OSRs resulted in more female-female meetings. As well, females were above the eelgrass more often than brooding males, thus exposing themselves to conspecifics and/or predators. In the second year, males arrived earlier than females on the breeding site and male pregnancies were shorter, because of higher water temperatures, so rematings occurred earlier. Males met more often during that year than the previous one, but male competitive interactions were still not observed. The field results support laboratory studies and demonstrate that behaviours associated with female-female competition are more prominent when the OSR is more female-biased.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002650050060
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