Responses of larval dragonflies to conspecific and heterospecific predator cues

Abstract.  1. In cannibalistic populations, smaller individuals are subject to predation by larger conspecifics, and small individuals commonly alter their behaviour in response to cannibals. Little is known, however, about the underlying cues that trigger such responses and how the behavioural responses to conspecific cannibals differ from heterospecific predators.
2. This study tests which cues are used for the detection of conspecific predators in the larva of the dragonfly Plathemis lydia and how the behavioural response to cannibals differed from the response to heterospecific predators.
3. Individuals were exposed to chemical cues, visual cues, and a combination of both cues from conspecifics as well as no predator and heterospecific predator controls during which their activity and feeding rates were observed.
4. Individuals increased their activity, spatial movement and feeding behaviour in response to either visual or chemical cues from conspecific predators, which was opposite to responses displayed with cues from heterospecific predators. Interestingly, the responses to visual and chemical cues from conspecifics combined were weaker than to either cue in isolation and similar to the no cue control.
5. The results clearly indicate that individuals are able to use chemical and visual cues to detect even very subtle differences in phenotype of conspecific predators.
6. The opposite response in behaviour when exposed to conspecific cannibals vs. heterospecific predators suggests that the presence of cannibals will increase the mortality risk of small individuals due to heterospecific predation. This risk-enhancement is likely to have important consequences for the dynamics of predator–prey interactions.     

European phenological response to climate change matches the warming pattern

Global climate change impacts can already be tracked in many physical and biological systems; in particular, terrestrial ecosystems provide a consistent picture of observed changes. One of the preferred indicators is phenology, the science of natural recurring events, as their recorded dates provide a high-temporal resolution of ongoing changes. Thus, numerous analyses have demonstrated an earlier onset of spring events for mid and higher latitudes and a lengthening of the growing season. However, published single-site or single-species studies are particularly open to suspicion of being biased towards predominantly reporting climate change-induced impacts. No comprehensive study or meta-analysis has so far examined the possible lack of evidence for changes or shifts at sites where no temperature change is observed. We used an enormous systematic phenological network data set of more than 125 000 observational series of 542 plant and 19 animal species in 21 European countries (1971–2000). Our results showed that 78% of all leafing, flowering and fruiting records advanced (30% significantly) and only 3% were significantly delayed, whereas the signal of leaf colouring/fall is ambiguous. We conclude that previously published results of phenological changes were not biased by reporting or publication predisposition: the average advance of spring/summer was 2.5 days decade⁻¹ in Europe. Our analysis of 254 mean national time series undoubtedly demonstrates that species' phenology is responsive to temperature of the preceding months (mean advance of spring/summer by 2.5 days°C⁻¹, delay of leaf colouring and fall by 1.0 day°C⁻¹). The pattern of observed change in spring efficiently matches measured national warming across 19 European countries (correlation coefficient r =−0.69, P <0.001).     

K+Nutrition and Na+Toxicity: The Basis of Cellular K+/Na+Ratios

The capacity of plants to maintain a high cytosolic K⁺/Na⁺ratiois likely to be one of the key determinants of plant salt tolerance.Important progress has been made in recent years regarding theidentification and characterization of genes and transportersthat contribute to the cytosolic K⁺/Na⁺ratio. For K⁺uptake,K⁺efflux and K⁺translocation to the shoot, genes have been isolatedthat encode K⁺uptake and K⁺release ion channels and K⁺carriersthat are coupled to either a H⁺or Na⁺gradient. Although thepicture is less clear for the movement of Na⁺, one pathway,in the form of non-selective ion channels, is likely to playa role in Na⁺uptake, whereas Na⁺efflux and compartmentationare likely to be mediated by H⁺-coupled antiport. In addition,several proteins have been characterized that play prominentroles in the regulation of K⁺and/or Na⁺fluxes. In this BotanicalBriefing we will discuss the functions and interactions of thesegenes and transporters in the broader context of K⁺nutritionand Na⁺toxicity. Copyright 1999 Annals of Botany Company Salinty, K⁺/N⁺ratio, transporter, membrane.     

Experimental investigation of drought induced acidification in a rich fen soil

Intact rich fen soil cores with controlled water levels near thesurface were installed in an open greenhouse. To simulate short termsummer drought, water levels were lowered (20 cm) after two weeks inhalf of the cores (experimental cores) and remained near the surface inthe other half (blanks). After two more weeks, the water levels werebrought back to the surface in the experimental cores and remainedthere for another two weeks. In the blanks, reduction and alkalinizationof the top peat layer occurred. In the experimental soil cores oxidationand acidification started within one week after drawdown. An indicationfor a drought induced rise in soluble reactive phosphorus has beenfound. The velocity of the acidification process illustrates the dynamicnature of the hydrochemical conditions in fen soils during drought. Theprocesses controlling the acid/base status of rich fen, the effect ofdrought induced acidification on P availability and the significance forthe vegetation are discussed.     

Regulation of Microtubule Synthesis and Utilization during Early Embryonic Development of the Sea Urchin

Microtubules deployed during early development of the sea urchinembryo are derived both from a preexisting pool of subunitspresent in the egg and from microtubule protein subunits synthesizedin the embryo. Several aspects of microtubule protein synthesisand utilization are reviewed. Microtubule protein synthesisin early development utilizes oogenetic messenger RNA species.Translation of this mRNA is under regulation. Microtubule proteinsynthesis rises concomitantly with overall protein synthesisat fertilization, but rises at a relatively higher rate laterin cleavage stages. Microtubule protein labeled with [³H]-leucinein early development is incorporated into cilia, indicatingthat newly synthesized protein enters the pool of subunits usedin organelle assembly. The microtubule protein pool comprisesabout 1%of the soluble protein of the egg, and remains constantin size at least until the blastula stage. Direct pool sizeestimates are consistent with results of experiments on recruitmentof microtubule protein subunits into the mitotic apparatus andinto regenerating cilia. Soluble and particulate colchicinebinding fractions, which have been reported from several systems,appear to be present in sea urchin embryos. The possible roleof such fractions are discussed, as are aspects of the regulationof ciliary assembly.     

Tubulin and Microtubules in the Early Development of the Axolotl and Other Amphibia

SYNOPSIS. Unfertilized eggs of the axolotl, Ambystoma mexicanum,contain a pool of soluble tubulin accumulated during oogenesis.After initiation of cleavage the tubulin pool decreases somewhatand then remains constant through early development. Some propertiesof tubulin alter during development, but at least some of thesechanges are not due to changes in tubulin perse. However, thetubulin in axolotl oocytes, eggs, and embryos differs in someelectrophoretic properties from tubulin in adult axolotl brainand testis. Equivalent differences were observed in Necturusmaculosus tubulins. Heterogeneity of axolotl tubulins was confirmedby peptide mapping: Different patterns of peptides were formedby specific limited proteolysis of soluble tubulin from eggsand testis. The heterogeneity was more marked in the a thanin the ß subunit. Mobilization of soluble tubulininto the mitotic apparatus depends on the functioning of microtubuleorganizing centers after activation of the egg at fertilization.In eggs of the nc mutant axolotl there is a lesion in some stepof activation, one effect of which is that even though the eggscontain an essentially normal pool of tubulin, microtubulesfail to assemble, no mitotic apparatus forms, and embryonicdevelopment does not begin. These eggs can be partially correctedby injection of heterologous microtubule fragments, which elicitthe mobilization of nc tubulin into arrays of microtubules,followed by initiation of cleavage and development to a partialblastula stage. The results of these experiments are discussedin comparison with other reports in the literature about thefunction of microtubule organizing centers during amphibianegg development.     

Grass Leaf Elongation Rate as a Function of Developmental Stage and Temperature: Morphological Analysis and Modelling

Elongation of successive leaves was measured following defoliationof tall fescue plants in controlled environments. Measurementswere made under constant temperatures of 24 °C and 14 °C,and after temperature changes from 24 to 14 °C andvice versa.A morphological analysis of the growing leaf was made from thetime it was 1 mm long until it was fully elongated. The timeelapsed from initiation until the leaf was 1 mm long was estimated.Young leaves less than 1.5 mm long elongated slowly at a constantleaf elongation rate (LER). By extrapolating this LER back toleaf initiation from the apex it was calculated that elongationlasted 42.5 d at 24 °C and 51 d at 14 °C. Lengths ofthe division zone (DZ) and the extension-only zone (E-OZ) increasedto a maximum and then decreased during leaf development. Temperaturechange had an immediate effect on LER but the response varieddepending on the direction of the temperature change. To describethese different features, an empirical model of DZ and E-OZwas designed. Its five parameters were optimized at constanttemperature. The model was then used to simulate the LER ofplants subjected to temperature changes. Instant and lastingeffects of the initial temperature on mean LER in plants transferredfrom 14 to 24 °C andvice versawere well simulated. It wasconcluded that the major reason for differences was due to thegrowth stage (DZ and E-OZ lengths) at which the changes occurredat both temperatures.Copyright 1999 Annals of Botany Company Festuca arundinaceaSchreb., tall fescue, growth zone, division zone.     

Temperature effects on forest herbs assessed by warming and transplant experiments along a latitudinal gradient

Slow‐colonizing forest understorey plants are probably not able to rapidly adjust their distribution range following large‐scale climate change. Therefore, the acclimation potential to climate change within their actual occupied habitats will likely be key for their short‐ and long‐term persistence. We combined transplant experiments along a latitudinal gradient with open‐top chambers to assess the effects of temperature on phenology, growth and reproductive performance of multiple populations of slow‐colonizing understorey plants, using the spring flowering geophytic forb Anemone nemorosa and the early summer flowering grass Milium effusum as study species. In both species, emergence time and start of flowering clearly advanced with increasing temperatures. Vegetative growth (plant height, aboveground biomass) and reproductive success (seed mass, seed germination and germinable seed output) of A. nemorosa benefited from higher temperatures. Climate warming may thus increase future competitive ability and colonization rates of this species. Apart from the effects on phenology, growth and reproductive performance of M. effusum generally decreased when transplanted southwards (e.g., plant size and number of individuals decreased towards the south) and was probably more limited by light availability in the south. Specific leaf area of both species increased when transplanted southwards, but decreased with open‐top chamber installation in A. nemorosa. In general, individuals of both species transplanted at the home site performed best, suggesting local adaptation. We conclude that contrasting understorey plants may display divergent plasticity in response to changing temperatures which may alter future understorey community dynamics.     

A Compartmental Analysis of Abscisic Acid in Roots of Hordeum distichon

An efflux compartmental analysis of abscisic acid (ABA) in barleyroots revealed two compartments of ABA, a fast exchanging one(probably the cytoplasm) containing 3.63 µM ABA and aslowly exchanging compartment (probably the vacuoles) whichcontained 0.39 µM ABA.