Ultrasonic acoustic emissions from excised stems of two Thryptomene species

ABA-dcficient ( aba-1 ) and ABA-insensitive ( abi3–1 ) double mutant seeds of Arabidopsis thaliana are desiccation-intolerant. Carbohydrates are supposed to fulfill a role in membrane protection during dehydration. Desiccation tolerance can be induced in douhle mutant seeds in vivo by supplying the ABA-analog LAB 173 711 to the plant root system. However. this does not lead to significant changes in the carbohydrate composition, in contrast, in vitro incubation of dissected immature seeds with ABA induced desiccation tolerance concomitant with an increase in the seed raffinose content. Thus, different desiccation tolerance-inducing treatments show contradictory effects on seed carbohydrate composition and accumulation. It is concluded that. although carbohydrates might be invohed in membrane protection or glass formation during dehydration, it is unlikely that they are the sole factor determining desiccation tolerance in Arabidopsis seeds     

Radial shrinkage and ultrasound acoustic emissions of fresh versus pre-dried Norway spruce sapwood

Acoustic emission (AE) and radial shrinkage were compared between fully saturated fresh and pre-dried Norway spruce sapwood during dehydration at ambient temperature. Hydraulic conductivity measurements, anatomical investigations on bordered pits and X-ray computed tomography (CT) scans were done to search for possible AE sources other than the breakage of the water columns inside the tracheids. Both fresh and pre-dried specimens showed radial shrinkage due to drying surface layers right from the beginning of dehydration, which induced almost no AE. Whereas no dimensional changes occurred in pre-dried wood thereafter, fresh wood showed a rapid shrinkage increase starting at 25% relative water loss. This dimensional change ceased when further moisture got lost and was even partially reversed. AE of fresh wood showed much higher activity and energy, which is a waveform feature that describes the strength of the acoustic signal. Extremely high single AE energy events were detected at this critical stage of dehydration. After partial recovery from shrinkage, neither dimensional changes nor AE activity showed differences between fresh and pre-dried wood after more than 80% relative moisture loss. Our results suggested that fresh sapwood is more prone to dehydration stresses than pre-dried sapwood. Differences in AE and shrinkage behavior might be due to the weakening or distortion of the pit membranes (cavitation fatigue), pit aspiration, structural changes of the cell walls and micro-checks, which occurred during the first dehydration cycle.     

Volatile emissions of eastern hemlock,Tsuga canadensis,and the influence of hemlock woolly adelgid

The volatile emissions of eastern hemlock, Tsuga canadensis Carriere, were identified and quantified using standard and chiral gas chromatography and mass spectrometry. All of the identified compounds were monoterpenes, and included alpha-pinene, myrcene, tricyclene, camphene, alpha-phellandrene, beta-pinene, limonene, beta-phellandrene, terpinolene, and bornyl acetate. alpha-Pinene, myrcene, and camphene comprised greater than 75% by mass of the total release. Infestation by the exotic insect, hemlock woolly adelgid (HWA, Adelges tsugae Annand), resulted in an increased release rate of monoterpenes from branch tips. Release rate was negatively correlated to the amount of the branch tip sample that was new growth, suggesting that release rate is greater from previous-year foliage. Additionally the percent composition of the volatile profile is slightly altered by infestation, with alpha-pinene comprising 57% of volatiles from infested foliage and 66% from uninfested foliage.     

Remating in Drosophila melanogaster: an examination of the trading-up and intrinsic male-quality hypotheses

Female Drosophila melanogaster remate more frequently than necessary to ensure fertilization. We tested whether polyandrous females gain genetic benefits for their offspring by (1) selecting secondary sires of higher genetic-quality than original partners or (2) because post-copulatory mechanisms bias fertilizations towards genetically superior males. We screened 119 hemiclones of males for lifetime fitness then selected eight hemiclones (four of extreme high fitness and four of extreme low fitness) and mated them to virgin females. Females were then given the opportunity to remate with males of benchmark-genetic quality and their propensity to remate (fidelity) and sperm displacement scored. A female's fidelity and her level of sperm displacement varied depending on which hemiclone she mated first, but not on male-genetic quality. These findings indicate that female remating and sperm displacement are strongly influenced by male genotype, but provide no evidence that these traits contribute to adaptive female choice to obtain superior genes for offspring.     

The evolution of polyandry: an examination of the genetic incompatibility and good‐sperm hypotheses

I have examined the adaptive significance of polyandry using the Australian field cricket Teleogryllus oceanicus. Previous studies of polyandry have examined differences in offspring production by females mated multiply to a single male or females mated multiply to different males. Here I combine this approach with a study of parentage of offspring produced in the later group. Females mated to two different males had a higher proportion of their eggs hatching than did females mating twice with a single male. Offspring fitness parameters were not effected. There was little evidence to suggest that females elevate their hatching success via fertilizing their eggs with sperm from genetically compatible males. Although the average paternity points towards random sperm mixing, there was considerable individual variation in sperm competition success. Patterns of parentage were consistent across females mating twice or four times. Sperm competition success was not related to offspring viability or performance. Thus, the notion that competitively superior sperm produce competitively superior offspring is not supported either. The mechanism underlying increased hatching success with polyandry requires further study.     

The effect of soil nutrient availability on retranslocation of Ca,Mg and K from senescing sapwood in Atlantic white cedar

Nutrient resorption from senescing tissues increases plant nutrient-use efficiency, and may be an adaptation to nutrient limitation. In some tree species, retranslocation of nutrients from sapwood during heartwood formation is a comparable process. We measured Ca, Mg and K concentrations in Atlantic white cedar (Chamaecyparis thyoides) stemwood samples taken from two swamps in the northeastern United States and compared them to soil mineral nutrient availability at each site. We found that Ca, Mg and K concentrations were 60–700% higher in sapwood than in the immediately adjacent heartwood, indicating retranslocation of these nutrients from senescing sapwood. Sapwood nutrient concentrations were similar between the two sites. However, nutrient concentrations in the heartwood differed significantly between the sites, as did the relative degree of Ca and Mg retranslocation from senescing sapwood. We found these differences between sites to be inversely related to significant differences in exchangeable Ca, Mg and K as well as Al concentrations in the soil. These findings suggest that the degree of nutrient retranslocation from senescing sapwood may be influenced by soil nutrient availability. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ultrasound acoustic emissions from dehydrating leaves of deciduous and evergreen trees

While drying, detached leaves produced ultrasound acoustic emissions (UAE) comparable to emissions from stem and twig wood. Experiments on Ilex aquifolium L. showed that the main source of these signals was cavitation in the veins, to which conduits and fibres probably both contributed. Regions of the leaf blade with abundant mesophyll and only small veins emitted few signals. More signals were counted on the adaxial side of the midrib than on the abaxial one and on the proximal third than on the distal one, in accordance with the anatomical structure. Sound attenuation was pronounced. Eight species were compared with respect to cavitation behaviour, field water relations and pressure–volume curves, and the data showed differences in cumulative number of events and resistance of leaves to cavitation. Data were generally in good agreement with anatomical structure and habitat preferences. The number of signals per conduit counted on cross-sections was in some leaves much higher than unity, which suggests short xylem elements or an acoustic activity of cells other than conduits. There was no correlation between cavitation threshold or cumulative number of signals and the degree of sclerophylly; unexpectedly, there was a correlation between the cumulative number of signals at a water potential of -1.3 MPa and the bulk modulus of elasticity.     

Feeding preference of three lady beetle predators of the hemlock woolly adelgid (Homoptera: Adelgidae)

In a laboratory study, we tested the feeding preferences of three coccinellid predators of hemlock woolly adelgid, Adelges tsugae Annand, an introduced pest of hemlock in the eastern United States. The species tested were Sasajiscymnus tsugae Sasaji & McClure (formerly Pseudoscymnus tsugae) from Japan, Scymnus ningshanensis Yu & Yao from China, and Harmonia axyridis (Pallas), a generalist species introduced from Asia that is currently widespread in eastern hemlock, Tsuga canadensis Carriere, forests. We measured the feeding preference of each beetle species when given the choice of A. tsugae and either 1) Pineus strobi (Hartig) on Pinus strobus L.; 2) Adelges laricis Vallot on Larix decidua Mill.; 3) Adelges cooleyi (Gillette) on Pseudotsuga menziesii (Mirb.) Franco; or 3) Paraprociphilus tessellatus (Fitch) on Alnus serrulata (Ait.) Willd. We evaluated beetle preference for adults, nymphs, and eggs of each prey species. Generally, when adult or nymphal prey stages were compared, S. tsugae preferred A. tsugae adults to P. strobi, A. cooleyi, A. laricis, and P. tessellatus. S. ningshanensis showed less preference between adelgid species, but it did not prefer P. tessellatus nymphs. When preferences for adelgid eggs were assayed, S. tsugae and S. ningshanensis showed no preference between A. tsugae and A. cooleyi or P. strobi, but S. tsugae did prefer A. tsugae to A. laricis. Larvae of S. tsugae were unable to survive on P. tessellatus nymphs. H. axyridis adults readily consumed both A. tsugae and P. tessellatus, but H. axyridis larvae did not complete their life cycle on A. tsugae. Our host range tests suggest that S. ningshanensis and S. tsugae may feed on several species of Adelgidae and that A. tsugae is often preferred.     

Growling for food: acoustic emissions during competitive feeding of the streaked gurnard

The streaked gurnard Trigloporus lastoviza produced only one sound type, a growl, lasting up to 3 s and consisting of repeated groups of typically one to three pulses. The foraging fish followed two different strategies. In the first, the fish circled the feeding area, grasped a food item and fled, sometimes displaying aggressively to competitors. With this foraging strategy, fish usually made sounds as they circled, grasped and fled. Fish that growled while circling were more likely to grasp a food item subsequently than were silent fish. The second feeding strategy occurred when a fish had already ingested food or failed to get any. In this case, typically fish searched for food on the substratum or approached and touched other individuals that were feeding, sometimes grabbing food that was spat out during food handling by the other fish. Although payback experiments would be needed to draw firm conclusions on the communicative function of growling during competitive feeding in the streaked gurnard, the results suggest that sound production confers advantages to individuals competing for limited food resources.     

Vireo song repertoires and migratory distance: three sexual selection hypotheses fail to explain the correlation

Previous studies have found a relationship between migrationand the degree of elaboration of sexually selected traits,but investigators have differed in the mechanisms they proposedto account for this association. We examined the relationshipbetween song repertoire size and distance migrated among birdsin the genus Vireo. There is a strong positive relationshipbetween migratory distance and repertoire size in this genus,but our data do not support the specific predictions of anyof the three proposed mechanisms (the "rapid pairing," "goodmigrations," and "territory lottery" hypotheses). Migrationdistance is presumably correlated with other life-history characteristicsthat influence the development of sexually selected traits.     

Paleoecology and coalescence: phylogeographic analysis of hypotheses from the fossil record

The application of principles from coalescence theory to genealogical relationships within species can provide insights into the process of diversification and the influence of biogeography on distributional patterns. There are several features that make some organisms more suitable for detailed studies of historical processes; in particular, limited dispersal, which serves to conserve the patterns of genetic variation that developed during colonization. We describe the potential benefits of studies that integrate analyses of genetic variation with information from the fossil pollen record and present recent examples of the application of quantitative methods of phylogeographic analysis.     

Universal common ancestry,LUCA, and the Tree of Life: three distinct hypotheses about the evolution of life

Common ancestry is a central feature of the theory of evolution, yet it is not clear what “common ancestry” actually means; nor is it clear how it is related to other terms such as “the Tree of Life” and “the last universal common ancestor”. I argue these terms describe three distinct hypotheses ordered in a logical way: that there is a Tree of Life is a claim about the pattern of evolutionary history, that there is a last universal common ancestor is an ontological claim about the existence of an entity of a specific kind, and that there is universal common ancestry is a claim about a causal pattern in the history of life. With these generalizations in mind, I argue that the existence of a Tree of Life entails a last universal common ancestor, which would entail universal common ancestry, but neither of the converse entailments hold. This allows us to make sense of the debates surrounding the Tree, as well as our lack of knowledge about the last universal common ancestor, while still maintaining the uncontroversial truth of universal common ancestry.     

Methane emissions from wetlands and their relationship with vascular plants: an Arctic example

This paper investigates the relationship between vascular plant production and CH₄ emissions from an arctic wet tundra ecosystem in north‐east Greenland. Light intensity was manipulated by shading during three consecutive growing seasons (1998–2000). The shading treatment resulted in lower carbon cycling in the ecosystem as mean seasonal net ecosystem exchange (NEE) decreased from ?336 to ?196 mg CO₂ m^?2 h^?1 and from ?476 to ?212 mg CO₂ m^?2 h^?1 in 1999 and 2000, respectively, and total ecosystem respiration decreased from 125 to 94 mg CO₂ m^?2 h^?1 in 1999 and from 409 to 306 mg CO₂ m^?2 h^?1 in 2000. Seasonal mean CH₄ emissions in controls and shaded plots were, respectively, 6.5 and 4.5 mg CH₄ m^?2 h^?1 in 1999 and 8.3 and 6.2 mg CH₄ m^?2 h^?1 in 2000. We found that CH₄ emission was sensitive to NEE and carbon turnover, and it is reasonable to assume that the correlation was due to a combined effect of vegetative CH₄ transport and substrate quality coupled to vascular plant production. Total above‐ground biomass was correlated to mean seasonal CH₄ emission, but separation into species showed that plant‐mediated CH₄ transport was highly species dependent. Potential CH₄ production peaked at the same depth as maximum root density (5–15 cm) and treatment differences further suggest that substrate quality was negatively affected by decreased NEE in the shaded plots. The concentration of dissolved CH₄ decreased in the control plots as the growing season progressed while it was relatively stable in the shaded plots. This suggests that a progressively better developed root system in the controls increased the capacity to transport CH₄ from the soil to the atmosphere. In conclusion, vascular plant photosynthetic rate and subsequent allocation of recently fixed carbon to below‐ground structures seemed to influence both vegetative CH₄ transport and substrate quality.     

Modelling the role of highly unsaturated fatty acids in planktonic food web processes: Sensitivity analysis and examination of contemporary hypotheses

Aquatic food web models typically treat the constituent trophic levels as static elements interacting with one another and the environment. Dynamic biological stoichiometry has relaxed this assumption and considers evolutionary responses in said elements. The incorporation of organismal response in food web models holds promise for a more realistic portrayal of ecosystem dynamics. Recent advances in aquatic ecology pinpoint the importance of highly unsaturated fatty acids (HUFAs) on food web interactions and ecosystem resilience. In this study, we utilized a HUFA explicit submodel in conjunction with a limiting nutrient–phytoplankton–zooplankton–detritus (NPZD) mathematical system to incorporate elements of the physiology of individual animals into the context of plankton dynamics. Our HUFA-augmented plankton model provided a realistic platform to examine functional properties and physiological strategies that modulate resource procurement in different trophic environments and to effectively link variability at the organismal level with ecosystem-scale patterns. First, we were able to illustrate the implications of the filling-cup hypothesis, in which species’ fitness stems from dynamic HUFA turnover rates in response to bottom-up stresses. We then examined an evolutionary hypothesis of consumer fitness dependence on HUFA quota management strategies, whereby adaptive individuals with low HUFA minimum and optimum requirements gain competitive advantage. Several studies have reported higher HUFA concentrations in consumers than producers, and our results suggest that this pattern could be driven by a combination of conservative turnover and elevated bioconversion rates. Oligotrophic settings showed strong reliance upon exogenous phosphorus subsidies and frequently yielded inverted food web biomass distributions. With the prevalence of eutrophic conditions, consumer growth is primarily controlled by HUFA availability, and the associated biochemical limitation can ultimately result in patterns of algal accumulation. Finally, our study discusses directions to improve the representation of the producer–grazer interactions and thus advance our understanding of the factors that determine the flow of nutrients and energy to the higher trophic levels.     

Phylogeny of the Ascaridoidea (Nematoda: Ascaridida) based on three genes and morphology: hypotheses of structural and sequence evolution

Ascaridoid nematodes parasitize the gastrointestinal tract of vertebrate definitive hosts and are represented by more than 50 described genera. We used 582 nucleotides (83% of the coding sequence) of the mitochondrial gene cytochrome oxidase subunit 2, in combination with published small- and large-subunit nuclear rDNA sequences (2,557 characters) and morphological data (20 characters), to produce a phylogenetic hypothesis for representatives of this superfamily. This combined evidence phylogeny strongly supported clades that, with 1 exception, were consistent with Fagerholm's 1991 classification. Parsimony mapping of character states on the combined evidence tree was used to develop hypotheses for the evolution of morphological, life history, and amino acid characters. This analysis of character evolution revealed that certain key features that have been used by previous workers for developing taxonomic and evolutionary hypotheses represent plesiomorphic states. Cytochrome oxidase subunit 2 nucleotides show a strong compositional bias to A+T and a substitution bias to thymine. These biases are most apparent at third positions of codons and 4-fold degenerate sites, which is consistent with the nonrandom substitution pattern of A+T pressure. Despite nucleotide bias, cytochrome oxidase amino acid sequences show conservation and retention of critical functional residues, as inferred from comparisons to other organisms.