Habitat deterioration promotes the evolution of direct development in metamorphosing species

Although metamorphosis is widespread in the animal kingdom, several species have evolved life-cycle modifications to avoid complete metamorphosis. Some species, for example, many salamanders and newts, have deleted the adult stage via a process called paedomorphosis. Others, for example, some frog species and marine invertebrates, no longer have a distinct larval stage and reach maturation via direct development. Here we study which ecological conditions can lead to the loss of metamorphosis via the evolution of direct development. To do so, we use size-structured consumer-resource models in conjunction with the adaptive-dynamics approach. In case the larval habitat deteriorates, individuals will produce larger offspring and in concert accelerate metamorphosis. Although this leads to the evolutionary transition from metamorphosis to direct development when the adult habitat is highly favorable, the population will go extinct in case the adult habitat does not provide sufficient food to escape metamorphosis. With a phylogenetic approach we furthermore show that among amphibians the transition of metamorphosis to direct development is indeed, in line with model predictions, conditional on and preceded by the evolution of larger egg sizes.     

Statistical Mechanics of Zooplankton

Statistical mechanics provides the link between microscopic properties of many-particle systems and macroscopic properties such as pressure and temperature. Observations of similar “microscopic” quantities exist for the motion of zooplankton, as well as many species of other social animals. Herein, we propose to take average squared velocities as the definition of the “ecological temperature” of a population under different conditions on nutrients, light, oxygen and others. We test the usefulness of this definition on observations of the crustacean zooplankton Daphnia pulicaria. In one set of experiments, D. pulicaria is infested with the pathogen Vibrio cholerae, the causative agent of cholera. We find that infested D. pulicaria under light exposure have a significantly greater ecological temperature, which puts them at a greater risk of detection by visual predators. In a second set of experiments, we observe D. pulicaria in cold and warm water, and in darkness and under light exposure. Overall, our ecological temperature is a good discriminator of the crustacean’s swimming behavior.     

Plant-growth regulators from common starfish (<Emphasis Type="Italic">Asterias amurensis</Emphasis> Lütken) waste

Starfish waste has been shown to be an effective compost material not only in the promotion of plant growth but also in terms of having insecticidal activity. In the present study, plant growth regulation by chemicals from starfish was examined. The aqueous fraction from a hot water extract of the starfish Asterias amurensis Lütken showed plant-growth activity, while the aqueous fraction from a methanol extract inhibited growth of Brassica campestris. The lipophilic fraction from the methanol extract also exhibited a plant growth-promoting effect. The active components from each extract were identified. Asterubine from the hot water extract promoted plant growth. A ceramide from the lipophilic fraction showed root growth promoting effect, and three glucocerebrosides had promotive effects on the entire plant. Asterosaponins were identified as the main growth inhibitors in the aqueous fraction of the methanol extract. These active compounds from starfish waste could be analyzed as potential plant growth regulators in agricultural applications in the future.     

Transcriptional profiling of the nucleus pulposus: say yes to notochord

This editorial addresses the debate concerning the origin of adult nucleus pulposus cells in the light of profiling studies by Minogue and colleagues. In their report of several marker genes that distinguish nucleus pulposus cells from other related cell types, the authors provide novel insights into the notochordal nature of the former. Together with recently published work, their work lends support to the view that all cells present within the nucleus pulposus are derived from the notochord. Hence, the choice of an animal model for disc research should be based on considerations other than the cell loss and replacement by non-notochordal cells.     

Effect of stocking density on the behavior of newly transformed juvenile Macrobrachium rosenbergii

This study characterized the behavioral activity of Macrobrachium rosenbergii in the early stages of development, under different stocking densities (25 and 40 animals/m²), and during the light and dark phases of a 24-h cycle. Observations of individuals were made in 8 aquariums. Behavioral recording lasted 15 min/aquarium, 4 times/day and 4 days/week, 4 weeks in total. Food was offered twice daily. Observational methods included a combination of behavioral sampling and scan sampling. During the light phase, inactivity, cleaning and remaining in a shelter were the most frequent behaviors. During the dark phase the subjects displayed a higher frequency of feeding, exploration, swimming, and digging. At low density, the animals gained more weight and exhibited greater growth overall. These results indicate a behavioral pattern that is more favorable to animals in the lower density cultivation environment that can also create better living conditions for these shrimp, favor survival rates and therefore improve management success.     

Zum Sauerstoffverbrauch von Myzus persicae (Sulz.) vor und nach Aufnahme des Blattrollvirus

Zusammenfassung Der Sauerstoffverbrauch virusfreier Myzus persicae (Sulz.) wird mit demjenigen blattrollvirusinfizierter Läuse verglichen. Der O₂-Verbrauch ist bei infizierten Tieren um rund 30% gegenüber virusfreien Kontrolltieren erniedrigt. Auf verschiedenen. Wirtspflanzen gehaltene Läuse zeigen keinen signifikanten Unterschied in ihrer Atmungsintensität. Die grö\te Erniedrigung des O₂-Bedarfs ist etwa 30 Stunden nach Ende des Infektionssaugens (d.h 38 Stunden nach Beginn der Nahrungsaufnahme) erreicht und steigt dann im Verlauf der folgenden 50 Stunden nicht weiter an. Der Stoffwechsel der Läuse wird offensichtlich durch die Aufnahme des Blattrollvirus gestört.

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Summary The intensity of respiration of virus-free aphids was compared with that of the same insects infected with potato leafroll virus. The former showed an average oxygen-consumption of 3.018 cm³/gm/hour, and the latter 1.992 cm³/gm/hour; which indicates a reduction of 33.9% in the oxygen-uptake in the infected animals. This reduction is associated with the infection and the multiplication of the virus in the insect. The oxygen-consumption was the same before the beginning and at the end of the infective suction period, falling afterwards over a period of 30 hours by about 30% of the first reading, and then remaining almost constant. This indicates a correlation between this variation in the oxygen-consumption and the multiplication of the virus in the aphid.