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.     

Percutaneous closure of a patent foramen ovale after cryptogenic stroke

A patent foramen ovale is a common intracardiac finding that is located between the left and right atrium. It can cause right-to-left shunting and has a high prevalence in patients who suffer a cryptogenic stroke. Earlier trials did not show superiority of percutaneous patent foramen ovale closure with standard medical therapy over standard medical therapy alone in the treatment of cryptogenic stroke. Interestingly, several meta-analyses show positive results regarding closure, suggesting underpowering of the individual trials. Recently, two large prospective trials and one long-term follow-up study showed benefit of percutaneous closure over standard medical therapy in treatment of cryptogenic stroke. A larger right-to-left shunt or the presence of an atrial septal aneurysm were predictors for a recurrent event. Therefore, percutaneous patent foramen ovale closure after cryptogenic stroke should be recommended over antiplatelet therapy alone in patients younger than 55 years of age with a high-risk patent foramen ovale.     

Life-history analysis of an Artemia population in a changing environment

The Anemia monica Verrill population in Mono Lake, Californiahas two generations per year. Despite similarities in the year-to-yearlife history patterns, some important differences developedbetween 1979 and 1981. The first generation hatches from overwinteringcysts in early spring and reaches maturity by the end of May.The first-generation females reproduce ovoviviparously, givingrise to a second generation which matures between mid-July andAugust. In July, both first and second generation females beginproducing overwintering cysts. The population reaches it maximumin late summer, then declines to low numbers by November. Theabundance of the first generation in June declined from a meanof 20 000 m^–2 to 2400 m^–2. Despite the smaller firstgeneration, the second generation in 1980 and 1981 was at leastas abundant as in 1979. These differences are indicative ofa change in the Artemia population dynamics in Mono Lake. ¹Address for correspondence: Hawaii Institute of Marine Biology,University of Hawaii, P.O. Box 1346 Kaneohe, HI 96744-1346,USA.     

The Chlamydomonas cell cycle is regulated by a light/dark-responsive cell-cycle switch

Cultures of the unicellular green alga Chlamydomonas reinhardii can be synchronized by light/dark cycling not only under photoautotrophic but also under mixotrophic growth conditions. We observed that cultures synchronized in the presence of acetate continue to divide synchronously for one cell-cycle period when transferred to heterotrophic growth conditions. This finding enabled us to investigate the differential effects of light on cell growth and cell division. When cells were exposed to continuous light at the beginning of the growth period they entered the division phase earlier than dark-grown cells as a consequence of an increased growth rate. Illumination at the end of the growth period, however, caused a considerable delay in cell division and an extended growth period. The light-induced delay in cell division was also observed in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of photosystem II. This finding demonstrates that cell division is directly influenced by a light/dard-responsive cell-cycle switch rather than by light/dark-dependent changes in energy metabolism. The importance of this light/dark control to the regulation of the Chlamydomonas cell cycle was investigated in comparison with other control mechanisms (size control, time control). We found that the light/dard-responsive cell-cycle switch regulates the transition from G1-to S-phase. This control mechanism is effective in cells which have attained the commitment to at least one round of DNA replication and division but have not attained the maximal cell mass which initiates cell division in the light.Abbreviations dCTP deoxycytidine 5-triphosphate - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea     

A machine for sawing 80-micrometer slices of carious enamel

Design and construction of a machine that cuts 80-microns slices of sound and carious dental enamel and other calcified tissues is described. These slices can be used for quantitative microradiographic studies. Preparation takes minutes. Thickness for a given slice is uniform within 2 microns, mean thickness is within 4 microns of the intended value and roughness is about 0.1 micron. Commercial components have been used where possible. Information is provided to permit purchase of the components of the machine and its construction in the average university workshop.     

Die Entwicklung der Laut?u?erungen bei der Graugans (Anser anser)

Zusammenfassung Das Lautrepertoire von sechs handaufgezogenen Graugänsen wurde in individuellen Längsschnitten vom Schlüpfen bis zum Alter von 100 Tagen mit sonagraphischer Methode analysiert. Die Einteilung des Repertoires erfolgte nach drei verschiedenen Kriterien: Klang, Sonagramm und Kontext. Im jugendlichen Repertoire ließen sich 4 Rufklassen voneinander trennen. Im Laufe der Jugendentwicklung veränderten sich vor allem die phonetischen Parameter der Rufe, während die syntaktischen weitgehend konstant blieben. Nach einem Anstieg in der ersten Woche fiel die Tonhöhe der Rufe bei allen untersuchten Individuen und Rufklassen gleichmäßig ab. Der Stimmbruch, meßbar an der Zunahme geräuschhafter Komponenten, war ein kontinuierlicher, langfristiger Prozeß. Die Individualität war nicht in einem einzelnen, wohl aber in der Kombination mehrerer Merkmale faßbar. Die Geschlechter waren schon früh an Unterschieden in der Tonhöhe erkennbar. An sonstigen ontogenetischen Veränderungen innerhalb des Untersuchungszeitraumes konnten die Erweiterung des Repertories durch Aufspaltung und Reifung sowie ein möglicher Verlust von Rufklassen beobachtet werden.

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Juvenile development of vocalizations in Greylag Geese (Anser anser)

Summary The juvenile vocal development of six Greylag Geese from hatching up to the age of 100 days was analysed by using sonagraphic methods. The calls were classified by means of the acoustic phenomenon, sonagrams, and context criteria. The juvenile repertoire included four main call types. During ontogeny, changes of call parameters mainly referred to phonetic characteristics, whereas syntactic parameters remained more or less constant. The frequency pitch of calls changed to higher levels during the first week of development while in older goslings this parameter decreased constantly. This held true for each individual and call type. Breaking of the voice, defined as an increment of noisy parts in the vocalizations, is described as a continuous long term process. Structural individuality of calls apparently was not based on one single parameter, but on the combination of several ones. Sex differences were found in the pitch of vocalizations, correlating with different body weights of male and female geese. Additional developmental processes of the vocal repertoire included differentiation, maturation of new call types, and apparent suppression of juvenile ones. The functional organization of the juvenile call system in Greylags is discussed.

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Herrn Dr. Hans Löhrl zum 75. Geburtstag gewidmet     

Effects of light and acetate on the liberation of zoospores by a mutant strain ofChlamydomonas reinhardtii

In light-dark-synchronized cultures of the unicellular green algaChlamydomonas reinhardtii, release of zoospores from the wall of the mother cell normally takes place during the second half of the dark period. The recently isolated mutant ls, however, needs light for the liberation of zoospores when grown photoautotrophically under a 12 h light-12 h dark regime. The light-induced release of zoospores was found to be prevented by addition of the photosystem-II inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Furthermore, light dependence of this process was shown to be abolished when the mutant ls was grown either photoautotrophically under a 14 h light-10 h dark regime or in the presence of acetate. Our findings indicate that the light-dependency of zoospore liberation observed in cultures of this particular mutant during photoautotrophic growth under a 12 h light-12 h dark regime might be attributed to an altered energy metabolism. The light-induced release of zoospores was found to be prevented by addition of cycloheximide or chloramphenicol, antibiotics which inhibit protein biosynthesis by cytoplasmic and organellar ribosomes, respectively. Actinomycin D, an inhibitor of RNA synthesis, however, did not affect the light-induced liberation of zoospores.Sporangia accumulate in stationary cultures of the mutant ls. Release of zoospores was observed when these sporangia were collected by centrifugation and incubated in the light after resuspension in fresh culture medium. Since liberation of zoospores was not observed after dilution of the stationary cultures with fresh culture medium, we suppose that components which interfere with the action of the sporangial autolysin are accumulated in the culture medium of the mutant ls.Abbreviation DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea