A comparison of the annual production and biomass in three monospecific stands of the seagrass Thalassia hemprichii (Ehrenb.) aschers.

Annual production and biomass data were collected in three seagrass communities of Thalassia hemprichii (Ehrenb.) Aschers. from Papua New Guinea. Leaf growth rates, determined by the marking technique, resulted in a growth rate of 8.3 mm day^?1 for the youngest leaves. Production of above-ground plant parts was assessed by the plastochrone interval. The annual mean values were 9.3, 10.0 and 9.9 days for Sites 1, 2 and 3, respectively. Annual mean total above-ground production amounted to 2.1 mg ADW shoot^?1 day^?1 at Site 1, and 5.5 and 4.5 mg ADW shoot^?1 day^?1 for Sites 2 and 3, respectively; 73–89% of the total net production was contributed by the leaves. Rhizome production was correlated to the plastochrone interval of the leaves. Annual mean biomass of leaves amounted to 16–27% of the total biomass. The mean biomass of the other plant parts remained constant during the year. The annual mean turnover time of the different plant parts (above- and below-ground) varied considerably between the sites.     

Non-breeding fæder Ruffs Philomachus pugnax associate according to sex,not morphology

Capsule Fæders (males that are female look-alikes) associate with males rather than females, at several different spatial scales.

Aims To test the prediction that the occurrence in space and time of fæders on ecological grounds should track that of females.

Methods The fraction of fæders was estimated in five morphometric data sets that were collected over four decades in four different countries in three different seasons (comprising 9133 Ruffs). The regression of fæder–female fractions was tested against the null model assuming that the number of fæders is 1.0% of females.

Results The fraction of fæders in catches averaged 1.03%, varying between 0.3% in autumn in the UK up to 0.85% in Sénégal in winter and 1.04% in The Netherlands in spring. On a stopover in The Netherlands the fraction decreased from 1.3% to 0.7% when the females started to arrive. At all four spatial and temporal scales the regression of fæder–female fractions deviated from the null model: we found high fractions of fæders in catches with low fractions of females, indicating that fæders rather associate with the larger-sized ‘normal’ males.

Conclusion We suggest that fæders spend the winter, and migrate with, the larger-sized lekking males, and we propose that any survival costs associated with the use of suboptimal habitats is compensated by higher reproductive success as sneakers on leks.     

Inheritance of gustatory sensitivity in F1 progeny of crosses between Yponomeuta cagnagellus and Y. malinellus (Lepidoptera)

Larvae of Yponomeuta cagnagellus and Y. malinellus display clearly different neural responses to dulcitol, phloridzin, prunasin and sorbitol (Van Drongelen, 1979). Reciprocal crosses of these species have been examined for gustatory sensitivity to these plant constituents. Evidence is obtained that sensitivity to a particular compound is dominant or semi-dominant over non-sensitivity. No significant differences coul 1 be found in neural responses between F1 progeny reared on different host plants. Quantitative results concerning inheritance of sorbitol sensitivity cannot be presented. This is due to a small signal-to-noise ratio in the sorbitol responses of the crosses.

---

Transmission de la sensibilite gustative ches les descendants F1 de croisements entre Yponomeuta cagnagellus et Y. Malinellus (Lepidoptera)

Résumé Les chenilles de Yponomeuta cagnagellus et Y. malinellus présentent des réponses nerveuses nettement différentes aux dulcitol, phloridzine, primasine et sorbitol (Van Drongelen, 1979). Des croisements réciproques entre ces espèces ont permis d'examiner la sensibilité gustative à ces constituants végétaux. La preuve est obtenue que la sensibilité à un composé particulier est dominante ou semi-dominante par rapport à l'insensibilité. Aucune différence significative n'a pu être observée dans les réponses nerveuses des F1 élevés sur différentes plantes hôtes.Il n'a pas été possible de quantifier la transmission de la sensibilité au sorbitol, parce que la réponse au sorbitol des F1 provenant de ces croisements ne se distingue pas suffisamment du bruit de fond.

     

Plutella xylostella (diamondback moth) and its parasitoid Diadegma semiclausum show different gustatory and longevity responses to a range of nectar and honeydew sugars

Parasitoids as well as many of their herbivorous hosts, depend on carbohydrate‐rich food during the adult stage. Different types of nectar and honeydew vary with regard to their sugar composition. In order to successfully exploit a food source, the insect must show a positive gustatory response to its component sugars and be able to digest and metabolise them. Here we tested the herbivore Plutella xylostella L. (Lepidoptera: Plutellidae) and its parasitoid Diadegma semiclausum (Hellén) (Ichneumonidae: Campopleginae) with respect to their feeding response and longevity when provided with one of nine sugars (fructose, glucose, lactose, maltose, melibiose, melezitose, raffinose, sucrose, or trehalose). Both species responded to and showed a prolonged life span on a broad range of sugars. The impact of food supply on life span was about sixfold higher for the parasitoid than for the herbivore. In general, there was a good fit between gustatory response and achieved longevity, with some outliers. Both species showed only weak responses to melibiose, which significantly prolonged life span. The parasitoid showed a gustatory response to melezitose, which did not prolong its life span. The parasitoid and its herbivorous host responded differently to trehalose. These differences in gustatory response and longevity show the potential for application of selective sugar sources in conservation biological control. At the same time it also reveals a risk that the indiscriminate application of sugar sources may stimulate herbivory.     

Spiral cleavage and cell position contribute to the specification of the dorsoventral axis in the embryo of the archaeogastropod Haliotis tuberculata

In the embryo of Haliotis tuberculata spiral cleavage induces size differences between the quadrants in the 4-cell embryo. These size differences, together with the formation of compact cell configurations, induce asymmetrical positions of equivalent cells in the 8- and 16-cell embryo. The asymmetries in size and position influence the final specification of the dorsoventral asymmetry in the 32-cell embryo, as well as formation of the mesentoblast. © 1994 Wiley-Liss, Inc.