Interrelationship between Abscisic Acid and Ethylene in the Control of Senescence Processes in Carnation Flowers

The involvement of abscisic acid (ABA) in senescence of carnationflowers, in the presence of silver ions (which inhibit ethyleneaction), and aminoethoxyvinylglycine (AVG) (an inhibitor ofethylene synthesis) was studied. ABA stimulated senescence asseen by advancement of ethylene surge, and time to the developmentof in-rolling of petal margins. ABA also increased the sensitivityof the flowers to ethylene. Silver ions did not affect the timeor extent of the ethylene surge, but prevented the appearanceof visual senescence symptoms, and lowered the sensitivity toethylene. AVG delayed the ethylene surge and lowered the maximumrate of ethylene production. Also, AVG delayed the developmentof visible senscence. In the presence of silver ions, ABA advanced the ethylene surgebut senescence symptoms did not develop. The effect of ABA onthe parameters measured was prevented by AVG. Thus it is suggestedthat ABA exerts its effect on senescence via ethylene. The possibleinvolvement of an ABA-ethylene sequence as a mediator of waterstress-promoted senescence is discussed.     

Shell-banding polymorphism of the land snail Xeropicta vestalis along the coastal plain of Israel

Along the coastal plain of Israel, shell darkness of the polymorphic land snail Xeropicta vestalis is positively related to the extent of perennial vegetation. It is not related to rain, temperature, geographic position or darkness of the ground.
White shells reflect more radiation than dark ones do, and therefore in Israel's coastal plain, where solar radiation is very strong, they are favoured. Perennial vegetation, where it occurs, shields the snails from the sun by absorbing radiation, so that snails amongst them can afford to be darker, and thus more cryptic. Hence, the more perennial vegetation in the habitat, the darker the shells.
Also during the Pleistocene, when temperatures were 5–10°C lower than today, the shells of the coastal plain were as pale as recent ones are. The distribution of a snail-predator, Gerbillus allenbyi , which is restricted to sandy biotopes where perennial bushes occur, and which was absent from Israel during the Pleistocene, could perhaps explain the distribution of X. vestalis morphs, both today and in the past.     

Oppositional responses to host density in Aphytis holoxanthus (Hymenoptera: Aphefinidae), an efficient gregarious parasite

Abstract. 1. Ovipositional responses of an efficient gregarious ectoparasite ( Aphytis holoxanthus ) to increasing densities of its host (the Florida red scale, Chrysomphalus aonidum , Homoptera: Diaspididae) were studied in a laboratory system.
2. The female parasite may lay one to several eggs at each encounter with a host.
3. As host density increased, the number of eggs laid by the female parasite during the experimental period increased at a decreasing rate. This type of functional response resulted in less parasitism at higher host densities.
4. As host density increased, the number of eggs laid per encounter decreased. This behavioural response partially compensated for the decrease in parasitism.     

Differential condition dependence among morphological traits inferred from responses to heat stress is predicted by sexual selection theory

Secondary sexual traits that are condition‐dependent are expected to reveal the physiological state and/or genetic quality of individuals, and therefore, should more often be found to be under sexual selection than (1) secondary sexual traits not currently condition‐dependent, and (2) nonsecondary sexual traits. In the present study, we contrasted the degree of condition dependence in three morphological traits of male Drosophila bipectinata: two secondary sexual traits (distinct components of the sex comb), one of which significantly predicts mating success in nature (segment 2), whereas the other does not (segment 1), and a nonsecondary sexual trait (sternopleural bristle number). As predicted, comb segment 2 decreased significantly in size, in response to increasing temperature during development, whereas comb segment 1 and sternopleural bristle number either did not change significantly, or increased with increasing temperature. These results support the hypothesis that condition‐dependence, inferred from stress‐induced reductions in trait expression, engenders a trait to sexual selection. Small‐combed genotypes did not exhibit disproportionate reductions in larva‐to‐adult survivorship and adult body size compared to large‐combed genotypes, suggesting that comb size does not reveal genotypic quality, at least as revealed by sensitivity in body size and juvenile survivorship to thermal stress. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 566–574.     

THE BRAINCASE and JAWS OF CLADODUS FROM THE LOWER CARBONIFEROUS OF SCOTLAND

Abstract:  The jaws and an allegedly associated orbitotemporal region of a shark braincase are described from the Lower Carboniferous (Upper Viséan, Brigantian Stage, Clackmannan Group, Lower Limestone Formation) of Lugton, Ayrshire, Scotland. The braincase specimen is important because it is associated with a tooth of Cladodus elegans Newberry and Worthen, 1870, a form considered to be close to the type species Cladodus mirabilis Agassiz, 1843. An occipital fragment, a basicranium and a fragment of palatoquadrate from the same locality are also described. All the material probably represents the same species, and it is even possible that some of the material came from a single individual. The braincase resembles those of Cladodoide s and Tamiobatis , especially in the proportions of its otic region, the presence of an extensive dorsum sellae, and the arrangement of canals for major nerves and blood vessels. The internal structure of the occipital region is remarkably like that found in Tamiobatis braincases in having a prominent subnotochordal septum and paired subnotochordal and paroccipital chambers. Cladodus is no longer regarded as a nomen dubium , since only a few species founded on isolated teeth are now retained in the re-diagnosed genus, and one of these ( C. elegans ) is now associated with skeletal remains. The best systematic placement for Cladodus sensu stricto is among the Ctenacanthiformes or even the Ctenacanthidae. Cladodus may be a synonym of Ctenacanthus , but this cannot be confirmed with the available material.     

Reproductive characteristics of Drosophila hibisci in the Northern Territory, Australia

Reproductive traits of Drosophila hibisci collected at 18 sites in the Northern Territory (NT) of Australia in May, 1998, as well as at two sites in north Queensland, in June, 1998, were compared to those from earlier work on a cline in ovariole number in D. hibisci along the east coast of Australia. The flies in the NT were considerably smaller, but had more ovarioles than comparably-sized flies on the east coast. Although the flies on the east coast showed an increasing number of ovarioles in populations at increasing distances from the equator, these new populations, both on the east coast and in the NT, reversed this trend, producing a generally U-shaped pattern of ovariole number with latitude among all populations. The northernmost and southernmost populations allocate more to ovariole numbers than populations in intermediate latitudes. Ovariole number is closely related to body size of females in all populations, but the regression coefficient is small at intermediate latitudes and increases at the northern and southern ends of the distribution. Egg volumes primarily varied with body size of the female (positive) and number of ovarioles per female (negatively), producing a generally inverted U-shaped pattern of egg volumes with latitude. Reproductive allocation patterns, but not thorax size or ovariole number, varied significantly in two samples taken 10 days apart at one NT site. This variation probably results from environmental differences across generations of developing larvae and is consistent with our earlier suggestion of substantial effects of the environment, primarily rainfall and temperature, on reproductive allocation in D. hibisci.     

The effect of body size on oviposition success of a minute parasitoid in nature

1. Individual fitness is often assumed to be positively correlated with body size, but this has rarely been explored under realistic field conditions. This assumption was tested in a minute parasitoid foraging for planthopper eggs in saltmarsh habitats. 2. We used a novel sampling technique that captures females as they naturally die and fall off the vegetation, and estimated their oviposition success according to the number of eggs remaining in their bodies. 3. Our results support a positive relationship between oviposition success and body size of female parasitoids. 4. Only a single female had exhausted her eggs before she died suggesting that the larger body size advantage is not realised primarily via increased fecundity, but instead via increased longevity or foraging‐efficiency.     

Contractility of Glycerinated Amoeba proteus and Chaos-chaos*

Immediate contact with large volumes of cold 50% (v/v) buffered glycerol preserved typical ameboid shape of Chaos chaos and Amoeba proteus with no visible distortions. These technics allowed determination of the contraction sites in these glycerinated models upon application of ATP-Ca-Mg-solutions. The ectoplasmic tube was the main site of contraction. Preliminary EM investigations revealed thick and thin filaments, associated with the ectoplasmic tube near the plasmalemma, which appeared to be the basis for the contractility of the ectoplasmic tube. There was no predominant contraction of the pseudopodial tips or the endoplasm in these models. The changes of volume were as much as 50%, and in some cases were not accompanied by any change in the length of the ameba; however, lengthwise contractions of the ectoplasmic tube in some amebae occurred to as much as 25%. The data substantiate a basic requirement of the ectoplasmic tube contraction theory of ameboid locomotion.