INHIBITION OF GERMINAL VESICLE BREAKDOWN AND POLAR BODY FORMATION BY NICOTINAMIDE IN STARFISH AND SURF CLAM OOCYTES*

Nicotinamide inhibited both germinal vesicle breakdown (GVBD) and polar body formation (PBF) in surf clam and starfish oocytes. In the surf clam nicotinamide at 0.3 mM completely blocked PBF in the fertilized oocytes. For blockage of GVBD higher concentration was required. In the starfish, nicotinamide (30 mM) prevented PBF but not GVBD, when added 7 min after the commencement of 1-methyladenine (1-MeAde) administration. These results suggest that PBF is blocked by nicotinamide independent of its effect on GVBD. In the case of starfish, NAD⁺was more effective than nicotinamide in inhibiting oocyte maturation. Nicotinamide also blocked GVBD induced by microinjection of the cytoplasm containing maturation-promoting factor (MPF) obtained from 1-MeAde-treatcd oocytes. These results suggest that nicotinamide prevents the action of MPF rather than inhibiting the interaction of 1-McAde with cell membrane or the induction of MPF.     

Concanavalin A-Induced Morphological Changes and Its Binding Sites in Starfish Follicle Cells as Revealed by Electron Microscopy

Concanavalin A (Con A) stimulates the production in starfish follicle cells of 1-methyladenine, a hormone which induces oocyte maturation. We have therefore investigated Con A-induced morphological changes and Con A-binding sites in the follicle cell using native Con A and horseradish peroxidase- or ferritin-labeled Con A (HRP-Con A, Fer-Con A). After isolated follicle cells were incubated with Con A (1 mg/ml), vacuoles, the Golgi complex and multivesicular body-like organelles (MVBs) became prominent in most of the cells. After follicle cells were prefixed and then incubated with Fer-Con A for 60 min, tagged ferritin was diffusely and randomly distributed as single or small clustered particles on the cell surface. The incubation of isolated follicle cells with Fer-Con A for 10 min before fixation resulted in numerous ferritin particles localized along the internalized membrane, and also in vacuoles, MVBs and small lysosome-like structures. After 60 min incubation with Fer-Con A, ferritin was further located in large lysosome-like structures and in vesicles near and in the Golgi area as well as in the organelles described above. HRP-Con A binding sites were also observed in vacuoles and MVBs of the intact cells.
These results suggest that Con A binds at first to the cell surface and causes rapid internalization and that membrane-bound Con A is easily endocytosed into vacuoles, MVBs and lysosome-like structures, and is later incorporated in some vesicles in the Golgi area.     

Morphological phylogeny of gall‐forming aphids of the tribe Eriosomatini (Aphididae: Eriosomatinae)

Aphids of the tribe Eriosomatini are typically associated with the tree genera Ulmus and Zelkova as the primary host, on which they induce several types of leaf gall. To elucidate evolutionary changes in the aphid–host associations and gall morphology, phylogenetic relationships were inferred using 36 species (28 in the ingroup) and based on 52 morphological characters. Phylogenetic analysis with equal character weighting led to hundreds of most‐parsimonious trees, and the strict consensus of these was poorly resolved. However, the successive weighting of characters yielded three most‐parsimonious trees. The strict consensus of these supported the monophyly of the Eriosomatini and the monophyly of most genera. Reconstruction of the aphid–host associations on the consensus tree indicated that the ancestral Eriosomatini were associated with Zelkova and that the association with Ulmus evolved twice independently. Ancestral reconstruction suggests that galls of the leaf‐roll type are ancestral to those of the completely and incompletely closed pouch type, and that each type of pouch galls evolved independently. It is suggested that despite early diversification of the Eriosomatini on Zelkova species, Zelkova‐associated eriosomatines had become extinct or survived as relict parthenogens on the secondary host due to the elimination of Zelkova in most regions since the late Tertiary. In contrast, two large genera in the Eriosomatini, Eriosoma and Tetraneura, are associated with the largest elm section Ulmus whose elements are distributed widely in Eurasia, including boreal regions. Therefore, the available evidence suggests that the present species diversity and distribution patterns of the eriosomatines have been largely affected by the diversification and extinction of their host plants during the late Tertiary and Quaternary.     

Differential responses to predator cues between two mosquito species breeding in different habitats

1. Natural selection favours females who can correctly assess the predation risk and hence avoid high‐risk oviposition sites and reduce the mortality rate of their offspring. In spite of the potential significance of such behaviour, relatively few studies have assessed the relationship between oviposition behaviour and predation risk. 2. The present study aimed to determine the sublethal effects of predators on oviposition site selection by gravid females, the foraging activity of larvae, and the life history traits of two mosquito species that breed in different habitats, Aedes albopictus Skuse (container breeder) and Culex tritaeniorhynchus Giles (wetland breeder). 3. Female C. tritaeniorhynchus avoided laying eggs at oviposition sites in the presence of a predator cue. In contrast, female A. albopictus laid eggs in both the absence and presence of the predator cue. 4. To examine the effects of predator cues on larval behaviour, experiments were conducted in the absence and presence of a predator cue. Although larval activity was lower in the presence of the predator cue than that in its absence in both species, C. tritaeniorhynchus responded to the predator cue more strongly than A. albopictus. Female A. albopictus that had been reared with caged predators exhibited an extended larval development period, whereas the adult C. tritaeniorhynchus reared in the presence of predators were smaller than those reared in their absence. 5. This finding might explain why C. tritaeniorhynchus avoid laying eggs in predator‐conditioned water, for example to increase the fitness of their offspring, but A. albopictus either cannot detect predator cues or are not sensitive to them.     

Evolution of Design Features in the Coding of Species-Specificity

Reproductive isolation between species is the major factor responsiblefor the evolution of species-specificity in communication signals.However, the actual physical or chemical structure of signalsmay be determined by a number of factors such as the physicallaws regulating the transmission of signal energy, locatability,the functional properties of sensory organs, the physical characteristicsof the habitats in which communication occurs, and prey-predatorrelationships. This fact implies that there is some degree ofpredictability in design features of signaling systems.     

Electron Microscopic Analysis of Phagocytic Activity of Chick Embryonic Retinal pigment cells in vitro

The phagocytosis of latex particles by retinal pigmented cells from chick embryos was studied in vitro. The pigment epithelial cells phagocytized latex particles within 2 hr without a latent period, as found in some mamalian species. The number of latex phagosomes increased with time, and the phagosomes eventually became distributed nearly uniformly in the cytoplasm. When cultures that had been exposed to latex particles for 24 hr were incubated without the particles for a further 7 days, numerous latex phagosomes remained inside the cells without any decrease in their number. This indicates that phagocytized particles are not ejected from the cells, presumably due to a defect in, or absence of, exocytotic activity.     

Role of photoperiod and temperature in seasonal morph determination of the butterfly Eurema hecabe

ABSTRACT. Environmental cues affecting seasonal morph determination of the pierid butterfly Eurema hecabe L. were examined in laboratory experiments and in the field. A sexual difference exists in the photoperiodic response for seasonal morph determination: in short days at 25C the proportion of the autumn morph is higher in females than in males, and as the rearing temperature is decreased the proportion of autumn morphs increases in both sexes. A 5C drop in temperature during the final larval stadium induces 100% autumn morph production in short-day animals. This increase in autumn morph production induced by temperature decrease explains the seasonal morph change of this butterfly occurring in early autumn in the field. The role of this sex-linked photoperiodic response is discussed as a seasonal strategy of reproduction.