Changes in Osmotic Pressure and Swelling in Horseshoe Crab Embryos During Development

Water influx accompanying the swelling of embryos during normal development of horseshoe crabs, Limulus polyphemus and Tachypleus tridentatus , following a rupture of the chorion, was analyzed. The increase in volume of perivitelline fluid during deveopment was about 90 percent of the increase in total embryo weight. Considerable water discharge was observed on drying the embryos in air and a reversible water influx occurred with a second immersion in sea water, even though the embryos died as a result of this treatment. Since the osmotic pressure of the perivitelline fluids decreased markedly during development until the end of swelling, a close correlation between swelling and osmotic pressure was recognized. These results indicate that certain osmoactive substances may be produced in the perivitelline fluid at the initial stage of swelling.     

Mass mortality of Japanese macaques in a western coastal forest of Yakushima

The mass mortality of wild Japanese macaques (Macaca fuscata Blyth) was observed in a warm temperate forest of Yakushima, southern Japan. Demographic changes of eight troops between August 1998 and August 1999 were studied and 56% of macaques disappeared from the five intensively studied troops. Mortality varied among troops: two troops became extinct, while another troop did not decrease in size. The rate of mortality of the other troops was between 33 and 80%. The variation in mortality among the troops was either the outcome of local concentrations of mortality or of intertroop competition. The rate of mortality decreased with increasing distance from the two extinct troops and with increasing troop size; these two factors could not be separated statistically. The direct cause of death was diagnosed as pneumonia for four out of five fresh carcasses. The fleshy fruit production in autumn 1998 was the lowest in 14years, and macaques had relied on leaves earlier than in usual years. It was exceptionally hot and dry in the summer of 1998. The exceptionally poor fruit production and hot summer of this year, with the resulting shortage of high-quality foods, was consistent with the scenario that mass mortality was due to the poor nutritional conditions. However, the possibility that epidemics caused the mass mortality cannot be ruled out. Our findings proved that primates in a seemingly stable habitat experience fluctuations in demographic parameters under natural conditions.     

Cells expressing Desiccate are essential for morphogenesis of labial sensilla in Drosophila melanogaster adults

We recently discovered a new gene, Desiccate (Desi), that is expressed in the epidermis and protects larvae from desiccation stress in Drosophila melanogaster. In the present study, we found that taste organs express more Desi than the epidermis both in larvae and adults. Green fluorescent protein (GFP) expression in larvae under the direction of a Desi promoter‐Gal4 line containing the 1,010‐bp 5′ flanking region of Desi produced no signal in the epidermis but strong signals in cells of the larval gustatory sense organs, indicating that this driver works specifically in the gustatory organs. In adults, GFP expression was also observed in basal cells of sensilla on labella, tarsi and wings. More precise morphological analysis of GFP expression located its expression in the outer accessory cells rather than neurons of the labial sensilla. Although Desi knockdown or induction of cell death in Desi‐expressing cells did not change the morphological or physiological characters of the larvae, larvae lacking Desi‐expressing cells failed to metamorphose normally, and all of them died inside puparia. Dying pharate adults were found to lack all labial sensilla. The proneural genes Achaete and Scute, which are involved in the development of the adult central and peripheral nervous system, were normally expressed in the pupae lacking Desi‐expressing cells. These results suggested that the lack of Desi‐expressing cells makes it impossible to produce outer accessory cells for development of the sensilla, thereby signifying that cells expressing Desi are essential for normal morphogenesis of the labial sensilla in Drosophila adults.     

OBSERVATIONS OF PRIMORDIAL GERM CELLS IN THE TURTLE EMBRYO (CARETTA CARETTA): LIGHT AND ELECTRON MICROSCOPIC STUDIES

Primordial germ cells (PGCs) in the turtle embryo ( Caretta caretta ) were observed with light and transmission electron microscopes. Identification of the PGCs for light microscopy was made by the periodic acid-Schiff (PAS) technique. PGCs were first found in the yolk-sac endoderm through the 5th to 6th day of development. PGCs freed from the endoderm then migrated to the root area of the dorsal mesentery and the coelomic angle between the 7th and the 11th day of development, and finally settled down in the gonadal anlage by the 14th day. Turtle PGCs were characterized by a large size (16 μm in diameter) and large nuclei with distinct nucleoli, and by the presence of large numbers of lipid droplets, yolk platelets and glycogen particles in the cytoplasm. Cell organelles were well-developed in PGCs at later stages. Amoeboid features of the PGCs were observed in the mesenchyme, indicating active locomotion. PGCs were usually surrounded or encircled by neighboring somatic cells. No intravascular PGCs were detected at any stage of development examined.     

Chemical Induction of Autogamy in Paramecium multimicronucleatum,Syngen 21

The combination of KCl + acriflavine + Ca²⁺-poor condition, known as conjugation-inducing-chemicals, was found to be autogamy-inducing-chemicals as well. Suspension of a single cell of Paramecium multimicronucleatum, syngen 2 in this medium for three hours or more resulted in autogamy that was evidenced by cytological similarity to conjugation.