Physiological Aspects of Zebra Mussel Reproduction: Maturation, Spawning, and Fertilization

SYNOPSIS. The prolific reproductive capabilities of the zebramussel, Dreissena polymorpha, have facilitated the rapid spreadand high densities of this biofouling organism since its accidentalintroduction into North America less than 10 years ago. Researchon its reproductive mechanisms and capabilities may be valuablenot only in predicting its further spread, but also in investigatingbasic mechanisms of reproduction and development and in developingnew strategies to mitigate its impact. Since zebra mussels aredioecious and fertilization occurs externally, coordinated maturation,spawning, and other mechanisms have evolved to increase theprobability of successful fertilization. The zebra mussel undergoesan annual cycle of gonadal growth and gamete maturation, culminatingin one or more spawning events in late spring or early summer.Temperature, rates of temperature change, food availability,and effects of neighboring mussels seem to be critical variablesthat determine reproductive responses. Serotonin is a biogenicamine which is implicated in spawning behavior and can reliablytrigger spawning. Serotonin is present in the gonad in neuralvaricosities that encircle groups of gametes, and specific serotonergicligands can mimic or block spawning caused by serotonin. Infemales, serotonin reinitiates meiosis causing maturation fromprophase I to metaphase I prior to spawning. Spawned oocytescontain substances that are species specific sperm chemoattractants.The sequence of binding, entry, and subsequent nuclear movementshave been observed with fluorescence and scanning microscopy.Despite their negative ecological and economic impacts, zebramussels have also provided a new and easily obtainable resourcefor studies of reproductive mechanisms.     

Effect of plasma components on the feeding response of the mosquito Aedes aegypti L. to adenine nucleotides

ABSTRACT. The gorging response of Aedes aegypti to the ATP dissolved in platelet-poor plasma is greater than that of ATP dissolved in 0.15 m NaCl. The plasma components NaHCO₃ and albumin account for the full effect of the potentiation. Phosphate or tris buffers do not duplicate the bicarbonate effect. In 0.15 m NaCl with bicarbonate but lacking albumin the concentrations inducing 50% feeding are 58 μM ATP, 140 μM ADP, 460 μM AMP and 1500 μM cAMP. Non-adenine nucleotides such as ITP and GTP and phytic acid, and 2,3-diphosphoglyceric acid had no activity.     

Specificity of Gibberellin and Sucrose-promoted Flower Bud Growth in Gladiolus

A critical stage in flower bud growth in the spike of Gladioluswhich is initiated by gibberellic acid (GA₃) and sustained bysucrose has been identified. This corresponds to the stage atwhich separation of the outer bract occurs. In buds at differentdevelopmental stages isolated and held in water, it is the samebud stage that first shows increased growth. Buds not inducedby light were shown to respond more significantly to GA₃ andsucrose than those induced by light. Since the separation ofthe outer bract results in light-induced amylase productionand starch hydrolysis leading to petal growth, it is proposedthat growth promotion by GA₃ is related to light-induced petalgrowth at this specific stage. flower bud growth, Gladiolus natalensis, gibberellic acid, sucrose