CARBONIC ANHYDRASE IN THE MARINE DIATOM THALASSIOSIRA WEISSFLOGII (BACILLARIOPHYCEAE)1

The zinc metalloenzyme carbonic anhydrase plays a critical role in inorganic carbon acquisition in marine diatoms, thus conferring on zinc a key role in oceanic carbon cycling. As a first step in determining the location and function of carbonic anhydrase (CA) in Bacillariophyceae, we purified and partially sequenced CA from T. weissflogii (Gru) Fryxell et Hasle (TWCA1) and cloned the corresponding cDNA (twca1). The twca1 sequence is different from other known algal carbonic anhydrase genes, and encodes a protein of roughly 34 kDa. The amino terminal amino acids sequenced from purified TWCA1 are 72 residues downstream of the putative starting methionine predicted by twca1. This difference may be due to the presence of a short-lived signal sequence designed to guide the enzyme to the correct cellular location. The absence of any homology between TWCA1 and previously sequenced CAs from Chlorophyceae may indicate either convergent evolution or that carbon acquisition represents a fundamental physiological difference among algal phyla.     

Use of anin situ labeling technique for the determination of seasonal14C distribution in Ponderosa pine

A¹⁴C labeling apparatus was developed to permit the labeling of four-year-old Ponderosa pine with¹⁴CO₂ in the field. The labeling system is a completely closed canopy system with¹⁴CO₂ monitored by a GM tube ratemeter apparatus. The level of¹⁴CO₂ corresponding to ambient levels is monitored by a microloggercomputer which controls a¹⁴CO₂ generating system. The generated¹⁴CO₂ is mixed in the canopy by circulating the atmosphere with 12V diaphram pumps. The portable system requires little operator attention. At approximately monthly intervals over a one-year period two four-year-old Ponderosa pine trees were labeled for three to five days using this labeling apparatus. After an assimilate distribution period, one tree was excavated and analyzed for¹⁴C distribution. During late spring and early summer most of the carbon assimilated (>60%) was found in the active growing tips and new needles, with little being allocated to the roots (<10%) or woody material (<20%). During mid to late fall there was an increase in root labeling along with an increase in carbon going to woody material. Over the winter period, most of the fixed carbon (65%) resided in the older leaves. The early spring labeling period showed another pulse of root labeling along with some labeling of woody tissues.     

Food and water deprivation effects on reproduction in female Blattella germanica

The effects of food and water deprivation on survival and reproduction of adult female German cockroaches were examined. Females, maintained under constant conditions, were deprived of food or water following adult maturation, mating, during the oothecal incubation period, and after first oothecal hatch. It was found that both food and water deprivations caused increased mortality, delays in the reproductive cycle and decreased oothecal hatch. The relative importance of food vs. water deprivation on reproduction is discussed along with possible reproductive strategies for this species.

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Résumé Les femelles, maintenues en conditions constantes, ont été privées d'aliments et d'eau après la maturité imaginale, l'accouplement, pendant la période d'incubation et après l'éclosion de la première oothèque. On a observé une mortalité accure, un retard dans le cycle de reproduction et une diminution des éclosions de l'oothèque. L'importance relative de l'alimentation par rapport au jeûne hydrique sur la reproduction est discutée en relation avec les stratégies reproductives possibles de cette espèce.

     

Rice straw decomposition in rice-field soil

Rice straw, buried in a rice-field during the dry season decomposed at a rate of 0.0075 day-1. Seventy five percent of the biomass, 70 percent carbon, 50 percent nitrogen and 30 percent phosphorus remained after 139 days of decomposition. Rice straw decomposition furnished 33% N and 8% P of the total nitrogen and phosphorus provided by man.     

RUNAWAY EVOLUTION TO SELF-EXTINCTION UNDER ASYMMETRICAL COMPETITION

We analyze a popular model of the evolution of traits related to performance in exploitative competition. This model has previously been used to explain a mechanism by which interspecific competition can cause taxon cycles. We show that purely intraspecific competition can cause evolution of extreme competitive abilities that ultimately result in extinction, without any influence from other species. The only change in the model required for this outcome is the assumption of a nonnormal distribution of resources of different sizes measured on a logarithmic scale. This suggests that taxon cycles, if they exist, may be driven by within- rather than between-species competition. Self-extinction does not occur when the advantage conferred by a large value of the competitive trait (e.g., size) is relatively small, or when the carrying capacity decreases at a comparatively rapid rate with increases in trait value. The evidence regarding these assumptions is discussed. The results suggest a need for more data on resource distributions and size-advantage in order to understand the evolution of competitive traits such as body size.     

Two-stage life cycle of a Cordylophora population in the Netherlands

A population of Cordylophora caspia was studied during a number of years in interconnected waters of different salinity and pollution. The distribution pattern of the colonies is only partly accounted for by these properties of the water. Part of it is also due to the availability of suitable substratum.Evidence is given that colonies of Cordylophora grow and survive on stones along the banks, but flourish during the summer on free-floating water-lily stalks.Zoological Laboratory, University of AmsterdamZoological Laboratory, University of Amsterdam     

INBREEDING DEPRESSION IN MORPHOLOGICAL AND PHYSIOLOGICAL TRAITS OF SCHIEDEA LYDGATEI (CARYOPHYLLACEAE) IN TWO ENVIRONMENTS

We compared inbreeding depression in hermaphroditic Schiedea lydgatei and its gynodioecious sister species, S. salicaria, to infer the level of inbreeding depression in their common ancestor. With measurements of selfing rates, this information can be used to assess the importance of inbreeding depression in the evolution of breeding systems in S. lydgatei and S. salicaria. Morphological and physiological characters related to fitness were compared for inbred and outcrossed S. lydgatei in high- and low-fertilizer environments in the greenhouse. Seed mass, number of seeds per capsule, germination, survival, biomass, number of flowers, and age at first flowering were compared for inbred versus outcrossed progeny. We also measured inbreeding depression in maximal rates of photosynthetic carbon assimilation and stomatal conductance to water vapor, traits that affect fitness through their influence on plant carbon balance and water-use efficiency (ratio of carbon gain to water loss). All traits except number of seeds per capsule in parents and survival showed inbreeding depression, with the magnitude depending on family and environment. High inbreeding depression is likely in the ancestor of S. lydgatei and S. salicaria, indicating that, with sufficiently high selfing rates, females could spread in populations. Hermaphroditism in S. lydgatei is probably favored by low selfing rates. In contrast, the evolution of gynodioecy in S. salicaria apparently has been favored by relatively high selfing rates in combination with high inbreeding depression.