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.

---

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.

     

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     

Changes in enzyme activity during differentiation in Chlamydomonas reinhardtii

The patterns of alanine dehydrogenase, glutamate dehydrogenase and malate dehydrogenase activity were studied during the normal vegetative cell cycle and during the process of gametic differentiation and dedifferentiation in synchronized cultures of Chlamydomonas reinhardtii. During all three phases of growth and differentiation the synthesis of DNA was also measured. During gametic differentiation all three enzyme levels were suppressed compared to vegetative cells although DNA and cell number were comparable. During gametic dedifferentiation no DNA synthesis occurred during the first 24 h cycle and only a doubling during the second. It was not until the third cycle that a normal 4-fold increase in DNA was observed. Cell number followed a similar pattern. Athough the levels of alanine dehydrogenase and malate dehydrogenase were uniformly low during the first cycle when glutamate dehydrogenase increased 4-fold, during the second cycle the patterns of these enzymes changed markedly. The enzymes did not attain levels characteristic of vegetative cells until the third cycle.     

The life history of Brotia hainanensis (Brot, 1872) (Gastropoda: Prosobranchia: Thiaridae) in a tropical forest stream

An investigation of the prosobranch snail Brotia hainanensis (Brot, 1872) (Gastropoda: Thiaridae) in Tai Po Kau Forest Stream, New Territories, Hong Kong, has been undertaken with population samples collected at approximately 14-day intervals between August, 1977 and March, 1979. This species shows two peaks of recruitment per annum, one in spring and a second in the latter part of summer. Growth to sexual maturity is rapid, taking approximately 8.5 months, and in this respect, as well as its dual peak of recruitment, B. hainanensis displayed some variation from the iteroparous pattern of life cycles considered to be characteristic of freshwater prosobranch snails. Mortality after the young snails reach maturity is high due to severe seasonal spates in the stream and it is suggested that the modification of the life cycle of B. hainanensis from the type more usually encountered in freshwater prosobranchs reflects that this is an r-selected species adapted to a habitat where high density-independent mortality occurs.     

Landing periodicity of the mosquito Aedes aegypti in Trinidad in relation to the timing of insecticidal space-spraying

Diel landing periodicity (biting cycle) of domestic Aedes aegypti (L.) in Trinidad, West Indies, was monitored using human bait during January-August 1980. The periodicity of females was predominantly diurnal (95.2% arriving during daylight or twilight) and bimodal, with consistent peaks at 06.00-07.00 and 17.00-18.00 hours. The diel periodicities at indoor and outdoor sites were virtually identical. Larger numbers of adults were collected outside than inside houses. It is recommended that the time of insecticidal ULV adulticiding should coincide with peaks in landing periodicity of the Ae.aegypti adults.     

Satiation and the functional response: a test of a new model

Abstract. 1. A model of the functional response to prey density is derived to include the reduction in time available for search, T_s , resulting from predator satiation.
2. For larger prey items predator satiation occurs at each prey capture and T_s is reduced by the attack time and digestive pause of a series of attack cycles. For small prey items predator foraging is continuous at low densities with T_s reduced solely by attack time. At higher densities predator satiation occurs after the capture of several small prey items and T_s is reduced by the attack time and digestive pause of a series of foraging cycles.
3. A comparison of the predicted asymptotic level of prey capture using experimentally estimated parameter values, with the maximum consumption of aphids by larval and adult coccinellids provides a test of the satiation model.
4. The limitation of prey capture by predator satiation is discussed with reference to handling time and the success of coccinellids in biological control.     

A flow fluorimetric analysis of the cell cycle during growth and differentiation inDictyostelium discoideum

Summary We report a flow fluorimetric analysis of the DNA content of cells and nuclei from vegetative populations and various developmental stages of the cellular slime mouldDictyostelium discoideum using the dyes Hoechst 33258 and mithramycin. Nuclei from all of these populations showed an identical single DNA-content peak, indicating that most vegetative cells and most cells in all developmental stages are in one phase of the cell cycle. Our own data and findings in the literature indicate that this phase is G₂. On the other hand, we also found that various stages, subpopulations of cells at early stages and the different differentiated cell types in the slug stage differ in DNA content per cell. Any particular population typically has one major peak of DNA content, with a modal value that is characteristic for the cell type and for the developmental stage. These differences presumably reflect differences in mitochondrial DNA content per cell.