What life cycle graphs can tell about the evolution of life histories

We analyze long-term evolutionary dynamics in a large class of life history models. The model family is characterized by discrete-time population dynamics and a finite number of individual states such that the life cycle can be described in terms of a population projection matrix. We allow an arbitrary number of demographic parameters to be subject to density-dependent population regulation and two or more demographic parameters to be subject to evolutionary change. Our aim is to identify structural features of life cycles and modes of population regulation that correspond to specific evolutionary dynamics. Our derivations are based on a fitness proxy that is an algebraically simple function of loops within the life cycle. This allows us to phrase the results in terms of properties of such loops which are readily interpreted biologically. The following results could be obtained. First, we give sufficient conditions for the existence of optimisation principles in models with an arbitrary number of evolving traits. These models are then classified with respect to their appropriate optimisation principle. Second, under the assumption of just two evolving traits we identify structural features of the life cycle that determine whether equilibria of the monomorphic adaptive dynamics (evolutionarily singular points) correspond to fitness minima or maxima. Third, for one class of frequency-dependent models, where optimisation is not possible, we present sufficient conditions that allow classifying singular points in terms of the curvature of the trade-off curve. Throughout the article we illustrate the utility of our framework with a variety of examples.     

A method for flow cytometric cell cycle analysis of normal and psoriatic human epidermis based on a detergent/citric acid technique for suspension of nuclei

A new method is described for flow cytometric cell cycle analysis of normal and psoriatic human epidermis, based on non-enzymatic tissue disaggregation. The epidermis was isolated by treatment with acetic acid and stored by freezing. After thawing, the epidermis was disintegrated into a nuclear suspension by 3 steps: incubation with dithiotreitol, whirling in a buffer (pH 7.4) with the non-ionic detergent Nonidet P40, EGTA, RNase and spermine, and whirling after addition of citric acid to a final concentration of 1% (pH 2.4). The suspension was stained with propidium iodide and filtered before flow cytometry. The yield of suspended nuclei was approximately 70% of the original number of cells in the tissue. The detergent/citric acid method was found to be preferable to an ultrasonication method previously used on human epidermis. All cell cycle and cell maturation stages were represented in the detergent/citric acid suspension, in contrast to the selection of immature G1, S and G2 stages with enzymatic methods. In the analysis of psoriatic epidermis inadequately matured (parakeratotic) cells were present in the suspension and had to be discriminated by gating on light scattering intensity, as they were not susceptible to lysis and did not stain properly. The fraction of S phase nuclei was on average 1.9% in normal and 7.7% in psoriatic epidermis, thus confirming the results of other investigators using enzymes. The presence of mitotic figures in the suspension was demonstrated by flow sorting. In this way the mitotic fraction was estimated to 0.06% in normal and 0.22% in psoriatic epidermis, confirming histological data of other investigators.     

Effects of glucose, tetrapyrroles and protein kinase C activators on cell proliferation in cultures of Saccharomyces cerevisiae

Abstract Saccharomyces cerevisiae was inoculated into a yeast nitrogen base with either glycerol or glucose as carbon source. Cell proliferation was followed by colony counts on agar medium. Cells in the glycerol-supplemented medium divided less than once in 10 days. When glucose, 6-deoxy-glucose or protoporphyrin IX was added, the cells had doubling times of about 24 h and increased in number to about 0.5 × 10⁶ cells ml⁻¹ Addition of either of the protein kinase C activators oleoyl-acetylglycerol or phorbol-12-myristate-13-acetate did not activate cell proliferation in the glycerol medium. However, when (i) glucose was combined with either protoporphyrin IX or chlorophyllin, or (ii) either protoporphyrin IX or chlorophyllin was combined with either of the protein kinase C activators, the cells had doubling times of about 12 h. Hence, (i) glucose can act as both a carbon source and a signalling molecule for proliferation, and (ii) two systems are involved in activating cell proliferation in S. cerevisiae : one operating through a protein kinase C system and another through a guanylate cyclase system.     

Demonstration of choleragen-dependent ADP-ribosylation in whole cells and correlation with the activation of adenylate cyclase

3T3C₂ mouse fibroblasts rendered permeable to (α^?32P)NAD⁺ show cholera toxin-dependent labeling of a 45,000 m.w. protein and of a doublet of polypeptides around 52,000 m.w. These same bands are ADP-ribosylated in broken cells. Membranes prepared from pigeon erythrocytes pretreated with choleragen show a decrease in subsequent cholera toxin-specific ADP-ribosylation of a 43,000 m.w. polypeptide. Both whole cell and broken cell adenylate cyclase activation and toxin-specific ADP-ribosylation are reversed specifically by low pH and high concentrations of toxin and nicotinamide in all systems. Thus ADP-ribosylation appears to be relevant to the molecular action of choleragen in whole cells as well as in broken cells.     

The posthatch physiology of the turkey poult--II. Hematology

Packed cell volume, total leukocytes, total erythrocytes, hemoglobin, mean cell volume and mean corpuscular hemoglobin concentration of the poult were analyzed daily for the first 10 days posthatch. Sexually dimorphic effects on hematological parameters were not apparent, but there was a sex X day interaction for all parameters except hemoglobin indicating that males were slower to develop/respond to critical stimuli. The study revealed a latency in production of erythrocytes and leukocytes in posthatch males and females which coincided temporally with early poult mortality.     

The fifteenth- and twentieth-century colonization of the Basin of Mexico by the Great-tailed Grackle (Quiscalus mexicanus)

Historical evidence indicates that Great‐tailed Grackles colonized the Basin of Mexico from the Gulf Coast lowlands in the fifteenth century. They were probably assisted by an intentional introduction, but colonization succeeded because of anthropogenic habitat alterations over the previous two centuries. During the Colonial period, grackles withdrew from the Basin, only to recolonize it in recent decades. This withdrawal was also due probably to changes in land use, including drainage of much of the water from the Basin's lakes.     

Explaining density-dependent regulation in earthworm populations using life-history analysis

At present there is little knowledge about how density regulates population growth rate and to what extent this is determined by life-history patterns. We compared density dependent population consequences in the Nicholsonian sense based on experimental observations and life-history modeling for the earthworms Lumbricus terrestris and Eisenia fetida . Both species differ in their life-histories, L. terrestris being a relatively long-lived species with slow reproduction and occurring at low densities compared to E. fetida which has a more opportunistic strategy with a high reproductive output. E. fetida is able to colonise new habitats rapidly and may occur at relatively high population densities. Density dependency of population growth rate was estimated by incorporating density dependent effects on reproduction and growth using a modified Euler equation. The results point out that E. fetida was not as strongly impacted by density as compared to L. terrestris . Population growth rate in E. fetida was hardly affected at low and moderate density, being reduced only at high level, this compares to L. terrestris where even relatively small density effects resulted in a strong negative effect on population growth rate. Our findings indicate that density-dependent regulation in earthworms can be quantified using life-history analysis. The outcomes are in agreement with empirical field observations for populations (i.e. L. terrestris occurs ar low density, E. fetida at high density). Consideration of the potential importance of Nicholsonian density dependence for field populations of these two species in light of their known biology however produces counterintuitive conclusions. In E. fetida , although density tolerant, rapid population growth may mean this species may be subject to density dependeny regulation. In L. terrestris , although density sensitive, complex behavioural ecology (surface activity, territoriality) may limit of feedback influence on population size.