Plastic inducible morphologies are not always adaptive: The importance of time delays in a stochastic environment

Summary We present a mathematical model for predicting the expected fitness of phenotypically plastic organisms experiencing a variable environment. We assume that individuals experience two discrete environments probabilistically in time (as a Markov process) and that there are two different phenotypic states, each yielding the highest fitness in one of the two environments. We compare the expected fitness of a phenotypically fixed individual to that of an individual whose phenotype is induced to produce the better phenotype in each environment with a time lag between experiencing a new environment and realization of the new phenotype. Such time lags are common in organisms where phenotypically plastic, inducible traits have been documented. We find that although plasticity is generally adaptive when time lags are short (relative to the time scale of environmental variability), plasticity can be disadvantageous for longer lag times. Asymmetries in environmental change probabilities and/or the relative fitnesses of each phenotype strongly influence whether plasticity is favoured. In contrast to other models, our model does not require costs for plasticity to be disadvantageous; costs affect the results quantitatively, not qualitatively.     

Oncogenes and the mammalian X chromosome

Summary None of the up to now localized and expressed oncogenes maps to the mammalian X chromosome. This fact is discussed in the light of a trans-acting regulation mechanism for oncogenes. Such a specific regulation mechanism is demonstrated here for a qualitative change — i.e., varying timing of DNA-replication — at the putative c-myc gene locus in band 15E of murine T-cell leukemia. In intraspecific hybrids between tumor and non-tumor cells this qualitative change spreads over to all chromosomes 15 of the same cell, irrespective of their origin. This effects is thought to reflect a binary trans-acting regulation mechanism between homologous chromosomal loci. In the past specific chromosomal aberrations have been described in various tumors but none of these aberrations involve the X chromosome. For the mammalian X chromosome where there is usually only one gene copy per cell active the described kind of binary trans-acting regulation between homologous gene loci is rendered impossible.     

Foraging by Passerine birds and Anolis lizards on St. Eustatius (Neth. Antilles): implications for interclass competition,and predation

Observations of foraging and diet for eight Passerine bird, two Anolis lizard, and one Ameiva lizard species in dry sclerophyll scrub on St. Eustatius (Neth. Antilles) show that none of the bird species competes as much with either anole as does the other anole, or the Ameiva. Anoles feed on insects, primarily on the ground and in low vegetation; on St. Eustatius no mainly insectivorous bird species feeds primarily in these places. Instead, the main presentday interaction between birds and anoles is predation. The abundant pearly-eyed thrasher (Margarops fuscatus) and the sparrow hawk (Falco sparverius) are the major predators on anoles. This predation has little effect on the niche relations of the anoles, according to a model for the coevolution of competing species.     

Localization of pyroantimonate-precipitable cation and surface coat anionic binding sites in developing erythrocytic cells and macrophages in normal human bone marrow

Summary The surfaces of developing erythrocytic cells and macrophages have been examined in normal human bone marrow by means of the pyroantimonate-osmium, ruthenium red and Thorotrast techniques for inorganic cations, surface glycoprotein-phospholipid complexes and surface anionic binding sites, respectively. No differences in the degree of surface coat reactivity were noted in the erythrocytic cells at different stages of maturation while pyroantimonate binding to the plasmalemma was not evident developmentally until the final stages of erythrocytic development. Rhopheocytotic invaginations proved to be chemically distinct from the remainder of the cell surface since they did not bind Thorotrast or pyroantimonate and gave more staining with ruthenium red. Pyroantimonate does not bind to the surface of macrophages and the binding of Thorotrast by these cells is less. Macrophage-erythrocytic cell contact zones did not stain with Thorotrast but stained with ruthenium red. The significance of these observations is discussed.Supported by Grant No. AM-HE-12084-14 from the National Institutes of Health, Bethesda, Maryland. — Appreciation is expressed to Anita Topson and Marjorie Griffith for their technical assistance and to Dr. Robert Hilberg for performing the bone marrow aspirations.