Enzyme polymorphism in a population of Calomys musculinus (Rodentia,Cricetidae)

NAD-linked lactate, malate, glycerophosphate, alcohol and nonspecific dehydrogenases, aspartate aminotransferases, and soluble esterases from extracts of tissues of individuals from a wild population of Calomys musculinus (Rodentia, Cricetidae) have been analyzed by means of starch gel electrophoresis and specific staining. Allelic frequencies and heterozygosity have been determined. Mendelian inheritance of some of the variants detected was confirmed by breeding experiments. Ten out of fifteen (66.6%) of the genetic loci investigated presented polymorphism. Mean heterozygosity per locus was very high (H=0.2014, se 0.046).This work has been supported, in part, by grants from the Secretaria de Ciencia y Tecnología de la Nación (National Program for Endemic Diseases) and from the Fundación Emilio Ocampo. C. N. G. is a Fellow and A. B. a Career Investigator of the Consejo Nacional de Investigaciones Científicas y Técnicas of Argentina.     

Variability of the inflorescence ofMicroseris laciniata (Compositae: Cichorieae)

Quantitative characters of the flowering head of a garden population ofMicroseris laciniata were scored during the second, third, and fourth season of growth. Number of achenes per head, number of phyllaries per head and the average number of pappus parts per achene in single heads show significant plant to plant variation. Achenes per head and pappus parts per achene were scored in identical plants in two subsequent seasons. The number of pappus parts per achene varies freely between five and ten. This contrasts with annual species ofMicroseris in which either five or ten pappus parts are found, depending on the species. In spite of a clear plant-specific average of pappus parts, both high and low pappus part determination can be demonstrated in all specimens. The number of pappus parts depends on the position of an achene on the receptacle, marginal achenes usually having fewer pappus parts than central ones. This gradient is not closely correlated with the position of an achene on the genetic spiral.     

Biosystematic investigations on the lady fern(Athyrium filix-femina)

In EuropeAthyrium filix-femina has a constant chromosome number (2n = 80) and is sexual. The normal type of reproduction is intergametophytic crossing. In the gametophyte phase there is a hormone system which induces dark germination of spores and antheridium formation. Sporophytes originating from single prothalli show that a genetic load is present in all population examined. It appears not to be a simple allelic load but a complicated balanced system. Morphological variability can be interpreted as the expression of the genetic heterogeneity of populations. There are no crossing barriers, not even between insular populations hundreds of kilometers apart.     

The effects of an unpredictable precipitation regime on vernal pool hydrology

1. Vernal pools are small precipitation‐fed temporary wetlands once common in California. They are known for their numerous narrowly endemic plant and animal species, many of which are endangered. These pools experience the typical wet season/dry season regime of Mediterranean climates. Their hydrological characteristics are determined by a complex interaction between the highly variable climate and topographic relief. 2. Hypotheses regarding the effects on ponding of total precipitation, storm intensity and pattern were examined using long‐term weather records combined with two decades of data on the length and depth of inundation in 10 individual pools. Similarly, data on pool landscape position and microtopography allowed examination of the interactions between topography and rainfall amount and pattern. 3. The total amount of precipitation and length of inundation were strongly correlated. Landscape position affected ponding duration, with collector pools holding water longer than headwater pools. Basin microtopography interacted with climatic variability to determine the nature and extent of within‐basin microhabitats sufficiently different in hydrological and/or soil conditions to support or exclude individual species. The effect on hydroperiod of precipitation concentrated in a few months rather than spread more evenly over the season depended on total precipitation. 4. Changes in climate, the mound‐and‐depression landscape or pool microtopography could have profound impacts on the hydrology of individual pools as well as the array of hydrological conditions in the system. Given the individualistic responses of the numerous endemic species supported by vernal pools, any of these environmental changes could diminish their sustainability and increase the risk of species extinction. Conservation, restoration and management decisions should take these factors into account.     

Density dependence of Anaphes sordidatus (Hymenoptera: Mymaridae) parasitism on eggs of Listronotus oregonensis (Coleoptera: Curculionidae)

Listronotus oregonensis (LeConte) (Coleoptera: Curculionidae) oviposits in carrot leaves and the larvae feed in carrot roots. Its eggs are parasitized by Anaphes sordidatus (Girault) (Hymenoptera: Mymaridae) throughout its oviposition period. This parasitoid is the major biotic mortality factor for L. oregonensis. Parasitism by A. sordidatus was studied for three years in sequentially sown plots of carrots, Daucus carota var. sativa. Over the scason, significantly fewer L. oregonensis eggs were oviposited in later sown carrots than in earlier sown carrots because oviposition started later in late sown plots of carrots. A positive temporal density-dependent relationship was observed each year between parasitism rates and host densities. This positive density dependence occurred in early and mid-summer for earlysown carrots where host density reached 1–2 host eggs per plant but disappeared in late summer when host density decreased while parasitism remained high. Latesown carrots had low host egg density (0.2 host egg per plant) and contributed little to the total number of eggs. In these late sown plots, parasitism increased rapidly to over 80% but no density dependence was observed. Spatially, few statistically significant regressions were found but all indicated a positive spatial density-dependence. Most non-significant regressions occurred because the range of egg density was too small between plots for a given date.     

Genetically identical copies of the mulberry silkworm

Summary Genetically identical copies of the silkworm female obtained via ameiotic parthenogenesis are insignificantly depressed by artificial reproduction, and notwithstanding their isogenous pattern, they show the same variability in quantitative characters as in the heterogenous forms.By means of androgenesis, genetically identical copies of strictly homozygous males were obtained; the latter were produced via meiotic parthenogenesis. The androgenetic clones of these males were transformed by backcrosses into homozygous bisexual lines. Viability and cocoon weight in these lines were higher than those in androgenetic clones of similar genotype, but they were far from the norm due to the depressing effect of semilethals left in them in a homozygous state. An extremely low phenotypical variability of quantitative characters is observed in the isogenous hybrids F₁ obtained from crossing two genetically dissimilar strictly homozygous individuals. These hybrids make excellent material for phenogenetical studies. The female and male isogenous clones have an increased combining ability which is acquired in the course of their selection for high disposition towards complete parthenogenesis. For practical purposes it is proposed to take a female and a male which when mated produce a high-quality family and clone them separately, the first via parthenogenesis, the latter via androgenesis. After mating these reproduced bisexual clones, it will be possible to obtain in successive generations a vast number of families repeating the prominent productivity of the initial family.     

Bioengineering Considerations for a Nurturing Way to Enhance Scalable Expansion of Human Pluripotent Stem Cells

Understanding how defects in mechanotransduction affect cell‐to‐cell variability will add to the fundamental knowledge of human pluripotent stem cell (hPSC) culture, and may suggest new approaches for achieving a robust, reproducible, and scalable process that result in consistent product quality and yields. Here, the current state of the understanding of the fundamental mechanisms that govern the growth kinetics of hPSCs between static and dynamic cultures is reviewed, the factors causing fluctuations are identified, and culture strategies that might eliminate or minimize the occurrence of cell‐to‐cell variability arising from these fluctuations are discussed. The existing challenges in the development of hPSC expansion methods for enabling the transition from process development to large‐scale production are addressed, a mandatory step for industrial and clinical applications of hPSCs.     

A review of phosphorus efficiency in wheat

More efficient utilization of phosphorus by wheat plants is needed to extend the useful life of the phosphate reserves in the world, to reduce the cost of producing crops, and to improve the value of the grain and the straw produced. In this paper definitions of efficient use of phosphorus by wheat are reviewed, genotypic variation in phosphorus efficiency is reported, some consequences of breeding for greater efficiency are discussed, and ways to select more efficient genotypes are suggested.