Models for contact-mediated pattern formation: cells that form parallel arrays

Kinetic continuum models are derived for cells that crawl over a 2D substrate, undergo random reorientation, and turn in response to contact with a neighbor. The integro-partial differential equations account for changes in the distribution of orientations in the population. It is found that behavior depends on parameters such as total mass, random motility, adherence, and sloughing rates, as well as on broad aspects of the contact response. Linear stability analysis, and numerical, and cellular automata simulations reveal that as parameters are varied, a bifurcation leads to loss of stability of a uniform (isotropic) steady state, in favor of an (anisotropic) patterned state in which cells are aligned in parallel arrays.     

Quantitative comparison of Fusarium oxysporum competitiveness in relation to carbon utilization

Abstract The competitive saprophytic interaction between pathogenic and non-pathogenic strains of Fusarium oxysporum was investigated by studying their ability to competitively colonize sterilized soil. It was demonstrated that carbon was the first limiting substrate of Fusarium oxysporum growth in sterilized soil. Moreover, the efficiency with which glucose was utilized in the formation of propagules varied from one strain to another. Results of competitiion experiments showed that a linear relationship existed between the ratio of inoculum densities at the plateau (carrying capacity) and the ratio of inoculum densities incorporated into non-amended sterilized soil. The slope of the regression line indicated the competitiveness index, i.e. the competitiveness of a non-pathogenic strain in relation to that of a pathogenic strain. This parameter could be related to the yield coefficient of the strains in glucose-amended soil.     

The Why and How of Species

The biological species concept deals both with the meaning of the sexual species as a harmonious gene pool and with its protection against deleterious outbreeding (effected by isolating mechanisms). According to the Darwin-Muller-Mayr theory isolating mechanisms are acquired by incipient species during alloparty. Isolating mechanisms are not the result of ad hoc selection, but of a change of function of properties acquired during the preceding isolation of the incipient species. The role of behavioral properties (recognition) among the isolating mechanisms has long been recognized and described by naturalists but was rejected as basis of a species definition for a number of valid reasons.     

Effect of biologically active plants used as netst material and the derived benefit to starling nestlings

Summary The European starling Sturnus vulgaris preferentially incorporates fresh sprigs of particular plant species for use as nesting material. Chemicals found in these plants may act to reduce pathogen and ectoparasite populations normally found in nest environments. The present experiments were performed to test this Nest Protection Hypothesis. In the fild, we experimentally determined that wild carrot Daucus carota, a plant species preferred as nest material, effectively reduced the number of hematophagous mites found within nests relative to control nests without green vegetation. Chicks from nests containing wild carrot had higher levels of blood hemoglobin than chicks from control nests. However, there were no differences in weight or feather development. In the laboratory, we found that wild carrot and fleabane, Erigeron philadelphicus, (also preferred by starlings as nest material) substantially reduced the emergence of feeding instars of mites, while garlic mustard, Alliaria officinalis, (commonly available but not preferred) had little effect on the emergence of mites. We infer that preferred plant material may act to inhibit feeding or otherwise delay reproduction of mites, thereby reducing risk of anemia to developing nestlings.     

The use of replicated progenies in marker-based mapping of QTL's

Summary Seven types of progeny are described which can be used in detection of linkage between marker loci and quantitative trait loci (QTL) in a cross between two inbred lines. Three types of progeny: recombinant inbred lines (RI); doubled haploid lines (DH); and S₁ lines can be used to detect linked main effects, d. DH and RI lines can be used to detect smaller effects than S₁ lines. However, S₁ lines can also be used to detect within-population dominance effects, h. The smallest d detectible is in the range of 1/2 to 1/12 the size of the corresponding LSD_(0.05) for the quantitative trait, using 100 lines and 6 replicates. The smallest h detectible is 3–4 times this size. Four types of progeny can be used to detect differences in the dominance behavior of alleles within the population relative to an allele in another inbred line (P₄: DH lines x P₄; RI lines x P₄; either F₂ x P₄ or S₁ lines x P₄; and progeny generated by crossing (F₁ x P₃) x P₄. Dominance differences in the range of 1 1/4 to 1/6 the size of the corresponding LSD_(0.05) are routinely detectible using 100 lines and 6 replicates. Increasing the numbers of progeny evaluated or the number of replicates allows for the detection of relatively smaller linked effects.Contribution of United AgriSeeds, Inc.     

Biology ofTyta luctuosa [Lep.: Noctuidae] and its potential value as a biological control agent for the weedConvolvulus arvensis

The biology of the noctuid,Tyta luctuosa (Denis & Schiffermüller) (Lep.: Noctuidae), a defoliator of field bindweed,Convolvulus arvensis L., was studied in southern Europe.T. luctuosa is widely distributed and feeds on both thick stands and scattered host populations growing in a diversity of habitats. It undergoes 2 and perhaps a partial 3rd generation/year in southern Europe and is active during most of the growing season ofC. arvensis. In the laboratory the total time from egg to adult averages 45.6 days. There are 5 larval instars. Adult females deposit on average over 400 eggs. The larvae being able to feed and develop on native North AmericanCalystegia spp. in the laboratory, there are some reservations about its release in North America. However, the moth has potential value as a biological control agent for field bindeed in the western USA where it would fill an almost unoccupied niche.      

Lutte biologique et intégrée dans les vergers de citrus en zone méditerranéenne

Les problèmes posés par les ravageurs des Citrus ont pris une importance considérable au cours de ces 3 dernières décennies et cela pour plusieurs raisons:

RFLP mapping using near-isogenic lines in the soybean [Glycine max (L.) Merr.]

Summary A molecular marker analysis of a near-isogenic line (NIL), its donor parent (DP), and its recurrent parent (RP) can provide information about linkages between molecular markers and a conventional marker introgressed into the NIL. If the DP and RP possess different alleles for a given molecular marker, and if the NIL possesses the same allele as the DP, then it is reasonable to presume a linkage between that molecular marker and the introgressed marker. In this study, we examined the utility of RFLPs as molecular markers for the NIL genemapping approach. The allelic status of fifteen RFLP loci was determined in 116 soybean RP/NIL/DP line sets; 66 of the Clark RP type and 50 of the Harosoy RP type. Of the 1740 possible allelic comparisons (116 NILs x 15 RFLP loci), 1638 were tested and 462 (33.9%) of those were informative (i.e., the RP and DP had different RFLP alleles). In 15 (3.2%) of these 462 cases the NIL possessed the DP-derived RFLP allele, leading to a presumption of linkage between the RFLP locus and the introgressed conventional marker locus. Two presumptive linkages, pK-3 — and pK-472 — Lf _i, were subsequently confirmed by cosegregation linkage analysis. Although not yet confirmed, two other associations, pk-7 ab and pK-229 — y ₉ seemed to be plausible linkages, primarily because the pk-7 — ab association was detected in two independently derived NILs and both markers of the pK-229 — y ₉ association were known to be linked to Pb. The data obtained in this investigation indicated that RFLP loci were useful molecular markers for the NIL gene-mapping technique.Published as Paper no. 9101, Journal Series, Nebraska Agric. Res. Div. Project no. 12-091. Research partially funded by a grant from the Nebraska Soybean Development, Utilization, and Marketing Board