Apomixis and hybridity inHypericum perforatum

A review is presented of breeding peculiarities inHypericum perforatum L. and their consequences. This species is a tetraploid hybrid (2n=4x=32) which is assumed to be allopolyploid. It is a facultative apomict with apospory and pseudogamy. Original results of chromosome number variation amongstH. perforatum regenerants are presented, and their seed offspring were studied. The results suggest that genetic diversity occurs in this taxon resulting in great phenotypic variation. Various records of natural and artificial hybridization, as published by several authors, are discussed.     

Structural features are as important as sequence homologies inDrosophila heat shock gene upstream regions

Summary Pelham has shown that theDrosophila hsp 70 gene is not transcribed under heat shock conditions unless a given upstream region is present. Davidson et al. have recently compiled a list of sequences homologous to this region in otherDrosophila heat shock genes. They proposed that a set of unlinked genes, such as the heat shock genes, could be coordinately induced through an interaction in cis with a common regulatory molecule. That this interaction involves structural elements is suggested by the fact that these upstream regions share inverted repeats as well as areas of Z-DNA potential. Furthermore, using the Calladine-Dickerson rules for local helical parameters, we show that these regions share structural homology. This is significant because the presence of regions homologous to a derived consensus sequence does not necessarily imply structural similarity. Therefore, we suggest that these structural features are at least as important as the sequence homologies in enabling the heat shock response.     

Oviduct development inDrosophila

Summary The lateral oviducts ofDrosophila virilis were investigated in normal unoperated adult females, after unilateral and bilateral ovariectomy, and following the transplantation of genital discs. Subsequent to unilateral ovariectomy at larval stages of development, mature adult females exhibited reproductive systems with a free lateral oviduct which appeared somewhat shorter and less distended than a lateral oviduct normally attached to an ovary. Histological examination revealed that such free lateral oviducts have undergone considerable growth and differentiation in the absence of direct ovarian attachment, but exhibited a smaller lumen and more highly folded epithelium. They may be distinguished from attached lateral oviducts by conformational differences and by a possibly lesser size of the epithelial cells. Free lateral oviducts observed among bilaterally ovariectomized and sham-ovariectomized specimens were indistinguishable from those obtained after unilateral ovariectomy. The results are at variance with the previously accepted conclusion that oviduct growth inDrosophila is dependent upon inductive influences emanating from the ovary and directing the outgrowth of the oviducts. Differences in the developmental performance of the oviducts as a function of age at the time of ovariectomy were not evident in the study which included larvae ranging from the second instar to late in the third instar. Transplants of larval female genital discs to other larvae revealed a lesser development of the lateral oviducts than that exhibited by a genital disc developingin situ. A range of oviducal growth which lacked any relation to ovarian influences or to other internal organs of the hosts was obtained. In general, decreased amounts of oviducal muscle were found associated with the transplants.Presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the University of Virginia. This investigation was supported in part by: a National Science Foundation Co-operative Fellowship, by the United States Public Health Service Predoctoral Grant 1F1-GM 19,262-1, and by a Summer Research Grant, University of Missouri-St. Louis.     

Centrophobism inDrosophila melanogaster

Summary The term centrophobism is introduced to describe a newly discovered modification of search behavior in the walking fruitfly,Drosophila melanogaster: the avoidance of the center of an arena after diethylether narcosis. Evidence for the effect is obtained by comparison of the tracks of etherized and non-etherized flies under the influence of olfactory attractant around the center of the arena (Fig. 3). The tracks can be distinguished by their mean radial distance from the central district of the arena. Centrophobia denotes the relative difference of the distances of etherized flies and non-etherized controls (Fig. 4).Etherized flies avoid the center of the arena in spite of the attraction of olfactory, thermal or visual cues. The avoidance is significant even in the absence of conspicuous sensory cues for the discrimination of center and surround. The centrophobia obtained in the arena can be used to estimate the efficacy of attractants in the non-etherized control flies (Figs. 6, 7).The lowest possible dose of ether sufficient to elicit narcosis is sufficient to induce centrophobia. None of the other prevalent insect anaesthetics, CO₂, N₂ and cold, substitutes ether in the present experiments (Figs. 8, 9).Centrophobia arises immediately after ether narcosis. Once induced the effect lasts apparently undiminished for the life time of the flies (Fig. 9).Centrophobia has been found in either sex of the 9 strains tested so far (Fig. 5). Four strains including mutants deficient in wing formation (vestigial) or learning (dunce) show either temporal decline or partial suppression of centrophobia. The anomalous properties are actually due to enhanced spontaneous centrophobism in the non-etherized control groups of these strains (Fig. 10).