Gabriella Rocchetta

The relationship between fitness and response to selection in Drosophila melanogaster

SummaryThe relationship between the selection response exhibited by a morphological trait and the correlated response observed on fitness values has been investigated to improve our understanding of micro-and macro-evolutionary processes. The research was designed to test the validity of the “homeostatic” and “metric deviation” models (Robertson 1956). The results show that:1)correlated changes in fertility values are larger when selection for minus-variant wing length is applied to males than when it is performed on females,2)within each of the selected lines, M, F and MF, the reproductive fitness of the populations obtained from vg/vg x +/vg crosses differs from that of the populations derived from +/vg X vg/vg crosses,3)reproductive fitness values of populations derived from vg/vg X +/vg crosses are fairly constant in selected lines obtained by means of different selective procedures, while mean wing length changes; the corresponding populations from +/vg X vg/vg crosses show, on the contrary, a proportionality between fitness and selected trait values. The lack of consistency of these results with the currently accepted hypotheses on the relationship between selection response and correlated changes in fitness leads to the conclusion that the two models considered do not satisfactorily interpret our results; these are better explained by a developmental relationship between fitness and selected trait.

Ag-NOR protein distribution correlates with patient survival in stage I endometrial adenocarcinoma

The relationship between argyrophil nucleolar organizer region (Ag-NOR) protein quantity and prognosis was studied in 33 cases of stage I endometrial adenocarcinoma. Ag-NOR protein quantity was measured by image analysis in silver-stained sections from paraffin-embedded samples of curettings. Patients had a minimum 10-year follow-up. Only 2 out of 25 patients exhibiting a mean Ag-NOR protein area of less than 3 μm2 died of cancer, whereas 5 of the 8 patients with a mean Ag-NOR protein area of more than 3 μm2 died of the disease. The present results demonstrate that the Ag-NOR protein value is closely related to patient survival in stage I endometrial carcinoma and that it is a reliable prognostic indicator in this type of carcinoma.

Somatic variation in micropropagated clones ofCichorium intybus

An experiment aiming to establish whether temporary or persistet somatic variation can arise in clones obtained in vitro by micropropagation has been performed onCichorium intybus. The results point out that persistent modifications of the phenotype can be observed after six cycles of cloning and that when the length of the cloning period is varied these appear to be differential responses of the same genotype to the micropropagation.

Somaclonal Variation in Chicory

Chicory (Cichorium intybus L., n = 9) is a species of the Compositae family that is concentrated in the warm temperate zone of the northern hemisphere, particularly in Europe and around the Mediterranean Basin. According to Vavilov (1951), the Mediterranean is the primary center of distribution of this plant. Chicory grows well in every type of soil and does not have particular climatic requirements, although the best qualitative and quantitative results have been obtained when it is cultivated in fresh well-drained soils. However, chicory needs all nutrient elements, above all phosphates (Antoniani et al. 1975).

Size and shape inPoecilia reticulata

In this paper some aspects of size and shape variation in 3 inbred lines ofPoecilia reticulata reared under different environmental conditions are described. The results obtained suggest that size variation is principally due to environmental and/or developmental modifications; differences in shape, on the other hand, seem to be mainly correlated with a different genetic constitution of the inbred lines considered.

Crossvein defects in disruptive selection lines of Drosophila melanogaster

Abstract The relationship between crossvein defects and wing length was investigated in lines of Drosophila under disruptive selection on the IV longitudinal vein to get a better knowledge of the mechanism by which this selection determines divergence. The results of selection showed that in a disruptive line (the more responsive to this type of selection) a differentiation is present between crossveinless and wild type individuals with regard to wing length: the former having a distribution of wing length coincident with the low mode, the latter with the high mode of the wing length curve. Individuals with cve incompletely expressed (only on a wing) behave as wild type in regard to the wing length. A genetical analysis performed on control lines and treated with shock of temperature demonstrated that the different relationship between wing length and crossvein presence or absence is attributable to a phenotypic rather than a genetic mechanism. The conclusion was drawn that two new patterns have been stab...

Interaction between artificial and natural selection.

SummaryIn order to understand how divergence may appear within a gene pool without limitations on gene flow, experiments were performed to investigate whether the genetic structure of a population may be effective in controlling the response to natural selection. Starting from plateaued populations of Drosophila melanogaster selected for wing length on the two sexes separately, the response to natural selection was studied after artificial selection had been discontinued. The results show that populations derived from artificial selection applied to the different sexes respond to subsequent natural selection in dissimilar ways, so as to suggest that the relationships between fitness and wing length have been changed. A second experiment comparing the response to natural and to artificial reversed selection suggests that different genes or gene complexes may be involved in wing length determination: these different genes show a dissimilar response in the different sexes and to natural and artificial selection. This variety of responses suggests that the interactions of different genes or gene complexes with artificial and natural selection could possibly lead to differentiation within the population.

A multivariate analysis of dominance inDrosophila

SummaryEleven wing measurements in twoDrosophila melanogaster lines (Canton and FLL) and their reciprocal crosses were analyzed by a multivariate technique in order to investigate changes in variability when dominance is manifested. FLL line was obtained by artificial selection for short wing applied on one measurement on the rightwing. Differences between left and right wing were observed in variabilities after selection. The comparison between F1 and parental populations shows that there is strong evidence for non-additivity which is manifested by a component of the variability due to multiple regression. This is interpreted as meaning that relationships between characters are affected in the heterozygote in a non-additive way, apparently due to interactions among the developmental patterns of the characters considered. It is suggested that a “character” should be defined in such a way as to include its developmental patterns, in order to achieve a better understanding of the dominance phenomenon.

Quantitative inheritance and divergence inDrosophila populations.

SummaryDivergent sub-populations were obtained following relaxation of artificial selection for short wing in a population ofDrosophila melanogaster. Different results were obtained by relaxing the selection pressure in lines resulting from different selection procedures. The divergence was actually observed between lines derived by reciprocal crosses between vestigial and wild-type heterozygotes belonging to the same selection line. There was a difference in phenotypic variability in the two sub-lines from the start, which might be responsible for the differential response to natural selection. No difference in reproductive fitness has been detected between the divergent lines. The results can not be easily understood in the framework of an additive polygenic model; it is suggested that some complex interaction may be involved, acting on the developmental processes. It seems, however, safe to suggest that the divergence observed is determined by factors which are present in the FM line.