Five natural samples of a recent South America invader, the drosophilid Zaprionus indianus, were investigated with the isofemale line technique. These samples were compared to five African mainland populations, investigated with the same method. The results were also compared to data obtained on mass cultures of other populations from Africa and India. Three quantitative traits were measured on both sexes, wing and thorax length and sternopleural bristle number. We did not find any latitudinal trend among the American samples, while a significant increase in body size with latitude was observed in the Indian and, to a lesser degree, in the African populations. American populations were also characterized by their bigger size. Genetic variability, estimated by the intraclass correlation among isofemale lines, was similar in American and African populations. The intraline, nongenetic variability was significantly less in the American samples, suggesting a better developmental stability, the origin of which is unclear. A positive relationship was evident between intraline variability of size traits and the wing-thorax length correlation. Altogether, our data suggest that the colonizing propagule introduced to Brazil had a fairly large size, preventing any bottleneck effect being detected. The big body size of American flies suggests that they came from a high-latitude African country. The lack of a latitudinal cline in America seems to be related to the short time elapsed since introduction. The very rapid spread of Z. indianus all over South America suggests that it might rapidly invade North America.

Zaprionus indianus is a cosmopolitan drosophilid, of Afrotropical origin, which has recently colonized South America. The sexual dimorphism (SD) of body size is low, males being almost as big as females. We investigated 10 natural populations, 5 from America and 5 from Africa, using the isofemale line technique. Three traits were measured on each fly: wing and thorax length and sternopleural bristle number. Two indices of SD were compared, and found to be highly correlated (r > 0.99). For the sake of simplicity, only the female/male (F/M) ratio was further considered. A significant genetic variability of SD was found in all cases, although with a low heritability (intra-class correlation of 0.13), about half the value found for the traits themselves. For size SD, we did not find any variation among continents or any latitudinal trend, and average values were 1.02 for wing length and 1.01 for thorax length. Bristle number SD was much greater (1.07). Among mass laboratory strains, SD was genetically much more variable than in recently collected populations, a likely consequence of laboratory drift. Altogether, SD, although genetically variable and prone to laboratory drift, is independent of size variations and presumably submitted to a stabilizing selection in nature.

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Chromosomal polymorphism in natural populations of Drosophila willistoni from Uruguay and southern Brazil was investigated in order to understand the genetic characteristics and evolutionary potential of these almost geographically marginal populations. The level of chromosomal polymorphism in samples from Uruguay was higher than in those from the southernmost Brazilian state of Rio Grande do Sul. The increase in the polymorphism of these populations, in which the species almost reaches its southern limit, contradicts the low level of paracentric inversion polymorphism expected under the central-marginal chromosomal polymorphism cline previously reported. The high frequency of some inversions and the presence of unique inversions in samples from Uruguay indicate the uniqueness of these populations.

1985.Geographic patterns of chromosomal variation in populations of the grasshopper (Trimerotropis pallidipennis) from southern Argentina. Can. J. Genet. Cytol. 27: 259-271. Geographic variation has been studied on seven south Argentina populations of Trimerotropis pallidipennis polymorphic with respect to centromere position. Univariate and multivariate statistical analysis were used to assess interpopulation relationships by considering the inversion frequency, the chiasma frequency, and the population distance from the Andes, which is considered to be the hypothetical pathway of migration of this typically North American species to southern latitudes. A cluster analysis indicated strong chromosomal differentiation between the almost monomorphic populations in the Andes' "precordillera" and the highly polymorphic populations in more eastern locations. It also showed that chromosomal similarity between populations could be predicted by geographic proximity. No attempt has been made to relate such a pattern of chromosome variation to ecological data. The lack of any clear relationship with phytogeographic regions or climatic characteristics suggests that microenvironmental factors related to aridity may be important in this case. The presence of inversions within a population has a notable effect on chiasma frequency and position. Chiasmata are suppressed within the inverted region of both inversion heterozygotes and homozygotes. The allelic sequences in the inverted region are thus preserved from recombination and exchanges are limited to terminal regions. Key words: geographic variation, chromosome polymorphism, chiasma frequency, B chromosome, pseudomultiple associations. GONI, B., E. S. DE VAIO, M. BELTRAMI, M. S. LEIRA, M. CRIVEL, F. PANZERA, P. CASTELLANOS et A. BASSO. 1985. Geographic patterns of chromosomal variation in populations of the grasshopper (Trimerotropis pallidipennis) from southern Argentina. Can. J. Genet. Cytol. 27: 259-271.La variation geographique a ete etudiee chez sept populations de Trimerotropis pallidipennis du sud de 1' Argentine, qui sont polymorphes relativement a la position du centromkre. Des analyses statistiques a une ou plusieurs variables ont ete utilisees pour determiner les relations entre populations, en considerant la frequence d'inversions, la frequence de chiasmata et la distance des populations par rappot aux Andes, qui sont considkrees comme le sentier de migration hypothetique de cette espkce typiquement nord-americaine vers les latitudes du sud. Une analyse de groupes a mis en evidence une forte differenciation chromosomique entre les populations presque monomorphes des Andes "precordillkres" et les populations hautement polymorphes localisees plus a l'est. Cette analyse a aussi demontre que la ressemblance des chromosomes pouvait Ztre predite par proximitk gkographique. Ce mode de variation chromosomique n'a en aucune fason kt6 relik aux donnkes Ccologiques. Toutefois, l'absence de relations claires entre les regions phytogeographiques ou les caracteristiques clima...