Chromosomal polymorphism in urban populations of Drosophila paulistorum

Abstract

Drosophila paulistorum populations colonizing the urban area of Porto Alegre, southern Brazil, were studied with the objective of characterizing their chromosomal polymorphism in this new environment. Despite being geographically and ecologically marginal and the fact that the colonization of the urban area seems to be a recent event, the populations showed a large number of inversions on all chromosome arms. Differences regarding inversion frequencies and percentage of heterozygosis were found when we compared the samples with respect to geographical, microenvironmental and temporal aspects. Such differences, however, could be attributed to both selective and stochastic factors<br>Populações de Drosophila paulistorum colonizadoras da área urbana de Porto Alegre, no sul do Brasil, foram estudadas com o objetivo de caracterizar o seu polimorfismo cromossômico neste novo ambiente. A despeito de serem geograficamente periféricas e ecologicamente marginais, e do processo de colonização ser um evento recente, as populações apresentaram um grande número de inversões em todos os braços cromossômicos. Diferenças nas freqüências de algumas inversões e na porcentagem de heterozigose foram encontradas quando se compararam as amostras quanto aos aspectos geográfico, microambiental e temporal. Tais diferenças, entretanto, podem ser atribuídas tanto a fatores seletivos como estocásticos

Chromosomal Evolution of Sibling Species of the Drosophila willistoni Group. I. Chromosomal Arm IIR (Muller’s Element B)

“…This is in accordance with our previous analysis (Garcia, 2002) with four different lines of AndeanBrazilian semispecies of D. paulistorum collected in the north (Para´State), center (Sa˜o Paulo State) and south of Brazil (Rio Grande do Sul and Santa Catarina States). On the other hand, Santos and Valente (1990) and Valiati and Valente (1997) described seven different inversions occurring in the IIR of marginal natural populations of Porto Alegre city (Rio Grande do Sul State), southern Brazil. Comparing our results with the photographic plates presented by Kastritsis (1966 and1967) we suppose that the inversions named by that author as 2R-I (more proximal) and 2R-II (more distal), are probably the same inversions that we describe as IIRh and IIRg, respectively, and that 2R-IV is probably the same IIRo inversion that segregates in Orinocan stock of D. paulistorum.…”

“…(1) analyses of chromosomal variation in local populations of D. willistoni from the south of Brazil and construction of a photomap of these populations with description of inversion break points (Regner et al, 1996); (2) analyses of chromosomal variation among 24 different populations of D. willistoni from Florida to Uruguay and preparation of a new photomap for the species with description of the inversions and new rearrangements fixed among populations (Rohde et al, in preparation); (3) analyses of chromosomal variation in southern populations of Andean-Brazilian semispecies of D. paulistorum (Santos and Valente, 1990;Valiati and Valente, 1997); (4) analyses of chromosomal variation among populations of Andean-Brazilian semispecies collected from north, center and south Brazil and construction of a photomap for this semispecies (Garcia et al, in preparation); (5) establishment of chromosomal homology and evolution of IIR chromosomal arm among the semispecies of D. paulistorum (present study); (6) establishment of chromosomal homology and evolution of IIR chromosomal arm among members of the D. willistoni species subgroup (present study).…”

Chromosomal polymorphism in Drosophila willistoni populations from Uruguay

“…Data on the chromosomal polymorphism of D. paulistorum samples from Porto Alegre (Santos and Valente, 1990;Valiati and Valente, 1997) may provide other explanations. Examination of the urban "colonizer" populations of D. paulistorum over a period of 10 years (1985 to 1995) revealed a progressive occupation of this unusual environment (Valiati and Valente, 1996 and unpublished data).…”

Studies of linkage in populations. XIII. A unique cause of linkage disequilibrium in natural populations of Drosophila robusta

“…Unlike the D. robusta situation, however, apparently no recombination occurs between these inversions in the double heterozygotes, despite the availability of ample genetic distance in many cases. Among the ‘presumptives’ on the list are the South and Central American sibling species, D. willistoni and D. paulistorum , which are very interesting because of their large amount of multiarm inversion polymorphism (Dobzhansky & Powell, 1975; Valiati & Valente, 1997); indeed D. paulistorum , with 99 known inversions, probably has the largest number of such variations known. Because these species are so difficult cytologically, the quantitative relations among their inversions are unknown, but the two, albeit sibling species, also exhibit different patterns: more than half of the inversions of D. paulistorum are in one autosome, and the chromosomal polymorphism is bound up with a complex system of subspeciation (Dobzhansky & Powell, 1975), whereas neither condition is true in its sibling species.…”