Chromosomal evolution and comparative gene mapping in the Drosophila repleta species group

Abstract

A review of our recent work on the cromosomal evolution of the Drosophila repleta species group is presented. Most studies have focused on the buzzatii species complex, a monophyletic set of 12 species which inhabit the deserts of South America and the West Indies. A statistical analysis of the length and breakpoint distribution of the 86 paracentric inversions observed in this complex has shown that inversion length is a selected trait. Rare inversions are usually small while evolutionary successful inversions, fixed and polymorphic, are predominantly of medium size. There is also a negative correlation between length and number of inversions per species. Finally, the distribution of inversion breakpoints along chromosome 2 is non-random, with chromosomal regions which accumulate up to 8 breakpoints (putative "hot spots"). Comparative gene mapping has also been used to investigate the molecular organization and evolution of chromosomes. Using in situ hybridization, 26 genes have been precisely located on the salivary gland chromosomes of D. repleta and D. buzzatii; another nine have been tentatively identified. The results are fully consistent with the currently accepted chromosomal homologies between D. repleta and D. melanogaster, and no evidence for reciprocal translocations or pericentric inversions has been found. The comparison of the gene map of D. repleta chromosome 2 with that of the homologous chromosome 3R of D. melanogaster shows an extensive reorganization via paracentric inversions and allows to estimate an evolution rate of ~1 inversion fixed per million years for this chromosome<br>Uma revisão de nosso recente trabalho sobre a evolução cromossômica do grupo de espécies de Drosophila repleta é apresentada. A maioria dos estudos refere-se ao complexo de espécies buzzatii, um conjunto monofilético de 12 espécies que habitam os desertos da América do Sul e das Índias Ocidentais. Uma análise estatística do comprimento e da distribuição do ponto de quebra de 86 inversões paracêntricas observadas neste complexo mostrou que o comprimento da inversão é um caráter selecionado. Inversões raras são geralmente pequenas, enquanto que inversões evolucionariamente bem sucedidas, fixas e polimórficas, são predominantemente de tamanho médio. Há também uma correlação negativa entre o comprimento e o número de inversões por espécie. Finalmente, a distribuição dos pontos de quebra nas inversões ao longo do cromossomo 2 não é aleatória, com regiões cromossômicas que acumulam até 8 pontos de quebra (possíveis "pontos quentes"). O mapeamento gênico comparativo também foi usado para investigar a organização molecular e a evolução dos cromossomos. Usando hibridização in situ, 26 genes foram precisamente localizados nos cromossomos da glândula salivar de D. repleta e D. buzzatii; outros 9 foram identificados por tentativa. Os resultados são completamente consistentes com as homologias cromossômicas correntemente aceitas entre D. repleta e D. melanogaster, não se encontrando evidências de translocações recíprocas ou inversõ...

Photomap of the polythenic chromosomes ofDrosophila malerkotlianaandin situmapping of the Hsp83locus

“…The homology of the chromosomal arms between the two groups was extended by mapping the genes Hsp83, Hsr, Hsp27 and Ubi (among others) of D. melanogaster in several species of the willistoni group, by RIEGER (1999). Similar studies had already been carried out for the obscura group (SEGARRA et al, 1999) and for the group full (RUIZ et al, 1997) of Drosophila species.…”

Reassignment of Drosophila willistoni Genome Scaffolds to Chromosome II Arms

“…This study contributes to a more accurate characterization of the genome of D. willistoni , providing a better basis for further genetic studies associated with it. As D. willistoni is an intriguing model for chromosomal and evolutionary studies, in particular, the results described here will help in analyses of interspecific chromosome evolution and genome evolution (as in Ruiz et al 1997 ; Ranz et al 2001 ; Papaceit et al 2006 with other species) and also in the characterization of chromosomal inversion breakpoints (as in Delprat et al 2009 ).…”

Variations on a theme: diversification of cuticular hydrocarbons in a clade of cactophilic Drosophila

“…Originally, we combined chromosomal inversion differences [ 41 , 53 ] with the per gene [ 46 ] and mtDNA COI sequence data [ 44 ] to reconstruct phylogenetic relationships for the seven D. buzzatii cluster species. Chromosome inversions have high phylogenetic utility in Drosophila [ 42 ], but because only four inversions are unique and thus phylogenetically informative in the D. buzzatii species cluster (Figure 2 ), populations of the same species were all coded with the same inversions.…”

“…D. buzzatii and D. borborema were not included in that classification because both species have aedeagi that were already well characterized and could be easily distinguishable from the other species. Chromosomal inversions, shown above the tree branches, are based on Ruiz et al [ 41 , 53 ] and used together with period gene data to reconstruct the phylogeny (see Figures 5 and 6). Host plant use and geographic distributions are based on Manfrin and Sene [ 34 ], Benado et al [ 106 ], Marín et al [ 107 ] and Vilela [ 108 ].…”