Phenotypic variation of the Aedeagus of Drosophila serido vilela & sene (Diptera: Drosophilidae).

Drosophila serido Vilela & Sene is a polytypic and cactophilic species with broad geographic distribution in Brazil. The morphology of the aedeagi of eight natural populations of D. serido was analyzed. Based on features of their aedeagi, populations of D. serido were discriminated with an efficiency of nearly 75%. The analysis using the Mantel test suggests that the morphological divergence of D. serido is correlated with the geographic distance among populations. There is no single cause to explain the observed pattern; therefore, the results were discussed considering the three main hypotheses to explain the aedeagus evolution: lock and key, pleiotropy and sexual selection. Alternatively, the aedeagus variability of D. serido might be related to environmental causes, such as temperature and/or host cacti.

Phenotypic variation of the Aedeagus of Drosophila serido vilela & sene (Diptera: Drosophilidae) / Variação fenotípica do edeago de Drosophila serido vilela & sene (Diptera: Drosophilidae)

Drosophila serido Vilela & Sene é uma espécie cactofílica e politípica, com ampla distribuição geográfica no Brasil. A morfologia do edeago de indivíduos provenientes de oito populações naturais de D. serido foi avaliada. De acordo com as características dos seus edeagos, as populações de D. serido foram discriminadas com eficiência de aproximadamente 75 por cento. O resultado do teste de Mantel sugere que a divergência morfológica de D. serido é correlacionada com a distância geográfica das populações. A explicação para o padrão observado não é única. Por esta razão, os resultados foram discutidos considerando-se as três principais hipóteses para explicar a evolução do edeago: chave-fechadura, pleiotropia e seleção sexual. Alternativamente, a variabilidade encontrada nos edeagos de D. serido poderia estar relacionada a fatores ambientais, tais como temperatura e/ou cacto hospedeiro.

Drosophila serido Vilela & Sene is a polytypic and cactophilic species with broad geographic distribution in Brazil. The morphology of the aedeagi of eight natural populations of D. serido was analyzed. Based on features of their aedeagi, populations of D. serido were discriminated with an efficiency of nearly 75 percent. The analysis using the Mantel test suggests that the morphological divergence of D. serido is correlated with the geographic distance among populations. There is no single cause to explain the observed pattern; therefore, the results were discussed considering the three main hypotheses to explain the aedeagus evolution: lock and key, pleiotropy and sexual selection. Alternatively, the aedeagus variability of D. serido might be related to environmental causes, such as temperature and/or host cacti.

Sequence analysis, chromosomal distribution and long-range organization show that rapid turnover of new and old pBuM satellite DNA repeats leads to different patterns of variation in seven species of the Drosophila buzzatii cluster.

We aimed to study patterns of variation and factors influencing the evolutionary dynamics of a satellite DNA, pBuM, in all seven Drosophila species from the buzzatii cluster (repleta group). We analyzed 117 alpha pBuM-1 (monomer length 190 bp) and 119 composite alpha/beta (370 bp) pBuM-2 repeats and determined the chromosome location and long-range organization on DNA fibers of major sequence variants. Such combined methodologies in the study of satDNAs have been used in very few organisms. In most species, concerted evolution is linked to high copy number of pBuM repeats. Species presenting low-abundance and scattered distributed pBuM repeats did not undergo concerted evolution and maintained part of the ancestral inter-repeat variability. The alpha and alpha/beta repeats colocalized in heterochromatic regions and were distributed on multiple chromosomes, with notable differences between species. High-resolution FISH revealed array sizes of a few kilobases to over 0.7 Mb and mutual arrangements of alpha and alpha/beta repeats along the same DNA fibers, but with considerable changes in the amount of each variant across species. From sequence, chromosomal and phylogenetic data, we could infer that homogenization and amplification events involved both new and ancestral pBuM variants. Altogether, the data on the structure and organization of the pBuM satDNA give insights into genome evolution including mechanisms that contribute to concerted evolution and diversification.

Molecular characterization of SSS139, a new satellite DNA family in sibling species of the Drosophila buzzatii cluster

We characterized sequences of a novel SSS139 RsaI satellite DNA family in Drosophila gouveai and Drosophila seriema, two members of the Drosophila buzzatii cluster (D. repleta group). The sequences were AT-rich (69 percent) with a monomer unit length of about 139 bp and contained two direct subrepeats of 14 bp and 16 bp, suggesting that it might have originated by the duplication of smaller sequences. Southern and dot-blot hybridization analyses also detected SSS139 in other Drosophila buzzatii cluster species (D. koepferae, D. antonietae, D. borborema and D. serido) but not in D. buzzatii. These results agree with the marginal phylogenetic position of D. buzzatii within the D. buzzatii cluster.

Low rates of homogenization of the DBC-150 satellite DNA family restricted to a single pair of microchromosomes in species from the Drosophila buzzatii cluster.

A satellite DNA family, termed DBC-150, comprises slightly GC-rich repeat units of approximately 150 bp that were isolated (by DNA digestions or PCR) from the genome of all seven Drosophila species from the buzzatii cluster (repleta group). The presence of subrepeats suggests that part of the extant DBC-150 monomer originated by the duplication of small sequence motifs. The DBC-150 family is compared to the previously described pBuM satDNA family, an abundant component of the genome of five species of the cluster. The two families are different in several aspects, including primary structure, A + T content, intraspecific and interspecific variability and rates of homogenization (or nucleotide spread). The data indicate a lower rate of homogenization (and absence of complete concerted evolution) of the DBC-150 compared to the pBuM family. FISH on metaphase chromosomes revealed that the DBC-150 family is located exclusively in the microchromosomes. To our knowledge this is the first record of a complex Drosophila satDNA restricted to a single pair of microchromosomes. The observed low rates of homogenization of the DBC-150 family might be related to a presumed reduction or suppression of meiotic recombination in the microchromosomes.

Aedeagus morphology as a discriminant marker in two closely related Cactophilic species of Drosophila (Diptera; Drosophilidae) in South America

Drosophila serido e D. antonietae são espécies crípticas pertencentes ao ''cluster'' Drosophila buzzatii. Morfologicamente, elas podem ser discriminadas apenas por diferenças quantitativas. Neste trabalho, nós analisamos o comprimento e a média da curvatura equalizada de quatro regiões do edeago de indivíduos de D. antonietae e D. serido. Os espécimes de D. serido e D. antonietae foram discriminados com 96,74% de eficiência. Apenas com base na variável que mais contribuiu para discriminação dos grupos (média da curvatura equalizada do arco IV do edeago), nós observamos significativa divergência morfológica intraespecífica em D. serido em relação a D. antonietae, o que está em concordância com outros marcadores. A alta divergência morfológica apenas na média da curvatura equalizada do arco IV do edeago mostra que essa região do edeago evoluiu mais rápido que as demais desde a divergência entre as duas espécies. A importância do presente estudo para o entendimento das bases genética que controlam a formação do edeago, nas espécies do ''cluster'' Drosophila buzzatii, é discutida.

Aedeagus morphology as a discriminant marker in two closely related cactophilic species of Drosophila (Diptera; Drosophilidae) in South America.

Drosophila serido and D. antonietae are sibling species belonging to the Drosophila buzzatii cluster. Morphologically, they can only be discriminated by quantitative traits. In this paper we analyze the length and equalized average curvature of four regions of the aedeagus of D. antonietae and D. serido. Specimens of D. serido and D. antonietae were classified correctly 96.74% of the time. Based only on the variable that most contributed to the discrimination of the groups (equalized average curvature of the arch IV of the aedeagus), we observed significant intraspecific morphological divergence in D. serido in relation to the D. antonietae, in agreement with other markers. The high morphological divergence in equalized average curvature of the arch IV of the aedeagus shows that this region evolved faster than others, since the divergence of the two species. The importance of the present study to the understanding of the genetic basis that controls the formation of the aedeagus, in the species of the Drosophila buzzatii cluster, is discussed.

Phylogenetic relationships in the Drosophila fasciola species subgroup (Diptera, Drosophilidae) inferred from partial sequences of the mitochondrial cytochrome oxidase subunit I (COI) gene

The repleta group is one of the largest and most complex species groups in the genus Drosophila, representing an important biological model for the elaboration of evolutionary and biogeographical hypotheses on the American Continent. It is divided into six subgroups, of which the fasciola subgroup is the only one with most of its species found in the humid forests of Central and South America. With the aim of understanding the origin and evolution of the fasciola subgroup, and consequently adding information about the repleta group, we analyzed partial sequences of the mitochondrial cytochrome oxidase subunit I (COI) gene of nine Drosophila species (D. carolinae, D. coroica, D. ellisoni, D. fascioloides, D. ivai, D. moju, D. onca, D. rosinae and D. senei). The phylogenetic hypotheses obtained neither defined the relationships between the subgroups of the repleta group nor defined all the interspecific relationships in the fasciola subgroup. We found that the species D. carolinae, D. coroica, D. onca, D. rosinae and D. senei comprised a clade in which D. carolinae, D. onca and D. senei appeared together at a polytomy while D. fascioloides and D. ellisoni comprised another clade with a high bootstrap value.

Population genetic structure of two columnar cacti with a patchy distribution in eastern Brazil.

The genetic variability and population genetic structure of six populations of Praecereus euchlorus and Pilosocereus machrisii were investigated. The genetic variability in single populations of Pilosocereus vilaboensis, Pilosocereus aureispinus, and Facheiroa squamosa was also examined. All of these cacti species have a patchy geographic distribution in which they are restricted to small areas of xeric habitats in eastern Brazil. An analysis of genetic structure was used to gain insights into the historical mechanisms responsible for the patchy distribution of P. euchlorus and P. machrisii. High genetic variability was found at the populational level in all species (P=58.9-92.8%, A(p)=2.34-3.33, H(e)=0.266-0.401), and did not support our expectations of low variability based on the small population size. Substantial inbreeding was detected within populations (F(IS)=0.370-0.623). In agreement with their insular distribution patterns, P. euchlorus and P. machrisii had a high genetic differentiation (F(ST)=0.484 and F(ST)=0.281, respectively), with no evidence of isolation by distance. Accordingly, estimates of gene flow (N(m)) calculated from F(ST) and private alleles were below the level of N(m)=1 in P. machrisii and P. euchlorus. These results favored historical fragmentation as the mechanism responsible for the patchy distribution of these two species. The genetic distance between P. machrisii and P. vilaboensis was not compatible with their taxonomic distinction, indicating a possible local speciation event in this genus, or the occurrence of introgression events.

Evolutionary turnover of two pBuM satellite DNA subfamilies in the Drosophila buzzatii species cluster (repleta group): from alpha to alpha/beta arrays.

The pBuM satellite DNA family was studied in seven Drosophila species from the buzzatii cluster (within the large Drosophila repleta group). The pBuM repeats are slightly AT-rich and show high levels of intraspecific sequence homogeneity. The pBuM family can be divided into two subfamilies. The pBuM-1 subfamily consists of tandemly arranged repetition units of approximately 190 bp, termed alpha. Alpha repeats were found in a high copy number in the genome of D. buzzatii, D. serido and D. antonietae. The pBuM-2 subfamily consists of tandemly arranged repetition units of 370 bp. Its origin is explained by an insertion of an approximately 180 bp foreign sequence (termed beta) in an alpha basic repeat unit, with subsequent homogenization/amplification events increasing its frequency. Alpha/beta repeats were found in a high copy number in the genome of D. serido, D. antonietae, D. seriema and D. gouveai. pBuM sequences were not detected in D. koepferae and D. borborema by hybridization experiments. The nucleotide analysis of 74 pBuM repeats revealed that apart from the beta insertion event, the evolution of the pBuM family has proceeded in a gradual fashion, mainly through accumulation and horizontal spread of nucleotide substitutions. Moreover, the data also indicate a faster evolutionary rate for the pBuM-2 subfamily than the pBuM-1 subfamily. Members of both subfamilies display a greater intraspecific than interspecific homogeneity, indicating a concerted mode of pBuM evolution. A scenario to explain the evolution of both satDNA subfamilies in the seven Drosophila species from the buzzatii cluster is proposed.

Characterisation and interpopulation variability of a complex HpaI satellite DNA of Drosophila seriema (repleta group).

A HpaI satellite DNA has been isolated and characterised from the genome of Drosophila seriema, a cactus-breeding species endemic to the rock fields of the Espinhaço Range in Brazil. The monomer sequences are slightly A + T rich (66%) and there is a significant variation of repetition length (343-391 bp). The length variability is mainly due to a 22 bp indel in some repeats and the presence of a highly variable region characterised by several DNA rearrangements, including indels, inversions and duplications of small sequence segments. The retarded mobility of monomers observed after gel electrophoresis suggests DNA curvature. Thirty satDNA repeats were analysed in samples from five populations which cover D. seriema geographical distribution. Previous studies showed that these populations present low levels of chromosomal divergence in contrast to high levels of mtDNA divergence. The variability among the 30 repeats is pretty low, on average 2%. The results showed that the satDNA sequences are rather homogeneous on both intra and interpopulational levels, presenting no specific feature(s) that could discriminate a particular population or groups of geographically close populations. Possible factors responsible for such homogeneity are discussed.

On the pBuM189 satellite DNA variability among South American populations of Drosophila buzzatii.

The pBuM189 satellite DNA was analysed in Drosophila buzzatii populations that cover most of the species distribution in South America. This satDNA consists of A + T-rich monomers of 189 bp and previous studies showed a fast rate of evolutionary change of this component of D. buzzatii genome. A total of 63 pBuM189 repetition units from 14 D. buzzatii populations (9 from Brazil and 5 from Argentina) were studied. The average nucleotide variability among the 63 repeats is 4.2 %. At least one repeat (Juan/4) seems to be part of another pBuM189 satDNA subfamily. The nucleotide alignment of all 63 repeats revealed no specific nucleotide substitutions, or indels, that could discriminate each population or groups of geographically close populations. Such lack of satDNA interpopulational differentiation is congruent with previous mtDNA data that indicate a high gene flow and very little population differentiation throughout most of the D. buzzatii distribution in South America. Gene flow might have been possible during glaciation events in the Pleistocene, such as the one occurred between 13,000 and 18,000 years ago, when D. buzzatii probably had a more continuous distribution than what is observed today.

Mitochondrial DNA phylogeography of Brazilian populations of Drosophila buzzatii

The Argentinean Chaco region has been considered the center of origin of Drosophila buzzatii in South America because it contains most of the chromosomal polymorphism detected in natural populations. Two hypotheses have been put forward to explain the distribution of D. buzzatii in Brazil, one proposing that it has only recently passively colonized Brazil via human dispersal and the other suggesting that D. buzzatii has actively migrated to Brazil some time ago. Data from chromosomal inversions support recent colonization, whereas data from allozymes and mtDNA variation indicate that D. buzzatii has been in Brazil longer, favoring an active dispersal hypothesis. In our present work we analyzed data on 56 South American flies, mostly from Brazil, sequenced for the 5Æ end of the mtDNA COI gene. The combined use of many neutrality tests and phylogeographic methods (e.g. nested clade analysis) indicated high gene flow throughout most of the range of D. buzzatii, although significant population structure was still detected. The high nucleotide diversity in the Northeast region of Brazil and the results from the nested clade analysis suggest that D. buzzatii has been in Brazil longer than proposed by the passive dispersal hypothesis. Our data indicate that D. buzzatii has been distributed throughout Brazil and Argentina since the Quaternary, though more data from different localities and markers need to be gathered to determine how the occupation of South America by D. buzzatii has occurred

Nested cladistic analysis of Brazilian populations of Drosophila serido.

The effects of Quaternary climatic cycles were investigated in Drosophila serido, a Brazilian cactophilic fly widely distributed outside the Amazonian region. Previous studies have indicated this species displays remarkable karyotypic, male genitalia, and mtDNA variation, so much so that it has been described as a species complex, or superspecies. In the present study we expand the analysis of the mtDNA COI gene on D. serido populations, particularly in central Brazil, by obtaining DNA sequences from 248 individuals distributed across 47 localities. This allowed us to perform a nested clade analysis to discriminate historical from recurrent forces shaping the evolution of D. serido populations. The nested analysis indicates one event of past fragmentation separating populations from south and central Brazil (referred to as type B) from populations in central and northeast Brazil (type D) and 15 other significant events. The most common outcome of our analysis was contiguous range expansion and we discuss why this was expected in D. serido. Our data indicate that D. serido has been distributed across Brazil at least since the Mid-Pleistocene, which contradicts the hypothesis of current distribution being determined by last glaciation cycle. Nonetheless, we present evidence that climatic cycles during the Quaternary and before have had a significant impact on the differentiation of D. serido in Brazil. Our study confirms the usefulness of the nested clade analysis for disentangling the effects of historical and present-day forces shaping the evolution and distribution of a taxon.