The evolutionary history of Drosophila buzzatii XXVII

The correlation between body size and longevity was tested in an Argentinian natural population of Drosophila buzzatii. Mean thorax length of flies newly emerging from rotting cladodes of Opuntia vulgaris was significantly smaller than that of two samples of flies caught at baits. The present results which might be interpreted as directional selection for longevity favoring larger flies are in agreement with previous results achieved in a Spanish natural population of D. buzzatii. Flies emerging from different substrates showed significant differences in thorax length, suggesting that an important fraction of phenotypic variance can be attributed to environmental variability. However, laboratory and field work in different populations of D. buzzatii showed a significant genetic component for thorax length variation.     

The evolutionary history of Drosophila buzzatii. XXX. Mitochondrial DNA polymorphism in original and colonizing populations

Both original and colonizer populations of Drosophila buzzatii have been analyzed for mtDNA restriction polymorphisms. Most of the mtDNA nucleotide variation in original populations of NW Argentina can be explained by intrapopulation diversity and only a small fraction can be accounted for by between-population diversity. Similar results are obtained using either the estimated number of nucleotide substitutions per site or considering each restriction site as a locus. Colonizer populations of the Iberian Peninsula are monomorphic and show only the most common haplotype from the original populations. Under the infinite island model and assuming that populations are in equilibrium, fixation indices indicate enough gene flow to explain why the populations are not structured. Yet, the possibility exists that populations have not reached an equilibrium after a founder event at the end of the last Pleistocene glaciation. Tajima's test suggests that directional selection and/or a recent bottleneck could explain the present mtDNA differentiation. Considering the significant population structure found for the chromosomal and some allozyme polymorphisms, the among- population uniformity for mtDNA variability argues in favor of the chromosomal and some allozyme polymorphisms being adaptive.      

The evolutionary history of Drosophila buzzatii. XXXIV. The distribution of the retrotransposon Osvaldo in original and colonizing populations

The frequency distribution of the retrotransposon Osvaldo in the haploid genome of Drosophila buzzatii has been studied in five natural populations from the Iberian Peninsula and six natural populations from Argentina. In Iberian populations, Osvaldo insertion sites do not follow a Poisson distribution, most probably due to eight euchromatic sites with high occupancy, found in all populations. The estimated alpha and beta parameters, which measure the relative importance of drift and negative selection in shaping frequency distributions, indicate that drift is the main force acting upon the distribution of Osvaldo in natural populations of D. buzzatii in the Iberian Peninsula. On the other hand, Osvaldo distribution in populations from Argentina is similar to the distribution of elements with low copy numbers, such as those described for Drosophila melanogaster and Drosophila simulans: there are no indications for deviation from a Poisson distribution, there is a low occupancy per insertion site, and genetic drift has no apparent effect on the frequency distribution. We propose that the unusual distribution found in the populations from the Iberian Peninsula is a consequence of the colonization process. Iberian Peninsula populations suffered a genomic redistribution of Osvaldo, most probably after a founder effect. Consequently, certain copies that arrived at high frequencies are showing a high occupancies today, and the mean copy number of Osvaldo is higher in Iberian Peninsula populations than in populations from Argentina. All other copies are the result of recent (after colonization) transposition events.     

The evolutionary history of Drosophila buzzatii. XVI. Fitness component analysis in an original natural population from Argentina

The adaptive significance of the chromosomal polymorphism of Drosophila buzzati has been studied by means of fitness component analysis in an original population from Argentina. The results show evidence of selection acting through pupal viability, longevity (adult viability) and fecundity on the second chromosome polymorphism, and through pupal viability and virility on the fourth chromosome polymorphism. Changes in chromosomal inversion frequencies throughout the life-cycle suggested an endocyclic pattern of directional selection, which at first seems to be the only detectable mechanism responsible for the maintenance of the polymorphism. However, slow, long-term frequency changes cannot be ruled out. The way in which endocyclic selection acts on this population is different from that in a colonized population previously studied; that is, different fitness components are involved in the maintenance of chromosomal polymorphism. The possible factors that may explain these differences are discussed.     

The evolutionary history of Drosophila buzzatii. XXIII. High content of nonsatellite repetitive DNA in D. buzzatii and in its sibling D. koepferae.

The frequency and types of repetitive nonsatellite DNA of two sibling species of the repleta group of Drosophila, D. buzzatii, and D. koepferae have been determined. For each species, the analysis is based on a sample of more than 100 clones (400 kb) obtained from genomic DNA. A theoretical model has been developed to correct for the presence of a mixture of repetitive and unique DNA in these clones. After correction, a high content of repetitive DNA has been demonstrated for both species (D. buzzatii, 19-26%; D. koepferae, 27-32%). The repetitive sequences have been classified according to their hybridization pattern when used as probes against genomic DNA and by their in situ hybridization signals on polytene chromosomes. Data suggest that the main nonsatellite component of these species is simpler and more repetitive than that of D. melanogaster, pointing to a wide variability in content and class size distribution of repetitive DNA among Drosophila species.     

The evolutionary history of Drosophila buzzatii. XX. Positive phenotypic covariance between field adult fitness components and body size

In the cactophilic species Drosphila buzzatii, it is feasible to infer the action of natural selection by simultaneously sampling different life history stages in the field. During four years of research, samples of mating and non-mating adults and pupae were taken from a natural population. The main adult fitness components, i.e., mating success, longevity, and fecundity, were recorded in relation to body size, as measured by thorax length. The age of flies was estimated by observing the developmental stage of the reproductive system. Our data showed that larger flies can outlive and outmate small flies, and that mating success is related to age. An estimate of the fitness function showed a linear increase of mating success with increasing thorax length. There was no assortative mating for this trait. We advance the hypothesis that mating success is related to the rate of encounter and courtship time through general activity, which in turn may be related to body size. A positive phenotypic correlation between thorax length and ovariole number, which is related to fecundity, was found in females emerged from wild pupae. Neither the phenotypic nor the genetic (additive) correlations between these two traits were statistically different from zero in laboratory reared females. The genetic consequences of the observed phenotypic selection on body size are discussed.     

The evolutionary history of Drosophila buzzatii XI. A new method for cytogenetic localization based on asynapsis of polytene chromosomes in interspecific hybrids of Drosophila

A new method for mapping gene differences between species is introduced. It is based on the asynapsis of homologous chromosomes in interspecific hybrids. Its validity has been investigated by comparing the pairing patterns of two Drosophila species and their hybrids, and by localizing on the chromosomes several diagnostic allozyme loci. The method can be used to map the genetic basis of any character exhibiting differences between species, although these species must fulfill some important conditions for the method to be applied with maximum efficiency.     

The evolutionary history of Drosophila buzzatii. XXXV. Inversion polymorphism and nucleotide variability in different regions of the second chromosome

Inversions are portions of a chromosome where the gene order is reversed relative to a standard reference orientation. Because of reduced levels of recombination in heterokaryotypes, inversions have a potentially important effect on patterns of nucleotide variability in those genomic regions close to, or included in, the inverted fragments. Here we report sequence variation at three anonymous regions (STSs) located at different positions in relation to second-chromosome inversion breakpoints in 29 isochromosomal lines derived from an Argentinean population of Drosophila buzzatii. In agreement with previous findings in Drosophila, gene flux (crossing over and/or gene conversion) between arrangements seems to appreciably increase as we approach the middle sections of inversion 2j, and patterns of nucleotide variability within, as well as genetic differentiation between chromosome arrangements, are comparable to those observed at the molecular marker outside the inverted fragments. On the other hand, nucleotide diversity near the proximal breakpoint of inversion 2j is reduced when contrasted with that found at the other regions, particularly in the case of derived inverted chromosomes. Using the data from the breakpoint, we estimate that the inversion polymorphism is approximately 1.63 N generations old, where N is the effective population size. An excess of low-frequency segregating polymorphisms is detected; mostly in the ancestral 2st arrangement and probably indicating a population expansion that predates the coalescent time of inversion 2j. Heterogeneity in mutation rates between the markers linked to the inversions may be sufficient to explain the different levels of nucleotide diversity observed. When considered in the context of other studies on patterns of variation relative to physical distance to inversion breakpoints, our data appear to be consistent with the conclusion that inversions are unlikely to be "long-lived" balanced polymorphisms.     

The evolutionary history of the amylase multigene family in Drosophila pseudoobscura

In Drosophila pseudoobscura, the amylase (Amy) multigene family is contained within a series of inversions, or gene arrangements, on the third chromosome. The Standard (ST), Santa Cruz (SC), and Tree Line (TL) inversions are central to the phylogeny of arrangements, and have clusters of other arrangements derived from them. The gene arrangements belonging to each of these three clusters have a characteristic number of Amy genes, ranging from three in ST to two in SC to one in TL. This distribution pattern can reflect a history of either duplications or deletions, although the data available in the past did not permit a decision between these alternatives. We provide unambiguous evidence that three Amy genes were present before the divergence of the ST, SC, and TL arrangements. Thus, the current status of the Amy multigene family is the result of deletions in the TL and SC arrangements, which created three new pseudogenes: TL Amy2-psi, TL Amy3-psi, and SC Amy3- psi. Analysis of pseudogene sequences revealed that, in the SC and ST arrangements, pseudogene evolution has been retarded, most likely due to the homogenization effect of gene conversion. Finally, by determining the original copy number, we have reconstructed the evolutionary history of the Amy multigene family and linked it with the evolution of the central gene arrangements.      

Genetic history of a colonizing population: Drosophila buzzatii (Diptera: Drosophilidae) in Australia

Drosophila buzzatii Patterson & Wheeler, a cactophilic species that feeds and breeds in the rotting tissues of various Opuntia cactus species, was inadvertently introduced to Australia from Argentina sometime during the period 1931–1936. After a bottleneck at introduction, its spread through the cactus distribution was probably very rapid as a result of natural dispersal from the site of introduction and from three other foci colonized from the introduction site by human intervention. By 1940, the Opuntia distribution and consequently that of D. buzzatii was reduced to spatially isolated populations, with probable further bottlenecking of at least some of the D. buzzatii populations. Allozyme data (primarily six polymorphic loci) from flies collected during April 1972 to February 1996 at 67 localities were used to examine current population differentiation and relationships, as well as to infer aspects of their demographic history. Although there is significant isolation‐by‐distance, genetic relationships among the populations are not simply related to geographical distance, implying that genetic drift has contributed to population differentiation. However, the biotic and, to an extent, the physical environment are not the same in Australia as in Argentina. Consequently, exposure to novel environments has led to local adaptation and further population differentiation. Genetic variation and the structure of Australian populations apparently are determined by founder effects (drift) at the level of individual breeding sites (cactus rots), by diversifying selection among rots within a locality, as well as by drift and geographically varying selection among localities. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 682–698.     

The transmission of yeasts by Drosophila buzzatii during courtship and mating

The transmission of yeasts from generation to generation for Drosophila buzzatii was shown to occur vertically through the pupal stage and horizontally during mating. Males and females transmitted yeasts to the opposite sex most often during mating but also during courtship. Yeasts transferred from the male to the female were more often associated with the abdomens of the females, while yeasts transferred from the female to the male were associated with both the head and the abdomen of the male. Mate choice was affected by the previous yeast diet of both males and females. Yeast transmission during courtship and mating represents the potential for parental care because mate choice is affected by previous yeast diet, and progeny development is a function of the yeasts inoculated onto the larval substrate by the adults.     

Genetics of wing size asymmetry in Drosophila buzzatii

Contemporary approaches that use fluctuating asymmetry (FA) as a possible target for natural and sexual selection are based on the premise that FA is a quantifiable expression of developmental instability (DI) that is inherited. Previous work with Drosophila buzzatii found that male mating success was correlated positively to body size (wing length) and negatively to FA, but these relationships seem to be environmentally induced. Heritability of FA was low and not significantly different from zero, but statistical power was also estimated to be very low and, hence, no conclusive evidence could be obtained. A large half‐sib mating design is used here to examine the relationships of different aspects of development for wing size. Consistently with previous findings, I found high heritabilities for wing length (WL) and wing width (WW), and positive correlations between both traits. Heritabilities of FA (FA_WL, FA_WW) were low (0.037) but significantly different from zero, and the genetic correlation between FA_WL and FA_WW was estimated as ?1 because the absolute value for the genetic covariance was similar in magnitude or even larger than the estimated genetic variances of both traits. This suggests that these two traits should be considered to be the same character. The between‐trait phenotypic correlation in FA, which reduces to the repeatability in this situation, was positive and statistically significant thus rendering an estimate of heritability for DI in D. buzzatii of . Nevertheless, the fact that left/right wing sizes were found to be determined by the same set of genes is difficult to reconcile with the presence of special genetic mechanisms that stabilize left/right development in this species. A qualitatively different pattern for asymmetry was observed when the nonlinear composite character wing area (WA ≈ WL × WW) was used, and . Although the results could be made compatible with the existence of a diallelic locus with antagonistic pleiotropic effects on FA_WL and FA_WW that combine multiplicatively to produce overdominance for FA_WA, the available evidence is extremely weak at best. Finally, a test to the null hypothesis of a nongenetic basis of FA, particularly relevant to those situations when directional asymmetry may be heritable, is suggested.     

The evolutionary history of childbirth

Consideration of the evolutionary and cross-cultural history of childbirth reveals many differences between the ways in which most human females have experienced childbirth and the ways in which most women in contemporary industrialized obstetric settings experience the event. In this paper I review two of these differences: the pain and anxiety of labor and delivery and the discontinuity of care provided for the mother and infant. I argue that much of the dissatisfaction with birth practices in the United States results from the failure of modern obstetric practice to meet the evolved needs of mothers and infants. Wenda Trevathan is an associate professor of anthropology at New Mexico State University. Her research interests focus on evolutionary and biosocial aspects of human female reproductive behavior, including childbirth, sexuality, and menopause. She is the recipient of the 1990 Margaret Mead Award and has received midwifery training.     

The non-regular orbit: three satellite DNAs in Drosophila martensis (buzzatii complex, repleta group) followed three different evolutionary pathways

The genome of species from the buzzatii cluster (buzzatii complex, repleta group) is hosted by a number of satellite DNAs (satDNAs) showing contrasting structural characteristics, genomic organization and evolution, such as pBuM-alpha (~190 bp repeats), pBuM-alpha/beta (~370 bp repeats) and the DBC-150 (~150 bp repeats). In the present study, we aimed to investigate the evolution of these three satDNAs by looking for homologous sequences in the genome of the closest outgroup species: Drosophila martensis (buzzatii complex). After PCR, we isolated and sequenced 9 alpha, 8 alpha/beta and 11 DBC-150 sequences from this species. The results were compared to all pBuM and DBC-150 sequences available in literature. After D. martensis split from the buzzatii cluster some 6 Mya, the three satDNAs evolved differently in the genome of D. martensis by: (1) maintenance of a collection of major types of ancestral repeats in the genome (alpha); (2) fixation for a single major type of ancestral repeats (alpha/beta) or (3) fixation for new divergent species-specific repeat types (DBC-150). Curiously, D. seriema and D. martensis, although belonging to different and allopatric clusters, became independently fixed for the same major type of alpha/beta ancestral repeats, illustrating a rare case of parallelism in satDNA evolution. The contrasting pictures illustrate the diversity of evolutionary pathways a satDNA can follow, defining a “non-regular orbit” with outcomes difficult to predict.     

Characterization of a species-specific satellite DNA of Drosophila buzzatii

The pBuM189 satellite DNA family was found to be species specific for Drosophila buzzatii . It consists of slightly AT-rich tandemly arranged repeats with a high copy number in the genome and shows a very high level of intraspecific sequence similarity. pBuM189 repeats cannot be detected in the genomes of closely related species such as Drosophila serido , Drosophila borborema and Drosophila koepferae . The data support the marginal systematic position of D. buzzatii within the buzzatii cluster of the Drosophila repleta group.     

Inferences on the evolutionary history of the S-element family of Drosophila melanogaster

The S-element family of transposable elements has been characterized in D. melanogaster. Attempts to find it in other Drosophila-related species have failed, suggesting that this element family may have recently invaded the D. melanogaster genome by horizontal transfer. In order to investigate its evolutionary history, we analyzed the patterns of DNA polymorphism among the S-element copies present in a sample genome (Drosophila Genome Project). The observed levels of nucleotide diversity are significantly lower than theoretical expectations based on the neutral model. This is consistent with evidence for ongoing gene conversion among copies and for purifying selection on the elements' sequences, particularly on the terminal inverted repeats. A phylogenetic analysis revealed that the members of the S-element family can be grouped into at least two genetically differentiated clusters. The level of divergence between these clusters suggests that the S elements invaded the genome of the ancestor of D. melanogaster before the speciation of the D. melanogaster complex. However, other relevant scenarios are also discussed.     

Allozyme genotype-environment relationships in natural populations of Drosophila buzzatii

Allozyme frequency data from natural populations of Drosophila buzzatii were analyzed for genotype-environment relationships. Allele frequency and heterozygosity at six loci polymorphic throughout eastern Australia and a number of environmental factors (both means and variabilities) were examined by a variety of multivariate techniques. Significant genotype-environment associations were found for five of the six loci, and after correcting for geographic location significant associations remained for Est-2 and Adh-1 gene frequencies and heterozygosities and for Pgm gene frequencies. The results are discussed in relation to selection and gene flow and provide the basis for laboratory studies to disentangle confounded effects of (1) environmental means and environmental variabilities and (2) allele frequency and heterozygosity, and thus to further test for and determine the nature of any natural selection at particular allozyme loci.This work was supported by a grant from the Australian Research Grants Committee to J. S. F. B.     

Climatic adaptation of Drosophila buzzatii populations in southeast Australia

Variation in 19 traits possibly relevant for thermal adaptation was studied in 11 populations of Drosophila buzzatii collected in southeast Australia. Using stepwise multiple regression, the variation was compared to variation in geographic coordinates and to a set of climatic variables estimated for each collection site. For 13 of the traits, a significant part of the variation was explained by climatic variables and/or geographic coordinates, suggesting directional selection for adaptation to the environment in the majority of traits studied. In 10 of the traits, both geographic coordinates and climatic variables explained significant proportions of the variation, with R2 ranging from 0.075 to 0.58. Although larvae, pupae and adults of D. buzzatii share a common habitat, the measured traits were not correlated across life stages and gender. Also, there seemed to be special conditions in marginal populations near species borders, giving rise to nonlinear relations with latitude. Climate apparently does influence the adaptive evolution of the traits studied, but they also are affected by other factors that vary with latitude, longitude and distance to coast. These results highlight the complex challenges imposed by the environment on the adaptive process.