Behavior genetics of olfactory responses inDrosophila. II. An odorant-specific variant in a natural population ofDrosophila melanogaster

Homozygous second chromosome lines were extracted from a natural population ofDrosophila melanogaster and tested for their olfactory responses to ethyl acetate. The chromosome lines were highly heterogeneous for this behavior, and the variability was also specific to other esters and ketones such as ethyl propionate, 2-butanone, 2-pentanone, and 3-pentanone. The responses to these odorants negatively correlated with the response to another odorant, lactic acid. A large part of this odorant-specific variation seemed to be controlled by genes located on the right arm of the second chromosome.This work was partly supported by a grant (034082) from the Ministry of Education.     

Characterization of the larval olfactory response inDrosophila and its genetic basis

Drosophila larvae are attracted to a wide variety of chemical stimuli. The olfactory response to ethyl acetate, a powerful attractant, was found to be surprisingly well conserved across a variety of different wild-type strains. Strain differences are documented, however, both in attraction to ethyl acetate and in another chemosensory behavior: avoidance of an aversive stimulus. As a means of analyzing the extent of genetic heterogeneity within strains, one wild-type population, Canton-S, was screened for variant X chromosomes. An enrichment procedure was characterized and used to make the screening more efficient. Lines homozygous for individual X chromosomes were established, and all were found to exhibit a strong olfactory response, although evidence was found for variation among them. The olfactory response was found to be conserved through an extended period of larval development, including the final period during which larvae leave the culture medium in preparation for metamorphosis. The results are discussed in terms of the genetic basis of the response and the use of single-gene mutations as a means of dissecting olfactory system function.This work was supported by NIH Grant GM-36862 to J.C.     

Behavior genetics of olfactory responses inDrosophila. I. Olfactometry and strain differences inDrosophila melanogaster

A simple olfactometer was constructed for measuring the responses of adultDrosophila to odoriferous substances, and an index (attractability index, AI) is proposed to evaluate the response. Five strains ofDrosophila melanogaster of different geographic origins were tested for their responses to five chemical attractants: ethyl alcohol, acetic acid, lactic acid, ethyl acetate, andn-butyraldehyde. Statistical analysis has shown that the differences of AI among strains are highly significant for all the odorants except acetic acid and that male flies are, in general, less sensitive than females. The number of flies which were inactive in the olfactometer also varied with strain, sex, and odorant, suggesting the involvement of some other behaviors, and this raises some difficulties in interpreting the heterogeneities of AI. Nevertheless, these results suggest that a considerable amount of genetic variation for olfactory response exists in natural population ofD. melanogaster.     

Factor Analysis of Olfactory Responses in Drosophila melanogaster Enhancer-Trap Lines as a Method for Ascertaining Common Reception Components for Different Odorants

Olfactory information is transmitted to the brain using combinatorial receptor codes; consequently, a single reception element can be activated by different odorants. Several methods have been applied to describe from a functional point of view those odorants sharing olfactory reception components. A genetic approach in Drosophila melanogaster used correlation between behavioral responses to different odorants for deducing common olfactory pathway-genes. A factor analysis applied to behavioral responses to five odorants of 27 antennal enhancer-trap lines revealed three components, explaining 82.1% of the total observed variance. A first factor affects simultaneously the response to ethyl acetate, propionaldehyde, and acetone. A second factor was related to responses to ethyl acetate, ethyl alcohol, and acetone, and, finally, the third factor associates responses to acetic acid and ethyl acetate. They contribute by 35.1%, 36.9%, and 28%, respectively, to the explained variance.     

Genetic diversity in Cronartium quercuum f.sp. fusiforme on loblolly pines in southern U.S.

Twelve random amplified polymorphic DNA (RAPD) markers were used to study genetic variability in three populations of Cronartium quercuum f. sp. fusiforme, the causal agent of fusiform rust on pines. Most of the variability (94%) was found within populations while 6% of the total variability was attributable to frequency differences between populations. The frequency of three markers was significantly different between regions of origin on an east-west transect. Three markers were completely absent from one of the populations while present in the others, and one marker was fixed in the western population but polymorphic in the eastern and central populations. However, no significant differences were observed when the western population was omitted from the analysis. The results suggest that C. quercuum f. sp. fusiforme is a highly heterogeneous pathogen with little geographic differentiation and underscores the importance of considering the population structure of the pathogen in resistance breeding programs.     

The genetic architecture of odor-guided behavior in Drosophila melanogaster

The avoidance response to repellent odorants in Drosophila melanogaster, a response essential for survival, provides an advantageous model for studies on the genetic architecture of behavior. Transposon tagging in a highly inbred strain of flies in combination with a rapid and simple statistical behavioral assay enables the identification of not only large phenotypic effects, but also small aberrations from wild-type avoidance behavior. The recent completion of the sequence of the Drosophila genome facilitates the molecular characterization of transposon-tagged genes and correlation between gene expression and behavior in smell-impaired (smi) mutant lines. Quantitative genetic analyses of a collection of smi lines in a coisogenic background revealed an extensive network of epistatic interactions among genes that shape the olfactory avoidance response. The identification and functional characterization of proteins encoded by smi genes that form part of the olfactory subgenome and correlation of polymorphisms in these genes with variation in odor-guided behavior in natural populations will advance our understanding of the genetic architecture of chemosensory behavior.     

Cytogenetic and molecular analysis of the satellite DNA of the genusCtenomys (Rodentia Octodontidae) from Uruguay

The genus of subterranean rodentsCtenomys presents the widest range of variability in diploid number among mammals (from2n=10 to2n=70). In Uruguay, this variability is observed in karyotypes with2n=44, 50 or 58 and two geographically isolated populations with 70 chromosomes but different karyotypic structure. The last three populations were analyzed in the present study. They present a satellite DNA, which was isolated from genomic DNA afterAlul digestion.In situ hybridization showed that this satellite DNA is located in the centromeric region of a few chromosomes, coincident with Hoechst 33258 staining and C-banding patterns. A similar satellite DNA was detected in Argentinian species of this genus. We established that, in spite of differences in number of positive heterochromatic blocks per karyotype, the C value is the same in the three populations studied. The nature and possible evolutionary path of this repeated DNA is discussed.Accepted for publication by M. Schmid     

A Genetic Analysis of Avian Personality Traits: Correlated,Response to Artificial Selection

Individuals in a range of species consistently differ in their behavior towards mild challenges, over age and time. Differences have been found for several personality traits in a range of species. In great tits these traits have a genetic basis and are phenotypically correlated. Estimates of genetic correlations are, however, fundamental to understanding the evolution of consistent individual differences in behavior. This study analyzed two selection experiments on two avian personality traits, early exploratory behavior and risk-taking behavior. The selection lines used were both started using wild great tits (Parus major) from two natural populations. Genetic correlations were calculated using the response and the correlated response to artificial selection. We found genetic correlations ranging from 0.51 to 0.66, based on individual values, and from 0.84 to 1.00 based on nest means. Genetic correlations can be due to pleiotropic effects or to linkage disequilibrium. The different behavioral traits might therefore have a common genetic basis, possibly constraining independent evolution of personality traits in natural populations. These results are discussed in relation to domain generality and domain specificity of personalities.     

Comparative study of some haematological parameters of two wild Chaetophractus villosus (mammalia, dasypodidae) populations

The study of haematological parameters of a species is of great interest both for the comprehension of its biological characteristics in general and its physiological adaptations in particular. In this work, we studied haematological parameters of two wild populations of armadilloChaetophractus villosus (population I,n=25 and population II,n=30). The animals came from a range of 150 km to the north west of Bahía Blanca, Argentina. Blood samples were obtained from anaesthetised animals by cardiac puncture, between 8:00 a.m. and 10:00 a.m. Blood was collected in EDTA and processed for haematological screen by routine techniques. Erythrocyte parameters (total erythrocytes, haematocrit, haemoglobin, erythrocyte indices and erythrocyte sedimentation rate) and leucocyte parameters (total leucocytes and percentage composition) were studied. Population I had higher values for erythrocytes, haematocrit and haemoglobin than population II. With the exception of eosinophils (p>0.05), no differences were found between populations of erythrocyte indices, erythrocyte sedimentation rate, total leucocytes and leucocyte percentage composition. The sample of population II featured a greater number of young animals than population I, age may therefore partially account for the differences. These results may also be influenced by a higher loading of parasites observed in population II.     

The Inositol 1,4,5-triphosphate kinase1 Gene Affects Olfactory Reception in Drosophila melanogaster

The Inositol 1,4,5-triphosphate (IP3) route is one of the two main transduction cascades that mediate olfactory reception in Drosophila melanogaster. The activity of IP3 kinase1 reduces the levels of this substrate by phosphorylation into inositol 1,3,4,5-tetrakiphosphate (IP4). We show here that the gene is expressed in olfactory sensory organs as well as in the rest of the head. To evaluate in vivo the olfactory functional effects of up-regulating IP3K1, individuals with directed genetic changes at the reception level only were generated using the UAS/Gal4 method. In this report, we described the consequences in olfactory perception of overexpressing the IP3Kinase1 gene at eight different olfactory receptor-neuron subsets. Six out of the eight studied Gal-4/UAS-IP3K1 hybrids displayed abnormal behavioral responses to ethyl acetate, acetone, ethanol or propionaldehyde. Specific behavioral defects corresponded to the particular neuronal olfactory profile. These data confirm the role of the IP3kinase1 gene, and consequently the IP3 transduction cascade, in mediating olfactory information at the reception level.     

Haematological characteristics of wild quokka (Setonix brachyurus)

Blood was collected from quokkas (Setonix brachyurus), from a mainland and an island population, and analysed as part of an assessment of animal health. Mean corpuscular haemoglobin concentration was the only analyte that was significantly different between the mainland and island populations. Quokkas from both the wild populations had lesser erythrocytic values than the captive animals. The wild quokkas also possessed three types of haemoparasites that were not recognised in the captive animals. This study illustrates the differences in the haematological characteristics between wild and captive animals.     

Habitat choice byDrosophila pseudoobscura: The roles of genotype and of experience

Microhabitat preferences ofDrosophila pseudoobscura strains were examined in a Waddington maze, with an emphasis on learning how early environment affected adult habitat choice. The genotypes were roughly those expected in a natural population; the environmental variables included light, temperature, and food. It was found that (1) the different genotypes chose habitats differently; (2) early experience affected subsequent habitat choice; and (3) the effect of early experience was complex, as preference for one niche dimension (temperature) was reinforced by experience with the generally preferred value, preference for another niche dimension (light) was weakened by experience with the generally preferred value, and preference for other niche dimensions (food) was generally unaffected by experience. In this study the contribution to the total chi square was about equal from genotype and from environment. The significance of these findings for studies of dispersal and population structure of natural populations is discussed.     

Fluorescencein situ hybridization with rDNA probes on chromosomes of two nucleolus organizer region phenotypes of a species ofEigenmannia (Pisces,Gymnotoidei, Sternopygidae)

Nucleolus organizer regions (NORs) were analysed in two related and geographically close populations ofEigenmannia sp. 1 (Pisces, Gymnotoidei, Sternopygidae) using silver staining and fluorescencein situ hybridization (FISH). The two populations differed in their Ag-NOR phenotypes, displaying fixed differences in the NOR-bearing chromosome pairs. FISH with rDNA probes showed that these differences were due to the location of rDNA cistrons. This finding, showing fixed NOR differences between two populations belonging to the same species in a connected river system, is highly significant in terms of evolutionary change, possibly indicating an initial step of genetic differentiation. This result also has important implications from the cytosystematic point of view, as NORs usually have a very constant karyotypic location in fish species and have been used as species-specific chromosome markers.accepted for publication by M. Schmid     

Analysis of helminth genetic data: comparative examples with Haemonchus contortus isozymes using exact tests or resampling procedures

Population genetic data on helminths are scarce and it is important to fine tune analyses of these data, the interpretation of which is based on between-(F _st) and within-(F _is) population variability. Several computer programs are available and confidence intervals of each index are based on different procedures. These programs (Genetix, Diploid, Genepop) were compared with a classical program (Biosys-1) using a large set of Haemonchus contortus isozyme data. The results were identical for all softwares for large differences when natural populations were studied (F _st>0.25 and F _is>0.15 or <−0.15). When small F _st were investigated in laboratory-reared populations, the significance of differences was often related to the software used. As a rule of thumb, it is suggested that at least two out of three software packages (based on different calculation procedures) should give similar results before differences are validated. Received: 8 March 1999 / Accepted: 27 April 1999     

Morphobiometrical and molecular study of two populations of <Emphasis Type="Italic">Demodex folliculorum</Emphasis> from humans

A morphobiometrical and molecular study of two populations of Demodex folliculorum from humans isolated from different habitats, skin and eyelashes follicles, were carried out. Morphological and biometrical studies revealed two closely related populations with any distinctive characteristics. For molecular study, a 436-bp region of the 16S rDNA gene and a 453-bp region of the cytochrome oxidase I (COI) gene from individual mites of each population considered were sequenced. Intraindividual and interindividual sequence variation was studied in both populations. Our data show that 16S rDNA is not a useful marker to discriminate between populations; however, COI gene sequences can help to identify the two populations considered, which are morphologically very close and difficult to separate by classic methods. These results are in agreement with the morphological and biometrical differences detected between D. folliculorum from eyelashes and human skin. This study appeals for the revision of the taxonomic status of the D. folliculorum populations, as well as for the species included within genus Demodex.     

Sexual Isolation Between Sympatric and Allopatric Populations of <Emphasis Type="Italic">Drosophila pseudoobscura</Emphasis> and <Emphasis Type="Italic">D. persimilis*</Emphasis>

According to reinforcement theory, sexual isolation between species in sympatry is strengthened by natural selection against maladaptive hybrids. Drosophila pseudoobscura and D. persimilis from four locations where these species are sympatric, and from three locations where only D. pseudoobscura has been found, were utilized in studies of sexual isolation. Multiple-choice observation chambers were used to record matings between sympatric and allopatric strains of the two species. There was a wide variation in sexual isolation between the two species in the four localities we studied. The average isolation index for sympatric strains of the species was not significantly different from the average index for allopatric strains. There were no meaningful differences between the isolation indices in sympatric and allopatric strains of the species. The failure to find a relationship is likely the result of gene flow among populations within the two species.This paper is dedicated to Prof. Lee Ehrman – excellent scientist, friend, and mentor.     

Genetic Variability of Conditioned Probing Responses to a Fruit Odor in Leptopilina boulardi(Hymenoptera: Eucoilidae), a DrosophilaParasitoid

The genetic variability of odor-conditioned probing behavior was investigated in a population of Leptopilina boulardi, a parasitoid of Drosophilalarvae. Ovipositor probing is the final step of host location, leading to the discovery of host larvae. It can be triggered by an odor previously experienced during an oviposition as a result of associative learning. This study was based on the analysis of female probing performance over two generations of isofemale lines (using both mother–daughter regressions and one-way analysis of variance). Individual performances of the conditioned response to the odor were characterized by (1) the latency (i.e., the time elapsed between the onset of the odor delivery and the start of the probing response), (2) the duration of the first probing phase, and (3) the total probing duration. Results suggested that the variability of two characters, the latency and the duration of the first probing phase, were under a genetic control in the studied population. This work is the first contribution to quantify the genetic component of this variability.     

Inter- and intra-site genetic diversity of natural field populations of rice tungro bacilliform virus in the Philippines

Summary.  The genetic structure of rice tungro bacilliform virus (RTBV) populations within and between growing sites was analyzed in a collection of natural field isolates from different rice varieties grown in eight tungro-endemic sites of the Philippines. Total DNA extracts from 345 isolates were digested with EcoRV restriction enzyme and hybridized with a full-length probe of RTBV, a procedure shown in preliminary experiments capable of revealing high levels of polymorphism in RTBV field isolates. In the total population, 17 distinct EcoRV-based genome profiles (genotypes) were identified and used as indicators for virus diversity. Distinct sets of genotypes occurred in Isabela and North Cotabato provinces suggesting a geographic isolation of virus populations. However, among the sites in each province, there were few significant differences in the genotype compositions of virus populations. The number of genotypes detected at a site varied from two to nine with a few genotypes dominating. In general the isolates at a site persisted from season to season indicating a genetic stability for the local virus population. Over the sampling time, IRRI rice varieties, which have green leafhopper resistance genes, supported similar virus populations to those supported by other varieties, indicating that the variety of the host exerted no apparent selection pressures. Insect transmission experiments on selected RTBV field isolates showed that dramatic shifts in genotype and phenotype distributions can occur in response to host/environmental shifts. Accepted September 1, 1999/Received June 25, 1999     

THE rdgB GENE OF DROSOPHILA: A LINK BETWEEN VISION AND OLFACTION

otal (ota = olfactory trap abnormal), an X–linked mutation of Drosophila isolated by virtue of abnormal olfactory behavior, is shown to be an allele of rdgB (retinal degeneration B), a gene required for normal visual system physiology. rdgB function is shown to be necessary for olfactory response of both adult files and larvae, which have distinct olfactory systems. Electrophysiological recordings from the adult antenna indicate that rdgB is required for normal response in the peripheral olfactory system: some rdgB mutants show a delayed return to the resting potential following stimulation with ethyl acetate vapor. These results indicate that rdgB is required for both visual and olfactory physiology, and they suggest that visual and olfactory transduction may share at least one common molecular step in Drosophila.     

Genetic variation and relationships at six VNTR loci in two distinct sample populations in Brazil

Background: The Brazilian population has been the focus of intensive genetic study due to admixture characteristics whereas there are few reports on the variability of VNTR loci in Brazil.

Primary objective: The aim of this study was to analyse genetic parameters in sample populations from two geographically distant regions: São Luís City, in Maranhão State and Campinas City, in São Paulo State. We investigated if distinct colonization influences could produce detectable differences in genetic background.

Subject and methods: DNA samples from peripheral drained blood were obtained from unrelated individuals who underwent paternity testing. Allelic variation in six VNTR loci (D2S44, D4S139, D5S110, D8S358, D10S28 and D17S79) was evaluated. The results were compared to reference databases available for general Latin-derived European and African–American populations as well as for other Brazilian groups.

Results: This study reveals that forensic population parameters did not show differences among regions, although we detected admixture values varying between the south-east and north-east of Brazil.

Conclusions: Differences between the two samples are probably due to different admixture proportions of European- and African-derived alleles in each region; both populations are in Hardy–Weinberg equilibrium. In addition, the allelic frequency for all loci, in both populations, can be used as database for forensic purposes.