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    William Starmer

    In 1967 Lewontin reviewed the correlations that have been made with environmental parameters on the degree of heterozygosity for chromosomal inversions within species (da Cunha et al., 1959; Carson, 1959; Dobzhansky, 1957) and pointed... more
    In 1967 Lewontin reviewed the correlations that have been made with environmental parameters on the degree of heterozygosity for chromosomal inversions within species (da Cunha et al., 1959; Carson, 1959; Dobzhansky, 1957) and pointed outthat the difficulty in these attempts are caused in part because of the lack of a real understanding of the ecology of Drosophila. A considerable amount of information now exists on Drosophila larval breeding sites (Carson, 1971) and this knowledge has provided more insight into the role of ecology in controlling the accumulation of inversions in some species groups (Heed and Russell, 1971; Spieth and Heed, 1972). However, the present report is considered exceptional because of the relative simplicity of conditions that may be controlling the inversion polymorphism. Drosophila pachea Patterson and Wheeler is one of the more abundant species of the Sonoran Desert in Mexico. Our attention has been focused on this interesting species for cytological and genetic studies because it manifests several unique properties. (1) The restrictive nutritional requirements of D. pachea are satisfied by the unusual sterols present in only one of the common Sonoran Desert cereus cacti, Lophocereus schottii (Engleman) Britton and Rose, known locally as "senita" (Heed
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    The diversity of Drosophila habitats attests to the evolutionary success of species in the genus. Drosophilae have been bred from a variety of substrates which include decaying plant tissue (fruits, stems, bark, wood, leaves and flowers),... more
    The diversity of Drosophila habitats attests to the evolutionary success of species in the genus. Drosophilae have been bred from a variety of substrates which include decaying plant tissue (fruits, stems, bark, wood, leaves and flowers), slime fluxes and exudates of trees and mushrooms (Carson, 197 1). Most of these habitats share the common characteristic of an abundant yeast microflora. The yeasts are saprophytic and serve to process the raw materials of the habitat into important dietary factors of the larval and adult stages of the Drosophila which feed on the decomposing substrate. In this paper, the yeast communities of various Drosophila habitats are compared. Such a comparison should tell us if evolution and diversification by the yeasts has any relevance to the evolution and speciation in the drosophilae. The rationale is as follows. First, it is postulated that the physiological abilities of a yeast community partially characterize the habitat of that community. Traditionally yeast taxa are described and identified by studying purified strains for a number of metabolic and physiological attributes as well as other traits (van der Walt, 1970). Thus, the information available from the taxonomy can be used directly to characterize the yeast community of a particular habitat. Second, if the yeast community characteristics are indicators of habitat characteristics, then a comparison of different yeast communities is a comparison of different habitats which contain them. A comparison of a wide variety of yeast communities could then be used to construct a classification (e.g., phenogram) of the habitats according to the characteristics of their respective yeast communities. This classification of the habitats would then relate habitats in accordance with their nutritional state of utilization by the drosophilae. Third, the classification of the habitats could then be utilized to follow and study the evolutionary pathways of groups of Drosophila for which phylogenetic arguments have been made. As H. L. Carson (1971) states: "The time now appears ripe to exploit the knowledge of breeding sites for an understanding of the genetic events which occur in natural populations and which are responsible for changes leading to adaptation and speciation."
    Fluctuating asymmetry (subtle departures from identical expression of a trait across an axis of symmetry) in many taxa is under stabilizing selection for reduced asymmetry. However, lack of reliable estimates of genetic parameters for... more
    Fluctuating asymmetry (subtle departures from identical expression of a trait across an axis of symmetry) in many taxa is under stabilizing selection for reduced asymmetry. However, lack of reliable estimates of genetic parameters for asymmetry variation hampers our ability to predict the evolutionary outcome of this selection. Here we report on a study, based on analysis of variation within and between isofemale lines and of generation means (line-cross analysis), designed to dissect in detail the quantitative genetics of positional fluctuating asymmetry (PFA) in bristle number in natural populations of Drosophila falleni. PFA is defined as the difference between the two sides of the body in the placement or position of components of a meristic trait. Heritability (measured at 25 degrees C) of two related measures of PFA were 13% and 21%, both of which differed significantly from zero. In contrast, heritability estimates for fluctuating asymmetry in the total number of anterior (0.7%) and transverse (2.4%) sternopleural bristles were smaller, not significant, and in quantitative agreement with previously published estimates. Heritabilities for bristle number (trait size) were considerably greater than that for any asymmetry measure. The experimental design controlled for the potentially confounding effects of common familial environment, and repeated testing revealed that PFA differences between lines were genetically stable for up to 16 generations in the laboratory at 25 degrees C. We performed line cross analysis between strains at the extremes of the PFA distribution (highest and lowest values); parental strains, F1, F1r (reciprocal), F2, backcross, and backcross reciprocal generations were represented. The inheritance of PFA was described best by additive and dominance effects localized to the X-chromosomes, whereas autosomal dominance effects were also detected. Epistatic, maternal, and cytoplasmic effects were not detected. The inheritance of trait size was notably more complex and involved significant autosomal additive, dominance, and epistatic effects; maternal dominance effects; and additive and dominance effects localized to the X-chromosomes. The additive genetic correlation between PFA and its associated measure of trait size was negative (-0.049), but not statistically significant, indicating that the loci contributing additive genetic effects to these traits are probably different. It is suggested that PFA may be a sensitive measure of developmental instability because PFA taps the ability of an organism to integrate interconnected developmental pathways.
    Sexual isolation is the tendency ofindividuals to avoid mating with those ofanother strain, race, or species. Isolation has been measured in Drosophila using a variety ofmethods and indices of isolation (e.g., Spiess, 1970; Parsons, 1973... more
    Sexual isolation is the tendency ofindividuals to avoid mating with those ofanother strain, race, or species. Isolation has been measured in Drosophila using a variety ofmethods and indices of isolation (e.g., Spiess, 1970; Parsons, 1973 for reviews). Statistical examination helps us evaluate the biological validity of these methods and indices. The multiple choice method, a common experimental design, counts the instances of four types of matings when males and females of two races are placed together. This is diagrammed in Table 1. If the like-type (homogamic; cells A and D of the diagram) matings occur more frequently than expected by chance, the races are said to exhibit isolation. Statistics that are commonly used to measure such isolation are the Joint Isolation Index (Joint 1) and Chi-square (Malogolowkin-Cohen et al., 1965; Zouros and d'Entremont, 1980). Two additional statistics which can measure isolation are Yule's Vand Yule's Q(Bliss, 1967). These statistics differ in their properties (e.g., bias) and their utility for measuring isolation. How they differ and which are best depend on several factors. Wattiaux (Wattiaux, 1964; Wattiaux and Elens, 1970; Elens et al., 1973) documented and discussed changes in measures ofisolation over the time course of experiments (up to 120 min) with Drosophila melanogaster. The relative numbers ofhomogamic and heterogamic matings change; thus, measured isolation values depend on how long observations are continued. This may in part be due to changes with time in the sexual interactions in the pool of available mates, but part of this can be measurement bias due to sampling from the pool without replacement. Sampling without replacement occurs in most isolation experiments because, even ifmated pairs are not physically removed, their copulation and subsequent refractory period for further mating biologically remove them from the pool of available mates. The ratios of available types, and the probability of matings, can change due to this removal, even though the presumed intrinsic isolation, or choice, probabilities remain unchanged. Manly (1980) discusses problems ofestimating such intrinsic choice probabilities when sampling without replacement. Another source of error in isolation estimates is the effect of vigor differences between races. Two hypothetically distinct properties th\1t determine whether matings occur are choice and vigor. We define vigor to be the likelihood that a male or female will engage in courtship and copulation, regardless ofits partner. We define choice as the joint likelilIood that a given male and female combination will mate, once they have initiated courtship. Sexual isolation occurs when choice is exercised between races, but vigor is usually considered distinct from isolation. In multiple choice experiments, vigor is measured from the marginal totals for a sex (F1 vs. F 2, and M, vs. M 2 in Table 1). Choice, or isolation, is measured from the interaction term (A + D vs. B + C). Care should be exercised in relating these two population properties to underlying biological processes. A final source oferror considered here is the effect that unequal pools ofmates may have on estimating intrinsic choice values. Unequal pools ofmates are used in frequency-dependence experiments to establish whether scarcity or overabundance ofa race will influence the intrinsic choice values. We examine here the ability of four statistics to distinguish choice from vigor or unequal pools, and their sensitivity to sampling without replacement. The statistics, Joint I, Yule's V, Chi-square, and Yule's Q,are tested using simulated multiple choice experiments. They are compared under conditions of no intrinsic isolation, symmetrical isolation, asymmetrical isolation, vigor differences, and unequal pools ofmates. The effects of sampling without replacement from a limited pool of mates are compared with asymptotic measures (i.e., sampling from an infinite pool).
    Variation in proteins and nucleic acid sequences can be used in a variety of ways to study evolutionary patterns and processes. In recent years, DNA sequences have largely superseded allozyme frequencies as the raw data for Drosophila... more
    Variation in proteins and nucleic acid sequences can be used in a variety of ways to study evolutionary patterns and processes. In recent years, DNA sequences have largely superseded allozyme frequencies as the raw data for Drosophila molecular evolutionary biologists. DNA sequencing has been applied to three areas of investigation: the estimation of population genetic parameters, phylogenetic reconstructions, including estimates of rates of change in specific gene products, and the molecular basis of structural and regulatory gene mutations.
    Ecological genetics concerns the adaptation of the individuals in natural populations to their habitats. Thus, in order to fully understand the adaptations, the phenotypes of individuals must be related to the ecological context of the... more
    Ecological genetics concerns the adaptation of the individuals in natural populations to their habitats. Thus, in order to fully understand the adaptations, the phenotypes of individuals must be related to the ecological context of the population and to the underlying genetic bases of those phenotypes. The interplay between ecology, phenotypes and genotypes is complex. For example, the structure of a population (effective size, system of mating, subdivision and gene flow) can influence not only the speed of a genetic response to an environmental change, but can constrain the nature of that response as well. If the latter is true, the genetic basis of adaptations may not always represent “optimal” solutions. Understanding the genetic basis of traits associated with fitness differences is therefore a fascinating challenge for ecological geneticists. Unfortunately in normal environmental conditions, differences in fitness traits are often associated with low heritabilities. However, in situations of environmental stress, adaptations have been studied which have a more clearly detectable genetic basis.
    Biochemical genetics examines the relationship between nucleotide sequence variation and physiological differences among members of the same or different species. If these differences are adaptive, the findings are central to a complete... more
    Biochemical genetics examines the relationship between nucleotide sequence variation and physiological differences among members of the same or different species. If these differences are adaptive, the findings are central to a complete understanding of the ecological and evolutionary significance of the genetic variation. Historically, two approaches have been taken. In the first, genetic variation at a locus is initially detected, often as allozymes or null mutants, and the effect of this variation on the properties of the protein product and/or the fitness of the individuals with the different genotypes is assessed. In other words, the investigator attempts to demonstrate that the genetic variants have meaningful physiological effects. The second approach begins with the detection of adaptively important phenotypic differences, and proceeds toward an analysis of the underlying, often cryptic, genetic variation.
    ABSTRACT Abstract Identifying sources of phenotypic variability in secondary sexual traits is critical for understanding their signaling properties, role in sexual selection, and for predicting their evolutionary dynamics. The present... more
    ABSTRACT Abstract Identifying sources of phenotypic variability in secondary sexual traits is critical for understanding their signaling properties, role in sexual selection, and for predicting their evolutionary dynamics. The present study tests for the effects of genotype, developmental temperature, and their interaction, on size and fluctuating asymmetry of the male sex comb, a secondary sexual character, in Drosophila bipectinata Duda. Both the size and symmetry of elements of the sex comb have been shown previously to be under sexual selection in a natural population in northeastern Australia. Two independent reciprocal crosses were conducted at 25d̀ and 29d̀C between genetic lines extracted from this population that differed in the size of the first (TC1) and third (TC3) comb segments. These temperatures are within the documented range experienced by the species in nature. Additive and dominance genetic effects were detected for TC1, whereas additive genetic, and Y-chromosomal effects were detected for TC3. TC2 and TC3 decreased sharply with increasing temperature, by 10% and 22%, respectively. In contrast, positional fluctuating asymmetry (PFA) significantly increased with temperature, by up to 38%. The results (1) document an important source of environmental variance in a sexual ornament expected to reduce trait heritability in field populations, and thus act to attenuate response to sexual selection, (2) suggest that variation in ornament size reflects differences in male condition; and (3) support the general hypothesis that asymmetry in a sexual ornament is indicative of developmental instability arising from environmental stress. The “environmental heterogeneity” (EH) hypothesis is proposed, and supportive evidence for it presented, to explain negative size-FA correlations in natural populations. Data and theory challenge the use of negative size-FA correlations observed in nature to support the FA-sexual selection hypothesis, which posits that such correlations are driven by differences in genetic quality among individuals.
    Publisher Summary This chapter reviews the studies of the ecology of yeasts in their natural habitats, and the ways in which yeasts have been used to investigate ecological questions. Yeasts are among the earlier colonizers of nutrient... more
    Publisher Summary This chapter reviews the studies of the ecology of yeasts in their natural habitats, and the ways in which yeasts have been used to investigate ecological questions. Yeasts are among the earlier colonizers of nutrient rich substrates, where they are followed by a succession of organisms that degrade dead organic matter. However, yeasts are not just decomposers but can assume a diversity of forms and functions in the natural world. Along with their role in the transformation of nutrients, they can engage in intimate relationships with other organisms as mutualists, competitors, parasites, or pathogens. They occur together in communities or guilds linked together through intricate interrelationships. Yeasts are widely distributed throughout all biomes of the world. They have been found in the upper levels of the atmosphere (above the clouds in the stratosphere), in the deepest parts of the oceans, in aquifers under the sea, in ancient glacial ice, and are abundant throughout the phyllosphere. Associates of yeasts include viruses, bacteria, other fungi, algae, vascular plants, and animals of almost any sort.
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    Quantitative genetic analysis of the ovariole number of the Australian Hibiscus flower-breeding Drosophila hibisci Bock was conducted on populations from two localities along a latitudinal cline in ovariole number previously observed in... more
    Quantitative genetic analysis of the ovariole number of the Australian Hibiscus flower-breeding Drosophila hibisci Bock was conducted on populations from two localities along a latitudinal cline in ovariole number previously observed in the species (Starmer et al., in press). Parental strains, F , F (reciprocal), F , backcross, and backcross reciprocal generations were used in a line-cross (generation means) analysis. This analysis revealed both additive and epistatic effects as important determinants of variation in ovariole number when larvae were reared at 25°C. Maternal effects and maternal-by-progeny genetic interactions were not significant. These results are comparable to previous studies that document epistatic components as genetic determinants of ovariole number in D. melanogaster. Parallel studies on ovariole number in D. hibisci parental and hybrid generations (F and F ) reared as larvae at three temperatures (18°, 21.5°, and 25°C) showed environmental effects and genotype-by-environment interactions as significant influences on the phenotype. Maternal effects were present when temperature of larval development was considered and significant, nonlinear environmental effects were detected. Field collections of D. hibisci females showed that field conditions result in significant departure of ovariole number from comparable laboratory reared females. The significant epistatic genetic effects, genotype-by-environment interactions, and maternal effects indicate that the genetic architecture of traits, such as ovariole number, may be more complex than often acknowledged and thus may be compatible with Wright's view of a netlike relationship between the genome and complex characters (Wright 1968).
    Geoff Parker’s investigations of the yellow dung fly mating system revitalized interest in sexual selection theory, sparked development of sperm competition and sexual conflict theories, and stimulated use of this species as an important... more
    Geoff Parker’s investigations of the yellow dung fly mating system revitalized interest in sexual selection theory, sparked development of sperm competition and sexual conflict theories, and stimulated use of this species as an important model system. Numerous studies across widespread populations have demonstrated large-male advantages in competition contests occurring on dung in cow pastures; however, recent work suggests that smaller males adopt an alternative mating tactic by avoiding dung and instead copulating with females at foraging sites. Though this finding has the potential to expand our understanding of sexual selection in yellow dung flies, such behavior has to date been documented at only one field site, raising the possibility that this phenomenon is highly localized. Here, we report the expression of size-dependent alternative mating tactics across three discrete populations. These findings provide a cautionary tale for researchers limiting their attention to aggrega...
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    Törbel provides an interesting test case for the study of the relationship between inbreeding measured by pedigrees and inbreeding measured by isonymy. At the start of this investigation, we were aware that isonymy could introduce biases... more
    Törbel provides an interesting test case for the study of the relationship between inbreeding measured by pedigrees and inbreeding measured by isonymy. At the start of this investigation, we were aware that isonymy could introduce biases into the calculation of the inbreeding coefficient in either direction. However, it was expected that in Switzerland, inbreeding from isonymy would be an overestimate due to patrilocal residence and polyphyletic names. One way of dealing with this problem [13] was not to be concerned with the absolute value of inbreeding but only in the difference between estimates. Any bias introduced in the estimate itself disappears in such comparisons, so that a trend of inbreeding can be ascertained correctly. However, it was considered equally important to subject several populations to both a complete pedigree analysis and an isonymic analysis to determine the relationship between estimates of inbreeding. Despite the fact that several authors (Swedlund [18], ...
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