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ABSTRACT: In frequency-dependent selection the fitness of a given genotype depends on its frequency. Frequency dependence may be positive or negative. In the positive case any rare variant is at a disadvantage, whereas rare forms are fa-voured in the negative case. One of the best-studied exam-ples of frequency-dependent selection is the rare male mating advantage or minority male mating advantage (negative frequency-dependent selection). This could be of considerable evolutionary significance as it can maintain high levels of genetic polymorphism without any genetic load at equilibrium. Rare male mating advantage has been extensively studied in the genus Drosophila where its exis-tence has been proved in twelve species. It has also been demonstrated in other insects and vertebrates. It has been shown to occur in morphological mutants, inversion karyo-types, isozyme variants, geographic strains, strains reared at different temperatures and those having behavioural differences. Rare male mating advantage has been shown to occur in inversion karyotypes of natural populations of certain species of Drosophila. In certain cases, the rare male mating advantage was tested for, but its existence could not be proved. The expression of rare male mating advantage may be affected by age of the females, tempera-ture or experimental protocol, exposure to other flies, pre-vious mating experience and sex ratio. The generality of this phenomenon where rare males are favoured in mating has been accepted, but there is still much discussion and controversy concerning its causes. A number of explana-tions have been proposed to account for the rare male ef-fect. THE force of natural selection is seldom constant and changes with the physical and biological factors in the envi-ronment. Since the discovery of the high level of genetic variability existing in natural populations, the study of the possible mechanisms responsible for the maintenance of this variability has become one of the main topics in popula-tion genetics. The classical mechanisms for maintaining genetic variability such as over-dominance, are based on the supposition that the selective values (fitness) of geno-types are constant.
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ABSTRACT: In this paper, the effect of sensitivity of randomness in system parameters on the nonlinear transverse central deflection
response of laminated composite plates subjected to transverse uniform lateral pressure and thermal loading is examined. System
parameters such as the lamina material properties, expansion of thermal coefficients, lamina plate thickness and lateral load
are modelled as basic random variables. A higher order shear deformation theory in the von-Karman sense is used to model the
system behavior of the laminated plate. A direct iterative-based C
0 nonlinear finite element method in conjunction with the first-order perturbation technique developed by the authors is extended
for thermal problem to obtain the second-order response statistics, i.e., mean and variance of the nonlinear transverse deflection
of the plate. Typical numerical results of composite plates with temperature independent and dependent material properties
subjected to uniform temperature and combination of uniform and transverse temperature are obtained for various combinations
of geometric parameters, uniform lateral pressures, staking sequences and boundary conditions. The results have been compared
with those available in the literature and an independent Monte Carlo simulation.
KeywordsStochastic nonlinear bending response–Finite element method–Random system properties
Archive of Applied Mechanics 04/2012; 81(6):727-743. · 0.95 Impact Factor
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ABSTRACT: This paper presents the nonlinear free vibration analysis of laminated composite plates resting on elastic foundation with
random system properties in thermal environments. System parameters are modeled as basic random variables for accurate prediction
of system behavior. A C
0 nonlinear finite element based on HSDT in von Karman sense is used to descretize the laminate. A direct iterative method
in conjunction with first-order perturbation technique is outlined and applied to solve the stochastic nonlinear generalized
eigenvalue problem. The developed stochastic procedure is successfully used for thermally induced nonlinear free vibration
problem with a reasonable accuracy. Numerical results for various combinations of boundary conditions, geometric parameters,
amplitude ratios, foundation parameters and thermal loading have been compared with those available in literature and an independent
MCS. Some new results are also presented which clearly demonstrate the importance of the randomness in the system parameters
on the response of the structures.
Computational Mechanics 04/2012; 44(1):15-29. · 2.07 Impact Factor
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ABSTRACT: The analysis of genetic behaviour within and between species provides important clues about the forces shaping the evolution
of behavioural genes. Genes can affect natural behavioural variation in different ways. Allelic variation causes alternative
behavioural phenotypes, whereas changes in gene expression can influence the initiation of behaviour at different ages. Identifying
the genes involved in polygenic traits has been difficult. Chromosomal analysis has been widely used as a first step in elucidating
the genetic architecture of several behaviours ofDrosophila. Behavioural genetic and molecular studies helped to reveal the genetic basis of circadian time keeping and rhythmic behaviours.
InDrosophila, a number of key processes such as emergence from the pupal case, locomotor activity, feeding, olfaction and aspects of mating
behaviour are under circadian regulation. Evolutionary biology considers migration behaviour as central in genetic structure
of populations and speciation. Genetic loci that influence behaviour are often difficult to identify and localise in part
due to the quantitative nature of behavioural phenotypes. Diapause is a hormonally mediated delayed response to future adverse
conditions and can occur at any stage of development in an insect. Diapauseassociated gene expression was studied inDrosophila using subtractive hybridisation. Several approaches have been made to unravel the genetic complexity of the behaviour, which
have provided information that may be useful in different ways. There is evidence that species do differ in genetic architecture
of photoresponse and this may be related to their natural environment. The classical experiments by Jerry Hirsh and Th. Dobzhansky
to know the nature of genetic basis for extreme selected geotactic behaviour in fruit flies constituted the first attempt
at the genetic dissection of a complex, polygenic behaviour. Understanding the genetic differences between these selected
lines would provide an important point of entry into the study of genetic mechanisms of sensing and responding to gravity,
as well as clues to the origins of genetic flexibility and plasticity in an organism’s response.
Journal of Genetics 04/2012; 84(2):195-216. · 1.09 Impact Factor
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ABSTRACT: Geographical variation in traits related to fitness is often the result of adaptive evolution. Stress resistance traits in Drosophila often show clinal variation, suggesting that selection affects resistance traits either directly or indirectly. Multiple stress resistance traits were investigated in 45 natural populations of Drosophila ananassae collected from all over India. There was significant positive correlation between starvation resistance and lipid content. Significant negative correlations between desiccation and lipid content and between desiccation and heat resistance were also found. Flies from lower latitudes had higher starvation resistance, heat resistance and lipid content but the pattern was reversed for desiccation resistance. These results suggest that flies from different localities varied in their susceptibility to starvation because of difference in their propensity to store body lipid. Multiple regression analysis provided evidence of climatic selection driven by latitudinal variation in the seasonal amplitude of temperature and humidity changes within the Indian. Finally, our results suggest a high degree of variation in stress resistance at the population level in D. ananassae.
Journal of Evolutionary Biology 09/2010; 23(9):1979-88. · 3.28 Impact Factor
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ABSTRACT: Forty-five natural populations of Drosophila ananassae and laboratory stocks made from these flies were analyzed for chromosome inversions. Quantitative data on the frequencies of these inversions were utilized to test intra- and interchromosomal interactions in D. ananassae. In most of the natural as well as laboratory populations no significant deviation from randomness of intra- and interchromosomal associations (2L-3L, 2L-3R, 3L-3R) was found hence, providing evidence for random associations. However, in some instances, significant deviation from randomness was found in both natural and laboratory populations, which could be due to excess of certain combinations, deficiency of others and complete absence of some combinations. Possible role of genetic drift could be implicated due to tight-linkage between linked gene arrangements. This strengthens the previous suggestion that there is lack of genetic coadaptation in D. ananassae.
Genetika. 01/2010;
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ABSTRACT: Using half-sib analysis, we analysed the consequences of extreme rearing temperatures on genetic and phenotypic variations in the morphological and life-history traits of Drosophila ananassae. Paternal half-sib covariance contains a relatively small proportion of the epistatic variance and lacks the dominance variance and variance due to maternal effect, which provides more reliable estimates of additive genetic variance. Experiments were performed on a mass culture population of D. ananassae collected from Kanniyakumari (India). Two extremely stressful temperatures (18 degree C and 32 degree C) and one standard temperature (25 degree C) were used to examine the effect of stressful and non-stressful environments on the morphological and life-history traits in males and females. Mean values of various morphological traits differed signifi cantly among different temperature regimens in both males and females. Rearing at 18 degree C and 32 degree C resulted in decreased thorax length, wing-to-thorax (w/t) ratio, sternopleural bristle number, ovariole number, sex comb-tooth number and testis length. Phenotypic variances increased under stressful temperatures in comparison with non-stressful temperatures. Heritability and evolvability based on among-sires (males), among-dams (females), and the sum of the two components (sire + dam) showed higher values at both the stressful temperatures than at the non-stressful temperature. These differences reflect changes in additive genetic variance. Viability was greater at the high than the low extreme temperature. As viability is an indicator of stress, we can assume that stress was greater at 18 degree C than at 32 degree C in D. ananassae. The genetic variations for all the quantitative and life-history traits were higher at low temperature. Variation in sexual traits was more pronounced as compared with other morphometric traits, which shows that sexual traits are more prone to thermal stress. Our results agree with the hypothesis that genetic variation is increased in stressful environments.
Journal of Biosciences 07/2009; 34(2):263-74. · 1.65 Impact Factor
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ABSTRACT: Variation in the subtle differences between the right and left sides of bilateral characters or fluctuating asymmetry (FA) has been considered as an indicator of an organism's ability to cope with genetic and environmental stresses during development. However, due to inconsistency in the results of empirical studies, the relationship between FA and stress has been the subject of intense debate. In this study, we investigated whether stress caused by artificial bidirectional selection for body size has any effect on the levels of FA of different morphological traits in Drosophila ananassae. The realised heritability (h2) was higher in low-line females and high-line males, which suggests an asymmetrical response to selection for body size. Further, the levels of FA were compared across 10 generations of selection in different selection lines in both sexes for sternopleural bristle number, wing length, wing-to-thorax ratio, sex combtooth number and ovariole number. The levels of FA differed significantly among generations and selection lines but did not change markedly with directional selection. However, the levels of FA were higher in the G10 generation (at the end of selection) than G0 (at the start of selection) but lower than the G5 generation in different selection lines, suggesting that the levels of FA are not affected by the inbreeding generated during the course of selection. Also, the levels of FA in the hybrids of high and low lines were signifi cantly lower than the parental selection lines, suggesting that FA is influenced by hybridisation. These results are discussed in the framework of the literature available on FA and its relationship with stress.
Journal of Biosciences 07/2009; 34(2):275-85. · 1.65 Impact Factor
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ABSTRACT: Thirteen laboratory populations (six mass cultures and seven isofemale lines) of Drosophila bipectinata were established from files collected from six different geographic localities (four in the north and two in the south) in India. These mass cultures and isofemale lines were maintained in food bottles in the laboratory for varying number of generations by transferring about 50 files (females and males in equal number) in each generation. After several generations, all the laboratory populations were analysed chromosomally to determine the frequency of different inversions. The results indicate that all the laboratory populations remained chromosomally polymorphic due to the persistence of inversions which were originally present ion the populations. The quantitative data on the frequency of inverted gene orders and the level of inversions heterozygosity in laboratory populations are compared with those in corresponding natural populations. This comparison clearly shows that there is a considerable increase in the frequency of inverted gene orders and the level of inversion heterozygosity in laboratory populations when compared with corresponding natural populations. This is most likely to be due to selective advantage of inversion heterozygotes under stringent competition in laboratory populations. Thus heterotic buffering is associated with chromosome inversion of Drosophila bipectinata.
Journal of Zoological Systematics and Evolutionary Research 04/2009; 35(4):153 - 157. · 1.95 Impact Factor
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ABSTRACT: In order to test whether there is genetic coadaptation in geographic populations of Drosophila bipectinata with respect to body size, reciprocal crosses were made among five strains derived from ecogeographically different localities in India. Wing length was used as an index of body size, and was measured in all the five strains, and their crosses in F and F2 generations. The statistical analysis of the data show that there is significant interpopulation variation in body size and in all the crosses, there is an increase in body size in F1 generation when compared with mid-parent value. Further, there is a decrease in body size in F2 generation as compared to F1 in most of the crosses with increased variability. These results provide evidence for genetic coadaptation in geographic populations of D. bipectinata.
Journal of Zoological Systematics and Evolutionary Research 04/2009; 36(1‐2):1 - 6. · 1.95 Impact Factor
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ABSTRACT: The association of fluctuating asymmetry and phenotypic and genetic variability with environmental stress was investigated using poor nutrition and larval density as stresses on 10 recently collected isofemale lines of Drosophila ananassae Doleschall, 1858. Trait means for different morphological traits were reduced by stress, whereas phenotypic and genetic variability increased. The levels of fluctuating asymmetry and positional fluctuating asymmetry were similar in flies reared on poor and standard media. In constrast, there is a significant difference in both asymmetry measures in the flies reared at different larval densities for all traits. However, when asymmetry values across all traits were combined into a single index, composite fluctuating asymmetry, significant differences were found in males and females reared at different larval densities but not under nutritional stress. Moreover, composite fluctuating asymmetry is higher in males than in females, suggesting that males are more vulnerable to developmental stress. The results suggest that trait means are more sensitive to stress than fluctuating-symmetry measures and that the effect of stress is trait- and sex-specific. Generalizations based on the use of fluctuating asymmetry as an indicator of environmental stress in D. ananassae should therefore be used with caution.Nous utilisons l'insuffisance de nourriture et la densité larvaire comme facteurs de stress pour étudier l'association entre l'asymétrie fluctuante et la variabilité phénotypique et génétique, d'une part, et le stress du milieu, d'autre part, chez 10 lignées isofemelles de Drosophila ananassae Doleschall, 1858 récemment récoltées. Les moyennes des différents traits morphologiques sont réduites par le stress, alors que la variabilité phénotypique et génétique augmente. Les niveaux d'asymétrie fluctuante et d'asymétrie fluctuante positionnelle sont semblables chez les mouches élevées sur un substrat de mauvaise qualité et sur un substrat normal. En revanche, il y a des différences significatives entre les deux mesures d'asymétrie pour tous les traits chez les mouches élevées à différentes densités larvaires. Cependant, lorsque les valeurs d'asymétrie pour l'ensemble des traits sont regroupées en un seul coefficient, l'asymétrie fluctuante combinée, il existe des différences significatives chez les mâles et les femelles élevés sous différentes densités larvaires, mais non sous un stress alimentaire. De plus, les mâles affichent un degré d'asymétrie fluctuante combinée plus important que les femelles, ce qui indique que les mâles sont peut-être plus sujets au stress durant leur développement. Nos résultats laissent croire que les moyennes des traits semblent être plus sensibles au stress que les mesures d'asymétrie fluctuante et que les effets du stress varient en fonction du trait et du sexe. Ceci devrait servir d'avertissement concernant la généralisation de l'utilisation de l'asymétrie fluctuante comme indicateur du stress environnemental chez D. ananassae.
Canadian Journal of Zoology 04/2008; 86(5):427-437. · 1.21 Impact Factor
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ABSTRACT: Fluctuating asymmetry (FA, non-directional deviations from perfect bilateral symmetry) often has been used as a measure of developmental instability (DI) in populations. It is expected to increase in the populations subjected to genetic stressors such as inbreeding or hybridization and environmental stressors such as toxins or parasites, although the results have not always been consistent. In the present study, we have tested the effect of inbreeding on trait size and fluctuating asymmetry in different morphological traits in seven laboratory strains of Drosophila ananassae, which are maintained in the laboratory for several generations under full–sib design. The trait size of sternopleural bristle number, wing length, wing to thorax ratio, sex comb tooth number, and ovariole number varies significantly among the strains. Fluctuating asymmetry of measured traits also differs significantly among the populations in females (except sternopleural bristle number) and in males (except sternopleural bristle number and wing to thorax ratio). Further, the positional fluctuating asymmetry, which is a sensitive measure of DI, varies significantly for sternopleural bristle number and sex comb tooth number. There is also significant difference among the strains and between sexes for the composite fluctuating asymmetry. These results are discussed in relation to the use of FA as an indicator of inbreeding.
Dros. Inf. Serv. 01/2008; 91.
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ABSTRACT: The present study, which is one of the longest temporal (two decades) and largest spatial (different parts of India covered) investigations on inversion polymorphism in natural populations of D. ananassae, was undertaken to understand the dynamics of inversion polymorphism in a broad and comprehensive manner. Forty-five natural populations from different ecogeographic regions of the country (covering the regions from Kashmir to Kanniyakumari and Gujarat to Nagaland) were analysed for chromosomal inversions. All the populations show the presence of the three cosmopolitan inversions, frequencies of which vary among the populations analysed. Simple correlations between frequencies of different inversions and regression analysis of inversion frequencies with latitude, longitude and altitude were insignificant. This reinforces the concept of rigid polymorphism in D. ananassae. Genetic divergence (spatial and temporal) at the level of chromosomal polymorphism among natural populations was calculated. Results show spatial divergence but no temporal divergence. Rigid polymorphic systems of D. ananassae did not show long-term directional trends. On the basis of the present study, and after including comparisons with the studies conducted more than two decades ago, the most important conclusion to be drawn is that the three cosmopolitan inversions in D. ananassae segregate within populations at fairly similar frequencies, and the general geographic pattern has remained constant.
Genetics Research 09/2007; 89(4):191-9. · 1.71 Impact Factor
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ABSTRACT: Fluctuating asymmetry (FA, subtle random deviations from perfect bilateral symmetry) is often used as a measure of developmental instability (DI), which results from perturbations in developmental pathways caused by genetic or environmental stressors. During the present study, we estimated FA in 5 morphological traits, viz. wing length (WL), wing to thorax ratio (W:T), sternopleural bristle number (SBN), sex-comb tooth number (SCTN), and ovariole number (ON) in 18 laboratory populations of Drosophila ananassae. FA levels of measured traits differed significantly among populations except for SBN (in males and females) and W:T ratio (in females). Positional fluctuating asymmetry (PFA), a sensitive measure of DI, also varied significantly among the populations for SBN in females and SCTN in males. Interestingly, both males and females were similar for nonsexual traits. However, when FA across all traits (sexual and nonsexual) was combined into a single composite index (CFA), significant differences were found for both populations and sexes. Males showed higher CFA values than females, suggesting that males are more prone to developmental perturbations. The magnitude of FA differed significantly among traits, being lowest for nonsexual traits (SBN, WL, W:T ratio) and highest for sexual traits (SCTN and ON). The trait size of sexual traits (SCTN and ON) was positively correlated with their asymmetry. The possible reasons for variation in FA both among traits and among populations, and the usefulness of FA as an indicator of developmental stress and phenotypic quality in D. ananassae are discussed.
Genome 08/2006; 49(7):777-85. · 1.65 Impact Factor
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Journal of Genetics 09/2005; 84(2):195-216. · 1.09 Impact Factor
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ABSTRACT: The analysis of genetics of behaviour within and between species provides important clues about the forces shaping the evolution of behavioural genes. In Drosophila, a number of key processes such as emergence from the pupal case, locomotor activity, feeding, olfaction and aspects of mating behaviour are under circadian regulation. Genes controlling sexual behaviour are likely to control species specific differences in courtship that are involved in reproductive isolation of closely related species. Courtship in Drosophila is characterized by a series of stereotyped behaviours that lead to copulation and more than 30 genes have been identified through mutations that affect one or more of these elements. Although curiosity about behavioural differences between the sexes undoubtedly predates recorded history, little efforts have been made to uncover the molecular basis of male and female courtship. The brain and nervous system functions that underlie sex-specific behaviour are of obvious importance to all animals including humans. To understand behaviour related to sex it is important to distinguish those aspects that are controlled genetically. The isolation and analysis of Drosophila mutants with altered sexual orientation lead to the identification of novel branches in the sex-determination cascade, which govern the sexually dimorphic development of the nervous system.
Indian journal of experimental biology 08/2005; 43(7):575-95. · 1.29 Impact Factor
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ABSTRACT: Experimental observations of dislocation decoration with self-interstitial atom (SIA) clusters and of SIA cluster rafts are analysed to establish the mechanisms controlling these phenomena in bcc metals. The elastic interaction between SIA clusters, and between clusters and dislocations is included in kinetic Monte Carlo (KMC) simulations of damage evolution in irradiated bcc metals. The results indicate that SIA clusters, which normally migrate by 1D glide, rotate due to their elastic interactions, and that this rotation is necessary to explain experimentally-observed dislocation decoration and raft formation in neutron-irradiated pure iron. The critical dose for raft formation in iron is shown to depend on the intrinsic glide/rotation characteristics of SIA clusters. The model is compared with experimental observations for the evolution of defect cluster densities (sessile SIA clusters and nano-voids), dislocation decoration characteristics and the conditions for raft formation.
Philosophical Magazine. 08/2005; 85(22):2561-2580.
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ABSTRACT: The genetic basis of hybrid male sterility among three closely related species, Drosophila bipectinata, D. parabipectinata and D. malerkotliana has been investigated by using backcross analysis methods. The role of Y chromosome, major hybrid sterility (MHS) genes (genetic factors) and cytoplasm (non-genetic factor) have been studied in the hybrids of these three species. In the species pair, bipectinata--parabipectinata, Y chromosome introgression of parabipectinata in the genomic background of bipectinata and the reciprocal Y chromosome introgression were unsuccessful as all males in second backcross generation were sterile. Neither MHS genes nor cytoplasm was found important for sterility. This suggests the involvement of X-Y, X-autosomes or polygenic interactions in hybrid male sterility. In bipectinata--malerkotliana and parabipectinata--malerkotliana species pairs, Y chromosome substitution in reciprocal crosses did not affect male fertility. Backcross analyses also show no involvement of MHS genes or cytoplasm in hybrid male sterility in these two species pairs. Therefore, X- autosome interaction or polygenic interaction is supposed to be involved in hybrid male sterility in these two species pairs. These findings also provide evidence that even in closely related species, genetic interactions underlying hybrid male sterility may vary.
Indian journal of experimental biology 06/2005; 43(5):455-61. · 1.29 Impact Factor
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ABSTRACT: Clusters of self-interstitial atoms (SIAs) in the form of parallel crowdions are created directly in high-energy displacement cascades produced in metals by neutron irradiation. They are equivalent to small perfect dislocation loops and, in isolation in pure metals, undergo fast thermally-activated glide in the direction of their Burgers vector. Their strain field and ability to glide allows long-range interaction with other extended defects. Indeed, dislocations decorated by dislocation loops are commonly observed after neutron irradiation. Dislocations gliding under applied stress also encounter these mobile defects. These effects influence mechanical properties and require further investigation. This paper presents results from an atomic-scale study of copper and α-iron at either 0 K or 300 K. Loop drag and breakaway effects are investigated for an edge dislocation under applied stress interacting with a row of SIA loops below its glide plane. The maximum speed at which a loop is dragged is lower in copper than iron, and the applied stress at which this occurs is also lower. These differences in the dynamics of cluster-dislocation interaction are determined by the atomic structure of the defects and cannot be investigated by continuum treatment.
Philosophical Magazine Letters 11/2004; 84(11):745-754. · 1.24 Impact Factor
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ABSTRACT: These experiments were conducted to study frequency-dependent sexual selection on the alpha inversion in the left arm of the second chromosome (2L) in Drosophila ananassae. Two different strains, ST/ST-standard gene arrangement and AL/AL-alpha inversion in 2L were used. Female-choice experiments were carried out in five different male ratios. Two different methods of observation have been employed, one in which copulating pairs are aspirated out and the other, in which pairs are not removed. Results were analyzed by chi(2) tests, and log odds plus regression analyses. Regression analyses revealed the presence of one-sided rare male mating advantages for AL/AL males. Preferential mating is present within the strain having AL/AL karyotype. The minority male advantage and preferential mating found in the AL/AL strain are different components of mating success. ANOVA fails to show any significant difference between the outcomes of rare-male experiments using these two different methods.
Behavior Genetics 06/2004; 34(3):335-42. · 2.52 Impact Factor
