Analysis of truncated distributions: Mating speed inDrosophila melanogaster

The distribution of mating speeds in wild-typeDrosophila melanogaster is shown to be log normal. The analysis of mating speeds by methods for truncated distributions is validated, and unbiased estimates of the mean mating speed, the variance of mating speed, and the proportion of flies capable of ever mating are produced. In pair matings, not all pairs are capable of copulating, given even a 7-day mating period.Supported by the National Research Council of Canada.     

Male mating speed inDrosophila melanogaster: Differences in genetic architecture and in relative performance according to female genotype

From a critical review of the literature on mating speed inDrosophila the importance of fast mating in male fitness is questioned. The genetic architecture of male mating speed (MMS) has been evaluated inD. melanogaster through a populational analysis and a full 5×5 diallel cross between inbred lines. The results emphasize the fundamental role of the female genotype in both the absolute and the relative MMS performances. Somewhat different genetic architectures for MMS are revealed according to the female used in the tests. It is suggested that different parts of the complex genetic system involved in the male's behavioral sexual phenotype are relevant depending on the female's characteristics, thus causing the heterogeneity in the MMS genetic architecture. An overall picture reveals a genetic system characterized by additivity, dominance for fast mating, and no influence of the X chromosome. There results do not support strong natural selection favoring fast mating inDrosophila males.     

The behavioral phenotype and mating behavior of two inbred strains ofDrosophila melanogaster

Time to copulation was measured in matings within and between two inbred Drosophilamelanogaster strains, Edinburgh (E) and 6C/L, using groups of one or five flies of each sex. The E males, which mated faster, usually mate with E females, which are less likely to be fertilized and have fewer progeny whose adult viability is lower. Although generally E males mated far faster with E females than did 6C/L males, there was no difference between the males when with 6C/L females. This need not imply any mating discrimination by E females, but only differences between the strains in the use of preening as a general repulsion movement toward other flies. It is suggested that a greater variety of behavioral and other characteristics (the behavioral phenotype) should be considered in studies of mating speed and assortative mating, especially where mating speed is being considered as a major component of fitness.This work was carried out while the author was in receipt of a University of Birmingham research fellowship and is part of a research program in psychogenetics supported by the British Medical Research Council.     

Mating-type differentiation and mate selection in the homothallic Chlamydomonas monoica

By using combinations of phenotypically-distinct — but sexually-compatible — mutant strains of C. monoica (zym-1, zym-27, and nit-2) and assaying for zygote genotypes in genetically-mixed mating populations (where gametes of the two parental homothallic strains were present at similar frequencies), we have found that matings occur preferentially between cells of the same genotype. Additional support for an hypothesis of non-random mate selection was provided by using an easily-selectable genetic marker (sup-1) to verify the frequent occurrence of matings between cells of identical genotype in populations where the selectable genotype was present at very low relative frequency (10^-2 or 10^-3) in a mixed mating population. Direct evidence for non-random mate selection was obtained by presenting nitrogen-starved cells with limiting nitrate to synchronize gametic differentiation in wild-type strains. Under these conditions, the four, eight, or 16 mitotic daughters released from the same mother sporangium often immediately established mating pairs within the group. Thus successive mitotic divisions of a single mother cell yielded progeny of opposite expressed mating-type.     

Age,experience, and rare-male mating advantages inDrosophila pseudoobscura

Because published experiments documenting frequency-dependent sexual selection have exclusively used young virgins, we endeavored to test for this same phenomenon in females who differed in age and in previous mating experiences. Direct observation tests were conducted employingDrosophila pseudoobscura females of the previously described Arrowhead (AR) and Chiricahua (CH) homokaryotypes. Four-day-old virgin females confer mating advantages on all tested rare males, i.e.,or. AR, and CH. Females who had a previous mating experience when younger award a rare-male advantage only when the rare male is of the same genotype of karyotype as their first mate, and matings are random when the first-mate type males are common. Equivalently aged (11 days) virgin females mate significantly more than expected with minority males if they are of the same karyotype as the females themselves. whereas matings are near random when the males are different. Frequency-dependent mating, therefore, is both age and experience dependent.A. P. is supported by funds from the Biopsychology Program, Hunter College and C.U.N.Y. L.F. is the recipient of USPHS Career Award 2KO3 HD 0903308: work supported by NIH Grant 5RO1 18907-02.Paper presented at the third annual meeting of the Behavior Genetics Association, Chapel Hill, North Carolina, April 7, 1973.     

Genetic Variation in Male and Female Reproductive Characters Associated with Sexual Conflict in <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

Recent studies have shown that elevated mating, courtship and seminal substances affect female fitness negatively in Drosophila melanogaster. It has also been shown that males vary with respect to these characters and that male harm to females correlates positively with components of male fitness. These results suggest that there is sexual conflict over the effect of such male characters. An important component of this scenario is that females have evolved counteradaptations to male harm, but so far there is limited evidence for this. Here I define female resistance as the ability to withstand an increased exposure to males. Across 10 genetically differentiated lines of D. melanogaster, I found genetic variation among females in the reduction of lifespan that followed from exposure to males of different durations. There was also genetic variation among males with regards to the degree to which they decrease the lifespan of their mates. These results suggest that genetic variation for female ability to endure male sexually antagonistic adaptations exists and may play an important role in male–female coevolution.     

Light-dependent mating ofDrosophila subobscura and species discrimination

Wild-type pairs ofDrosophila subobscura do not mate in darkness and males do not produce a courtship song, suggesting that visual signals are instrumental in finding the mating partner and in distinguishing it from members of other species. Among pairs of a strain selected for light independence, 28% mate in the dark. Results of intraspecific matings and of interspecific matings withD. pseudoobscura andD. persimilis suggest some reduction in activity level as a consequence of selection for mating in the dark. This is supported by direct observation of courtship behavior in both white and red light. In the light-independent strain courtship is less lively, mating speed is reduced, and certain elements of courtship are omitted. To determine which senses contribute in bothD. subobscura strains to successful courtship, organs that carry various sensory receptors were amputated. Results suggest that the sensory pattern in courtship has changed during selection for light independence, mainly by substituting tactile and olfactory for optical signals.     

Genotype and anesthetic determine mate choice in drosophila melanogaster

Genetic differences that influence mating preferences were studied in genetically defined lines ofDrosophila melanogaster. Initial results suggested substantial differences between two types of females with respect to the types of male preferred as mates, but further experimentation showed that the mating patterns were conditional on the mode of anethesia (CO₂ versus ether). In a statistical test of independence, the major determinant of mating choice in these experiments was due to an interaction effect between genotypes and mode of anesthesia. The observations might be explained by the differential sensitivity of male genotypes to ether. Etherization at emergence has lasting effects on mating behavior; it alters not only the latency and frequency of mating 4 days later, but also the pattern of matings observed.Research supported by a grant from the National Science Foundation (BSR 8211667) to J.W.C. We thank Drs. L. Heisler, K. Oberhauser, L. Patridge, and T. Tully for their critical comments.     

Fitness Among Individuals with Early Childhood Deafness: Studies in Alumni Families from Gallaudet University

The genetic fitness of an individual is influenced by their phenotype, genotype and family and social structure of the population in which they live. It is likely that the fitness of deaf individuals was quite low in the Western European population during the Middle Ages. The establishment of residential schools for deaf individuals nearly 400 years ago resulted in relaxed genetic selection against deaf individuals which contributed to the improved fitness of deaf individuals in recent times. As part of a study of deaf probands from Gallaudet University, we collected pedigree data, including the mating type and the number and hearing status of the children of 686 deaf adults and 602 of their hearing siblings. Most of these individuals had an onset of severe to profound hearing loss by early childhood. Marital rates of deaf adults were similar to their hearing siblings (0.83 vs. 0.85). Among married individuals, the fertility of deaf individuals is lower than their hearing siblings (2.06 vs. 2.26, p = 0.005). The fitness of deaf individuals was reduced (p = 0.002). Analysis of fertility rates after stratification by mating type reveals that matings between two deaf individuals produced more children (2.11) than matings of a deaf and hearing individual (1.85), suggesting that fertility among deaf individuals is influenced by multiple factors.     

Dynamics and genetics of mating behavior inTribolium castaneum (Coleoptera: Tenebrionidae)

Three aspects of mating behavior—time to mating, repetitiveness, and mate selection—were investigated in six genetic strains of the flour beetleTribolium castaneum and their hybrids. The data were compared with predictions from theoretical models. Time to mating was found to be heritable and characteristic of a strain. In homotypic strain combinations the duration of mating was longer than in heterotypic combinations. In repeated matings the male mating rate declined with time. In a multiple-choice experiment there was a tendency for positive assortative mating; this did not occur in female-choice or male-choice tests. Keeping beetles of two strains together prior to the experiment removed this tendency. Males almost exclusively preferred virgin to fertilized females when given a choice. The data fitted Taylor's [(1975).Behav. Genet. 5:381–393] model better than Kence and Bryant's [(1978).Am. Nat. 112:1047–1062] model. The absence of assortative mating when males (and females) of two strains were held together can be explained by the pheromone-saturation model of Averhoff and Richardson [(1974).Behav. Genet. 4:207–225] but not by Bryant's [(1979).Behav. Genet. 9:249–256] alternative.     

Wing—Beat Frequency Mutants and Courtship Behavior in Drosophila melanogaster males

Flightless mutations that affect wing-beat frequency (WBF) of Drosophila melanogaster were examined for their effect on male courtship. WBFs were measured using a fixed-wire tether that completely supports the fly in an attitude similar to hovering flight. The two spontaneous mutations, one of which reduces WBF to one-half normal and the other to zero, were placed on an isogenic background and were compared to an isogenic wildtype strain and to a genetically heterogeneous wildtype strain. Time to mating under noncompetitive conditions (single pair matings) was not significantly different among the four male types in one experiment. In a second experiment, although the time to mating varied significantly among the four male types, there was no association between the WBF that was characteristic of a male type and the length of time to mating. Time to mating was not significantly correlated with WBF, wing size, or body mass in either experiment. Genetically heterogeneous wild-type females were significantly more receptive (had shorter times to mating) than inbred wild-type females toward all four male types. During the time-to-mating tests, all four male types appeared to show typical courtship behaviors. Therefore, the male types were compared for possible differences in four components of the male courtship song: sine song frequency, interpulse interval, intrapulse frequency (=carrier frequency), and wing cycles per pulse. One or another of these components showed significant differences among the four male types (e.g., genetically heterogeneous, wild-type males showed a significantly higher sine song frequency and intrapulse frequency than males of the three isogenic types). However, the average values for all four male types were within reported wild-type ranges for each courtship song component. Although the two mutations drastically reduce WBF during tethered flight, they do not have any similar major effect on courtship. Apparently they affect muscles or neuronal control mechanisms that are not common elements shared by the wing movement of flight and male courtship song.     

Long-termebony polymorphisms: A comparison of the contributions of behavioral and nonbehavioral fitness characters

Theebony ¹¹ mutant allele was observed to be polymorphic in three sets of duplicated populations which differed in their genetic backgrounds. The polymorphisms were maintained for over 5 years (130 generations) and showed no signs of decay, withebony frequencies fluctuating from 10 to 30%. Studies of fitness characters suggested that male mating speed may be an important factor in maintaining these polymorphisms, as heterozygous males mate significantly faster than either homozygote. Other characters such as female fecundity, larval viability, and developmental rate showed little evidence either for heterosis or for frequency-dependent effects which might contribute to the polymorphism.     

Inbreeding and mating patterns inDrosophila pseudoobscura

Inbreeding, up to 12 generations of single-pair matings, did not cause significant deviation from random mating among two sets of strains inDrosophila pseudoobscura. This contrasts with reports that inbreedingD. melanogaster induces negative assortative mating among lines.This research was supported by NSF Grant DEB-76-19971 and NIH Genetics Training Grant GM 07499.     

A note on barometric pressure and behavior inDrosophila pseudoobscura

During a study ofDrosophila mating behavior we observed unexpected changes in performance under ostensibly identical experimental conditions. We related the behavior during the 17 days of the experiment to changes in ambient humidity and barometric pressure. Humidity had no significant effect, but reduced barometric pressure was found to be associated with reduced mating activity (R ²=0.29,P<0.025), accounting for close to 30% of the variation in total number of matings.This research was supported by NIH Grant GM30638-02 to Therese Markow.     

Natural Genetic Variation in Complex Mating Behaviors of Male <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

Mating behavior, including courtship and copulation, is a main component of male fitness, especially in species with no parental care. Variation in this behavior can thus be a target for mate choice and sexual selection, and can lead to evolution. The fruit fly, Drosophila melanogaster, has well-documented complex male courtship comprised of a sequence behaviors, and is an ideal model for behavior-genetic analysis. In order to evaluate genetic differences in the temporal pattern of mating behavior, we developed a high-throughput method that allows us to document the progression of male courtship and copulation using an ordinal scale (male mating progression scale, MMP). Using this method, we document natural genetic variation in the temporal pattern of behavior that was not detected using other metrics. This method was robust enough to detect genetic variation in this trait for males placed with both virgin and mated female targets.     

Mating ability in laboratory-adapted and field-derivedDrosophila melanogaster: The stress of domestication

Mating ability differences between flies of different alcohol dehydrogenase (Adh) genotypes have been assessed in the temperature range 15 to 29°C for laboratory-adapted and field-derivedDrosophila melanogaster. Significant differences amongAdh genotypes were detected principally for the laboratory-adapted strains due to departures from random mating associated with heterozygote superiority at the relatively extreme temperature of 29°C, although mating ability differences could not be attributed directly to theAdh locus. The difference between the laboratory and the field populations can be explained by the effects of genetic back-ground manifested in the form of fitness differences, being enhanced for the laboratory-adapted flies as a consequence of the stress of laboratory culture. In contrast with larval survival and development time, laboratory and field flies do not differe appreciably in their overall abilities to obtain mates, which indicates that mating ability is a direct fitness character not greatly affected by laboratory culture. It follows that direct fitness traits are the least amenable to change under domestication.     

Unassisted isolated-pair mating of Anopheles gambiae (Diptera: Culicidae) mosquitoes

Female Anopheles mosquitoes usually mate only once, but mating is seldom seen in small containers containing only one female and male. Therefore, matings are often performed among many adults in large cages or by forced copulation. Isolated-pair mating of Anopheles gambiae G3 strain-derived mosquitoes without forced copulation in small vials is described. We observed that the experimental variables eye color and male number were significant factors in the mating frequency. Females mated more frequently when three males were present over only one male. White-eyed females were more likely to be mated than wild-eyed females, but wild males mated more frequently than did white-eyed males. Experiments were also conducted to determine when mating was occurring by using wild-eye-color mosquitoes in isolated pairs. Almost no matings were observed before day 6 rather than the frequencies typically observed after 1-2 d in standard large-cage matings among large numbers of adults.     

Relative male age,fertility, and competitive mating success inDrosophila melanogaster

Female choice experiments were used to investigate the effect of relative male age on mating success inD. melanogaster. Experiments were conducted with a Canton-S (CS) strain, in which two virgin males of different ages (2, 4, or 8 days old) were offered to virgin females. Older males were found to be more successful under competitive conditions. In another group of experiments, vermilion (v) males of different ages competed with CS males of different ages. The competitive success ofv males was found to increase with their relative age. Male fertility at 2, 4, and 8 days of age was documented for both male genotypes mated with CS females. CS males fathered more offspring per copulation thanv males, and the fertility of all males was found to increase with age. Discussion focuses on the changes in male mating success and fertility with age and genotype.This work was supported by NIH Grants MH 30382 and NS 15263 to T. A. M.     

Adaptiveness of a rare male mating advantage under heterosis

It is shown that minority mating advantages, so commonly observed inDrosophila, would be selectively advantageous in a heterotic system. When an allele is below the equilibrium frequency maintained by heterosis, females mating with that homozygote produce offspring of highest mean fitness.     

Genetic variability of sexual behavior in a natural population ofDrosophila melanogaster

Although many experiments on laboratory stocks ofDrosophila have suggested that mate choice is a major feature of sexual selection in this organism, few attempts have been made to measure its extent in wild populations. In this study, a crossing design was used to obtain a set of 13 genetically identical independent lines representative of genotypes from an African population ofDrosophila melanogaster. They were tested for variation in sexual behavior using dyadic tests. Significant variation in orientation and vibration latencies was found for males, and in mating speed and copulation duration for both sexes. No evidence of assortative mating, either positive or negative, was found. The absence of a correlation in mating speed between males and females sharing the same genotype leads us to doubt the applicability of the notion of male eagerness and female reluctancy inDrosophila and the importance of vigor as a factor in mating speed. The absence of mate choice in natural populations ofDrosophila seems to us the most likely hypothesis on the basis of both theory and empirical evidence.