Infection densities of three Spiroplasma strains in the host Drosophila melanogaster

Maternally transmitted endosymbiotic bacteria of the genus Spiroplasma associate with numerous insect species, including the genus Drosophila. Among the Spiroplasma strains associated with Drosophila, several manipulate their host??s reproduction by killing the male offspring of the infected females. Although the male-killing mechanism is not well understood, previous studies of non-native strains transferred to D. melanogaster (strain Oregon-R) indicate that the male-killing strain achieves higher densities than two non-male-killing strains. Whether this pattern of higher male-killing strain densities occurs in other host-symbiont strain combinations is not known. Herein, we used quantitative PCR to examine infection densities of one non-male-killing strain native to D. hydei (Hyd1), and two male-killing strains; one native to D. nebulosa (NSRO), and one native to D. melanogaster (MSRO; recently discovered), upon artificial transfer to D. melanogaster (strain Canton-S). Infection densities were examined at four weekly intervals in adult flies, across three consecutive generations following artificial transfer. Infection densities of the non-male-killing strain were significantly lower than those of the two male killers immediately after adult emergence. At later time points, however, the non-male-killing strain (Hyd1) is capable of proliferating to densities similar to those of the two male-killing strains (NSRO and MSRO) in D. melanogaster (Canton-S). We also examined the effect of co-infection by the heritable bacterium Wolbachia, on Spiroplasma densities and male-killing ability. Wolbachia had little to no effect of Spiroplasma densities, but the male-killing ability of MSRO was lower in the presence of Wolbachia. Generation post-infection had little effect on Spiroplasma densities, but affected the male-killing ability.     

Natural Variation in the Strength and Direction of Male Mating Preferences for Female Pheromones in Drosophila melanogaster

Many animal species communicate using chemical signals. In Drosophila, cuticular hydrocarbons (CHCs) are involved in species and sexual identification, and have long been thought to act as stimulatory pheromones as well. However, a previous study reported that D. melanogaster males were more attracted to females that were lacking CHCs. This surprising result is consistent with several evolutionary hypotheses but is at odds with other work demonstrating that female CHCs are attractive to males. Here, we investigated natural variation in male preferences for female pheromones using transgenic flies that cannot produce CHCs. By perfuming females with CHCs and performing mate choice tests, we found that some male genotypes prefer females with pheromones, some have no apparent preference, and at least one male genotype prefers females without pheromones. This variation provides an excellent opportunity to further investigate the mechanistic causes and evolutionary implications of divergent pheromone preferences in D. melanogaster males.     

The different effects on courtship of volatile compounds from mated and virgin Drosophila females

Virgin Drosophila melanogaster females, which are courted vigorously, emit pheromones which stimulate males to court each other (Tompkinset al., 1980). Females which have recently copulated are courted less vigrously, and volatile compounds produced by mated females stimulate less courtship between males. Analysis of these compounds from fertilized females by gas chromatography and behavioral assays indicates that mated females emit less of the sex attractant made by virgins and may also produce material which inhibits courtship. These changes in pheromone production are initiated after the first few minutes of copulation.     

GENETIC VARIATION FOR FEMALE MATE DISCRIMINATION IN DROSOPHILA MELANOGASTER

Comparisons between the Canton-S and Tai-Y strains of Drosophila melanogaster (both wild type) revealed variation in female mate discrimination based on chemical courtship signals present as hydrocarbons on the male cuticle. Mating tests indicated that 7-tricosene, which is the primary hydrocarbon on the Canton-S male cuticle but is nearly absent from Tai-Y, was a significant component of the signal. The discrimination was asymmetrical in that Canton-S females clearly distinguished between the two types of males in no-choice tests, but Tai-Y females did not. F₁ females expressed an intermediate ability to discriminate, and female progeny of backcrosses expressed a mating phenotype very similar to that of the parental strain to which the backcross was made. Analysis of independent effects from the X and both major autosomes indicated that the discrimination is controlled by gene(s) on chromosome 3.     

Sex-linked lethal frequencies produced by 7,12-dimethylbenz[a]anthracene in five Drosophila melanogaster wild strains

7,12-Dimethylbenz[a]anthracene (DMBA) was tested for the induction of mutations in 5 strains of Drosophila melanogaster. Larvae were fed mixtures containing either 1.0 or 4.0 mM DMBA in darkness. After emergence the males were mated to Basc females to test for sex-linked lethals. Canton-S males produced the highest frequency with no significant differences in the induction of lethals by the 2 concentrations. DMBA was slightly mutagenic in Oregon-R males over controls without significant differences between the 2 concentrations. Berlin-K, Lausanne-S and Urbana-S males all produced significantly more mutations at the 4.0-mM than the 1.0-mM concentrations. DMVA produced partial sterility in Canton-S and Urbana-S males. The DMBA mutation frequencies of all 5 wild strains are interpreted as being related to the levels of activating enzymes that metabolize DMBA.     

Aggregation pheromones in Collembola

The existence of aggregation pheromones is demonstrated in the Collembola Orchesella cincta, Orchesella villosa, and Tomocerus minor. Places conditioned by these animals can be considered as pheromone-sources, causing aggregation. Although for Tomocerus minor perception is not strictly species specific, all species investigated appear to be more responsive to their own pheromone than to those produced by other species. Both males and females appear to produce and perceive the aggregation pheromone. The distant action of the pheromone points to an olfactorially acting pheromone, in the perception of which the antennae play an important rôle. The behavioural reaction of the perceiving animals is orthokinetic.     

Association of P-mobile element activity and DNA methylation pattern changes in conditions of Drosophila Melanogaster prolonged irradiation

Changes of DNA methylation patterns of two Drosophila melanogaster strains (Canton-S and ri) irradiated with gamma-radiation in laboratory conditions with a low dose rate (1.2 × 10^?8, 0.3 × 10^?8, and 0.12 × 10^?8 Gy/s) have been studied. Two restrictases GluI and GlaI have been used taking in to account methylation peculiarities of Drosophila melanogaster. The difference between the patterns of DNA methylation in males and females in every studied strain in the control has been identified. The decrease of the methylation level in recognition sites for restrictase GluI in males and females of the ri-strain with higher activity of the P-mobile element as the result of chronic irradiation has been found. The decrease of the methylation level in recognition sites for restrictase GlaI in females of both strains has been noted. The question on the association of DNA methylation processes and activation of mobile elements has been discussed.     

Cuelure but not zingerone make the sex pheromone of male Bactrocera tryoni (Tephritidae: Diptera) more attractive to females

In tephritid fruit flies of the genus Bactrocera Macquart, a group of plant derived compounds (sensu amplo ‘male lures’) enhance the mating success of males that have consumed them. For flies responding to the male lure methyl eugenol, this is due to the accumulation of chemicals derived from the male lure in the male rectal gland (site of pheromone synthesis) and the subsequent release of an attractive pheromone. Cuelure, raspberry ketone and zingerone are a second, related group of male lures to which many Bactrocera species respond. Raspberry ketone and cuelure are both known to accumulate in the rectal gland of males as raspberry ketone, but it is not known if the emitted male pheromone is subsequently altered in complexity or is more attractive to females. Using Bactrocera tryoni as our test insect, and cuelure and zingerone as our test chemicals, we assess: (i) lure accumulation in the rectal gland; (ii) if the lures are released exclusively in association with the male pheromone; and (iii) if the pheromone of lure-fed males is more attractive to females than the pheromone of lure-unfed males. As previously documented, we found cuelure was stored in its hydroxyl form of raspberry ketone, while zingerone was stored largely in an unaltered state. Small but consistent amounts of raspberry ketone and β-(4-hydroxy-3-methoxyphenyl)-propionic acid were also detected in zingerone-fed flies. Males released the ingested lures or their analogues, along with endogenous pheromone chemicals, only during the dusk courtship period. More females responded to squashed rectal glands extracted from flies fed on cuelure than to glands from control flies, while more females responded to the pheromone of calling cuelure-fed males than to control males. The response to zingerone treatments in both cases was not different from the control. The results show that male B. tryoni release ingested lures as part of their pheromone blend and, at least for cuelure, this attracts more females.     

Dosage Compensation of Serine-4 Transfer RNA in DROSOPHILA MELANOGASTER

A dosage series of the X chromosome site for serine-4 transfer RNA consisting of one of three copies in females and one to two in males was constructed to test whether transfer RNA expression is governed by dosage compensation. A dosage effect on the level of the serine-4 isoacceptor was observed in both females and males when the structural locus was varied. However, in males, each dose had a relatively greater expression so the normal one dose was slightly greater than the total female value and the duplicated male had the highest relative expression of all the types examined. Serine-4 levels in males and females from an isogenic Oregon-R stock were similar. Thus the transfer RNA levels conform to the expectations of dosage compensation.     

The chemical basis for sex recognition in Drosophila melanogaster

Chemical cues were recognized to play a predominant role in initiating male courtship behaviour in Drosophila melanogaster as measured by the number and duration of wing-vibration responses elicited in test males. The effect was associated with compounds specific to the female cuticle, for which we describe a simple extraction procedure. Female active extracts were compared with behaviourally non-active extracts from males, using gas-liquid and thin-layer chromatography. Using these preparative methods, long-chain hydrocarbons were isolated and activity was found only among unsaturated molecules. One, heptacosadiene, inducing the highest level of courtship, appears to be the main aphrodisiac pheromone of the female D. melanogaster. This compound is specific to females of the species and is the most abundant of their cuticular hydrocarbons.     

Effect of Drosophila melanogaster Female Size on Male Mating Success

In this study, we examined the influence of female size on mating success in Drosophila melanogaster. The results that were obtained from experiments performed in mating chambers allowed us to confirm the results of previous studies, demonstrating higher mating success of larger D. melanogaster males, and to conclude that female size also affects mating success, either when considering a single male or two competing males. We observed that the advantage for larger males depends on their size relative to that of the female, demonstrating a previously unknown role for female size in mating behavior studies. This effect of female size on mating success depends on various factors: males take longer to initiate courtship toward larger females, large females receive more wing vibrations from males prior to mating, and large females tend to keep moving for longer periods during male courtship. The importance of this finding is discussed in the context of recent reports on sexual conflict in D. melanogaster, in which males were observed to depress fitness in females as a result of intercourse.     

Nippostrongylus brasiliensis: factors influencing movement of males toward a female pheromone

Single, responding males of Nippostrongylus brasiliensis exhibited a dose-dependent movement toward a pheromone source that was derived from incubation or homogenization of female helminths in Tyrode's solution. Increases in female homogenate beyond an optimum concentration resulted in reduced male movement toward the pheromone source. Crowding of male N. brasiliensis prior to their exposure to female pheromone gradients diminished the males' response. However, crowding of females had no effect on response to the pheromone. The locomotory responses of males exposed to various mixed male and female pheromone sources reaffirmed earlier suggestions of a pheromone feedback system in which males influence the pheromone released from females.     

Sex-linked lethal mutations induced in Drosophila melanogaster by 7,12-dimethylbenz[a]anthracene

One of the most potent carcinogens, 7,12-dimethylbenz[a]anthracene (DMBA), was tested for the induction of mutations in 2 strains of Drosophila melanogaster. Larvae were fed mixtures containing DMBA, peanut oil and solubilizing agents in darkness. After emergence the males were mated with Basc or FM7a females to test for sex-linked lethals. For Canton-S males, all DMBA treatments produced highly significant increases in mutation frequencies over controls. DMBA was slightly mutagenic for Oregon-R males.     

CHEMICAL COMMUNICATION IN HAWAIIAN DROSOPHILA

We are interested in elucidating the extent to which lekking Hawaiian Drosophila species have diverged from their continental counterparts, which engage in sexual behavior at communal food sources, with regard to the chemical communication systems that the flies employ. Accordingly, we have analyzed flies from three closely related Hawaiian Drosophila species in the adiastola subgroup. These species are of interest because the males engage in a unique behavior: while courting, they raise their abdomens over their heads and emit anal droplets. Analysis of the flies' behavior, the hydrocarbons in males' anal droplets, and males' cuticular hydrocarbons suggest that females' responses to males may be mediated by cuticular pheromones and/or pheromones in males' extruded droplets that enable the females to distinguish conspecific from heterospeciflc males. Conversely, perception of cuticular hydrocarbons from conspecific females enables D. adiastola males to distinguish females from a closely related species from conspecific females. On the basis of these observations, we suggest that the adiastola subgroup species are unique among drosophilids in that they utilize an anal droplet-mediated pheromone communication system, some or all components of which are species specific. However, the lekking Hawaiian Drosophila species are similar to D. melanogaster and related continental species in that the Hawaiian flies employ a cuticular pheromone communication system, some components of which are sex and species-specific.     

The protective role of parsley extract against vincristine mutagenicity in Drosophila melanogaster

In this study, Drosophila melanogaster males were treated with parsley plant extract and the anticancer drug vincristine (VCR) singly and in combined treatments (pre, co and post-treatments) to detect the mutagenic effects by using sex-linked recessive lethal test (SLRL) and estimation of cholinesterase enzyme (ChE) activities in order to compare the sensitivity of the two test systems. A wild type strain Oregon-R (Or-R) male flies of D. melanogaster were reared on a medium containing one concentration of each of VCR and parsley (4 ml/100 ml medium) in each single and combined treatment. Also the activity of ChE was estimated in some insects of the two generations: F1 females, F2 bar eye females (heterozygous) and F2 wild types males. The results indicate that both of parsley and vincristine did not cause significant increases of SLRL test in either the single or combined treatments. In contrast, estimation of ChE activities showed significant increase in all the broods within single and combination treatments, except female of the second generation of spermatid brood which treated with parsley and VCR at the same time. It is concluded that enzyme estimation is more sensitive than SLRL test for detection the mutagenic effect for parsley’s extract and vincristine.     

Variation in Male Mate Choice in Drosophila melanogaster

Male mate choice has been reported in the fruit fly, Drosophila melanogaster, even though males of this species were previously thought to maximise their fitness by mating with all available females. To understand the evolution of male mate choice it is important to understand variation in male mating preferences. Two studies, using different stock populations and different methods, have reported contrasting patterns of variation in male mate choice in D. melanogaster. Two possible explanations are that there are evolved differences in each stock population or that the methods used to measure choice could have biased the results. We investigated these hypotheses here by repeating the methods used in one study in which variable male mate choice was found, using the stock population from the other study in which choice was not variable. The results showed a significant resource-independent male preference for less fecund, smaller females, which contrasts with previous observations of male mate choice. This indicates that different selection pressures between populations have resulted in evolved differences in the expression of male mate choice. It also reveals phenotypic plasticity in male mate choice in response to cues encountered in each choice environment. The results highlight the importance of variation in male mate choice, and of identifying mechanisms in order to understand the evolution of mate choice under varying ecological conditions.     

Does sexual experience affect the strength of male mate choice for high‐quality females in Drosophila melanogaster?

Although females are traditionally thought of as the choosy sex, there is increasing evidence in many species that males will preferentially court or mate with certain females over others when given a choice. In the fruit fly, Drosophila melanogaster, males discriminate between potential mating partners based on a number of female traits, including species, mating history, age, and condition. Interestingly, many of these male preferences are affected by the male''s previous sexual experiences, such that males increase courtship toward types of females that they have previously mated with and decrease courtship toward types of females that have previously rejected them. D. melanogaster males also show courtship and mating preferences for larger females over smaller females, likely because larger females have higher fecundity. It is unknown, however, whether this preference shows behavioral plasticity based on the male''s sexual history as we see for other male preferences. Here, we manipulate the sexual experience of D. melanogaster males and test whether this manipulation has any effect on the strength of male mate choice for large females. We find that sexually inexperienced males have a robust courtship preference for large females that is unaffected by previous experience mating with, or being rejected by, females of differing sizes. Given that female body size is one of the most common targets of male mate choice across insect species, our experiments with D. melanogaster may provide insight into how these preferences develop and evolve.     

Production and perception of pheromones by the beetle Tribolium confusum

Adults of Tribolium confusum secrete two pheromones. The first, produced by the male, is attractive to both sexes and the second, produced by the female, is attractive to the male only. Pheromone production and perception was studied in relation to habituation, beetle age, time of day and previous mating. A living source of each pheromone habituates the responding beetles, the male pheromone habituating more strongly; female pheromone habituates only in the absence of the male pheromone. Habituation to one pheromone was always accompanied by an enhanced response to the other.Five days after emergence, production of male pheromone reaches a peak that is maintained. Production of female pheromone peaks after 3 days. Both sexes are responsive to male pheromone immediately upon eclosion, males reaching maximum response at 14 days, females at 8 days. Males are also responsive to female pheromone upon eclosion reaching maximum response at 8 days; female response to female pheromone is imperceptible. Males but not females display a 24 hr rhythm in pheromone production. Mated beetles did not differ significantly from unmated beetles in their ability to perceive pheromones. Alteration in male pheromone production after mating was detected by females but not males; this pheromone may, therefore, act as both a sex and aggregation pheromone.     

Evidence against an antiaphrodisiac role for cis-vaccenyl acetate in Drosophila melanogaster

The male lipid of Drosophila melanogaster, cis-vaccenyl acetate, is transferred to females during mating, and reduces the attractiveness of virgin females when applied topically. This has led to the hypothesis that cis-vaccenyl acetate functions as a mated-female antiaphrodisiac. Using gas chromatography, we measured the cis-vaccenyl acetate recovered from female reproductive tracts and cuticular washes at various times after mating to investigate whether cis-vaccenyl acetate meets criteria that would be expected of an antiaphrodisiac pheromone in this species. Our results do not indicate a direct antiaphrodisiac role for cis-vaccenyl acetate. Specifically, cis-vaccenyl acetate is not transferred to females within the first 3 min of copulation, even though the first 3 min are sufficient to induce the post-mating loss of attractiveness characteristic of D. melanogaster females. Furthermore, the cis-vaccenyl acetate on the female's cuticle at any time after mating is probably not sufficient to effectively inhibit courtship, and no detectable transfer to the cuticle occurs during exposure to courting males. These results suggest that cis-vaccenyl acetate plays a limited role, if any, as a D. melanogaster antiaphrodisiac.