The Effects of Selection for early (day) and late (dusk) Mating lines of Hybrids of Bactrocera tryoni and Bactrocera neohumeralis

Bactrocera neohumeralis and Bactrocera tryoni are closely related tephritid fruit fly species. B. neohumeralis mates throughout the day (in bright light) and B. tryoni mates at dusk. The two species can also be distinguished by the colour of their calli (prothoracic sclerites) which are brown and yellow, respectively. The F1 hybrids can mate both in bright light just before dusk and during dusk and have calli that are partly brown and partly yellow. The F2 hybrids have a wider range of callus patterns and mating occurs more widely in the day as well as at dusk. We directly selected hybrid stocks for mating time, creating 'early' (day-mating) and 'late' (dusk-mating) lines. As an apparently inadvertent consequence, the two types of line respectively had predominantly brown and predominantly yellow calli and thus came to closely resemble the original two species in both behaviour and appearance. Lines that were evenly selected (half for day and half for dusk) essentially retained the mating pattern of F2 hybrids. Selection for callus colour alone also affected the distribution of mating times in a predictable way. We propose a genetical model to account for the results and discuss them in the light of the apparent maintenance of species integrity in nature.     

Close genetic similarity between two sympatric species of tephritid fruit fly reproductively isolated by mating time

Abstract.— Two sibling species of tephritid fruit fly, Bactrocera tryoni and B. neohumeralis , occur sympatrically throughout the range of B. neohumeralis in Australia. Isolation between the two species appears to be maintained by a difference in mating time: B. tryoni mates at dusk, whereas B. neohumeralis mates during the middle of the day. A morphological difference in humeral callus color also distinguishes the two species. Despite clear phenotypic evidence that B. tryoni and B. neohumeralis are distinct species, genetic differentiation as measured by four markers–nuclear DNA sequences from the white gene and the ribosomal internal transcribed spacer (ITS2), and mitochondrial DNA sequences from the cytochrome b (cytb) and cytochrome oxidase subunit II (COII) genes–is very small. Minor fixed differences occur in the ITS2 sequence, however, in all other cases the two species exhibit a high level of shared polymorphic variation. The close genetic similarity suggests either that speciation has occurred very rapidly and recently in the absence of any mitochondrial DNA sorting or that the sharing of polymorphisms is due to hybridization or introgression. A third species within the tryoni complex, B. aquilonis , is geographically isolated. Bactrocera aquilonis is also genetically very similar, but in this case there is clear differentiation for the mitochondrial loci. The three species form a group of considerable interest for investigation of speciation mechanisms.     

Genetic manipulation of the circadian clock's timing of sexual behaviour in the Queensland fruit flies, Dacus tryoni and Dacus neohumeralis

ABSTRACT. Mating in Dacus tryoni is restricted to dusk, whereas that of a sibling species, Dacus neohumeralis , occurs in the middle of the day. The timing of sexual behaviour in both species is determined by an interaction between a circadian clock and light intensity. In D. tryoni peak mating responsiveness is at the time of dusk, and the optimal light intensity for mating is approximately 91x. In D.neohumeralis peak responsiveness is in the middle of the day, and the optimal light intensity for mating is greater than 10 000 lx. The two species were crossed and the time of mating and response to light intensity of F₁, F₂ and backcross progeny determined. The circadian clock set a mating phase ('gate') as narrow in F₁ flies as in their parents, suggesting the circadian timing mechanism to be common between the two species. The results indicate that the genetic mechanism controlling timing is independent of that controlling response to light intensity, and that both genetic mechanisms are complex.     

DNA microsatellite analysis of naturally occurring colour intermediates between Bactrocera tryoni (Froggatt) and Bactrocera neohumeralis (Hardy) (Diptera: Tephritidae)

Abstract  The sympatric tephritid fruit flies Bactrocera tryoni (Froggatt) (Queensland fruit fly) and B. neohumeralis (Hardy) differ in time of mating and for the colour of the humeral callus ('shoulder pad'), which is typically entirely yellow in B. tryoni and typically entirely brown in B. neohumeralis . Field collections in sympatric regions usually include at least 1% of individuals whose humeral calli show mixed patches of yellow and brown ('intermediates'). Over 40 years, a number of studies have debated the possibility that these intermediates are interspecific hybrids. In the present study, we have used microsatellites to show that few if any of these intermediates are hybrids. Instead, most variation humeral callus appears to be confined to one species, B. tryoni . We discuss these results in the context of geneflow between the two species and suggest directions for future research.     

Genetic delineation of sibling species of the pest fruit fly Bactocera (Diptera: Tephritidae) using microsatellites

Using a large set of microsatellites, the genetic relationships between three closely related Australian fruit fly species, Bactrocera tryoni (Froggatt), B. neohumeralis (Hardy) and B. aquilonis(May) were investigated. Bactrocera tryoni and B. neohumeralis are sympatric, while B. aquilonisis allopatric to both. The sympatric species, B. tryoni and B. neohumeralis, were found to be genetically distinct. It is likely that despite differences in mating time between these two species, some gene flow still occurs. In contrast, the sibling species B. tryoni and B. aquilonis were found to be closely related, despite allopatry. The level of genetic divergence was similar to that found within eastern Australian populations of B. tryoni. Consideration of all available genetic data suggests that this similarity is not due to recent (i.e. within the last 30 years) displacement of B. aquilonis by B. tryoni from the B. aquilonis region (north-western Australia). Instead the data suggests that, at least in the areas sampled, asymmetrical hybridization may have occurred over a longer timescale.     

Attributes pertinent to overwintering potential do not explain why Bactrocera neohumeralis (Hardy) (Diptera: Tephritidae) does not spread further south within the geographical range of B. tryoni (Froggatt)

Abstract  The geographical range of Bactrocera neohumeralis does not extend as far south as that of its sibling species, B. tryoni . However, there was no evidence of any difference between the two species in terms of physiological limitation to southerly spread when comparisons were made of low temperature torpor thresholds of adults, survival time of adults at −4°C and development rates of all stages in either warm or cool regimes. The survival schedule of the two species was similar in the laboratory and also in the moderately cold conditions experienced by caged cohorts that were exposed to winter field temperatures between late April and early November at Richmond, New South Wales (500 km south of the usual southerly limit of B. neohumeralis ). Overwintered cohorts of both species laid similar numbers of eggs in September in terms of eggs per emerged female (an indicator of the reproductive potential). However, because the proportion of B. tryoni surviving to the period of 1–15 September was less than half that for B. neohumeralis , the production per surviving female was more than double in B. tryoni . The possibility of the southerly spread of B. neohumeralis being limited by an Allee effect is discussed.     

Influence of male aggregation size on female visitation in Bactrocera tryoni (Froggatt) (Diptera: Tephritidae)

Abstract  The importance of male aggregation size for female visitation and initiation of male pheromone-calling was investigated in Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) using artificial male aggregations in large laboratory cages. Female B. tryoni visited the largest aggregation more frequently than single males in association with a higher proportion of calling males, but there was no correlation between aggregation size and female visitation. Female B. tryoni had a limited capacity to perceive a difference between the number of calling males. Calling propensity of male B. tryoni was increased by the presence of conspecific males. Increased calling propensity in larger groups of male B. tryoni may be due to social facilitation of male calling behaviour. Female visitation at aggregations was only weakly associated with male calling, suggesting that aggregation size and the number of pheromone-calling males are not the only factors important in locating mates in B. tryoni , and it is possible that low-density populations could persist so long as females can encounter single males.     

Australian Distribution of 17 Species of Fruit Flies (Diptera: Tephritidae) Caught in Cue Lure Traps in February 1994

We report the first widespread survey of tephritid fruit flies attempted in a single time period. 1,471 cue lure traps caught 17 species, and extensions to previously recorded geographical ranges were detected for seven of them: Bactrocera tryoni, B. neohumeralis, B. frauenfeldi, B. aeroginosa, Dacus absonifascies, D. aequalis and D. newmani. the traps also unexpectedly caught several B. cacuminata and also both males and females of Dirioxa pornia and Ceratitis capitata. the geographical variation in the relative abundance of B. tryoni and B. neohumeralis in the region of their co-occurrence was in substantial agreement with earlier estimates. the regional variation in abundance of B. tryoni in the eastern states was in accordance with the predictions of a published bioclimatic model. Furthermore, the spread of this species (expected from the model) to several locations in the Northern Territory is recorded here for the first time.     

Mechanisms of Mate Investment in the Polygamous Fowl,Gallus gallus

Male fowl (Gallus gallus) that have recently mated invest in their mates by producing antipredator alarm signals at a higher rate. It remains unclear, however, whether these males are investing judiciously in their mates, or responding more generally to recent mating success. Here, we manipulated each male’s mating experience with two different females to test whether males invest selectively in their mates. For 1 wk, males could interact with both females, but could mate with only one of them. In the second week, we removed either the mated or the unmated female and measured the male’s rate of alarm calling. Males did not invest preferentially in their mates, suggesting that increased alarm calling is a more general response to recent mating experience. This relationship could be based on a relatively simple cognitive rule of thumb or on an underlying physiological mechanism. Testosterone and corticosterone are associated with reproduction and antipredator behaviour in other species and so could provide the necessary physiological link in fowl. To test this, we measured plasma levels of testosterone and corticosterone before, during and after mating. Results show that hormone levels did not change as a function of male mating status and hence cannot provide the link between mating and calling behaviour. Instead, we suggest that a general cognitive mechanism is more likely to explain prudent mate investment in this species.     

Effects of parent age at mating on reproductive response of Glyptapanteles flavicoxis (Hymenoptera: Braconidae), a larval parasitoid of the gypsy moth (Lepidoptera: Lymantriidae)

Glyptapanteles flavicoxis (Marsh) (Hymenoptera: Braconidae) is a gregarious larval parasitoid of the Indian gypsy moth Lymantria obfuscata (Walker) (Lepidoptera: Lymantriidae), that is believed to have potential for inundative releases against gypsy moth populations, because it can be reared in large numbers with few hosts. Unfortunately, sex ratios in laboratory reared G. flavicoxis are usually male-biased, hindering efforts to mass release this species for biological control by making the production of females costly. Because parental age at time of mating is known to affect the sex ratio in some Braconidae, we crossed haploid males and virgin females at 0, 1, 4, 9, and 16 d old with at least 10 trials for each of the 25 combinations. Numbers and sex ratios of progeny produced by females each day were recorded. Both progeny and sex ratios (percentage of females) among progeny produced by ovipositing females of G. flavicoxis decreased markedly over time, so only the first days production need be used in mass rearing. The reduction in the proportion and numbers of females among progeny as females aged is consistent with sperm depletion. Approximately 30% of females in all age classes mated to newly emerged males (day 0) produced all male progeny, whereas only 10-15% of those mated to older males failed to produce any daughters. When crosses with only male progeny were excluded from the analysis, females mated to males 1 d old had higher sex ratios in progeny than those mated to males in other age classes. In addition, females mated the day that they emerged tended to have progeny with the highest sex ratios.     

Remating inhibition in female Queensland fruit flies: effects and correlates of sperm storage

Reproductive success of male insects commonly hinges both on their ability to secure copulations with many mates and also on their ability to inseminate and inhibit subsequent sexual receptivity of their mates to rival males. We here present the first investigation of sperm storage in Queensland fruit flies (Tephritidae: Bactrocera tryoni; a.k.a. 'Q-flies') and address the question of whether remating inhibition in females is directly influenced by or correlated with number of sperm stored from their first mates. We used irradiation to disrupt spermatogenesis and thereby experimentally reduce the number of sperm stored by some male's mates while leaving other aspects of male sexual performance (mating probability, latency until copulating, copula duration) unaffected. Females that mated with irradiated rather than normal males were less likely to store any sperm at all (50% vs. 89%) and, if some sperm were stored, the number was greatly reduced (median 11 vs. 120). Despite the considerable differences in sperm storage, females mated by normal males and irradiated males were similarly likely to remate at the next opportunity, indicating (1) number of sperm stored does not directly drive female remating inhibition and (2) factors actually responsible for remating inhibition are similarly expressed in normal and irradiated males. While overall levels of remating were similar for mates of normal and irradiated males, factors responsible for female remating inhibition were positively associated with presence and number of sperm stored by mates of normal but not irradiated males. We suggest seminal fluids as the most likely factor responsible for remating inhibition in female Q-flies, as these are likely to be transported in proportion to number of sperm in normal males, be uninfluenced by irradiation, and be transported without systematic relation to sperm number in irradiated males.     

THESIS ABSTRACT

Geographical distribution, seasonal abundance and habitat preference of fruit fly species (Diptera: Tephritidae) in South-East Queensland, with special reference to Bactrocera tryoni (Froggatt) and Bactrocera neohumeralis (Hardy) . S. Raghu.     

Effects of multiple matings on reproductive fitness of male and female Diaeretiella rapae

Mating frequency and the amount of sperm transferred during mating have important consequences on progeny sex ratio and fitness of haplodiploid insects. Production of female offspring may be limited by the availability of sperm for fertilizing eggs. This study examined multiple mating and its effect on fitness of the cabbage aphid parasitoid Diaeretiella rapae McIntosh (Hymenoptera: Aphidiidae). Female D. rapae mated once, whereas males mated with on average more than three females in a single day. The minimum time lag between two consecutive matings by a male was 3 min, and the maximum number of matings a male achieved in a day was eight. Sperm depletion occurred as a consequence of multiple mating in D. rapae. The number of daughters produced by females that mated with multiple‐mated males was negatively correlated with the number of matings achieved by these males. Similarly, the proportion of female progeny decreased in females that mated with males that had already mated three times. Although the proportion of female progeny resulting from multiple mating decreased, the decrease was quicker when the mating occurred on the same day than when the matings occurred once per day over several days. Mating success of males initially increased after the first mating, but then males became ‘exhausted’ in later matings; their mating success decreased with the number of prior matings. The fertility of females was affected by mating with multiple‐mated males. The study suggests that male mating history affects the fitness of male and female D. rapae.     

The influence of soil type and moisture on pupal survival of Bactrocera tryoni (Froggatt) (Diptera: Tephritidae)

Abstract  Larvae of the Queensland fruit fly, Bactrocera tryoni , pupate in the soil, but the influence of soil variables on B. tryoni pupal mortality is not known. For other tropical tephritid species, soil moisture has been identified as a major pupal mortality factor. In the laboratory, we tested the effects of soil moisture and soil type on pupal survival through a factorial experiment which used three soil types (loamy sand, loam, sandy clay) and seven soil moisture levels (0%, 10%, 25%, 50%, 75%, 90% and 100%). Minor, but significant, differences in pupal mortality were observed between the soil types, but the most significant factor affecting pupae was extremes of soil moisture. Eighty-five percent pupal mortality occurred at 0% soil moisture and 30% mortality at 100% soil moisture: very low levels of mortality occurred at all intermediate levels. We detected a significant interaction between soil type and moisture level but cannot explain it. In a follow-up experiment, we demonstrated that prepupal wandering larvae of B. tryoni could discriminate between different moisture levels, with significantly greater pupation in loam soil at 75% soil moisture than at either 0% or 100% soil moisture. Results are used to modify a pupal mortality/soil moisture equation used in a recently published DYMEX model of B. tryoni population dynamics .     

An effect of mate fertility on the attractiveness and oviposition rates of mated Drosophila melanogaster females

Mate fertility has a strong influence on the sexual receptivity of mated Drosophila melanogaster females, but an effect of mate fertility on the attractiveness of mated females has not previously been demonstrated. We compared the declines in attractiveness over the first 10 h after mating for females mated to fertile (XY) males and those mated to sterile (XO) males, and found a significant effect of mate fertility. A large and significant decrease in attractiveness, that is the same for both XY- and XO-mated females, is evident during the first 4 h after mating. However, a further decline in attractiveness occurs between 4 and 6 h after mating for XY-mated females, but not until between 6 and 10 h after mating for females with sterile mates. Thus, XY-mated females are significantly less attractive than XO-mated females at 6–8 h post-mating, but not at any other time. A sharp increase in oviposition rates for both types of mated females is associated with the decline in attractiveness that occurs between 4 and 10 h after mating.     

Females use self-referent cues to avoid mating with previous mates

Females of many species mate repeatedly throughout their lives, often with many different males (polyandry). Females can secure genetic benefits by maximizing their diversity of mating partners, and might be expected, therefore, to forego matings with previous partners in favour of novel males. Indeed, a female preference for novel mating partners has been shown in several taxa, but the mechanism by which females distinguish between novel males and previous mates remains unknown. We show that female crickets (Gryllodes sigillatus) mark males with their own unique chemical signatures during mating, enabling females to recognize prior mates in subsequent encounters and to avoid remating with them. Because self-referent chemosensory cues provide females with a simple, but reliable mechanism of identifying individuals with whom they have mated without requiring any special cognitive ability, they may be a widespread means by which females across a broad range of animal mating systems maximize the genetic benefits of polyandry.     

The female perspective of mating in A. femoralis, a territorial frog with paternal care--a spatial and genetic analysis

The adaptive significance of sequential polyandry is a challenging question in evolutionary and behavioral biology. Costs and benefits of different mating patterns are shaped by the spatial distribution of individuals and by genetic parameters such as the pairwise relatedness between potential mating partners. Thus, females should become less choosy as costs of mating and searching for mates increase. We used parentage assignments to investigate spatial and genetic patterns of mating across a natural population of the Neotropical frog Allobates femoralis, a species characterized by male territoriality and care and female iteroparity. There was no correlation between genetic and spatial distances between adult individuals across the population. In 72% of cases, females mated with males available within a radius of 20 m. Mean pairwise relatedness coefficients of successful reproducers did not differ from random mating but had a lower variance than expected by chance, suggesting maximal reproductive output at intermediate genetic divergence. We also found evidence for selection in favor of more heterozygous individuals between the embryo and adult stage. The level of sequential polyandry significantly increased with the number of spatially available males. Females that had more candidate males also produced more adult progeny. We hypothesize that the benefits associated with female multiple mating outweigh the costs of in- and outbreeding depression, and consequently precluded the evolution of 'choosy' mate selection in this species.     

The effect of interspecific mating on sex ratios in the twospotted spider mite and the Banks grass mite (Acarina: Tetranychidae)

Mixed populations of the twospotted spider mite (TSM),Tetranychus urticae (Koch), and the Banks grass mite (BGM),Oligonychus pratensis (Banks), occur on corn and sorghum plants in late summer in the Great Plains. Interspecific matings between these arrhenotokous species occur readily in the laboratory but yield no female offspring. The effect of interspecific mating on female: male sex ratios was measured by examining the F₁ progeny of females that mated with both heterospecific and conspecific males in no-choice situations. TSM females that mated first with BGM males and then with TSM males produced a smaller percentage of female offspring than TSM females that mated only with TSM males (43.1±5.8 and 78.9±2.8% females, respectively). Similarly, BGM females mated with heterospecific males and then with conspecific males produced fewer female offspring than females mated only with BGM males (55.7±5.2 and 77.5±2.5%, respectively). Lower female: male sex ratios were produced also by BGM females that mated with TSM males after first mating with conspecifics (62.4±3.4%). In mixed populations containing males of both species, females also produced lower female: male sex ratios, but these ratios were not as low as expected based on mating propensities and progeny sex ratios observed in no-choice tests. These data suggest that interspecific mating may substantially reduce female fitness in both mite species by reducing the output of female offspring, but in mixed populations this effect is mitigated by unidentified behavioral mechanisms.     

Impact of mating on Anagyrus kamali Moursi (Hym., Encyrtidae) lifetime fecundity, reproductive longevity, progeny emergence and sex ratio

Abstract: The solitary endoparasitoid Anagyrus kamali Moursi (Hym., Encyrtidae) and the Hibiscus mealybug Maconellicoccus hirsutus Green (Hom., Pseudococcidae), were used as a parasite/host model to test the effect of mating on several fitness parameters, i.e. longevity, lifetime fecundity, progeny emergence and sex ratio. At 27 ± 2°C, 8 h light : 16 h dark, mating significantly affected the survival of male parasitoids. Virgin males lived longer (32.2 ± 9.51 days) than mated males (23.9 ± 7.52 days). Female longevity (40.7 ± 16.3 days for virgins and 36.2 ± 10.7 days for mated females) was not affected by mating. The lifetime fecundity of female parasitoids and their oviposition period was not significantly affected by mating. However, the number of hosts parasitized was greater for mated wasps (7.54 ± 4.85 hosts parasitized/day) compared with virgin ones (5.12 ± 2.19 hosts parasitized/day). This resulted in greater progeny production from mated A. kamali females. The progeny of virgin females consisted only of males, whereas the mated ones had a more female‐biased sex ratio. The lowest sex ratio (0.41 M/F ± 0.123) was attained when females had free access to males and were multi‐mated.