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Wolf U Blanckenhorn - One of the best experts on this subject based on the ideXlab platform.
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intraspecific mating system evolution and its effect on complex male secondary sexual traits does male male competition increase selection on size or shape
Journal of Evolutionary Biology, 2020Co-Authors: Wolf U Blanckenhorn, Martin A Schafer, Nalini Puniamoorthy, Patrick T. Rohner, Julian BaurAbstract:: Sexual selection is generally held responsible for the exceptional diversity in secondary sexual traits in animals. Mating system evolution is therefore expected to profoundly affect the covariation between secondary sexual traits and mating success. Whereas there is such evidence at the interspecific level, data within species remain scarce. We here investigate sexual selection acting on the exaggerated male fore femur and the male wing in the common and widespread Dung Flies Sepsis punctum and S. neocynipsea (Diptera: Sepsidae). Both species exhibit intraspecific differences in mating systems and variation in sexual size dimorphism (SSD) across continents that correlates with the extent of male-male competition. We predicted that populations subject to increased male-male competition will experience stronger directional selection on the sexually dimorphic male foreleg. Our results suggest that fore femur size, width and shape were indeed positively associated with mating success in populations with male-biased SSD in both species, which was not evident in conspecific populations with female-biased SSD. However, this was also the case for wing size and shape, a trait often assumed to be primarily under natural selection. After correcting for selection on overall body size by accounting for allometric scaling, we found little evidence for independent selection on any of these size or shape traits in legs or wings, irrespective of the mating system. Sexual dimorphism and (foreleg) trait exaggeration is therefore unlikely to be driven by direct precopulatory sexual selection, but more so by selection on overall size or possibly selection on allometric scaling.
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Sublethal effects of the parasiticide ivermectin on male and female reproductive and behavioural traits in the yellow Dung fly.
Chemosphere, 2020Co-Authors: Nicola Van Koppenhagen, Patrick T. Rohner, Natalia Gourgoulianni, Jeannine Roy, Alexandra Wegmann, Wolf U BlanckenhornAbstract:Abstract The veterinary pharmaceutical ivermectin is commonly used against parasites of livestock. Excreted in Dung it can have lethal and sublethal effects on non-target organisms developing in and living around cattle Dung. Research in this realm typically investigates the impact of pharmaceuticals on Dung-feeding insects by looking at juvenile development and survival, while fitness effects of adult exposure are largely neglected. We conducted laboratory experiments to assess combined effects of ivermectin on life history and reproductive traits of juvenile and adult yellow Dung Flies (Scathophaga stercoraria). Two treatments (12 and 24 μg ivermectin/kg wet Dung) were used for the larvae reared in Dung, and one much higher concentration (3000 μg ivermectin/kg sugar) for the adult Flies (in addition to uncontaminated controls). Juvenile ivermectin exposure lead to smaller body size of male and female Flies. Adult feeding on ivermectin-contaminated Dung additionally resulted in adult male Flies with smaller testes (and likely fewer sperm) that experienced reduced mating durations, resulting in lower probability of producing offspring. Exposure of adult Flies to ivermectin lowered offspring production and survival for both sexes. Thus, treatment of livestock with pharmaceuticals such as ivermectin appears to have even more far-reaching sublethal ecological consequences than previously assumed by affecting not only Flies at their larval stage but also adult mating behaviour and reproduction.
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Size- and sex-specific predation on Dung Flies by amphibian and arthropod predators – size match matters
2019Co-Authors: Wolf U Blanckenhorn, G. Cozzi, G. Jaeggli, J. P. BussoAbstract:Because predator-prey interactions in nature are multifarious, linking phenomenological predation rates to the underlying behavioural or ecological mechanisms is challenging. Size- and sex-specific predation has been implicated as a major selective force keeping animals small, affecting the evolution of body size and sexual size dimorphism. We experimentally assessed predation by various amphibian (frogs and toads) and arthropod predators (bugs, Flies, spiders) on three species of Dung Flies with similar ecology but contrasting body sizes, sexual size dimorphism and coloration. Predators were offered a size range of Flies in single- or mixed-sex groups. As expected based on optimal foraging theory, some anurans (e.g. Bufo bufo) selected larger prey, thus selecting against large body size of the Flies, while others (Bombina variagata and Rana esculenta) showed no such pattern. Small juvenile Rana temporaria metamorphs, in contrast, preferred small Flies, as did all arthropod predators, a pattern that can be explained by larger prey being better at escaping. The more mobile males were not eaten more frequently or faster than the cryptic females, even when conspicuously colored. Predation rates on Flies in mixed groups permitting mating activity were not higher, contrary to expectation, nor was predation generally sex-specific. We conclude that the size-selectivity of predators, and hence the viability selection pattern exerted on their prey, depends foremost on the relative body sizes of the two in a continuous fashion. Sex-specific predation by single predators appears to contribute little to sexual dimorphism. Therefore, the mechanistic study of predation requires integration of both the predator’s and the prey’s perspectives, and phenomenological field studies of predation remain indispensable.
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size and sex specific predation on Dung Flies by amphibian and arthropod predators size match matters
bioRxiv, 2019Co-Authors: Wolf U Blanckenhorn, G. Cozzi, G. Jaeggli, J. P. BussoAbstract:Because predator-prey interactions in nature are multifarious, linking phenomenological predation rates to the underlying behavioural or ecological mechanisms is challenging. Size- and sex-specific predation has been implicated as a major selective force keeping animals small, affecting the evolution of body size and sexual size dimorphism. We experimentally assessed predation by various amphibian (frogs and toads) and arthropod predators (bugs, Flies, spiders) on three species of Dung Flies with similar ecology but contrasting body sizes, sexual size dimorphism and coloration. Predators were offered a size range of Flies in single- or mixed-sex groups. As expected based on optimal foraging theory, some anurans (e.g. Bufo bufo) selected larger prey, thus selecting against large body size of the Flies, while others (Bombina variagata and Rana esculenta) showed no such pattern. Small juvenile Rana temporaria metamorphs, in contrast, preferred small Flies, as did all arthropod predators, a pattern that can be explained by larger prey being better at escaping. The more mobile males were not eaten more frequently or faster than the cryptic females, even when conspicuously colored. Predation rates on Flies in mixed groups permitting mating activity were not higher, contrary to expectation, nor was predation generally sex-specific. We conclude that the size-selectivity of predators, and hence the viability selection pattern exerted on their prey, depends foremost on the relative body sizes of the two in a continuous fashion. Sex-specific predation by single predators appears to contribute little to sexual dimorphism. Therefore, the mechanistic study of predation requires integration of both the predator’s and the prey’s perspectives, and phenomenological field studies of predation remain indispensable.
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the role of larval substrate specialization and female oviposition in mediating species diversity of closely related sepsid Flies diptera sepsidae
European Journal of Endocrinology, 2019Co-Authors: Amelie Laux, Wolf U Blanckenhorn, Natalia Gourgoulianni, Jeannine Roy, Alexandra Wegmann, Patrick T. RohnerAbstract:Coprophagous insect communities play a critical role in the decomposition of vertebrate Dung and provide ecosystem functions fundamental to modern agriculture. While the ecology of Dung beetles is rather well understood, niche differentiation in coprophagous Flies is poorly studied. Sepsid Flies (Diptera: Sepsidae) are a vital part of the European community of coprophages, with 6-7 widespread species of Sepsis often found co-occurring in the same pasture. To advance our ecological understanding of the mechanisms that enable species to coexist, we investigated the oviposition preferences and larval performance of 7 common species of Sepsis in the Dung of different large domestic and wild mammals. Substrate preferences and subsequent performance of larvae in laboratory experiments did not vary greatly. All species did very well on cow Dung, the most common substrate in Central Europe, but also on Dung of horse and wild boar. In contrast, Flies did not prefer or grow well in Dung of red and roe deer, two of the most common wild vertebrates. Thus there were only minor differences among the species tested along the specialist-generalist (Dung) gradient, indicating that differences in the choice of oviposition sites by the adults of the different fly species and larval performance do not constitute a major axis of ecological differentiation. Nevertheless, there was a positive correlation between substrate choice and larval performance indicating the preference of gravid females for particular oviposition sites is adaptive. We conclude that sepsids are common in Europe because they are well adapted to the Dung of herbivorous livestock rather than wild animals. Nevertheless, specialization on particular types of Dung does not define the niche of Sepsis Dung Flies and hence plays a minor role in mediating their species diversity.
Paul I. Ward - One of the best experts on this subject based on the ideXlab platform.
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Adaptive maternal plasticity in response to perceptions of larval competition
Functional Ecology, 2013Co-Authors: Claudia C. Buser, Paul I. Ward, Luc F BussiereAbstract:Summary Because the developmental performance of a genotype can vary substantially depending on the conditions to which it is exposed, mothers are known to exercise strong choice concerning oviposition sites. Females potentially adjust the provisioning or paternity of offspring by responding to multiple environmental factors, but how those factors interact in the context of female assessment has been under investigated and remains poorly understood. In this study, we examine how female perceptions of the larval environment affect the size, fitness and paternity of her brood. We mated female yellow Dung Flies, Scathophaga stercoraria, with two different males each, manipulated female perception of larval competition levels, and subsequently split clutches across high and low-competition conditions. We found that females (especially large females) laid more eggs when they perceived low levels of competition for their brood. Females further adjusted brood size depending on the size of their last mate (who typically sires most offspring), increasing brood size for large second mates when perceiving low levels of competition, and for small second mates when they perceived competition to be high. Larval survival was highest for females who perceived the same larval conditions that their larvae experienced, and whose last mate was well suited to such conditions (e.g. small for competitive conditions, or large in the absence of competition). In contrast, the effects of competition on paternity did not depend on maternal perceptions of larval competition, as would be expected if females exercise adaptive cryptic choice to favour alternate male phenotypes depending on the intensity of larval competition. Our experimental approach supports complex and sophisticated changes in female behaviour in response to cues of larval fitness. Our results further emphasize that most plasticity in maternal behaviour serves to improve larval fitness directly, providing valuable empirical support for theoretical assertions of the primacy of material benefits over good-genes.
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Temperature-mediated microhabitat choice and development time based on the pgm locus in the yellow Dung fly Scathophaga stercoraria
Biological Journal of the Linnean Society, 2012Co-Authors: Wolf U Blanckenhorn, Marco Demont, Ursula Briegel, Yves Choffat, Roland Gautier, Katherine L. Pemberton, Heidi Roschitzki-voser, Yvonne Willi, Paul I. WardAbstract:Temperature can affect the performance of insects through its influence on enzyme function. We report a series of laboratory and field experiments investigating the putatively adaptive temperature-dependent effects of phosphoglucomutase (pgm) genotype on development time, a central life-history fitness component, as mediated by the microhabitat choice of ovipositing female yellow Dung Flies (Scathophaga stercoraria). The allozyme corresponding to the most common pgm allele 3 (approximate 90% natural frequency) had the highest Q 10 and showed higher in vitro activity at warmer temperatures (17–27 °C), whereas the allozyme corresponding to allele 4 (4.5%) showed relatively higher activity at the lowest temperature (7 °C), and the allozyme corresponding to allele 2 (2.5%) showed lower activity throughout. A laboratory experiment revealed that egg development time for allele 3 was shortest (i.e. best) at all temperatures tested, although egg-to-adult development time was longest for offspring derived from field females bearing allele 3. Importantly, over 3 years in the field, allele 4 did not increase in frequency late in the season as the temperatures dropped. Although females augmented their proportion of eggs laid on the warmer south slope of a Dung pat (adaptive response), the development times of their offspring consistently increased towards the end of the season (maladaptive response). Regardless, females did not systematically bias the pgm composition of eggs laid on the north versus south slopes, as was expected from previous work hypothesizing that females exert microhabitat choice based on the pgm locus. We conclude that, although PGM allozymes differ in activity and the pgm genotype does differentially affect development time, these effects are inconsistent, and not predictable from in vitro allozyme assays, and therefore difficult to reconcile with an adaptive framework of cryptic female choice. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 107, 686–696.
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A Possible Explanation for Cryptic Female Choice in the Yellow Dung Fly, Scathophaga stercoraria (L.)
Ethology, 2010Co-Authors: Paul I. WardAbstract:Cryptic, or post-copulatory, female choice could markedly affect the outcome of sperm competition, i.e. a female could differentially manipulate ejaculates within her own body, affecting the fertilization successes of her mating partners. Female yellow Dung Flies, Scathophaga (Scatophaga) stercoraria, have three spermathecae, the sperm-storage organs, and can to some extent store the sperm of different males in different places. I show that a female's body size, as well as those of her mates, influences the process of sperm storage. Furthermore, females lay eggs of different genotypes under different environmental conditions. Females use both cues correlated with single locus variation (at the locus for the enzyme phosphoglucomutase, PGM) and quantitative trait variation (in body size and development time) when using sperm to fertilize their eggs. It is proposed that this allows a female to match the genotypes of her offspring to the conditions in which the larvae must grow, thus increasing their subsequent fitness. I describe an experiment where larvae of different PGM genotypes were raised in different environments and the most successful genotype was different in different environments. The complexity of the female reproductive sysrem may therefore have evolved because rhe best father for a female's offspring, from the female's viewpoint, is different under different environmental conditions. The effect interacts with the established male-determined effects to influence the outcome of sperm competition.
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The assessment of insemination success in yellow Dung Flies using competitive PCR.
Molecular Ecology Resources, 2010Co-Authors: Luc F Bussiere, Marco Demont, Andrew J. Pemberton, Matthew Hall, Paul I. WardAbstract:In spite of considerable interest in postcopulatory sexual selection, separating the effects of sperm competition from cryptic female choice remains difficult because mechanisms underlying postcopulatory processes are poorly understood. One methodological challenge is to quantify insemination success for individual males within the sperm stores of multiply mated females to discover how insemination translates into eventual paternity. Any proposed method must be applicable in organisms without extensive DNA sequence information (which include the majority of model species for sexual selection). Here, we describe the development and application of microsatellite competitive-multiplex-PCR for quantifying relative contributions to a small number of sperm in storage. We studied how DNA template characteristics affect PCR amplification of known concentrations of mixed DNA and generated regressions for correcting observations of allelic signal strength based on such characteristics. We used these methods to examine patterns of sperm storage in twice-mated female yellow Dung Flies, Scathophaga stercoraria. We confirm previous findings supporting sperm displacement and demonstrate that average paternity for the last mate accords with the mean proportion of sperm stored. We further find consistent skew in storage across spermathecae, with more last male sperm stored in the singlet spermatheca on one side of the body than in the doublet on the opposite side. We also show that the time between copulations may be important for effectively sorting sperm. Finally, we demonstrate that male size may influence the opportunity for sperm choice, suggesting future work to disentangle the roles of male competition and cryptic female choice.
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The anatomy of fertilization in the yellow Dung fly Scathophaga stercoraria
Journal of Morphology, 2008Co-Authors: Benjamin I. Arthur, Andrew J. Pemberton, Sonja H. Sbilordo, Paul I. WardAbstract:Female yellow Dung Flies, Scathophaga stercoraria, can influence the traffic of sperm stored in their spermathecae to the site of fertilization in the bursa copulatrix. However, the anatomical mechanisms employed are largely unknown. We investigated the anatomy of the female genital tract, seeking structures involved in sperm transfer and egg fertilization. We found a membranous structure descending from the ends of the spermathecal and accessory gland ducts into the bursa copulatrix. We call this the prolatus. Sperm accumulate in the prolatus during oviposition. When an egg is in the bursa the egg micropyle, rather than being aligned towards the dorsal openings of the spermathecal ducts, lies on the opposite, ventral side. We also confirm the presence, and suggest a function for, a cuticularized pouch on the ventral wall of the anterior bursa copulatrix. This pouch, plus a previously undescribed chamber, may be homologous to the ventral receptacle/fertilization chamber found in other dipterans. Further, we describe a translucent cap, apparently transversed by channels, covering the micropyle. Sperm were observed to aggregate on and in the micropyle cap, which appears to attract and hold sperm. We interpret the prolatus as a structure that allows an ovipositing female to transfer a few sperm onto the ventral bursal wall and thus, indirectly, onto the micropyle cap. Such anatomy potentially gives the female a large degree of control over sperm traffic from storage to the site of fertilization.
Luc F Bussiere - One of the best experts on this subject based on the ideXlab platform.
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the developmental plasticity and functional significance of an additional sperm storage compartment in female yellow Dung Flies
Functional Ecology, 2013Co-Authors: Martin A Schafer, Wolf U Blanckenhorn, Ralf Jochmann, David Berger, Luc F BussiereAbstract:Summary The mechanistic basis for and adaptive significance of variation in female sperm storage organs are important for a range of questions concerning sexual selection and speciation, as such variation influences the evolutionary trajectories of male fertilization related traits and may facilitate speciation through its effects on gamete recognition. Female yellow Dung Flies (Scathophaga stercoraria) usually develop three sperm storage compartments, and this subdivision may be an adaptation for sorting sperm during postcopulatory choice. Using lines artificially selected to express four spermathecae (4s), we explored the fitness consequences of the novel phenotype relative to the naturally prevalent three-spermatheca (3s) phenotype by manipulating the opportunity for postcopulatory sexual selection (females mated either with three or only one male prior to oviposition). In addition, we examined the developmental plasticity of spermathecal number in response to different larval food environments and estimated its genetic correlation with growth rate. Mating treatments with and without the opportunity for postcopulatory sexual selection revealed no significant fitness differences between alternative spermathecal phenotypes within selection lines despite overall benefits associated with multiple mating, and moderate egg-to-adult survival costs in response to artificial selection for 4s. Manipulations of the larval food environment revealed that the expression of 4s is highly plastic and tightly linked to environmental conditions promoting fast somatic growth and development. Likewise, siblings with fast intrinsic (genetic) growth were more likely to express 4s within and across food environments. The present results highlight a great potential for rapid evolutionary change in female sperm storage morphology through indirect selection on life-history traits, and further suggest genetic assimilation as a potential mechanism facilitating phylogenetic transitions in spermatheca number as frequently observed within the Dipterans.
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Adaptive maternal plasticity in response to perceptions of larval competition
Functional Ecology, 2013Co-Authors: Claudia C. Buser, Paul I. Ward, Luc F BussiereAbstract:Summary Because the developmental performance of a genotype can vary substantially depending on the conditions to which it is exposed, mothers are known to exercise strong choice concerning oviposition sites. Females potentially adjust the provisioning or paternity of offspring by responding to multiple environmental factors, but how those factors interact in the context of female assessment has been under investigated and remains poorly understood. In this study, we examine how female perceptions of the larval environment affect the size, fitness and paternity of her brood. We mated female yellow Dung Flies, Scathophaga stercoraria, with two different males each, manipulated female perception of larval competition levels, and subsequently split clutches across high and low-competition conditions. We found that females (especially large females) laid more eggs when they perceived low levels of competition for their brood. Females further adjusted brood size depending on the size of their last mate (who typically sires most offspring), increasing brood size for large second mates when perceiving low levels of competition, and for small second mates when they perceived competition to be high. Larval survival was highest for females who perceived the same larval conditions that their larvae experienced, and whose last mate was well suited to such conditions (e.g. small for competitive conditions, or large in the absence of competition). In contrast, the effects of competition on paternity did not depend on maternal perceptions of larval competition, as would be expected if females exercise adaptive cryptic choice to favour alternate male phenotypes depending on the intensity of larval competition. Our experimental approach supports complex and sophisticated changes in female behaviour in response to cues of larval fitness. Our results further emphasize that most plasticity in maternal behaviour serves to improve larval fitness directly, providing valuable empirical support for theoretical assertions of the primacy of material benefits over good-genes.
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Wild yellow Dung fly females may not select sperm based on Dung pat microclimate but could nevertheless benefit from polyandry
Evolutionary Ecology, 2011Co-Authors: Marco Demont, Oliver Y. Martin, Luc F BussiereAbstract:Molecular techniques have substantially improved our knowledge of postcopulatory sexual selection. Nevertheless, studies examining sperm utilization in natural populations of nonsocial insects are rare, support for sperm selection (biased use of stored sperm, e.g. to match offspring genotypes to prevailing environmental conditions) is elusive, and its relevance within natural populations unknown. We performed an oviposition site choice experiment in the field where female yellow Dung Flies Scathophaga stercoraria could deposit eggs into three different microenvironments on a Dung pat (the east–west ridge, north- or south-exposed side), and genotyped the offspring and sperm remaining in storage after oviposition. Females exhibited plasticity in the number of eggs deposited according to pat age. Additionally, temperature strongly influenced egg placement: the warmer the temperature, the higher the proportion of eggs laid into the north-exposed side of Dung. The number of ejaculates in storage differed amongst spermathecae, and females stored sperm from more males than fathered their offspring (2.11 sires vs. 2.84 males within sperm stores). Mean last male paternity was 83.4%, roughly matching previous laboratory estimates. Importantly, we found no evidence that females selectively lay eggs of different genotypes, by biasing paternity towards certain males, depending on offspring’s microclimate. Thus, while we show female choice over number of eggs and where these are deposited, there was no evidence for sperm selection. We further revealed positive effects of multiple mating on total number of offspring and proportion of offspring emerging from the Dung. We argue that the integration of field studies and laboratory experiments is essential to promote our understanding of polyandry and cryptic female choice.
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Natural levels of polyandry: Differential sperm storage and temporal changes in sperm competition intensity in wild yellow Dung Flies
Functional Ecology, 2011Co-Authors: Marco Demont, Oliver Y. Martin, Claudia C. Buser, Luc F BussiereAbstract:Summary 1. Polyandry is common in insects. Nevertheless, the evolutionary causes and consequences of this phenomenon remain contentious, in part because of a lack of information about natural mating rates and the fact that most post-copulatory processes are hidden from view within female reproductive tracts. 2. We captured wild female yellow Dung Flies (Scathophaga stercoraria) over the whole spring season and genotyped the sperm from their spermathecae to obtain information on sperm transfer, sperm storage and natural levels of polyandry for this model species of post-copulatory sexual selection research. 3. On average, females stored sperm from a minimum of 2·47 males (based on the most conservative estimate). Incorporating knowledge of population allele frequencies yielded a slightly higher estimate of 3·33 mates per female. 4. Sperm storage and therefore sperm competition intensity showed high temporal variation. The proportion of multiply mated females (i.e. females with sperm from ≥2 males within their sperm stores) and the absolute number of ejaculates detected within females increased strongly over the spring season before sharply decreasing as midsummer approached. 5. Interestingly, we detected a positive relationship between the number of stored ejaculates and females’ wing injuries, suggesting that mating not only causes measurable cumulative damage to wild females but also provides a potential mechanism by which males may be able to assess the intensity of sperm competition within a female. 6. Our study found no evidence for intraejaculate sperm sorting, but importantly, the number of ejaculates in storage differed amongst the three sperm storage organs (spermathecae) of female yellow Dung Flies. Different sperm mixtures across the spermathecae could enable females to bias paternity towards certain males if females can selectively use sperm from a certain spermatheca at the time of fertilization.
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The assessment of insemination success in yellow Dung Flies using competitive PCR.
Molecular Ecology Resources, 2010Co-Authors: Luc F Bussiere, Marco Demont, Andrew J. Pemberton, Matthew Hall, Paul I. WardAbstract:In spite of considerable interest in postcopulatory sexual selection, separating the effects of sperm competition from cryptic female choice remains difficult because mechanisms underlying postcopulatory processes are poorly understood. One methodological challenge is to quantify insemination success for individual males within the sperm stores of multiply mated females to discover how insemination translates into eventual paternity. Any proposed method must be applicable in organisms without extensive DNA sequence information (which include the majority of model species for sexual selection). Here, we describe the development and application of microsatellite competitive-multiplex-PCR for quantifying relative contributions to a small number of sperm in storage. We studied how DNA template characteristics affect PCR amplification of known concentrations of mixed DNA and generated regressions for correcting observations of allelic signal strength based on such characteristics. We used these methods to examine patterns of sperm storage in twice-mated female yellow Dung Flies, Scathophaga stercoraria. We confirm previous findings supporting sperm displacement and demonstrate that average paternity for the last mate accords with the mean proportion of sperm stored. We further find consistent skew in storage across spermathecae, with more last male sperm stored in the singlet spermatheca on one side of the body than in the doublet on the opposite side. We also show that the time between copulations may be important for effectively sorting sperm. Finally, we demonstrate that male size may influence the opportunity for sperm choice, suggesting future work to disentangle the roles of male competition and cryptic female choice.
Patrick T. Rohner - One of the best experts on this subject based on the ideXlab platform.
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intraspecific mating system evolution and its effect on complex male secondary sexual traits does male male competition increase selection on size or shape
Journal of Evolutionary Biology, 2020Co-Authors: Wolf U Blanckenhorn, Martin A Schafer, Nalini Puniamoorthy, Patrick T. Rohner, Julian BaurAbstract:: Sexual selection is generally held responsible for the exceptional diversity in secondary sexual traits in animals. Mating system evolution is therefore expected to profoundly affect the covariation between secondary sexual traits and mating success. Whereas there is such evidence at the interspecific level, data within species remain scarce. We here investigate sexual selection acting on the exaggerated male fore femur and the male wing in the common and widespread Dung Flies Sepsis punctum and S. neocynipsea (Diptera: Sepsidae). Both species exhibit intraspecific differences in mating systems and variation in sexual size dimorphism (SSD) across continents that correlates with the extent of male-male competition. We predicted that populations subject to increased male-male competition will experience stronger directional selection on the sexually dimorphic male foreleg. Our results suggest that fore femur size, width and shape were indeed positively associated with mating success in populations with male-biased SSD in both species, which was not evident in conspecific populations with female-biased SSD. However, this was also the case for wing size and shape, a trait often assumed to be primarily under natural selection. After correcting for selection on overall body size by accounting for allometric scaling, we found little evidence for independent selection on any of these size or shape traits in legs or wings, irrespective of the mating system. Sexual dimorphism and (foreleg) trait exaggeration is therefore unlikely to be driven by direct precopulatory sexual selection, but more so by selection on overall size or possibly selection on allometric scaling.
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Sublethal effects of the parasiticide ivermectin on male and female reproductive and behavioural traits in the yellow Dung fly.
Chemosphere, 2020Co-Authors: Nicola Van Koppenhagen, Patrick T. Rohner, Natalia Gourgoulianni, Jeannine Roy, Alexandra Wegmann, Wolf U BlanckenhornAbstract:Abstract The veterinary pharmaceutical ivermectin is commonly used against parasites of livestock. Excreted in Dung it can have lethal and sublethal effects on non-target organisms developing in and living around cattle Dung. Research in this realm typically investigates the impact of pharmaceuticals on Dung-feeding insects by looking at juvenile development and survival, while fitness effects of adult exposure are largely neglected. We conducted laboratory experiments to assess combined effects of ivermectin on life history and reproductive traits of juvenile and adult yellow Dung Flies (Scathophaga stercoraria). Two treatments (12 and 24 μg ivermectin/kg wet Dung) were used for the larvae reared in Dung, and one much higher concentration (3000 μg ivermectin/kg sugar) for the adult Flies (in addition to uncontaminated controls). Juvenile ivermectin exposure lead to smaller body size of male and female Flies. Adult feeding on ivermectin-contaminated Dung additionally resulted in adult male Flies with smaller testes (and likely fewer sperm) that experienced reduced mating durations, resulting in lower probability of producing offspring. Exposure of adult Flies to ivermectin lowered offspring production and survival for both sexes. Thus, treatment of livestock with pharmaceuticals such as ivermectin appears to have even more far-reaching sublethal ecological consequences than previously assumed by affecting not only Flies at their larval stage but also adult mating behaviour and reproduction.
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the role of larval substrate specialization and female oviposition in mediating species diversity of closely related sepsid Flies diptera sepsidae
European Journal of Endocrinology, 2019Co-Authors: Amelie Laux, Wolf U Blanckenhorn, Natalia Gourgoulianni, Jeannine Roy, Alexandra Wegmann, Patrick T. RohnerAbstract:Coprophagous insect communities play a critical role in the decomposition of vertebrate Dung and provide ecosystem functions fundamental to modern agriculture. While the ecology of Dung beetles is rather well understood, niche differentiation in coprophagous Flies is poorly studied. Sepsid Flies (Diptera: Sepsidae) are a vital part of the European community of coprophages, with 6-7 widespread species of Sepsis often found co-occurring in the same pasture. To advance our ecological understanding of the mechanisms that enable species to coexist, we investigated the oviposition preferences and larval performance of 7 common species of Sepsis in the Dung of different large domestic and wild mammals. Substrate preferences and subsequent performance of larvae in laboratory experiments did not vary greatly. All species did very well on cow Dung, the most common substrate in Central Europe, but also on Dung of horse and wild boar. In contrast, Flies did not prefer or grow well in Dung of red and roe deer, two of the most common wild vertebrates. Thus there were only minor differences among the species tested along the specialist-generalist (Dung) gradient, indicating that differences in the choice of oviposition sites by the adults of the different fly species and larval performance do not constitute a major axis of ecological differentiation. Nevertheless, there was a positive correlation between substrate choice and larval performance indicating the preference of gravid females for particular oviposition sites is adaptive. We conclude that sepsids are common in Europe because they are well adapted to the Dung of herbivorous livestock rather than wild animals. Nevertheless, specialization on particular types of Dung does not define the niche of Sepsis Dung Flies and hence plays a minor role in mediating their species diversity.
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Geographic clines in wing morphology relate to colonization history in New World but not Old World populations of yellow Dung Flies.
Evolution, 2018Co-Authors: Martin A Schafer, David Berger, Stephanie S. Bauerfeind, Charles W. Fox, Patrick T. Rohner, Anders Kjærsgaard, Frédéric Guillaume, Wolf U BlanckenhornAbstract:Geographic clines offer insights about putative targets and agents of natural selection as well as tempo and mode of adaptation. However, demographic processes can lead to clines that are indistinguishable from adaptive divergence. Using the widespread yellow Dung fly Scathophaga stercoraria (Diptera: Scathophagidae), we examine quantitative genetic differentiation (QST ) of wing shape across North America, Europe, and Japan, and compare this differentiation with that of ten microsatellites (FST ). Morphometric analyses of 28 populations reared at three temperatures revealed significant thermal plasticity, sexual dimorphism, and geographic differentiation in wing shape. In North America morphological differentiation followed the decline in microsatellite variability along the presumed route of recent colonization from the southeast to the northwest. Across Europe, where S. stercoraria presumably existed for much longer time and where no molecular pattern of isolation by distance was evident, clinal variation was less pronounced despite significant morphological differentiation (QST >FST ). Shape vector comparisons further indicate that thermal plasticity (hot-to-cold) does not mirror patterns of latitudinal divergence (south-to-north), as might have been expected under a scenario with temperature as the major agent of selection. Our findings illustrate the importance of detailed phylogeographic information when interpreting geographic clines of dispersal traits in an adaptive evolutionary framework.
D J Hosken - One of the best experts on this subject based on the ideXlab platform.
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Response to selection and realized heritability of sperm length in the yellow Dung fly (Scathophaga stercoraria)
Heredity, 2010Co-Authors: R Dobler, D J HoskenAbstract:Sperm length shows considerable phenotypic variation both inter- and intra-specifically, but a general explanation for this variation is lacking. In addition, our understanding of the genetic variation underlying sperm length variation is also limited because there have been few studies on the genetics of sperm size. One factor that could explain the variation in sperm length is that length influences sperm competitiveness, and there is some evidence for this. However, in yellow Dung Flies ( Scathophaga stercoraria ), microevolutionary responses to experimental variation at levels of sperm competition indicate that sperm length does not influence sperm competitiveness, although this lack of response may simply indicate sperm length lacks evolutionary potential (that is, it is constrained in some way), in spite of evidence that sperm length is heritable. Here we report on a laboratory study, in which we artificially selected upwards and downwards on sperm length in S. stercoraria . We found that sperm length significantly diverged after four generations of selection, but the response to selection was asymmetrical: upward selection generated a rapid response, but downward did not. We estimated the realized heritability of sperm length to be approximately 50%, which is consistent with previous sire–son estimates. We also assessed the fertility of males from upward and downward lines and found they did not differ. Results are discussed in the context of sperm competition.
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Copula in yellow Dung Flies (Scathophaga stercoraria): investigating sperm competition models by histological observation.
Journal of Insect Physiology, 2000Co-Authors: D J Hosken, Paul I. WardAbstract:While sperm competition has been extensively studied, the mechanisms involved are typically not well understood. Nevertheless, awareness of sperm competition mechanisms is currently recognised as being of fundamental importance for an understanding of many behavioural strategies. In the yellow Dung fly, a model system for studies of sperm competition, second male sperm precedence appears to result from a combination of sperm displacement and sperm mixing. Displacement was until recently thought to be directly from the female's sperm stores, the spermathecae (i.e. males were thought to ejaculate directly into these stores), and under male control. However, recent work indicates displacement is indirect (i.e. males do not ejaculate directly into the sperm stores) and that it is female-aided, although the evidence was not based on direct observation. Here, we used histological techniques to directly determine interactions during copula and sperm transfer. Our results are consistent with inference and clearly show that males ejaculate into the bursa copulatrix. Our data are also consistent with active female involvement in sperm displacement, which is indirect, and indicate the aedeagus may remove some spermatozoa from the bursa at the end of copula. In addition, evidence suggests females aid sperm transport to and from the spermathecae, possibly by muscular movement of a spermathecal invagination.
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Internal female reproductive anatomy and genital interactions during copula in the yellow Dung fly, Scathophaga stercoraria (Diptera: Scathophagidae)
Canadian Journal of Zoology, 1999Co-Authors: D J Hosken, E P Meyer, P I WardAbstract:Insect genitalia have been extensively studied for taxonomic purposes, but functional anatomy has rarely been examined. We report here on the detailed internal anatomy of the reproductive tract of female yellow Dung Flies (Scathophaga stercoraria) and the mechanics of copula and sperm transfer. Female Dung Flies have paired accessory glands, three spermathecae (one singlet and one doublet), each with its own narrow duct, a large muscular bursa copulatrix, which is met by the common oviduct dorso-anteriorly, and paired lateral oviducts and ovaries. The bursa is lined internally with a thick cuticle. During copula and while ejaculating, the male aligns the gonopore with the spermathecal duct entrances to the bursa and pinches the female's abdomen at approximately this point. Sperm packing in the spermathecae appears quite orderly, and structurally the sperm appear typical of many insects. Aedeagus withdrawal appears to remove some bursal sperm. The results are discussed in relation to other Diptera.
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Female accessory reproductive gland activity in the yellow Dung fly Scathophaga stercoraria (L.).
Journal of Insect Physiology, 1999Co-Authors: D J Hosken, Paul I. WardAbstract:The role of the female accessory reproductive glands has been investigated in relatively few insects. Gland secretion has a number of potential functions, including lubrication during copula, involvement in fertilization and protection of eggs. Female yellow Dung Flies (Scathophaga stercoraria) have large paired accessory glands whose function(s) prior to this study were unknown. Our study indicated glands were involved in copulation and egg laying. The volume of secretion remaining in glands was negatively associated with copulation duration, and this effect was most pronounced in non-ovipositing females. Gland volume and secretion volume remaining in the glands were significantly smaller in females which were allowed to oviposit. In addition, there was a significant interaction between male size, female size and whether or not females were allowed to oviposit which affected the volume of the secretion remaining in the glands, with changes in secretion volume being greatest when males were large. Sperm were found in the accessory glands of some females and this was apparently not related to age, mating history of either sex, to female nutrition or male size. Our results indicate that either large males stimulate greater secretory responses from females or that females alter their responses based on male size.
