Mating Competitiveness Of Males Research Articles

The silver cyprinid <i> Rastrineobola argentea</i> as the main diet source for rearing <i>Anopheles arabiensis</i> mosquitoes

Background & objectives: All organisms that are cultured for laboratory bioassays need food for sustenance and amplification of the colony to such numbers that would not compromise the progress of the research at hand. For effective turnover rate in the population generation, the diet should be such that it is readily available and provide adequate nutrients to the organisms. The aim of this study was to test and evaluate the efficacy of Rastrineobola argentea as a diet source for rearing Anopheles arabiensis Patton mosquitoes for research. Methods: Crushed fish, Rastrineobola argentea and two other commercial larval feeds (Tetramin  Baby fish food and baker's yeast) were compared for their efficacy as diet sources for feeding Anopheles arabiensis mosquito larvae. The effects of these diet types were determined against fecundity, size, longevity and male mating competitiveness.

Sugar administration to newly emerged Aedes albopictus males increases their survival probability and mating performance

Aedes albopictus male survival in laboratory cages is no more than 4–5 days when kept without any access to sugar indicating their need to feed on a sugar source soon after emergence. We therefore developed a device to administer energetic substances to newly emerged males when released as pupae as part of a sterile insect technique (SIT) programme, made with a polyurethane sponge 4cm thick and perforated with holes 2cm in diameter. The sponge was imbibed with the required sugar solution and due to its high retention capacity the sugar solution was available for males to feed for at least 48h. When evaluated in lab cages, comparing adults emerged from the device with sugar solution vs the device with water only (as negative control), about half of the males tested positive for fructose using the Van Handel anthrone test, compared to none of males in the control cage. We then tested the tool in semi-field and in field conditions with different sugar concentrations (10%, 15%, and 20%) and compared results to the controls fed with water only. Males were recaptured by a battery operated manual aspirator at 24 and 48h after pupae release. Rather high share 10–25% of captured males tested positive for fructose in recollections in the vicinity of the control stations, while in the vicinity of the sugar stations around 40–55% of males were positive, though variability between replicates was large. The sugar positive males in the control test may have been released males that had access to natural sugar sources found close to the release station and/or wild males present in the environment. Only a slight increase in the proportion of positive males was obtained by increasing the sugar concentration in the feeding device from 10% to 20%. Surprisingly, modification of the device to add a black plastic inverted funnel above the container reduced rather than increased the proportion of fructose positive males collected around the station. No evidence of difference in the capacity of sterile (irradiated with 30Gy) males to take a sugar meal relative to fertile males was observed in field comparison. A clear effect of temperature and relative humidity (RH) on the rate of sugar positive males was observed, with an increase of temperature and a decrease in RH strongly increasing the % of sugar positive males. In large enclosures we tested the effect of our sugar supplying tool on the mating competitiveness of sterile vs fertile males, which produced an evident favorable effect both on sterile and fertile males.

Evolution of sexual size dimorphism and its relationship with sex ratio in carabid beetles of Genus Ceroglossus Solier

Abstract Although the degree of mate competition, given extreme differences in sex ratio, explains much of the pattern of male-biased size dimorphism among diverse taxa, it fails for some species which have potential for intense male competition for mates and yet exhibit little or no sexual size dimorphism (SSD). This fact suggest that species with low SSD should be express the effect of evolutionary pressure in non-obvious geometrical shape promoted by sex ratio in an evolutionary time scale. To evaluate this hypothesis we used phylogenetic comparative method in a Bayesian framework to investigate the evolution of SSD and the role of sex ratio at inter-specific level in the species of Ceroglossus (Coleoptera: Carabidae). In our results the proportion farthest from 1:1 is associated with more disparate body shape, even though the entire group has minimum variation in sex ratio, which is an intrinsic life history character of this group considering its phylogenetic conservatism or phylogenetic signal. We suggest that the sex ratio has determined the dimorphism degree during evolution of this group, since both traits have increased or decreased together during the species divergence (i.e. positive phylogenetic correlation: r2≈0.85). We suggest that morphological studies of SSD will benefit from using comparative method with Bayesian approaches to assess the effect of phylogenetic history and its uncertainty. Finally, this will be allow to researchers to quantify the uncertainty of specific evolutionary hypotheses accounting for observed sexual dimorphism patterns.

The size‐number trade‐off and components of fitness in clonal parasitoid broods

AbstractBody size can strongly influence the components of fitness. We investigated the role of body mass in the reproductive success of the parasitoid Copidosoma bakeri (Howard) (Hymenoptera: Encyrtidae). Copidosoma bakeri develops polyembryonically, producing thousands of genetically identical individuals from one egg. In this species, the brood size and body mass of clonal individuals developing within a host are in a trade‐off relationship, which flexibly responds to the environment while maintaining female‐biased sexual size dimorphism. We addressed the following questions regarding several possible effects of body mass on male and female reproductive success. (1) Is longevity positively related to body size in both sexes? (2) Is potential fecundity positively related to female body size? (3) Is mating competitiveness positively correlated with male body size? We found that body size increased with longevity of females, but not of males. Copidosoma bakeri was weakly synovigenic; a few eggs were produced after female maturation. Also, egg volume increased with age of the females. We did not detect a relationship between body size and potential fecundity, but mated females produced more eggs than unmated females. Thus, larger females may increase their opportunities to mate, find hosts, and oviposit primarily by living longer. Male mating competitiveness was not related to body mass. Mating reduced male longevity, suggesting a cost of mating that was independent of body mass. Differences between males and females in the effects of body mass on longevity suggest sex‐specific selection pressures on body mass that may explain female‐biased sexual size dimorphism.

The relevance of age and nutritional status on the mating competitiveness of medfly males (Diptera: Teprhitidae)

Results of previous investigations trying to ascertain which physiological factors are more important to the mating success of medfly males are controversial. In part, this controversy owes to the fact that each factor was evaluated by an independent study using different experimental designs and populations. In the present study we compare the roles of age and nutritional status (immature and adult phases) on the mating competitiveness of Ceratitis capitata (Wiedemann, 1824) males. Three parameters were used to evaluate the male mating success: calling behavior (pheromone emission), lek participation and copulation (ability to be chosen by a female). Females gave preference to the males that were given a high protein diet in the larval phase. By contrast, females did not give preference to males that had been well-nourished in the adult phase only. The other parameters evaluated followed the same pattern: young males and males that had been fed a high protein diet during their immature phase had a greater participation in leks and called more often than older males and males that had been fed a diet poor in protein during their larval phase. Therefore, we conclude that the mating success of C. capitata males is determined both by age and nourishment during the immature stage.

Male–male contests for mates, sexual size dimorphism, and sex ratio in a natural population of a solitary parasitoid

Understanding how different behavioural and life history traits interact is fundamental to developing ethological theory. Here we study the interaction of male–male competition for mates and sexual size dimorphism in a solitary wasp, with implications for sex allocation. In Hymenoptera, females are normally larger than males suggesting that males do not benefit as much as females from larger size. However, in our focal species, a solitary Eurytoma wasp, males compete for mates by pairwise contests at female emergence sites, suggesting that male size may strongly affect fitness. In contests observed in the field, larger males were more likely to win fights, and males fighting at female emergence sites were much larger than average males. Males showed higher variance in body size than females, such that all the smallest individuals were males, a majority of medium-to-large individuals were female, but the majority of largest individuals were male. Our data suggest that sexual size dimorphism in this species has been affected by intra-sexual selection for male size, which may have implications for sex allocation.

Wolbachia-Host Interactions: Host Mating Patterns Affect Wolbachia Density Dynamics.

Wolbachia are maternally inherited intracellular bacteria that infect a wide range of arthropods and cause an array of effects on host reproduction, fitness and mating behavior. Although our understanding of the Wolbachia-associated effects on hosts is rapidly expanding, our knowledge of the host factors that mediate Wolbachia dynamics is rudimentary. Here, we explore the interactions between Wolbachia and its host, the two-spotted spider mite Tetranychus urticae Koch. Our results indicate that Wolbachia induces strong cytoplasmic incompatibility (CI), increases host fecundity, but has no effects on the longevity of females and the mating competitiveness of males in T. urticae. Most importantly, host mating pattern was found to affect Wolbachia density dynamics during host aging. Mating of an uninfected mite of either sex with an infected mite attenuates the Wolbachia density in the infected mite. According to the results of Wolbachia localization, this finding may be associated with the tropism of Wolbachia for the reproductive tissue in adult spider mites. Our findings describe a new interaction between Wolbachia and their hosts.

Chilling and flight ability and mating competitiveness of sterile males of the Mediterranean fruit fly

AbstractThe Sterile Insect Technique (SIT) is widely used to suppress or eradicate infestations of the Mediterranean fruit fly, Ceratitis capitata (Wied.). In large‐scale programs, sterile males are chilled (4°C) to allow their transfer and storage in the aircraft used for the releases. Sterile males may remain chilled for as long as 3 h prior to release. Here, we describe the results of experiments that assessed the effect of chilling on flight ability and mating competitiveness of sterile male Mediterranean fruit flies held under conditions of low (plastic buckets) or high (emergence tower trays) density. Males from both densities were subject to 0 (no chill), 1, or 3 h of chilling at 3 days of age. Chill treatment had no effect on flight ability for males held at low density. However, for males held at high density, chilling for 1 or 3 h significantly reduced flight ability below that observed for the no chill treatment. Consistent with the flight data, chill treatment had no effect on the mating success of males held at low density. However, among males held at high density, 3 h of chilling significantly reduced mating success below levels observed for unchilled males or males chilled for 1 h only in trials conducted 1 day after the cold treatment. An auxiliary experiment revealed that this reduction in mating performance was temporary: in mating trials conducted 3 days after 3 h of chilling, sterile males derived from tower trays had similar mating success as unchilled males. Implications of these findings for Mediterranean fruit fly SIT are discussed.

A Wolbachia wMel Transinfection in Aedes albopictus Is Not Detrimental to Host Fitness and Inhibits Chikungunya Virus

Background Wolbachia inherited intracellular bacteria can manipulate the reproduction of their insect hosts through cytoplasmic incompatibility (CI), and certain strains have also been shown to inhibit the replication or dissemination of viruses. Wolbachia strains also vary in their relative fitness effects on their hosts and this is a particularly important consideration with respect to the potential of newly created transinfections for use in disease control.Methodology/Principal FindingsIn Aedes albopictus mosquitoes transinfected with the wMel strain from Drosophila melanogaster, which we previously reported to be unable to transmit dengue in lab challenges, no significant detrimental effects were observed on egg hatch rate, fecundity, adult longevity or male mating competitiveness. All these parameters influence the population dynamics of Wolbachia, and the data presented are favourable with respect to the aim of taking wMel to high population frequency. Challenge with the chikungunya (CHIKV) virus, for which Ae. albopictus is an important vector, was conducted and the presence of wMel abolished CHIKV dissemination to the saliva.Conclusions/significanceTaken together, these data suggest that introducing wMel into natural Ae. albopictus populations using bidirectional CI could be an efficient strategy for preventing or reducing the transmission of arboviruses by this species.

Male mating competitiveness and age-dependent relationship between testosterone and social rank in bighorn sheep

In males, the acquisition and development of behavioral and morphological secondary sexual traits typically depends on testosterone and correlates with mating success. Testosterone level could affect competition for mates and thus be a target of sexual selection. We sought to relate testosterone levels to male mating competitiveness, by teasing apart the relationships between testosterone, behavior, and growth before the mating period. We monitored 24 adult bighorn rams (Ovis canadensis) at Ram Mountain, Alberta, from 2008 to 2011. Using linear mixed models, we tested the relationships between testosterone metabolites in feces, social rank, and both growth and size of two sexually selected traits: horns and body mass. The correlation between testosterone and social rank varied with age. Testosterone and rank were weakly and negatively correlated for young rams, positively correlated for prime-aged rams, and negatively correlated for older rams. Although testosterone had an increasingly positive effect on total horn length until 8 years of age, we could not detect any effects on annual growth rate of horns or body mass. Testosterone may be related to male’s ability to compete for mates through its relationship with behaviors determining social rank, rather than by influencing the development of morphological traits. Differences in testosterone levels among competitors may be a proximate cause of variance in fitness.

Different ontogenetic patterns of testosterone production reflect divergent male reproductive strategies in chimpanzees and bonobos

Male reproductive effort is often strongly related to levels of the steroid hormone testosterone. However, little research has examined whether levels of testosterone throughout development might be tied to individual or species differences in the reproductive strategies pursued by adult males. Here, we tested the hypothesis that inter-specific differences in male reproductive strategy are associated with differences in the pattern of testosterone production throughout early life and puberty. We compared testosterone levels from infancy to adulthood in two closely related species where levels of mating competition and male–male aggression differ significantly, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes). We predicted that the reduction in male mating competition found in bonobos would be accompanied by a lesser developmental increase in testosterone production. We performed radioimmunoassay of salivary testosterone levels in a mixed-longitudinal sample of both species, collected from individuals living in semi free-ranging populations. This allowed us to examine the effects of development in a more naturalistic setting than possible in a zoo or laboratory. We found that among chimpanzees, testosterone levels declined slightly from infancy to juvenility, then remained low until increasing markedly during adolescence (with pubertal increases most pronounced among males). In contrast, there was little change in testosterone production with age in bonobos of either sex, with levels of testosterone consistent throughout infancy, juvenility, and the transition to adulthood. Our data are therefore consistent with the hypothesis that the ontogenetic pattern of testosterone production can be subject to rapid evolutionary change, shifting in association with species differences in male reproductive strategy.

Effects of Age and Size on <I>Anopheles gambiae</I> s.s. Male Mosquito Mating Success

Before the release of genetically-modified or sterile male mosquitoes in an attempt to control local populations of malaria vectors, it is crucial to determine male traits involved in mating success. The effects of male size and age as determinants of male mating success in Anopheles gambiae s.s. were measured in the field and under laboratory conditions in Burkina Faso. First, the body sizes (estimated by wing length) of mating, swarming, and indoor-resting male mosquitoes were compared over a 3-yr period (2006-2009) from July to October in Soumousso and Vallée du Kou, two villages in western Burkina Faso. Second, the age structure of swarming and resting male mosquitoes were characterized based on the number of spermatocysts and the proportion of sperm in the reservoir of wild-caught male testis. Third, male age effects on the insemination rate of female An. gambiae were investigated in the laboratory. The mean size of males collected in copula was significantly larger than the mean for swarming males and indoor-resting males. The optimum male age for successful insemination of females was 4-8 d. These results suggest that male size is an important trait in determining male mating competitiveness in the field. Although age was not found to be a significant factor in mating competitiveness, it was significantly correlated with swarming behaviors in the field and insemination success in the laboratory. The implications of these results in terms of sexual selection in An. gambiae and vector control programs are further discussed.

Precocious sexual signalling and mating in Anastrepha fraterculus (Diptera: Tephritidae) sterile males achieved through juvenile hormone treatment and protein supplements

Sexual maturation of Anastrepha fraterculus is a long process. Methoprene (a mimic of juvenile hormone) considerably reduces the time for sexual maturation in males. However, in other Anastrepha species, this effect depends on protein intake at the adult stage. Here, we evaluated the mating competitiveness of sterile laboratory males and females that were treated with methoprene (either the pupal or adult stage) and were kept under different regimes of adult food, which varied in the protein source and the sugar:protein ratio. Experiments were carried out under semi-natural conditions, where laboratory flies competed over copulations with sexually mature wild flies. Sterile, methoprene-treated males that reached sexual maturity earlier (six days old), displayed the same lekking behaviour, attractiveness to females and mating competitiveness as mature wild males. This effect depended on protein intake. Diets containing sugar and hydrolyzed yeast allowed sterile males to compete with wild males (even at a low concentration of protein), while brewer´s yeast failed to do so even at a higher concentration. Sugar only fed males were unable to achieve significant numbers of copulations. Methoprene did not increase the readiness to mate of six-day-old sterile females. Long pre-copulatory periods create an additional cost to the management of fruit fly pests through the sterile insect technique (SIT). Our findings suggest that methoprene treatment will increase SIT effectiveness against A. fraterculus when coupled with a diet fortified with protein. Additionally, methoprene acts as a physiological sexing method, allowing the release of mature males and immature females and hence increasing SIT efficiency.

Measuring mating competition correctly: available evidence supports operational sex ratio theory

AbstractCentral to sexual selection theory is the question of when individuals should compete for mates. Theory predicts that the sex ratio of ready-to-mate individuals (operational sex ratio; OSR) affects male and female mating competition. In accordance with this, the strength of mating competition, measured by agonistic behaviors and courtship displays, has been found to co-vary with the OSR in field populations of several species. However, laboratory experiments have often produced results that seemingly contradict OSR theory, especially for courtship behavior. We argue that this may be because experiments typically measure frequencies of competitive behaviors. Frequencies of courtship and agonistic behavior are not only affected by the level of mating competition, but also by the number of potential mates or competitors encountered. In contrast, the propensity to behave competitively at a given encounter represents a behavioral response, and thus directly reflects mating competition. We show in 2 simple models that 1) courtship frequency can be expected to respond differently from courtship propensity to changes in OSR and 2) an increase in frequency of agonistic behaviors could occur even if the propensity is not affected by the OSR. In a meta-analysis of studies on courtship competition, we show that frequency measures produced largely opposite results to propensity measures, as predicted by our model. Moreover, courtship propensity increased when the OSR became more biased toward competitors. This presents strong evidence that the OSR affects competition, in the form of courtship, as predicted by OSR theory.

Improving sterile male performance in support of programmes integrating the sterile insect technique against fruit flies

Abstract The sterile insect technique (SIT) is being applied against fruit fly pests in many areas of the world. Currently, factories have a capacity to produce several billion sterile insects per week, to irradiate them and to make them available for shipment to their destinations. There the emerging flies are fed and maintained for various periods of time in fly emergence and release facilities, and then collected for release. While much research effort has been invested in improving mass rearing and quality control procedures at the fly factory level, the post‐factory handling of sterile flies has received much less attention. A 6‐year FAO/IAEA Coordinated Research Project (CRP) was initiated with the participation of 31 research institutes from 17 countries to assess and validate ways to improve sterile male performance through better management during the critical period that starts with the arrival of pupae at the fly emergence and release facility and ends with the release of the sterile flies in the field. This review summarizes the research that was conducted under the CRP focusing on fruit fly species from the genera Anastrepha, Bactrocera and Ceratitis against which the SIT is being applied. To increase the effectiveness of SIT programmes, exposure of sterile males to nutritional, hormonal and semiochemical supplements was assessed and improved handling and release methods tested. Incorporation of protein and juvenile hormone into pre‐release diets significantly accelerated sterile male maturation and improved sexual performance among several species, while semiochemical treatments using ginger root oil or citrus oils in Ceratitis capitata and methyl eugenol in Bactrocera dorsalis complex species significantly increased sterile male mating competitiveness. Improved fly emergence, holding and release procedures were also assessed, together with the compilation of all this knowledge into a manual. Several of these findings have been transferred to and are being applied in operational programmes.

The effect of methyl eugenol exposure on subsequent mating performance of sterile males of Bactrocera dorsalis

AbstractMethyl eugenol (ME) is ingested and used by several fruit fly species of the genus Bactrocera as a precursor of the sexual pheromone produced by adult males. This can result in an increase in male sexual activity and performance, which is important to the development of an effective sterile insect technique programme in China. The effect of ME on mating competitiveness, multiple mating, and the incidence of female remating were studied in sterile males from a genetic sexing strain of Bactrocera dorsalis (Hendel) irradiated with 100 Gy of 137Cs. The results obtained in field cages showed that feeding on ME did not increase the frequency of multiple mating by sterile males, but significantly increased the mating competitiveness of sterile males against that of semi‐wild males. At the same time, sterile males fed ME did not significantly affect the remating of semi‐wild females 5 days after the initial mating with a semi‐wild male, but the ME‐fed males increased the remating frequency of females 10 and 15 days after the initial mating.

By any name, female-female competition yields differential mating success.

By any name, female-female competition yields differential mating success.

Male dispersal in a provisioned multilevel group ofRhinopithecus roxellanain Shennongjia Nature Reserve, China

Most Old World monkeys show male-biased dispersal. We present the first systematic data on male dispersal in a provisioned multilevel group of Rhinopithecus roxellana, based on 4.5 years of field observations in Shennongjia National Nature Reserve, China. We evaluated both ultimate (inbreeding avoidance and male mating competition) and proximate (food availability and predation risk) factors influencing male dispersal. The focal group contained 34-53 individuals, in 3-4 one-male units (OMUs) and 1 all-male unit (AMU). We observed 37 dispersal events involving 10 of 11 adults, 7 of 8 subadults, and 7 of 15 juveniles. Most interunit transfers within the focal group occurred around the months of mating season. Adult males competed for the leader positions of OMUs mainly through aggressive takeovers, and young males transferred from the OMUs to the AMU at the median age of 41 months, forced out by leader males. No young males older than 4 years remained in natal or non-natal OMUs. The male mating competition hypothesis was supported. The young males emigrated voluntarily from the focal group at the average age of 58.6 months, and no young emigrating male was observed to return, suggesting inbreeding avoidance also played a role in the dispersal of young males. Most emigration/immigration events were parallel dispersal and occurred during intergroup encounters, suggesting increased predation risk during the dispersal period. Males were more likely to emigrate/immigrate during the months when preferred foods were most available. We compared the dispersal patterns in R. roxellana with those in gelada baboons and hamadryas baboons, both living in multilevel societies. Similar to R. roxellana, young male geladas disperse at puberty, but they may return and breed in their natal groups. Males in hamadryas also disperse, but much less commonly than in R. roxellana. Provisioning may have influenced results, and confirming studies on unprovisioned groups would be valuable.

Dual reproductive cost of aging in male medflies: Dramatic decrease in mating competitiveness and gradual reduction in mating performance

Although age-based effects on the reproductive success of males have been reported in several animal taxa the cost of aging on male mating success in lekking species has not been fully explored. We used the Mediterranean fruit fly, a lekking species, to investigate possible cost of aging on male reproductive success. We performed no choice and choice mating tests to test the hypothesis that aging does not affect the mating performance (mating success in conditions lacking competition) or the mating competitiveness (mating success against younger rivals) of males. The mating probability of older males decreased significantly when competing with younger males. Aging gradually reduced the mating performance of males but older males were still accepted as mating partners in conditions lacking competition. Therefore, older males are capable of performing the complete repertoire of sexual performance but fail to be chosen by females in the presence of young rivals. Older males achieved shorter copulations than younger ones, and female readiness to mate was negatively affected by male age. Older and younger males transferred similar amount of spermatozoids to female spermathecae. Females stored spermatozoids asymmetrically in the two spermathecae regardless the age of their mating partner. Aging positively affected the amount of spermatozoids in testes of both mated and nonmated males. No significant differences were observed on the amount of spermatozoids between mated and nonmated males.

Understanding Sex Differences in Human Mortality Rates Through Tinbergen’s Four Questions

Sex differences in human mortality rates emerge from a complex interaction of genetic heritage and developmental environment. Although mortality is not in itself a behavior, it is an indirect product of behavior and physiology and thus responsive to life history variation in resource allocation, behavioral tendencies, and relevant environmental conditions. The explanatory framework of Tinbergenʹs Four Questions is sufficiently powerful in generalization to promote understanding of this phenomenon. Excess male mortality is a result of a trade‐off between competitiveness and longevity. Male life history gives greater emphasis to reproductive effort at the expense of somatic effort, and mating effort at the expense of longevity compared to female life history. Men exhibit riskier behavioral patterns and greater physiological susceptibility, dying at higher rates from behavioral and most non‐behavioral causes across the lifespan. The magnitude of the sex difference in mortality in developed nations peaks when males sexually mature and enter into mating competition. Social and environmental conditions intensifying male competition for resources, status, and mates lead to increased male mortality.