Unmated Males Research Articles

Is sexual ornamentation an honest signal of male quality in the Chinese grouse (Tetrastes sewerzowi)?

We examined the variation in sexual ornamentation of male Chinese grouse (Tetrastes sewerzowi) in the Gansu Province, China, seeking to identify factors involved in whether ornament size and brightness are honest signals of male quality. Compared to unmated males, mated males had significantly larger and redder combs and, although they did not have significantly larger territories, they defended them more vigorously. Mated males had significantly higher blood carotenoid and testosterone levels, significantly better body condition, and significantly lower parasite loads than unmated males. Our findings are thus consistent with the hypothesis that comb size and color are honest signals of better male quality in the grouse, mediated through lower parasite loads and/or higher testosterone levels.

Relationship between male age, accessory gland, sperm transferred, and fitness traits in Drosophila bipectinata.

The number of cells and the size of the cells in the male accessory gland, the quantity of accessory gland proteins, and their effects on fitness in males of different ages were studied in Drosophila bipectinata Duda (Diptera: Drosophilidae). Male age was significantly positively correlated with the size of accessory gland, the number of main cells of the accessory gland, the quantity of protein in unmated males, the duration of copulation, the transferred quantity of protein and sperm to the mated female, fecundity, and fertility, while male age was significantly negatively correlated with the size of main cell in the accessory gland and the quantity of protein in mated males. The size of the main cells was significantly positively correlated with the quantity of protein in unmated males but significantly negatively correlated with the size of the accessory gland and the number of main cells in the accessory gland. These results suggest that D. bipectinata young males, with their smaller size of their accessory glands and having fewer and larger main cells in their accessory glands, produced the least quantity of protein and transferred significantly less protein and sperm to the mated female than did middle and old age males. Thus, this study suggests that in D. bipectinata, male age affects the number of accessory gland cells and the quantity of protein in the accessory gland. The size and number of main cells in the accessory gland and the size of the accessory gland were related to the production of protein. Females who mated with old males obtained a fitness benefit.

Flight responses of Sitotroga cerealella (Lepidoptera: Gelechiidae) to corn kernel volatiles in a wind tunnel

The flight behavioral responses of males and females of Sitotroga cerealella (Lepidoptera: Gelechiidae) to corn kernel volatiles, in a wind tunnel, and the determination and identification of the active compounds of corn kernel volatiles were investigated. A wind tunnel bioassay was carried out to test the response of males and females to 15, 30, 60, and 120 g equivalents of corn kernel volatiles. Gas chromatography-electroantennography was used to determine which components in corn kernel volatiles elicited an EAD response using male and female antennae. Gas chromatography-mass spectrometry technique was used to identify the active compounds of corn kernel volatiles. A 60-g equivalent of corn kernel volatiles elicited attractant behavior of unmated males to landing near the source. Mated males and virgin females were not attracted to corn kernel volatiles. The number of mated females landing was significantly higher in 60- and 120-g equivalents of corn kernel volatiles, compared to the other concentrations and the control. The antennae of males and females responded to four active compounds of corn kernel volatiles. Three of these compounds were identified, namely nonanal, decanal, and geranyl acetone. It is suggested that host finding and selection by S. cerealella is associated with its host volatiles.

Role of nutritional reserves and body size in Anopheles gambiae males mating success

A better knowledge of the different parameters that account for male mating success in the wild is critical to the development of genetic control strategies. In this study, we measured energy budgets (total sugar and glycogen) as the daily energetic investment in swarming males of An. gambiae s.s. M and S molecular forms from two different field locations, VK7 and Soumousso. We also looked at the difference between energetic reserves in mated males compared to unmated ones, and assessed wing length in both molecular forms to explore whether this phenotypic trait was involved in swarming behavior or mating success. The current study showed that the energetic cost of 25min of swarming was around 50% of the male's sugar (M form: 48.5%, S form: 56.2%) and glycogen (M form: 53.1%, S form: 59%) reserves. However, no difference in carbohydrate content was observed between mated and unmated males. Mated males were found to be bigger than unmated ones, while intermediate size of males is advantageous in mating system, both in M and S molecular forms and when collected in two different locations. Regardless of the collection location, no difference in wing size was observed in swarming males collected early or late during a particular swarm. The results are discussed in the context sexual selection in different ecological locations.

Standard metabolic rate of the bed bug, Cimex lectularius: Effects of temperature, mass, and life stage

Metabolic rates provide important information about the biology of organisms. For ectothermic species such as insects, factors such as temperature and mass heavily influence metabolism, but these effects differ considerably between species. In this study we examined the standard metabolic rate of the bed bug, Cimex lectularius L. We used closed system respirometry and measured both O2 consumption and CO2 production across a range of temperatures (10, 20, 25, 30, 35°C) and life stages, while also accounting for activity. Temperature had a stronger effect on the mass specific V̇O2 (mlg−1h−1) of mated males (Q10=3.29), mated females (Q10=3.19), unmated males (Q10=3.09), and nymphs that hatched (first instars, Q10=3.05) than on unmated females (Q10=2.77) and nymphs that molted (second through fifth instars, Q10=2.78). First instars had significantly lower respiratory quotients (RQ) than all other life stages. RQ of all stages was not affected by temperature. V̇O2 (mlh−1) scaled more with mass than values previously reported for other arthropods or that would be predicted by the 3/4-power law. The results are used to understand the biology and ecology of the bed bug.

Female mate choice by chemical signals in a semi-terrestrial crab

Information about the roles of both sexes in pair formation is required to better understand the mechanisms involved in sexual selection. Mate choice could depend on the courtship behavior, involving chemical, tactile and visual signals. We determined if Neohelice granulata mate choice is based on female or male choice, considering visual and chemical with contact and without contact signals between partners and different categories of individuals: receptive and unreceptive females; and large, small, mated or unmated males. Experiments showed that mate selection was based on receptive female's choice using chemical signals, but not visual ones. Since copulation occurs during high and low tides, water-borne chemical signals would be preferentially used during high tide, while contact ones during low tide. Females preferred large and unmated males, while males did not seem to recognize receptive females using chemical neither visual signals. Females were capable of detecting the presence of the chemical signals released by large and unmated males, but not its amount. It is proposed that small and mated males are probably releasing different types of chemical signals, not attractive to females, or that they are not emitting any signal.

Age specific mating incidence and reproductive behavior of the ladybird beetle, Anegleis cardoni (Weise) (Coleoptera: Coccinellidae)

Age specific mating incidence, mating behavior, mate recognition cues and effect of sexual status on mating of ladybird beetle, Anegleis cardoni (Weise) (Coleoptera: Coccinellidae) were studied in detail. The mating duration was very short (14.40±0.72min) in comparison to other ladybirds. Courtship was male dominated and was displayed in steps, viz. approach, watch, examine, sharp turns, mount, attempt and mate. Sharp turns is an additional behavior observed during courtship in this ladybird, and is characterized by sharp turning movements towards the mate, and is undertaken by both males and females. Active mating of A. cardoni involved multiple strokes of the aedeagus. Mating duration and the number of strokes were higher in unmated males than in mated ones. Results reveal that physical cues probably play a role in the initiation of courtship, while chemical signals are probably involved in the continuation of courtship, culminating in intromission. The removal of male antennae and obscurity of elytral patterns significantly decreased mating success, whereas female antennal ablation and obscuring of the pronotum did not affect mate recognition.

Premating isolation is determined by larval rearing substrates in cactophilic Drosophila mojavensis. IX. Host plant and population specific epicuticular hydrocarbon expression influences mate choice and sexual selection

Sexual signals in cactophilic Drosophila mojavensis include cuticular hydrocarbons (CHCs), contact pheromones that mediate female discrimination of males during courtship. CHCs, along with male courtship songs, cause premating isolation between diverged populations, and are influenced by genotype × environment interactions caused by different host cacti. CHC profiles of mated and unmated adult flies from a Baja California and a mainland Mexico population of D. mojavensis reared on two host cacti were assayed to test the hypothesis that male CHCs mediate within-population female discrimination of males. In multiple choice courtship trials, mated and unmated males differed in CHC profiles, indicating that females prefer males with particular blends of CHCs. Mated and unmated females significantly differed in CHC profiles as well. Adults in the choice trials had CHC profiles that were significantly different from those in pair-mated adults from no-choice trials revealing an influence of sexual selection. Females preferred different male CHC blends in each population, but the influence of host cactus on CHC variation was significant only in the mainland population indicating population-specific plasticity in CHCs. Different groups of CHCs mediated female choice-based sexual selection in each population suggesting that geographical and ecological divergence has the potential to promote divergence in mate communication systems.

Reproductive Trade-Offs and Direct Costs for Males in Arthropods

Until 30 years ago, the emphasis on reproductive costs for males was mainly on costs related to mate searching, courtship and fighting with rival males. However, costs for males are substantial and varied and often resemble the more thoroughly studied female reproductive costs. Costs can be referred to as trade-off costs, where investment in reproductive activity comes at the expense of another important activity or fitness component. Investment in reproduction at the expense of longevity and future reproduction is the ultimate cost, because it affects fitness directly. In contrast, flawed performance (e.g., of the immune system) is perceived as a mechanistic trade-off, because it affects fitness indirectly through a mediator (i.e., parasites). Finally, direct costs refer to direct measurements of the energy expenditure during involvement in reproduction-related activities. Both direct and mechanistic trade-off costs often result in decreased longevity compared to unmated males (an ultimate cost). Males incur costs during different reproductive phases: before copulation, when producing sperm, while searching for, courting and copulating with females, and subsequently when guarding females or taking care of offspring. This synthesis follows previous pioneering reviews addressing specific aspects of male costs, but strives to summarize all known male reproductive cost types more comprehensively, including their classification. We suggest several directions for targeted future research. While costs for males have been fairly well described, it is now necessary to uncover the ecological and evolutionary factors responsible for differences between closely related species and systems and to better link between directly-measured costs, mechanistic trade-off costs and ultimate trade-off costs.

Variation in energy reserves and role of body size in the mating system ofAnopheles gambiae

Anopheles gambiae mates in flight. Males gather at stationary places at sunset and compete for incoming females. Factors that account for male mating success are not known but are critical for the future of any genetic control strategy. The current study explored variations in nutritional reserves (sugars, glycogen, lipids, and proteins) in wild-caught swarming and resting males and evaluated the effect of body size and wing symmetry on male mating success. Our results showed that glycogen and sugar reserves are mobilized for flight. Males consume proportionally 5.9-fold as much energy derived from sugars in swarming activities than when they are at rest. Mated males were on average bigger than unmated ones (P<0.0001). A strong correlation between the left and right wings in both mated and unmated males was found and additional analysis on fluctuating asymmetry did not show any indication of mated males being more symmetrical than unmated ones. The distribution of wing size of mated males was focused around a central value, suggesting that intermediate size of males is advantageous in the An. gambiae mating system. The results are discussed in the context of sexual selection.

Patterns of acceptance of artificial eggs and chicks by Magellanic Penguins (Spheniscus magellanicus)

Life history theory predicts that parents will not raise unrelated offspring. For seabirds, an ability to recognize their own eggs and chicks can prevent a costly mistake. We tested whether Magellanic Penguins (Spheniscus magellanicus) would discriminate against artificial eggs by presenting nine types of egg-objects and one type of artificial chick to penguins at their nests. Magellanic Penguins regardless of their sex or breeding status accepted all egg-objects. A generalized linear mixed model showed that mass and number of dimensions were the most important factors in predicting whether the object was accepted: flat egg-objects and light egg-objects were less likely to be incubated than round, normally weighted ones. We also tested whether Magellanic Penguins would retrieve egg-objects more frequently if the object was within 1 m of the nest cup. Penguins retrieved 75 % of objects that were 1 m from the nest cup, but only 25 % of objects that were 2 m from the nest cup. Lastly, we tested whether penguins would accept artificial chicks. We found that pairs with chicks less than 3 weeks of age (i.e., not out of the guard stage) were at least twice as likely to brood an artificial chick than pairs with chicks older than 3 weeks, pairs that had lost their chicks, or unmated males.

Mating and Breeding Success Decline with Elevation for the Pacific Wren (Troglodytes pacificus) in Coastal Mountain Forests

We studied the population ecology of Pacific Wrens (Troglodytes pacificus) in 2003 and 2004 breeding across elevations from 100 to 1,300 m in coastal mountain forests in southwestern British Columbia, Canada to examine if this species is adapted to upper montane and subalpine habitats. We found fewer territories at high elevation, a higher proportion of unmated males, fewer nests per mated male, and no returns of banded adults or juveniles. The breeding season was 61% shorter (31 vs. 79 days), and mass of nestlings (at 11–12 days of age) and nest survival were lower at high elevation compared to lower elevation sites. Clutch size, incubation and nestling periods, parental provisioning rates of nestlings, and adult morphology did not vary with elevation. Annual fecundity measures declined with increasing elevation with no apparent compensatory increases in other vital rates such as survival of adults or offspring.

Mating systems in cooperative breeders: the roles of resource dispersion and conflict mitigation

Within animal societies, the ecological and social underpinnings of mating system variation can be related to resource dispersion, sexual conflict between breeders, and the effects of non-breeders. Here, we conducted a broad-scale investigation into the evolution of mating systems in the cooperatively breeding cichlid, Neolamprologus pulcher, a species that exhibits both monogamy and polygyny within populations. Using long-term field data, we showed that polygynous groups were more spatially clustered and held by larger competitively superior males than were monogamous groups, supporting the role of resource dispersion. To explore the role of sexual conflict, we forced polygynous males to become experimentally monogamous (EM) in the field. EM males spent more time on their remaining territory than naturally polygynous males but otherwise did not change behaviorally or physiologically. Females mated to EM males performed more submissive acts, and in a forced choice experiment, females did not preferentially associate with the larger of two unmated males. Females may therefore incur an unexpected cost from mating monogamously with a large and competitively superior male, a cost that mitigates sexual conflict over the mating system. Helpers were more closely related in monogamous groups but did not behave differently under monogamy or polygyny. Helpers therefore seem neither to be affected by nor affect the mating system of breeders. Our results demonstrate the roles of resource availability and conflict mitigation in determining the mating system, and highlight the importance of experimental manipulation for revealing hidden costs of hypothetical mating patterns. Key words: cooperative breeding, mating system, monogamy, polygyny, resource dispersion, sexual conflict. [Behav Ecol]

黄色LED点滅光によるオオタバコガの飛翔抑制

We aimed to clarify the pulse conditions of a yellow LED that can be pulsed at the high speed required to control noctuid moths without suppressing the blooming of chrysanthemum. We used a lemon-yellow LED (central wavelength: 571 nm) of similar wavelength to yellow fluorescent light, with an intensity of 20 mW/m2 and pulsed-LED light period of 20 ms. We measured the flight activity of adult Helicoverpa armigera (Hübner) under various light to dark period ratios of the LED pulse: 20 ms : 0 ms (continuous lighting), 20 ms : 40 ms, 20 ms : 80 ms, 20 ms : 160 ms, 20 ms : 400 ms and these were compared with dark conditions 0 ms : 0 ms without illumination, using an actograph system. As a result, Helicoverpa armigera became accustomed to the LED lighting conditions over time and the number of flight activities gradually increased in unmated females in 20 : 0, 20 : 160 and 20 : 400 groups and in unmated males in 20 : 0 and 20 : 400 groups over one day. However, in the 20 : 40 and 20 : 80 groups, Helicoverpa armigera adults, either unmated females or males, did not become accustomed, but flight activity was clearly controlled over five continuous days. It was found that the flight of adult moths was strongly suppressed under the conditions of 20 : 40 ms and 20 : 80 ms pulsed-LED light.

Pheromone Production, Attraction, and Interspecific Inhibition among Four Species ofIpsBark Beetles in the Southeastern USA

Hindgut volatiles from attacking, unmated males ofIps avulsus, I. calligraphus, I. grandicollis, andI. piniwere analyzed by combined gas chromatography and mass spectrometry. Based on the quantitative identifications of hindguts and subsequent individual aerations, baits were formulated and a combined species-specific subtractive field bioassay was set up for the four bark beetle species. The bioassays were subtractive for the compounds identified in the hindgut analysis of each species, and volatiles identified in sympatric species were added as potential inhibitors alone and in combination. The trap catches from this bioassay revealed strong interspecific inhibition. The subtractive assays showed thatI. grandicollisandI. calligraphusshare (–)-(4S)-cis-verbenol as one pheromone component, while their second, synergistic pheromone component, (–)-(S)-ipsenol inI. grandicollisand (±)-ipsdienol inI. calligraphus, acts as an interspecific inhibitor to the other species.I. avulsusandI. piniwere found to have very similar production of hindgut volatiles, and both use ipsdienol and lanierone as synergistic pheromone components. No beetle-produced interspecific inhibitor was identified between these two species. Lanierone was found to be an interspecific inhibitor for bothI. calligraphusandI. grandicollis.

Mate choice and polyandry benefit reproduction and progeny fitness in the ladybird Hippodamia variegata (Goeze)

The effect of mate choice and polyandry on the reproductive performance and progeny fitness of a predaceous ladybird, Hippodamia variegata Goeze, was studied. The following mating combinations were used: (i) virgin female paired with the same and initially unmated male once per day (monogamy with limited mating), (ii.) virgin female paired once daily with an unmated male (polyandry with no mate choice) and (iii.) virgin female kept with five unmated males (polyandry with mate choice), with the food in each case an ad libitum supply of Aphis craccivora. Polyandrous females that had a free choice of mates were significantly more fecund (585.50± 13.80 eggs) and higher percentage of their eggs hatched (95.32± 1.99 %) than was the case for polyandrous females with no choice of mates (495.20± 14.25 eggs and 88.81± 3.29 %) followed by monogamous females (405.00± 16.20 eggs and 83.13± 2.07 %). Thus, mate choice and multiple mating by females is advantageous in terms of progeny production. The larvae that hatched from the eggs laid by these females were reared to maturity and their survival, duration of development and fitness determined. The fitness of offspring of polyandrous females (0.4787 ± 0.01) was better than that of polyandrous females that did not choose their mates (0.4418 ± 0.02) and monogamous (0.4057 ± 0.01) females. In addition, a greater percentage of the offspring of polyandrous females that chose their mates survived and developed faster than those of monogamous females with limited mating. These results reveal that polyandry with mate choice results in increased reproduction and better offspring quality. Hence, if one is interested increasing the production of H. variegata it is recommended that systems of production are developed that enable the females to be polyandrous and to select their mates.

Weight Loading and Reproductive Status Affect the Flight Performance of Pieris napi Butterflies

Weight-induced mobility reductions can have dramatic fitness consequences and winged animals are especially sensitive to the trade-off between mass and locomotion. Data on how natural weight fluctuations influence a flying insect’s ability to take off are scarce. We therefore quantified take-off flight ability in Pieris napi butterflies in relation to reproductive status. Take-off flight ability (velocity and take-off angle) under suboptimal temperature conditions was recorded with a 3D-tracking camera system and was predicted to decrease with relatively larger weight loads. Our results show that relatively larger weight loads generally reduce flight speed in male butterflies and lower take-off angles in females. However, despite having a lower wing loading, mated male butterflies flew slower than unmated males. Our study suggests that retention of weight loads associated with reproduction impairs insect flight performance.

Proteomic Analysis of Insecticide Triazophos-Induced Mating-Responsive Proteins of Nilaparvata lugens Stål (Hemiptera: Delphacidae)

The brown planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), is a classic example of a resurgent pest induced by insecticides. It has been demonstrated that triazophos treatment causes an increase in the content of male accessory gland proteins (Acps) that can be transferred to females via mating, influencing female reproduction. However, the mechanism of this type of insecticide-induced Acps in males and the subsequent stimulation of reproduction in females are not well understood. To identify changes in the types of Acps and reproductive proteins in mated females, we conducted a comparative proteomic analysis. Six samples were categorized into four different groups: (1) untreated unmated males compared to treated unmated males (UUM vs TUM); (2) treated unmated males compared to treated mated males (TUM vs TMM); (3) untreated unmated females compared to treated unmated females (UUF vs TUF); (4) treated unmated females compared to treated mated females (TUF vs TMF). Protein expression changes among the four different groups were examined by two-dimensional gel electrophoresis (2-DE) and liquid chromatography tandem mass spectrometry (LC-MS/MS). Of the 500-600 reproducibly detected protein spots on each gel, 107 protein spots were differentially expressed between the four different groups. Of the 63 proteins identified by LC-MS/MS analysis, 38 were up-regulated and 25 were down-regulated in the four different groups. Some novel proteins related to fecundity were observed including spermatogenesis-associated protein 5, testis development protein NYD-SP6, arginine kinase, actin-5C, vitellogenin, and ovarian serine protease nudel. The elevated expression of novel fecundity proteins in six samples of N. lugens females and males due to exposure to triazophos was confirmed by quantitative real-time PCR (qRT-PCR). The results suggest that these proteins may participate in the reproductive process of N. lugens adult females and males. Our findings fill a gap in understanding the relationship between insecticide-treated males and the stimulated reproduction of N. lugens females.

Mating increases male's interest in other females: A cognitive study in socially monogamous prairie voles (Microtus ochrogaster)

To determine whether socio-sexual interactions with females influence the male prairie vole's cognitive processing, three groups of males were simultaneously exposed to sensory stimuli of a control and a focal female then tested for their behavioral and neuronal responsiveness to the female cues. From the control female, all males received distal cues. From the focal female, the Unmated males received distal cues, the Unmated-Contact males received all cues but did not mate with her, and the Mated-Contact males received all cues and mated with her. Males were tested for their attentiveness to enclosures holding each female and for their memory of the females' previous location. Males' brains were then examined to localize activated regions following exposure to the odor of familiar versus unfamiliar focal females. The Mated-Contact males spent more time in the cage of the control female attending to her enclosure than in the cage of the focal female. Exposure to odors of unfamiliar focal females activated the cingulate cortex of Unmated-Contact males. There was a negative correlation between the level of neuronal activation in the retrosplenial cortex of males that were exposed to the odors of a familiar focal female and their attentiveness to the enclosure of the control female. The data suggest that the effect of socio-sexual interactions with a female on males' cognition depends on the type of sensory signals males receive from females and how individual males perceive those signals.

Sperm depletion and a test of the phenotype-linked fertility hypothesis in Gray Treefrogs (Hyla versicolor)

The phenotype-linked fertility hypothesis (PLFH) predicts that ejaculate characteristics correlate with male phenotype, and that females may select for exaggerated phenotypes to guarantee high fertilization success. Female Gray Treefrogs ( Hyla versicolor LeConte, 1825) prefer males with long-duration calls and (or) calls produced at a fast rate. I tested the prediction that call duration or call rate were indicators of sperm number or viability. To assess whether female H. versicolor might benefit by identifying males with low sperm numbers, I examined the effect of mating history on sperm number and looked for evidence of sperm depletion. My study found no support for the PLFH in relation to call quality, as neither sperm number nor viability was related to call duration. I found that sperm stores are severely reduced after a single mating, and that sperm stores of males calling late in the season are often more similar to those of depleted males than unmated males. Thus, calling males may attempt to attract females without the sperm numbers necessary to fertilize the entire clutch. However, selection for females to identify males with high fertilization success may be low when all other factors that affect reproductive success (e.g., genetic benefits) are considered.