Male Competition Research Articles

Reproductive behaviours in male parasitoids: From mating system to pairing pattern

AbstractIt is now acknowledged that mating system is a dynamic characteristic within species or populations. Indeed, behavioural characteristics shaping the mating system can vary at the inter‐individual level, providing raw material for sexual and natural selections, and at the intra‐individual level, because of phenotypic plasticity and ontogeny of individual behaviours. Social environment is an additional source of variation in sexual behaviours. By focusing on males of the parasitoid wasp Venturia canescens, we assessed how sexual behaviours (courtship and mating) vary between and within individuals, considering males' size as inter‐individual source of variation, and age and mating experience as intra‐individual sources of variation. Consequences of the variations in sexual behaviours at the individual level are appraised by quantifying the costs in longevity and offspring production incurred by (repeatedly) mated males. At the population level, we tested the “agility hypothesis” predicting that smaller males win the male–male competition to access females, resulting in a non‐random assortative mating by size and a negative sexual selection on body size. We showed that V. canescens males are polygynous and that mating incurred longevity cost. Old males had a higher probability to court females, but no mating advantage. Smaller males tended to have a higher mating probability, but size was not under sexual selection and there was a random mating pattern according to individual size. Male–male competition intensity did not influence pairing pattern but tended to influence mating dynamic. Overall, our results suggest that sexual behaviours tended to vary at the inter‐ and intra‐individual levels and the effect of social environment remains to be more precisely described. These variations may impact individuals' reproductive success with potential ecological and evolutionary consequences that are discussed.

Do manager characteristics matter in equity mutual fund performance? New evidence based on the double-adjusted alpha

Numerous studies investigate the relationships between fund manager characteristics and fund performance. However, most evaluate fund performance by using traditional factor alphas, such as the Fama–French–Carhart four- and six-factor alphas. In the present study, we analyze data from Taiwanese equity mutual funds from January 2009 to December 2018 and reevaluate the relationships between fund manager characteristics (namely gender, education level, and tenure) and fund performance by using a recently proposed performance measure: the double-adjusted alpha. Double-adjusted alphas reflect fund manager skill more accurately than do the traditional four- or six-factor alphas because they control for returns attributable to fund holding characteristics. In contrast to the fact that team management has become the dominant management structure in the U.S. recently, domestic mutual funds in Taiwan are all managed by solo managers, and one manager can manage more than one fund. This solitary working environment in Taiwan's domestic fund industry motivates us to re-examine the relationship between fund performance and characteristics of these solitary managers at the manager level but through using the recently developed double-adjusted alpha method.Our results indicate that female fund managers tend to achieve higher double-adjusted alphas than do male competitors, with the difference remaining significant over the 1, 6, and 12 months following the initial ranking month. Managers' education level and tenure do not have any statistically significant effect on either the double-adjusted four- or six-factor alpha values. However, using the traditional factor alpha measures would lead to different and misleading results. In contrast to the current literature, our findings provide new insights into the relationships between fund manager characteristics and fund performance.

Power

This article focuses on the evolutionary reality of power-driven competitive humans. It documents how evolutionary biologists describe successful power-driven males as ‘alpha males’ and later references Darwin’s extensively documented account of ‘the law of battle’ that drives male–male competition for females on behalf of reproduction. The article proceeds to show how male–male competition across species has been exapted by humans in their harming and killing of other humans in wars of all kinds: ethnic, religious, territorial, racial, and so on. The article questions whether war is an inevitable practice of humans. It continues by exemplifying wars in today’s global world; wars activated by power-driven autocratic leaders and their power-driven followers. The closest psychotherapy comes to recognizing the sickness of such power-driven humans is via diagnoses of narcissism that take addictions into account. Self-addiction, however, is not among the addictions taken into account. In effect, no matter the cost to other humans, power-driven self-addicted humans are not recognized as psychologically deficient but remain free to perpetuate their own glory.

Correction to: Black and orange coloration predict success during male–male competition in the guppy

Correction to: Black and orange coloration predict success during male–male competition in the guppy

Developing the radiation-based sterile insect technique (SIT) for controlling Aedes aegypti: identification of a sterilizing dose.

The sterile insect technique (SIT) is emerging as a tool to supplement traditional pesticide-based control of Aedes aegypti, a prominent mosquito vector of microbes that has increased the global burden of human morbidity and mortality over the past 50 years. SIT relies on rearing, sterilizing and releasing large numbers of male mosquitoes that will mate with fertile wild females, thus reducing production of offspring from the target population. In this study, we investigated the effects of ionizing radiation (gamma) on male and female survival, longevity, mating behavior, and sterility of Ae.aegypti in a dose-response design. This work is a first step towards developing an operational SIT field suppression program against Ae.aegypti in St. Augustine, Florida, USA. Exposing late-stage pupae to 50 Gy of radiation yielded 99% male sterility while maintaining similar survival of pupae to adult emergence, adult longevity and male mating competitiveness compared to unirradiated males. Females were completely sterilized at 30 Gy, and when females were dosed with 50 Gy, they had a lower incidence of blood-feeding than unirradiated females. Our work suggests that an ionizing radiation dose of 50 Gy should be used for future development of operational SIT in our program area because at this dose males are 99% sterile while maintaining mating competitiveness against unirradiated males. Furthermore, females that might be accidentally released with sterile males as a result of errors in sex sorting also are sterile and less likely to blood-feed than unirradiated females at our 50 Gy dose. © 2022 Society of Chemical Industry.

The oxidative cost of competing for egg fertilization exceeds the cost of egg production.

Measuring reproductive costs is crucial to understanding sexual conflict and its evolutionary outcomes. Sexual conflict is thought to originate from anisogamy-the size difference between male and female gametes; if sperm are tiny and not produced in vastly greater numbers than eggs, at any mating females' gametic investment is larger than that of males. Testing this prediction has proven difficult, especially because males and females differ in many more traits than just gamete size. We overcame this difficulty by exposing simultaneously hermaphroditic polychaete worms Ophryotrocha diadema (two sexual functions in the same body) to two social conditions, pairs, and groups >2, where hermaphrodites invest either relatively more in the female function or relatively more in the male function, respectively. Then we measured four markers of cellular oxidative status, a physiological mediator of life-history strategies. Less female-biased hermaphrodites produced fewer eggs but, unexpectedly, had lower levels of antioxidant protection than more female-biased hermaphrodites, which produced more eggs. Male-biased hermaphrodites compete for mating as males (hermaphrodites in pairs do not) suggesting that in the short-term male competition might be costlier than egg production in terms of regulation of oxidative status. These results highlight the need of including behavioral traits, namely competition over egg fertilization, in the measures of reproductive costs.

Bacterial Diversity Associated with Anastrepha obliqua Males Change Under Mass-Rearing Conditions and with Irradiation

Recent advances in understanding the symbiotic interactions between bacteria and fruit flies have shown that they are relevant for mass rearing and the sterile insect technique (SIT). SIT involves mass production and release of sterile insects that would copulate with their wild conspecifics and thus decrease the population growth rate. The irradiation process used to sterilize mass-reared flies can modify the diversity and structure of the midgut bacterial communities, which could affect sterile male survival, flight capacity, and sexual competitiveness. Our aim was to compare bacterial communities in the midgut of wild and mass-reared Anastrepha obliqua (Macquart) males irradiated at 0, 60, and 80Gy. After adult's emergence, their midguts were dissected, DNA was extracted, and high-throughput sequencing of the V3-V4 region of the 16S rDNA gene was performed. A total of 11 phyla, 17 classes, 47 families, and 52 genera of bacteria were identified. The most representative phylum was Proteobacteria and the predominant family was Enterobacteriaceae. We found that wild males had a different intestinal bacterial community from mass-reared males. In addition, irradiation at 60 and 80Gy caused changes in the diversity and structure of the midgut microbiota of these sterile males, suggesting that mass rearing and irradiation cause artificial selection of the bacterial communities in the gut of A. obliqua males.

Female control of sperm ejection and retention in the cornsilk fly Euxesta eluta (Diptera: Ulidiidae).

Promiscuous mating systems provide the opportunity for females to bias fertilization toward particular males. However, distinguishing between male sperm competition and active female sperm choice is difficult for species with internal fertilization. Nevertheless, species that store and use sperm of different males in different storing structures and species where females are able to expel all or part of the ejaculates after copulation may be able to bias fertilization. We report a series of experiments aimed at providing evidence of female sperm choice in Euxesta eluta (Hendel), a species of ulidiid fly that expels and consumes ejaculates after copulation. We found no evidence of greater reproductive success for females mated singly, multiply with the same male, or mated multiply with different males. Female E. eluta possesses two spherical spermathecae and a bursa copulatrix for sperm storage, with a ventral receptacle. There was no significant difference in storing more sperm in spermathecae 24 h after copulation than immediately after copulation. Females mated with protein-fed males had greater reproductive success than similar females mated to protein-deprived males. Protein-fed females prevented to consume the ejaculate, retained more sperm when mated to protein-fed males than when mated to protein-deprived males. Our results suggest that female E. eluta can exert control of sperm retention of higher quality males through ejaculate ejection.

Kinship and similarity drive coordination of breeding-group choice in male spotted hyenas.

When and where animals reproduce influences the social, demographic and genetic properties of the groups and populations they live in. We examined the extent to which male spotted hyenas (Crocuta crocuta) coordinate their breeding-group choice. We tested whether their propensity to settle in the same group is shaped by passive processes driven by similarities in their socio-ecological background and genotype or by an adaptive process driven by kin selection. We compared the choices of 148 pairs of same-cohort males that varied in similarity and kinship. We found strong support for both processes. Coordination was highest (70% of pairs) for littermates, who share most cumulative similarity, lower (36%) among peers born in the same group to different mothers, and lowest (7%) among strangers originating from different groups and mothers. Consistent with the kin selection hypothesis, the propensity to choose the same group was density dependent for full siblings and close kin, but not distant kin. Coordination increased as the number of breeding females and male competitors in social groups increased, i.e. when costs of kin competition over mates decreased and benefits of kin cooperation increased. Our results contrast with the traditional view that breeding-group choice and dispersal are predominantly solitary processes.

Exploring sexual differences in external morphology and limb muscles of Hylarana guentheri (Anura: Ranidae) during non‐breeding season

AbstractStudying sexual dimorphism facilitates better understanding of the general intersexual divergence of the same species and gives insights into the impact of selective forces on each sex. The sexual dimorphism in anuran external morphology or limb muscles has been well studied in reproductive context, but less so outside the breeding season. Herein, the intersexual differences in 12 external morphological characteristics, 11 forelimb and 12 hindlimb muscles of Hylarana guentheri during non‐breeding season were investigated. We found that the males possessed significantly greater head width and tympanum diameter, while the females had significantly larger body size and head length; there was no sexual differences in the examined limb muscles, except for the mass of flexor carpi radialis. The larger body size means greater fertility for the females, and the longer head may be related to the allometry and reduce resource competition. For the males, the wider head is likely correlated with prey size and male–male competition, and also, the larger tympanum and heavier flexor carpi radialis probably aid the productive success. This study provides the comprehensive morphological accounts about the sexual differences of H. guentheri during non‐breeding season, which will contribute to clarify the sex‐specific resource allocation and reproductive strategies of anurans.

Reduced injury risk links sociality to survival in a group-living primate

Sociality has been linked to a longer lifespan in many mammals, including humans. Yet, how sociality results in survival benefits remains unclear. Using 10 years of data and over 1,000 recorded injuries in rhesus macaques (Macaca mulatta), we tested two injury-related mechanisms by which social status and affiliative partners might influence survival. Injuries increased individual risk of death by 3-fold in this dataset. We found that sociality can affect individuals' survival by reducing their risk of injury but had no effect on the probability of injured individuals dying. Both males and females of high social status (measured as female matrilineal rank and male group tenure) and females with more affiliative partners (estimated using the number of female relatives) experienced fewer injuries and thus were less likely to die. Collectively, our results offer rare insights into one mechanism that can mediate the well-known benefits of sociality on an individual's fitness.

Population dynamics of western gorillas at Mbeli Bai.

Long-term studies of population dynamics can provide insights into life history theory, population ecology, socioecology, conservation biology and wildlife management. Here we examine 25 years of population dynamics of western gorillas at Mbeli Bai, a swampy forest clearing in Nouabalé-Ndoki National Park, the Republic of Congo. The Mbeli population more than doubled from 101 to 226 gorillas during the study. After adjusting for a net influx of gorillas into the study population, the increase represents an inherent growth rate of 0.7% per year, with 95% confidence limits between -0.7% and 2.6%. The influx of gorillas mainly involved immigration of individuals into existing study groups (social dispersal), but it also included the appearance of a few previously unknown groups (locational dispersal). The average group size did not change significantly during the study, which is consistent with the possibility that western gorillas face socioecological constraints on group size, even when the population is increasing. We found no significant evidence of density dependence on female reproductive success or male mating competition. The distribution of gorillas among age/sex categories also did not change significantly, which suggests that the population had a stable age structure. Our results provide evidence of population stability or growth for some western gorillas (albeit within a small area). The results highlight the value of law enforcement, long-term monitoring, and protected areas; but they do not diminish the importance of improving conservation for this critically endangered species.

Black and orange coloration predict success during male–male competition in the guppy

AbstractInvestigating how intrasexual competition and intersexual mate choice act within a system is crucial to understanding the maintenance and diversity of sexually-dimorphic traits. These two processes can act in concert by selecting for the same trait, or in opposition by selecting for different extremes of the same trait; they can also act on different traits, potentially increasing trait complexity. We asked whether male–male competition and female mate choice act on the same male traits using Trinidadian guppies, which exhibit sexual size dimorphism and male-limited color patterns consisting of different colors arranged along the body and fins. We used behavioral assays to assess the relationship between color and competitive success and then compared our results to the plethora of data on female choice and color in our study population. Males initiated more contests if they were larger than their competitor. Males won contests more often if they had more black coloration than their competitor, and the effect of black was stronger when males had less orange than their competitor. Additionally, males won more often if they had either more structural color (iridescence) and more orange, or less structural color and less orange than their competitor, suggesting multiple combinations of color traits predict success. Females from our study population exhibit a strong preference for more orange coloration. Thus, traits favored in male contests differ from those favored by intersexual selection in this population. These results suggest that inter- and intrasexual selection, when acting concurrently, can promote increased complexity of sexually selected traits.

Observation of a golden cheeked warbler (Setophaga chrysoparia), utilizing a typical B-song but an atypical A-song

From 27 March through 2 June 2017, a golden cheeked warbler (Setophaga chrysoparia), code named “Piccolo,” claimed a territory within the Balcones Canyonland Preserve near Austin, Texas and sang a combination of atypical A-songs combined with typical B-songs. To the authors’ knowledge, this A-song variant has not been previously reported. In situ observations of Piccolo’s movements were used to determine the extent of Piccolo’s defended territory. In addition, between 14 April and 7 June, an acoustic recorder was deployed in the territory to record the variant song along with the soundscape. On April 28, a second-year competitor male entered Piccolo’s territory and intense and prolonged counter-singing was recorded through May 24. The competitor produced typical A- and B-songs while Piccolo counter-sang in the aforementioned variant A-songs and typical B-songs. During the recording period, Piccolo did not vocalize any typical A-songs. Two additional competitor males that used typical B-songs were also observed and recorded. The in situ observations and acoustic analysis of Piccolo’s atypical countersigning were compared to typical interactions between other nearby birds to ascertain whether the variant song provided an advantage or disadvantage for Piccolo. [Work supported by the City of Austin.]

Correlated evolution between colour conspicuousness and drum speed in woodpeckers.

Sexual selection drives the evolution of many spectacular animal displays that we see in nature. Yet, how selection combines and elaborates different signal traits remains unclear. Here, we investigate this issue by testing for correlated evolution between head plumage colour and drumming behaviour in woodpeckers. These signals function in the context of mate choice and male–male competition, and they may appear to a receiver as a single multimodal display. We test for such correlations in males of 132 species using phylogenetic linear models, while considering the effect of habitat. We find that the plumage chromatic contrast is positively correlated with the speed of the drum, supporting the idea that species evolving more conspicuous plumage on their head also evolve faster drum displays. By contrast, we do not find evidence of correlated evolution between drum speed and head colour diversity, size of the head's red patch, or extent of the plumage achromatic contrast. Drum length was not correlated with any of the plumage coloration metrics. Lastly, we find no evidence that habitat acts as a strong selective force driving the evolution of head coloration or drumming elaboration. Coevolution between different signal modalities is therefore complex, and probably depends on the display components in question.

Prespawning and Spawning Migrations of the Southern Greenling Pleurogrammus azonus (Mathematical Model)

Prespawning and spawning migrations of the southern one-finned greenling Pleurogrammus azonus in the bay are considered on the basis of the author's and literary numerical material. Peter the Great, in the summer-autumn period. As part of the spatiotemporal model building, the pre-spawning and spawning migrations were formalized. The dynamics of diurnal displacements is made in terms of transport equations. The recording of their representations follows the modified Patlack-Keller-Segel equations, according to which the flow of objects/substance is directed along the gradients of the stimulus zone functions introduced here. It is believed that in the pre-spawning period, morphophysiological and behavioral adaptations to a rather long and energyconsuming spawning occur. It is shown that the intensity of daily movements is proportional to their linear size (the larger the fish, the faster it moves). The equations for the spawning stage take into account the spatial competition of males, which under natural conditions is observed only in the vicinity of spawning areas. For females, clusters of males act as an incentive for movement. The simulation results turn out to be close to the observed migration regime.

Sexual selection leads to positive allometry but not sexual dimorphism in the expression of horn shape in the blue wildebeest, Connochaetes taurinus

Sexual selection is thought to be an important driver of adaptation, speciation and extinction. Empirically testing these predictions across macroevolutionary timescales first requires an understanding of the morphology of secondary sexual traits in extant taxa. We used three-dimensional geometric morphometrics to analyse a large sample of the skull of the blue wildebeest, Connochaetes taurinus, in which horns are found in both sexes but only used in intrasexual competition in males. We show that the horns fit several predictions of secondary sexual traits; overall skull shape is significantly correlated with size (R2 = 0.38, p = 0.001), and the sexually selected horns show drastically higher growth rates and variation than any other skull element, supporting previous findings. We also find that despite showing significant sexual dimorphism in shape and size (R2 = 0.21, p = 0.001), allometric growth trajectories of sexes are identical (R2 = 0.01, p = 0.635) and dimorphism is not readily detectable without prior knowledge of sex, and is not possible when shape is corrected for size. Our results show that even with strong sexual selection operating in only one sex, the expression of secondary sexual traits may show characteristic and indistinguishable patterns of growth and variance in both sexes.

Boldness predicts divorce rates in wandering albatrosses (Diomedea exulans).

Personality predicts divorce rates in humans, yet how personality traits affect divorce in wild animals remains largely unknown. In a male-skewed population of wandering albatross (Diomedea exulans), we showed that personality predicts divorce; shyer males exhibited higher divorce rates than bolder males but no such relationship was found in females. We propose that divorce may be caused by the intrusion of male competitors and shyer males divorce more often because of their avoidance of territorial aggression, while females have easier access to mates regardless of their personality. Thus, personality may have important implications for the dynamics of social relationships.

Movement and olfactory signals: Sexually dimorphic antennae and female flightlessness in moths

Darwin argued a role for sexual selection in the evolution of male sensory structures, including insect antennae, the strength of which will depend upon the importance of early arrival at receptive females. There is remarkable variation in the nature and degree of sexual dimorphism in moth antennae, with males of some species having spectacular, feathery antennae. Although it is widely assumed that these elaborate structures provide greater sensitivity to chemical signals (sex pheromones), the factors underlying the interspecific diversity in male antennal structure and size are poorly understood. Because male antennal morphology may be affected by several female life–history traits, including flight ability, we conducted a phylogenetic comparative analysis to test how these traits are linked, using data from 93 species of moths across 11 superfamilies. Our results reveal that elaborate antennae in males have evolved more frequently in species where females are monandrous. Further, female loss of flight ability evolved more frequently in species where males have elaborate antennae. These results suggest that elaborate antennae have evolved in response to more intense male competition, arising from female monandry, and that the evolution of elaborate antennae in males has, in turn, shaped the evolution of female flightlessness.

Sperm competition in yellow dung flies: No consistent effect of sperm size.

The male competition for fertilization that results from female multiple mating promotes the evolution of increased sperm numbers and can impact sperm morphology, with theory predicting that longer sperm can at times be advantageous during sperm competition. If so, males with longer sperm should sire more offspring than competitors with shorter sperm. Few studies have directly tested this prediction, and findings are inconsistent. Here we assessed whether longer sperm provide a competitive advantage in the yellow dung fly (Scathophaga stercoraria; Diptera: Scathophagidae). Initially, we let brothers with different temperature-mediated mean sperm lengths compete - thus minimizing confounding effects of genetic background - and found no clear advantage of longer sperm. We then used flies from lines subjected to bidirectional selection on phenoloxidase activity that had shown correlated evolutionary responses in sperm and female spermathecal duct lengths. This experiment also yielded no main effect of sperm size on siring success. Instead, there was a trend for a shorter-sperm advantage, but only when competing in females with longer spermathecal ducts. Our data corroborated many previously reported findings (last-male precedence, effects of copula duration and body size), suggesting our failure to find sperm size effects is not inherently due to our experimental protocols. We conclude that longer sperm are not competitively superior in yellow dung flies under most circumstances, and that, consistent with previous work, in this species competitive fertilization success is primarily determined by the relative numbers of sperm competing.