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125 results for “male–male competition”
Combined cues of male competition influence spermatozoal investment in a moth
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Data from: Sibling rivalry vs mother's curse: can kin competition facilitate a response to selection on male mitochondria?
<p>Assuming that fathers never transmit mitochondrial DNA (mtDNA) to their offspring, mitochondrial mutations that affect male fitness are invisible to direct selection on males, leading to an accumulation of male-harming alleles in the mitochondrial genome (mother's curse). However, male phenotypes encoded by mtDNA can still undergo adaptation via kin selection provided that males interact with females carrying related mtDNA, such as their sisters. Here, using experiments with <i>Drosophila melanogaster</i> carrying standardised nuclear DNA but distinct mitochondrial DNA, we test whether the mitochondrial haplotype carried by interacting pairs of larvae affects survival to adulthood, as well as the fitness of the adults. Although mtDNA had no detectable direct or indirect genetic effect on larva-to-adult survival, the fitness of male and female adults was significantly affected by their own mtDNA and the mtDNA carried by their social partner in the larval stage. Thus, mtDNA mutations that alter the effect of male larvae on nearby female larvae (which often carry the same mutation, due to kinship) could theoretically respond to kin selection. We discuss the implications of our findings for the evolution of mitochondria and other maternally inherited endosymbionts.</p>
Male competition reverses female preference for male chemical cues
<p>Females must choose among potential mates with different phenotypes in a variety of social contexts. Many male traits are inherent and unchanging, but others are labile to social context. Competition, for example, can cause physiological changes that reflect recent wins and losses which fluctuate throughout time. We may expect females to respond differently to males depending on the outcome of their most recent fight. In <i>Bolitotherus cornutus</i> (forked fungus beetles), males compete for access to females, but copulation requires female cooperation. In this study we use behavioural trials to determine if females use chemical cues to differentiate between males and if the outcome of recent male competition alters female preference. We measured female association time with chemical cues of two size-matched males both before and after male-male competition. Females in our study preferred to associate with future losers before males interacted, but changed their preference for realized winners following male competitive interactions. Our study provides the first evidence of change in female preference based solely on the outcome of male-male competition.</p>
Males adjust their manipulation of female remating in response to sperm competition risk
<p>To reduce the potential for sperm competition, male insects are thought to inhibit the post-mating reproductive behaviour of females through receptivity inhibiting compounds transferred in the ejaculate. Selection is expected to favour phenotypic plasticity in male post-copulatory expenditure, with males investing strategically in response to their perceived risk of sperm competition. However, the impact that socially cued strategic allocation might have on female post-mating behaviour has rarely been assessed. Here, we varied male perception of sperm competition risk, both prior to and during mating, to determine if a male's competitive environment impacts the extent to which he manipulates female remating behaviour. We found that female Australian field crickets<i> </i>(<i>Teleogryllus oceanicus</i>) mated to males that were reared under sperm competition risk emerged from a shelter in search of male song sooner than did females mated to males reared without risk, but only when mating occured in a risk free environment. We also found that females reared in a silent environment where potential mates were scarce displayed greater post-mating mate searching behaviour than females exposed to male calls during development. Collectively, our findings suggest complex interacting effects of male and female sociosexual environments on female post-mating sexual receptivity.</p>
Data from: Male serrate-legged treefrogs adjust competition strategies according to visual or chemical cues from females
<p>There is increasing evidence that many anurans use multimodal cues to detect, discriminate and/or locate conspecifics and thus modify their behaviors. To date, however, most studies have focused on the roles of multimodal cues in female choice or male–male interactions. In the present study, we conducted an experiment to investigate whether male serrate-legged small treefrogs (Kurixalus odontotarsus) used visual or chemical cues to detect females and thus altered their competition strategies in different calling contexts. Three acoustic stimuli (advertisement calls, aggressive calls and compound calls) were broadcast in a randomized order after a spontaneous period to focal males in one of four treatment groups: combined visual and chemical cues of a female, only chemical cues, only visual cues and a control (with no females). We recorded the vocal responses of the focal males during each 3 min period. Our results demonstrate that males reduce the total number of calls in response to the presence of females, regardless of how they perceived the females. In response to advertisement calls and compound calls, males that perceived females through chemical cues produced relatively fewer advertisement calls but more aggressive calls. In addition, they produced relatively more aggressive calls during the playback of aggressive calls. Taken together, our study suggests that male K. odontotarsus adjust their competition strategies according to the visual or chemical cues of potential mates and highlights the important role of multisensory cues in male frogs' perception of females.</p>
Data from: Sperm competition games: a general model for pre-copulatory male-male competition
Reproductive males face a trade-off between expenditure on pre-copulatory male-male competition – increasing the number of females that they secure as mates – and sperm competition – increasing their fertilisation success with those females. Previous sperm allocation models have focused on scramble competition in which males compete by searching for mates and the number of matings rises linearly with pre-copulatory expenditure. However, recent studies have emphasised contest competition involving pre-copulatory expenditure on armaments, where winning contests may be highly dependent on marginal increases in relative armament level. Here we develop a general model of sperm allocation that allows us to examine the effect of all forms of pre-copulatory competition on sperm allocation patterns. The model predicts that sperm allocation decreases if either the 'mate-competition loading', a, or the number of males competing for each mating, M, increases. Other predictions remain unchanged from previous models: (i) expenditure per ejaculate should increase and then decrease, and (ii) total post-copulatory expenditure should increase, as the level of sperm competition increases. A negative correlation between a and M is biologically plausible, and may buffer deviations from the previous models. There is some support for our predictions from comparative analyses across dung beetle species and frog populations.
Data from: The mutational decay of male-male and hermaphrodite-hermaphrodite competitive fitness in the androdioecious nematode C. elegans
Androdioecious Caenorhabditis have a high frequency of self-compatible hermaphrodites and a low frequency of males. The effects of mutations on male fitness are of interest for two reasons. First, when males are rare, selection on male-specific mutations is less efficient than in hermaphrodites. Second, males may present a larger mutational target than hermaphrodites because of the different ways in which fitness accrues in the two sexes. We report the first estimates of male-specific mutational effects in an androdioecious organism. The rate of male-specific inviable or sterile mutations is ≤ 5 x 10-4/generation, below the rate at which males would be lost solely due to those kinds of mutations. The rate of mutational decay of male competitive fitness is ~0.17%/generation; that of hermaphrodite competitive fitness is ~0.11%/generation. The point estimate of ~1.5X faster rate of mutational decay of male fitness is nearly identical to the same ratio in Drosophila. Estimates of mutational variance (VM) for male mating success and competitive fitness are not significantly different from zero, whereas VM for hermaphrodite competitive fitness is similar to that of non-competitive fitness. Two independent estimates of the average selection coefficient against mutations affecting hermaphrodite competitive fitness agree to within two-fold, 0.33%-0.5%.
Data from: Male responses to sperm competition risk when rivals vary in their number and familiarity
Males of many species adjust their reproductive investment to the number of rivals present simultaneously. However, few studies have investigated whether males sum previous encounters with rivals, and the total level of competition has never been explicitly separated from social familiarity. Social familiarity can be an important component of kin recognition and has been suggested as a cue that males use to avoid harming females when competing with relatives. Previous work has succeeded in independently manipulating social familiarity and relatedness among rivals, but experimental manipulations of familiarity are confounded with manipulations of the total number of rivals that males encounter. Using the seed beetle Callosobruchus maculatus we manipulated three factors: familiarity among rival males, the number of rivals encountered simultaneously, and the total number of rivals encountered over a 48-hour period. Males produced smaller ejaculates when exposed to more rivals in total, regardless of the maximum number of rivals they encountered simultaneously. Males did not respond to familiarity. Our results demonstrate that males of this species can sum the number of rivals encountered over separate days, and therefore the confounding of familiarity with the total level of competition in previous studies should not be ignored.
Data from: Fluctuating selection strength and intense male competition underlie variation and exaggeration of a water strider's male weapon
Sexually selected traits can reach high degrees of expression and variation under directional selection. A growing number of studies suggest that such selection can vary in space, time and form within and between populations. However, the impact of these fluctuations on sexual trait expression is poorly understood. The water strider Microvelia longipes displays a striking case of exaggeration and phenotypic variation where males display extreme differences in the size of their rear legs. To study the origin and maintenance of this exaggerated trait, we conducted comparative behavioral and morphometric experiments in a sample of Microvelia species. We uncovered differences both in the mating behavior and the degree of sexual dimorphism across these species. Interestingly, M. longipes evolved a specific mating behavior where males compete for egg-laying sites, consisting of small floating objects, to intercept and copulate with gravid females. Through male-male competition assays, we demonstrated that male rear legs are used as weapons to dominate egg-laying sites and that intense competition is associated with the evolution of rear leg length exaggeration. Field observations revealed rapid fluctuation in M. longipes habitat stability and the abundance of egg-laying sites. Paternity tests using genetic markers demonstrated that small males could only fertilize about 5% of the eggs when egg-laying sites are limiting, whereas this proportion increased to about 20% when egg-laying sites become abundant. Furthermore, diet manipulation and artificial selection experiments also showed that the exaggerated leg length in M. longipes males is influenced by both genetic and nutritional factors. Collectively, our results highlight how fluctuation in the strength of directional sexual selection, through changes in the intensity of male competition, can drive the exaggeration and phenotypic variation in this weapon trait.
Data from: Sperm blocking is not a male adaptation to sperm competition in a parasitoid wasp
The extent to which sperm or ejaculate-derived products from different males interact during sperm competition – from kamikaze sperm to sperm incapacitation – remains controversial. Repeated matings in the parasitoid wasp Nasonia vitripennis lead to a short-term reduction of efficient sperm use by females, which is crucial for a haplodiploid organism when needing to allocate sex adaptively (i.e. by fertilizing eggs to produce daughters). Repeated matings by females in this species therefore constrain sex allocation through this "sperm-blocking" effect, eliciting a cost to polyandry. Here we explore the causes and consequences of sperm-blocking, and test the hypothesis that it is an ejaculate-related trait associated with sperm competition. First, we show that sperm blocking, which leads to an over-production of sons, is not correlated with success in either offensive or defensive roles in sperm competition. Then, we show that the extent of sperm blocking is not affected by self-self or kin-kin ejaculate interactions when compared to self vs non-self or kin versus non-kin sperm competition. Our results suggest that sperm blocking is not a sperm competition adaptation, but is instead associated with the mechanics of processing sperm in this species, which are likely shaped by selection on female reproductive morphology for adaptive sex allocation.
Data from: Intraspecific competition and inbreeding depression: increased competitive effort by inbred males is costly to outbred opponents
A recent theoretical model suggests that intraspecific competition is an important determinant of the severity of inbreeding depression. The reason for this is that intraspecific competition is density dependent, leading to a stronger negative effect on inbred individuals if they are weaker competitors than outbred ones. In support of this prediction, previous empirical work shows that inbred individuals are weaker competitors than outbred ones and that intraspecific competition often exacerbates inbreeding depression. Here, we report an experiment on the burying beetle Nicrophorus vespilloides, in which we recorded the outcome of competition over a small vertebrate carcass between an inbred or outbred male resident caring for a brood and a size-matched inbred or outbred male intruder. We found that inbred males were more successful as intruders in taking over a carcass from a male resident and were injured more frequently as either residents or intruders. Furthermore, inbred males gained less mass during the breeding attempt and had a shorter adult life span than outbred males. Finally, successful resident males reared a substantially smaller brood comprised of lighter larvae when the intruder was inbred than when it was outbred. Our results shows that inbred males increased their competitive effort, thus contradicting previous work suggesting that inbred males are weaker competitors. Furthermore, our results shows that inbred intruders impose a greater cost to resident males, suggesting that outbred individuals can suffer fitness costs as a result of competition with inbred ones.
Data from: A general description of additive and non-additive elements of sperm competitiveness and their relation to male fertilization success
A complete understanding of male reproductive success, and thus sexual selection, often requires an insight into male success in sperm competition. Genuine conclusions on male sperm competitiveness can only be made in real competitive situations. However, statistical analyses of sperm competitiveness from fertilization success data have been shown to be problematic. Here, I first outline a comprehensive general description of the different additive and non-additive elements relevant for the outcome of sperm competition staged between two males. Based on this description, I will highlight two main problems that are frequently encountered in experiments aiming at estimating sperm competitiveness. First, I focus on potential problems when using standardized competitors vs. random mating trials, because trials with standardized competitors do not allow generalization if male-male interactions are important. Second, I illustrate the necessity to analyse data on the logit scale rather than on raw proportions, because only the logit scale allows a clean separation of additive and non-additive effects (i.e. male×male- and female×male interactions).
Data from: Male burying beetles extend, not reduce, parental care duration when reproductive competition is high
Male parents spend less time caring than females in many species with biparental care. The traditional explanation for this pattern is that males have lower confidence of parentage, so they desert earlier in favor of pursuing other mating opportunities. However, one recent alternative hypothesis is that prolonged male parental care might also evolve if staying to care actively improves paternity. If this is the case, an increase in reproductive competition should be associated with increased paternal care. To test this prediction we manipulated the level of reproductive competition experienced by burying beetles, Nicrophorus vespilloides (Herbst, 1783). We found that caregiving males stayed for longer and mated more frequently with their partner when reproductive competition was greater. Reproductive productivity did not increase when males extended care. Our findings provide support for the increased paternity hypothesis. Extended duration of parental care may be a male tactic both protecting investment (in the current brood) and maximising paternity (in subsequent brood(s) via female stored sperm) even if this fails to maximise current reproductive productivity and creates conflict of interest with their mate via costs associated with increased mating frequency.
Data from: Flexible memory controls sperm competition responses to male Drosophila melanogaster
Males of many species use social cues to predict sperm competition and tailor their reproductive strategies, such as ejaculate or behavioural investment, accordingly. Whilst these plastic strategies are widespread, the underlying mechanisms remain largely unknown. Plastic behaviour requires individuals to learn and memorise cues associated with environmental change before using this experience to modify behaviour. Drosophila melanogaster respond to an increase in sperm competition threat by extending mating duration after exposure to a rival male. This behaviour shows lag times between environmental change and behavioural response suggestive of acquisition and loss of memory. Considering olfaction is important for a male's ability to assess the sperm competition environment, we hypothesised that an olfactory learning and memory pathway may play a key role in controlling this plastic behaviour. We assessed the role of genes and brain structures known to be involved in learning and memory. We show that sperm competition responses depend on anaesthesia sensitive memory, specifically the genes rut and amn. We also show that the γ lobes of the mushroom bodies are integral to the control of plastic mating behaviour. These results reveal the genetic and neural properties required for reacting to changes in the sperm competition environment.
Data from: Male competition fitness landscapes predict both forward and reverse speciation
Speciation is facilitated when selection generates a rugged fitness landscape such that populations occupy different peaks separated by valleys. Competition for food resources is a strong ecological force that can generate such divergent selection. However, it is unclear whether intrasexual competition over resources that provide mating opportunities can generate rugged fitness landscapes that foster speciation. Here we use highly variable male F2 hybrids of benthic and limnetic threespine sticklebacks, Gasterosteus aculeatus Linnaeus, 1758, to quantify the male competition fitness landscape. We find that disruptive sexual selection generates two fitness peaks corresponding closely to the male phenotypes of the two parental species, favouring divergence. Most surprisingly, an additional region of high fitness favours novel hybrid phenotypes that correspond to those observed in a recent case of reverse speciation after anthropogenic disturbance. Our results reveal that sexual selection through male competition plays an integral role in both forward and reverse speciation.
Data from: The copulatory plug delays ejaculation by rival males and affects sperm competition outcome in house mice
Females of many species mate with multiple males (polyandry), resulting in male–male competition extending to post-copulation (sperm competition). Males adapt to such post-copulatory sexual selection by altering features of their ejaculate that increase its competitiveness and/or by decreasing the risk of sperm competition through female manipulation or interference with rival male behaviour. At ejaculation, males of many species deposit copulatory plugs, which are commonly interpreted as a male adaptation to post-copulatory competition and are thought to reduce or delay female remating. Here, we used a vertebrate model species, the house mouse, to study the consequences of copulatory plugs for post-copulatory competition. We experimentally manipulated plugs after a female's first mating and investigated the consequences for rival male behaviour and paternity outcome. We found that even intact copulatory plugs were ineffective at preventing female remating, but that plugs influenced the rival male copulatory behaviour. Rivals facing intact copulatory plugs performed more but shorter copulations and ejaculated later than when the plug had been fully or partially removed. This suggests that the copulatory plug represents a considerable physical barrier to rival males. The paternity share of first males increased with a longer delay between the first and second males' ejaculations, indicative of fitness consequences of copulatory plugs. However, when males provided little copulatory stimulation, the incidence of pregnancy failure increased, representing a potential benefit of intense and repeated copulation besides plug removal. We discuss the potential mechanisms of how plugs influence sperm competition outcome and consequences for male copulatory behaviour.
Female choice and male-male competition are affected by noise-filled calls in a treefrog
<p>Both human and non-human a<span>nimals communicating acoustically face the problem of noise interference, especially anuran</span>s during mating activities.<span> Previous studies focused on the e</span>ffect of continuous noise on signal recognition, but it is still unknown whether different notes in advertisement calls filled by noise affect female choice and male-male competition or not. In this study, we tested female preferences and male evoked vocal responses in serrate-legged small treefrog (<i><span>K</span></i><i><span>ur</span></i><i><span>ixalus odontotarsus</span></i>), by broadcasting the five-note advertisement call and the advertisement call with the second, third or fourth note filled by noise respectively. In phonotaxis experiments, females significantly discriminated against the advertisement call with the fourth note filled by noise, although they did not discriminate against other two noise-filled calls, which indicates that the effect of noise on female preference is related to the order of filled notes in the advertisement call. In playback experiments, males increased the total number of notes and notes/call in response to noise-filled calls compared with spontaneous calls. More interesting, the vocal responses evoked by noise-filled calls were similar to those evoked by complete advertisement calls, suggesting that males may recognize the noise-filled calls as complete advertisement calls. Taken together, our study shows that different notes in advertisement calls filled by noise have different effects on female choice and male-male competition.</p>
Data from: Reproductive foragers: spider males choose mates by selecting among available competitive environments
Mate choice frequently operates differently for males and females as a consequence of male competition for mates. Competitive interactions can alter the fitness payoffs of choice and the realisation of preferences under natural conditions, yet the majority of male choice studies still use binary trials that ignore social factors. Here we test the importance of contest dynamics in male choice with a large scale experiment, using a framework where females are considered analogous to foraging patches that are subject to competition. We track the mate choices and interactions of 640 spiders (Nephila plumipes) before and after manipulation of competition within enclosures, modelling the expected fitness payoffs of each male's actual choices and comparing these with all alternative choices available. We find that many males choose new females once social conditions change, and achieve higher fitness than predicted under random movement. Males increase their fitness not by moving to larger females but by choosing favourable competitive environments that balance competition and female fecundity. Further, we show for the first time that prior residence effects have a strong influence in male reproductive contests and can shape male mate choice. These results highlight the importance of situating male choice studies in the relevant social context, as intrasexual interactions can have profound effects on the realisation and payoffs of male mate choice strategies.
Data from: Male seminal fluid substances affect sperm competition success and female reproductive behavior in a seed beetle
Male seminal fluid proteins are known to affect female reproductive behavior and physiology by reducing mating receptivity and by increasing egg production rates. Such substances are also though to increase the competitive fertilization success of males, but the empirical foundation for this tenet is restricted. Here, we examined the effects of injections of size-fractioned protein extracts from male reproductive organs on both male competitive fertilization success (i.e., P2 in double mating experiments) and female reproduction in the seed beetle Callosobruchus maculatus. We found that extracts of male seminal vesicles and ejaculatory ducts increased competitive fertilization success when males mated with females 1 day after the females' initial mating, while extracts from accessory glands and testes increased competitive fertilization success when males mated with females 2 days after the females' initial mating. Moreover, different size fractions of seminal fluid proteins had distinct and partly antagonistic effects on male competitive fertilization success. Collectively, our experiments show that several different seminal fluid proteins, deriving from different parts in the male reproductive tract and of different molecular weight, affect male competitive fertilization success in C. maculatus. Our results highlight the diverse effects of seminal fluid proteins and show that the function of such proteins can be contingent upon female mating status. We also document effects of different size fractions on female mating receptivity and egg laying rates, which can serve as a basis for future efforts to identify the molecular identity of seminal fluid proteins and their function in this model species.
Male competition reverses female preference for male chemical cues
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