Rival Males Research Articles

Evolution: A kit for fooling your rivals

Some male swordtail fish mimic female 'pregnancy spots' to reduce aggression from rival males and gain a fitness advantage. This sexual mimicry is linked to evolutionary changes in the regulatory region of the kit-liganda gene that controls melanocyte development.

In the presence of rivals, males allocate less ejaculate per mating in Japanese pygmy squid with female sperm rejection

Abstract When mating is promiscuous, the ejaculate volume allocated to each female is expected (intuitively) to be linked with the presence and number of rival males. Previous theories have indicated that, in the absence of rival males, males will allocate the minimum ejaculate volume sufficient for fertilization of all available oocytes. However, it is unclear if this ejaculation strategy is still effective where females have a mechanism to remove sperm after copulation (“female sperm rejection”). In the Japanese pygmy squid, Idiosepius paradoxus, female sperm rejection was observed to occur frequently, but males were able to increase the remaining sperm volume available for fertilization, suggesting that there is no significant impact of female sperm rejection on male ejaculation strategy. However, males decreased ejaculate volume in the presence of rival males and increased it in their absence, a pattern counterintuitive to predictions from previous theories. Females reject sperm at every copulation, so after copulation, the amount of a given male’s sperm remaining with the female may decrease after each subsequent rival copulates with the female. Perhaps in this species, the presence of rivals signals the risk of further sperm rejection, so males choose to conserve their resources and move on.

Dynamics of multilevel alliances in St. Johns River, Florida, Tamanend's bottlenose dolphins (Tursiops erebennus) with respect to an epizootic unusual mortality event

AbstractDisturbance events can alter a community's association patterns, which can influence mating tactics. The St. Johns River (SJR) bottlenose dolphin (Tursiops erebennus) community was impacted by the 2013–2015 unusual mortality event (UME), caused by cetacean morbillivirus, through mortality and social network changes. We analyzed male alliance stability and behavior from April 2011 through March 2017 with respect to the UME. During the UME, 12 first‐order alliance dyads ended due to a partner's death or disappearance. Alliance tactics varied: forming second‐order alliances (n = 21 alliances; teams of first‐order alliances), forming first‐order alliances (n = 13 alliances) or remaining unallied after an alliance dissolved (n = 8 individuals). During‐ and post‐UME, fewer allied males formed second‐order alliances (55%) compared to pre‐UME (68%). While the UME likely indirectly influenced alliance behavior through demographic changes, female presence and breeding season consistently influenced alliance associations and consortships (cooperatively flanking a female), indicating a reproductive function for SJR alliances. Increased consortships when a second‐order partner was present suggests second‐order alliances may provide consortship support against rival males. These results enhance our understanding of multilevel alliance reproductive benefits and demonstrate the adaptability of male mating tactics in response to disturbances resulting in demographic changes.

Sperm performance in the race for fertilization, the influence of female reproductive fluid.

In studies of sperm competition, particularly in external fertilizers, the importance of the fertilization environment on the paternity share among rival males often goes overlooked. The female reproductive fluid (FRF), produced and released by females, creates the microenvironment that sperm encounter on their quest for fertilization and can generate paternity biases by affecting key traits in sperm competition. Yet, whether there is a direct link between FRF effects on sperm traits and its effect on competitive fertilization dynamics remains to be explored. Here, using the zebrafish Danio rerio, we compare within-female paternity share among two competing males and predictors of fertilization success (i.e. sperm traits) in the presence/absence of FRF. Our results unequivocally reveal a direct link between the direction and magnitude of the effect of FRF on sperm traits and the change in the competitive fertilization success of each male. This study demonstrates that the FRF directly mediates post-mating female control through its differential effect on sperm performance and that the FRF's effect on sperm quality alone is sufficient to predict the magnitude of the fitness effects. These findings highlight the need to consider the role of FRF in fertilization, avoiding biases resulting from an exclusive focus on male intrinsic sperm quality.

The transfer of male cuticular hydrocarbons provides a reliable cue of the risk and intensity of sperm competition in decorated crickets.

Theoretically, males should increase their ejaculate expenditure when the probability of sperm competition occurring (or risk) is high but decrease ejaculate expenditure as the number of competing ejaculates (or intensity) increases. Here we examine whether male decorated crickets (Gryllodes sigillatus) use cuticular hydrocarbons (CHCs) transferred to females by rival males at mating to assess the risk and intensity of sperm competition and adjust their ejaculate accordingly. Unmated females and those perfumed with CHCs extracted from one, three, or five males could be distinguished chemically, providing a reliable cue of the risk and intensity of sperm competition. In agreement with theory, males mating with these females increased sperm number with the risk of sperm competition and decreased sperm number with the intensity of sperm competition. Similarly, as the risk of sperm competition increased, males produced a larger and more attractive spermatophylax (an important non-sperm component of the ejaculate) but these traits did not vary with the intensity of sperm competition. Our results therefore demonstrate that both sperm and non-sperm components of the male ejaculate respond to the risk and intensity of sperm competition in different ways and that CHCs provide males with an important cue to strategically tailor their ejaculate.

Male allocation to ejaculation and mating effort imposes different life history trade-offs.

When males compete, sexual selection favors reproductive traits that increase their mating or fertilization success (pre- and postcopulatory sexual selection). It is assumed that males face a trade-off between these 2 types of sexual traits because they both draw from the same pool of resources. Consequently, allocation into mate acquisition or ejaculation should create similar trade-offs with other key life history traits. Tests of these assumptions are exceedingly rare. Males only ejaculate after they mate, and the costs of ejaculation are therefore highly confounded with those of mating effort. Consequently, little is known about how each component of reproductive allocation affects a male's future performance. Here, we ran an experiment using a novel technique to distinguish the life history costs of mating effort and ejaculation for mosquitofish (Gambusia holbrooki). We compared manipulated males (mate without ejaculation), control males (mate and ejaculate), and naïve males (neither mate nor ejaculate) continuously housed with a female and 2 rival males. We assessed their growth, somatic maintenance, mating and fighting behavior, and sperm traits after 8 and 16 weeks. Past mating effort significantly lowered a male's future mating effort and growth, but not his sperm production, while past sperm release significantly lowered a male's future ejaculate quantity, but not his mating effort. Immune response was the only trait impacted by both past mating effort and past ejaculation. These findings challenge the assumption that male reproductive allocation draws from a common pool of resources to generate similar life history costs later in life. Instead, we provide clear evidence that allocation into traits under pre- and postcopulatory sexual selection have different trait-specific effects on subsequent male reproductive performance.

Sensory perception of rivals has trait-dependent effects on plasticity in Drosophila melanogaster.

The social environment has myriad effects on individuals, altering reproduction, immune function, cognition, and aging. Phenotypic plasticity enables animals to respond to heterogeneous environments such as the social environment but requires that they assess those environments accurately. It has been suggested that combinations of sensory cues allow animals to respond rapidly and accurately to changeable environments, but it is unclear whether the same sensory inputs are required in all traits that respond to a particular environmental cue. Drosophila melanogaster males, in the presence of rival males, exhibit a consistent behavioral response by extending mating duration. However, exposure to a rival also results in a reduction in their lifespan, a phenomenon interpreted as a trade-off associated with sperm competition strategies. D. melanogaster perceive their rivals by using multiple sensory cues; interfering with at least two olfactory, auditory, or tactile cues eliminates the extension of mating duration. Here, we assessed whether these same cues were implicated in the lifespan reduction. Removal of combinations of auditory and olfactory cues removed the extended mating duration response to a rival, as previously found. However, we found that these manipulations did not alter the reduction in lifespan of males exposed to rivals or induce any changes in activity patterns, grooming, or male-male aggression. Therefore, our analysis suggests that lifespan reduction is not a cost associated with the behavioral responses to sperm competition. Moreover, this highlights the trait-specific nature of the mechanisms underlying plasticity in response to the same environmental conditions.

Effects of past mating behavior versus past ejaculation on male mate choice and male attractiveness.

Past reproductive effort allows males to assess their ability to acquire mates, but it also consumes resources that can reduce their future competitive ability. Few studies have examined how a male's reproductive history affects his subsequent mate choice, and, to date, no study has determined the relative contribution of past mating behavior and past ejaculate production because these two forms of investment are naturally highly correlated. Here, we disentangled the relative effects of past mating behavior and past ejaculate production in mosquitofish (Gambusia holbrooki) by experimentally preventing some males from ejaculating when trying to mate. We assessed the effect of mating behavior on mate choice by comparing males that had previously been with or without access to females and male rivals for 8 and 16 weeks and assessed the effect of ejaculation on mate choice by comparing males that either could or could not ejaculate when they had access to females for 16 weeks. Reproductive treatment did not affect male attractiveness, but it did affect male mate choice. Somewhat surprisingly, in five of the six treatment-by-age at testing combinations, males preferred a female in the vicinity of a male rival over a solitary female. This preference was marginally stronger for males that had previously engaged in mating behavior but were unaffected by past ejaculate production. We discuss the potential benefits to males of associating with another male when seeking mates. This is the first study to quantify the relative influence of pre- and post-copulatory reproductive investment on male mate choice.

Counter-strategies to infanticide: The importance of cubs in determining lion habitat selection and social interactions.

Animal social and spatial behaviours are inextricably linked. Animal movements are driven by environmental factors and social interactions. Habitat structure and changing patterns of animal space use can also shape social interactions. Animals adjust their social and spatial behaviours to reduce the risk of offspring mortality. In territorial infanticidal species, two strategies are possible for males: they can stay close to offspring to protect them against rivals (infant-defence hypothesis) or patrol the territory more intensively to prevent rival intrusions (territorial-defence hypothesis). Here, we tested these hypotheses in African lions (Panthera leo) by investigating how males and females adjust their social and spatial behaviours in the presence of offspring. We combined datasets on the demography and movement of lions, collected between 2002 and 2016 in Hwange National Park (Zimbabwe), to document the presence of cubs (field observations) and the simultaneous movements of groupmates and competitors (GPS tracking). We showed a spatial response of lions to the presence of offspring, with females with cubs less likely to select areas close to waterholes or in the periphery of the territory than females without cubs. In contrast, these areas were more selected by males when there were cubs in the pride. We also found social responses. Males spent more time with females as habitat openness increased but the presence of cubs in the pride did not influence the average likelihood of observing males with females. Furthermore, rival males relocated further after an encounter with pride males when cubs were present in the prides, suggesting that the presence of cubs leads to a more vigorous repulsion of competitors. Males with cubs in their pride were more likely to interact with male competitors on the edge of the pride's home range and far from the waterholes, suggesting that they are particularly assiduous in detecting and repelling rival males during these periods. In general, the strategies to avoid infanticide exhibited by male lions supported the territorial-defence hypothesis. Our study contributes to answer the recent call for a behavioural ecology at the spatial-social interface.

Ripple effects in a communication network: anti-eavesdropper defence elicits elaborated sexual signals in rival males.

Emitting conspicuous signals into the environment to attract mates comes with the increased risk of interception by eavesdropping enemies. As a defence, a commonly described strategy is for signallers to group together in leks, diluting each individual's risk. Lekking systems are often highly social settings in which competing males dynamically alter their signalling behaviour to attract mates. Thus, signalling at the lek requires navigating fluctuations in risk, competition and reproductive opportunities. Here, we investigate how behavioural defence strategies directed at an eavesdropping enemy have cascading effects across the communication network. We investigated these behaviours in the túngara frog (Engystomops pustulosus), examining how a calling male's swatting defence directed at frog-biting midges indirectly affects the calling behaviour of his rival. We found that the rival responds to swat-induced water ripples by increasing his call rate and complexity. Then, performing phonotaxis experiments, we found that eavesdropping fringe-lipped bats (Trachops cirrhosus) do not exhibit a preference for a swatting male compared to his rival, but females strongly prefer the rival male. Defences to minimize attacks from eavesdroppers thus shift the mate competition landscape in favour of rival males. By modulating the attractiveness of signalling prey to female receivers, we posit that eavesdropping micropredators likely have an unappreciated impact on the ecology and evolution of sexual communication systems.

Rates of male rivalry and mate choice vary with density and determine whether size-assortative mating is absent, positive, or negative in the clown weevil, Eudiagogus pulcher

At four sites in Texas, the density of the clown weevil, Eudiagogus pulcher, in stands of rattlebox, Sesbania drummondii, increased with proximity to water. Size-assortative mating (SAM) was negative at high density, positive at intermediate density, and absent at low density. Only at intermediate density were relatively small potential mates frequently rejected. Females rejected males via resistance to attempts to mount while males rejected females by abandoning them soon after mounting. A laboratory experiment showed that mate rejection is more likely when individuals experience intermediate densities, but not low or high densities, prior to courtship. In the field, rival males displaced mounting males that were small relative to either the female or rival. Rates of rivalry increased with density. At high density, low rates of mate rejection and high rates of rivalry resulted in the formation of displacement-resistant pairs consisting of large males and small females. This left small males to vie for large females and resulted in negative SAM. At intermediate density, low rates of rivalry coupled with rejection of small individuals favored the formation of pairs consisting of similarly sized males and females, causing positive SAM. At low density, low rates of both mate rejection and rivalry resulted in random mating by size and the absence of SAM.

The Orthodox Woman: Jerome on the Relation Between Asceticism, Orthodoxy, and Gender

Abstract While previous scholarship has shown that the rhetorical figure of the “heretical woman” was important in Jerome’s slandering of male rivals, this article argues that the “orthodox woman” played a just as important role in his self-presentation as an orthodox teacher. The “orthodox woman” is characterized by true asceticism which, according to Jerome’s ascetic theology, implies that she transcends her sex. Rather than being a “woman”, in the ordinary sense of the word, she is an angelic being with a supernatural understanding, which allows her to discern the spiritual meaning of the Scriptures and to distinguish between orthodoxy and heresy. It is argued that the presentation of the “orthodox woman” as very learned, independent and strong-willed makes her the direct opposite of Jerome’s “heretical woman”, and that such a portrayal suited Jerome’s purposes, as his great reliance on women readers called for a defence of female spiritual authority.

Female reproductive fluid and male seminal fluid: a non-gametic conflict for post-mating control.

Growing evidence shows that non-gametic components released by both males and females can significantly drive sperm competition outcomes. Seminal fluid (SF) was shown to influence paternity success by affecting rival males' sperm performance, and, in some species with male alternative reproductive tactics, to selectively decrease the fertilization success of males of the opposite tactic. Female reproductive fluid (FRF) has been proven to differentially influence ejaculates of different males and bias fertilization towards specific partners. Whether, and with what outcome, these two processes can intersect to influence sperm competition is still unknown. Here we explore this scenario in the grass goby (Zosterisessor ophiocephalus), a fish with territorial-sneaker reproductive tactics, where sneaker males can exploit the territorials' SF while penalizing territorial sperm performance with their own fluid. To test whether FRF can rebalance the ejaculate competition in favour of territorial males, we used in vitro fertilization with a SF mixture (territorial + sneaker), using increasing concentrations of FRF, to simulate the natural conditions that ejaculates encounter towards the eggs. Our findings revealed a differential effect of FRF on the different tactics' fertilization success, favouring territorial ejaculates, possibly through an attenuation of the detrimental effects of sneaker SF, and enabling females to regain control over the fertilization process.

Spider mite males undress females to secure the first mating

Intense mate competition favors the evolution of extraordinary mating strategies such as the ability of males to identify premature females that are close to becoming mature and associate with them until they are sexually receptive (dubbed precopulatory mate guarding). Owing to possible take-overs by rival males, precopulatory guarding is a high-risk, time- and energy-intensive strategy. Here, we provide experimental evidence that guarding spider mite males undress females by actively removing the exuvia during ecdysis to adult; females undressed by guarding males eclose faster than unguarded females. Such behavior is adaptive because it maximizes the guard's chances of being the first mate.

The simultaneously representation of women at the audit demand and supply sides and audit quality

PurposeEven though the gender literature has addressed the independent effects of female audit committee members and female audit partners on audit quality, this research primary analyses whether the association between the presence of a female audit partner and audit quality depends on (fe)male participation on the audit committee of the audited client-firm. It further examines whether the relationship between female participation on the company's audit committee and audit quality is contingent on having a (fe)male audit partner.Design/methodology/approachA large sample of firm-year observations from the Swedish Corporation has been analyzed for the period that covers the years 2010–2019. The research hypotheses have been analyzed using the year and the industry fixed effect estimations clustered at the firm level.FindingsIn accordance with “the similarity-attraction theory”, the research findings provide support for a positively (negatively) significant relationship between female audit committee female representation and both audit fees and the audit reporting lag (earnings management) in client-firms of female audit partners, albeit insignificant in client-firms of male audit partners. This underscores that the presence of a female audit partner leads the beneficial link between female audit committee directorship and audit quality. Regression results on whether the relationship between female audit committee directorship and audit fees is contingent on having a (fe)male audit partner indicate that female audit partners earn higher (lower) audit fees in companies with gender-diverse (all male) audit committees. This corroborates (in somewhat) the male-female disparities in compensation within the public-audit firms' leading ranks, regarded as a male-dominated workplace worldwide. In conjunction with the argument that (compared to their male rivals) female auditors face more difficulties to reach partnership positions in the public-audit firms and are, thereby, more cautious about the loss of these positions through (in almost cases) exerting more audit efforts, and preventing their audited client-firms from manipulating earnings, the authors reveal that female audit partners are associated with longer (lower) audit reporting lags (earnings management) in both companies with gender-diverse and companies with all-male audit committees. The authors therefore conjuncture that the beneficial female auditor effect on audit quality is not contingent (in somewhat) on (fe)male participation on the company's audit committee. Collectively, the baseline reported results seem sound as they dissipate for a host of alternative metrics for both the dependent and the independent variables. Collectively, the baseline reported results seem sound as they dissipate for a host of alternative metrics for both the dependent and the independent variables.Originality/valueThis study heeds the recent claim for examining the gender effect on the interpersonal interaction between the main participants in the company's auditing process.

Sperm allocation in relation to male–male aggression and courtship in an externally fertilizing fish, the medaka

Sperm production is physiologically costly; therefore, males that mate multiple times are expected to allocate sperm prudently to maximize their fitness. Sperm allocation theory has been widely tested in internally fertilizing animals; however, few studies have investigated whether males adjust the number of sperm released according to their premating experience and cues from rival males. Here, we investigated sperm allocation strategies in an externally fertilizing fish, the medaka, Oryzias latipes, in controlled conditions. We used three treatments: direct interaction with a rival (two males were allowed to interact directly with each other), visual cue only (presenting a male in a separate compartment) and no rivals (control). In the direct interaction treatment, two types of alternative male mating behaviour, simultaneous sperm release and postspawn sperm release, were observed. Premating experiences affected subsequent mating behaviour: males that were more aggressive and exhibited more prominent courtship behaviour mated females without any disturbance from the other males, whereas simultaneous sperm release frequently occurred when both males exhibited similar levels of aggression and courtship behaviours. We also counted the sperm released per mating from the water tank. There was no change in the number of sperm released in the presence of visual cues of competition or direct interaction with the other males before mating. However, males (focal and/or rival) released more sperm only when sperm competition was high, that is, when a rival male successfully disrupted mating before simultaneous sperm release. Our results indicate that medaka males may adjust the number of sperm released per mating in different mating environments.

An Evolutionary Advantage of the Human Glans Penis

To account for the bell- or acorn-shaped glans penis, in 1995 Baker and Bellis put forward their ‘semen-displacement hypothesis’. They argued that the existence of the glans penis is indicative of a promiscuous phase in our evolutionary past, in which females would commonly mate with several males in rapid succession. They argued that within this promiscuous scenario the distinctive shape of the glans penis evolved so as to enable the displacement of rival males’ semen. The idea that there was an influential promiscuous phase in our evolutionary past has faced several powerful criticisms that are here briefly reviewed. However, the critics of the semen-displacement hypothesis have not put forward an alternative evolutionary explanation of the glans penis. I try to redress that here, albeit speculatively. I suggest an alternative hypothesis that may more convincingly account for the shape and texture of the human glans penis.

Drivers and consequences of female reproductive competition in an egalitarian, sexually monomorphic primate

Even after the 150th anniversary of sexual selection theory, the drivers and mechanisms of female sexual selection remain poorly studied. To understand demographic circumstances favoring female-female competition, trade-offs with kin selection and interactions with male reproductive strategies, we investigated female evictions in redfronted lemurs (Eulemur rufifrons). Based on 24 years of demographic data of known individuals, we show that female redfronted lemurs target close female kin for forcible, permanent, and presumably lethal eviction, even though groups contain multiple unrelated males whose voluntary emigration actually mitigated the probability of future female evictions. Female eviction and male emigration were predicted by group size, but male emigration was primarily driven by a proportional increase of male rivals. Female evictions were more likely than male emigrations when there were more juvenile females in a group, but the identity of evicted females was not predicted by any intrinsic traits. While birth rates were reduced by the number of juvenile females, they were higher when there were more adult females in a group and in years with more rainfall. Early infant survival was reduced with increasing numbers of juvenile females, but variation in female lifetime reproductive success was not related to any of the predictors examined here. Thus, there seems to be a limit on female group size in this lemur species. More generally, our study demonstrates a balanced interplay between female reproductive competition, competition over group membership between both sexes, and kin selection, contributing new insights into the causes and consequences of female competition in animal societies.Significance statementThe evolutionary causes of female competition in vertebrate societies remain poorly known. Evictions represent an extreme form of female competition because even close kin are evicted when same-sized unrelated males are theoretically also available as victims. We studied drivers and consequences of evictions in redfronted lemurs (Eulemur rufifrons) using 24 years of demographic data from multiple groups. We show that while voluntary male emigration mitigates the probability of future female evictions, females nonetheless appear to accept the fitness costs of evicting female kin. While group size seems to be the main driver of departures by either sex, the number of juvenile females present in groups is the key variable triggering eviction events as well as physiological responses that could be interpreted as female reproductive restraint. Our study therefore revealed that competition does trump cooperation under some circumstances in the intricate interplay between sexual selection and kin selection on females.

Male attention allocation depends on social context

Allocation of attention, typically a limited capacity, is a mechanism used to filter large amounts of information and determine what stimuli are most relevant at a particular moment. In dynamic social environments as found in almost all species, including humans, multiple individuals may play a pivotal role in any given interaction where a male’s attention may be divided between a rival, a current mate, and/or future potential mates. Although clearly important, the role of the social environment on attention in animals is not well understood. Here, we investigated impacts of the social environment on attention allocation using male sailfin mollies, Poecilia latipinna, which are a part of a sexual-unisexual mating system with the Amazon molly, Poecilia formosa. We asked: 1) Does the species of female influence the amount of attention a male allocates to her? And 2) Is a male’s attention towards his mate influenced by different social partners? We show that males perceive a larger male as a more relevant stimulus to pay attention to compared to a smaller male, and a conspecific female (either a partner or audience) as a more relevant stimulus compared to a heterospecific female. Our results show that differential allocation of attention is dependent upon multiple components of the social environment in which an individual interacts. Understanding what qualities of rival males or potential mates provide enough meaning to males to cause a shift in attention away from a mating opportunity is essential to understanding the influence of the social environment in sexual selection.

Reading the signs: Camera-trapping provides new insights on scent marking in the large-antlered muntjac (Muntiacus vuquangensis).

We present evidence of scent marking in the large-antlered muntjac (Muntiacus vuquangensis). Given the importance of scent marking in individual recognition among ungulates, this behavior may serve to communicate the fitness cost of antagonistic interactions among rival males and could serve as a mechanism for mate assessment among females.