Mediating male–male interactions: the role of the UV blue crest coloration in blue tits

Badges of status, usually color patches, are hypothesized to serve as important signals within natural populations by communicating an individual’s fighting ability or aggressiveness before an interaction ever takes place. These signals, which may evolve via sexual and/or social selection, mediate intra-specific competition by influencing the outcome or escalation of contests between individuals. The last 10 years saw the rise of interest in the role of ultraviolet (UV)-based coloration in intra-sexual communication. However, the rare experimental studies that tested this hypothesis found opposite results, which may originate from the different methodological procedures used to assess the badge of status theory. We present here the results of an experiment testing whether male blue tits (Cyanistes caeruleus) respond differently to unfamiliar conspecifics presenting contrasted UV crest coloration. In an aviary, we simultaneously presented two caged blue tits with enhanced (UV+) or reduced (UV−) crest coloration to a focal bird. We found that focal males acted more aggressively towards the UV− males than UV+ males. In addition, focal males fed more often close to males that were similar in brightness or duller than themselves. We conclude that, in blue tits, UV blue crest coloration affects both social and aggressive responses towards unfamiliar individuals, and thus it has some properties of a badge of status.     

The effects of male–male contests and female eavesdropping on female mate choice and male mating success in the jumping spider, <Emphasis Type="Italic">Thiania bhamoensis</Emphasis> (Araneae: Salticidae)

In experiments that comprised of three phases (fight, choice, and mating) under “seen” and “unseen” conditions, we examined the effects of the outcomes of male–male contests and female eavesdropping on female mate choice and male mating success in the fighting spider, Thiania bhamoensis (Salticidae). The results revealed female eavesdropping on agonistic interactions. Females that had watched an aggressive interaction showed no distinctive preference for the winner over the loser, but they preferred the loser when they had not observed a fight. Winners, however, achieved a greater mating success than did losers during the mating phase. Gaining access to females was based on the insistence of the winners in courtship in terms of the number of quivers, rather than on the fighting behavior of the males. Hence, the outcome of male–male contests may not be an important determinant of a male’s mating success in T. bhamoensis. Instead, courtship display plays an important role in determining the success of male mating in this species. This study also suggests that female mate preference may not be a good indicator of eventual female mate choice and male mating success. Thus, a causal relationship between female mate preference and male mating success cannot be inferred. Joanna P. Y. Chan, Pei Rong Lau, and Ai Jie Tham contributed equally.     

Extrapair paternity in the swamp sparrow, <Emphasis Type="Italic">Melospiza georgiana</Emphasis>: male access or female preference?

Over the past two decades, the combination of molecular and field methods has revealed considerable variation in the level of extrapair fertilizations among socially monogamous birds. Models predicting extrapair young range in scale from a single population to multiple Orders, and there is no single, unifying theory for these reproductive tactics. We investigated proximate explanations of extrapair fertilizations in two subspecies of the swamp sparrow, Melospiza georgiana georgiana and Melospiza georgiana nigrescens, across a range of social and environmental conditions. The presence of extrapair young was best predicted by the size of two male plumage badges (one correlated with parental care and one with territorial aggression) relative to the badge size of their immediate neighbors, the interaction of these two measures, mean territory size, and the maximum size of the aggression badge among neighbors. The size of the male’s parental care badge (relative to neighbors) was negatively correlated with the probability of lost paternity. The relative size of the aggression badge was positively correlated with the presence of extrapair young when the parental care badge was small and negatively correlated when the badge was large. Controlling for these crown measures, males with larger territories were less likely to suffer losses in paternity. There was no effect of breeding density, breeding synchrony, their interaction, subspecies, or weather during the fertile period on the presence of extrapair young. These results suggest that female preference for males that provide more parental care (or preference for genes that convey this trait) plays a dominant role in extrapair interactions among swamp sparrows. Models based on female assessments of relative mate quality offer a promising explanation of patterns in extrapair fertilizations among bird species.     

Surplus territory contenders in male red-winged blackbirds: where are the desperados?

Summary We tested whether payoff asymmetries could explain why floater red-winged blackbirds seldom escalate contests to acquire territories. We removed territorial male \ldowners\rd and allowed floater replacements to claim territories. We then released owners to see how three currencies of payoff asymmetries (replacement occupancy) owners' likelihood and speed of reclaiming their territories (owner success). Neither the duration of an owner's internment nor the amount of time that a floater replacement had held the territory affected owner success (Figs. 1 and 2). Owner success was also not affected by the number of neighbors that they had (Fig. 3). Finally, owner success was the same irrespective of whether or not he was the likely sire of offspring on the territory, or the size of his harem (Fig. 4). Although these results are consistent with the proposal that payoff asymmetries will be irrelevant in contests for valuable resources, they are inconsistent with the proposal's corollary that excluded individuals should become \lddesperados\rd and escalate or even fight to the death in contests for those resources. Expected payoffs for passive acquisition of territories in this species may be higher than from a more aggressive desperado strategy.Correspondence to: P.J. Weatherhead     

Does the cost of polygyny in house wrens include reduced male assistance in defending offspring?

Summary This study investigated whether reduced male aid in defending offspring potentially reduces the fitness of females choosing already-mated males in the house wren (Troglodytes aedon), a small, territorial songbird. Frozen snakes were placed at 23 nests of monogamously mated males and 12 secondary nests of bigamously mated males. All presentations were made during incubation stages of females attending focal nests. Snakes were placed at nests of secondary females when nests of their primary counterparts contained young 5–9 days old. Males are most attentive to primary nests during this period and should therefore be relatively inattentive to secondary mates and nests. Nevertheless, an equal proportion of monogamous and bigamous males discovered snakes within 15 min, and mean time to discovery, when discovery occurred, did not differ with nest status. Monogamous and bigamous males were also equally likely to attack snakes physically once discovered. Monogamous males appeared no more likely to discover snakes than bigamous males for two main reasons. First, although monogamous males were near focal nests (i.e., < 10 m) more often than bigamous males, monogamous males tended to stay out of view of nests for long periods. In contrast, bigamous males always went immediately to focal nests upon arriving in their vicinity. Second, about one-third of monogamous males in this study spent much of their time during trials at the far edges of their territories advertising for secondary mates. Our experiment suggests that reduced male aid in defending nests against small, diurnal predators probably does not contribute to the cost of polygyny in house wrens. Correspondence to: L.S. Johnson     

Mating skew in Barbary macaque males: the role of female mating synchrony,female behavior,and male–male coalitions

A fundamental question of sexual selection theory concerns the causes and consequences of reproductive skew among males. The priority of access (PoA) model (Altmann, Ann NY Acad Sci 102:338–435, 1962) has been the most influential framework in primates living in permanent, mixed-sex groups, but to date it has only been tested with the appropriate data on female synchrony in a handful of species. In this paper, we used mating data from one large semi-free ranging group of Barbary macaques: (1) to provide the first test of the priority-of-access model in this species, using mating data from 11 sexually active females (including six females that were implanted with a hormonal contraceptive but who showed levels of sexual activity comparable to those of naturally cycling females) and (2) to determine the proximate mechanism(s) underlying male mating skew. Our results show that the fit of the observed distribution of matings with sexually attractive females to predictions of the PoA model was poor, with lower-ranking males mating more than expected. While our work confirms that female mating synchrony sets an upper limit to monopolization by high-ranking individuals, other factors are also important. Coalitionary activity was the main tactic used by males to lower mating skew in the study group. Coalitions were expressed in a strongly age-related fashion and allowed subordinate, post-prime males to increase their mating success by targeting more dominant, prime males. Conversely, females, while mating promiscuously with several males during a given mating cycle, were more likely to initiate their consortships with prime males, thus reducing the overall effectiveness of coalitions. We conclude that high-ranking Barbary macaque males have a limited ability to monopolize mating access, leading to a modest mating skew among them.     

Chelipeds are the real weapon: cheliped size is a more effective determinant than body size in male–male competition for mates in a hermit crab

To understand the evolution of weapons, we must understand both their functions and relative importance compared to body size in determining fighting success. Many decapod crustaceans develop disproportionately large chelipeds for their body size and use them as a weapon in agonistic interaction. There are, however, examples where weapons are merely signals of resource holding potential (RHP) and the RHP is actually determined by body size. We investigated the function and relative efficacy of body size and major cheliped size in male–male contests for females in the hermit crab Diogenes nitidimanus. Contests over females took two forms: (1) males preemptively guarded females and opponents did not fight with the guarding male. Cheliped size contributed significantly to the settlement of these contests and probably functioned as a visual signal for the opponents. (2) Guarding males engaged in physical combat with an opponent. In these cases, both body and cheliped sizes affected contest outcomes. The effect size for cheliped size was as strong, or stronger, than that for body size. These results suggest that large chelipeds have evolved as a true weapon and are effective in escalated fights for resources. Therefore they are also efficient visual signals for settling contests with only display. Our results are a rare example that clearly demonstrate that weapons are a more important determinant of fights than body size when both body and weapon size affect resource acquisition.     

When is a male not a male? Sex recognition and choice in two sex-changing species

For dioecious species, choosing a mate of the same sex can have reproductive costs. For sex-changing animals, however, a lack of sex recognition may not carry a reproductive cost, as pairs that were initially same-sex can become opposite-sex pairs as one partner changes sex. The strength of sex discrimination in sex changers, then, should depend on the duration of mating associations and whether the time of sex change is influenced by social situation (“flexible” sex change). We studied two species of marine snails that change sex from male to female, one with flexible sex change and long-term or permanent mating associations (Crepidula fornicata) and one with short-term pairings and relatively fixed time of sex change (Crepidula convexa), to determine whether either species exhibits sex recognition and whether members of C. convexa show stronger sex discrimination. In laboratory experiments, small males, the choosing animals, were placed with either a male or a female conspecific (no-choice experiments) or given a choice of a male or female (choice experiments). We controlled for shell length in all experiments, as relative size may influence sex change or choice. Males of both species paired more often with females than males, but, as predicted, males of C. convexa showed stronger discrimination: When given a choice, no C. convexa male paired with another male. In contrast, some C. fornicata males always chose other males even when given the choice of a female. These results suggest that sex recognition can be adaptive even for sex changers but demonstrate that the level of sex recognition will depend on other aspects of reproductive behavior.     

Sex allocation and paternity in a cooperatively breeding passerine: evidence for the male attractiveness hypothesis?

Sex allocation theory predicts that female birds with high-quality mates will benefit from producing more sons, since sons will inherit their father’s superior traits and enjoy a great reproductive success, whereas females with low-quality mates will benefit from producing more daughters, since the variance in reproductive success among daughters is typically lower. The male attractiveness hypothesis may apply to extra-pair paternity (EPP) because socially monogamous females routinely mate with higher quality males outside the pair bond. We test these predictions using the Tibetan ground tit (Pseudopodoces humilis), a sexually monomorphic, socially monogamous, facultatively cooperative breeder. There was greater variation in actual reproductive success among males than females due to EPP. An excess of sons was detected for bi-parental (i.e., non-cooperative) broods wherein EPP was mainly sired by bi-parental males. The pattern was attributed to male-biased sex ratios produced for both EPP and within-pair offspring within the same broods. The reason for the latter case might be a random allocation of more offspring to sons by the potentially EPP-exposed females that have an inability to control fertilization by specific males. In cooperative broods where EPP mostly resulted from within-group helpers of presumed low-quality, as indicated by their failure in acquiring a social mate, there was a non-significant tendency for EPP offspring to be daughters and for within-pair offspring in the same broods to be unbiased. These results support the EPP-related male attractiveness hypothesis especially in terms of the overproduction of sons. Offspring produced through quasi-parasitism was unbiased towards either sex, suggesting a weak female choiceness with respect to the quality of host males.     

Male mating history and female fecundity in the Lepidoptera: do male virgins make better partners?

In insects, large ejaculate and associated materials, including spermatophores, appear to have evolved via sexual selection acting on males to either delay female remating or to increase the rate of egg-laying. It is also possible, however, that females use nutrients transferred during mating to increase their lifetime fecundity. If so, male ejaculate size may also have evolved under natural selection as a form of paternal investment. In Lepidoptera, males with a greater number of prior matings tend to produce smaller spermatophores. However, the reported effects of male mating history on female fecundity vary widely among species. We therefore performed a meta-analysis using data from 29 studies of 25 species. Overall, the reproductive output of females mated to virgin males was significantly higher than that of females mated to sexually experienced males (Hedges d=0.33, P<0.01). A sample size of around 145 females per male mating type is required to detect an effect of this size with 80% statistical power at =0.05 (two-tailed). There was no difference in mean effect size between butterflies/skippers and moths. After controlling for any effect of taxonomic group, however, the mean effect size for polyandrous species was significantly greater than that for monandrous species (Hedges d=0.45 vs 0.25, P=0.01). We then discuss possible reasons why male mating history, presumably acting through its effect on spermatophore size, might have a stronger effect in polyandrous than monandrous species.Communicated by A. Cockburn     

Do male plumage and song characteristics influence female off-territory forays and paternity in the hooded warbler?

Extra-pair fertilizations are common in many socially monogamous species, and paternity studies have indicated that females may use male vocal performance and plumage ornaments as cues to assess male quality. Female off-territory forays may represent a key component of female choice and male extra-pair mating success, and female foray behaviour is expected to be strongly influenced by indictors of male quality. In this study, we examined how male song and ornamentation affect how often females left their territories, which males they visited and extra-pair paternity in a socially monogamous passerine, the hooded warbler (Wilsonia citrina). We radiotracked 17 females during the fertile period and quantified male vocal performance (song output and rate) and plumage characteristics (size of the black melanin hood and colour of the black hood, yellow cheeks and breast areas). We obtained blood samples and determined paternity at 35 nests including those of 14 females that we radiotracked. Eleven (65%) of the 17 females forayed off-territory, whilst fertile and female foray rate was positively correlated with the number of extra-pair young in the nest. Females that left their territories more frequently were paired with males that sang at a low rate. In addition, extra-pair mates had higher song rates than the social mates they cuckolded (5.3 songs/min vs. 4.4 songs/min). Female off-territory forays or extra-pair paternity were not significantly related to male plumage characteristics. Our results indicate that a high song rate influences both the foray behaviour of a male’s social mate and the likelihood that he will sire extra-pair offspring with neighbouring females.     

Multiple color signals may reveal multiple messages in male Schreiber’s green lizards, <Emphasis Type="Italic">Lacerta schreiberi</Emphasis>

Multiple traits may either signal different characteristics of a male or be redundant. These multiple signals may convey different messages if they are intended for different receivers (e.g., male or females) that have different interests. We examined the functions of multiple colorful visual traits of male Schreiber’s green lizard (Lacerta schreiberi). Results showed that interindividual variation in the characteristics of coloration of males can be related to variation in morphology, health state, dominance status, and pairing status, but that different relationships were found for each color signal. For example, dominant males had brighter “blue” throat and with higher values of ultraviolet (UV) and bluish coloration and darker and greenish dorsal coloration than subordinate males. Health state was also reflected in coloration; males with a higher immune response had “blue” throats with lower amounts of UV coloration, but had “yellow” chests with higher amounts of UV coloration. Males found guarding females also differed in coloration from males found alone. These data suggest that characteristics of coloration of the different multiple signals may reveal different messages for different receivers, either male or female conspecifics. The development of the different signals, based on different morphological and physiological mechanisms and trade-offs, may allow signal reliability of multiple colorful traits in different social contexts.     

Are vocal signals used to recognize individuals during male–male competition in greater prairie-chickens (Tympanuchus cupido)?

Vocal signaling can be an important component of vertebrate communication during social interactions. If vocalizations vary among individuals but are consistent within a given individual, they may be used to discriminate among individuals. In many species, territorial males use vocalizations to discriminate between neighbors and strangers and either respond more aggressively toward strangers relative to neighbors (“dear enemy” effect) or they respond more aggressively toward neighbors relative to strangers (“nasty neighbor” effect). In the greater prairie-chicken (Tympanuchus cupido), male vocalizations are an integral part of the display males produce on leks. We investigated whether male greater prairie-chickens discriminate among familiar individuals on their own territory, familiar individuals outside their normal territory and strangers from a nearby lek. Vocal characteristics varied among males, suggesting that vocalizations may potentially be used by prairie-chickens to identify individuals. Males responded to playback of prairie-chicken calls by vocalizing at a faster rate and approaching the playback speaker, but did not vary in their response to the vocalizations based on the identity of the caller. Our results suggest that variation is present among the vocalizations of individual male greater prairie-chickens, but males do not appear to discriminate among familiar individuals and strangers based solely on their “boom” vocalizations. Greater prairie-chicken vocalization likely functions as a way of announcing that a territory is occupied and defended, but it may also serve as a way of advertising to conspecifics or as a signal that is secondary to other forms of communication.     

Alteration of male reproductive system in rats fed on red or white meat from tuna fish caught in the Gulf of Gab��s in Tunisian coast

Fish, a widely claimed healthy food for humans, could also pose problems to health due to (1) accumulation of pollutants, especially heavy metals, (2) presence of marine toxins such as tetrodotoxin, ciguatoxin or okadaic acid and (3) metabolic production of large amount of uric acid which may crystallize in kidney or in articulations. As tuna fish represents a large part of the traditional food in some countries, the possible impact of its consumption on public health was investigated, with special attention to biochemical and histological alterations related to the genital function. For that purpose, white or red muscle from tuna fish was added for 60 days to the diet of male rats, and attention was paid to biochemical and histological alterations related to the genital function. Feeding rats with white muscle, and much more markedly with red muscle known to be more metabolically active, resulted in (1) an elevated uric acid level in blood, (2) an increase in lead level in testis, (3) an atrophy of the genital tract, including testes, epididymis, prostate and seminal vesicles, (4) a lowering of plasma testosterone level, (5) a decrease in spermatozoids number and motility, (6) an oxidative stress in testes including an increase in lipids peroxidation level and enhanced superoxide-dismutase, catalase and glutathione-peroxidase activities. We conclude that consumption of tuna fish meat, especially the dark one, should be reduced.     

Does the presence of non-breeders enhance the fitness of breeders? An experimental analysis in the clown anemonefish<Emphasis Type="Italic"> Amphiprion percula</Emphasis>

The stability of animal societies depends on individuals decisions about whether to tolerate or evict others and about whether to stay or leave. These decisions, in turn, depend on individuals costs and benefits of living in the group. The clown anemonefish, Amphiprion percula, lives in groups composed of a breeding pair and zero to four non-breeders. To determine why breeders accept the presence of non-breeders in this species I investigated the effect of non-breeders on multiple components of the breeders fitness. Non-breeders did not assist breeders in any obvious way. Experimental removal of non-breeders had no significant effect on the survival, growth, or reproductive success of breeders. Experimental removal of one of the breeding pair showed that non-breeders had little effect on the time taken for a widowed breeder to recommence breeding. The results indicate that the presence of non-breeders neither enhances, nor reduces, the fitness of breeders in A. percula. I suggest that non-breeders might modulate their effect on the fitness of breeders, either by reducing the costs they inflict or by increasing the benefits they provide, such that it just pays breeders to tolerate, rather than to evict, them. This study illustrates that animal societies can be stable even when some individuals gain nothing from the association.Communicated by M. Abrahams     

Do male barn swallows (<Emphasis Type="Italic">Hirundo rustica</Emphasis>) experience a trade-off between the expression of multiple sexual signals?

Some sexual selection models envisage exaggerated male secondary sexual characters to be costly and therefore reliable indicators of the quality of potential mates to choosy females. If male secondary sexual characters have a natural selection cost, they may be linked to each other by reciprocally constraining relationships that would prevent individual males from increasing their level of multiple signaling. Barn swallow (Hirundo rustica) males have at least two costly signals relevant to socio-sexual interactions: tail length and song. Under the hypothesis that a trade-off exists between male signals, we manipulated the maintenance cost of tail ornaments to test whether this reduced the quantity and quality of song, a condition-dependent, phenotypically plastic signal. Contrary to our expectation, tail elongation had no effect on singing activity and song complexity. However, tail-elongated males produced songs with longer terminal parts ('rattles'). Long rattles are associated with highly competitive social contexts and high circulating levels of testosterone, suggesting that tail-elongated males were more frequently involved in either male-male aggressive or inter-sexual interactions. Therefore, this study shows that males are not displaying multiple signals at the maximum possible level, implying that this system is open to unreliable communication. However, long-term trade-offs between signal expression and viability may prevent males from displaying both signals at higher rates.Communicated by: M. Webster     

Optimal maternal investment in the dung beetle<Emphasis Type="Italic"> Onthophagus taurus</Emphasis>?

Optimal investment theory is based on the assumption that the proximate constraint acting on parental investment is resource based. A trade-off between per offspring investment and total investment seems intuitive. Consequently, a parents investment strategy is expected to represent a trade-off between the benefits of investment for current offspring and the costs to future reproduction for parents. In this study, we provide clear evidence that the costs and benefits of maternal provisioning in the dung beetle Onthophagus taurus influence the amount of provisions provided by the mother. Horse dung is typically of a higher nutritional value than cow dung and females were shown to provide 20% less dung to offspring when provisioning with horse dung. By reducing their investment per offspring and exhibiting a clear preference to provision offspring with horse dung, females were able to produce significantly more offspring. Females provisioning with horse dung received greater fitness returns per unit of investment and experienced lower provisioning costs, in terms of the minimum amount of dung required to produce a surviving offspring, than females provisioning with cow dung. Females provisioning in soil of low moisture content were found to have higher tunneling costs than those provisioning in soil of high moisture content, while the fitness returns per unit of investment did not differ. We adopted a marginal value theorem (MVT) approach to calculate the theoretical optimal level of investment for each dung type and for each soil moisture. Predicted levels of provisioning were lower for horse dung than for cow dung and for moist soil than for dry soil. Therefore, the results of this study are in qualitative agreement with MVT predictions and provide empirical support for the proposal that females can adaptively adjust their level of investment in response to resource and/or habitat quality. However, the theoretically predicted optimal investment yielded a poor quantitative fit with our observed levels of investment, with females providing over twice the investment predicted by the MVT approach. We suggest that this difference may reflect either our inability in directly quantifying all the necessary costs and benefits of investment in O. taurus and/or the applicability of the underlying assumptions of MVT.Communicated by D. Gwynne     

Sibling species or poecilogony in the polychaete<Emphasis Type="Italic"> Scoloplos armiger</Emphasis>?

In marine invertebrates multiple modes of development, or poecilogony, may occur in a single species. However, after close examination, many of such putative cases turned out to be sibling species. A case in point may be the cosmopolitan orbiniid polychaete Scoloplos armiger, which inhabits marine shallow sediments. In addition to the well-known direct, holobenthic development from egg cocoons, pelagic larvae have also been described. Our culture experiments revealed a spatially segregated source of the two developmental modes. All females of an intertidal population produced egg cocoons and no pelagic larvae. All but 2 out of 15 females of an adjacent subtidal population produced pelagic larvae and no egg cocoons. Based on these results we performed a molecular genetic analysis (RAPD-PCR) on three intertidal and four subtidal populations in the North Sea. Selected samples from all sites were analysed also by the AFLP method. We found significantly higher genetic diversity within subtidal than within intertidal populations. This is consistent with a wider dispersal by pelagic larvae and a smaller effective population size when development is holobenthic. Total genetic divergence is not related to distance but to the intertidal/subtidal division. We suggest that S. armiger actually represents two sibling species.     

Female and male behavioral response to advertisement calls of graded complexity in túngara frogs, <Emphasis Type="Italic">Physalaemus pustulosus</Emphasis>

We investigated the natural dynamics in a sexual signal that combines different call components and explored the role of call complexity in sexual selection using a neotropical frog. Male túngara frogs, Physalaemus pustulosus, facultatively add up to seven short, multi-harmonic components (chucks) to the simple form of their calls (whines). Female túngara frogs are preferentially attracted to whines with chucks over whines without chucks, and males also call more in response to calls containing chucks. Because acoustic predators prefer complex calls, in the context of simple (no chucks) versus complex (any number of chucks) calls, the variably complex call appears to have evolved in response to the opposing selective forces of natural and sexual selection. There is no evidence, however, for the function of increasing the number of chucks within complex calls. We tested two aspects of increasing call complexity: natural patterns of use of call types in males and how both sexes respond to variation in multi-chuck calls. Males incrementally change call complexity by the addition or subtraction of a single chuck and usually do not produce more than two chucks. Variation in call complexity, for calls with at least one chuck, does not influence response calling in males or phonotaxis in females. Our results suggest that one reason for not increasing call complexity beyond a single chuck is the diminishing effectiveness on the responses of both sexes. This is a posthumous publication for A. Stanley Rand