Use of female nest characteristics in the sexual behaviour of male sockeye salmon

On three island beaches in Iliamna Lake, Alaska, large numbers of male sockeye salmon gathered and spawned in artificial excavations that mimicked a female's nest immediately prior to spawning, while apparently ignoring the control site. The number of males attracted was correlated positively with changes in the operational sex ratio. In contrast, on the mainland beach examined, no reaction to the artificial nests was apparent. The results are discussed in terms of mate searching behaviour by males, the duration of the spawning period, and associated selection pressures on males to use characteristics of their environment that provide information on availability of females.     

Reproductive behavior and mate fidelity in the monogamous goby,Valenciennea longipinnis

Reproductive behavior and mate fidelity of the gobiid fish,Valenciennea longipinnis, were studied on the coral reef at Sesoko Island, Okinawa, Japan. These fish usually live in pairs, not only foraging together for benthic animals in sandy areas, but also constructing several burrows within their home range. Before spawning, both fish, although mainly the male, constructed a mound, piling up dead-coral fragments, pebbles, shells, sand and algae onto one of the burrows. After spawning an egg mass on the ceiling of the burrow, the female stayed outside and continued the construction and maintenance of the mound for 3–5 days until hatching, while the male tended the eggs inside. Mate guarding of females seemed to prevent males from monopolizing several females. Although some pairs showed mate fidelity through several spawnings, more than half of the pairs broke up after only one spawning. The pair bond was broken by mate desertion and the disappearance of each sex. Both sexes preferred larger spawning partners; larger females spawned more eggs and larger males provided better egg care. Mate desertion occurred when larger potential mates, relative to the current partner, became available. The frequency of solitary individuals was higher in males than in females, resulting in females deserting their mates more often than males. Two factors seem to have facilitated mate desertion: (1) occurrence of size mis-matched pairing and (2) overlapping home ranges.     

Mate sampling and choosiness in the sand goby

To date, mate choice studies have mostly focused on establishing which mates are chosen or how the choices are performed. Here, we combined these two approaches by empirically testing how latency to mate is affected by various search costs, variation in mate quality and female quality in the sand goby (Pomatoschistus minutus). Our results show that females adjust their mating behaviour according to the costs and benefits of the choice situation. Specifically, they mated sooner when access to males was delayed and when the presence of other females presented a mate sampling cost. We also found a positive link between size variation among potential mating partners and spawning delay in some (but not all) experimental conditions. By contrast, we did not find the number of available males or the females'' own body size (‘quality’) to affect mating latency. Finally, female mating behaviour varied significantly between years. These findings are notable for demonstrating that (i) mate sampling time is particularly sensitive to costs and, to a lesser degree, to variation among mate candidates, (ii) females'' mating behaviour is sensitive to qualitative rather than to quantitative variation in their environment, and (iii) a snapshot view may describe mate sampling behaviour unreliably.     

Female mate choice and spawning behaviour of Chinook salmon under experimental conditions

After spawning their first nest, female chinock salmon Oncorhynchus tshawytscha paired with small males ( c. 46% of female weight) spent an average of 16·2 h between spawning of successive nests compared with 9·6 h for females paired with large males ( c. 112% of female weight) ( P< 0·05). Neither frequencies of female nest construction behaviours (digging and probing) nor male courtship behaviour (crossovers and quivers) differed between large- and small-male pairs. Male quivering frequencies were correlated significantly with female digging and probing frequencies, whereas the crossover frequencies were not. It is suggested that delayed spawning by females in the presence of relatively small males is a primary mechanism by which females in the genus Oncorhynchus exhibit mate choice.     

Natal dispersal and parental escorting predict relatedness between mates in a passerine bird

Although relatedness between mates is of considerable evolutionary and ecological significance, the way in which the level of relatedness is determined by different behavioural processes remains largely unknown. We investigated the role of behaviour in predicting mate relatedness in great tits using genotypic markers and detailed observations. We studied how mate relatedness is influenced by natal dispersal, inbreeding/outbreeding avoidance after natal dispersal and a behaviour not previously considered that influences membership to social aggregations, namely family escorting behaviour by parents. Among locally born individuals, the level of mate relatedness decreased with natal dispersal distance for females, but not for males. In contrast, mate relatedness was negatively related to the extent of family movements for males, but not for females. However, family movements did not predict dispersal distance for either sex. Local recruits were more related to their mates than immigrants, but this was only significant for females. No evidence was found for inbreeding/outbreeding avoidance after dispersal. Our results suggest that, in highly mobile species, mating options are spatially and/or socially limited, and that parents influence mating options of their offspring before dispersal.     

Sex-role reversal revisited: choosy females and ornamented, competitive males in a pipefish

In the pipefish Syngnathus typhle sex roles are reversed, thatis, females compete more intensely than males over mates. However,competition over mates among individuals of one sex does notnecessarily prevent members of that same sex from being choosy,and choosiness in the other sex does not prevent competitionwithin it. In an experiment we allowed a female pipefish tochoose freely between two males, after which we released themales and let the three interact. Comparisons with earlier resultsshow that both sexes courted partners and competed with consexuals.However, females courted more often than did males, and courtshipwas more frequent in treatments involving large individualsthan in treatments with small individuals. Males competed amongthemselves for access to mates but for a shorter duration thanfemales in the same situation. Males displayed an ornament towardsfemales but not to males during mating competition. Females,however, used their ornament in both contexts. Females did notalways mate with the male of their previously made choice, whichwe interpret as females being constrained by male-male competition,male motivation to mate, or both. Thus, in this sex-role reversedspecies, mate choice in the more competitive sex may be circumventedand even overruled by mate competition and mating willingnessin the least competitive sex. Hence, sex roles should not beconsidered as sexes being either choosy or competitive but ratherthat males and females may exhibit different combinations ofchoice and competition.     

Male sexual cannibalism in a sand‐dwelling wolf spider with sex role reversal

Sexual cannibalism usually involves females attacking and consuming males before, during or after copulation. Sex role reversed systems may provide insight into the debate about whether it arises as mistaken identity, a spillover in female aggressiveness, foraging decisions, and/or extreme mate choice. In such systems, males may be selective and voracious to compensate for their higher reproductive costs, and thus males may be the sexually cannibalistic sex. Allocosa brasiliensis shows a reversal in sex roles and male‐biased sexual size dimorphism (the opposite of the common pattern in spiders). The present study aimed to test whether males cannibalize or mate according to female reproductive status or body characteristics. Each of 20 adult males was consecutively exposed to one virgin and one mated female, alternating the order of exposure. Males preferred to mate with virgin females in good body condition and heavier‐mated females. Males attacked 15% of virgins and 40% of mated females and cannibalized 10% and 25% of the total trials, respectively. The astonishing male cannibalistic behaviour best agrees with extreme mate choice hypotheses because attacks were more frequent on mated females of low body condition. This is the first report of male sexual cannibalism in a sex role reversed system. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 68–75.     

Size, operational sex ratio, and mate-guarding success of the carrion beetle, Necrophila americana

When male insects guard females until oviposition, the benefitsfrom last-male sperm precedence must outweigh the costs of relinquishingadditional fertilizations. The profitability of guarding isincreased when males guard large, fecund females and when femalesare scarce because fewer fertilizations are sacrificed. However,the male reproductive success is not only determined by theprofitability of guarding but also by his ability to maintainguarding. In this study, we used male carrion beetles (Necrophilaamericana) to examine the effects of sex ratio, male relativesize, and female quality on the ability to guard. First, wepresent a model of mate guarding that explores factors, suchas sperm precedence, sex ratio, male size, and female quality,that influence the profitability of postcopulatory riding. Ourmodel predicts that large N. americana males should preferentiallyguard the largest female only when the sex ratio is male biasedand sperm precedence is above 80%. In contrast, small malesgain little from guarding because they are not likely to maintainit and be the last male to mate. Then, we tested these predictionsby manipulating sex ratio, relative male size, and female quality.All males in equal sex ratio and large males in male-biasedsex ratio guarded females significantly longer than did malesin female-biased sex ratio. In male-biased sex ratio, largemales guarded significantly longer and achieved more takeoversthan small males. Large females were guarded longer. The successof guarding males in this beetle depends on their size relativeto other males and the operational sex ratio.     

Size‐Dependent Male Mate Preference and its Association with Size‐Assortative Mating in a Mangrove Snail,Littoraria ardouiniana

In many animals, body size plays a crucial role in mating success in the context of competition and preference for mates. Increasing evidence has shown that male mate preference can be size‐dependent and, therefore, an important driver of size‐assortative mating. To test this theory, mate choice experiments were performed during the three consecutive stages of mating behaviour, namely trail following, shell mounting and copulation, in the dioecious mangrove snail, Littoraria ardouiniana. These experiments identified two possible forms of size‐dependent male mate preference which could contribute to the formation of size‐assortative mating in these snails. Firstly, whereas small males were unselective, large males were selective and preferred to follow mucus trails laid by large females. Alternatively, the results can also be interpreted as all males were selective and adopted a mating strategy of selecting females similar to, or larger than, their own sizes. Both small and large males also copulated for longer with large than with small females, and this was more pronounced in large males. When two males encountered a female, they engaged in physical aggression, with the larger male excluding the smaller male from copulating with the female. This study, therefore, demonstrated that size‐dependent male mate preference may, along with male–male competition, play an important role in driving size‐assortative mating in these mangrove snails, and this may also be the case in other species that exhibit male mate choice.     

Indirect mate choice, direct mate choice and species recognition in a bower-building cichlid fish lek

Sexual selection arising through female mate choice typically favours males with larger, brighter and louder signals. A critical challenge in sexual selection research is to determine the degree to which this pattern results from direct mate choice, where females select individual males based on variation in signalling traits, or indirect mate choice, where male competition governs access to reproductively active females. We investigated female mate choice in a lekking Lake Malawi cichlid fish, Hemitilapia oxyrhynchus, in which males build and aggressively defend sand 'bowers'. Similar to previous studies, we found that male reproductive success was positively associated with bower height and centrality on the lek. However, this pattern resulted from males holding these territories encountering more females, and thus their greater success was due to indirect mate choice. Following initial male courtship, an increase in the relative mating success of some males was observed, but this relative increase was unrelated to bower size or position. Crucially, experimentally manipulating bowers to resemble those of a co-occurring species had no appreciable effect on direct choice by females or male spawning success. Together, these results suggest indirect mate choice is the dominant force determining male-mating success in this species, and that bowers are not signals used in direct mate choice by females. We propose that, in this species, bowers have a primary function in intraspecific male competition, with the most competitive males maintaining larger and more central bowers that are favoured by sexual selection due to higher female encounter rates.     

Male mate choice relies on major histocompatibility complex class I in a sex‐role‐reversed pipefish

Mate choice for compatible genes is often based on genes of the major histocompatibility complex (MHC). Although MHC‐based mate choice is commonly observed in female choice, male mate choice remains elusive. In particular, if males have intense paternal care and are thus the choosing sex, male choice for females with dissimilar MHC can be expected. Here, we investigated whether male mate choice relies on MHC class I genes in the sex‐role reversed pipefish Syngnathus typhle. In a mate choice experiment, we determined the relative importance of visual and olfactory cues by manipulating visibility and olfaction. We found that pipefish males chose females that maximize sequence‐based amino acid distance between MHC class I genotypes in the offspring when olfactory cues were present. Under visual cues, large females were chosen, but in the absence of visual cues, the choice pattern was reversed. The use of sex‐role reversed species thus revealed that sexual selection can lead to the evolution of male mate choice for MHC class I genes.     

SEXUAL SELECTION AND FITNESS VARIATION IN A POPULATION OF SMALLMOUTH BASS,MICROPTERUS DOLOMIEUI (PISCES: CENTRARCHIDAE)

Monogamy is often presumed to constrain mating variance and restrict the action of sexual selection. We examined the reproductive patterns of a monogamous population of smallmouth bass (Micropterus dolomieui), and attempted to identify sources of within-season fitness variation among females and known-age males. Many males did not acquire a nest site, and many territorial males were unsuccessful in acquiring a mate. The likelihood that territorial males mated depended on several aspects of nest sites. Mated males of age three were larger than the average size of age-three males in the population. The mean sizes of age-four and age-five mated males were not different from the average of same-age males in the population. Thus, selection resulting from the acquisition of a mate favored large size among only age-three males. Timing of nest construction and breeding among territorial males was negatively related to male size and did not depend on male age after taking male size into account. Indirect evidence (numbers of eggs deposited in nests) suggests that the timing of spawning among females was also negatively related to female size. Fertility selection favored early reproduction within the season by males of all ages, but large male size was favored among only age-four males. The combined early breeding of fecund females and female mate choice of large males may explain the positive correlation between the size of age-four males and the number of eggs acquired. Despite large differences of female fecundity, however, the variance of relative mate number contributed about two times more than the variance of relative fertility among females to the total variance of relative fitness within each sex.     

The evolution of male mate choice in insects: a synthesis of ideas and evidence

Mate choice by males has been recognized at least since Darwin's time, but its phylogenetic distribution and effect on the evolution of female phenotypes remain poorly known. Moreover, the relative importance of factors thought to underlie the evolution of male mate choice (especially parental investment and mate quality variance) is still unresolved. Here I synthesize the empirical evidence and theory pertaining to the evolution of male mate choice and sex role reversal in insects, and examine the potential for male mating preferences to generate sexual selection on female phenotypes. Although male mate choice has received relatively little empirical study, the available evidence suggests that it is widespread among insects (and other animals). In addition to 'precopulatory' male mate choice, some insects exhibit 'cryptic' male mate choice, varying the amount of resources allocated to mating on the basis of female mate quality. As predicted by theory, the most commonly observed male mating preferences are those that tend to maximize a male's expected fertilization success from each mating. Such preferences tend to favour female phenotypes associated with high fecundity or reduced sperm competition intensity. Among insect species there is wide variation in mechanisms used by males to assess female mate quality, some of which (e.g. probing, antennating or repeatedly mounting the female) may be difficult to distinguish from copulatory courtship. According to theory, selection for male choosiness is an increasing function of mate quality variance and those reproductive costs that reduce, with each mating, the number of subsequent matings that a male can perform ('mating investment') Conversely, choosiness is constrained by the costs of mate search and assessment, in combination with the accuracy of assessment of potential mates and of the distribution of mate qualities. Stronger selection for male choosiness may also be expected in systems where female fitness increases with each copulation than in systems where female fitness peaks at a small number of matings. This theoretical framework is consistent with most of the empirical evidence. Furthermore, a variety of observed male mating preferences have the potential to exert sexual selection on female phenotypes. However, because male insects typically choose females based on phenotypic indicators of fecundity such as body size, and these are usually amenable to direct visual or tactile assessment, male mate choice often tends to reinforce stronger vectors of fecundity or viability selection, and seldom results in the evolution of female display traits. Research on orthopterans has shown that complete sex role reversal (i.e. males choosy, females competitive) can occur when male parental investment limits female fecundity and reduces the potential rate of reproduction of males sufficiently to produce a female-biased operational sex ratio. By contrast, many systems exhibiting partial sex role reversal (i.e. males choosy and competitive) are not associated with elevated levels of male parental investment, reduced male reproductive rates, or reduced male bias in the operational sex ratio. Instead, large female mate quality variance resulting from factors such as strong last-male sperm precedence or large variance in female fecundity may select for both male choosiness and competitiveness in such systems. Thus, partial and complete sex role reversal do not merely represent different points along a continuum of increasing male parental investment, but may evolve via different evolutionary pathways.     

Male size does not affect the strength of male mate choice for high-quality females in Drosophila melanogaster

Theory predicts that the strength of male mate choice should vary depending on male quality when higher-quality males receive greater fitness benefits from being choosy. This pattern extends to differences in male body size, with larger males often having stronger pre- and post-copulatory preferences than smaller males. We sought to determine whether large males and small males differ in the strength (or direction) of their preference for large, high-fecundity females using the fruit fly, Drosophila melanogaster. We measured male courtship preferences and mating duration to show that male body size had no impact on the strength of male mate choice; all males, regardless of their size, had equally strong preferences for large females. To understand the selective pressures shaping male mate choice in males of different sizes, we also measured the fitness benefits associated with preferring large females for both large and small males. Male body size did not affect the benefits that males received: large and small males were equally successful at mating with large females, received the same direct fitness benefits from mating with large females, and showed similar competitive fertilization success with large females. These findings provide insight into why the strength of male mate choice was not affected by male body size in this system. Our study highlights the importance of evaluating the benefits and costs of male mate choice across multiple males to predict when differences in male mate choice should occur.     

Behaviour before beauty: Signal weighting during mate selection in the butterfly Papilio polytes

Mating displays often contain multiple signals. Different combinations of these signals may be equally successful at attracting a mate, as environment and signal combination may influence relative signal weighting by choosy individuals. This variation in signal weighting among choosy individuals may facilitate the maintenance of polymorphic displays and signalling behaviour. One group of animals known for their polymorphic patterning are Batesian mimetic butterflies, where the interaction of sexual selection and predation pressures is hypothesized to influence the maintenance of polymorphic wing patterning and behaviour. Males in the female‐limited polymorphic Batesian mimetic butterfly Papilio polytes use female wing pattern and female activity levels when determining whom to court. They court stationary females with mimetic wing patterns more often than stationary females with non‐mimetic, male‐like wing patterns and active females more often than inactive females. It is unclear whether females modify their behaviour to increase (or decrease) their likelihood of receiving male courtship, or whether non‐mimetic females spend more time in cryptic environments than mimetic females, to compensate for their lack of mimicry‐driven predation protection (at the cost of decreased visibility to males). In addition, relative signal weighting of female wing pattern and activity to male mate selection is unknown. To address these questions, we conducted a series of observational studies of a polymorphic P. polytes population in a large butterfly enclosure. We found that males exclusively courted active females, irrespective of female wing pattern. However, males did court active non‐mimetic females significantly more often than expected given their relative abundance in the population. Females exhibited similar activity levels, and selected similar resting environments, irrespective of wing pattern. Our results suggest that male preference for non‐mimetic females may play an active role in the maintenance of the non‐mimetic female form in natural populations, where males are likely to be in the presence of active, as well as inactive, mimetic and non‐mimetic females.     

SIZE,SYMMETRY, AND SEXUAL SELECTION IN THE HOUSEFLY,MUSCA DOMESTICA

Relationships between measures of body size, asymmetry, courtship effort, and mating success were investigated in the housefly, Musca domestica (Diptera: Muscidae). A previous study indicated that both male and female flies with low fluctuating asymmetry enjoyed enhanced mating success. The aim of our investigations was to determine whether the greater success of symmetrical males is due to variation in male mating effort or to female choice and whether males exhibited mate choice. However, our study found directional rather than fluctuating asymmetry with both male and female flies having, on average, longer left wings than right. Also, asymmetry was not related to mating success in either sex. Rather, both males and females appeared to exhibit choice on the basis of the size of potential mates, with males preferring females with long bodies and females preferring heavy males. Possible benefits from choice of large mates are discussed. The initial mating strikes (in which the male leaps onto the back of the female) did not appear to be targeted according to female morphology, and their frequency did not vary according to male morphology. This indicates that mate choice by both sexes according to size probably occurs during the later stages of courtship, when the flies are in intimate contact. Possible reasons for the absence of choice according to asymmetry are discussed.     

Female mate choice and mate search tactics in a sex role reversed population of the peacock blenny Salaria pavo (Risso, 1810)

Behavioural observations were carried out on a sex role reversed population of the blenny Salaria pavo to investigate possible mate choice behaviour of the females. Females mated with relatively larger males, with a larger head crest, anal gland and genital papilla, which had more eggs in their nests and that courted the female. Thus, these male traits were potentially assessed by females when choosing their mates. In order to mate, females visited one to four males (eight females spawned with the first male they had visited and eight visited more than one male). The majority of the females spawned with the last male visited but three of them returned to mate with males visited previously (two with the penultimate visited male). Additionally, the outcome of the first visit of each female depended on the quality of the males: males that were accepted on this first visit had larger head crest than rejected males. Therefore, the mate searching model that best fitted the data was a threshold tactic that allowed the searching individual to return to any potential mate visited before, i.e. that allowed for complete recall. Moreover, three females returned to mate with males rejected earlier during the search, which indicates that they lowered their thresholds. These results suggest that females use a 'one step decision' tactic to search for mates. In this tactic, females mate with males that satisfy an adjustable threshold criterion, balancing the quality of the mates expected to find in the next step of the search and the effort of finding them.     

The role of female dominance hierarchies in the mating behaviour of mosquitofish

While studies of sexual selection focus primarily on female choice and male-male competition, males should also exert mate choice in order to maximize their reproductive success. We examined male mate choice in mosquitofish, Gambusia holbrooki, with respect to female size and female dominance. We found that the number of mating attempts made by a male was predicted by the dominance rank of females in a group, with dominant females attracting more mating attempts than subordinates. The number of mating attempts made by males was independent of the female size. The observed bias in the number of mating attempts towards dominant females may be driven either by straightforward male mate choice, since dominance and female fecundity are often closely related, or via the dominant females mediating male mating behaviour by restricting their access to subordinate females.     

Correlation of acoustic and visual signals in the cichlid fish, <Emphasis Type="Italic">Tramitichromis intermedius</Emphasis>

We investigated acoustic and visual communication concurrently in wild caught adult and captive-born, first generation offspring of the East African Rift Lake cichlid fish Tramitichromis intermedius. Only males emit sound during courtship. Sound production is always accompanied by quivering, but quiver behavior is not always accompanied by sound. This separation of quivering and sound supports the hypothesis that sound production is intentional serving a communicative role. As spawning nears, both sound production and quiver behavior increase. In terms of the ontogeny of sound production, the first observation of courtship occurs just days before the first spawning event and the first sound emission accompanies the first courtship activity. The accompaniment of quivering with sound as well as the escalation of the two behaviors with the approach of spawning follows similar patterns in wild caught and captive-born males. The tight correlation between behavior and sound production in both groups indicates their simultaneous performance plays an important role in reproduction. It is probable that the ability to produce sound and perform quiver behavior at the same time may be a measure of mate quality.     

Male and Female Soldier Beetles Relax Choice for Mate Quality Across Daily Courtship Periods

Mutual mate choice occurs when members of each sex will reject some potential mates in efforts to encounter better prospects later. The decision to reject may represent the interaction between mate preferences, mate availability, and temporal constraints. Theory predicts that mutual mate choice will favor relaxed choosiness as mate availability and time for courtship decline. We explored mutual mate choice in the soldier beetle, Chauliognathus pennsylvanicus (Cantharidae), where courtship consisted of males attempting to secure evasive females. We employed field observations, laboratory experiments, and stochastic simulations to investigate the decline in choosiness over the daily courtship period, during which individuals can mate at most once. We found that reproductive success of males and females increases with mate size and mating frequency. Females biased copulations toward larger mates by attempting to evade suitors, while males biased copulations by releasing the smaller females they capture. However, late in the day males and females may increase reproductive success by accepting rather than rejecting lower quality mates to maintain high mating rates. Stochastic simulations indicated that reproductive success, the product of mating frequency and mean mate size, was maximized in males and females by incrementally reducing mate standards across daily courtship periods. In the field, large males who rejected small females early in the daily courtship period rarely did so later. Large females used less effective evasive maneuvers later in the courtship period, resulting in copulations with progressively smaller males. These results support models of mutual mate choice that predict that individuals of high quality will maximize reproductive success by relaxing choosiness as the courtship period wanes.