Familiarity adds to attractiveness in matters of siskin mate choice

There is currently considerable controversy in evolutionary ecology revolving around whether social familiarity brings attraction when a female chooses a mate. The topic of familiarity is significant because by avoiding or preferring familiar individuals as mates, the potential for local adaptation may be reduced or favoured. The topic becomes even more interesting if we simultaneously analyse preferences for familiarity and sexual ornaments, because when familiarity influences female mating preferences, this could very significantly affect the strength of sexual selection on male ornamentation. Here, we have used mate-choice experiments in siskins Carduelis spinus to analyse how familiarity and patterns of ornamentation (i.e. the size of wing patches) interact to influence mating success. Our results show that females clearly prefer familiar individuals when choosing between familiar and unfamiliar males with similar-sized wing patches. Furthermore, when females were given the choice between a highly ornamented unfamiliar male and a less ornamented familiar male, half of the females still preferred the socially familiar birds as mates. Our finding suggests that male familiarity may be as important as sexual ornaments in affecting female behaviour in mate choice. Given that the potential for local adaptation may be favoured by preferring familiar individuals as mates, social familiarity as a mate-choice criterion may become a potential area of fruitful research on sympatric speciation processes.     

State-Dependent Mate-Assessment and Mate-Selection Behavior in Female Threespine Sticklebacks (Gasterosteus aculeatus, Gasterosteiformes: Gasterosteidae)

Most investigations of mate-choice have focused on the outcomes of mate-choice (i.e. which mates are chosen), and thus we generally know very little about how mates are chosen (i.e. how mates are found, assessed, and selected). Mate-choice by females has been shown to be dependent on the state of the female, with females being less selective when limited by time or energy. This result could be caused by changes in female mate-assessment or mate-selection behavior. We examined whether manipulations of time and energy affected the mate-choice behavior of female threespine stickleback ( Gasterosteus aculeatus ). We found that female mate-choice behavior, when not divided into stages, was affected by both of the manipulations. This matches previous findings. When we divided female courtship behavior into six stages, we found that the two manipulations affected different portions of the mate-choice process. The holding-time manipulation changed female behavior at the beginning and end of the mate-choice process and the swimming manipulation changed female behavior only at the end of the mate-choice process. Neither of the manipulations significantly affected female behavior in the middle portion of the mate-choice process. Thus, the mate-choice process appears to be composed of multiple state-dependent decisions. We discuss how a better mechanistic understanding of how female state affects female mate-choice behavior can produce testable predictions and provide a basis for investigating the evolution of mating systems.     

Male and female mate choice affects offspring quality in a sex-role-reversed pipefish.

Where both sexes invest substantially in offspring, both females and males should discriminate between potential partners when choosing mates. The degree of choosiness should relate to the costs of choice and to the potential benefits to be gained. We measured offspring quality from experimentally staged matings with preferred and non-preferred partners in a sex-role-reversed pipefish, Syngnathus typhle L. Here, a substantial male investment in offspring results in a lower potential reproductive rate in males than in females, and access to males limits female reproductive success rather than vice versa. Thus, males are choosier than females and females compete more intensely over mates than do males. Broods from preferred matings were superior at escaping predation, when either males or females were allowed to choose a partner. However, only 'choosing' females benefited in terms of faster-growing offspring. Our results have important implications for mate-choice research: here we show that even the more competitive and less choosy sex may contribute significantly to sexual selection through mate choice.     

Courting strategies and conflicts in a monogamous,biparental termite

In species where parental investment is extensive for both sexes, both males and females are predicted to exhibit choosiness when seeking their lifetime partners. Evidence is presented that both courting males and females are choosy in the wood-dwelling, biparental termite Zootermopsis nevadensis. There are, however, sex differences both in the method of mate rejection and in the mate-choice criteria. In particular, females are more likely than males to invite an extra suitor into the nest, whereas males are more likely than females to leave their nest and partner and seek a replacement elsewhere. Correlational analyses of adults show that head width is a mate-choice criterion used by females, whereas body mass and fat mass are used by males. Among males and females that sought replacement mates, those that had been rejected previously were more likely to end up paired with an adult that also had been rejected, compared with adults that had not been rejected. Additional findings reveal a rich repertoire of courting behaviours characterized by extensive intra- and intersexual conflict, including mate rejection, intrasexual combat, and even intrapair aggression.     

The evolution of mate choice and the potential for conflict between species and mate-quality recognition

Understanding how individuals select mates becomes complex when high-quality conspecifics resemble heterospecifics. Individuals facing such a situation may be unable to effectively identify both conspecifics (species recognition) and high-quality mates that can confer fitness benefits to the choosy individual or its offspring (mate-quality recognition). Here I suggest when a conflict may occur between species and mate-quality recognition, discuss the evolutionary consequences stemming from this conflict, and present a model of mate-preference evolution in response to heterospecifics. Determining how species and mate-quality recognition interact to shape mate-choice decisions is important for understanding the diversification of sexually selected traits among closely related taxonomic groups, the use of complex sensory systems for detecting mates, and seemingly inappropriate mate-choice decisions.     

Public Information Influences Sperm Transfer to Females in Sailfin Molly Males

In animals, including humans, the social environment can serve as a public information network in which individuals can gather public information about the quality of potential mates by observing conspecifics during sexual interactions. The observing individual itself is also a part of this information network. When recognized by the observed conspecifics as an audience, his/her presence could influence the sexual interaction between those individuals, because the observer might be considered as a potential mate or competitor. One of the most challenging questions in sexual selection to date is how the use of public information in the context of mate choice is linked to the fitness of individuals. Here, we could show that public information influences mate-choice behaviour in sailfin molly males, Poecilia latipinna, and influences the amount of sperm males transfer to a female partner. In the presence of an audience male, males spent less time with the previously preferred, larger of two females and significantly more time with the previously non-preferred, smaller female. When males could physically interact with a female and were faced with an audience male, three audience females or no audience, males transferred significantly more sperm to a female partner in the presence of an audience male than with female audience or no audience and spent less time courting his female partner. This is the first study showing that public information use turns into fitness investment, which is the crucial factor to understand the role of public information in the dynamic processes in sexual selection.     

Dynamics of House Sparrow Biparental Care: What Contexts Trigger Partial Compensation?

Nest attendance during incubation is characterized by an inequitable division of labor in house sparrows, Passer domesticus, with females spending more time at the nest than males. Previous research has shown that if male contributions are reduced experimentally via testosterone (T) implants, females compensate partially for those reductions, consistent with predictions from most models of negotiated biparental care. In this study, we attempted to identify the cues and contexts generating partial compensation, using data from both unmanipulated parents and pairs with T‐males. Both males and females of this species sometimes leave the nest before their mate returns to relieve them, and we found that these unrelieved departures by unmanipulated individuals occur when partners are on lengthy recesses. Females compensated partially for long male recesses by marginally extending their bouts; most females also slightly reduced their next recess. By contrast, when males left before their mate returned, they left earlier than when they waited for the female. Neither males nor females adjusted their recess lengths after returning to the nest and discovering that their partner was absent. More pronounced changes in nest attendance of unmanipulated parents occurred in the context of ‘visits’, when individuals returned to the nest but then left without relieving their mate. Such visits effectively prolonged the bout of the on‐duty partner and extended the visitor’s recess. Analyses of behavior of T‐males and their mates revealed that T‐males had significantly longer recesses than control males, and that their mates, in turn, had elevated rates of unrelieved departures. T‐males also visited their on‐duty mates more often than control males, whereas female visits to T‐males were rare. Collectively, the predicted changes in female nest attendance associated with lengthy male recesses and male and female visits account reasonably well for the compensatory response of females paired to T‐males. The majority of female compensation was attributable to changes in visit behavior, however, suggesting that much of the negotiation over nest attendance in this species occurs during direct interactions between mates.     

Sex differences in behavioral and corticosterone responses to mild stressors in ICR mice are altered by ovariectomy in peripubertal period

Among rodents, females are generally considered to be highly responsive in terms of emotionality under stressful conditions, and have higher corticosterone levels and activity. In this study, we examined sex differences in mice by evaluating anxiety behaviors and corticosterone responses to mild stressors. In our first experiment, we analyzed the behavioral and corticosterone responses to the elevated plus-maze test and open-field test in male and female mice, and compared sex differences. Principal component analysis (PCA) was used to investigate the correlation of these responses between males and females. The corticosterone level was higher in females under both basal and stressed conditions. In the behavioral response, higher locomotor activity was seen in females in the elevated plus-maze test. PCA showed little association among anxiety behavior, locomotor activity, and corticosterone secretion. In our second experiment, we examined the activational effects of sex steroids on the corticosterone response to the elevated plus-maze test by gonadectomizing male and female mice and using testosterone or estrogen capsules as hormonal replacements. Sex differences at the basal corticosterone level were not altered by the hormonal milieu in adults, however the higher corticosterone level of females in response to stress was diminished by ovariectomy, although replacement with neither testosterone nor estrogen had any effect. These results suggest that the sex difference in novelty exposure observed in the form of a greater hypothalamic-pituitary-adrenal (HPA) axis response in female ICR mice is controlled by ovary-derived factors in adults.     

Intrasexual copulation and mate discrimination in a population of Nodilittorina radiata (Gastropoda: Littorinidae)

Intrasexual copulation and mate discrimination by Nodilittorina radiata (Gastropoda: Littorinidae) were studied on a concrete breakwater at Hakodate Bay, southern Hokkaido, Japan. Intrasexual (male–male) copulations were observed in 4.7–21.1% of copulating pairs on the shore. As females were relatively larger than males and males copulated with females larger than themselves, we hypothesized that males choose potential mates larger than themselves. However, two male mates showed no significant size preference in intrasexual copulations, suggesting that males do not choose relatively larger individuals as mates. In a laboratory mate-choice experiment, male N. radiata preferred to mate with females, indicating precopulatory sex identification. They copulated with males, however, at the frequency of 37%, perhaps because of sex misidentification.     

Mated pairs of owl monkeys (Aotus nancymaae) exhibit sex differences in response to unfamiliar male and female conspecifics

In socially monogamous species, mate‐guarding could be a reproductive strategy that benefits both males and females, especially when males contribute to parental care. By actively guarding mates, males may reduce their chances of being cuckolded, whereas females that mate‐guard may reduce the likelihood that their mates will desert them or acquire additional mates, and hence limit or reduce paternal care of offspring. Owl monkeys (Aotus spp.) are socially monogamous with biparental care of young and, hence, potential beneficiaries of mate‐guarding. We presented mated pairs of captive owl monkeys (A. nancymaae) with unfamiliar male and female conspecifics, to determine if either member of the pair exhibits intraspecific aggression toward an intruder or stays close to its mate, behaviors indicative of mate‐guarding. Male mates were more responsible for the maintenance of close proximity between mates than females. Male mates also exhibited elevated levels of behavior that signify arousal when presented with a male conspecific. These responses by mated male owl monkeys are consistent with patterns that may help prevent cuckoldry. Am. J. Primatol. 72:942–950, 2010. © 2010 Wiley‐Liss, Inc.     

Sex-Specific Audience Effect in the Context of Mate Choice in Zebra Finches

Animals observing conspecifics during mate choice can gain additional information about potential mates. However, the presence of an observer, if detected by the observed individuals, can influence the nature of the behavior of the observed individuals, called audience effect. In zebra finches (Taeniopygia guttata castanotis), domesticated males show an audience effect during mate choice. However, whether male and female descendants of the wild form show an audience effect during mate choice is unknown. Therefore, we conducted an experiment where male and female focal birds could choose between two distinctive phenotypes of the opposite sex, an artificially adorned stimulus bird with a red feather on the forehead and an unadorned stimulus bird, two times consecutively, once without an audience and once with an audience bird (same sex as test bird). Males showed an audience effect when an audience male was present and spent more time with adorned and less time with unadorned females compared to when there was no audience present. The change in time spent with the respective stimulus females was positively correlated with the time that the audience male spent in front of its cage close to the focal male. Females showed no change in mate choice when an audience female was present, but their motivation to associate with both stimulus males decreased. In a control for mate-choice consistency there was no audience in either test. Here, both focal females and focal males chose consistently without a change in choosing motivation. Our results showed that there is an audience effect on mate choice in zebra finches and that the response to a same-sex audience was sex-specific.     

Elevated stress hormone diminishes the strength of female preferences for acoustic signals in the green treefrog

Mate selection can be stressful; time spent searching for mates can increase predation risk and/or decrease food consumption, resulting in elevated stress hormone levels. Both high predation risk and low food availability are often associated with increased variation in mate choice by females, but it is not clear whether stress hormone levels contribute to such variation in female behavior. We examined how the stress hormone corticosterone (CORT) affects female preferences for acoustic signals in the green treefrog, Hyla cinerea. Specifically, we assessed whether CORT administration affects female preferences for call rate — an acoustic feature that is typically under directional selection via mate choice by females in most anurans and other species that communicate using acoustic signals. Using a dual speaker playback paradigm, we show that females that were administered higher doses of CORT were less likely to choose male advertisement calls broadcast at high rates. Neither CORT dose nor level was related to the latency of female phonotactic responses, suggesting that elevated CORT does not influence the motivation to mate. Results were also not related to circulating sex steroids (i.e., progesterone, androgens or estradiol) that have traditionally been the focus of studies examining the hormonal basis for variation in female mate choice. Our results thus indicate that elevated CORT levels decrease the strength of female preferences for acoustic signals.     

In the eye of the beholder: visual mate choice lateralization in a polymorphic songbird

Birds choose mates on the basis of colour, song and body size, but little is known about the mechanisms underlying these mating decisions. Reports that zebra finches prefer to view mates with the right eye during courtship, and that immediate early gene expression associated with courtship behaviour is lateralized in their left hemisphere suggest that visual mate choice itself may be lateralized. To test this hypothesis, we used the Gouldian finch, a polymorphic species in which individuals exhibit strong, adaptive visual preferences for mates of their own head colour. Black males were tested in a mate-choice apparatus under three eye conditions: left-monocular, right-monocular and binocular. We found that black male preference for black females is so strongly lateralized in the right-eye/left-hemisphere system that if the right eye is unavailable, males are unable to respond preferentially, not only to males and females of the same morph, but also to the strikingly dissimilar female morphs. Courtship singing is consistent with these lateralized mate preferences; more black males sing to black females when using their right eye than when using their left. Beauty, therefore, is in the right eye of the beholder for these songbirds, providing, to our knowledge, the first demonstration of visual mate choice lateralization.     

HETEROGENIC COPULATORY BEHAVIOUR PRODUCES NON-RANDOM MATING IN LABORATORY TRIALS IN THE LAND SNAIL HELIX ASPERSA MULLER

This study reports the results of mate-choice experiments betweenresident and non-resident individuals of the simultaneous hermaphonteland snail Helix aspersa. Snails from different sites differedin their mating proclivity, which resulted in non-random matingin laboratory mate-choice tests. Those snails with the highermating propensity therefore tended to mate with their own typeand tended to be chosen as partner because they were also activelyseeking mates. Keeping snails under crowded conditions did noteffect a lasting influence on mating behaviour in laboratorytests, despite the decline in copulatory behaviour under crowdedfield conditions. (Received 7 November 1994; accepted 31 August 1995)     

Female preference for multiple condition-dependent components of a sexually selected signal

Theoretical models explain the evolution of multi-cue mate-choice decisions from a trade-off between benefits owing to improved assessment of potential mates and costs linked to the use of multiple signals. However, empirical support for these basic assumptions is lacking. In field crickets (Gryllus campestris) we experimentally investigated the female preference to variation in two key components of the male calling song: carrier frequency and chirp rate. Previous studies have revealed carrier frequency and chirp rate as reliable indicators of male quality that reflect past condition and current condition, respectively. In a two-way choice experiment, females significantly preferred test songs of lower carrier frequency and higher chirp rate, but prioritized the carrier frequency over the chirp rate. Hence, the static long-term indicator of mate quality was weighted more than the dynamic short-term one. Our results thus indicate that females integrate information from independent condition-dependent cues to discriminate between available males in mate-choice decisions.     

Fitness costs of female choosiness are low in a socially monogamous songbird

Female mate choice is thought to be responsible for the evolution of many extravagant male ornaments and displays, but the costs of being too selective may hinder the evolution of choosiness. Selection against choosiness may be particularly strong in socially monogamous mating systems, because females may end up without a partner and forego reproduction, especially when many females prefer the same few partners (frequency-dependent selection). Here, we quantify the fitness costs of having mating preferences that are difficult to satisfy, by manipulating the availability of preferred males. We capitalize on the recent discovery that female zebra finches (Taeniopygia guttata) prefer males of familiar song dialect. We measured female fitness in captive breeding colonies in which one-third of females were given ample opportunity to choose a mate of their preferred dialect (two-thirds of all males; “relaxed competition”), while two-thirds of the females had to compete over a limited pool of mates they preferred (one-third of all males; “high competition”). As expected, social pairings were strongly assortative with regard to song dialect. In the high-competition group, 26% of the females remained unpaired, yet they still obtained relatively high fitness by using brood parasitism as an alternative reproductive tactic. Another 31% of high-competition females paired disassortatively for song dialect. These females showed increased levels of extra-pair paternity, mostly with same-dialect males as sires, suggesting that preferences were not abolished after social pairing. However, females that paired disassortatively for song dialect did not have lower reproductive success. Overall, females in the high-competition group reached equal fitness to those that experienced relaxed competition. Our study suggests that alternative reproductive tactics such as egg dumping can help overcome the frequency-dependent costs of being selective in a monogamous mating system, thereby facilitating the evolution of female choosiness.

Being highly selective in partner choice may be problematic, because widely preferred mates are rapidly claimed. However, this study of the socially monogamous zebra finch reveals that females have evolved effective ways of coping with this situation.     

Pigment-based skin colour in the blue-footed booby: an honest signal of current condition used by females to adjust reproductive investment

In monogamous species, the value of present reproduction is affected by the current condition of the mate, and females may use male ornaments to evaluate his condition and adjust their level of investment according. Many animals display colour in fleshy structures which may be accurate indicators of quality due to their potentially rapid response to changes in condition. Here we show that in the blue-footed booby, Sula nebouxii, male foot colour is structurally (collagen arrays) and pigment based. In 48 h foot colour became duller when males were food deprived and brighter when they were re-fed with fresh fish. Variation of dietary carotenoids induced comparable changes in cell-mediated immune function and foot colour, suggesting that carotenoid-pigmentation reveals the immunological state of individuals. These results suggest that pigment-based foot colour is a rapid honest signal of current condition. In a second experiment, we found that rapid variation in male foot colour caused parallel variation in female reproductive investment. One day after the first egg was laid we captured the males and modified the foot colour of experimental males with a non-toxic and water resistant duller blue intensive make-up, mimicking males in low condition. Females decreased the size of their second eggs, relative to the second egg of control females, when the feet of their mates were experimentally duller. Since brood reduction in this species is related to size differences between brood mates at hatching, by laying lighter second eggs females are facilitating brood reduction. Our data indicate that blue-footed booby females are continuously evaluating their mates and can perform rapid adjustments of reproductive investment by using dynamic sexual traits. We suggest that this fine-tuned adjustment may be widespread in socially monogamous animals.     

Sexual selection: copycat mating in birds

Female zebra finches may be influenced by the choices of other females when selecting mates, challenging the view that mate-choice copying should not occur in species with biparental care.     

Sex-specific responses to sexual familiarity,and the role of olfaction in Drosophila

Studies of mating preferences have largely neglected the potential effects of individuals encountering their previous mates (‘directly sexually familiar’), or new mates that share similarities to previous mates, e.g. from the same family and/or environment (‘phenotypically sexually familiar’). Here, we show that male and female Drosophila melanogaster respond to the direct and phenotypic sexual familiarity of potential mates in fundamentally different ways. We exposed a single focal male or female to two potential partners. In the first experiment, one potential partner was novel (not previously encountered) and one was directly familiar (their previous mate); in the second experiment, one potential partner was novel (unrelated, and from a different environment from the previous mate) and one was phenotypically familiar (from the same family and rearing environment as the previous mate). We found that males preferentially courted novel females over directly or phenotypically familiar females. By contrast, females displayed a weak preference for directly and phenotypically familiar males over novel males. Sex-specific responses to the familiarity of potential mates were significantly weaker or absent in Orco¹ mutants, which lack a co-receptor essential for olfaction, indicating a role for olfactory cues in mate choice over novelty. Collectively, our results show that direct and phenotypic sexual familiarity is detected through olfactory cues and play an important role in sex-specific sexual behaviour.     

Sex differences in adrenal function in the lizard Cnemidophorus sexlineatus: II. Responses to acute stress in the laboratory.

Circulating concentrations of plasma corticosterone and gonadal steroids were measured in intact and gonadectomized male and female lizards (Cnemidophorus sexlineatus) following acute stress (handling) in the laboratory. There was a significant increase in plasma corticosterone after stress. Whereas intact females exhibited greater concentrations of corticosterone relative to intact males, ovariectomized females exhibited lower concentrations of corticosterone relative to castrated males. In addition to sex differences in corticosterone responses to gonadectomy, progesterone was elevated by stress in both intact and ovariectomized females but not in males. Corticosterone adjusted for castration and handling in males was negatively correlated with the plasma androgen level. The adrenal responsiveness of males to acute stress may be attenuated by androgens presumably secreted by the testis. Not only does adrenal function influence reproduction, but adrenal responses differ between males and females, and appear to be influenced by the gonadal axis. The sex differences in adrenal responses to stress likely reflect different reproductive strategies and nutritional requirements of males and females during the breeding season.