Mate copying versus preference for actively courting males by female Japanese medaka (Oryzias latipes)

We determined whether female Japanese medaka (Oryzias laiipes)copied the choice of other females or independently preferredactively courting males. We allowed focal females to observeand subsequently choose between a male that courted and potentiallyspawned with a receptive female and a male that courted andwas rejected by an unreceptive female. When the receptive femaledid not spawn, the focal female preferred the male with thehigher courtship rate; whereas when the receptive female spawned,the focal female preferred the spawning male. Our results suggestthat female medaka prefer actively courting males, unless theyhave the opportunity to copy the mate choice of another female.     

Mate choice copying as public information

We outline a framework that views mate choice copying as public information. In this framework, all individuals assess the quality of potential mates. Individuals can benefit by copying when they cannot discriminate differences in potential mates, as copying can result in better discrimination. This framework predicts that the discrimination ability of individuals will strongly determine the frequency of copying behaviour observed: individuals with poor discrimination ability should often copy, whereas individuals with superior discrimination ability should rarely copy. Copying behaviour may occur in a wide variety of taxa but only be observed when individuals are presented with difficult discrimination tasks.     

Polygyny and its fitness consequences for primary and secondary female pied flycatchers

In polygynous species with biparental care, the amount of paternal support often varies considerably. In the pied flycatcher (Ficedula hypoleuca), females mated with monogamous males receive more male assistance during the nestling phase than females mated with bigynous males, as the latter have to share their mates with another female. Bigynous males, however, give more support to their primary broods than to their secondary broods. Using a long-term dataset (31 years), the present study revealed that direct reproductive success, i.e. number of fledglings, was lower in females that mated with bigynous males, especially in secondary broods without male assistance, than in females that mated with monogamous males. Secondary broods with male assistance were more affected than primary broods. Female survival was independent of mating status. In primary broods, a delayed compensation for inferior direct reproductive success was found in terms of the number of grandoffspring, a phenomenon that did not occur in secondary broods. Delayed compensation in primary broods refers to indirect effects, i.e. good genes. According to the sexy son hypothesis, genetically superior (i.e. sexy) males may have sons with a higher number of broods belonging to a polygynous breeding status than do sons from broods with a monogamous father. This was indeed the case for sons descending from primary broods, but not for sons descending from secondary broods.     

Female pied flycatchers trade between male quality and mating status in mate choice

According to mate choice theory, females should consider both male quality and mating status when choosing a mate. In birds, strong experimental evidence indicates that females prefer males with elaborate traits. No comparable evidence exists to determine whether females take male mating status into account or how they may trade between male quality and male mating status. We studied mate choice of female pied flycatchers (Ficedula hypoleuca) in outdoor aviaries where the effect of territory quality could be eliminated and where we could control which males were mated and which were unmated. We used male plumage colour as our measure of male quality. In the aviaries, focal females could easily compare males and assess their plumage colour and mating status, and resident females were prevented from attacking prospecting females because of separation in different compartments. The study provided evidence for a trade-off in mate choice. Females may compromise by choosing an already mated male if he is more brightly coloured and, presumably, of higher quality than available unmated males. The study did not support the idea that polygyny is based on male deception of females, but the results were consistent with the female aggression hypothesis.     

Evolution of female preference for younger males

Previous theoretical work has suggested that females should prefer to mate with older males, as older males should have higher fitness than the average fitness of the cohort into which they were born. However, studies in humans and model organisms have shown that as males age, they accumulate deleterious mutations in their germ-line at an ever-increasing rate, thereby reducing the quality of genes passed on to the next generation. Thus, older males may produce relatively poor-quality offspring. To better understand how male age influences female mate preference and offspring quality, we used a genetic algorithm model to study the effect of age-related increases in male genetic load on female mate preference. When we incorporate age-related increases in mutation load in males into our model, we find that females evolve a preference for younger males. Females in this model could determine a male's age, but not his inherited genotype nor his mutation load. Nevertheless, females evolved age-preferences that led them to mate with males that had low mutation loads, but showed no preference for males with respect to their somatic quality. These results suggest that germ-line quality, rather than somatic quality, should be the focus of female preference in good genes models.     

Degree of male ornamentation affects female preference for conspecific versus heterospecific males.

Several studies have shown female preference for conspecific males with the attached artificial ornaments of more elaborate heterospecifics. However, preference for heterospecifics under natural conditions is relatively rare. We tested what factors affect behavioural mechanisms of species isolation using three species of estrildid finch (genus Uraeginthus) that occur in both sympatry and allopatry. These finches differ in degree of sexual dimorphism; male ornamentation; behavioural and morphological similarity; and phylogenetic distance. Paired mate-choice trials were used in which females were presented with a conspecific and heterospecific male to test which of the above between-species differences best predicted the degree of premating isolation. The three species differed in the degree of species-specific mate preference shown. Females from the brighter two species discriminated against dull males, independently of sympatry-allopatry, similarity and phylogenetic distance. Females from the dull species reacted to conspecific males and brighter heterospecific males equally strongly, independently of similarity and phylogenetic distance. In contrast to previous studies, an equal preference for heterospecific and conspecific males was found under natural conditions. It is suggested that differences between closely related species in male ornamentation affect the likelihood that premating isolation will occur due to the fact that sexual selection tends to drive preferences for exaggerated ornamentation.     

On the cost of searching for a mate in female pied flycatchers Ficedula hypoleuca

Female pied flycatchers, Ficedula hypoleuca, were trapped in one area and released in another a few kilometres away, where the positions of all available nest sites and males were known beforehand. Many of the females moved only a short distance before mating, settling after about 2 (0–6) days in early spring and about 1 day later on. The length of the premating period was negatively correlated with female body weight and prevailing air temperature, indicating that the females were subject to an energy constraint when searching. The premating period was longer for females that settled with an alreadymated male than for those mating with an unmated male. The significance of the results is discussed in relation to the evolution of avian mating systems, and of male behaviour and plumage colour. Competition for a mate, rather than for food, may explain the spacing of males (territoriality).     

Reproductive effort and T-lymphocyte cell-mediated immunocompetence in female pied flycatchers Ficedula hypoleuca

The physiological mechanism underlying the cost of reproduction may consist of immunodepression caused by increased parental effort. Here, we report effects of experimental manipulation of clutch size on T-lymphocyte cell-mediated immune response in female pied flycatchers, Ficedula hypoleuca. Parents with reduced broods provisioned at lower rates than those caring for control and enlarged broods three days after hatching. Parents caring for enlarged broods provisioned nests at higher rates 13 days after chick hatching than those feeding control and reduced broods. Females with enlarged broods weighed less than females with control or reduced broods. No effect of experimental treatment on nestling mass and size was found. The response to the injection of phytohaemagglutinin in the wing-web of females decreased with increasing brood size and with increasing provisioning rate when the chicks were three days old, when controlling for the negative effect of female mass on response. The T-lymphocyte cell-mediated response decreased from the reduced to the control, and from this to the enlarged group, when controlling for female mass. This effect of experimental manipulation of clutch size was significant and consistent with a trade-off between maternal effort and immunocompetence.     

Handicapped males and extrapair paternity in pied flycatchers: a study using microsatellite markers

We report an attempt to induce extrapair copulations and fertilizations in a species with a low intensity of sperm competition, the pied flycatcher Ficedula hypoleuca. Shortly after pair formation males were made less attractive to females by removing certain wing and tail feathers. Earlier research has shown that this manipulation reduces a male's pairing success. The idea was to test whether females mated to such males (N= 9) were more likely to obtain extrapair fertilizations than females mated to unmanipulated controls (N= 9). Paternity testing was carried out on all 98 young in the 18 broods, using a set of six microsatellite markers isolated from the species. Extrapair fertilizations were revealed in only three (17%) broods; two broods of handicapped males and one of a control male. A total of seven (7%) offspring were not genetically related to their putative father, a level which agrees well with results of other studies of this and other populations. We conclude that there was no evidence to suggest that the fertilization pattern was altered by the experimental manipulation. One reason for the lack of response could be that female mate choice in this species is based on male phenotypic, and not genotypic, quality.     

Experimentally activated immune defence in female pied flycatchers results in reduced breeding success

Traditional explanations for the negative fitness consequences of parasitism have focused on the direct pathogenic effects of infectious agents. However, because of the high selection pressure by the parasites, immune defences are likely to be costly and trade off with other fitness-related traits, such as reproductive effort. In a field experiment, we immunized breeding female flycatchers with non-pathogenic antigens (diphtheria-tetanus vaccine), which excluded the direct negative effects of parasites, in order to test the consequences of activated immune defence on hosts' investment in reproduction and self-maintenance. Immunized females decreased their feeding effort and investment in self-maintenance (rectrix regrowth) and had lower reproductive output (fledgling quality and number) than control females injected with saline. Our results reveal the phenotypic cost of immune defence by showing that an activated immune system per se can lower the host's breeding success. This may be caused by an energetic or nutritional trade-off between immune function and physical workload when feeding young or be an adaptive response to 'infection' to avoid physiological disorders such as oxidative stress and immunopathology.     

Prey choice and nestling hunger: an experiment with pied flycatchers,Ficedula hypoleuca

Prey choice variation was studied in a multiple-prey loader, the pied flycatcher, Ficedula hypoleuca, by manipulating the body condition of the adults and the hunger level of the nestlings. Parents with high and low body weight brought back similar prey when they were feeding an experimental brood of five hungry nestlings, but parents with high body weight fed the brood at a higher frequency than those with low body weight. Parents with high body weight took more small prey when they were feeding five hungry nestlings than when they were feeding two well-fed nestlings. The latter result is consistent with a recent model of central place foraging, which takes into account the costs of staying away from the nest. Alternatively, the parents may have changed the currency for energy maximization, and hence the criteria for prey choice; e.g. a shift from net to gross energy maximization would imply a less selective prey choice.     

Cryptic female preference for colorful males in guppies

Cryptic female choice (CFC) refers to female-mediated processes occurring during or after copulation that result in biased sperm use in favor of preferred or compatible males. Despite recent empirical support for this hypothesis, evidence that CFC contributes towards the evolution of male body ornaments, in the same way that precopulatory female choice does, is currently lacking. Here, we tested the possibility that CFC selects for increased male attractiveness in the guppy Poecilia reticulata, a freshwater fish exhibiting internal fertilization. Specifically, we examined whether females are able to manipulate the number of sperm transferred or retained at copulation in favor of relatively attractive males. In support of this prediction, we found that following solicited copulations the number of sperm inseminated is influenced exclusively by the female's perception of relative male coloration, independent of any direct manipulation of males themselves. Because females prefer brightly colored males during precopulatory mate choice, our finding that colorful males are also favored as a consequence of enhanced insemination success indicates that cryptic female choice can reinforce precopulatory preferences for extravagant male ornaments.     

Mate choice in lekking sage grouse revisited: the roles of vocal display, female site fidelity, and copying

In lekking sage grouse (Centrocercus urophasianus), femalesexhibit relatively unanimous mate choice for particular males,but a satisfactory explanation for this unanimity has been elusive.We present analyses of mating distributions from two leks over4 years that provide evidence for female choice based on differencesin vocal display performance of males, the locations at whichhens mated in the previous year, and the choices of other females(copying). The unanimity of female choice varied markedly amongleks and years in correlation with changes in the mean numbersof hens that mated at the same time and hence the opportunityto copy. The results confirm that hens assess phenotypic traitsof males directly but also indicate that the secondary tacticsof site fidelity and copying are often important componentsof female choice. The occurrence of these secondary tacticshas three implications: the variance in mating success amonglek males will be a poor predictor of the intensity of sexualselection on specific traits; female preferences may generatemore clustered dispersions of displaying males than predictedby hotspot settlement models; and direct assessment of malesby females may be difficult or costly, a conclusion that supportsadaptive models of sexual selection over a nonadaptive Fisherianprocess. [Behav Ecol 1991;2:165–180]     

Mate choice copying and conspecific cueing in Japanese quail, Coturnix coturnix japonica

In four experiments, we examined the effects on the affiliative preferences of 'focal' female Japanese quail given the opportunity to watch a conspecific male interact with a 'model' female. Experiments were conducted in three, 10-min phases: (1) a pretest, during which a 'focal' female chose between two males; (2) an observation phase, when each focal female watched the male she had spent less time near during the pretest (her 'nonpreferred' male) interact with a 'model' quail; and (3) a post-test, during which each focal female again chose between her nonpreferred and preferred males. Focal females increased their preferences for nonpreferred males after seeing them together with a model female (but not a model male), even if the nonpreferred male and model female were separated by an opaque barrier that prevented them from interacting. A focal female's preference for the end of the enclosure containing her nonpreferred male was not increased when she either watched him court a concealed model female or watched a model female that was being courted by him. Taken together, the present results suggest that a simple tendency for females to approach areas where they have previously seen a male and female quail, in preference to locations where they have seen only a male quail, can explain some of the effect of watching a nonpreferred male mate on a female's tendency to affiliate with him. However, focal females also showed enhanced preferences for nonpreferred males they had seen mating after we both moved those males and controlled for effects of transposition. Thus, processes akin to both 'mate choice copying' and 'conspecific cueing' remain viable explanations for the increase in a focal female quail's tendency to affiliate with a male she watched mate with another female. Copyright 1999 The Association for the Study of Animal Behaviour.     

Mate choice decision rules: Trait synergisms and preference shifts

An important and understudied question in sexual selection is how females evaluate information from multiple secondary sexual traits (SSTs), particularly when expression of traits is phenotypically uncorrelated. We performed mate choice experiments on zebra finches (Taeniopygia guttata castanotis Gould) to evaluate two hypotheses: preference shifts (obstacles to choice using one trait increase chooser reliance on others) and trait synergisms (choice based on the sum/product of two or more independently varying traits). The first experiment, which employed males raised on diets that impact SST expression, supported the trait synergism hypothesis: overall, male pairing success was best predicted by synergisms involving beak color and cheek patch size. Results did not support the preference shift hypothesis. Results of a follow‐up experiment that included males reared on a single diet, and in which male beak color and cheek patch size were manipulated, were also consistent with the trait synergism hypothesis. Results have implications for understanding the long‐term persistence of multiple SSTs in populations and for the measurement of repeatability and heritability of mate preferences.     

Evidence of an emerging female preference for an artificial male trait and the potential for spread via mate choice copying in Poecilia latipinna

The initial purpose of the project described herein was to assess the preference of female Poecilia latipinna for an artificial novel male trait—an orange‐colored distal fringe added to the caudal fin of an otherwise wild‐type conspecific. Analysis of the preliminary data revealed consistent individual differences in the strength of female preference for either orange‐tailed or wild‐type males. This finding inspired the study's second aim—to evaluate whether the preference for orange‐tailed males observed among a subset of females could spread via mate choice copying to others in the population that initially preferred wild‐type males. Two experiments and a control were conducted wherein females were simultaneously presented with an orange‐tailed and a wild‐type dummy male using a standard dichotomous choice design. In the first experiment, female preference was assessed on two separate occasions in order to characterize the variability and consistency in preference for orange‐tailed versus wild‐type males. The second experiment addressed mate choice copying: Female preference was again assessed on two separate occasions, but involved pairing a model female with the non‐preferred male for a period of time between preference tests. A third set of control tests were conducted using the same protocol as the copying experiment except that subject females were unable to see the model paired with the non‐preferred male. Results showed that, although females collectively preferred neither the orange‐tailed nor the wild‐type dummy male in the first round of preference tests, the majority showed relatively strong individual preferences. The subset of females that preferred the orange‐tailed over the wild‐type male in the first round of testing all maintained their preferences in the second round whether or not they had observed a model in association with the non‐preferred wild‐type male between tests. However, females that preferred the wild type over the orange male in the first round of testing copied the model's choice of the non‐preferred orange‐tailed male in their second round of preference testing. These results highlight the importance of recognizing the likelihood that only a subset of females will express a preference as it first emerges within a population. In such instances, the preference may not be detected at the population level—a point frequently overlooked in studies of mate choice. Additionally, these data highlight the importance of assessing the preferences of individual females and their capacity to drive evolutionary change within populations. Lastly, this study offers evidence of a possible mechanism by which a novel male trait might spread via mate choice copying by exploiting an emerging sensory bias within a subset of females in the population.     

Are incubation costs in female pied flycatchers expressed in humoral immune responsiveness or breeding success?

Although clutch size variation has been a key target for studies of avian life history theory, most empirical work has only focused on the ability of parents to raise their altricial young. In this study, we test the hypothesis that costs incurred during incubation may be an additional factor constraining clutch size in altricial birds. In the pied flycatcher (Ficedula hypoleuca), we manipulated the incubation effort of the female by enlarging and reducing clutch sizes. To manipulate incubation effort only, the original clutch sizes were restored shortly after hatching. We found that fledging success was lower among broods whose clutches were enlarged during incubation. There was, however, no effect of manipulation on female body condition or on their ability to mount a humoral immune response to diphtheria or tetanus toxoid during the incubation or nestling provisioning period. Instead, we found that the original clutch size was related to the immune response so that females with seven eggs had significantly lower primary antibody responses against tetanus compared to those with six eggs. Our results suggest that incubating females are not willing to jeopardise their own condition and immune function, but instead pay the costs of incubating a larger clutch by lower offspring production. The results support the view that costs of producing and incubating eggs may be substantial and hence that these costs are likely to contribute to shaping the optimal clutch size in altricial birds.