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PubMed1997

Mate choice and competition for mates in the boat-tailed grackle

Behavioural studies have implicated both female choice of mates and male competition for access to mates as proximate mechanisms of sexual selection. Few studies have examined the interactions between these mechanisms in a natural setting. In this study, I explored how dominance interactions between male boat-tailed grackles, Quiscalus majordetermine the mating success of males and how the behaviour of female boat-tailed grackles influences this process. Male grackles defended colonies of females and performed courtship displays to females that were building nests. These conspicuous displays incited dominance interactions between males, with the result that dominant males interrupted subordinate males' attempts to copulate. Female grackles were receptive only to males that performed courtship displays, but their receptivity to males did not vary with male dominance rank or tail length. Females were more likely to be receptive in a colony than away from a colony, and females became receptive asynchronously during the breeding season. The timing and spacing of females' receptivity to males permitted dominance interactions between males to determine male mating success. By establishing the conditions for male competition, females indirectly chose high-ranking males. Recent studies have emphasized discrimination among potential mates as a behavioural mechanism for mate choice. The results reported here, however, demonstrate that other aspects of females' behaviour can produce mate choice, indirectly rather than directly.1997The Association for the Study of Animal Behaviour

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PubMed1997

Behavioural correlates of monogamy in the noisy miner, Manorina melanocephala

Mating behaviour of female cooperatively breeding noisy miners was examined. Dow & Whitmore (1990, Cooperative Breeding in Birds (Ed. by P. B. Stacey & W. D. Koenig), pp. 559-592, Cambridge: Cambridge University Press) suggested that female noisy miners mate promiscuously to recruit males as helpers to their nests, and that the benefit of doing so might be (1) increased genetic variability of their broods or (2) increased survival of their offspring as a direct result of multi-male care. Multilocus DNA profiling has since shown that 96.5% of nestlings resulted from monogamous matings and that extra-group and multiple paternity within broods were rare (Poldmaa et al. 1995, Behav. Ecol. Sociobiol.37, 137-143). In this study, strong behavioural correlates of monogamy were found. A breeding female associated more often with only one male in her social group, and most of the female's sexual behaviours were directed towards this male. Females were observed copulating repeatedly with the same male, but never with more than one male. Home ranges of breeding females rarely overlapped with each other, but home ranges of breeding males overlapped greatly. Furthermore, a greater percentage of a female's home range was shared with that of her genetic mate than with those of other males. Thus, behavioural evidence is consistent with the genetic evidence that noisy miners mate monogamously in some populations.1997The Association for the Study of Animal Behaviour

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PubMed1997

The adaptive value of 'friendships' to female baboons: experimental and observational evidence

Lactating female baboons, Papio cynocephalusoften maintain close associations with particular males. There are at least three proposed benefits of 'friendships' to females: (1) male protection against potentially infanticidal males; (2) male protection against harassment by dominant females; (3) male attachment to an infant that develops into future care of juveniles. These hypotheses were examined in a population of chacma baboons, P. c. ursinusin which male infanticide accounted for at least 38% of infant mortality. Almost all mothers of young infants formed strong bonds with one or two males with whom they had copulated during the cycle in which they conceived their infants. Females were primarily responsible for maintaining friendships during lactation, but they terminated these relationships if their infants died. In playbacks of females' screams, male friends responded more strongly than control males. They also responded more strongly to the screams of female friends than to the screams of control females. Following an infant's death, however, male friends responded less strongly than control males to the same females' screams. Finally, male friends responded more strongly than control males to playback sequences in which female screams were combined with the threat vocalizations of a potentially infanticidal alpha male, but not when female screams were combined with the threat calls of a non-infanticidal male or the alpha female. Both observations and experiments suggest that the benefits of friendships to females derive from the protection of their infants against infanticide.1997The Association for the Study of Animal Behaviour

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PubMed1997

Behaviourally mediated sexual selection: characteristics of successful male black grouse

Recent studies of lekking animals suggest that a suite of characters may be favoured by sexual selection. Examples of such traits are high survival, increased androgen levels, territory features and morphological characters including exaggerated morphological ornaments. Here we argue that such selection is often mediated by behavioural differences and we use results from a field study of lekking black grouse, Tetrao tetrixas an example of our argument. In the absence of females, males display a range of stereotyped behaviours including vocalizations, visual displays and fighting. When females attend the lek, the behavioural repertoire of the males becomes more limited. Time budget analyses reveal that in the vast majority of cases, males in the presence of females perform only three types of behaviour: a vocal display called rookooing; a courtship behaviour called circling; and fighting. This suggests that female preference could be based on male courtship and fighting behaviour while females visit individual male territories and that displays not used in the presence of females could be ruled out as important for female preference. Sexual selection in black grouse, however, is a complex interplay between male-male competition and female choice and therefore female preference is not the only determinant of male success. Successful males were more often involved in fights in the absence of females on the lek and defended territories that were larger than expected. Therefore, we hypothesize that differences in male fighting ability result in some males occupying relatively large territories at the centre of the leks. Relatively large territories seem to be needed for successful courtship. Therefore behavioural differences mediate differences in male copulation success both through female preference and male-male competition.

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PubMed1997

Parenting and potency: alternative routes to reproductive success in male Mongolian gerbils

Adult male Mongolian gerbils, Meriones unguiculatusgestated in intrauterine positions between two female fetuses (2F males) are less likely than are adult males gestated between two male fetuses (2M males) to impregnate strange female gerbils with whom they are paired. The reduced copulatory success of 2F males is correlated with both lower circulating levels of and reduced sensitivity to testosterone. We asked whether 2F male gerbils compensated for their reduced copulatory success by increasing their parental effort. 2F male gerbils engaged in less sexual activity with their mates, but were more frequently in contact with pups than were 2M males, huddling over the young when their mates were absent from the nest. Although there were no differences in rates of survival or growth of pups reared by pairs consisting of a female and either a 2M or 2F male, mates of 2F males delivered significantly more pups as a consequence of copulations occurring during postpartum oestrus than did either mates of 2M males or females rearing young alone. We interpreted these results as consistent with Ketterson & Nolan's (1992, Am. Nat. (Supplement)140, 533-562) hypothesis of a testosterone-mediated trade-off between investment in sexual and parental behaviours.1997The Association for the Study of Animal Behaviour

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PubMed1997

Sexual selection constrained by internal fertilization in the livebearing fish Xenotoca eiseni

Fish of the family Goodeidae have an advanced form of viviparity but males lack a specialized copulatory organ. Goodeids show reduced sexual-size dimorphism compared with the other livebearing families of the order Cyprinodontiformes. I investigated some mechanisms of sexual selection acting on body size in the goodeid fish Xenotoca eiseni. Both males and females strongly prefer mates of their own size. Comparison of mating activities in pairs with various degrees of size difference between males and females showed that matched pairs copulated more successfully. Similar mate preference in the two sexes thus appears to be the consequence of the primitive method of internal fertilization that requires the partners to be exactly synchronized during sperm transfer. Competition for access to a female was intense and body size determined the hierarchy in a small group. However, unless the size of the female was close to that of the dominant male, assortative mate preferences prevailed and the large-male advantage in competition was offset. Reduced size dimorphism in X. eiseni and in other goodeids may be explained by constraints on the action of sexual selection imposed by the need for effective fertilization.Copyright 1997 The Association for the Study of Animal BehaviourCopyright 1997The Association for the Study of Animal Behaviour.

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PubMed1997

Courtship feeding in tree crickets increases insemination and female reproductive life span

Courtship feeding in the majority of insects may influence female reproductive patterns either directly, through effects of the gift material, or indirectly, through correlated effects of prolonged copulation and larger ejaculates. This distinction is important because the cause of changes in fecundity may influence patterns of the allocation of resources between the sexes, with implications for the intensity of sexual selection and magnitude of sexual conflict. I show that post-copulatory feeding on the secretions of a gland on the metanotum of male Oecanthus nigricornis. Walker correlates with oviposition and affects the number of sperm remaining within the spermatophore. Manipulations of gland feeding and insemination duration showed that changes in fecundity are due to the gift rather than the ejaculate. Metanotal gland feeding increased female fecundity by increasing reproductive life span without significantly increasing oviposition rate. These changes in reproduction were directly due to the gift itself. Although gland feeding was positively correlated with the duration of insemination and thus the number of sperm transferred from the spermatophore to the female, experimentally prolonging or reducing insemination had no significant effect on reproductive life span. Male phenotype was also associated with female fecundity but in this case the effect was caused by an increase in the oviposition rate of females that mated with relatively large males. Male size had no significant effect on female reproductive life span, suggesting that its effect is not simply due to a quantitative increase in gift size. Three other measures of male phenotype, fluctuating asymmetry, condition (i.e. size-standardized wet body mass) and age, had no significant effects on female reproduction.Copyright 1997 The Association for the Study of Animal BehaviourCopyright 1997The Association for the Study of Animal Behaviour.

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PubMed1997

Antennal asymmetry and sexual selection in a cerambycid beetle.

Cerambycid beetles have exaggerated antennae that are usually sexually size-dimorphic. We investigated the relationship between antenna morphology and sexual selection in the species Stenurella melanura (L.) in which males on average have antennae that are 13% longer than those of females. Males and females aggregate at flowers near oviposition sites for feeding during June-August. We sampled both copulating and single individuals at these sites. Fluctuating asymmetry (a measure of developmental instability) in antennae was considerably larger than in tibia and elytra and males had larger degrees of asymmetry in their antennae than females. Mated individuals did not differ from unmated individuals with respect to any of three size variables, but antennal asymmetry was smaller in mated individuals of both sexes. When two males were released with a female on a flower, males with symmetric antennae more often won the fight over the female than expected by chance. When two females and a male were released on a flower, the male more often preferred the female with more symmetric antennae than expected by chance. These results suggest that antennal symmetry, but not length, is currently under sexual selection.Copyright 1997 The Association for the Study of Animal Behaviour

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PubMed1998

No relationship between territory size and the risk of cuckoldry in birds.

It has been suggested that male birds adjust their territory size in order to prevent potential intruders from gaining extra-pair copulations. The risk of cuckoldry is supposed to be highest when the distance between a female and the neighbouring males is shortest. This paper describes the variation in territory size of the chiffchaff, Phylloscopus collybita, in relation to the breeding cycle. Contrary to the risk of cuckoldry hypothesis, chiffchaff territories were larger prior to the fertile period of the females and at a minimal size during the fertile period. A review of the literature shows little, if any, evidence of a peak in territory size during the fertile period of the females for most species studied. It is suggested that territoriality is in need of an operational definition. Without such a definition, it is difficult to make and test predictions about the adaptive basis of variation in territory size. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

Mate-choice copying in Japanese quail, Coturnix coturnix japonica

We performed four experiments to examine effects on the mate choices of female Japanese quail, Coturnix coturnix japonica, of observing a male mate with another female. Each experiment was conducted in three phases: (1) a pre-test during which subject females were allowed to choose between two males with which to affiliate; (2) an observation phase, in which subject females either watched or did not watch the male they had spent less time near during the pre-test (their 'non-preferred' male) copulate with a 'model' female; and (3) a post-test when subject females again chose between non-preferred and preferred males. Only females that had watched their non-preferred male mate with a model female during the observation phase spent significantly more time affiliating with him during the post-test than they had during the pre-test. Watching mating did not change females' criteria for choosing males, and non-preferred males that had mated recently were no more attractive to females than were non-preferred males that had not done so, unless subject females actually observed the mating take place. The results were consistent with the hypothesis that female quail copy one another's mate choices. Copyright 1998 The Association for the Study of Animal Behaviour Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

Two-note syllables in canary songs elicit high levels of sexual display

Male canaries, Serinus canaria, sing a special phrase ('A') that elicits very high levels of sexual display in conspecific females. This phrase is characterized by the repetition of a complex but brief two-note syllable. We tested the sexual responsiveness of female canaries to these A phrases, extracted from eight male repertoires. Five of the phrases elicited very high levels of copulation solicitation displays in the females. We suggest that the females may use the very rapid temporal patterning of the distinct notes in these two-note syllables to assess male quality. These syllables may be an honest indicator of a male's condition and may thus attract and arouse females. Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

Tibial coloration, fluctuating asymmetry and female choice behaviour in the damselfly Platycypha caligata.

The territorial damselfly Platycypha caligata (Odontata: Chlorocyphidae) has a courtship behaviour where males wave the white anterior surface of all six laterally enlarged tibiae at females. I experimentally altered this white tibial surface using black paint to determine the effect on male behaviour of a 25% reduction in area, or an increase in asymmetry between the left and right side of the body. I collected behavioural data on courtship, mating and fighting for males already holding territories. Neither a reduction in the area nor an increase in asymmetry of tibial whiteness affected male mating rate, courtship rate or fighting behaviour. These manipulations also had no significant effect on the daily presence at the study site. Males whose tibial whiteness was experimentally removed also showed no decrease in mating rate or change in fighting behaviour while territorial. The complete removal of tibial whiteness did, however, lead to a significant reduction in daily presence, possibly due to a reduced ability to acquire or hold a territory. There was no relationship between natural levels of asymmetry in tibial whiteness and mating rate, courting rate or fighting behaviour for males with territories. However, the natural area of tibial whiteness was significantly positively related to both mean male mating rate and copulation duration for territorial males. This result suggests that a phenotypic correlate of area of tibial whiteness, probably body size, is sexually selected through female choice among males that already hold territories.Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

Male parental effort and paternity in a variable mating system

Recent theoretical models suggest that males may respond to changes in paternity by adjusting their parental effort. Male response will depend on the availability of reliable paternity cues and the relative costs and benefits of parental effort to the male (i.e. its effect on the survival of young and alternative mating opportunities). Males breeding in pairs may be constrained because reductions in male parental effort are unlikely to be compensated for by the female and thus the survival of both related and unrelated young may decrease. In contrast, males breeding in cooperative groups (i.e. with helpers or co-breeders) may not have this constraint if other individuals in the group compensate for reductions in male parental effort. White-browed scrubwrens, Sericornis frontalis, breed in pairs and cooperative groups, typically with one female and two males (alpha and beta). We found that male parental effort was related positively to paternity for beta males, but not for alpha or pair males. Alpha males had paternity in all broods and always fed young. In contrast, beta males often had no paternity and sometimes did not feed young. Time spent near the fertile female was not an accurate predictor of the percentage of young sired in a brood, but it was a good predictor of having sired young in a brood. Our results are consistent with the idea that male parental effort is allocated according to whether or not the male copulated with the female. We suggest that the relationship between male parental effort and paternity may vary among cooperatively breeding species depending on the type and availability of cues to a male's paternity. Copyright 1998 The Association for the Study of Animal Behaviour Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

Mating behaviour in the cellar spider, Pholcus phalangioides, indicates sperm mixing.

In insects and spiders, the pattern of sperm priority is often attributed to the shape of the spermathecae and should entail marked consequences for mating behaviour. Since last-male priority is assumed to occur in haplogyne spiders such as the cellar spider, females of this species are predicted to be more attractive to males shortly before, than shortly after, egg laying and males may guard females after copulation until oviposition. To test these predictions, I individually marked spiders of a natural population and recorded their position and the distance between potential mating partners twice a day over 100 days. The distance between female and male was taken as a measure of the female's attractiveness. The behaviour of cellar spider males was not in accordance with the predictions; females were visited throughout the observation period with no significant increase in attractiveness before egg laying and there was no evidence for mate guarding. However, female attractiveness was correlated with female size, which was correlated with the number of eggs laid. Behaviour and genital morphology suggest sperm mixing occurs in this species. This is discussed in the light of conflicting data on sperm priority. Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

Sperm allocation in the simultaneously hermaphroditic land snail Arianta arbustorum.

To test the idea that individuals of the simultaneously hermaphroditic land snail Arianta arbustorum can control the number of spermatozoa in their spermatophores, we investigated whether they differentially release sperm to virgin or nonvirgin partners with respect to the potential risk of sperm competition in a given mating. The number of sperm transferred ranged from 802 620 to 3 968 800 (X= 2 185 100; N=91), but was related neither to the mating history of the partner nor to copulation duration. This indicates that individuals of A. arbustorum are not able to adjust sperm expenditure to the mating history of the partner. Furthermore, the number of sperm transferred was correlated neither with the size of the donor nor with the size of the recipient. It has been proposed that the sexual conflict between the two genders in simultaneous hermaphrodites could be resolved by gamete trading. Theory predicts that sperm trading should occur in hermaphrodites in which the female role controls fertilization, for example in gastropods with a gametolytic gland and/or sperm storage such as A. arbustorum. To see whether sperm trading occurs, we also examined whether individuals of A. arbustorum adjust the number of sperm they release to the number they receive from their mating partner. There was a high degree of reciprocity in spermatophore transfer: in 45 of the 46 mating pairs investigated both partners delivered a spermatophore that contained spermatozoa. The numbers of sperm transferred by the two mating partners were not correlated, however. This indicates that sperm trading does not occur in this simultaneously hermaphroditic land snail. Copyright 1998 The Association for the Study of Animal Behaviour.

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PubMed1998

The risk of sperm competition and the evolution of sperm heteromorphism.

Members of the Drosophila obscura species group exhibit sperm heteromorphism in which males simultaneously produce two different morphologies of sperm, short and long. Short sperm represent at least 50% of the ejaculate in several species but do not function in fertilization and thus, the evolutionary significance of this phenomenon is unknown. Selective pressures associated with the risk of sperm competition have been suggested to explain the maintenance of sperm heteromorphism. Here I test: (1) whether males alter their behaviour or ejaculate characteristics in response to the risk of sperm competition, and (2) whether short, nonfertilizing sperm serve as 'cheap filler' in the female reproductive tract, thereby delaying female receptivity to subsequent matings. Males did not alter tactics based on the risk of sperm competition; copulation durations of males mated to nonvirgin females were unexpectedly shorter than when both sexes were virgin and, contrary to sperm competition predictions, males did not alter the ratio of fertilizing:nonfertilizing sperm relative to female mating status or female age. Short sperm had a small, if any, role in influencing female remating behaviour. The number and proportion of short sperm present in sperm storage organs did not differ between nonvirgin receptive and nonvirgin nonreceptive females. The proportion of short sperm present in the ventral receptacle, however, was lower in receptive than nonreceptive females. Remating behaviour was strongly linked to oviposition patterns. Nonvirgin receptive females oviposited more eggs than nonreceptive females, and female remating interval was positively related to both the number of eggs and progeny produced. Although, oviposition parameters are related to fertilization and thus, the use of long sperm, nonvirgin receptive and nonreceptive females did not predictably differ in the number or proportion of long sperm in storage. These results suggest oviposition per se is probably more important than sperm in determining female receptivity and that sperm heteromorphism may play a marginal, if any, role in affecting female remating. (c) 1998 The Association for the Study of Animal Behaviour.

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PubMed1999

Individual differences in den maintenance effort in a communally dwelling mammal: the Eurasian badger.

Group living has potential costs in terms of relative fitness for individuals that invest effort in activities providing general benefit, if other competing individuals exploit those activities and accrue similar benefits at no cost. We examined the roles of individual badgers, Meles meles, in the den maintenance activities of digging and bedding collection at their communal setts. Twenty per cent of adults and yearlings were responsible for 60-90% of the observed digging and bedding collection effort. Overall males tended to dig more than females, while durations of bedding collection were similar. Among adult and yearling males and females, individuals with a high percentage of days observed at the sett (high site fidelity) performed more digging and collected more bedding than transients and badgers of low site fidelity. Males of high status (large, mature, frequently copulating individuals) were more likely to dig than males of low status. Principal component analysis indicated negligibly low correlation between status and site fidelity for males. We hypothesize that while highly resident adult females benefit from extending the sett to avoid direct reproductive competition, males of high status and site fidelity might extend the sett to encourage receptive breeding females in their home group to stay and/or to improve survivorship of sired litters. Other categories of individual depend on the sett for shelter but, perhaps having less to gain from extending it, adopt a less active role in sett maintenance. Copyright 1999 The Association for the Study of Animal Behaviour.

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PubMed1999

Optimal copula duration in yellow dung flies: effects of female size and egg content.

We examine data on copula duration in dung flies, Scatophaga stercoraria, in relation to female phenotype. We use a marginal value theorem approach based on the plausible mechanisms of sperm competition to predict the effect of female variation on optimal copula duration, t *, from the male perspective. Future fertilizations are expected to have a trivial effect on t * with fully gravid females, but an increasing relative effect on t * towards completion of oviposition. t * is expected to be affected by female size because of variation in (1) a female's egg content, which increases the maximum egg gain available from a mating, and (2) the female reproductive tract, which affects the rate at which sperm are displaced. In fully gravid females, t * was not dependent on egg number variation, but showed a positive relation with egg content in females that had laid a varying proportion of their mature egg load at the time of mating, and were therefore not fully gravid. Our models predict that if a male can estimate egg content only by the distension of a female's abdomen, t * should increase in a similar way to that seen with 'take-over' females. We predict t * for fully gravid females by assuming that males can monitor female size. The data showed that sperm displacement rate decreased, and average egg content increased, with female size. Under two models for a sperm displacement mechanism, one (which assumes indirect displacement at a rate proportional to the increase in spermathecal volume) predicts the observed relation between t * and female size almost exactly. Small males copulated for longer than large males (as predicted and reported previously). Copyright 1999 The Association for the Study of Animal Behaviour.

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