The efficacy of female choice in chimpanzees of the Taï Forest, Côte d’Ivoire

Male–male competition has historically been considered the major force driving sexual selection. However, female choice and inter-sexual conflict are increasingly recognized as important influences affecting differential mating and reproductive success. Many females exhibit preferences for particular males; however, male strategies may conflict with females’ ability to obtain their mate preferences. To influence paternity, females must affect both (1) whether or not sexual interactions occur, particularly during the periovulatory period (POP) and (2) the outcome of sexual interactions. This study focuses on the effectiveness of female choice in wild chimpanzees (Pan troglodytes verus). Over 2,600 h of data were collected on two habituated chimpanzee communities in the Taï National Park, Côte d’Ivoire. Female mate preferences were measured by quantifying proceptive and resistance behavior toward males in both the periovulatory period and non-POP phases of estrus. The efficacy of female preference was measured both (1) by measuring success rates of female proceptivity and resistance behaviors and (2) by determining how well measures of female mate preference (proceptivity and resistance rates) predict male mating success. Though male chimpanzees are clearly dominant to females, the results indicate that females could effectively resist male solicitations and, in most cases, unwanted copulations were averted. Both female proceptivity and resistance rates correlate (positively and inversely, respectively) with male mating success in POP. Outside POP, female proceptivity rates corresponded with male mating success, but resistance rates did not. Males (irrespective of rank) that were preferred by females obtained higher mating success compared to other males during the POP, suggesting that females were effective in their mate choice and that, despite clear male dominance, female choice influences paternity in wild chimpanzees.     

Male coloration and chick condition in blue-footed booby: a cross-fostering experiment

Sexual selection models suggest that female choice is based on male traits that indicate their genetic or environmental condition, consequently enhancing her reproductive success by direct or indirect benefits. We investigated the relationship between male foot colour and offspring condition in the blue-footed booby, a socially monogamous seabird, with conspicuous and variably condition-dependent coloured feet that are selected by females. In a cross-fostering experiment, we found that chick condition was related to the foot colour of the foster father and, to some extent, to the foot colour of the genetic father; thus overall, the fathers sexual ornamentation (genetic and foster) explained 32% of variance of chick condition. These data suggest that foot colour, a dynamic sexually selected trait, is mostly a signal of parental contribution. In species in which males provide parental care, females may choose mates with higher parental ability. Overall, our data suggest that colourful integuments are honest signals of parental ability.Communicated by J. Graves     

Sexual conflict over sperm ejection in monogamous pairs of kittiwakes<Emphasis Type="Italic"> Rissa tridactyla</Emphasis>

Socially monogamous partners suffer conflicting interests concerning various aspects of reproduction such as parental care, copulation and fertilization. Female black-legged kittiwakes commonly eject their mates' sperm immediately following copulations. Because sperm ejection reduces male sperm competitiveness and paternity assurance, males and females have conflicting interests as regards sperm ejection. Males whose mates ejected their sperm at least once remained longer on their mates' backs after the last insemination which apparently prevented the females from ejecting sperm. These results suggest that compelling females to retain their sperm may be a previously unidentified tactic employed by males to assure their paternity. Females tried to prevent their mates from witnessing sperm ejection by ejecting sperm after their mates departed from the nest. Females were more likely to eject sperm when they terminated the copulations by unbalancing the male. The conflict over sperm ejection was related to the ability of the females to end the copulations which covaried with the body mass of their mates. These findings suggest that conflicts in monogamous pairs also exist over the disposition of sperm.Communicated by C.R. Brown     

The tactics of mutual mate choice and competitive search

A model of mutual mate choice is described, formulated as a dynamic game, which yields predictions about mating behaviour under the influence of time constraints, choice costs and competition for mates. These variables were examined because they may result in a change in the distribution of qualities among unmated individuals of both sexes over the course of the breeding season. The model predicts that mutual choice gives rise to assortative mating, although high costs of choice and/or inaccurate assessment both lead to lower overall correlations between the qualities (or the attractiveness) of mates. When all individuals are present from the start of the breeding season, the correlation between the qualities of individuals pairing at a given time declines throughout the season, so that mates are more closely matched among individuals who pair early than among those who pair late (and extra-pair copulation may thus be more common among the latter). Delayed arrival of lower-quality individuals may, however, lead to an increase in this correlation with time during the early part of the season. The mean quality of unmated males and females declines over time, because more attractive individuals tend to mate sooner. As a result of this decline, and because of time constraints, superior individuals become less choosy as the season progresses. If choice is costly, however, then inferior individuals become more selective with time during the early part of the season, and the level of choosiness peaks later for such individuals. Received: 28 March 1996 / Accepted after revision: 21 September 1996     

Mate preferences in <Emphasis Type="Italic">Drosophila</Emphasis> infected with <Emphasis Type="Italic">Wolbachia</Emphasis>?

The maternally inherited bacterium Wolbachia pipientis generates strong reproductive incompatibilities between uninfected females and infected males (cytoplasmic incompatibility), significantly reducing both female and male reproductive success. Such fitness costs are thought to place selective pressure on hosts to evolve pre-copulatory preferences for mating with compatible mates, thereby enabling them to avoid the reproductive incompatibilities associated with Wolbachia. Therefore, uninfected females are predicted to prefer mating with uninfected males, whereas infected males are predicted to prefer mating with infected females. Despite these predictions, previous investigations of pre-copulatory mate preferences in Wolbachia-manipulated Drosophila have not found evidence of female preference for uninfected or compatible males. However, none of these studies utilised a design where focal individuals are provided with a simple choice in a relatively non-competitive situation. We examined both female and male pre-copulatory mate preference based on mate infection status in Drosophila simulans and D. melanogaster using simple choice assays involving between 30–50 replicates per treatment. Although we found no evidence of female pre-copulatory mate preferences in either species, male D. simulans exhibited some preference for mating with females of the same infection status. However, this preference was not evident when we repeated the experiment to confirm this finding. Consequently, we conclude that neither male nor female D. melanogaster and D. simulans exhibit significant Wolbachia-associated pre-copulatory mate preferences.     

The effect of rearing environment on blue structural coloration of eastern bluebirds (<Emphasis Type="Italic">Sialia sialis</Emphasis>)

We used a brood-size manipulation to test the effect of rearing environment on structural coloration of feathers grown by eastern bluebird (Sialia sialis) nestlings. Ultraviolet (UV)-blue structural coloration has been shown to be sexually selected in this species. Our experimental design took advantage of the growth of UV-blue wing feathers in nestlings that are retained as part of the first nuptial plumage. We cross-fostered nestlings to create enlarged and reduced broods with the purpose of manipulating parental feeding rates and measured the effect on nestling growth and plumage coloration. Brood size influenced feeding rates to offspring, but the effect varied with season. In general, male nestlings reared in reduced broods were fed more often, weighed more, and displayed brighter structural plumage compared to nestlings reared in enlarged broods. Female nestlings appeared to experience less adverse affects of brood enlargement, and we did not detect an effect of brood-size manipulation on the plumage coloration of female nestlings. Measures of plumage coloration in both males and females, however, were correlated to hatching date and nestling mass during feather development. These data provide empirical evidence that environmental quality can influence the development of the blue structural coloration of feathers and that males may be more sensitive to environmental fluctuations than females.     

Copulatory plug displacement and prolonged copulation in the Iberian rock lizard (Lacerta monticola)

Male Iberian rock lizards (Lacerta monticola) produce copulatory plugs that adhere firmly inside the female cloaca and occlude both oviducts. These plugs do not prevent rival male insemination, as they neither reduce female attractiveness or receptivity to rival males nor do they function as chastity belts. Prior to copulation, males bite various regions of the female body, including the cloacal region. A previous plug in the female cloaca is expelled only after rival male intromission. We hypothesized that: (1) such male pre-copulatory behaviours function to loosen plug adherence to the female cloaca, thereby facilitating intromission, and that (2) the hemipenis plays a role in displacing a previous plug prior to the delivery of a new plug. Neither of these hypotheses was supported. Instead, our results indicate that rival males can intromit the hemipenis past a previous plug in the female cloaca and deliver their own plug underneath it. Consequently, previous plugs are pushed away from the oviductal openings and even dislodged from the female cloaca. Copulation duration was determined both by the time used by males to deliver a plug and by the fact that males prolonged copulation beyond plug delivery. There seemed to be sexual conflict over prolonged copulation, which was resolved by the male/female head-length ratio. The adaptive value of Iberian rock lizard copulatory plugs and prolonged copulation in Iberian rock lizards is discussed in the context of sperm competition.Communicated by S. Downes     

Bat serenades—complex courtship songs of the sac-winged bat (<Emphasis Type="Italic">Saccopteryx bilineata</Emphasis>)

Vocalisations of many songbirds, anurans, and insects are shaped by sexual selection. Males acoustically compete for territories, and females choose their mates by means of male courtship songs. In courtship, richness and complexity of elements are often favoured characters. Only a few examples of complex songs are known in mammals. Males of the harem-polygynous sac-winged bat (Saccopteryx bilineata, Emballonuridae) have an uncommonly complex vocal repertoire, and different song types of males are used in the context of territorial defence and in courting females. We classified the daytime vocalisations of 16 male S. bilineata from a colony in Costa Rica, both on the basis of their acoustical properties and the social context in which they occurred. Seven vocalisation types were differentiated: echolocation pulses, barks, chatter, whistles, screeches, territorial songs and courtship songs. Territorial songs were short, rather stereotyped and not obviously directed towards a certain conspecific. They appear to be of importance in male competition for harem territories, in which females roost during the day. Courtship songs were exclusively observed when males displayed towards a female; they were long and complex, and consisted of highly variable elements (calls). We classified the calls in courtship songs of six males into call types, based on acoustical properties, mainly spectral purity and duration. Four call types are described in detail: trills, noise-bursts, short tonal calls, and quasi constant frequency calls. Twelve parameter values were extracted from the most common call type, the trill. Discriminant function analysis of trills showed that different males had different repertoires. This could allow females to use trill parameters for recognition of individual males and thus for mate choice.Communicated by G. Wilkinson     

Male signaling behavior and sexual selection in a wolf spider (Araneae: Lycosidae): a test for dual functions

Male signaling behaviors are often studied in a single context but may serve multiple functions (e.g., in male–male competition and female mate choice). We examined the issue of dual function male signals in a wolf spider species Schizocosa ocreata (Hentz) that displays the same species-specific signaling behaviors in both male–male and male–female contexts. These signaling behaviors have been described as either aggression or courtship according to the context observed. We tested the possibility of dual functions by comparing the relationship between behaviors and outcome of male–male contests (winner/loser) and male–female mating encounters (mating success). Frequency, rate, and mean duration of signaling behaviors did not vary with outcome of male–male contests, which appears instead to be based upon relative size and body mass. Winners of contests had significantly greater body mass than losers, and greater mass relative to opponents was significantly associated with probability of winning. Overall, signaling rates were much higher in male–female interactions than in male–male contests and were higher for males that successfully mated than for those that did not mate. Mean duration of some male displays was also greater for males that successfully mated. However, male size was not associated with probability of mating. Taken together, results suggest an intersexual selection context for the current function of male signals in these wolf spiders and that increased display vigor is associated with male mating success.     

Male influence on sex allocation in the parasitoid wasp Nasonia vitripennis

Sex allocation is an important reproductive decision for parents. However, it is often assumed that females have substantial control over sex allocation decisions, and this is particularly true in haplodiploid insects, in which females apparently determine sex by deciding whether to fertilise an egg (and produce a diploid daughter) or not (and produce a haploid son). Mechanisms by which males may influence sex allocation are not so straightforward, and their potential influence on sex ratios has been somewhat neglected. Here, we test whether males influence offspring sex ratios in the parasitoid wasp Nasonia vitripennis. We show that some of the variation in observed sex ratios can be attributed to males when comparing the affect of male strain on sex ratio. We did not find among-male variation in sex ratio with a less powerful experiment using males from only one strain or an effect of male mating environment. Our data suggest that males can influence female sex ratios and contribute to the variation around the sex ratios optimal for females. However, the influence is not large, suggesting that females have more influence on sex allocation than do males. We conclude by considering whether male influences on sex ratio represent differences in male reproductive competence or deliberate attempts by males to increase their fitness by influencing daughter production.