Costs and consequences of variation in the size of ruff leks

Summary We studied 13 ruff leks in a small region on the island of Gotland (Sweden) to investigate the effect of lek size on the costs and benefits of lekking for individual males. Male ruffs occur in two behaviourally and morphologically distinct forms, independents (residents plus marginals) and satellites, whose costs and benefits we have assessed separately. These ruff leks had from 1–10 resident (territory-holding) males and were visited daily by satellites, marginals and females from 5–25 May, when most copulations occurred. We used the average number of independent males, counted during censuses taken every 5 min during 2-h observation periods at each lek, as an index of mean lek size. Per independent male, the numbers of both satellites and females increased significantly with mean lek size. Female arrival rate and attendance (total female-minutes) also increased significantly with mean lek size as did the average per capita rate of mating success for resident males (that of satellites was not quite significant). Thus, the dispersion of both of these male categories did not appear to fit an ideal free distribution with respect to mating success. In addition, the number of independent-independent fights per independent and the rate of satellite-resident dyad formation per resident increased significantly with mean lek size. These results suggest that ruffs on larger leks enjoy higher mating success than those on smaller leks but also that costs increase with lek size. We suggest that independent males distribute themselves so as to maximize their own net benefits and that this factor can account for both the occurrence of ruff leks and the variation in their size. Correspondence to: J. Höglund     

Active mate choice at cock-of-the-rock leks: tactics of sampling and comparison

Summary The importance of active mate choice as a component of sexual selection remains controversial, despite recent studies identifying traits that correlate with male mating success. We analyzed the sampling sequences of individual female Guianan cock-of-the-rock, providing quantitative documentation of active female choice in this lekbreeding species. We compared observed sampling patterns with null models of random female movement and of movement weighted by the observed distribution of male success. The courts actually visited by individual females were significantly more clumped and centrally located than predicted by computer simulations of either random or weighted movement. Contrary to simplified hypotheses of female choice, hen cock-of-the-rock were not limited either to sequential comparisons or to threshold decision rules when selecting mates. Instead, they repeatedly sampled a subset of potential mates, using the pool-comparison tactic. Within this pool, females preferentially mated with the males ranked highest in terms of total courtship visits received, and rejected low-ranking males. Our results suggest complex interactions between patterns of female sampling and male dispersion in lek mating systems, and also provide insights into the constraints on female sampling in lek species.     

Correlates of male mating success in the ruff Philomachus pugnax,a lekking shorebird

Summary Male ruffs (Philomachus pugnax), a lekking shorebird, can generally be divided into two morphs according to behavior and plumage coloration. Predominantly dark-colored, independent male ruffs defend small territories on a lek, whereas lighter colored satellite males are non-territorial and less site-faithful to a particular lek. The traits associated with the mating success of independent male ruffs were studied at two leks during two seasons on the island of Öland, Sweden in May and June of 1985 and 1987. Using multivariate analyses, three characteristics were found to be significantly related to mating success: high frequency of visits by satellites to an independent male's residence, consistency of lek attendance, and low rates of aggressive behavior. In contrast, mating success was unrelated to the degree of darkness of the independent male nuptial plumage, territory location on the lek, or rate of courtship displays. The use of multivariate analyses helped to resolve conflicting conclusions from previous studies which employed simple statistical analyses, or none at all. Experimental manipulations are suggested which will help to further determine the influence of female mate choice in this lekking system.     

Females prefer larger leks: field experiments with ruffs (Philomachus pugnax)

Summary Preference by females for choosing mates at male aggregations has been hypothesized as the primary selective pressure favoring the formation of leks, but alternative hypotheses account for lek formation without invoking female preference. Observational studies to determine whether male mating success increases with lek size, as predicted under the female preference hypothesis, have produced inconsistent results, possibly due to covariation of lek size with other variables or to male-male or intersexual conflict over lek size. We tested whether females prefer larger leks in a field experiment with ruffs (Philomachus pugnax), a lekking sandpiper, in which male group size, composition, and location were controlled. Wild females chose the larger of two adjacent groups often enough such that males in larger groups had significantly higher per capita rates of female visitation (Table 3). Such behavior would probably lead to higher per male mating rates at larger leks, which is generally considered a necessary condition for female choice to select for lek display (Fig. 2). Lek size in nature will reflect both female preference for larger leks and competition among males, which may favor smaller lek size. All else being equal, however, female ruffs preferred to visit larger groups strongly enough to maintain lekking by males.     

Sexual selection in a monomorphic lek-breeding bird: correlates of male mating success in the great snipe Gallinago media

Summary In the lek-breeding great snipe, male morphology, behaviour, and territory features were recorded for individually marked birds on two adjacent leks. Partial correlation sshowed that male mating success, expressed as the number of female solicitations and copulations, was negatively correlated with the distance of a display territory to the lek center and positively correlated with the number of displays per unit time given by a male. No other variables were directly correlated with male matin success. Thus, central males obtain more matings than peripheral males and successful males display more per unit time than do less successful males, independently of position on the lek. Central males were found to be older than peripheral ones and were present more often on the lek. Furthermore, central males had a larger number of white tail feathers, which are usea as visual signals in the displays, but this may be explained by the fact that these males were older. It is suggested that male great snipe are subject to sexual selection mainly in behavioural and vocal cues and that this may explain the absence of size and plumage dimorphism in this species.     

Extra-pair copulations in a lek: the secondary mating system of monogamous razorbills

Summary I studied the mating strategies of razorbills Alca torda, a monogamous colonial seabird, during 1987–1989 in Wales, U.K. The outstanding feature of the study population's mating system was the performance of most copulations in mating arenas outside the colony. Females visited the arenas and sometimes accepted extra-pair copulations (EPCs), and males aggressively competed for EPCs. During the fertilizable period of most females, the arenas resembled leks because they contained no resources except mates, and males contributed only sperm to extra-pair females. Typical of leks, the operational sex ratio was strongly male-biased, and male mating success was highly skewed. To examine the potential for sexual selection to operate in this system, I correlated male EPC success with variables that could be associated with male-male competition and/or female choice. The frequencies of three behaviors (interference of copulation attempts, fights won against other males, and EPC attempts), accounted for 62% of the variance in EPC success and were strongly intercorrelated, with interference explaining most of the variance in a multivariate test. EPC success was not correlated with body size, age, paired status or either of two estimates of the time spent in the arena. The hypothesis that male EPC success was determined by active female choice was tested by examining the relative success (EPCs per attempt) of males. Relative success was not correlated with any of the three behaviors associated with absolute success, or with age, body size or attendance, suggesting that male-male competition, mainly in the form of copulation interference, is the principal correlate of EPC success. These findings in a monogamous species illustrate that EPC is a secondary mating system of razorbills in which sexual selection operates. The existence of this system outside the colony raises the possibility that lekking for EPCs may also occur within the nesting territories of other monogamous, colonial species but is hidden by competition for nests and breeding partners.     

Mating success on white-bearded manakin (Manacus manacus) leks: male characteristics and relatedness

Morphological, territorial, and behavioural characteristics were measured on white-bearded manakin (Manacus manacus) males from two leks in two consecutive years. These data were combined with data on marker-inferred relatedness to study possible co-variation with mating success. In one year, male size and male condition were correlated with mating success. In both years, males holding courts nearer the lek centre gained more matings. No observed male display behaviour appeared to be an independently important factor in explaining variance in male mating success. Successful males made more aggressive displays than non-successful males and more displays were between close relatives. Number of aggressive displays increased as the distance between male courts decreased. Mating success in the white-bearded manakin is most likely mediated by a combination of morphological and behavioural characteristics, influencing both male-male competition and female choice. Females could potentially use centrality on the lek as an indicator of male characteristics. However, levels of relatedness may influence spatial arrangement of males on a lek thereby affecting male-male interactions and ultimately influencing patterns of mating success.     

Fighting behaviour as a correlate of male mating success in black grouse Tetrao tetrix

Fighting is a fundamental determinant of male fitness in species where females prefer socially dominant males as mates or where dominants can prevent subordinates from mating. This in turn can lead to the evolution of honest inter- and intra-sexual cues of male dominance. Fighting as a behaviour comprises both fighting rate (number of fights per unit of time) and fighting performance (success in winning fights), but it is not always clear which of these components are important for female choice and how they link to signals of male quality. To quantify the relative importance of fighting as a cue for females, we recorded detailed behavioural data from male black grouse Tetrao tetrix at leks. We explored the relationship between phenotypic traits (body mass, eye comb size, tail (lyre) length and blue chroma colouration) and fighting performance and rates and how these were related to male mating success. In older males' pairwise fights, winners had lower blue chroma than losers, but there were no differences in other morphological traits. In yearlings, no morphological trait predicted success in pairwise contests. Both fighting rate and performance were positively related to the number of copulations acquired by a male; however, when controlled for lek centrality, fighting performance and not fighting rate was significantly related to mating success. Our results indicate that females may be using components of fighting behaviour as cues for mate choice.     

Imperfect female choice and male mating skew on leks of different sizes

We present a model of error-prone female choice on leks, and investigate the effects of different degrees of error on the distribution of mating success among males present at leks of different sizes. At higher levels of error, the best male is predicted to gain a smaller share of matings, while low-ranking males gain a larger share. Males who are of high rank but not the most desirable on the lek do best at intermediate levels of error, since the top-ranked male does not then claim all the matings, but assessment is still sufficiently accurate for females to discriminate between high-ranking and low-ranking competitors. The effects of error are shown to be more pronounced on larger leks, due to smaller expected differences in mating value between males of adjacent ranks. This interaction between lek size and error suggests that observed negative relationships between lek size and mating skew need not be attributed solely to intrasexual competition, as previously suggested, but could also be a result of imperfect choice. Received: 20 February 1998 / Accepted after revision: 25 October 1998     

Uganda kob mating success does not increase on larger leks

One explanation for the movement of sexually receptive females to clusters of male territories in lek-breeding species is that larger clusters provide females with higher-quality mating partners, as would be the case if males were distributed between leks in an ideal free distribution for unequal competitors. This ideal free model of lek evolution predicts that male competitive ability and mating success will be greater on larger leks than smaller ones. I tested these predictions by comparing the mean number of males on 19 different Uganda kob leks with the sex ratio, the availability of oestrous females, mating rates, male fighting rates and male turnover rates. Contrary to the predictions of the model, numbers of females, receptive females and fights increased proportionally with lek size, but were no greater per male on larger leks. Multivariate analyses of male and female numbers on leks showed that male numbers were associated with female numbers, female numbers in the past, and a variety of habitat variables which may have related to the costs of holding a lek territory, but female numbers varied only with male numbers and female density in the area. These data do not provide evidence that females gain access to superior males by mating on larger leks, though they do support the possibility that lekking may be promoted by a tendency for larger leks to retain females longer.     

Multiple signals in the palmate newt: ornaments help when courting

There is increasing evidence that female mate choice is often based on the assessment of multiple male traits, involving both morphology and behavior. We investigated female mate choice for multiple male traits in the palmate newt, Lissotriton helveticus, including male tail filament length, hind foot web size, crest development, body size, ventral coloration, and courtship display activity. Observations of courtship display in the field revealed that females spent more time in front of males with longer tail filaments. Laboratory experiments revealed a more detailed relationship between filament length and courtship display. We found that females took more sperm masses from males with both longer filaments and greater display activity. Experimental shortening of the tail filament length substantially decreased the number of male sperm masses transferred. However, when we experimentally reversed relative filament length between two males in mating trials, male mating success was explained by courtship activity and not by filament length. Our results show that female palmate newts value multiple traits during mate choice, including both morphological ornaments and reproductive behaviors in males. Our results further suggest that, when filament length is below a certain threshold, females may value the information content of courtship activity over that of filament length.     

Sexual selection in lekking sage grouse: phenotypic correlates of male mating success

Summary Mate choice cues in sage grouse were reinvestigated by analyzing relationships between male mating success and a range of suggested cues. Display cues were implicated by significant relationships between mating status (whether or not a male mated) and lek attendance, display rate (corrected for effects of female proximity and time of day) and an acoustic component related to temporal and frequency measure of a whistle emltted during the strut display. Although display rate and the acoustic component were intercorrelated, both exerted significant partial effects on mating success in mutivariate analyses. These display measures also differed significantly between males. In contrast, mating success was not significantly related to measures of territory characteristics, including size and proximity to the lek center, or to body size. These results resolve discrepancies between previous studies and provide a basis for experimental analysis of the role of female choice in this lek system.     

The evolution of leks through female choice: differential clustering and space utilization in six sympatric manakins

Summary The degree to which lekking and non-lekking male manakins select display sites in order to maximise proximity to females was examined by contrasting movements of females with male dispersion. Data on female visiting patterns, male courtship disruption, and mating skew were also collected over three successive breeding seasons. For the five lek-breeding species, female home-ranges were 3–7 times larger than those of adult males. Female movements were concentrated around leks, fruiting places and stream bathing sites. None of the females monitored by radio-tracking expanded her normal range in order to visit males on leks. On the contrary, feeding bouts of females frequently preceded a visit to potential mates at neighboring leks. Despite small sample sizes, significant correlations were found between female home-range size and male clustering (distances between neighboring leks and distances between neighboring males), as predicted by the female choice model and the hotspot model. Adult and immature male home-range sizes were not significantly correlated with male dispersion or female ranges. On the other hand, males and females of the only non-lekking species exhibited similar use of space and home-range size. Male settlement at sites with high levels of female traffic showed that the hotspot model is adequate to explain differences in male dispersion among sympatric lekking species. Comparisons with other studies suggest that apparent female choice could be overidden by past and present male-male interactions or female mate-comparison tactics. In fact, both the hotspot model and the attractiveness hypothesis appear to shape male dispersion on leks: males appear to settle under hotspot conditions with despotic rules generated through bias in female choice or male-male interference. It is proposed that the evolution of leks is ecologically motivated by the spatio-temporal distribution of trophic resources, initially leading to a dispersed male-advertisement polygyny. Following this, a foraging ecology that promotes high mobility by females and the magnetic effect of mating skew in particular males may have favored clustering on exploded leks. Later, the development of male-male interference and the increasing female home-range size could have led to the evolution of classical leks.     

Passing the buck: resource defence,lek breeding and mate choice in fallow deer

Summary Lek breeding systems, where males defend small, clustered mating territories, are thought to occur where the distribution of females is heavily clumped but males are unable to defend resources used by females. In this paper, we describe a breeding system in fallow deer where males are able to defend resources used by females but the most successful bucks instead defend small territories on a traditional mating ground; where the lek is sited in an area not heavily used by females at other times of year and is visited primarily by females in or close to oestrus; and where mating success on the lek is related to territory position and to male phenotype but not to the resources available on different lek territories. Comparisons with other ungulates suggest that lek breeding species fall into two groups: those where leks are regularly visited by herds of females many of which are not in oestrus and those, like fallow deer, where leks are visited primarily by oestrous females. In the latter species, it is unlikely that females visit the lek for ecological reasons.     

Characteristics that influence male reproductive success on a lek of Lethrinops c.f. parvidens (Teleostei: Cichlidae)

Sexual selection has long been proposed as a mechanism leading to the diverse cichlid (Teleostei: Cichlidae) fauna of Lake Malawi, Africa. Many of the shallow-water, sand-dwelling, bower-building cichlid species are particularly well suited for studies of sexual selection because they participate in leks. Since females in lekking systems appear to acquire only genetic material from their mates, it has been suggested that leks are ideal systems to study female mate choice. The objectives of the investigation were to examine Lethrinops c.f. parvidens male bower characteristics (i.e., bower size and location) as well as other male characteristics (i.e., length, gular color, and duration on the lek) for their influence on male mating success as measured by the number of visits, circles, and eggs laid by females. These measures are nested in that a visit by a female may or may not lead to circling, and circling by a female may or may not lead to egg-laying. We found increased bower height and higher numbers of conspecific neighbors (analogous to shallow-water, near-shore bower positions) to be positively, significantly associated with the number of visits by females. The only significant correlate with the number of circles was visits, and similarly circles was the only significant correlate with the number of eggs laid. The R ² value for the egg-laying regression was quite low (19.8%) compared with visits (54.3%) and circling (78.9%), suggesting that females may be using additional cues, that we failed to measure, when in close proximity to males or simply that a small proportion of the females were ready to spawn. Both indirect selection and direct selection pressure due to egg predation may have influenced female choice on the lek. Received: 10 April 1999 / Received in revised form: 26 July 1999 / Accepted: 18 September 1999     

Phenotypic correlates and survival consequences of male mating success in lek-mating greater prairie-chickens (<Emphasis Type="Italic">Tympanuchus cupido</Emphasis>)

Female choice and male–male aggression are two modes of sexual selection that can lead to elaboration of male morphological and behavioral traits. In lek-mating species, male mating success is often strongly skewed, and it is puzzling why variation in male traits is still observed given directional female choice. If male traits correlated with reproductive success are honest signals of male quality, there may be survival costs associated with the expression of those traits. In this study, we examined whether morphological, behavioral, and territorial traits are correlated with male mating success and survival in the lek-mating greater prairie-chicken (Tympanuchus cupido). We introduce a novel application of multinomial discrete choice models for analysis of female mate choice behavior. We found that behavioral and territorial attributes showed 6.5 times more variability among males than morphological traits. Both display and aggressive behaviors were strong predictors of male mating success, suggesting that both female choice and male–male aggression were important in determining mating success among male greater prairie-chickens. Moreover, annual survival of male prairie-chickens was independent of mating success and male traits. Females appear to be choosing males based on behavioral traits where large variation exists between males (coefficient of variation >30%). Behavioral traits were the most important factor in determining mating success of male prairie-chickens, but the mechanism underlying this relationship is unknown. In the future, experimental manipulations of male hormones or parasite loads could bridge the proximate mechanisms and ultimate consequences of factors mediating male mating success in lek-mating grouse.     

Repeatable female preferences, mating order and mating success in the poeciliid fish, Heterandria formosa

Sexual selection via female choice can afford preferred males comparably higher mating success than those males that lack preferred traits. In addition, many models of sexual selection assume that both male traits and female preferences are heritable. In this study we test whether females of the poeciliid fish, Heterandria formosa, have repeatable pre-copulatory preferences for larger males. We also test whether female pre-copulatory preferences are always reliable indicators of male mating success. When given a choice between a large and a small male, females prefer larger males, and the repeatability of this preference is high. Although there are no overall differences in male mating success between large and small males, large males have a higher mating success when they are the first to mate than when they are the second to mate. Likewise, preferred males also have higher mating success when they are the first to mate than when they mate second. Therefore, the repeatable female preferences observed in this study only predict male mating success when the preferred male mates first. These results illustrate that even significantly repeatable female preferences do not translate into male mating success, which is an assumption of many examinations of the importance of female choice in sexual selection.     

Age before beauty? Relationships between fertilization success and age-dependent ornaments in barn swallows

When males become more ornamented and reproduce more successfully as they grow older, phenotypic correlations between ornament exaggeration and reproductive success can be confounded with age effects in cross-sectional studies, and thus say relatively little about sexual selection on these traits. This is exemplified here in a correlative study of male fertilization success in a large colony of American barn swallows (Hirundo rustica erythrogaster). Previous studies of this species have indicated that two sexually dimorphic traits, tail length and ventral plumage coloration, are positively correlated with male fertilization success, and a mechanism of sexual selection by female choice has been invoked. However, these studies did not control for potential age-related variation in trait expression. Here, we show that male fertilization success was positively correlated with male tail length but not with plumage coloration. We also show that 1-year-old males had shorter tails and lower fertilization success than older males. This age effect accounted for much of the covariance between tail length and fertilization success. Still, there was a positive relationship between tail length and fertilization success among older males. But as this group consisted of males from different age classes, an age effect may be hidden in this relationship as well. Our data also revealed a longitudinal increase in both tail length and fertilization success for individual males. We argue that age-dependent ornament expression and reproductive performance in males complicate inferences about female preferences and sexual selection.     

Mate choice in the yellow-shouldered widowbird: correlates of male attractiveness

Recent investigations of male ornaments in sexual selection have used experimental manipulation of tail length in three widowbird species, but only for one of these have correlates of male reproductive success been reported. I examined correlates of male attractiveness to nesting females over two breeding seasons for the polygynous yellow-shouldered widowbird, Euplectes macrourus, in order to discover which cues females may be using to select mates. The black, long-tailed ( 10 cm) males defend large territories and build nest frames, or cock's nests, which females then line and use for nesting. I examined various aspects of male morphology, five behavioral displays, territory characteristics, and the number of cock's nests that males built. Few correlates of mating success were found. The best predictor was the number of cock's nests that a male builds, though one courtship display also correlated with male mating success in 1 year, as did average grass height. Tail length did not correlate with male mating success. A partial correlation analysis confirmed that cock's nests and, in 1 year, grass height, were the primary contributers to male success. Females may choose where to nest primarily on the availability of suitable nesting sites. Long tails may be used by females seeking extra-pair copulations or in male-male competition for territories.     

Bat predation and the evolution of leks in acoustic moths

Theories of lek evolution generally invoke enhanced mating success experienced by males signalling in aggregations. Reduced predation has also been acknowledged as a potential factor driving lek formation, but its role is more ambiguous. Although lekking is a complex behaviour, few empirical studies have investigated the role of both claims. We studied the potential pressures imposed by mating success and predation in an acoustic moth, Achroia grisella, in which males gather in leks and broadcast a calling song attractive to females. We exploited the ability to manipulate the distribution of singing males in laboratory arenas to create different-sized leks and tested female preferences for these aggregations. Because A. grisella are vulnerable to predation by bats while in flight and on the substrate, we also tested the responses of a potential predator, Rhinolophus ferrumequinum, a bat species that feeds on moths, to the experimental leks. We found that the per capita attractiveness of A. grisella males to females rose with increasing lek size. R. ferrumequinum also oriented toward experimental A. grisella leks, but this attraction did not increase at larger leks. Thus, a male’s per capita exposure to predation risk declined as more moths joined the lek. A. grisella males appear to benefit from advertising in larger leks in terms of both increased mate attraction and reduced predation risk. Our results support the idea that multiple factors operating simultaneously may maintain lekking behaviour.