Coevolution of non-fertile sperm and female receptivity in a butterfly

Sexual conflict can promote rapid evolution of male and female reproductive traits. Males of many polyandrous butterflies transfer nutrients at mating that enhances female fecundity, but generates sexual conflict over female remating due to sperm competition. Butterflies produce both normal fertilizing sperm and large numbers of non-fertile sperm. In the green-veined white butterfly, Pieris napi, non-fertile sperm fill the females'' sperm storage organ, switching off receptivity and thereby reducing female remating. There is genetic variation in the number of non-fertile sperm stored, which directly relates to the female''s refractory period. There is also genetic variation in males'' sperm production. Here, we show that females'' refractory period and males'' sperm production are genetically correlated using quantitative genetic and selection experiments. Thus selection on male manipulation may increase the frequency of susceptible females to such manipulations as a correlated response and vice versa.     

Behavioral changes associated with introductions of male maned wolves (Chrysocyon brachyurus) to females with pups

Three male maned wolves were successfully introduced to their mates and 7‐ to 12‐week‐old pups at the Houston Zoological Gardens and Fossil Rim Wildlife Center in 1994 and 1995. The introductions took 3–7 weeks and had three stages: 1) allowing the male to see the female and pups through a chain‐link panel or a full chain‐link fence, 2) introducing the male and female without the pups present, and 3) introducing the male to the pups. For 7 days before Stage 2 and 7 days during Stage 3, the adults were observed for 150 hr. The amount of time they spent active and the amount of time they spent near the pups were recorded, as well as all behaviors they directed to the pups. After the males were introduced, the females' activity decreased, and the males' activity increased. The females spent less time near the pups after the introduction. The introduction did not affect the females' rates of affiliative or aggressive behaviors to the pups, and there was no difference between males' and females' rates of affiliative or aggressive behaviors. This introduction procedure offers an alternative to leaving the male with the pups from the time they are born. The adults' behavioral changes after the introduction show the benefits that occur when captive male maned wolves are allowed to help rear their pups. Zoo Biol 18:189–197, 1999. © 1999 Wiley‐Liss, Inc.     

Male-male Competition and Female Mate Choice through Courtship Display in the Territorial Damselfish Stegastes nigricans

Both sexes of the herbivorous damselfish Stegastes nigricans maintain individual feeding territories. These territories are distributed contiguously, forming distinct colonies. Females visit male territories to spawn, and eggs are guarded by males until hatching. Male-male competition and female mate choice were studied in two colonies of different size compositions. Only larger individuals bred in both colonies. Some males in the large colony, that were larger than the breeding males in the small colony, did not succeed in reproducing probably because of severe attacks by the larger males while courting. However, females did not choose large size among breeding males. The most important male characteristic in female choice was the frequency of courtship displays in both colonies. Females in the large colony chose males mainly on the basis of the frequency of displays conducted in the females' territories, whereas females in the small colony chose males on the basis of the frequency of displays conducted in the males' territories. This difference may be a result of the difference in colony size. The distances between females' and males' territories were much greater in the large colony, and, because females cannot see courtship displays conducted in distant male territories, males in the large colony may have had to visit female territories frequently in order to conduct courtship near the females.     

Leg impairment magnifies reproductive costs in male Mediterranean fruit flies,Ceratitis capitata

Injuries frequently accumulate with age in nature. Despite the commonality of injury and the resulting impairment, there are limited experimental data for the effects of impairment on life history trade‐offs between reproduction and survival in insects. We tested the effects of artificial injury and the resulting impairment on the reproductive costs and behavior of male medflies, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). Treatment flies were impaired by amputating tarsomere segments 2–5 from the right foreleg at either eclosion or age 22 days. The effect of impairment and age on the cost of reproduction was tested by varying the timing of female availability among the treatments. Courtship behavior and copulation rates were observed hourly from age 2–5 days to determine the effects of impairment on reproductive behavior. Female access combined with the impairment reduced the life expectancy of males more than the impairment alone, whereas the health effect of amputation was influenced by age. Conversely, the risk of death due to impairment was not influenced by the males' mating status prior to amputation. The males' copulation success was reduced due to impairment, whereas courtship behavior was not affected. Impairment does not reduce the males' impulse to mate, but decreases the females' receptivity to copulation, while also increasing the cost of each successful mating. Overall, minor impairment lowers the reproductive success of males and reduces longevity.     

From maternal tending to adolescent befriending: The adolescent transition of social support

Attachment theory holds that parental relationships have lifelong effects on offspring social lives. The tend-and-befriend hypothesis posits that female friendships among humans evolved as part of a primate-wide coping mechanism to mediate stress by relying on social support. Here we bridge developmental and evolutionary frameworks to examine adolescent girls’ perception of their reliance on female friendship for social support, how perceptions of parental relationships affect peer relationships, and the extent to which parent and peer relationships buffer depressive symptoms. We predict perceived maternal relationship quality will be positively associated with close female friendships, and maternal relationships, paternal relationships, and female friendship will buffer depressive symptoms. Participants were adolescent girls from a summer science camp (N = 95). Participants filled out demographic information, social network surveys, the Parent-Adolescent Communication Scale, and the Center for Epidemiology Depression Scale. Data was analyzed with Pearson's correlations, t tests, and path analysis. Adolescent girls with few female friends, compared with girls who had more than two very close female friends, experienced more depressive symptoms (t = 3.382, p = .001, D = 0.784). Adolescent girls with few female friends experienced more depressive symptoms compared to girls with two or more very close female friends (t = 3.382, p = .001, D = 0.784). Stronger maternal and paternal relationships were associated with having more female friends (maternal: t = −3.213, p = .003, D = 0.837; paternal: t = −2.432; p = .017). In the path analysis model, only maternal relationship quality significantly predicted female friendship category (β = .33, CR = 2.770, p < .006). Furthermore, participants with two or more very close female friends and higher paternal relationship quality had significantly fewer depressive symptoms (friends; β = −.19, CR = −2.112, p = .035; paternal: β = −.33, CR = −3.220, p < .001), and older participants had more depressive symptoms (β = .17, CR = −1.931, p = .036). These results provide additional support for the tend-and-befriend hypothesis, suggesting that maternal tending sets the stage for close female friendships.     

The effects of injecting Juvenile Hormone III into the prothoracic ganglion on phonotaxis by female crickets Gryllus bimaculatus

Nanoinjection of Juvenile Hormone III (JH III) into the prothoracic ganglion causes virgin female crickets Gryllus bimaculatus De Geer to become more phonotactically selective for the syllable periods (SPs) of model calling songs. Females responding to all, or almost all, of the SPs presented before JH III injection significantly narrow their responses to a range of SPs that is usually centered on the SPs included in the conspecific males' calling song. Control injections of acetone (i.e. the solvent for JH III) into the prothoracic ganglion do not significantly change the recipient females' phonotactic responses. Injection of JH III into the metathoracic ganglion also has no effect the females' phonotactic choices.     

Different positions of males approaching towards females and male choices between webs with and without stabilimentum in a sexually cannibalistic orb‐web spider,Argiope bruennichi

Males of the orb‐weaving spider species Argiope bruennichi (Araneidae) are frequently victims of sexual cannibalism. Therefore, a male spider approaching a female should have strategies to avoid being killed before copulation. Our present field study detected six types of A. bruennichi male positions vis‐à‐vis the female web. In 78% of situations (39/50), only one male attached to a female. Two males attached to the same female in 11 cases. We observed no cases of three or more males on the same female web. We most commonly observed the situation of a male staying in its own web and connecting to a female's web with its silk thread (46% of cases). Of the female webs chosen by males, 68% were decorated with both an upper and lower portion of stabilimentum – a conspicuous white silk structure that reflects much more ultraviolet light than other spider silks in the web. Only 14% (7/50) of the selected webs lacked stabilimentum. Therefore, we conducted an experiment to investigate the males' choice between females' webs with and without stabilimentum. Of the 24 males used in the experiment, 10 chose webs with stabilimentum. This result did not show a strong preference of the male for stabilimentum between equally sized webs, and thus did not support an earlier suggestion that stabilimentum in A. bruennichi might function to guide males to females for mating.     

CHEMICAL COMMUNICATION IN HAWAIIAN DROSOPHILA

We are interested in elucidating the extent to which lekking Hawaiian Drosophila species have diverged from their continental counterparts, which engage in sexual behavior at communal food sources, with regard to the chemical communication systems that the flies employ. Accordingly, we have analyzed flies from three closely related Hawaiian Drosophila species in the adiastola subgroup. These species are of interest because the males engage in a unique behavior: while courting, they raise their abdomens over their heads and emit anal droplets. Analysis of the flies' behavior, the hydrocarbons in males' anal droplets, and males' cuticular hydrocarbons suggest that females' responses to males may be mediated by cuticular pheromones and/or pheromones in males' extruded droplets that enable the females to distinguish conspecific from heterospeciflc males. Conversely, perception of cuticular hydrocarbons from conspecific females enables D. adiastola males to distinguish females from a closely related species from conspecific females. On the basis of these observations, we suggest that the adiastola subgroup species are unique among drosophilids in that they utilize an anal droplet-mediated pheromone communication system, some or all components of which are species specific. However, the lekking Hawaiian Drosophila species are similar to D. melanogaster and related continental species in that the Hawaiian flies employ a cuticular pheromone communication system, some components of which are sex and species-specific.     

Low-investment copulation: Sex differences in motivations and emotional reactions

Samples of male (n = 113) and female (n = 175) college students were surveyed. Majorities of both sexes agreed with statements indicating that males' sexual attractiveness varied more than females' sexual attractiveness as a function of their status. Subjects who reported more sex partners and a greater aversion to sexual monogamy were slightly more likely to agree that they tested their partners to see how far they could push them. Interviews with highly sexually active females (n = 32) and males (n = 24) indicated that low-investment copulation and lack of control over the sexual access-investment ratio caused even women with very permissive attitudes and multiple sex partners to develop an aversion to low-investment copulation. Three levels were identified in this process. The techniques that women with multiple partners used to deal with their feelings are described. Females tested their partners for ability and willingness to invest. Males tested for opportunities to reduce investment and pursue other women. High status, for example athletic stardom, transformed males' sexual attractiveness to women and numbers of sex partners. Results were consistent with the view that the emotional-motivational mechanisms that moderate sexual arousal and attraction are sexually dimorphic.     

Relationship tenure differentially influences pair-bond behavior in male and female socially monogamous titi monkeys (Callicebus cupreus)

Pair-bonded primates have uniquely enduring relationships and partners engage in a suite of behaviors to maintain these close bonds. In titi monkeys, pair bond formation has been extensively studied, but changes across relationship tenure remain unstudied. We evaluated differences in behavioral indicators of pair bonding in newly formed (~6 months paired, n = 9) compared to well-established pairs (average 3 years paired, n = 8) of titi monkeys (Callicebus cupreus) as well as sex differences within the pairs. We hypothesized that overall males would contribute more to maintenance than females, but that the pattern of maintenance behaviors would differ between newly formed and well-established pairs. Each titi monkey (N = 34) participated in a partner preference test (PPT), where the subject was placed in a middle test cage with grated windows separating the subject from the partner on one side and an opposite-sex stranger on the other side. During this 150-min behavioral test, we quantified four key behaviors: time in proximity to the partner or stranger as well as aggressive displays toward the partner or stranger. Overall, we found different behavioral profiles representing newly formed and well-established pair-bond relationships in titi monkeys and male-biased relationship maintenance. Males spent ∼40% of their time in the PPT maintaining proximity to the female partner, regardless of relationship tenure. Males from well-established bonds spent less time (14%) near the female stranger compared to males from newly formed bonds (21%) at the trend level. In contrast, females from well-established bonds spent less (23%) time near the male partner in the PPT compared to females from newly formed bonds (47%). Aggressive displays were more frequent in newly formed bonds compared to well-established bonds, especially for females. Scan sampling for homecage affiliation showed that newly formed pairs were more likely to be found tail twining than well-established pairs.     

Roles of testosterone and amygdaloid LTP induction in determining sex differences in fear memory magnitude

Women are thought to form fear memory more robust than men do and testosterone is suspected to play a role in determining such a sex difference. Mouse cued fear freezing was used to study the sex-related susceptibility and the role of testosterone in fear memory in humans. A 75-dB tone was found to provoke weak freezing, while 0.15-mA and 0.20-mA footshock caused strong freezing responses. No sex differences were noticed in the tone- or footshock-induced (naïve fear) freezing. Following the conditionings, female mice exhibited greater tone (cued fear)-induced freezing than did male mice. Nonetheless, female mice demonstrated indistinctive cued fear freezing across the estrous phases and ovariectomy did not affect such freezing in female mice. Orchidectomy enhanced the cued fear freezing in male mice. Systemic testosterone administrations and an intra-lateral nucleus of amygdala (LA) testosterone infusion diminished the cued fear freezing in orchidectomized male mice, while pretreatment with flutamide (Flu) eradicated these effects. Long-term potentiation (LTP) magnitude in LA has been known to correlate with the strength of the cued fear conditioning. We found that LA LTP magnitude was indeed greater in female than male mice. Orchidectomy enhanced LTP magnitude in males' LA, while ovariectomy decreased LTP magnitude in females' LA. Testosterone decreased LTP magnitude in orchidectomized males' LA and estradiol enhanced LTP magnitude in ovariectomized females' LA. Finally, male mice had lower LA GluR1 expression than female mice and orchidectomy enhanced the GluR1 expression in male mice. These findings, taken together, suggest that testosterone plays a critical role in rendering the sex differences in the cued fear freezing and LA LTP. Testosterone is negatively associated with LA LTP and the cued fear memory in male mice. However, ovarian hormones and LA LTP are loosely associated with the cued fear memory in female mice.     

Low-quality females prefer low-quality males when choosing a mate

Mate choice studies routinely assume female preferences for indicators of high quality in males but rarely consider developmental causes of within-population variation in mating preferences. By contrast, recent mate choice models assume that costs and benefits of searching or competing for high-quality males depend on females'' phenotypic quality. A prediction following from these models is that manipulation of female quality should alter her choosiness or even the direction of her mating preferences. We here provide (to our knowledge) the first example where an experimental manipulation of female quality induced a mating preference for low-quality males. Zebra finches (Taeniopygia guttata) reared in small or large experimental broods became high- or low-quality adults, respectively. Only high-quality females preferred high-quality males'' mate-advertising songs, while all low-quality females preferred low-quality males'' song. Subsequent breeding trials confirmed this pattern: latency until egg laying was shortest in quality-matched pairs, indicating that quality-matched birds were accepted faster as partners. Females produced larger eggs when mated with high-quality males, regardless of their own quality, indicating consensus regarding male quality despite the expression of different choices. Our results demonstrate the importance of considering the development of mating preferences to understand their within-population variation and environmentally induced change.     

Female extra-pair behaviour and environmental quality in the serin (Serinus serinus): a test of the 'constrained female hypothesis'

Recent behavioural and molecular studies have shown that in most monogamous bird species extra-pair copulations and fertilizations outside the pair bond occur routinely. The consequences of female extra-pair behaviour might comprise effects on important life-history traits, such as the extent of male parental care. In this study we test the assumption that, within a species, females'' options for extra-pair mating depend on female quality and the environments that females occupy. This ''constrained female hypothesis'' predicts that females in good environments or high-quality females are able to resist males'' control efforts better than females in poor environments or low-quality females. We test the idea in the socially monogamous serin. We found that the likelihood of extra-pair paternity is significantly higher in territories with high availability of food. There was a negative relationship between environmental quality (food availability) and paternity both in natural and in experimentally manipulated habitats. Male feeding rates were negatively related to food availability and positively related to paternity. These data and the additional result that in better environments all of a females'' offspring were sired by one extra-pair male provide support for Gowaty''s ''constrained female hypothesis''.     

Elephant

ABSTRACT

The aim of this exploratory study was to determine heart rate and the levels of oxytocin, cortisol, and insulin in dogs and their owners in response to a short-term interaction. In addition, the dogs' behavior was studied. The owners' responses were compared with those obtained from a control group. Ten female volunteers and their own male Labrador dogs participated in an experiment during which the owner stroked, petted, and talked with her dog during the first 3 minutes. Blood samples were collected from both dog and owner before (0) and at 1, 3, 5, 15, 30, and 60 minutes after the start of the interaction. Blood samples were analyzed by EIA. Heart rate was monitored telemetrically. The data were analyzed using linear mixed models and paired t-tests. The dogs' oxytocin levels were significantly increased 3 minutes after the start of the interaction (p = 0.027). Cortisol levels were significantly increased after 15 and 30 minutes (p = 0.004 and p = 0.022, respectively), and heart rate was significantly decreased after 55 minutes (p = 0.008). The dogs displayed normal behaviors during the experiment. The owners' oxytocin levels peaked between 1 and 5 minutes after interaction (p = 0.026). No such effect was seen in the controls. Cortisol levels displayed a significant decrease at 15 or 30 minutes in both owners and controls, and insulin levels did so at 60 minutes (p = 0.030, p = 0.002 and p = 0.002, p < 0.0001, respectively). Heart rate decreased significantly in the owners at 55 and 60 minutes (p = 0.0008) but not in the controls. In conclusion, short-term sensory interaction between dogs and their owners influences hormonal levels and heart rate. However, further studies need to be performed in order to better understand the effects of interaction between dogs and their owners.     

Sociosexual behavioral patterns involving nulliparous female orangutans (Pongo sp.) reflect unique challenges during the adolescent period

The primate adolescent period is characterized by a series of changes in physiology, behavior, and social relationships. Orangutans have the slowest life history and the longest period of dependency of all primates. As members of a semisolitary species with high levels of sexual coercion, adolescent female orangutans face a unique combination of challenges when achieving independence from their mother. This study examined the mating behavior of adolescent female orangutans and compared it with that of adult females to assess whether mating behavior reflects distinct strategies at these different points in the life cycle. Data were collected in Gunung Palung National Park on the island of Borneo over 20 years. Mating events from adolescent (n = 19) and adult females (n = 26) were scored and compared. Adolescent female mating events had significantly higher mating scores (indicating more proceptivity) than those of adult females (β = 1.948, p = .001). Adolescent females also engaged in elaborate sociosexual interactions with different flanged males, behaviors that were never observed during mating events of adult females. These interactions involved characteristic behavior on the part of both the adolescent females and the flanged males. Given these findings and the documentation of similar accounts of adolescent female–flanged male mating from the island of Sumatra, we propose that adolescent female orangutans display distinctive behavioral repertoires throughout the genus Pongo which serves to overcome male ambivalence toward nulliparous females, establish familiarity, and evaluate coercive tendencies in flanged males. We suggest that these behavioral patterns are an integral part of female social development in a female philopatric, but highly dispersed species where consistent social support is absent after ranging independence is achieved.     

The Importance of Social Condition in the Hormonal and Behavioral Responses to an Acute Social Stressor in the Male Siberian Dwarf Hamster (Phodopus sungorus)

Social condition is an important factor in determining the behavioral and hormonal responses to a social stressor in the Siberian dwarf hamster (Phodopus sungorus). We predict that males housed with a female or a family (female and pups) will show an increase in the magnitude of the behavioral and hormonal responses to a male intruder compared to those of individually housed males. Three treatment groups were studied: individually housed males that had been previously group-housed in same-sex colonies (males,n= 10), males housed with a female (male + female,n= 9), and males housed with their female and pups (male + family,n= 12). Males were monitored for aggressive behavior toward an intruder male for 10 min. Blood samples were taken at baseline and after the encounter. Male + female and male + family groups spent more time in aggressive behavior (P< 0.05), such as attacking (P< 0.05) and fighting (P<0.05), than did individually housed males. These same groups showed significant increases in plasma cortisol after the encounter (P< 0.01) whereas there were no significant increases in plasma cortisol in solitary males. All groups showed significantly lower levels of plasma testosterone (male,P< 0.001, male + female,P< 0.05; male + family,P< 0.01) whereas a significant increase in prolactin occurred only in the male + family group (P< 0.05). There was a significant positive correlation between postencounter cortisol levels and total number of minutes spent in aggressive behavior (P< 0.05). These results demonstrate that the introduction of a novel intruder male results in an activation of the hypothalamic–pituitary–adrenocortical axis and a suppression of the reproductive axis. Furthermore, pairing of a male with a female alters the behavioral and hormonal responses to an intruder male.     

Does reproductive effort influence the metabolic rate of Tomodon dorsatus snakes?

In Squamate reptiles, vitellogenesis in females is marked by an increase in the number and size of follicles, leading to an increase in aerobic metabolism to support the rising energy demand during reproductive activity. Male gametes are smaller than female gametes, and spermiogenesis requires less energy than vitellogenesis. This investigation compares the relationship between aerobic metabolism and reproductive effort in male and female viviparous Tomodon dorsatus snakes. We evaluated the influence of the males' and females' reproductive stages, along with the masses of follicles and testicles, on their aerobic metabolic rate. Our findings show that females have higher maintenance cost of pregnancy than metabolic costs of vitellogenesis. In males, we found no evidence of the reproductive effort influencing aerobic metabolic rates. In T. dorsatus, females have a long period of development and high fecundity. Therefore, the metabolic costs of vitellogenesis represent a critical component in the reproductive effort. On the other hand, males of T. dorsatus maintain a similar mass of gonads throughout the year with constant energy demand. These results reflect the difference in reproductive efforts between females and males of T. dorsatus.     

Female Remating Behavior in a Lekking Moth

In polyandrous species, male reproductive success will at least partly be determined by males' success in sperm competition. To understand the potential for post‐mating sexual selection, it is therefore important to assess the extent of female remating. In the lekking moth Achroia grisella, male mating success is strongly determined by female choice based on the attractiveness of male ultrasonic songs. Although observations have indicated that some females will remate, only little is known about the level of sperm competition. In many species, females are more likely to remate if their first mating involved an already mated male than if the first male was virgin. Potentially, this is because mated males are less well able to provide an adequate sperm supply, nutrients, or substances inhibiting female remating. This phenomenon will effectively reduce the strength of pre‐copulatory sexual selection because attractive males with high mating success will be more susceptible to sperm competition. We therefore performed an experiment designed both to provide a more precise estimate of female remating probability and simultaneously to test the hypothesis that female remating is influenced by male mating history. Overall, approximately one of five females remated with a second male. Yet, although females mated to non‐virgin males were somewhat more prone to remate, the effect of male mating history was not significant. The results revealed, however, that heavier females were more likely to remate. Furthermore, we found that females' second copulations were longer, suggesting that, in accordance with theory, males may invest more sperm in situations with an elevated risk of sperm competition.     

Effect of Mother's Dominance Rank on Offspring Temperament in Infant Rhesus Monkeys (Macaca mulatta)

In humans, temperament plays an important role in socialization and personality. Some temperaments, such as behavioral inhibition are associated with an increased risk for psychopathology. Nonhuman primates can serve as a model for neurobiological and developmental contributions to emotional development and several recent studies have begun to investigate temperament in nonhuman primates. In rhesus monkeys, dominance rank is inherited from the mother and is associated with social and emotional tendencies that resemble differences in temperament. The current study assessed differences in temperament in infant rhesus monkeys as a function of maternal dominance rank. Temperament was assessed in 26 infants (13 males) from birth until 6 months of age with a battery that included Brazelton test, human intruder test, human intruder‐startle, cortisol stress reactivity, and home cage observations of interactions with peers and the mother. Throughout testing, infants lived with their mothers and a small group of other monkeys in indoor/outdoor runs. Dominance rank of the mothers within each run was rated as either low/middle (N = 18, 9 male) or high/alpha (N = 8, 4 female). Infants of high‐ranking mothers displayed more intruder‐directed aggression and reduced startle potentiation in the human intruder tests. Dominant offspring also had reduced levels cortisol and startle across development and spent more time away from mothers in the interaction tests. These results suggest that dominance of the mother may be reflected in behavioral reactivity of infants early in life. These findings set up future studies, which may focus on contributing factors to both dominance and temperament such as genetics, rearing, and socialization. Such factors are likely to interact across development in meaningful ways. These results also suggest future human‐based studies of a similar relationship may be warranted, although social dominance is clearly more complex in human than macaque societies. Am. J. Primatol. 75:65‐73, 2013. Published 2012 by Wiley Periodicals, Inc.?     

Wind turbine noise limits propagation of greater prairie‐chicken boom chorus,but does it matter?

Acoustic signals are often critical elements of mating displays, and lekking male greater prairie‐chickens (Tympanuchus cupido pinnatus) use their boom vocalization for this purpose. We quantified the acoustic characteristics of the boom chorus created by multiple male greater prairie‐chickens vocalizing simultaneously at leks in Brown County, NE, USA, in 2013 and 2014. We used these data to evaluate (a) the role of the boom chorus in prairie‐chicken breeding dynamics and (b) the impact of a wind energy facility on the acoustic signal of the boom chorus. We sampled the chorus using audio recorders placed in transects extending from leks; the chorus exhibited an average peak frequency of 297 ± 13 Hz. The mean chorus signal‐to‐noise ratio declined from 15.7 dB (50 m) to 2.6 dB (800 m), and wind speed and direction, topography, and relative humidity caused variation in signal‐to‐noise ratio at a given distance and location. Chorus recordings from leks within 1,000 m of a wind turbine had lower signal‐to‐noise ratio (β_turbine = ?5.659, SE = 1.289) than leks farther from turbines. The chorus signal‐to‐noise ratio increased slightly with more males present on the lek (~0.1 dB for each additional male; β_males = 0.177; SE = 0.037) and considerably more as more females visited the lek (~1.4 dB for each additional female; β_females = 2.498, SE = 0.235; β_females² = ?0.309, SE = 0.039). Our results provide support for the signal enhancement hypothesis that proposes the boom chorus is influenced notably by male–male competition for females on the lek, rather than functioning solely to advertise the presence of the lek to recruit females. Our results also suggest the choruses emanating from small leks have the greatest potential to be masked by anthropogenic (wind turbine) noise, which may affect the breeding success of male and female prairie‐chickens.