Sexual Selection Research Papers - Academia.edu (original) (raw)

Signaling plays a critical role in social behavior, particularly in polygynous systems where males compete with rival males and use signals to attract mates. We quantified visual signals and social behavior in two previously unstudied species of chameleons in Madagascar, Furcifer labordi and F. verrucosus. Females of both species displayed distinct color patterns that signaled either nonreceptivity or potential sexual receptivity. Nonreceptive females rejected all male courtship. Potentially receptive F. verrucosus females mainly allowed males to attempt copulation, whereas potentially receptive F. labordi females were selective. We found that the fleshy, paddle-like rostral appendage in F. labordi was used only during courtship, whereas other studies showed that hard, keratinized appendages were used for male combat. During male-male contests, F. labordi had much more physically intense encounters, possibly to assess opponent quality more accurately since adult male F. labordi were significantly more size-matched than adult male F. verrucosus. Our study elucidated the role of social signals in these species, illustrated the atypical social behavior of chameleons compared to other lizards, and provided testable hypotheses to further delineate sexual selection in this understudied group. Sexual selection, especially intersexual selection, appears more likely in F. labordi than in F. verrucosus.

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- Zoology, Sexual Selection, Social behavior, Signaling

In polygynous mating systems, sexual selection can drive the evolution of male characters beneficial to winning fights for mates (intrasexual selection), for improving the mating success of males through mate choice (intersexual selection), or both. However, it may be difficult to disentangle the relative contributions of intra and intersexual selection on multiple traits that may be of dual utility. We used field arena trials to determine which morphological traits best explained male fighting ability and male mating success in 2 species of chameleons in Madagascar, Furcifer labordi and Furcifer verrucosus. In F. labordi, male fighting success was best predicted by body size and size-corrected shorter rostral appendages and male mating success was best predicted by width of the rostral appendage and body size. In F. verrucosus, we found strong intrasexual selection for increased male body size and fewer counted dorsal cones, a trait that may correspond to increased age and experience. Although females in this species are generally passive toward courting males, male mating success with potentially receptive females is highly variable. Fewer counted dorsal cones and larger size-corrected casque height best explained male mating success; traits that may be selected by the female and/or correlated with increased age and experience. Although difficult to determine the relative contributions of intra and intersexual selection on traits with dual benefits (both fighting and mate choice), we documented both types of selection on body size and secondary sexual characters in these 2 chameleon species.

- by Stanley Fox
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- Evolutionary Biology, Zoology, Mate Choice, Sexual Selection

Many animal species have complex cognitive abilities previously assumed to be limited to humans. Explanations for how these abilities evolved have focused on ways in which cognitive performance may influence survival, such as solving ecological problems or navigating complex social environments. However, sexual selection (differences in the reproductive success of individuals) can also lead to the evolution of complex traits. This could occur, for example, if females prefer males with better cognitive ability. A common assumption of models of female choice for male cognitive ability is that performance scores on different cognitive tasks are intercorrelated. In the present study, we evaluated performance of male satin bowerbirds on six cognitive tasks. Although we found little intercorrelation amongst males' performance scores of these tasks, males with better scores for two integrative measures of these cognitive tasks had higher mating success, which is a good indicator of reproductive success in this species. In addition, a multiple regression analysis suggested that performance on most cognitive tasks independently predicted mating success. Our results point to an important link between sexual selection and cognitive ability that has not been well appreciated and appears to be quite complex. Ó

- by Gerald Borgia
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- Cognition, Reproduction, Sexual Selection, Animal Behaviour

Carotenoid-dependent plumage displays are widely assumed to be honest indicators of individual health or quality, which are used as cues during mate choice and/or agonistic signalling. Despite the fact that red, yellow and orange pigmentation of bills is common, and also variable between individuals, comparatively little is known about bill colouration as a condition-dependent trait. Furthermore, many studies of avian colouration are confounded by the lack of objective colour quantification and the use of overly simplistic univariate techniques for analysis of the relationship between the condition-dependent trait and individual quality variables. In this study, we correlated male blackbird bill colour (a likely carotenoid-dependent sexually selected trait) with body/condition variables that reflect male quality. We measured bill colour using photometric techniques, thus ensuring objectivity. The data were analysed using the multivariate statistical techniques of canonical ordination. Analyses based on reflectance spectra of male blackbird bill samples and colour components (i.e. hue, chroma and brightness) derived from the reflectance spectra were very similar. Analysing the entire reflectance spectra of blackbird bill samples with Redundancy Analysis (RDA) allowed examination of individual wavelengths and their specific associations with the body/condition variables. However, hue, chroma and brightness values also provided useful information to explain colour variation, and the two approaches may be complimentary. We did not find any significant associations between male blackbird bill colour and percent incidence of ectoparasites or cloaca size. However, both the colour component and full spectral analyses showed that culmen length explained a significant amount of variation in male blackbird bill colour. Culmen length was positively associated with greater reflectance from the bill samples at longer wavelengths and a higher hue value (i.e. more orange-pigmented bills). Larger males may have larger territories or be better at defending territories during male-male interactions, ensuring access to carotenoid food sources. Future studies should elucidate the relationship between bill colour and behavioural measures such as aggressiveness, territory size, song rate and nest attendance.

- by Carolyn King
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- Psychology, Cognitive Science, Multivariate Statistics, Pigmentation

In this paper, we examine allometric and sexual-selection explanations for interspecific differences in the amount of sexual dimorphism among 60 primate species. Based on evidence provided by statistical analyses, we reject Leutenegger and Cheverud's [(1982). Int. J. Primatol. 3: 387-402] claim that body size alone is the major factor in the evolution of sexual dimorphism. The alternative proposed here is that sexual selection due to differences in the reproductive potential of males and females is the primary cause of sexual dimorphism. In addition, we propose that the overall size of a species determines whether the dimorphism will be expressed as size dimorphism, rather than in some other form.

- by Steven Gaulin
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- Zoology, Primatology, Sexual Selection, Sexual dimorphism

In many hummingbird species there is an opposite pattern of sexual dimorphism in bill length and other morphometric measures of body size. These differences seem to be closely related with differences in foraging ecology directly associated with a different resource exploitation strategy. The aim of this study was to assess if natural selection is acting on wing length and bill size in hummingbird males and females with different resource exploitation strategies (i.e., territorial males and non-territorial females). If competition for resources promotes sexual dimorphism as a selective pressure, males should be subjected to negative directional selection pressure for wing length and no selection pressure over bill size, while females should undergo positive directional selection pressure for both bill size and wing length. The morphometric data we collected suggests that there is no selection for wing length and bill size in male hummingbirds. In contrast, our females exhibited positive directional selection for both wing length and bill size. Although we cannot reject sexual selection acting on sexually dimorphic traits, this study suggests that natural selection may promote sexual dimorphism in traits that are closely related with hummingbird foraging ecology and resource exploitation strategies.

- by Cristian Estades
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- Zoology, Ornithology, Sexual Selection, Foraging ecology

Because sexual selection pressures are high in sexually dimorphic organisms, morphological, physiological and performance traits are often studied in a sexual selection context. The proximate mechanisms underlying evolutionary change in these traits, however, remain largely unstudied. Here, we examined the role of steroids in shaping morphology and physiological performance in males of a sexually dimorphic lizard (Gallotia galloti). We compared morphology and physiological performance of males with experimentally elevated testosterone levels to sham-operated males. Before surgery, inter-individual variation in plasma testosterone levels correlated positively with bite force capacity. Administration of exogenous testosterone resulted in an increase of the mass of both jaw closing and locomotory muscles compared with sham-operated individuals, but the responsiveness varied considerably among muscle groups. In contrast to our expectations, the dramatic testosterone-induced changes in muscle masses did not result in concordant changes in bite force performance or sprint speed.

- by Jerry Husak and +3
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- Evolutionary Biology, Genetics, Zoology, Skeletal muscle biology

Sexual selection has driven the evolution and elaboration of a wide variety of displays and ornaments in male nonhuman primates, including capes, cheek flanges, and sexual coloration. Among the most sexually dimorphic of all primates is the drill (Mandrillus leucophaeus), the males of which can be 3 times the mass of females, possess large canines, and exhibit extremely bright sexual skin coloration. However, the function of male coloration in this species has never been examined. Here, we present data on male color (measured objectively using digital photography), dominance rank, measures of male-female association, and key sexual behaviors, of adult male drills (n=17) living in four semi free-ranging enclosures at the Drill Rehabilitation and Breeding Center in Nigeria. We test the hypothesis that male coloration is a badge of status, indicating dominance rank, and the hypothesis that male coloration attracts females. We found that male coloration did indicate rank, and that high ranking, strongly colored males were more likely to associate with adult females, and more specifically with fully tumescent females. These males also engaged in more sexual activity. However, measures of male-female association and sexual behaviors were not related to male color once rank had been taken into consideration; i.e., for males of a given rank, females did not prefer those that were more colorful. We discuss the results in light of what is known about the wild drill social system, in which unfamiliar Int J Primatol (

- by Caroline Ross
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- Zoology, Primatology, Digital Photography, Sexual Selection

We conducted an experiment to test competing hypotheses regarding the effects of hunting on American black bear (Ursus americanus) demographic parameters. Specifically, we tested for the existence and the relative influence of sexually selected infanticide (SSI) and density dependence in regulating demographic parameters. We monitored 290 bears in 2 hunted areas and an adjoining unhunted area in the boreal forest of Alberta, Canada, during a 4-year study (2002)(2003)(2004)(2005). We manipulated the areas using a modified before-after control-impact (BACI) design whereby bait sites for hunting were closed in 1 of the 2 hunted areas in years 3 and 4 and adult males in the unhunted area were removed in year 3. Results did not support a significant influence of SSI, if it occurs, on population parameters compared with the effects of density dependence. We found lower cub survival (66% versus 83%) and older age of first reproduction in the unhunted, higher-density area than in the lower-density, hunted area. We found no difference in body condition of males and females between areas, suggesting that if SSI restricted females to suboptimal areas, the effect was not strong enough to affect reproduction. We did not detect an influx of new males or a change in cub survival after removal of adult males from the unhunted area (66% before versus 73% after). Our results suggest that SSI does not affect the population growth rate of hunted black bear populations, and that target hunting quotas do not require including potential effects of SSI in population projections. However, SSI should be considered in unhunted or lightly hunted populations approaching carrying capacity (K). We advocate the inclusion of density dependence in population projection models for bear populations. However, for specific cases where harvesting maintains a population size well below K, density-dependent effects are predicted to be negligible due to the non-linear relationship between demographic parameters and density.

- by Fiona K.a Schmiegelow
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- Zoology, Sexual Selection, Hunting, Ursus

Males of many animals have more than a single exaggerated secondary sexual character, but inter-specific variability in the number of ornaments has never been explained. We examine three hypotheses that may account for the presence of multiple ornaments. First, the multiple message hypothesis proposes that each display reflects a single property of the overall quality of an animal. This is likely to be the case for ornaments that respond to condition on different time scales. Second, the redundant signal hypothesis suggests that each ornament gives a partial indication of condition. Females pay attention to several sex traits because in combination they provide a better estimate of general condition than does any single ornament. The redundant signal hypothesis predicts that (i) multiple ornaments should be particularly common among taxa with relatively uncostly and fine-tuned female choice, and (ii) females pay equal attention to the expression of all the secondary sex traits in order to obtain an estimate of overall male condition. Finally, the unreliable signal hypothesis argues that some ornaments are unreliable indicators of overall condition and are only maintained because they are relatively uncostly to produce and there is a weak female preference for them. This predicts that (i) multiple sexual ornaments should be particularly common in taxa with the most intense sexual selection (i.e. lekking and other polygynous taxa), and (ii) there should be more evidence for condition dependence in ornaments of species with single as opposed to multiple ornaments. Both the latter predictions are supported by data on feather ornaments in birds.

- by Adhem Hussein
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- Sexual Selection, Biological Sciences, Environmental Sciences, Condition dependence

Great tits, Parus major, display their white cheek patches to one another during intraspecific encounters. We measured the size of these patches and the regularity of their borders (immaculateness) as part of an investigation into their function as signals. Patch size was not significantly related to any of our measures of fitness, but male great tits with more immaculate cheek patches had significantly greater access to a safer feeding site in winter and produced heavier chicks in small woods. Females with more immaculate patches bred significantly earlier in 2 of the 3 years of the study in both large and small woods. We decreased the immaculateness of both sexes with dye and found that competition with other tits significantly increased their exposure to danger when feeding. Factors resulting in reduced immaculateness included ectoparasites, fighting with conspecifics, faster feather wear in young birds and the timing of the autumn moult. Selection for immaculateness by conspecifics may be one mechanism responsible for the evolution of regular head and body patterns in several species of birds and in other animals.

- by Peter Ferns
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- Sexual Selection, Morphometry, Animal Behaviour, Animal communication

We documented the loss of brown bear (Ursus arctos) cubs-of-the-year (cubs) in 2 Swedish populations for 11 years in the north and 12 years in the south, and made spatial and temporal comparisons to examine whether nutritional, social... more

- by Sven Brunberg
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- Sexual Selection, Ursus, Brown bear, Social Factor
- by Dobrosława Ziółkowska
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- Adaptation, Sexual Selection, Evolution, Natural Selection

The mbuna cichlids of Lake Malawi are a diverse, monophyletic, and recently derived clade. Sexual selection is thought to have accelerated their rapid diversification, though the mechanism by which this has occurred remains unknown. In this study, we examine the effect that male-male interactions have on female preference. We first used a short interaction experiment as a proxy for male dominance. We then measured female preference for (1) a single, isolated male; (2) a group of three, highly ranked males, relative to a group of lower ranked males; and (3) a group of three, mixed-ranked males against a similar group of mixed-rank males. We found that male dominance was highly correlated with male standard length. Female preference for male standard length and for dominance rank was significant in both isolated and group interactions. However, females only showed preference for groups of interacting males when males were segregated by dominance rank, not when groups were composed of both dominant and subordinate males. The results suggest that male-male contests influence female mating decisions. By investigating the rules that dictate the outcomes of such interactions we can elucidate the role that behavior plays in the diversification of this species-rich lineage.

- by Rebecca Jordan
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- Zoology, Ethology, Mate Choice, Sexual Selection

Fire plays an important role in the evolution of life-history characteristics of organisms living in fire-prone regions. Although there are many reports of plants exhibiting adaptations to reduce the harmful or lethal effects of fire, little is known about fire-resistance mechanisms among animals, other than fleeing responses. Here, we report observations that may represent a type of fire adaptation in a bird species: bowers in one population of the Great Bowerbird Chlamydera nuchalis remained unburned after fire. If a bower is destroyed by fire or other mechanisms during courtship and breeding season, the male may lose the opportunity to mate with females, thereby reducing his apparent fitness. Therefore, traits that minimise the damage to bowers from fires may be beneficial. By measuring the unburned areas surrounding bowers after fires, we showed that the survival of bowers after fires is unlikely to be solely related to chance. Our observations are consistent with the hypothesis that bower resistance to fire is an adaptation of the Great Bowerbird. However, it is also possible that unburned bowers are by-products of sexual selection.

- by Richard Noske and +1
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- Zoology, Ethology, Fire Ecology, Adaptation
- by Adhem Hussein
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- Sexual Selection, Morphology, Biological Sciences, Allometry

Acoustic signals mediate mate choice, resource defense, and species recognition in a broad range of taxa. It has been proposed, therefore, that divergence in acoustic signals plays a key role in speciation. Nonetheless, the processes driving divergence of acoustic traits and their consequences in terms of speciation are poorly understood. A review of empirical and comparative studies reveals strong support for a role of sexual selection in acoustic divergence, but the possible concomitant influences of ecological context are rarely examined. We summarize a conceptual framework for testing the relative significance of both adaptive and neutral mechanisms leading to acoustic divergence, predictions for cases where these processes lead to speciation, and how their relative importance plays out over evolutionary time.

- by Matthew Wilkins
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- Acoustics, Speciation, Sexual Selection, Population Dynamics
- by Moira van Staaden
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- Sexual Selection, Biological Sciences

Genes and culture represent two streams of inheritance that for millions of years have flowed down the generations and interacted. Genetic propensities, expressed throughout development, influence what cultural organisms learn. Culturally transmitted information, expressed in behaviour and artefacts, spreads through populations, modifying selection acting back on populations. Drawing on three case studies, I will illustrate how this gene-culture coevolution has played a critical role in human evolution. These studies explore (i) the evolution of handedness, (ii) sexual selection with a culturally transmitted mating preference, and (iii) cultural niche construction and human evolution. These analyses shed light on how genes and culture shape each other, and on the significance of feedback mechanisms between biological and cultural processes.

- by Kevin Laland
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- Genetics, Evolutionary Psychology, Human Evolution, Coevolution

Female superb fairy-wrens Malurus cyaneus initiate extragroup fertilizations by forays to the territory of preferred males, just before sunrise, 2-4 days before egg laying. Over a prolonged breeding season, males advertise their availability to foraying females by singing during the dawn chorus. Here, we show that 1) males commence dawn advertisement at the same time of the year regardless of their quality or status; 2) subordinate males advertise by singing in close proximity to the dominant, or by using the dominant's song perch, despite inevitable punishment; 3) low-quality dominants and their helpers sing from the boundary of their own territory, which increases their proximity to attractive neighboring dominants; 4) each spatial cluster of males use a common dialect of a song that is implicated in extragroup choice, despite the ability of individual males to sing several dialects; and 5) there is leakage of paternity to lower-quality helpers and neighbors as a result of their ''satellite'' behavior. Collectively, these data suggest that Wagner's hidden lek hypothesis (Wagner RA, 1998. Hidden leks: sexual selection and the clustering of avian territories. In: Parker PG, Burley NT, editors. Avian reproductive tactics: female and male perspectives. Ornithological Monographs No. 49. Allen Press. p. 123-145) can be extended to birds that defend year-round all-purpose territories and that mating induced by parasitic behavior of low-quality satellites can be one explanation for polyandry in birds.

- by Megan Head and +1
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- Evolutionary Biology, Zoology, Sexual Selection, Ecology

Odonates exhibit a wide range of territorial and nonterritorial mating tactics and are ideal for investigating alternative reproductive behaviours. We studied male mating tactics in the American rubyspot damselfly, Hetaerina americana, a species that exhibits red wing spots that have been suggested to have evolved as a consequence of maleemale contests. In this species mating success is enhanced by the ability of males to defend territories along streams and rivers, which depends on the amount of thoracic fat reserves available. Previous studies on this species have distinguished between territorial and nonterritorial males, in which the former obtain significantly more matings than the latter. In our study, however, we found a third reproductive tactic: switching. Switcher males exhibit both territorial and nonterritorial tactics and a mating success similar to that of territorial and nonterritorial males, although this result may be confounded by the small sample size used for this analysis. We suggest that the different mating tactics may be condition determined: territorial males contained the highest fat reserves, nonterritorial males had the least fat content and switchers had intermediate fat loads. We also show that there were no age differences between males using these tactics. Our results suggest that territorial behaviour is extremely plastic in this species. Finally, we discuss the implications of our study and directions for future work on territorial and nonterritorial reproductive tactics in odonates.

We studied supra-orbital combs in lekking black grouse (Tetrao tetrix) in relation to sexual selection at five leks in Finland 1991 and four leks in Sweden 1992. Comb size was estimated in two ways: by observing its natural size in the field at different behaviors (''observed comb size''), and by measuring the comb size from captured birds (''measured comb size''). The size of combs is highly variable, and individuals can change it within seconds. Males express their larger combs during display, as compared to other behaviors. Observed mean comb sizes were larger on leks with a higher number of males and a higher number of copulations. Measured and observed comb sizes and copulatory success did not significantly correlate when all males where analyzed, but a positive and significant relationship between observed comb size and copulatory success was found within males that achieved copulations. Measured comb length correlated positively with the amount of testosterone. While females were present on the lek, displaying and successful males showed the largest observed comb size. When we compared observed comb size during fighting between successful and unsuccessful males and correlated comb size of pairs of fighting males with their fighting activity, no significant differences in comb size were found. The result that comb size correlated significantly with an increase in testosterone level and that larger comb size, within successful males, predicted higher copulatory success suggests that combs may be a cue for females to assess male quality. The lack of a significant relationship between observed comb size and fighting behavior suggests that comb size either has minor importance in male-male signaling on the lek or that males may express similar-sized combs during fighting to avoid serious fights and thus risk of comb injuries.

- by Niklas Björklund and +1
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- Evolutionary Biology, Zoology, Sexual Selection, Ecology

The genus Phanaeus Macleay comprises an important part of the Neotropical dung beetle fauna. With a few exceptions, these beetles are preferentially coprophagous, exploiting the moist excrement of large herbivores and omnivores. The nesting behavior (nidification) of Phanaeus is characterized mainly by tunneling rather than rolling behavior. Phanaeus species are Pattern II nesters: during the breeding season, the male and female cooperate in provisioning the nesting gallery, even though females can perform these activities alone. Their intricate behaviors and extravagant colors and horns have made these beetles the subject of numerous publications dealing with male-male competition, bisexual cooperation, nidification and more. This review is meant to give an overview of published and new behavioral observations for these species as well as to suggest directions for future research.

- by Michael May
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- Sexual Selection, Competition, Dung Beetles, Behavioral Ecology

2006. Using a proxy of plant productivity (NDVI) to find key periods for animal performance: the case of roe deer. Á/ Oikos 112: 565 Á/572. Animals in seasonal environments are affected by climate in very different ways depending on season and part of the climatic effects operates indirectly through the plants. Vegetation conditions in spring and summer are regarded as decisive for the reproductive success and the offspring's condition of large herbivores, but objective ways to determine key periods during the growing season have not been done often due to limitations in plant data. Using satellite data (NDVI), we determined how plant productivity from birth to fall influences the following winter body mass of roe deer fawns. We do this in two populations, the first inhabiting the low productive Chizé reserve in south western France with an oceanic climate and the second from Trois Fontaines, a highly productive forest with continental climate in east France. The effect of plant productivity was similar for male and female fawn mass, as expected from the weak intensity of sexual selection in roe deer life history traits. We found contrasting results between sites, with a strong effect of plant productivity in spring (April-May) in the Chizé population, but no effect in the Trois Fontaines population. The relatively low variability in winter fawn body mass could account for the absence of NDVI effects at Trois Fontaines. However, such results might also point to a limitation in the use of the NDVI, since the relationship between the canopy and the plant productivity at the ground level might be weak in the highly productive forest of Trois Fontaines.

- by Jean-Michel Gaillard
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- Sexual Selection, Ecology, Seasonality, Roe Deer

Hypotheses of parasite-mediated sexual selection (PMSS) propose that elaborate male ornaments have evolved due to female preferences. Females would benefit from mating with more ornamented males if males' ornamentation signals their health status and ability to provide parasite resistance genes for the offspring. Carotenoid-based plumage coloration of birds has been hypothesised to honestly reflect an individual's health status due to trade-off in allocation of carotenoids between maintenance and signalling functions. The prediction of this hypothesis, namely that individuals with brighter plumage are able to mount stronger immune responses against novel antigens and reveal generally better health state, was tested in captive male greenfinches (Carduelis chloris). Greenfinches with brighter yellow breast feathers showed stronger humoral immune response against novel antigen (SRBC) while no relationship between plumage coloration and an estimate of cellmediated immune responsiveness (PHA response) was detected. Elaborately ornamented individuals had better general health state as indicated by the negative correlations between plumage brightness and heterophil haemoconcentration. Consistent with the concept of PMSS, these results suggest that carotenoid-based plumage coloration in greenfinches honestly signals immunocompetence and health status.

- by Peeter Hõrak
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- Pigmentation, Immune response, Sexual Selection, Ecology

Many animals use coloration to communicate with other individuals. Although the signalling role of avian plumage colour is relatively well studied, there has been much less research on coloration in avian bare parts. However, bare parts could be highly informative signals as they can show rapid changes in coloration. We measured bill colour (a ubiquitous bare part) in over 1600 passerine species and tested whether interspecific variation in carotenoid-based coloration is consistent with signalling to potential mates or signalling to potential rivals in a competitive context. Our results suggest that carotenoid bill coloration primarily evolved as a signal of dominance, as this type of coloration is more common in species that live in social groups in the nonbreeding season, and species that nest in colonies; two socio-ecological conditions that promote frequent agonistic interactions with numerous and/or unfamiliar individuals. Additionally, our study suggests that carotenoid bill c...

- by Bart Kempenaers
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- Evolutionary Biology, Zoology, Communication, Mate Choice

The bill is a sexually dimorphic structure in many bird species and implicated in numerous functions. Sexual differences may arise from sexual selection or ecological divergence. Here, we examined differences in bill size and shape between males and females and explored to what extent these relate to feeding ecology of each sex in Cory's shearwater (Calonectris diomedea). We applied linear measurements and geometric morphometric methods to examine sexual differences in bill size and shape. We investigated feeding ecology by tracking foraging movements during the breeding period and by analysing stable isotope signatures in blood during the breeding period and in feathers grown during the non-breeding period. Bill traits were all sexually dimorphic, both in absolute and relative terms, and scaled hypermetrically with body mass in several characters in males. However, males and females did not differ in their feeding areas or isotopic signatures and no significant correlation was observed between these traits and bill dimorphism. Therefore, we discard the foraging-niche divergence hypothesis, and suggest that sexual dimorphism in bill size in this species is more likely driven by sexual selection related to antagonistic interactions.

- by Antigoni Kaliontzopoulou
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- Zoology, Sexual Selection, Natural Selection, Sexual dimorphism

Across 5 experimental studies, the authors explore selective processing biases for physically attractive others. The findings suggest that (a) both male and female observers selectively attend to physically attractive female targets, (b) limiting the attentional capacity of either gender results in biased frequency estimates of attractive females, (c) although females selectively attend to attractive males, limiting females' attentional capacity does not lead to biased estimates of attractive males, (d) observers of both genders exhibit enhanced recognition memory for attractive females but attenuated recognition for attractive males. Results suggest that different mating-related motives may guide the selective processing of attractive men and women.

- by Steven Neuberg
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- Marketing, Psychology, Cognitive Science, Personality

This overview paper presents the leading theories which attempt to explain the emergence of one of the prominent features specific to our species – the protruding chin. Established theories discussing this phenomenon include the effect of masticatory stress theory, a sexual selection theory and theories relating the human chin to the emergence of spoken language. However, these explanations have proved inconclusive and the processes responsible for the emergence of mentum osseum in the Late Pleistocene remain unclear.

Male reproductive success in many mammals depends on their ability to allocate sufficient energetic resources to mating competition. Such costs are particularly pronounced in species with high levels of sexual body dimorphism, intense polygyny and distinct breeding seasons. I tested the hypothesis that male reproductive effort incurs significant energetic costs in wild chimpanzees (Pan troglodytes), a species with moderate sexual dimorphism, promiscuous mating and lack of breeding seasonality. My field studies combined behavioral observations on male chimpanzee behavior with non-invasive sampling of urinary C-peptide (UCP). UCP is a biomarker of insulin production that indexes individual energy balance. This dissertation contributes to the understanding of UCP as an energy assay by (1) validating the application of UCP for assessing dietary quality in bonobos (Pan paniscus) at Kokolopori, DRC and (2) providing a detailed assessment of diurnal variation in UCP levels in relation to short-term changes in food intake in chimpanzees at Kanyawara, Kibale NP, Uganda. I used UCP measurements in conjunction with full-day focal observations of male chimpanzees to assess the energetic costs of male-male competition for status and mating opportunities. Data on feeding time and rates of aggression suggested that males experience a reduction in energy intake and an increase in energy expenditure when highly attractive parous females were in estrus. UCP iv data supported these conclusions because males had lower UCP levels on mating days, and rates of aggression were negatively associated with UCP levels. Mean daily party size was also associated with low UCP levels, controlling for the presence of estrous females. Habitat-wide availability of preferred fruits was positively associated with male rates of aggression suggesting that energy availability mediates male investment towards energetically costly competitive behaviors. Contrary to expectations males who were most successful in obtaining copulations (high-ranking males) did not suffer higher energetic costs than lower-ranking males during periods of mating competition. Costs or reproductive effort include both direct competition for matings and long-term competition over social status. Maintenance of social rank over long periods appears to be particularly important in this slow-reproducing, long-lived and nonseasonally breeding primate.

- by Alexander Georgiev
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- Evolutionary Biology, Mating Systems, Sexual Selection, Primates

Many vertebrates use carotenoid-based signals in social or sexual interactions. Honest signalling via carotenoids implies some limitation of carotenoid-based colour expression among phenotypes in the wild, and at least five limiting proximate mechanisms have been hypothesized. Limitation may arise by carotenoid-availability, genetic constraints, body condition, parasites, or detrimental effects of carotenoids. An understanding of the relative importance of the five mechanisms is relevant in the context of natural and sexual selection acting on signal evolution. In an experimental field study with carotenoid supplementation, simultaneous cross-fostering, manipulation of brood size and ectoparasite load, we investigated the relative importance of these mechanisms for the variation in carotenoid-based coloration of nestling great tits (Parus major). Carotenoid-based plumage coloration was significantly related to genetic origin of nestlings, and was enhanced both in carotenoidsupplemented nestlings, and nestlings raised in reduced broods. We found a tendency for ectoparasite-induced limitation of colour expression and no evidence for detrimental effects of carotenoids on growth pattern, mortality and recruitment of nestlings to the local breeding population. Thus, three of the five proposed mechanisms can generate individual variation in the expression of carotenoid-based plumage coloration in the wild and thus could maintain honesty in a trait potentially used for signalling of individual quality. J . E V O L . B I O L . 1 6 ( 2 0 0 3 ) 9 1 -1 0 0 ª 2 0 0 3 B L A C K W E L L P U B L I S H I N G L T D Variation in carotenoid-based colours 99 J . E V O L . B I O L . 1 6 ( 2 0 0 3 ) 9 1 -1 0 0 ª 2 0 0 3 B L

- by Heinz Richner
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- Evolutionary Biology, Genetics, Zoology, Sexual Selection

In his pioneering work on cryptic female choice, Eberhard identified a wide range of mechanisms that potentially allow multiply-mated females to bias paternity in favour of certain types of male following the start of copulation. The aim of this chapter is to review critically the empirical evidence for a range of these mechanisms of cryptic female choice in crickets and relatives (Orthoptera: Ensifera), while taking into account coevolutionary interactions between the sexes. There is compelling evidence that female crickets control the duration of spermatophore attachment and/or the uptake of sperm to the sperm storage organ to bias paternity in favour of males expressing a variety of favourable traits, or in favour of non-kin males. There is also some evidence that females can bias paternity to favour males with certain traits by choosing to remain with them for repeated mating. For other potential mechanisms of cryptic female choice, such as differential allocation of resources to the production of eggs, there is currently insufficient evidence to distinguish male-induced effects from cryptic female choice (if, indeed, such a distinction can be made). The evidence that mechanisms of cryptic female choice have resulted in coevolutionary adaptations in males is strong: males have evolved a wide range of behaviours to facilitate ejaculate transfer by deterring the female from removing the ampulla of the spermatophore prematurely, for example. How such adaptations affect the form and intensity of cryptic female choice and whether or not they result in ongoing sexually antagonistic coevolution deserve further investigation.

- by Karim Vahed
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- Sexual Selection

The ability to see colors is not universal in the animal kingdom. Those animals that can detect differences in the wavelengths of the electromagnetic spectrum glean valuable sensory information about their environment. They use color vision to forage, avoid predators, and find highquality mates. In the past, the colors that humans could see clouded scientists' study of animals' color perception. Leaving that bias behind has led to new insights about how and why the color vision of animals evolved. This paper provides a brief introduction to color vision, the genetics of color vision in humans, what colors other animals see, and how scientists study color vision. We examine the consequences of having color vision, including speciation, loss of olfactory capabilities, and sexual selection.

- by Molly Morris
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- Genetics, Perception, Sexual Selection, Evolution

Males in many bird species mimic the vocalizations of other species during sexual displays, but the evolutionary and functional significance of interspecific vocal mimicry is unclear. Here we use spectrographic cross-correlation to compare mimetic calls produced by male satin bowerbirds (Ptilonorhynchus violaceus) in courtship with calls from several model species. We show that the accuracy of vocal mimicry and the number of model species mimicked are both independently related to male mating success. Multivariate analyses revealed that these mimetic traits were better predictors of male mating success than other male display traits previously shown to be important for male mating success. We suggest that preference-driven mimetic accuracy may be a widespread occurrence, and that mimetic accuracy may provide females with important information about male quality. Our findings support an alternative hypothesis to help explain a common element of male sexual displays.

- by Gail Patricelli
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- Sexual Selection, Biology, Biological Sciences, Cross Correlation

Among the most familiar sexual signals are red, yellow, and orange sexual traits pigmented by carotenoids. Many birds can detect near-ultraviolet (UV) light, and UV signals can play key roles in mate choice. Grouse (Tetraonidae) exhibit bright carotenoid-dependent sexual ornaments, their supra-orbital combs, which to humans appear orange-red. Combs also reflect in the UV, which is not visible to humans but is likely to be visible to grouse. In male red grouse Lagopus lagopus scoticus, we show that comb UV reflectance decreases with increasing comb size and redness. By removing the epidermis of combs, where carotenoid pigments are, we show that the UV reflectance is a property of the dermis, underneath the red pigmented epidermis. Carotenoid pigmentation of combs acted as a mask to reduce reflectance by the dermis in the range 400-550 nm and in the UV, 300-400 nm. Patagium skin (nonornamental skin under the wing) also reflects in the UV, but epidermis removal on this bare part tended to reduce UV reflectance, whereas removal of the red epidermis of combs increased UV reflectance. Males in better condition (greater body mass relative to size) had bigger and redder combs, but with less UV. Thus, carotenoid pigments of grouse combs are deposited on a white background with significant UV reflectance, which can influence how the signal is perceived by conspecifics. Carotenoid-based traits exhibit UV reflectance in a number of species, but how UV reflectance and carotenoid pigmentation influence colour remains little known for integumentary ornaments compared to plumage traits. UV vision is not uncommon in birds and other animals, so future studies should investigate how UV reflectance influences the perception of carotenoid-based signals of quality.

Animal color pattern phenotypes evolve rapidly. What influences their evolution? Because color patterns are used in communication, selection for signal efficacy, relative to the intended receiver's visual system, may explain and predict the direction of evolution. We investigated this in bowerbirds, whose color patterns consist of plumage, bower structure, and ornaments and whose visual displays are presented under predictable visual conditions. We used data on avian vision, environmental conditions, color pattern properties, and an estimate of the bowerbird phylogeny to test hypotheses about evolutionary effects of visual processing. Different components of the color pattern evolve differently. Plumage sexual dimorphism increased and then decreased, while overall (plumage plus bower) visual contrast increased. The use of bowers allows relative crypsis of the bird but increased efficacy of the signal as a whole. Ornaments do not elaborate existing plumage features but instead are innovations (new color schemes) that increase signal efficacy. Isolation between species could be facilitated by plumage but not ornaments, because we observed character displacement only in plumage. Bowerbird color pattern evolution is at least partially predictable from the function of the visual system and from knowledge of different functions of different components of the color patterns. This provides clues to how more constrained visual signaling systems may evolve.

- by John A Endler
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- Evolutionary Biology, Pigmentation, Molecular Evolution, Sexual Selection

SYNOPSIS. We studied blood parasite infections in relation to aspects of sexual selection and mate choice in 10 species of birds of paradise. Across species there was a significant, positive correlation between relative parasite intensity and showiness in males. Parasite infections also correlated across species with the degree of sexual dimorphism and varied with mating systems. Promiscuous species were showier and had significantly higher parasite prevalences than monogamous species. Within one species, Lawes' Parotia (Parotia lawesii), parasite intensity was negatively correlated with all phenotypic traits examined, a pattern significantly different than random. The mating success of males with low parasite intensities varied, but males with high intensities did not mate. Sampling of individual males on repeated occasions revealed large temporal differences in parasite counts which spanned the range believed to affect behavior and mating success. Whereas the interspecific correlations support one prediction of the Hamilton and Zuk hypothesis on parasites and sexual selection, the intraspecific data are equivocal with respect to a second prediction of this hypothesis. Parasites appear to influence the behavior of Lawes' Parotia, but alternative explanations to that of Hamilton and Zuk for this effect are equally plausible and there is no evidence of a link between female choice and the traits in males indicative of parasite loads. We suggest that female Lawes' Parotia may be avoiding highly infected males rather than actively choosing parasite-resistant males.

- by Stephen Pruett-Jones
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- Zoology, Sexual Selection, American

We disagree with the idea of Roughgarden et al. that because sexual reproduction is cooperative it can only be understood in a cooperative framework that ignores conflict. In our view, it is conflict that has generated the array of... more

- by Luca Borger (Börger)
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- Animal Behavior, Mating Systems, Sexual Selection, Biology
- by Joan Roughgarden
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- Game Theory, Sexual Selection, Sexual Conflict, Animal Behaviour

Studies in evolutionary psychology and sexual selection theory show that heterosexual men prefer younger mating partners than heterosexual women in order to ensure reproductive success. However, previous research has generally not examined differences in mating preferences as a function of sexual orientation or the type of relationship sought in naturalistic settings. Given that homosexual men seek partners for reasons other than procreation, they may exhibit different mating preferences than their heterosexual counterparts. Moreover, mating preferences may show important differences depending on whether an individual is seeking a long-term versus a short-term relationship. The purpose of the present study was to examine these issues by comparing partner preferences in terms of age and relationship type between homosexual and heterosexual men placing internet personal advertisements. Participants included 439 homosexual and 365 heterosexual men who placed internet ads in the U.S. or Canada. Ads were coded for the participant's age, relationship type (longer-term or shortterm sexual encounter) sought, and partner age preferences. Significantly more homosexual than heterosexual men sought sexual encounters, although men (regardless of sexual orientation) seeking sexual encounters preferred a significantly wider age range of partners than men seeking longer-term relationships. These findings suggest that partner preferences are independent of evolutionary drives to procreate, since both types of men preferred similar ages in their partners. In addition, they highlight the importance of examining relationship type in evolutionary studies of mating preferences, as men's partner preferences show important differences depending upon the type of relationship sought.

- by Kyle Gobrogge
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- Psychology, Evolutionary Psychology, Research Design, Heterosexuality
- by Lorena Madrigal
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- Evolutionary Biology, Geography, Archaeology, Anthropology

Music is ubiquitous. Yet, its biological relevance is still an ongoing debate. Supporting the view that music had an ancestral role in courtship displays, a pilot study presented here provides preliminary evidence on the link between music and sexual selection. The underlying hypothesis is based on the fact that the sexually dimorphic neuropeptide vasopressin has its receptors in the part of the brain involved in music and dance performance (the basal ganglia), and its concentrations rise during sexual arousal in men. In addition, music, dance, and courtship phenotypes seem to be in part regulated by vasopressin and its genes. Hence, to test this hypothesis, a rhythmic synchronization task was employed here on one male subject during sexual arousal. Results revealed a significant effect of sexual arousal on rhythm synchronization. This is the first report that empirically supports the hypothesis on the role of music in sexual selection. Further studies are clearly required.

- by Alessandro Miani
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- Rhythm, Evolution of Music, Sexual Selection, Dance

Explaining sexual ornamentation in the limiting sex, usually females, requires information on the proximate background of ornaments and their consequences for sexual selection. Phenotypic variation within individuals has received little attention in either of these research directions. We used 6 years of data to examine the information content and potential role of white wing patch size in female collared flycatchers, Ficedula albicollis. Female wing patch size differed among years. Yearling females had smaller wing patches than older females. The negative effect of original patch size on intraindividual patch size change was stronger in yearling than in older birds, which may reflect an age-dependent trade-off. Change in wing patch size was strongly positively related to the summer North Atlantic Oscillation (NAO) index. Clutch size laid in the previous breeding season had a negative effect on patch size change, but only in high-NAO years. Thus, the immediate effect of poor climate during moult apparently overrode the more indirect influence of reproductive effort. Two sexually selected ornaments of mates were unrelated to female wing patch size at the population level, but intraindividual changes of female wing patch size significantly predicted differences in wing patch size between mates obtained in the 2 years. Our data suggest that significant mating advantages to more ornamented females may not be detected from population-level mating patterns. Research on potential female ornaments should also pay more attention to age-dependent phenotypic plasticity, the trade-off between current and future ornament size and the costs of reproduction to apparent future attractiveness.

- by Marcel Eens
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- Sexual Selection, Phenotypic Plasticity, Animal Behaviour, Biological Sciences

It is estimated that 4%, to 5%, of the adult population within the United States, are openly engaging in polyamorous style relationship s. Black Americans are substantially underrepresented in that percentage. This composition discusses
polyamory and how polyamorous relationship structures may be beneficial in black community building, restoration, and strengthening efforts. The first section focuses on polyamory, its history, manifestations, and theory. The second section dissects Black American social conditions throughout American history. The third section discusses polyamory and its implementation within the Black American community. The fourth section highlights a personal interview with a Black American polyamorous woman to provide an intimate insight into life as a polyamorous Black American.

We conducted 10 mark-recapture experiments in natural populations of Trinidadian guppies to test hypotheses concerning the role of viability selection in geographic patterns of male color variation. Previous work has reported that male guppies are more colorful in low-predation sites than in high-predation sites. This pattern of phenotypic variation has been theorized to reflect differences in the balance between natural (viability) selection that disfavors bright male color (owing to predation) and sexual selection that favors bright color (owing to female choice). Our results support the prediction that male color is disfavored by viability selection in both predation regimes. However, it does not support the prediction that viability selection against male color is weaker in low-predation experiments. Instead, some of the most intense bouts of selection against color occurred in low-predation experiments. Our results illustrate considerable spatiotemporal variation in selection among experiments, but such variation was not generally correlated with local patterns of color diversity. More complex selective interactions, possibly including the indirect effects of predators on variation in mating behavior, as well as other environmental factors, might be required to more fully explain patterns of secondary sexual trait variation in this system.

- by Michael Kinnison and +1
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- Evolutionary Biology, Pigmentation, Sexual Selection, Evolution

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / m o l m u t C o m m u n i t y a d d r e s s : w w w . e l s e v i e r . c o m / l o c a t e / m u t r e s Factors affecting germline mutations in a... more

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / m o l m u t C o m m u n i t y a d d r e s s : w w w . e l s e v i e r . c o m / l o c a t e / m u t r e s Factors affecting germline mutations in a hypervariable microsatellite: A comparative analysis of six species of swallows (Aves: Hirundinidae) .no (J.A. Anmarkrud).

- by Jarl Anmarkrud and +3
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- Population Genetics, Molecular Evolution, Sperm Competition, Sexual Selection

Research has failed to reach consensus on the characteristics of attractive male faces. Different studies have reported preferences for phenotypically average faces, and faces with both exaggerated and reduced sexual dimorphism. Recent studies demonstrate cyclic changes in female sexual behavior and preferences for odors and facial characteristics that may reflect conditional mating strategies. We employed computer graphic techniques to manipulate the "masculinity" or "femininity" of a composite male face by exaggerating or reducing the shape differences between female and male average faces. Five stimuli with varying levels of masculinity and femininity were presented in a national U.K. magazine, with a questionnaire. Female respondents in the follicular phase of their menstrual cycle ( n ϭ 55) were significantly more likely to choose a masculine face than those in menses and luteal phases ( n ϭ 84). This study provides further evidence that when conception is most likely, females prefer testosteronerelated facial characteristics that may honestly advertise immunocompetence.

- by David Perrett
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- Psychology, Cognitive Science, Anthropology, Sexual Selection

Current theoretical and empirical findings suggest that mate preferences are mainly cued on visual, vocal and chemical cues that reveal health including developmental health. Beautiful and irresistible features have evolved numerous times in plants and animals due to sexual selection, and such preferences and beauty standards provide evidence for the claim that human beauty and obsession with bodily beauty are mirrored in analogous traits and tendencies throughout the plant and animal kingdoms. Human beauty standards reflect our evolutionary distant and recent past and emphasize the role of health assessment in mate choice as reflected by analyses of the attractiveness of visual characters of the face and the body, but also of vocal and olfactory signals. Although beauty standards may vary between cultures and between times, we show in this review that the underlying selection pressures, which shaped the standards, are the same. Moreover we show that it is not the content of the standards that show evidence of convergence -it is the rules or how we construct beauty ideals that have universalities across cultures. These findings have implications for medical, social and biological sciences.

- by Karl Grammer and +1
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- Evolutionary Psychology, Mate Choice, Sexual Selection, Face

Most theories of human mental evolution assume that selection favored higher intelligence and larger brains, which should have reduced genetic variance in both. However, adult human intelligence remains highly heritable, and is genetically correlated with brain size. This conflict might be resolved by estimating the coefficient of additive genetic variance (CVA) in human brain size, since CVAs are widely used in evolutionary genetics as indexes of recent selection. Here we calculate for the first time that this CVA is about 7.8, based on data from 19 recent MRI studies of adult human brain size in vivo: 11 studies on brain size means and standard deviations, and 8 studies on brain size heritabilities. This CVA appears lower than that for any other human organ volume or life-history trait, suggesting that the brain has been under strong stabilizing (average-is-better) selection. This result is hard to reconcile with most current theories of human mental evolution, which emphasize directional (more-is-better) selection for higher intelligence and larger brains. Either these theories are all wrong, or CVAs are not as evolutionarily informative as most evolutionary geneticists believe, or, as we suggest, brain size is not a very good index for understanding the evolutionary genetics of human intelligence.

- by Lars Penke
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- Psychology, Cognitive Science, Evolutionary Psychology, Brain Imaging