Alan H. Krakauer

Kin selection and cooperative courtship in wild turkeys

In the few species of birds in which males form display partnerships to attract females, one male secures most or all of the copulations. This leads to the question of why subordinate males help in the absence of observable reproductive benefits. Hamiltons concept of kin selection, whereby individuals can benefit indirectly by helping a relative, was a crucial breakthrough for understanding apparently altruistic systems. However in the only direct test of kin selection in coordinated display partnerships, partners were unrelated, discounting kin selection as an explanation for the evolution of cooperation. Here I show, using genetic measures of relatedness and reproductive success, that kin selection can explain the evolution of cooperative courtship in wild turkeys. Subordinate (helper) males do not themselves reproduce, but their indirect fitness as calculated by Hamiltons rule more than offsets the cost of helping. This result confirms a textbook example of kin selection that until now has been controversial and also extends recent findings of male relatedness on avian leks by quantifying the kin-selected benefits gained by non-reproducing males.

The opportunity for sexual selection: not mismeasured, just misunderstood

Evolutionary biologists have developed several indices, such as selection gradients (β) and the opportunity for sexual selection (Is), to quantify the actual and/or potential strength of sexual selection acting in natural or experimental populations. In a recent paper, Klug et al. (J. Evol. Biol.23, 2010, 447) contend that selection gradients are the only legitimate metric for quantifying sexual selection. They argue that Is and similar mating‐system‐based metrics provide unpredictable results, which may be uncorrelated with selection acting on a trait, and should therefore be abandoned. We find this view short‐sighted and argue that the choice of metric should be governed by the research question at hand. We describe insights that measures such as the opportunity for selection can provide and also argue that Klug et al. have overstated the problems with this approach while glossing over similar issues with the interpretation of selection gradients. While no metric perfectly characterizes sexual selection in all circumstances, thoughtful application of existing measures has been and continues to be informative in evolutionary studies.

Experimental Chronic Noise Is Related to Elevated Fecal Corticosteroid Metabolites in Lekking Male Greater Sage- Grouse (Centrocercus urophasianus)

There is increasing evidence that individuals in many species avoid areas exposed to chronic anthropogenic noise, but the impact of noise on those who remain in these habitats is unclear. One potential impact is chronic physiological stress, which can affect disease resistance, survival and reproductive success. Previous studies have found evidence of elevated stress-related hormones (glucocorticoids) in wildlife exposed to human activities, but the impacts of noise alone are difficult to separate from confounding factors. Here we used an experimental playback study to isolate the impacts of noise from industrial activity (natural gas drilling and road noise) on glucocorticoid levels in greater sage-grouse (Centrocercus urophasianus), a species of conservation concern. We non-invasively measured immunoreactive corticosterone metabolites from fecal samples (FCMs) of males on both noise-treated and control leks (display grounds) in two breeding seasons. We found strong support for an impact of noise playback on stress levels, with 16.7% higher mean FCM levels in samples from noise leks compared with samples from paired control leks. Taken together with results from a previous study finding declines in male lek attendance in response to noise playbacks, these results suggest that chronic noise pollution can cause greater sage-grouse to avoid otherwise suitable habitat, and can cause elevated stress levels in the birds who remain in noisy areas.

Cooperating to compete: altruism, sexual selection and causes of male reproductive cooperation

Competition among males for access to reproductive opportunities is a central tenet of behavioural biology that has critical implications for studies of mating systems, sexual selection and the evolution of numerous phenotypic traits. Given the expectation that males should compete vigorously for access to females, it may at first seem paradoxical that males in some species cooperate to reproduce, often resulting in the apparent sacrifice of direct fitness by some members of these cooperative partnerships. Because this form of cooperation lies at the interface between natural, sexual and kin selection, studies of the adaptive consequences of male reproductive cooperation may yield important insights into how complex and sometimes conflicting selective pressures shape individual behaviour. Here, we define and review examples of reproductive cooperation among male animals. We take an integrative approach to reviewing the potential causes of maleemale cooperation, including potential adaptive hypotheses, ecological correlates, phylogenetic patterns and physiological mechanisms. The impact of male reproductive cooperation on sexual selection theory is also discussed. We conclude by outlining several important directions for future research, including efforts to improve understanding of the ecological and demographic contexts in which male reproductive cooperation occurs. Collectively, such analyses promise to improve our understanding of multiple fundamental concepts in evolutionary biology. 2013 The Authors. Published on behalf of The Association for the Study of Animal Behaviour by Elsevier Ltd. All rights reserved.

WHY DOES THE YELLOW‐EYED ENSATINA HAVE YELLOW EYES? BATESIAN MIMICRY OF PACIFIC NEWTS (GENUS TARICHA) BY THE SALAMANDER ENSATINA ESCHSCHOLTZII XANTHOPTICA

Abstract Color patterns commonly vary geographically within species, but it is rare that such variation corresponds with divergent antipredator strategies. The polymorphic salamander Ensatina eschscholtzii, however, may represent such a case. In this species, most subspecies are cryptically colored, whereas E. e. xanthoptica, the Yellow eyed ensatina, is hypothesized to be an aposematic mimic of highly toxic Pacific newts (genus Taricha). To test the mimicry hypothesis, we conducted feeding trials using Western Scrub-Jays, Aphelocoma californica. In every feeding trial, we found that jays, following presentation with the presumed model (T. torosa), were more hesitant to contact the presumed mimic (E. e. xanthoptica) than a control subspecies lacking the postulated aposematic colors (E. e. oregonensis). The median time to contact was 315 sec for the mimic and 52 sec for the control. These results support the mimicry hypothesis, and we suggest that E. e. xanthoptica is likely a Batesian mimic, rather a Müllerian or quasi-Batesian mimic, of Pacific newts.

Do birds vocalize at higher pitch in noise, or is it a matter of measurement?

Studies have found that some birds use vocalizations with higher minimum frequency in noisy areas. Minimum frequency is often measured by visual inspection of spectrograms (“by-eye practice” (BEP)), which is prone to bias, e.g., if low-frequency components are masked by noise. We tested for this bias by comparing measurements of minimum frequency obtained with the BEP for the same set of red-winged blackbird vocalizations (songs and two call types “checks” and “cheers”) played back under ambient, medium, and high noise conditions using a dual playback experiment where both vocalizations and noise were introduced. We compared BEP measurements to those obtained from power spectrum analyses using a preset amplitude threshold (“threshold method” (TM)). The BEP was biased when measuring the minimum frequencies of songs and checks, which are masked by noise, but not when measuring cheers, which are higher pitched and thus not masked. Measures using the TM were not affected by noise, but this method may fail to identify the vocalizations’ lowest frequency if noise necessitates a low (i.e., conservative) threshold. Using the BEP, we also found a bias toward shorter-duration measurements for songs in increasing noise, and for checks, a bias toward increased measures of an energy distribution parameter (Freq5%), likely in correlation with increased measured minimum frequency. Measures taken from the unmasked cheers were similar regardless of the technique used. We discuss limitations of each approach and encourage the use of the TM, as studies using the BEP may lead to spurious results.Significance statementNoise from human activities is ubiquitous. Researchers have found that some birds vocalize at higher frequency (pitch) in noise, hypothesizing that this may improve signal detection in low-frequency noise. Noise may also hinder detection of signal components by researchers using the most common measurement technique (the BEP), which may be mistaken for increasing frequency. To examine this bias, we conducted a dual playback experiment, in which we broadcast the same vocalizations at three background noise levels. We found that BEP measures of minimum frequency increased with increasing noise even though the vocalizations did not change. We recommend the TM which yielded similar measures across noise levels, although it excluded some lower-frequency elements included by the BEP. We encourage researchers to use the TM over the BEP and to validate their methods across noise levels of interest.

Drawn into the vortex: The facing-past encounter and combat in lekking male greater sage-grouse (Centrocercus urophasianus)

Lekking male greater sage-grouse (Centrocercus urophasianus) compete with neighbours not only by strutting to attract females but also by directly challenging other males. These challenges include approaching another male and adopting an anti-parallel orientation at close quarters (‘facing past encounter’) and fighting, in which the birds strike one another with their wings. Facing past encounters and facing past encounters that led to fights in free-living sage-grouse were videotaped and analysed to test predictions arising from two sets of hypotheses to account for the features of such encounters. They could be used to assess or threaten opponents (index signal or threat signal hypotheses) or they may be the result of a stalemate in which one bird’s attempts to gain an vantage point for attack are neutralised by counter moves by the other bird (combat hypothesis). Frame-by-frame analyses of both facing past encounters and fights were used to extract data to test specific predictions arising from the three hypotheses. The results, overall, support the hypothesis that the facing past orientation arises from combat. However, the results also suggest that, once in the anti-parallel orientation, opportunities emerge for communication to take place.

Investigating female mate choice for mechanical sounds in the male Greater Sage-Grouse

ABSTRACT Although birds are generally known for their vocally produced songs and calls, some species have evolved alternate means of acoustic communication that do not require the syrinx. While many of these mechanical sounds are used in a courtship context, the importance of among- and within-individual variation in these sounds is almost entirely unknown. We investigated feather-produced sounds in male Greater Sage-Grouse (Centrocercus urophasianus), which congregate on leks during the spring breeding season and perform elaborate displays to attract females. Despite decades of research on the vocal components of the display, the frequency-modulated and mechanically generated “swish” sounds remain poorly studied. We used 2 years of acoustic data to evaluate the relationship between the time and frequency characteristics of the swish display and male mating success. Although characteristics of the swish sounds showed individual-specific patterns of variation, neither univariate nor multivariate analyses revealed direct effects of the acoustic qualities of these mechanical sounds on number of copulations. However, we did find that the frequency range of individual notes was correlated with note duration, and that males who successfully copulated showed a larger frequency range for a given duration than unsuccessful males. Furthermore, successful males increased this frequency change more strongly with the approach of a female than did unsuccessful males. These results parallel previous findings that successful and unsuccessful males show different patterns of adjustment with changing courtship conditions. Our results emphasize the importance of considering the interaction among multiple components of displays in analyses of mate choice, and help to broaden our understanding of the function of mechanical sounds in this and other species of birds.

Successfully mating male sage-grouse show greater laterality in courtship and aggressive interactions

Lateral biases in behaviours are common across animals. Greater laterality may be beneficial if it allows for more efficient neural processing, yet few studies have considered the possible importance of individual variation in lateral biases in wild animals, particularly for social behaviours. We examined lateral biases in lekking greater sage-grouse, Centrocercus urophasianus, a species in which males show lateral orientations during aggressive encounters and courtship interactions. For aggression, we found no significant lateral bias in fights, but when examining another agonistic behaviour, the side-to-side facing-past encounter, we found a left-eye bias but only in males that successfully mated with females. For courtship behaviour, we found that successfully mating males were more strongly lateralized than nonmating males, but the direction of laterality depended on whether males were using their binocular frontal field (left-eye bias) or monocular lateral hemifield (right-eye bias). Bias depended on social context as well; nonmating males showed a bias in courtship orientation only when far from the female. Our results reveal a complex pattern of laterality depending on the mating success of the male, his behaviour and the social environment in which he is acting. We found support for the hypothesis that greater laterality may be beneficial, although the mechanism for this relationship in this species remains unknown.

Necklace-style radio-transmitters are associated with changes in display vocalizations of male greater sage-grouse

Radio-transmitters are used widely in wildlife research because they allow researchers to track individual animals and monitor their activity. However, to provide unbiased information about a population, transmitters must be deployed on a representative sample of animals and must not alter the behavior of the individuals. The greater sage-grouse Centrocercus urophasianus has been studied intensively using radio-transmitters for the last several decades. A previous study demonstrated that males fitted with necklace-style radio-transmitters could be less likely to attend breeding grounds than those without transmitters. However, how transmitters affect the behavior of males that do attend leks has not been investigated. Therefore, we investigated whether radio-transmitters alter the characteristics of strut vocalizations or display frequency of male sage-grouse. We measured time and frequency characteristics of vocalizations from six collared and seven non-collared adult male sage-grouse on three leks in south-central Idaho, and for two collared and four non-collared males from two leks in northern Nevada. Only one vocalization characteristic (maximum frequency of the primary whistle) differed between collared and non-collared males across both populations. Collared males showed a lower maximum frequency of the primary whistle that typically fell outside the range of variation for non-collared males. This was the only difference found in the sample from Nevada, while in Idaho, collared males also exhibited a narrower bandwidth for the primary whistle (lower maximum frequency and higher minimum frequency), a shorter primary whistle, and a shorter secondary coo than non-collared males. Some acoustic characteristics of sage-grouse strut vocalizations are linked to mate choice by females, and therefore our results suggest that collars could reduce male mating success by altering the production of breeding vocalizations. Therefore, we recommend using alternative attachment techniques for behavioral studies of male sage-grouse.