The fitness landscape of a community of Darwin’s finches

Divergent natural selection should lead to adaptive radiation—that is, the rapid evolution of phenotypic and ecological diversity originating from a single clade. The drivers of adaptive radiation have often been conceptualized through the concept of “adaptive landscapes,” yet formal empirical estimates of adaptive landscapes for natural adaptive radiations have proven elusive. Here, we use a 17-year dataset of Darwin’s ground finches (Geospiza spp.) at an intensively studied site on Santa Cruz (Galápagos) to estimate individual apparent lifespan in relation to beak traits. We use these estimates to model a multi-species fitness landscape, which we also convert to a formal adaptive landscape. We then assess the correspondence between estimated fitness peaks and observed phenotypes for each of five phenotypic modes (G. fuliginosa, G. fortis [small and large morphotypes], G. magnirostris, and G. scandens). The fitness and adaptive landscapes show 5 and 4 peaks, respectively, and, as expected, the adaptive landscape was smoother than the fitness landscape. Each of the five phenotypic modes appeared reasonably close to the corresponding fitness peak, yet interesting deviations were also documented and examined. By estimating adaptive landscapes in an ongoing adaptive radiation, our study demonstrates their utility as a quantitative tool for exploring and predicting adaptive radiation

A fine-scale, broadly applicable index of vocal performance: frequency excursion

Our understanding of the evolution and function of animal displays has been advanced through studies of vocal performance. A widely used metric of vocal performance, vocal deviation, is limited by being applicable only to vocal trills, and also overlooks certain fine-scale aspects of song structure that might reflect vocal performance. In light of these limitations we here introduce a new index of vocal performance, \u27frequency excursion\u27. Frequency excursion calculates, for any given song or song segment, the sum of frequency modulations both within and between notes on a per-time basis. We calculated and compared the two performance metrics in three species: chipping sparrows, Spizella passerina, swamp sparrows, Melospiza georgiana, and song sparrows, Melospiza melodia. The two metrics correlated as expected, yet frequency excursion accounted for subtle variations in performance overlooked by vocal deviation. In swamp sparrows, frequency excursion values varied significantly by song type but not by individual. Moreover, song type performance in swamp sparrows, according to both metrics, varied negatively with the extent to which song types were shared among neighbours. In song sparrows, frequency excursion values of trilled song segments exceeded those of nontrilled song segments, although not to a statistically significant degree. We suggest that application of frequency excursion in birds and other taxa will provide new insights into diverse open questions concerning vocal performance, function and evolution. (c) 2016 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved

Calibration of song learning targets during vocal ontogeny in swamp sparrows,Melospiza georgiana

Song learning in songbirds often includes an extended sensorimotor phase, in which birds gradually refine their vocal output to produce accurate copies of previously memorized song models. Increasing accuracy of song model reproduction during this phase occurs as birds refine the neural substrates that underlie vocal control, and as they develop proficiency with the vocal apparatus. We here test the hypothesis that sensorimotor learning also provides birds with an opportunity to calibrate their vocal learning targets, in the event that a bird's own vocal proficiency differs from that required to successfully reproduce song models to which it is exposed. We tutored hand-reared male swamp sparrows with song models that we manipulated to vary in how challenging they would be to reproduce, and then tracked patterns of song development. The calibration hypothesis was supported by two lines of evidence. First, we found that copies of manipulated models underwent comparatively large-scale modifications in syntax and note composition over development, in directions consistent with expectations about motor proficiency relative to the structure of learned models. Second, we found that birds tended to retain selectively, in their crystallized repertoires, song types that appeared to be comparatively easy to produce. Our results are consistent with an 'active' model of song learning, and also suggest a specific mechanism by which learning can act as a creative or a stabilizing force in song evolution

A collection of best practices for the collection and analysis of bioacoustic data

The field of bioacoustics is rapidly developing and characterized by diverse methodologies, approaches and aims. For instance, bioacoustics encompasses studies on the perception of pure tones in meticulously controlled laboratory settings, documentation of species’ presence and activities using recordings from the field, and analyses of circadian calling patterns in animal choruses. Newcomers to the field are confronted with a vast and fragmented literature, and a lack of accessible reference papers or textbooks. In this paper we contribute towards filling this gap. Instead of a classical list of “dos” and “don’ts”, we review some key papers which, we believe, embody best practices in several bioacoustic subfields. In the first three case studies, we discuss how bioacoustics can help identify the ‘who’, ‘where’ and ‘how many’ of animals within a given ecosystem. Specifically, we review cases in which bioacoustic methods have been applied with success to draw inferences regarding species identification, population structure, and biodiversity. In fourth and fifth case studies, we highlight how structural properties in signal evolution can emerge via ecological constraints or cultural transmission. Finally, in a sixth example, we discuss acoustic methods that have been used to infer predator–prey dynamics in cases where direct observation was not feasible. Across all these examples, we emphasize the importance of appropriate recording parameters and experimental design. We conclude by highlighting common best practices across studies as well as caveats about our own overview. We hope our efforts spur a more general effort in standardizing best practices across the subareas we’ve highlighted in order to increase compatibility among bioacoustic studies and inspire cross-pollination across the discipline.Publisher PDFPeer reviewe

Acoustic discrimination of sympatric morphs in Darwin's finches: a behavioural mechanism for assortative mating?

Populations with multiple morphological or behavioural types provide unique opportunities for studying the causes and consequences of evolutionary diversification. A population of the medium ground finch (Geospiza fortis) at El Garrapatero on Santa Cruz Island, Galápagos, features two beak size morphs. These morphs produce acoustically distinctive songs, are subject to disruptive selection and mate assortatively by morph. The main goal of the present study was to assess whether finches from this population are able to use song as a cue for morph discrimination. A secondary goal of this study was to evaluate whether birds from this population discriminate songs of their own locality versus another St Cruz locality, Borrero Bay, approximately 24 km to the NW. I presented territorial males with playback of songs of their own morph, of the other morph, and of males from Borrero Bay. Males responded more strongly to same-morph than to other-morph playbacks, showing significantly shorter latencies to flight, higher flight rates and closer approaches to the playback speaker. By contrast, I found only minor effects of locality on responsiveness. Evidence for morph discrimination via acoustic cues supports the hypothesis that song can serve as a behavioural mechanism for assortative mating and sympatric evolutionary divergence

Female mate choice based upon male motor performance

Our goal in this essay is to review the hypothesis that females choose mates by the evaluation of male motor performance. We define motor performance as vigor, the ability to perform energetically expensive acts repeatedly, or as skill, the ability to perform difficult motor tasks well. Motor performance reflects most aspects of whole-organism performance that relate to survival, and thus should indicate, more reliably than ornaments do, individual male genetic quality and/or developmental history. Male sexual displays in many animal taxa contain elements of vigor and/or skill, and accumulating evidence suggests that females choose mates in nature based upon their evaluations of male motor performance. We note that male ornaments in many species are accompanied by conspicuous motor display, and we propose that ornaments often arise secondarily as a way to enhance the apparent skill or vigor of male motor performance. More and better methods to measure male vigor and skill are needed, as well as additional studies on the abilities of females to make discriminations of this type

Extremely loud mating songs at close range in white bellbirds

Holzner et al. show that macaques provide a net benefit to oil palm harvest by reducing losses due to rodent pests on oil palm plantations. © 2019 Elsevier LtdSexual selection in many animal species favors the evolution of elaborate courtship traits. Such traits might help signalers convey, and receivers discern, information about signaler quality; or they might be favored by perceptual or aesthetic preferences for elaborateness or beauty [1–3]. Under either scenario we expect sexual trait elaboration to be countered by proximate constraints rooted in animals’ morphology, physiology and phylogenetic history [3,4]. During expeditions to a montane rainforest in the Brazilian Amazon, we obtained amplitude-calibrated measures of mating songs in two species of cotingas, the white bellbird (Procnias albus) and the screaming piha (Lipaugus vociferans). The screaming piha sings the loudest songs of any passerine bird previously documented [5]. However, we find that white bellbirds are >9 dB louder, and thus achieve roughly triple the sound pressure levels of pihas. Mechanical constraints on amplitude, and thus limits on the reach of sexual selection, are revealed by trade-offs between maximal sound pressure and song duration. We find that song amplitude in bellbirds is context-dependent: when a female was on the display perch, a male bellbird sang only his louder song type, swiveling his body mid-song to face the female head on. We know of no other species in which such high-amplitude vocal signals are directed to receivers in such close proximity. We propose that bellbird females balance an interest in sampling males at close range with a need to protect themselves from hearing damage. © 2019 Elsevier Lt

2013 Shift of song frequency in response to masking tones

Keywords: black-capped chickadee communication frequency interference masking noise overlap plasticity Poecile atricapillus song Ambient noise can interfere with signal transmission and detection across many taxa and modalities. Evidence suggests that, over time, signals evolve to minimize interference from ambient noise and other signalling animals. Less well studied is the possibility of short-term behavioural responses to transient ambient noise, in which animals actively adjust signal parameters to recover signalling efficacy. Here we test animals' capacity to adjust vocal signal parameters in the face of transient acoustic interference. In field trials we monitored the songs of territorial male black-capped chickadees, Poecile atricapillus, determined the frequencies of their 'fee-bee' songs, and broadcast tones to closely mask subjects' 'bee' notes. We also presented control nonmasking tones of 5 kHz, well above birds' song frequencies. Our main finding was that males responded to masking tones by shifting song frequencies after an average of 66.4 s from tone onset, whereas frequency shifts in the presence of nonmasking tones occurred only after an average of 95.8 s. The quicker shift in frequencies in the face of masking noise provides new evidence for vocal behavioural plasticity, and further reveals how behavioural plasticity together with evolutionary adaptations can minimize the detrimental effects of ambient noise on communication.

Uneven Sampling and the Analysis of Vocal Performance Constraints

Studies of trilled vocalizations provide a premiere illustration of how performance constraints shape the evolution of mating displays. In trill production, vocal tract mechanics impose a tradeoff between syllable repetition rate and frequency bandwidth, with the trade-off most pronounced at higher values of both parameters. Available evidence suggests that trills that simultaneously maximize both traits are more threatening to males or more attractive to females, consistent with a history of sexual selection favoring high performance trills. Here, we identify a sampling limitation that confounds the detection and description of performance trade-offs. We reassess 70 data sets (from 26 published studies) and show that sampling limitations afflict 63 of these to some degree. Traditional upper-bound regression, which does not control for sampling limitations, detects performance trade-offs in 33 data sets; yet when sampling limitations are controlled, performance trade-offs are detected in only 15. Sampling limitations therefore confound more than half of all performance trade-offs reported using the traditional method. An alternative method that circumvents this sampling limitation, which we explore here, is quantile regression. Our goal is not to question the presence of mechanical trade-offs on trill production but rather to reconsider how these trade-offs can be detected and characterized from acoustic data