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  • 1.
    Griesser, Michael
    et al.
    Jagiellonian Univ, Inst Environm Sci, Gronostajowa 7, PL-30387 Krakow, Poland.
    Wheatcroft, David
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Suzuki, Toshitaka N.
    Kyoto Univ, Ctr Ecol Res, 2-509-3 Hirano, Otsu, Shiga 5202113, Japan;Grad Univ Adv Studies, SOKENDAI, Dept Evolutionary Studies Biosyst, Hayama, Kanagawa 2400193, Japan.
    From bird calls to human language: exploring the evolutionary drivers of compositional syntax2018In: CURRENT OPINION IN BEHAVIORAL SCIENCES, ISSN 2352-1546, Vol. 21, p. 6-12Article, review/survey (Refereed)
    Abstract [en]

    Compositional syntax, where lexical items are combined into larger units, has been assumed to be unique to human language. Recent experiments, however, showed that Japanese tits combine alert and recruitment calls into alert-recruitment sequences when attracting conspecifics to join in mobbing a predator. We speculate that such call combinations are favoured when: Firstly, callers and receivers have shared interests in exchanging information; secondly, species produce different types of calls in different situations, leading to distinct behavioural responses in receivers; and finally, complex situations exist in which receivers benefit by combining two or more behaviours. These preconditions were also present in human ancestors. Thus, future work on bird calls may provide insights into the evolution of compositional syntax in human language.

  • 2.
    Hoglund, Jacob
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Saether, Stein Are
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics.
    Fiske, Peder
    Wheatcroft, David
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Kalas, John Atle
    A hybrid snipe Gallinago gallinago x G-media found in the wild2015In: Journal of Ornithology = Journal fur Ornithologie, ISSN 0021-8375, E-ISSN 1439-0361, Vol. 156, no 3, p. 819-827Article in journal (Refereed)
    Abstract [en]

    A hybrid snipe male was observed and caught in 2009 in the Norwegian mountains. We report behaviour, vocalizations, morphology, and genetic data for this bird. Mitochondrial and nuclear DNA sequences revealed that the hybrid had a great snipe mother and a common snipe father. The hybrid was intermediate in most measured morphometric traits and showed some intermediate plumage characteristics. The behaviour was similar to that of a great snipe-it displayed and vocalised at a great snipe lek for more than a week. The song was somewhat reminiscent of a great snipe's, but lacked the frequency-modulated whistles that are part of the great snipe song, consisting of more rapid click notes of a narrower frequency spectrum. This is the only putative hybrid that we have found among the more than 4,400 adult individuals we have examined between 1986 and 2014 at great snipe leks in Norway, Sweden, Poland, and Estonia. Common snipes invariably occur near these sites. Reports on putative hybrids among snipe species are very rare, and we question the validity of previous claims. This is the first where the parental origins-and, indeed, the hybrid status-have been unequivocally determined. We speculate on how a great snipe female, known for being extremely choosy about mating, came to mate with a common snipe male. We also note that, although perhaps behaviourally more likely, physical constraints on chick development (caused by the smaller egg size of the common snipe and larger body size of the great snipe) might prevent any successful male great snipe x female common snipe hybridisation-a possible example of an unidirectional post-zygotic barrier.

  • 3.
    McFarlane, S. Eryn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Söderberg, Axel
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Wheatcroft, David
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Qvarnström, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Song discrimination by nestling collared flycatchers during early development2016In: Biology Letters, ISSN 1744-9561, E-ISSN 1744-957X, Vol. 12, no 7, article id 20160234Article in journal (Refereed)
    Abstract [en]

    Pre-zygotic isolation is often maintained by species-specific signals and preferences. However, in species where signals are learnt, as in songbirds, learning errors can lead to costly hybridization. Song discrimination expressed during early developmental stages may ensure selective learning later in life but can be difficult to demonstrate before behavioural responses are obvious. Here, we use a novel method, measuring changes in metabolic rate, to detect song perception and discrimination in collared flycatcher embryos and nestlings. We found that nestlings as early as 7 days old respond to song with increased metabolic rate, and, by 9 days old, have increased metabolic rate when listening to conspecific when compared with heterospecific song. This early discrimination between songs probably leads to fewer heterospecific matings, and thus higher fitness of collared flycatchers living in sympatty with closely related species.

  • 4.
    Rybinski, Jakub
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Sirkia, Paivi M.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology. Univ Helsinki, Zool Unit, Finnish Museum Nat Hist, FIN-00014 Helsinki, Finland..
    McFarlane, S. Eryn
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Vallin, Niclas
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Wheatcroft, David
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Ålund, Murielle
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Qvarnström, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Competition-driven build-up of habitat isolation and selection favoring modified dispersal patterns in a young avian hybrid zone2016In: Evolution, ISSN 0014-3820, E-ISSN 1558-5646, Vol. 70, no 10, p. 2226-2238Article in journal (Refereed)
    Abstract [en]

    Competition-driven evolution of habitat isolation is an important mechanism of ecological speciation but empirical support for this process is often indirect. We examined how an on-going displacement of pied flycatchers from their preferred breeding habitat by collared flycatchers in a young secondary contact zone is associated with (a) access to an important food resource (caterpillar larvae), (b) immigration of pied flycatchers in relation to habitat quality, and (c) the risk of hybridization in relation to habitat quality. Over the past 12 years, the estimated access to caterpillar larvae biomass in the habitat surrounding the nests of pied flycatchers has decreased by a fifth due to shifted establishment possibilities, especially for immigrants. However, breeding in the high quality habitat has become associated with such a high risk of hybridization for pied flycatchers that overall selection currently favors pied flycatchers that were forced to immigrate into the poorer habitats (despite lower access to preferred food items). Our results show that competition-driven habitat segregation can lead to fast habitat isolation, which per se caused an opportunity for selection to act in favor of future "voluntarily" altered immigration patterns and possibly strengthened habitat isolation through reinforcement.

  • 5.
    Sirkiä, Päivi M
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    McFarlane, S. Eryn
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Jones, William
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Wheatcroft, David
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Ålund, Murielle
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Rybinski, Jakub
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Qvarnström, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Climate-driven build-up of temporal isolation within a recently formed avian hybrid zone.2018In: Evolution, ISSN 0014-3820, E-ISSN 1558-5646, Vol. 72, no 2, p. 363-374Article in journal (Refereed)
    Abstract [en]

    Divergence in the onset of reproduction can act as an important source of reproductive isolation (i.e., allochronic isolation) between co-occurring young species, but evidence for the evolutionary processes leading to such divergence is often indirect. While advancing spring seasons strongly affect the onset of reproduction in many taxa, it remains largely unexplored whether contemporary spring advancement directly affects allochronic isolation between young species. We examined how increasing spring temperatures affected onset of reproduction and thereby hybridization between pied and collared flycatchers (Ficedula spp.) across habitat types in a young secondary contact zone. We found that both species have advanced their timing of breeding in 14 years. However, selection on pied flycatchers to breed earlier was weaker, resulting in a slower response to advancing springs compared to collared flycatchers and thereby build-up of allochronic isolation between the species. We argue that a preadaptation to a broader niche use (diet) of pied flycatchers explains the slower response to raising spring temperature, but that reduced risk to hybridize may contribute to further divergence in the onset of breeding in the future. Our results show that minor differences in the response to environmental change of co-occurring closely related species can quickly cause allochronic isolation.

  • 6.
    Suzuki, Toshitaka N.
    et al.
    Univ Tokyo, Dept Gen Syst Studies, 3-8-1 Komaba, Meguro, Tokyo 1538902, Japan.
    Griesser, Michael
    Univ Zurich, Dept Evolutionary Biol & Environm Studies, Zurich, Switzerland.
    Wheatcroft, David
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Syntactic rules in avian vocal sequences as a window into the evolution of compositionality2019In: Animal Behaviour, ISSN 0003-3472, E-ISSN 1095-8282, Vol. 151, p. 267-274Article, review/survey (Refereed)
    Abstract [en]

    Understanding the origins and evolution of language remains a deep challenge, because its complexity and expressive power are unparalleled in the animal world. One of the key features of language is that the meaning of an expression is determined both by the meanings of its constituent parts and the syntactic rules used to combine them; known as the principle of compositionality. Although compositionality has been considered unique to language, recent field studies suggest that compositionality may have also evolved in vocal combinations in nonhuman animals. Here, we discuss how compositionality can be explored in animal communication systems and review recent evidence that birds use an ordering rule to generate compositional expressions composed of meaningful calls. Also, we suggest that bird-songs, particularly when incorporating calls, may represent unrecognized examples of compositionality in animal communication. Finally, we outline future research directions to uncover the development, neural mechanisms and evolution of compositionality. 

  • 7.
    Suzuki, Toshitaka N.
    et al.
    Grad Univ Adv Studies, SOKENDAI, Dept Evolutionary Studies Biosyst, Hayama, Kanagawa, Japan.
    Wheatcroft, David
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Griesser, Michael
    Univ Zurich, Dept Evolutionary Biol & Environm Studies, Zurich, Switzerland.
    Call combinations in birds and the evolution of compositional syntax2018In: PLoS biology, ISSN 1544-9173, E-ISSN 1545-7885, Vol. 16, no 8, article id e2006532Article in journal (Refereed)
    Abstract [en]

    Syntax is the set of rules for combining words into phrases, providing the basis for the generative power of linguistic expressions. In human language, the principle of compositionality governs how words are combined into a larger unit, the meaning of which depends on both the meanings of the words and the way in which they are combined. This linguistic capability, i.e., compositional syntax, has long been considered a trait unique to human language. Here, we review recent studies on call combinations in a passerine bird, the Japanese tit (Parus minor), that provide the first firm evidence for compositional syntax in a nonhuman animal. While it has been suggested that the findings of these studies fail to provide evidence for compositionality in Japanese tits, this criticism is based on misunderstanding of experimental design, misrepresentation of the importance of word order in human syntax, and necessitating linguistic capabilities beyond those given by the standard definition of compositionality. We argue that research on avian call combinations has provided the first steps in elucidating how compositional expressions could have emerged in animal communication systems.

  • 8.
    Suzuki, Toshitaka N.
    et al.
    SOKENDAI Grad Univ Adv Studies, Dept Evolutionary Studies Biosyst, Kamiyamaguchi 1560-35, Hayama, Kanagawa 2400193, Japan.;Rikkyo Univ, Dept Life Sci, Toshima Ku, Nishi Ikebukuro 3-34-1, Tokyo 1718501, Japan..
    Wheatcroft, David
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology. Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Developmental Neuroscience.
    Griesser, Michael
    Univ Zurich, Anthropol Inst & Museum, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Experimental evidence for compositional syntax in bird calls2016In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 7, article id 10986Article in journal (Refereed)
    Abstract [en]

    Human language can express limitless meanings from a finite set of words based on combinatorial rules (i.e., compositional syntax). Although animal vocalizations may be comprised of different basic elements (notes), it remains unknown whether compositional syntax has also evolved in animals. Here we report the first experimental evidence for compositional syntax in a wild animal species, the Japanese great tit (Parus minor). Tits have over ten different notes in their vocal repertoire and use them either solely or in combination with other notes. Experiments reveal that receivers extract different meanings from 'ABC' (scan for danger) and 'D' notes (approach the caller), and a compound meaning from 'ABCD' combinations. However, receivers rarely scan and approach when note ordering is artificially reversed ('D-ABC'). Thus, compositional syntax is not unique to human language but may have evolved independently in animals as one of the basic mechanisms of information transmission.

  • 9.
    Suzuki, Toshitaka N.
    et al.
    Kyoto Univ, Ctr Ecol Res, 2-509-3 Hirano, Otsu, Shiga 5202113, Japan.;SOKENDAI, Dept Evolutionary Studies Biosyst, Hayama, Kanagawa 2400193, Japan..
    Wheatcroft, David
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Griesser, Michael
    Univ Zurich, Dept Anthropol, Winterthurerstr 190, CH-8057 Zurich, Switzerland.;Jagiellonian Univ, Inst Environm Sci, Gronostajowa 7, PL-30387 Krakow, Poland..
    Wild Birds Use an Ordering Rule to Decode Novel Call Sequences2017In: Current Biology, ISSN 0960-9822, E-ISSN 1879-0445, Vol. 27, no 15, p. 2331-2336.e3Article in journal (Refereed)
    Abstract [en]

    The generative power of human language depends on grammatical rules, such as word ordering, that allow us to produce and comprehend even novel combinations of words [1-3]. Several species of birds and mammals produce sequences of calls [4-6], and, like words in human sentences, their order may influence receiver responses [7]. However, it is unknown whether animals use call ordering to extract meaning from truly novel sequences. Here, we use a novel experimental approach to test this in a wild bird species, the Japanese tit (Parus minor). Japanese tits are attracted to mobbing a predator when they hear conspecific alert and recruitment calls ordered as alert-recruitment sequences [7]. They also approach in response to recruitment calls of heterospecific individuals in mixed-species flocks [8, 9]. Using experimental playbacks, we assess their responses to artificial sequences in which their own alert calls are combined into different orderings with heterospecific recruitment calls. We find that Japanese tits respond similarly to mixed-species alert-recruitment call sequences and to their own alert-recruitment sequences. Importantly, however, tits rarely respond to mixed-species sequences in which the call order is reversed. Thus, Japanese tits extract a compound meaning from novel call sequences using an ordering rule. These results demonstrate a new parallel between animal communication systems and human language, opening new avenues for exploring the evolution of ordering rules and compositionality in animal vocal sequences.

  • 10.
    Wheatcroft, David
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology. Univ Chicago, Comm Evolutionary Biol, Chicago, IL 60637 USA..
    Repetition rate of calls used in multiple contexts communicates presence of predators to nestlings and adult birds2015In: Animal Behaviour, ISSN 0003-3472, E-ISSN 1095-8282, Vol. 103, p. 35-44Article in journal (Refereed)
    Abstract [en]

    In multispecies communities, animals may come to recognize the signals of other species both by responding to common signal features and by learning about associations between signals and relevant threats. However, some signals are produced in multiple contexts. To a given receiver, such a signal may only sometimes be relevant. Here, I demonstrate that receivers use contextual variation in signal form as a cue to their relevance. Individuals from 15 species of songbirds repeated their calls rapidly when confronting widely threatening predators, but repeated the same calls more slowly during other types of social interactions. In playback experiments, repetition rate was a cue to nestling Ficedula flycatchers, which reduced their activity in response to quickly but not slowly repeated calls, and also to adult birds from a variety of species, which responded more strongly to the calls of their own and other species produced at faster rates. These results show that repetition rate is an innate or early learned contextual cue and, in combination with learning about heterospecific signals, allows receivers to fine-tune their responses to the calls of their own and other species according to their relevance, suggesting that simple rules facilitate widespread heterospecific communication networks. (C) 2015 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

  • 11.
    Wheatcroft, David
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Reproductive interference via display signals: the challenge of multiple receivers2015In: Population Ecology, ISSN 1438-3896, E-ISSN 1438-390X, Vol. 57, no 2, p. 333-337Article in journal (Refereed)
    Abstract [en]

    Sexually selected traits important in both mate and competitor recognition provide an opportunity to understand the tradeoffs associated with reproductive and competitive interference. When co-occurring species compete over similar resources, selection may promote signal similarity to facilitate competitive interactions in opposition to selection for signal divergence to maintain assortative mating. Bird song provides a classic example of contrasting selection on signal design, because songs function both in mate discrimination and in territorial advertisement. Similarity in songs aids competitor recognition both within and across species, and song convergence or mixing is widespread in the songbirds. Two related mechanisms can maintain mate recognition in the face of song convergence. First, multiple recognition signals, both across and within signaling modalities, provide a basis for mate and competitor discrimination using different sets of cues. Second, stricter female song preferences may allow interspecific male-male competitive communication without compromising female mate discrimination. I suggest that increased understanding of the neurobiology underlying song recognition will provide insight into the relative importance and prevalence of these different mechanisms along a continuum of species divergence.

  • 12.
    Wheatcroft, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Gallego-Abenza, Mario
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Qvarnström, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Species replacement reduces community participation in avian antipredator groups2016In: Behavioral Ecology, ISSN 1045-2249, E-ISSN 1465-7279, Vol. 27, no 5, p. 1499-1506Article in journal (Refereed)
    Abstract [en]

    Individuals living in diverse communities often depend on understanding the alarm signals of other species to gain critical information about predators. Here, we show that songbirds more rarely respond to the alarms of a colonizing songbird than those of the closely related species it is replacing. These results suggest that even small changes in community composition may have large impacts on species interactions and community antipredator behaviors.In diverse communities, recognizing other species' alarm signals is critical for evading predators. Recognition among community members is thought to build up predictably and quickly as individuals learn to associate previously unrecognized calls with the presence of a predator. Here, we use a natural range expansion in which a songbird species, the pied flycatcher (Ficedula hypoleuca), is being gradually displaced on a Baltic island by an ecologically similar congeneric, the collared flycatcher (Ficedula albicollis), to test this prediction. We conducted 2 field experiments to evaluate the abilities of both species to recruit local heterospecifics to antipredator groups, called mobs. First, we stimulated mobs by exposing breeding collared and pied pairs to taxidermied predators. Second, to isolate the effect of alarm call recognition from other potential confounds, such as behavioral cues or differences in the locations of pied and collared flycatcher nests, we broadcast alarm calls of both species in breeding areas and measured the responses of heterospecifics. We found that pied flycatcher pairs were more likely to attract heterospecifics than were collared flycatcher pairs. This difference is driven by weak responses of community members to collared flycatcher alarm calls: The alarm calls of the native pied flycatcher were much more likely to attract heterospecifics than those of the colonist, collared flycatchers. Our results show that subtle changes in species composition may have large, unpredictable consequences on community-wide communication. Because many avian breeding communities are heavily affected by predation, disturbed communication networks may, in turn, have cascading effects on community composition.

  • 13.
    Wheatcroft, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology. Univ Chicago, Dept Ecol & Evolut, 940 E 57Th St, Chicago, IL 60637 USA.
    Price, Trevor D.
    Univ Chicago, Dept Ecol & Evolut, 940 E 57Th St, Chicago, IL 60637 USA.
    Collective Action Promoted by Key Individuals2018In: American Naturalist, ISSN 0003-0147, E-ISSN 1537-5323, Vol. 192, no 4, p. 401-414Article in journal (Refereed)
    Abstract [en]

    Explaining why individuals participate in risky group behaviors has been a long-term challenge. We experimentally studied the formation of groups of birds (mobs) that aggressively confront predators and avian nest parasites and developed a theoretical model to evaluate the conditions under which mobs arise. We presented taxidermied mounts of predators on adult birds (hawks and owls) and of nest threats (crows and cuckoos) at different distances to nests of Phylloscopus warblers. Even when alone, birds are aggressive toward predators of adult birds, both at and away from their nests. By contrast, birds aggressively confront nest threats alone only when they have a nest nearby. However, strong initial responses by nest owners lead individuals without nearby nests to increase their responses, thereby generating a mob. Building on these findings, we derive the conditions in which individuals are incentivized to invest more when joining a high-gain individual compared to when acting alone. Strong responses of high-gain individuals acting alone tend to reduce the investments of other high-gain individuals that subsequently join. However, individuals that benefit sufficiently little from acting alone increase their investments when joining a high-gain individual and can even be sufficiently incentivized to join in when they would otherwise not act alone. Together, these results suggest an important role for key individuals in the generation of some group behaviors.

  • 14.
    Wheatcroft, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Price, Trevor D.
    Learning and signal copying facilitate communication among bird species2013In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 280, no 1757, p. 20123070-Article in journal (Refereed)
    Abstract [en]

    Signals relevant to different sets of receivers in different contexts create a conflict for signal design. A classic example is vocal alarm signals, often used both during intraspecific and interspecific interactions. How can signals alert individuals from a variety of other species in some contexts, while also maintaining efficient communication among conspecifics? We studied heterospecific responses to avian alarm signals that drive the formation of anti-predator groups but are also used during intraspecific interactions. In three species-rich communities in the western Himalayas, alarm signals vary drastically across species. We show that, independently of differences in their calls, birds respond strongly to the alarm signals of other species with which they co-occur and much more weakly to those of species with which they do not co-occur. These results suggest that previous exposure and learning maintain heterospecific responses in the face of widespread signal divergence. At an area where only two species regularly interact, one species' calls incorporate the call of the other. We demonstrate experimentally that signal copying allows strong responses even without previous exposure and suggest that such hybrid calls may be especially favoured when pairwise interactions between species are strong.

  • 15.
    Wheatcroft, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Price, Trevor D.
    Rates of signal evolution are associated with the nature of interspecific communication2015In: Behavioral Ecology, ISSN 1045-2249, E-ISSN 1465-7279, Vol. 26, no 1, p. 83-90Article in journal (Refereed)
    Abstract [en]

    Some signals vary greatly, whereas others are remarkably similar across distantly related species. Here, we ask how the suite of receivers and information communicated correlates with signal evolution by comparing 2 different signals across the same set of species. Within the Old World leaf warblers (Phylloscopidae), each species utters 2 acoustically distinct alarm calls. The first, termed a "general" call, is used in interactions with conspecifics as a well as during confrontations with predators and nest-parasitic cuckoos. The second, termed a "rasp" call, is primarily used in the presence of nest-parasitic cuckoos. The rasp call precedes aggressive attacks on cuckoos and attracts surrounding heterospecifics that are also potential hosts. The general call attracts a wide range of species threatened by predators, including those that are not cuckoo hosts. Acoustic features of general calls evolve >5x faster than rasp calls. We argue that rasp calls show strong stasis because they have a restricted function as aggressive antiparasite signals, whereas multiple contexts and receivers have promoted divergence in general calls. These results support the idea that variation in the suite of receivers is a powerful force affecting signal evolution.

  • 16.
    Wheatcroft, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Qvarnström, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    A blueprint for vocal learning: auditory predispositions from brains genomes2015In: Biology Letters, ISSN 1744-9561, E-ISSN 1744-957X, Vol. 11, no 8, article id 20150155Article, review/survey (Refereed)
    Abstract [en]

    Memorizing and producing complex strings of sound are requirements for spoken human language. We share these behaviours with likely more than 4000 species of songbirds, making birds our primary model for studying the cognitive basis of vocal learning and, more generally, an important model for how memories are encoded in the brain. In songbirds, as in humans, the sounds that a juvenile learns later in life depend on auditory memories formed early in development. Experiments on a wide variety of songbird specie's suggest that the formation and lability of these auditory memories, in turn, depend on auditory predispositions that stimulate learning when a juvenile hears relevant, species-typical sounds. We review evidence that variation in key features of these auditory predispositions are determined by variation in genes underlying the development of the auditory system. We argue that increased investigation of the neuronal basis of auditory predispositions expressed early in life in conibination with modem comparative genomic approaches may provide insights into the evolution of vocal learning.

  • 17.
    Wheatcroft, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Qvarnström, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Genetic divergence of early song discrimination between two young songbird species2017In: NATURE ECOLOGY & EVOLUTION, ISSN 2397-334X, Vol. 1, no 7, article id UNSP 0192Article in journal (Refereed)
    Abstract [en]

    Juvenile songbirds express species-specific song discrimination from an early age, which focuses learning onto the songs of their parental species. However, it remains unknown whether this early song discrimination is influenced by early social experience or maternal effects or whether it is instead largely genetically determined. We manipulated early social experience by swapping young embryos between the nests of two co-occurring songbird species-pied and collared flycatchers. We show that nestlings are more active in response to playbacks of conspecific songs, even when raised by adults from the other species, thus enabling us to reject social experience as the main determinant of early song discrimination. We then crossed the two species in captivity and showed that the song responses of hybrid nestlings do not depend on social experience or maternal species, implying genetic divergence of early song discrimination. Our results provide conclusive evidence that early song discrimination has a largely genetic component, which can stabilize reproductive isolation by reducing song learning across closely related species.

  • 18.
    Wheatcroft, David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Qvarnström, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
    Reproductive character displacement of female, but not male song discrimination in an avian hybrid zone2017In: Evolution, ISSN 0014-3820, E-ISSN 1558-5646, Vol. 71, no 7, p. 1776-1786Article in journal (Refereed)
    Abstract [en]

    Divergence of male sexual signals and female preferences for those signals often maintains reproductive boundaries between closely related, co-occurring species. However, contrasting sources of selection, such as interspecific competition, can lead to weak divergence or even convergence of sexual signals in sympatry. When signals converge, assortative mating can be maintained if the mating preferences of females diverge in sympatry (reproductive character displacement; RCD), but there are few explicit examples. Pied flycatchers (Ficedula hypoleuca) are sympatric with collared flycatchers (F. albicollis) on the Baltic island of oland, where males from both species compete over nestboxes, their songs converge, and the two species occasionally hybridize. We compare song discrimination of male and female pied flycatchers on oland and in an allopatric population on the Swedish mainland. Using field choice trials, we show that male pied flycatchers respond similarly to the songs of both species in sympatry and allopatry, while female pied flycatchers express stronger discrimination against heterospecific songs in sympatry than in allopatry. These results are consistent with RCD of song discrimination of female pied flycatchers where they co-occur with collared flycatchers, which should maintain species assortative mating despite convergence of male sexual signals.

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