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Our understanding of bird song, a model system for animal communication and the neurobiology of learning, depends critically on making reliable, validated comparisons between the complex multidimensional syllables that are used in songs. However, most assessments of song similarity are based on human inspection of spectrograms, or computational methods developed from human intuitions. Using a novel automated operant conditioning system, we collected a large corpus of zebra finches’ (Taeniopygia guttata) decisions about song syllable similarity. We use this dataset to compare and externally validate similarity algorithms in widely-used publicly available software (Raven, Sound Analysis Pro, Luscinia). Although these methods all perform better than chance, they do not closely emulate the avian assessments. We then introduce a novel deep learning method that can produce perceptual similarity judgements trained on such avian decisions. We find that this new method outperforms the established methods in accuracy and more closely approaches the avian assessments. Inconsistent (hence ambiguous) decisions are a common occurrence in animal behavioural data; we show that a modification of the deep learning training that accommodates these leads to the strongest performance. We argue this approach is the best way to validate methods to compare song similarity, that our dataset can be used to validate novel methods, and that the general approach can easily be extended to other species.

In studies of cumulative cultural evolution in non-human animals, the focus is most often on incremental changes that increase the efficacy of an existing form of socially learned behaviour, such as the refinement of migratory pathways. In this paper, we compare the songs of different species to describe patterns of evolution in the acoustic structure of bird songs, and explore the question of what building blocks might underlie cumulative cultural evolution of bird song using a comparative approach. We suggest that three steps occurred: first, imitation of independent sounds, or notes, via social learning; second, the formation of categories of note types; and third, assembling note types into sequences with defined structures. Simple sequences can then be repeated to form simple songs or concatenated with other sequences to form segmented songs, increasing complexity. Variant forms of both the notes and the sequencing rules may then arise due to copy errors and innovation. Some variants may become established in the population because of learning biases or selection, increasing signal efficiency, or because of cultural drift. Cumulative cultural evolution of bird songs thus arises from cognitive processes such as vocal imitation, categorization during memorization and learning biases applied to basic acoustic building blocks.This article is part of a discussion meeting issue ‘The emergence of collective knowledge and cumulative culture in animals, humans and machines’.

Emotional facial expressions critically impact social interactions and cognition. However, emotion research to date has generally relied on the assumption that people represent categorical emotions in the same way, using standardized stimulus sets and overlooking important individual differences. To resolve this problem, we developed and tested a task using genetic algorithms to derive assumption-free, participant-generated emotional expressions. One hundred and five participants generated a subjective representation of happy, angry, fearful and sad faces. Population-level consistency was observed for happy faces, but fearful and sad faces showed a high degree of variability. High test–retest reliability was observed across all emotions. A separate group of 108 individuals accurately identified happy and angry faces from the first study, while fearful and sad faces were commonly misidentified. These findings are an important first step towards understanding individual differences in emotion representation, with the potential to reconceptualize the way we study atypical emotion processing in future research.

Evaluating sound similarity is a fundamental building block in acoustic perception and computational analysis. Traditional data-driven analyses of perceptual similarity are based on heuristics or simplified linear models, and are thus limited. Deep learning embeddings, often using triplet networks, have been useful in many fields. However, such networks are usually trained using large class-labelled datasets. Such labels are not always feasible to acquire. We explore data-driven neural embeddings for sound event representation when class labels are absent, instead utilising proxies of perceptual similarity judgements. Ultimately, our target is to create a perceptual embedding space that reflects animals' perception of sound. We create deep perceptual embeddings for bird sounds using triplet models. In order to deal with the challenging nature of triplet loss training with the lack of class-labelled data, we utilise multidimensional scaling (MDS) pretraining, attention pooling, and a triplet mining scheme. We also evaluate the advantage of triplet learning compared to learning a neural embedding from a model trained on MDS alone. Using computational proxies of similarity judgements, we demonstrate the feasibility of the method to develop perceptual models for a wide range of data based on behavioural judgements, helping us understand how animals perceive sounds.

“Culture” is generally regarded as a population’s shared array of traditions, transmitted between individuals by processes of social learning, and which may persist from one generation to later ones. If we consider genetic material to provide the primary system of inheritance in living things, then social learning—learning from others—provides a second inheritance system in those species of animals that have the cognitive capacity to learn in this way. Once it was thought that cultural traditions inherited in this way were unique to, and defining of, our own species. This view was challenged by research arising particularly in the middle of the 20th century, which revealed evidence of the spread of innovations in the behavior of nonhuman species, generating traditions that passed from one generation to the next. Early examples included regional birdsong dialects and novel foraging techniques in Japanese macaque monkeys. Research over the last seventy years or so has accumulated a wealth of evidence that animal traditions exist in many aspects of behavior, from migration to mate choice and predator avoidance, and in numerous taxa including fish, birds, and mammals. Social learning has also been well documented in insects, although the existence of traditions in the wild remains less clear. Once such a second inheritance system does emerge, supporting the transmission of behavioral traditions, the potential exists for a second system of evolution—cultural evolution—which can be defined most simply as changes in culture over time. As in the case of organic evolution based on genetic inheritance, imperfect copying and sampling error may be sufficient to cause evolutionary changes, known as drift. Alternatively, some innovations may prove to be more adaptive than others, in which case we can expect the essential Darwinian processes of variation, selection, and inheritance to generate some directional cultural evolution. Both drift and Darwinian evolution have long been evident in human cultural evolution, but evidence has begun to accumulate for them also in nonhuman species. Humans additionally display cumulative culture, in which some form of progress builds cumulatively on the achievements of previous generations. Examples are legion, from the evolution of wheeled vehicles to languages and religions. A currently contentious issue is whether such cumulative cultural evolution is unique to our species, or is shared in some ways with others. Other current areas of uncertainty include which cognitive mechanisms underlie animal social learning and whether the precision of animal social learning can support long-lasting traditions; the degree to which animal cultures extend broadly enough across behavioral repertoires, or deeply enough in the complexity of individual traits, to be usefully compared to those of humans; and whether culture creates selection pressures that are long lasting enough to shape animals’ genomes. In general, while it is very clear that human culture is more extensive than in any other species, there is less agreement about which qualitative differences in psychological and cultural processes are responsible for this gulf.

Inbreeding is often avoided in natural populations by passive processes such as sex-biased dispersal. But, in many social animals, opposite-sexed adult relatives are spatially clustered, generating a risk of incest and hence selection for active inbreeding avoidance. Here we show that in long-tailed tits (Aegithalos caudatus), a cooperative breeder that risks inbreeding by living alongside opposite-sex relatives, inbreeding carries fitness costs and is avoided by active kin discrimination during mate choice. First, we identified a positive association between heterozygosity and fitness, indicating that inbreeding is costly. We then compared relatedness within breeding pairs to that expected under multiple mate choice models, finding that pair relatedness is consistent with avoidance of first-order kin as partners. Finally, we show that the similarity of vocal cues offers a plausible mechanism for discrimination against first-order kin during mate choice. Long-tailed tits are known to discriminate between the calls of close kin and non-kin, and they favor first-order kin in cooperative contexts, so we conclude that long-tailed tits use the same kin discrimination rule to avoid inbreeding as they do to direct help towards kin.

Biologists often seek to geographically provenance organisms using their traits. This is typically achieved by defining spatial groups using distinct patterns of trait variation. Here, we present a new spatial provenancing and trait boundary identification methodology, based on correlations between geographic and trait distances that require no a priori group assumptions. We apply this to three datasets where spatial provenance is sought: morphological rat and vole dentition data (human commensal translocation datasets); and birdsong data (cultural transmission dataset). We also present the results of cross‐validation testing. Spatial provenancing is possible with differing degrees of accuracy for each dataset, with birdsong providing the most accurate geographic origin (identifying an average spatial region of 0.22 km2 as the area of origin with 99.9% confidence). Our method has a wide range of potential applications to diverse data types—including phenotypic, genetic and cultural—to identify trait boundaries and spatially provenance the origin of unknown or translocated specimens where trait differences are geographically structured and correlated with spatial separation.

N.J.B. was funded by a Netherlands Organisation for Scientific Research Rubicon Fellowship during the experimental phase of this study and by a Royal Society Dorothy Hodgkin Fellowship during the write-up. K.A.S. was funded by a BBSRC David Phillips Research Fellowship during the experimental phase. C.N.T. was supported by an NERC Postdoctoral Fellowship during the experimental phase of the study. D.R.F. was funded by the Max Planck Society and received additional funding from the Deutsche Forschungsgemeinschaft (FA 1420/4-1). The use of information provided by others is a common short-cut adopted to inform decision-making. However, instead of indiscriminately copying others, animals are often selective in what, when and whom they copy. How do they decide which 'social learning strategy' to use? Previous research indicates that stress hormone exposure in early life may be important: while juvenile zebra finches copied their parents' behaviour when solving novel foraging tasks, those exposed to elevated levels of corticosterone (CORT) during development copied only unrelated adults. Here, we tested whether this switch in social learning strategy generalizes to vocal learning. In zebra finches, juvenile males often copy their father's song; would CORT-treated juveniles in free-flying aviaries switch to copying songs of other males? We found that CORT-treated juveniles copied their father's song less accurately as compared to control juveniles. We hypothesized that this could be due to having weaker social foraging associations with their fathers, and found that sons that spent less time foraging with their fathers produced less similar songs. Our findings are in line with a novel hypothesis linking early-life stress and social learning: early-life CORT exposure may affect social learning indirectly as a result of the way it shapes social affiliations. This article is part of the theme issue 'Causes and consequences of individual differences in cognitive abilities'. Publisher PDF

Cultural traditions have been observed in a wide variety of animal species. It remains unclear, however, what is required for social learning to give rise to stable traditions: what level of precision and what learning strategies are required. We address these questions by fitting models of cultural evolution to learned bird song. We recorded 615 swamp sparrow (Melospiza georgiana) song repertoires, and compared syllable frequency distributions to the output of individual-based simulations. We find that syllables are learned with an estimated error rate of 1.85% and with a conformist bias in learning. This bias is consistent with a simple mechanism of overproduction and selective attrition. Finally, we estimate that syllable types could frequently persist for more than 500 years. Our results demonstrate conformist bias in natural animal behaviour and show that this, along with moderately precise learning, may support traditions whose stability rivals those of humans., ‘Conformist bias’, in which individuals learn a common behavioural variant more often than expected by chance, has not been demonstrated convincingly in non-human animals. This study analyses song recordings and models of cultural evolution to show conformist bias in swamp sparrow populations.

The enormity of the breadth and depth of specimens held within the world's biological collections offers unparalleled opportunities to capture genomic data from across the entire range of known biological diversity. Such a task would take many lifetimes to complete if we could rely only on fresh samples. High-throughput sequencing provides a technical solution to the long-term problems of recalcitrant and degraded DNA typical of museum specimens, suggesting that we may be on the verge of a major collections-based revolution. Although the potential is great, the feasibility of using preserved collections for large-scale, taxonomically comprehensive phylogenomic studies remains unknown. In the present study, we demonstrate the continued relevance of fungarium collections in the genomic era by analyzing a genomic dataset composed of 39 genomes representing 26 family-level clades, including 14 newly generated draft genomes derived from short-read shotgun sequencing of preserved specimens, frozen and freeze-dried material, representing most of the known families of Agaricales. We predicted homologues of 210 putative single copy genes in the newly generated draft genome assemblies, of which 208 were used for phylogenetic reconstruction. Our analyses resulted in a robust and, for the first time, fully supported phylogeny of the Agaricales, enabling the recognition of seven suborders and providing a resource for testing hypotheses of the evolution of mushrooms. Our analysis of optimal combinations of ranked genes using an information theory-based method provides guidance on gene selection for future studies, enabling efficient application of high-throughput sequencing techniques toward unlocking the potential of collections-based research in the genomic era.

Speed–accuracy trade-offs are well studied in human decision making, but we are only beginning to understand how such trade-offs affect other animals. Similarly, it is poorly understood how consistent individual differences in decision making are influenced by their social context. Here we investigated whether zebrafish, Danio rerio, show individual consistency (‘personality’) in speed–accuracy trade-offs based on a colour discrimination task, and how pairs of fish with distinct personalities make consensus choices. The results showed that zebrafish exhibit between-individual speed–accuracy trade-offs: some fish made ‘careful’, slow but accurate decisions, while others made swift but less accurate choices. We also found that these decision-making strategies were constant over time: fish retained the same strategy for 3 days. When testing pairs of careful and fast-and-inaccurate individuals, the combined choice strategy was intermediate in speed, but statistically indistinguishable from the careful individual, whereas accuracy of the dyad decision was moderately higher than that of each individual when tested singly, although this was again not significantly different from the more careful individual. For the first time, our study thus demonstrates that two individuals influence one another's speed–accuracy trade-off in decision making.

Bumblebees are influenced by socially acquired information when deciding on which flowers to forage. In some circumstances, however, this attraction towards conspecifics may lead to suboptimal foraging performance because the presence of multiple pollinators typically results in a faster rate of nectar depletion in the flower. We tested the capacity of bees to learn to avoid flowers occupied by conspecifics when they offered a lower reward than unoccupied similar flowers. Bumblebees were able to discriminate between poorly and highly rewarding flowers by using the presence of a nonsocial cue (a wooden rectangular white block). When poorly rewarding flowers were indicated by social cues (model bees), however, bees did not discriminate between the two flower types except when an additional cue was provided (flower colour). These findings indicate that bumblebees attach particular meaning to conspecific presence on flowers, even when this could lead to suboptimal foraging performance. The relatively lower flexibility in the use of social than nonsocial cues suggests a biased positive value of conspecifics as indicators of rewarded flowers.

That many species of songbirds learn their songs imitatively is well established, but it is less clear why they do so. A component of the developmental-stress hypothesis posits that young males in good condition learn songs more accurately than males in poor condition and that females use learning accuracy as an honest signal of male developmental history. An unresolved problem is how females reliably assess learning accuracy when they are not certain of the identity of the male's tutor and thus the specific model from which a song was copied. We therefore investigated whether song learning accuracy assessment (SLAA) can be reliable, using evolutionary simulation models of song learning. We found that SLAA is indeed less reliable than assessment in which male signals are compared to an unlearned standard, as a result of three types of errors in matching songs to their models. In the simplest models, SLAA was particularly unreliable, but when the model is made more realistic by including features such as geographically constrained learning, repertoire complexity, and, in particular, song categorization, the reliability of SLAA increased. Our results demonstrate a range of conditions under which the assessment of song learning accuracy might be reasonably reliable and therefore likely to evolve.

Background One of the biggest challenges in avian taxonomy is the delimitation of allopatric species because their reproductive incompatibility cannot be directly studied in the wild. Instead, reproductive incompatibility has to be inferred from multiple, divergent character sets that indicate a low likelihood of allopatric populations amalgamating upon secondary contact. A set of quantitative criteria for species delimitation has been developed for avian taxonomy. Results Here, we report a broad multi-trait comparison of the two insular subspecies of the Blue Chaffinch Fringilla teydea, endemic to the pine forests of Tenerife (ssp. teydea) and Gran Canaria (ssp. polatzeki) in the Canary Islands. We found that the two taxa were reciprocally monophyletic in their whole mitogenomes and two Z chromosome introns. The genetic distance in mitogenomes indicates around 1 Mya of allopatric evolution. There were diagnostic differences in body morphometrics, song and plumage reflectance spectra, whose combined divergence score (=11) exceeds the threshold level (=7) set for species delimitation by Tobias et al. (Ibis 152:724–746, 2010). Moreover, we found a marked divergence in sperm lengths with little range overlap. Relatively long sperm with low intra- and intermale CV compared to other passerines suggest a mating system with high levels of sperm competition (extrapair paternity) in these taxa. Conclusion The large and diagnostic divergences in multiple functional traits qualify for species rank, i.e., Tenerife Blue Chaffinch (Fringilla teydea) and Gran Canaria Blue Chaffinch (Fringilla polatzeki). We encourage a wider use of sperm traits in avian taxonomy because sperm divergences might signal reproductive incompatibility at the postcopulatory prezygotic stage, especially in species with sperm competition.

Comunicació presentada a l'Interspeech 2016, celebrat els dies 8 a 12 de setembre de 2016 a San Francisco, California. This paper focuses on the synthesis of bird songs using Hidden Markov Models (HMM). This technique has been widely used for speech modeling and synthesis. However, features and contextual factors typically used for human speech are not appropriate for modeling bird songs. Moreover, while for speech we can easily control the content of the recordings, this is not the case for bird songs, where we have to rely on the spontaneous singing of the animal. In this work we briefly overview the characteristics of bird songs, compare them to speech, and propose strategies for adapting the widely-used HTS (HMM-based Speech Synthesis System) framework to model and synthesize bird songs. In particular, we focus on Chaffinch species and a database of recordings of several song bouts of one male bird. At the end we discuss the synthesis results obtained.

Adaptive radiations play key roles in the generation of biodiversity and biological novelty, and therefore understanding the factors that drive them remains one of the most important challenges of evolutionary biology. Although both intrinsic innovations and extrinsic ecological opportunities contribute to diversification bursts, few studies have looked at the synergistic effect of such factors. Here we investigate the Teloschistales (Ascomycota), a group of1,000 lichenized species with variation in species richness and phenotypic traits that hinted at a potential adaptive radiation. We found evidence for a dramatic increase in diversification rate for one of four families within this order--Teloschistaceae--which occurred ∼ 100 Mya (Late Cretaceous) and was associated with a switch from bark to rock and from shady to sun-exposed habitats. This adaptation to sunny habitats is likely to have been enabled by a contemporaneous key novel phenotypic innovation: the production in both vegetative structure (thallus) and fruiting body (apothecia) of anthraquinones, secondary metabolites known to protect against UV light. We found that the two ecological factors (sun exposure and rock substrate) and the phenotypic innovation (anthraquinones in the thallus) were all significant when testing for state-dependent shifts in diversification rates, and together they seem likely to be responsible for the success of the Teloschistaceae, one of the largest lichen-forming fungal lineages. Our results support the idea that adaptive radiations are driven not by a single factor or key innovation, but require a serendipitous combination of both intrinsic biotic and extrinsic abiotic and ecological factors.

Many models have investigated how the process of speciation may occur in sympatry. In these models, individuals are either asexual or mate choice is determined by very simple rules. Females, for example, may be assumed either to compare their phenotype to that of a potential mate, preferring to mate with similar males (phenotype matching), or to possess preference genes that determine which male phenotype they prefer. These rules often do not reflect the mate-choice rules found in empirical studies. In this paper, we compare these two modes of female choice with various types of sexual imprinting. We examine the efficacy of different mate-choice behavior in causing divergence in male traits under simple deterministic one-locus population genetic models as well as under polygenic, individual-based simulations based on the models of Dieckmann and Doebeli (1999). We find that the inheritance mechanism of mate choice can have a large effect on the ease of sympatric speciation. When females imprint on their mothers, the result of the model is similar to phenotype matching, where speciation can occur fairly easily. When females imprint on their fathers or imprint obliquely, speciation becomes considerably less likely. Finally, when females rely on preference genes, male trait evolution occurs easily, but the correlation between trait and preference can be weak, and interpreting these results as speciation may be suspect.

Conformity is an important aspect of many communication systems in which signals are culturally transmitted. We suggest that one reason for it to evolve is if nonconforming individuals are discriminated against, and we therefore investigated how this might arise. We designed a spatial simulation, in which individuals occupied a territory on a lattice, and played a territorial game with their neighbours in which one individual could challenge another and, if successful, obtain some of the latter's resources. We then examined the relative success of pairs of strategies. We found that aggression targeted towards nonconformers (conformity-enforcing behaviour) was more successful than randomly targeted aggression in both a simple model and a more complicated one in which the conditions were based on the specific case of song sharing between songbirds. The reason for this result is that individuals could use patterns of vocal sharing to gang up on neighbours with locally uncommon song types, increasing their own chances of success. In both models, a critical parameter was how the number of contests an individual was previously involved in altered the chance of winning: conformity-enforcing behaviour was the most successful strategy only if the more contests an individual had been involved in, the less likely it was to win. Our results may explain the origin of conformity-enforcing behaviour and discrimination in nonhuman animals and may have relevance to similar behaviour in humans.

Geographical variation in song is a common feature of populations of territorial songbirds. However, the factors responsible for the levels and patterns of variation have not been examined in detail. We measured geographical variation of songs in chaffinches, Fringilla coelebs , in samples from five locations in Scotland, U.K. We found substantial variation in the level of song sharing between locations. It was highest in isolated island areas and in a recently populated area. By comparing our data with a spatial simulation model designed to mimic the different areas, we calculated estimates of cultural mutation that ranged between 0.001 and 0.03, with a maximum possible value of 0.05, and found that chaffinches had a significant preference for learning songs not from immediate neighbours, but from males about 500 m away. We discuss the implications of these findings for the process and function of cultural transmission of song in the chaffinch. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.

In this study we examined how social learning of feeding preferences by zebra finches was affected by the identity of different demonstrators. We presented adult zebra finches with two demonstrators, one male and one female, that exhibited different food choices, and we recorded their subsequent preference when given a choice between the two food types. Previously it was found that young zebra finches' patterns of social learning are affected by the sex of the individual demonstrating a feeding behaviour. This result could be explained by the lack of exposure these animals had to the opposite sex, or by their mating status. Therefore, we investigated the social learning preferences of adult mated zebra finches. We found the same pattern of directed social learning of a different type of feeding behaviour (food colour): female zebra finches preferred the colour of food eaten by male demonstrators, whereas male zebra finches showed little evidence of any preference for the colour of food eaten by female demonstrators. Furthermore, we found that female observers' preferences were biased by demonstrators' relative feeding activity: the female demonstrator was only ever preferred if it ate less than its male counterpart.

The degree to which culture and cultural evolution are unique to humans has been a subject of continuous debate in the biological and social sciences. Bird song provides one of the most convincing animal examples, and the study of song learning and cultural transmission in chaffinches (Fringilla coelebs) has been central in this research, but has not been reviewed systematically. Not only can the classic work on song learning in chaffinches by Thorpe and Marler be said to have kick-started the field of vocal learning and traditions in animals, but subsequent work in this species has provided an exceptional depth and breadth of data on geographic variation in song and its cultural evolution. Here we review the work on chaffinch song that has been carried out in the 60 or so years since Thorpe and Marler's pioneering studies. In addition to further work on vocal learning and on dialects, the chaffinch has become a prime subject for studies of cultural evolution, particularly through studies on the Atlantic islands, as well as in Britain, Europe, and New Zealand. As well as describing such studies, we identify further areas likely to be fruitful for research on this species, which remains one of the icons of bird song research.

We tested sexually mature zebra finches to see whether social learning influenced their feeding preferences, in particular whether they followed the preference of a male or a female demonstrator, of a red-ringed or a green-ringed male, and of a familiar or an unfamiliar male. Each observer was exposed to two demonstrators feeding at different-coloured hoppers, and then tested with a choice of hoppers to see which of the two colours they preferred. Males showed no preference between male and female demonstrators when choosing from which colour of food hopper to feed, but females preferred to feed from the hopper colour the male demonstrator had used. Both males and females exposed to male demonstrators wearing red or green leg rings fed preferentially from the same colour hopper as the red-ringed demonstrators had used. Finally, male birds exposed to familiar and unfamiliar demonstrators, preferred the food hopper from which the familiar demonstrator had fed. We interpret the results as indicating differences between the demonstrators in the amount of attention they attracted from observers. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

Vocal learning has evolved in several groups of animals, yet the reasons for its origins and maintenance are controversial, with none of the theories put forward appearing to apply over a broad range of species. The theory of gene-culture coevolution is applied to this problem taking the specific case of the maintenance of song learning in birds. The interaction between genes underlying the filter for recognizing and learning conspecific song and the culturally transmitted songs themselves sets up an evolutionary force that may maintain vocal learning. We evaluate this hypothesis using a spatial simulation model. Our results suggest that selection that would maintain song learning exists over a wide range of conditions. Song learning may persist due to an evolutionary trap even though the average fitness in a population of learners may be lower than in a population of non-learners.

The preference of insect herbivores to oviposit into larger structures might be explained by the superior food resource a larger structure offers to herbivore offspring or as an adaptive strategy by the herbivore to protect its offspring against parasitoids, should larger structures provide a partial refuge against parasitoids. We investigated whether larger fruits provide a partial refuge for rose-hip fly (Rhagoletis basiola) offspring against the specialist parasitoid Halticoptera rosae. We tested whether female parasitoids exhibit a preference to land on larger rose-hips into which females of the host fly prefer to oviposit and whether parasitoids are less successful in locating host eggs on large, compared to small, fruits. Female parasitoids showed no clear preference for larger fruits. When searching fruits, they were about equally successful in locating fly eggs on large and small fruits, with a slight, though nonsignificant trend for fly offspring in large fruits to be located more easily. Furthermore, wasps did not require more time to locate host eggs on large fruits than on small fruits, suggesting a nonrandom searching behavior. Consequently, large rose-hips do not provide a partial refuge to fly offspring and the preference of flies to oviposit into larger fruits cannot be explained as an adaptation against parasitoid searching efficiency.

Summary Cultural transmission can increase the flexibility of behavior, such as bird song. Nevertheless, this flexibility often appears to be constrained, sometimes by preferences for learning certain traits over others, a phenomenon known as "biased" learning or transmission [1]. The sequential colonization of the Atlantic Islands by the chaffinch ( Fringilla coelebs ) [2] provides a unique model system in which to investigate how the variability of a cultural trait has evolved. We used novel computational methods to analyze chaffinch song from twelve island and continental populations and to infer patterns of evolution in song structure. We found that variability of the subunits within songs ("syllables") differed moderately between populations but was not predicted by whether the population was continental or not. In contrast, we found that the sequencing of syllables within songs ("syntax") was less structured in island than continental populations and in fact decreased significantly after each colonization. Syntactical structure was very clear in the mainland European populations but was almost entirely absent in the most recently colonized island, Gran Canaria. Our results suggest that colonization leads to the progressive loss of a species-specific feature of song, syntactical structure.

The deutonymphs (or hypopi) of two new species of Hemisarcoptidae (Acari) of the genera Congovidia Fain & Elsen, 1971 and Divilia Sevastianov, 1969, are described from coccinellid beetles (Coleoptera: Coccinellidae) from Britain, i.e. Congovidia coccinellidarum n. sp. from eight genera and nine species of Coccinellidae and Divilia occidentalis n. sp., represented by only one deutonymph collected from Chilocorus renipustulatus. Congovidia coccinellidarum was also collected from Rhinocimus hemirostris (Coleoptera: Pythidae) from Britain. The most infested ladybird beetle was Halyzia sedecimguttata, a broad-leaved deciduous woodland specialist showing a marked preference for sycamores.

Previous studies of learned bird song have suggested the existence of species-universal patterns in song organization: clear clusters in produced songs that do not vary within a species. Here the authors combine a computational method of comparing songs with statistical methods of assessing cluster structure to investigate this issue in a more quantitative manner. The authors first analyze song phonology and then examine song syntax at a population level in 3 species with very different song structure: chaffinches (Fringilla coelebs), zebra finches (Taenopygia guttata), and swamp sparrows (Melospiza georgiana). The authors used a dynamic time-warping algorithm to compare song elements, which closely matched the judgments of human observers. Clustering tendency and validation statistics showed that broad phonological categories existed in all 3 species, but these categories explained no more than half of the overall phonological variation. The authors developed a novel statistic to assess syntactical structure, which indicated that element transitions were not randomly distributed. In the clearest case, in chaffinches, this could be explained by syllables being linked to certain positions within the song. These results demonstrate measures of song organization that can be applied across species, enhancing the potential of comparative studies.

Language change has been described as an unintended eect of language in use (Keller 1994). In this view, change results from the way individuals use their language; the challenge is thus to explain change and its properties in terms of factors operating on the individual level, and population dynamics. An intriguing example of such a phenomenon is the finding that language change shows some highly regular tendencies. This has recently received considerable attention in the literature (Bybee et al. 1994; Heine and Ku- teva 2002; Traugott and Dasher 2002; Hopper and Traugott 2003). In un- related languages, similar words often change in similar ways, along similar ''trajectories'' of development. This phenomenon is called ''unidirectional- ity'', and it is an important part of processes of grammaticalization, items changing from a lexical meaning to a grammatical function. It has been claimed that around 90-99% of all processes of grammaticalization are uni- directional (Haspelmath 1999). This article explores several mechanisms that may lead to language change, and examines whether they may be responsible for unidirectional- ity. We use a cultural evolutionary computational model with which the ef- fects of individual behavior on the group level can be measured. By using this approach, regularities in semantic change can be explained in terms of very basic mechanisms and aspects of language use such as the frequency with which particular linguistic items are used. One example is that fre- quency dierences by themselves are a strong enough force for causing uni- directionality. We argue that adopting a cultural evolutionary approach may be useful in the study of language change.

Birdsong is a sexually selected and culturally transmitted multidimensional signal. Sexually selected traits are generally assumed to indicate condition. In oscine songbirds, song is learned early in life. The developmental stress hypothesis proposed that poor early developmental condition can adversely affect song learning. The quality and accuracy of learned song features could thus indicate male quality to conspecifics. Surprisingly, studies testing this hypothesis to date mostly compared adult males' song repertoires without looking at song imitation. The few that did reported inconsistent effects and analyzed a limited number of song features. Here, we examined the effects of early condition (by brood size manipulation) on learned song in zebra finches, Taeniopygia guttata, in comparing both the number of specific elements copied from an adult song tutor and a great number of previously neglected syntax-, complexity-, and performance-related song features. The treatment did not significantly affect average number of imitated elements, the standard measure of quality of song imitation in this species. However, developmental condition had 2 significant main effects on adult song: birds from large broods (i.e., of poor early condition) in comparison to birds from small broods copied syntactical dependencies of song elements from the song motif of their tutor less accurately and had less consistent sound duration between song motifs. These findings support the developmental stress hypothesis. We discuss how this sheds light on the potential role of such long-term signals of male developmental condition in female mate choice and potential constraints underlying condition-dependent expression of song features. Copyright 2008, Oxford University Press.

Many models have investigated how the process of speciation may occur in sympatry. In these models, individuals are either asexual or mate choice is determined by very simple rules. Females, for example, may be assumed either to compare their phenotype to that of a potential mate, preferring to mate with similar males (phenotype matching), or to possess preference genes that determine which male phenotype they prefer. These rules often do not reflect the mate-choice rules found in empirical studies. In this paper, we compare these two modes of female choice with various types of sexual imprinting. We examine the efficacy of different mate-choice behavior in causing divergence in male traits under simple deterministic one-locus population genetic models as well as under polygenic, individual-based simulations based on the models of Dieckmann and Doebeli (1999). We find that the inheritance mechanism of mate choice can have a large effect on the ease of sympatric speciation. When females imprint on their mothers, the result of the model is similar to phenotype matching, where speciation can occur fairly easily. When females imprint on their fathers or imprint obliquely, speciation becomes considerably less likely. Finally, when females rely on preference genes, male trait evolution occurs easily, but the correlation between trait and preference can be weak, and interpreting these results as speciation may be suspect.

The songs of many birds are unusual in that they serve a role in identifying conspecific mates, yet they are also culturally transmitted. Noting the apparently high rate of diversity in one avian taxon, the songbirds, in which song learning appears ubiquitous, it has often been speculated that cultural transmission may increase the rate of speciation. Here we examine the possibility that song learning affects the rate of allopatric speciation. We construct a population-genetic model of allopatric divergence that explores the evolution of genes that underlie learning preferences (predispositions to learn some songs over others). We compare this with a model in which mating signals are inherited only genetically. Models are constructed for the cases where songs and preferences are affected by the same or different loci, and we analyze them using analytical local stability analysis combined with simulations of drift and directional sexual selection. Under nearly all conditions examined, song divergence occurs more readily in the learning model than in the nonlearning model. This is a result of reduced frequency-dependent selection in the learning models. Cultural evolution causes males with unusual genotypes to tend to learn from the majority of males around them, and thus develop songs compatible with the majority of the females in the population. Unusual genotypes can therefore be masked by learning. Over a wide range of conditions, learning therefore reduces the waiting time for speciation to occur and can be predicted to accelerate the rate of speciation.

In several communication systems that rely on social learning, such as bird song, and possibly human language, the range of signals that can be learned is limited by perceptual biases--predispositions--that are presumably based on genes. In this paper, we examine the coevolution of such genes with the culturally transmitted communication traits themselves, using deterministic population genetic models. We argue that examining how restrictive genetic predispositions are is a useful way of examining the evolutionary origin and maintenance of learning. Under neutral cultural evolution, where no cultural trait has any inherent advantage over another, there is selection in favour of less restrictive genes (genes that allow a wider range of signals to recognized). In contrast, cultural conformity (where the most common cultural trait is favoured) leads to selection in favour of more restrictive genes.

The learned songs of songbirds often cluster into population-wide types. Here, we test the hypothesis that male and female receivers respond differently to songs depending on how typical of those types they are. We used computational methods to cluster a large sample of swamp sparrow ( Melospiza georgiana ) songs into types and to estimate the degree to which individual song exemplars are typical of these types. We then played exemplars to male and female receivers. Territorial males responded more aggressively and captive females performed more sexual displays in response to songs that are highly typical than to songs that are less typical. Previous studies have demonstrated that songbirds distinguish song types that are typical for their species, or for their population, from those that are not. Our results show that swamp sparrows also discriminate typical from less typical exemplars within learned song-type categories. In addition, our results suggest that more typical versions of song types function better, at least in male–female communication. This finding is consistent with the hypothesis that syllable type typicality serves as a proxy for the assessment of song learning accuracy.