A new study, published in Nature Communications, show that Japanese great tits combine their calls using specific rules to communicate important compound messages. Credit: Toshitaka Suzuki Human communication is powered by rules for combining words to generate novel meanings. Such syntactical rules have long been assumed to be unique humans. A new study, published in Nature Communications, show that Japanese great tits combine their calls using specific rules to communicate important compound messages. These results demonstrate that syntax is not unique to humans. Instead, syntax may be a general adaptation to social and behavioural complexity in communication systems. Language is one of humans' most important defining characteristics. It allows us to generate innumerable expressions from a finite number of vocal elements and meanings, and underlies the evolution of other characteristic human behaviours, such as art and technology. The power of language lies in combining meaningless sounds into words that in turn are combined into phrases. Research on the communication systems of non-human primates and birds suggests that the ability to combine meaningless vocal elements has evolved repeatedly, but the evolution of syntax (i.e. combining different words to form more complex expressions) was so far considered to be unique to human language. A recent study by researchers from Japan, Germany and Sweden challenges this view, demonstrating that the Japanese great tit, known for its diverse vocal repertoire, have evolved syntax. This small bird species experiences a number of threats, and in response to predators, they give a variety of different calls. These calls can be used either alone or in combination with other calls. Using playback experiments, Dr. Suzuki and colleagues could demonstrate that ABC calls signifies "scan for danger", for example when encountering a perched predator, whereas D calls signify "come here", for example when discovering a new food source, or to recruit the partner to their nest box. Tits often combine these two calls into ABC-D calls such as when approaching and deterring predators. When these two calls are played together in the naturally occurring order (ABC-D), then birds both approach and scan for danger. However, when the call ordering is artificially reversed (D-ABC), birds do not respond. 'This study demonstrates that syntax is not unique to human language, but also evolved independently in birds. Understanding why syntax has evolved in tits can give insights into its evolution in humans', says David Wheatcroft, post doc at the Department of Ecology and Genetics at Uppsala University and co-author of the study. Japanese great tits use different calls to coordinate a variety of social interactions, each of which requires specific behavioural responses. Syntax provides rules for combining the elements from a small vocabulary to generate novel meanings that can be readily recognized. These rules may be an adaptation to social and behavioural complexity in communication systems, such as in human language. Explore further: Syntax in our primate cousins More information: Toshitaka Suzuki, David Wheatcroft, and Michael Griesser (2016) Experimental evidence for compositional syntax in bird calls, Nature Communications, DOI: 10.1038/ncomms10986
The new research findings are published today in PLOS ONE. In behavioural experiments, the scientists have studied the ability to resolve visual detail in time in three small wild passerine species: blue tit, collared flycatcher and pied flycatcher. This ability is the temporal resolution of eyesight, i.e. the number of changes per second an animal is capable of perceiving. It may be compared to spatial resolution (visual acuity), a measure of the number of details per degree in the field of vision. The researchers trained wild-caught birds to receive a food reward by distinguishing between a pair of lamps, one flickering and one shining a constant light. Temporal resolution was then determined by increasing the flicker rate to a threshold at which the birds could no longer tell the lamps apart. This threshold, known as the CFF (critical flicker fusion rate), averaged between 129 and 137 hertz (Hz). In the pied flycatchers it reached as high as 146 Hz, some 50 Hz above the highest rate encountered for any other vertebrate. For humans, the CFF is usually approximately 60 Hz. For passerines, the world might to be said to be in slow motion compared with how it looks to us. It has been argued before, but never investigated, that small and agile wild birds should have extremely fast vision. Nevertheless, the blue tits and flycatchers proved to have higher CFF rates than were predicted from their size and metabolic rates. This indicates an evolutionary history of natural selection for fast vision in these species. The explanation might lie in small airborne birds' need to detect and track objects whose image moves very swiftly across the retina—for blue tits, for example, to be able to see and avoid all branches when they take cover from predators by flying straight into bushes. Moreover, the three avian species investigated all, to a varying degree, subsist on the insects they catch. Flycatchers, as their name suggests, catch airborne insects. For this ability, aiming straight at the insect is not enough. Forward planning is required: the bird needs high temporal resolution to track the insect's movement and predict its location the next instant. The new results give some cause for concern about captive birds' welfare. Small passerines are commonly kept in cages, and may be capable of seeing roughly as fast as their wild relatives. With the phase-out of incandescent light bulbs for reasons of energy efficiency, tame birds are increasingly often kept in rooms lit with low-energy light bulbs, fluorescent lamps or LED lighting. Many of these flicker at 100 Hz, which is thus invisible to humans but perhaps not to small birds in captivity. Studies have shown that flickering light can cause stress, behavioural disturbances and various forms of discomfort in humans and birds alike. Of all the world's animals, the eagle has the sharpest vision. It can discern 143 lines within one degree of the field of vision, while a human with excellent sight manages about 60. The magnitude of this difference is almost exactly the same as between a human's top vision speed and a pied flycatcher's: 60 and 146 Hz respectively. Thus, the flycatcher's vision is faster than human vision to roughly the same extent as an eagle's vision is sharper. So small passerines' rapid vision is an evolutionary adaptation just as impressive as the sharp eyesight of birds of prey. Anders Ödeen, the lecturer at Uppsala University's Department of Ecology and Genetics who headed the study, puts the research findings in perspective. 'Fast vision may, in fact, be a more typical feature of birds in general than visual acuity. Only birds of prey seem to have the ability to see in extremely sharp focus, while human visual acuity outshines that of all other bird species studied. On the other hand, there are lots of bird species similar to the blue tit, collared flycatcher and pied flycatcher, both ecologically and physiologically, so they probably also share the faculty of superfast vision.' Explore further: Genes from the father facilitate the formation of new species More information: Jannika Boström, Marina Dimitrova, Cindy Canton, Olle Håstad, Anna Qvarnström, Anders Ödeen (2016) Ultra-rapid Vision in Birds, PLOS ONE, dx.plos.org/10.1371/journal.pone.0151099
News Article | September 7, 2016
A research team at Uppsala University has determined the complete genetic code of 11 members of a flycatcher pedigree. Doing this, they have for the first time been able to estimate the rate of new mutations in birds. When they combined the new results with mutation rate estimates from other organisms, a clear pattern emerged: The more common a species is, the lower its mutation rate. The research team at the Department of Ecology and Genetics at Uppsala University has sequenced the whole genome of 11 members of a three-generation flycatcher family consisting of grandparents, parents and offspring. By carefully screening letter by letter in the 1.1 billion letter genetic code of each individual they searched for new genetic variants. These represent mutations arisen in the germ cells of parents. 'This is really like looking for a needle in the haystack. There were just on average eight mutations found per individual. Mutations were randomly distributed across the genome, hence there were not short-cut to their identification', says Hans Ellegren, professor in evolutionary biology and leader of the study, Based on the occurrence of mutations in the family the team could estimate the rate at which new mutations arise to one per 100 million letter per generation. This is the first time someone has been able to estimate the rate of mutation in birds. Mutation rate estimates are only available for a limited number of other organisms. The comprehensive computer work was performed by bioinformatician Linnéa Smeds. Anna Qvarnström provided blood samples from the analysed birds. One major goal of the study was to shed light on the long-standing question of why there are mutations. One would think that mutations occur to ensure that there will be evolution - without them new life forms cannot evolve and all species would eventually become extinct. However, natural selection operates on the level of individuals and there is no benefit for individuals to mutate just because it might be good for the species to have genetic variation in the future. On the contrary, there is typically a cost associated with mutations: most mutations that affect the fitness of offspring are more or less deleterious. Theory therefore suggests that parents should avoid as much as possible to provide their offspring with new mutations. Ideally, the rate of mutation should be zero. 'When we combined our results with estimate rates of mutation in other species, a clear pattern emerged. The more common a species, the lower its mutation rate', says Hans Ellegren. It is known that natural selection is generally more efficient in large populations. Selection can therefore better improve the machinery that replicates DNA in germ cells in abundant species, to save their offspring from deleterious mutations. But even in the most common species selection is not efficient enough for a replication machinery with 100 percent accuracy to evolve. The answer to the question of why there are mutations (despite their deleterious effects) is thus probably that they cannot be avoided. The findings were published in Genome Research.
Pavlova A.,Monash University |
Amos J.N.,Monash University |
Joseph L.,CSIRO |
Loynes K.,Ecology and Genetics |
And 6 more authors.
Evolution | Year: 2013
Relationships among multilocus genetic variation, geography, and environment can reveal how evolutionary processes affect genomes. We examined the evolution of an Australian bird, the eastern yellow robin Eopsaltria australis, using mitochondrial (mtDNA) and nuclear (nDNA) genetic markers, and bioclimatic variables. In southeastern Australia, two divergent mtDNA lineages occur east and west of the Great Dividing Range, perpendicular to latitudinal nDNA structure. We evaluated alternative scenarios to explain this striking discordance in landscape genetic patterning. Stochastic mtDNA lineage sorting can be rejected because the mtDNA lineages are essentially distinct geographically for > 1500 km. Vicariance is unlikely: the Great Dividing Range is neither a current barrier nor was it at the Last Glacial Maximum according to species distribution modeling; nuclear gene flow inferred from coalescent analysis affirms this. Female philopatry contradicts known female-biased dispersal. Contrasting mtDNA and nDNA demographies indicate their evolutionary histories are decoupled. Distance-based redundancy analysis, in which environmental temperatures explain mtDNA variance above that explained by geographic position and isolation-by-distance, favors a nonneutral explanation for mitochondrial phylogeographic patterning. Thus, observed mito-nuclear discordance accords with environmental selection on a female-linked trait, such as mtDNA, mtDNA-nDNA interactions or genes on W-chromosome, driving mitochondrial divergence in the presence of nuclear gene flow. © 2013 The Author(s). Evolution © 2013 The Society for the Study of Evolution..
Clark H.L.,Ecology and Genetics |
Backwell P.R.Y.,Ecology and Genetics
Behavioral Ecology and Sociobiology | Year: 2015
Female mating preferences can vary temporally, with females choosing different males at different times; and spatially, with females in different populations preferring different males. This level of complexity is now well established, but we know of no evidence for a mosaic of female preferences within a single population. Here we show that, in the banana fiddler crab, Uca mjoebergi, female preferences vary both temporally and spatially. Females living in the high inter-tidal zone changed their mating preference for male size over the duration of the 9-day mating period every semi-lunar cycle: early mating females selected larger males with cooler burrows, slowing embryonic development; those mating later, selected smaller males with warmer burrows, accelerating development. Females living lower in the inter-tidal zone, however, did not show this temporal variation: they select the same sized males throughout the mating period. It is only in the high inter-tidal zone, at the start of the fortnightly mating period, that large size confers a mating advantage to males. © 2015 Springer-Verlag Berlin Heidelberg