Song Feature Specific Analysis of Isolate Song Reveals Interspecific Variation in Learned Components

Studies of avian vocal development without exposure to conspecific song have been conducted in many passerine species, and the resultant isolate song is often interpreted to represent an expression of the genetic code for conspecific song. There is wide recognition that vocal learning exists in oscine songbirds, but vocal learning has only been thoroughly investigated in a few model species, resulting in a narrow view of birdsong learning. By extracting acoustic signals from published spectrograms, we have reexamined the findings of isolate studies with a universally applicable semi‐automated quantitative analysis regimen. When song features were analyzed in light of three different production aspects (respiratory, syringeal, and central programming of sequence), all three show marked interspecific variability in how close isolate song features are to normal. This implies that song learning mechanisms are more variable than is commonly recognized. Our results suggest that the interspecific variation shows no readily observable pattern reflecting phylogeny, which has implications for understanding the mechanisms behind the evolution of avian vocal communication. We emphasize that song learning in passerines provides an excellent opportunity to investigate the evolution of a complex, plastic trait from a phylogenetic perspective.     

GEOGRAPHIC VARIATION IN THE SONGS OF NEOTROPICAL SINGING MICE: TESTING THE RELATIVE IMPORTANCE OF DRIFT AND LOCAL ADAPTATION

Patterns of geographic variation in communication systems can provide insight into the processes that drive phenotypic evolution. Although work in birds, anurans, and insects demonstrates that acoustic signals are sensitive to diverse selective and stochastic forces, processes that shape variation in mammalian vocalizations are poorly understood. We quantified geographic variation in the advertisement songs of sister species of singing mice, montane rodents with a unique mode of vocal communication. We tested three hypotheses to explain spatial variation in the song of the lower altitude species, Scotinomys teguina: selection for species recognition in sympatry with congener, S. xerampelinus, acoustic adaptation to different environments, and stochastic divergence. Mice were sampled at seven sites in Costa Rica and Panamá; genetic distances were estimated from mitochondrial control region sequences, between‐site differences in acoustic environment were estimated from climatic data. Acoustic, genetic and geographic distances were all highly correlated in S. teguina, suggesting that population differentiation in song is largely shaped by genetic drift. Contrasts between interspecific genetic‐acoustic distances were significantly greater than expectations derived from intraspecific contrasts, indicating accelerated evolution of species‐specific song. We propose that, although much intraspecific acoustic variation is effectively neutral, selection has been important in shaping species differences in song.     

Vocal Learning in Songbirds and Humans: A Retrospective in Honor of Peter Marler

Peter Marler made a number of significant contributions to the field of ethology, particularly in the area of animal communication. His research on birdsong learning gave rise to a thriving subfield. An important tenet of this growing subfield is that parallels between birdsong and human speech make songbirds valuable as models in comparative and translational research, particularly in the case of vocal learning and development. Decades ago, Marler pointed out several phenomena common to the processes of vocal development in songbirds and humans—including a dependence on early acoustic experience, sensitive periods, predispositions, auditory feedback, intrinsic reinforcement, and a progression through distinct developmental stages—and he advocated for the value of comparative study in this domain. We review Marler's original comparisons between birdsong and speech ontogeny and summarize subsequent progress in research into these and other parallels. We also revisit Marler's arguments in support of the comparative study of vocal development in the context of its widely recognized value today.     

Draft genome of an iconic Red Sea reef fish,the blacktail butterflyfish (Chaetodon austriacus): current status and its characteristics

Butterflyfish are among the most iconic of the coral reef fishes and represent a model system to study general questions of biogeography, evolution and population genetics. We assembled and annotated the genome sequence of the blacktail butterflyfish (Chaetodon austriacus), an Arabian region endemic species that is reliant on coral reefs for food and shelter. Using available bony fish (superclass Osteichthyes) genomes as a reference, a total of 28 926 high‐quality protein‐coding genes were predicted from 13 967 assembled scaffolds. The quality and completeness of the draft genome of C. austriacus suggest that it has the potential to serve as a resource for studies on the co‐evolution of reef fish adaptations to the unique Red Sea environment, as well as a comparison of gene sequences between closely related congeneric species of butterflyfish distributed more broadly across the tropical Indo‐Pacific.     

Laying the foundations of evolutionary and systematic studies in crickets (Insecta,Orthoptera): a multilocus phylogenetic analysis

Orthoptera have been used for decades for numerous evolutionary questions but several of its constituent groups, notably crickets, still suffer from a lack of a robust phylogenetic hypothesis. We propose the first phylogenetic hypothesis for the evolution of crickets sensu lato, based on analysis of 205 species, representing 88% of the subfamilies and 71% tribes currently listed in the database Orthoptera Species File (OSF). We reconstructed parsimony, maximum likelihood and Bayesian phylogenies using fragments of 18S, 28SA, 28SD, H3, 12S, 16S, and cytb (~3600 bp). Our results support the monophyly of the cricket clade, and its subdivision into two clades: mole crickets and ant‐loving crickets on the one hand, and all the other crickets on the other (i.e. crickets sensu stricto). Crickets sensu stricto form seven monophyletic clades, which support part of the OSF families, “subfamily groups”, or subfamilies: the mole crickets (OSF Gryllotalpidae), the scaly crickets (OSF Mogoplistidae), and the true crickets (OSF Gryllidae) are recovered as monophyletic. Among the 22 sampled subfamilies, only six are monophyletic: Gryllotalpinae, Trigonidiinae, Pteroplistinae, Euscyrtinae, Oecanthinae, and Phaloriinae. Most of the 37 tribes sampled are para‐ or polyphyletic. We propose the best‐supported clades as backbones for future definitions of familial groups, validating some taxonomic hypotheses proposed in the past. These clades fit variously with the morphological characters used today to identify crickets. Our study emphasizes the utility of a classificatory system that accommodates diagnostic characters and monophyletic units of evolution. Moreover, the phylogenetic hypotheses proposed by the present study open new perspectives for further evolutionary research, especially on acoustic communication and biogeography.     

The impact of environmental factors in birdsong acquisition using automated recorders

The use of automatic acoustic recorders is becoming a principal method to survey birds in their natural habitats, as it is relatively noninvasive while still being informative. As with any other sound, birdsong degrades in amplitude, frequency, and temporal structure as it propagates to the recorder through the environment. Knowing how different birdsongs attenuate under different conditions is useful to, for example, develop protocols for deploying acoustic recorders and improve automated detection methods, an essential part of the research field that is becoming known as ecoacoustics. This article presents playback and recapture (record) experiments carried out under different environmental conditions using twenty bird calls from eleven New Zealand bird species in a native forest and an open area, answering five research questions: (1) How does birdsong attenuation differ between forest and open space? (2) What is the relationship between transmission height and birdsong attenuation? (3) How does frequency of birdsong impact the degradation of sound with distance? (4) Is birdsong attenuation different during the night compared to the day? and (5) what is the impact of wind on attenuation? Bird calls are complex sounds; therefore, we have chosen to use them rather than simple tones to ensure that this complexity is not missed in the analysis. The results demonstrate that birdsong transmission was significantly better in the forest than in the open site. During the night, the attenuation was at a minimum in both experimental sites. Transmission height affected the propagation of the songs of many species, particularly the flightless ones. The effect of wind was severe in the open site and attenuated lower frequencies. The reverberations due to reflective surfaces masked higher frequencies (8 kHz) in the forest even at moderate distances. The findings presented here can be applied to develop protocols for passive acoustic monitoring. Even though the attenuation can be generalized to frequency bands, the structure of the birdsong is also important. Selecting a reasonable sampling frequency avoids unnecessary data accumulation because higher frequencies attenuate more in the forest. Even at moderate distances, recorders capture significantly attenuated birdsong, and hence, automated analysis methods for field recordings need to be able to detect and recognize faint birdsong.     

The evolution of birdsong on islands

Islands are simplified, isolated ecosystems, providing an ideal set‐up to study evolution. Among several traits that are expected to change on islands, an interesting but poorly understood example concerns signals used in animal communication. Islands are typified by reduced species diversity, increased population density, and reduced mate competition, all of which could affect communication signals. We used birdsong to investigate whether there are systematic changes in communication signals on islands, by undertaking a broad comparison based on pairs of closely related island‐mainland species across the globe. We studied song traits related to complexity (number of different syllables, frequency bandwidth), to vocal performance (syllable delivery rate, song duration), and also three particular song elements (rattles, buzzes, and trills) generally implicated in aggressive communication. We also investigated whether song complexity was related to the number of similar sympatric species. We found that island species were less likely to produce broadband and likely aggressive song elements (rattles and buzzes). By contrast, various aspects of song complexity and performance did not differ between island and mainland species. Species with fewer same‐family sympatric species used wider frequency bandwidths, as predicted by the character release hypothesis, both on continents and on islands. Our study supports the hypothesis of a reduction in aggressive behavior on islands and suggests that discrimination against closely related species is an important factor influencing birdsong evolution.     

Microsatellite evolution: polarity of substitutions within repeats and neutrality of flanking sequences.

Though extensively used in a variety of disciplines, the evolutionary pattern of microsatellite sequences is still unclear. We addressed several questions relating to microsatellite evolution by analysing historically accumulated mutation events in a large set of artiodactyl (CA)n repeats, through sequence analysis of orthologous bovine and ovine loci. The substitution rate in microsatellite flanking sequences was not different from that in intron sequences, suggesting that if intron sequences in general are selectively neutral, sequences close to microsatellites are similarly so. This observation thus does not support the idea that successful heterologous amplification of microsatellites across distantly related taxa would be due to flanking sequences generally being under some form of selection. Interestingly, the substitution rate at the first nucleotide positions flanking repeats was significantly higher than in sequences further away. Moreover, the substitution rate in repeat units in the very end of microsatellites was significantly higher than that in the middle of repeat regions. Together these observations suggest a relative instability close to the boundary between repetitive and unique sequences. We present three models that potentially could explain such a feature, all involving inefficiency of mismatch repair systems.     

Male‐specific alterations in structure of isolation call sequences of mouse pups with 16p11.2 deletion

16p11.2 deletion is one of the most common gene copy variations that increases the susceptibility to autism and other neurodevelopmental disorders. This syndrome leads to developmental delays, including speech impairment and delays in expressive language and communication skills. To study developmental impairment of vocal communication associated with 16p11.2 deletion syndrome, we used the 16p11.2del mouse model and performed an analysis of pup isolation calls (PICs). The earliest PICs at postnatal day 5 from 16p11.2del pups were found altered in a male‐specific fashion relative to wild‐type (WT) pups. Analysis of sequences of ultrasonic vocalizations (USVs) emitted by pups using mutual information between syllables at different positions in the USV spectrograms showed that dependencies exist between syllables in WT mice of both sexes. The order of syllables was not random; syllables were emitted in an ordered fashion. The structure observed in the WT pups was identified and the pattern of syllable sequences was considered typical for the mouse line. However, typical patterns were totally absent in the 16p11.2del male pups, showing on average random syllable sequences, while the 16p11.2del female pups had dependencies similar to the WT pups. Thus, we found that PICs were reduced in number in male 16p11.2 pups and their vocalizations lack the syllable sequence order emitted by WT males and females and 16p11.2 females. Therefore, our study is the first to reveal sex‐specific perinatal communication impairment in a mouse model of 16p11.2 deletion and applies a novel, more granular method of analysing the structure of USVs.     

Automated birdsong recognition in complex acoustic environments: a review

Conservationists are increasingly using autonomous acoustic recorders to determine the presence/absence and the abundance of bird species. Unlike humans, these recorders can be left in the field for extensive periods of time in any habitat. Although data acquisition is automated, manual processing of recordings is labour intensive, tedious, and prone to bias due to observer variations. Hence automated birdsong recognition is an efficient alternative. However, only few ecologists and conservationists utilise the existing birdsong recognisers to process unattended field recordings because the software calibration time is exceptionally high and requires considerable knowledge in signal processing and underlying systems, making the tools less user‐friendly. Even allowing for these difficulties, getting accurate results is exceedingly hard. In this review we examine the state‐of‐the‐art, summarising and discussing the methods currently available for each of the essential parts of a birdsong recogniser, and also available software. The key reasons behind poor automated recognition are that field recordings are very noisy, calls from birds that are a long way from the recorder can be faint or corrupted, and there are overlapping calls from many different birds. In addition, there can be large numbers of different species calling in one recording, and therefore the method has to scale to large numbers of species, or at least avoid misclassifying another species as one of particular interest. We found that these areas of importance, particularly the question of noise reduction, are amongst the least researched. In cases where accurate recognition of individual species is essential, such as in conservation work, we suggest that specialised (species‐specific) methods of passive acoustic monitoring are required. We also believe that it is important that comparable measures, and datasets, are used to enable methods to be compared.     

Recent northward range expansion promotes song evolution in a passerine bird,the Light‐vented Bulbul

In common with human speech, song is culturally inherited in oscine passerine birds (‘songbirds’). Intraspecific divergence in birdsong, such as development of local dialects, might be an important early step in the speciation process. It is therefore vital to understand how songs diverge, especially in founding populations. The northward expansion of the Light‐vented Bulbul Pycnonotus sinensis (J. F. Gmelin, 1789) into north China in the last 30 years provides an excellent opportunity to study birdsong evolution. We compared ~4400 songs from newly established northern populations with ~2900 songs from southern populations to evaluate song divergence after recent expansion. The total pool of syllables and especially song types was considerably smaller in the north than in the south, indicating ‘founder effects’ in the new population. The ancestral pattern of mosaic song dialects changed into a pattern of wide geographical sharing of a few song types and syllables, likely the result of fewer geographical barriers to ‘meme flow’, and the recent spread across a large area in the north. Our results suggest that song evolution and vocal trait shifts can arise rapidly after range expansion, and that in the Light‐vented Bulbul ‘founder effects’, geographical isolation, and recent rapid expansions played important roles in the evolution of song dialects.     

Bluffing in the forest: Neotropical Neomorphus ground‐cuckoos and peccaries in a possible case of acoustic mimicry

Acoustic communication is particularly important in environments such as dense tropical forests, where the dim light constrains the efficacy of visual signals. In these environments, complex species interactions could promote the evolution of acoustic signals and result in intriguing patterns of mimicry and convergence. In the Neotropical region, Neomorphus ground‐cuckoos frequently associate with herds of collared peccaries and white‐lipped peccaries. Bill clacking behavior in ground‐cuckoos closely resembles the sound of teeth clacking in peccaries and these acoustic signals are used in agonistic and foraging contexts in both species. Here we demonstrate that the acoustic characteristics of bill clacking in ground‐cuckoos are more similar to teeth clacking of peccaries than to bill clacking of the more closely related Geococcyx roadrunner. We propose that two hypotheses may explain the evolution of the clacking behavior in these taxa. First, because peccaries are known to successfully ward off attacks from large predators to defend their herds, mimicking their clacking can deceive predators, either by triggering clacking from nearby peccaries, or making it appear to the predators that peccaries are present when they are not. Second, ground‐cuckoos and peccaries could mutually benefit from the use of similar signals to alert each other of the presence of predators. In this context, ground‐cuckoos could serve as sentinels while peccaries could confer protection. We also discuss alternative explanations for this striking acoustic resemblance. Ground‐cuckoos and peccaries provide an interesting opportunity to study how an ecological association could foster the evolution of acoustic mimicry.     

Sexually dimorphic phrase organization in the song of the indris (Indri indri)

Animal acoustic communication often takes the form of complex sequences, composed of multiple distinct acoustic units, which can vary in their degree of stereotypy. Studies of sequence variation may contribute to our understanding of the structural flexibility of primates' songs, which can provide essential ecological and behavioral information about variability at the individual, population, and specific level and provide insights into the mechanisms and drivers responsible for the evolutionary change of communicative traits. Several methods have been used for investigating different levels of structural information and sequence similarity in acoustic displays. We studied intra and interindividual variation in the song structuring of a singing primate, the indri (Indri indri), which inhabits the montane rain forests of Madagascar. Indri groups emit duets and choruses in which they combine long notes, short single units, and phrases consisting of a variable number of units (from two to six) with slightly descending frequency. Males' and females' contributions to the song differ in the temporal and frequency structure of song units and repertoire size. We calculated the similarity of phrase organization across different individual contributions using the Levenshtein distance, a logic distance that expressed the minimum cost to convert a sequence into another and can measure differences between two sequences of data. We then analyzed the degree of similarity within and between individuals and found that: (a) the phrase structure of songs varied between reproductive males and females: female structuring of the song showed a higher number of phrases if compared to males; (b) male contributions to the song were overall more similar to those of other males than were female contributions to the song of other females; (c) male contributions were more stereotyped than female contributions, which showed greater individual flexibility. The picture emerging from phrase combinatorics in the indris is in agreement with previous findings of rhythmic features and song repertoire size of the indris, which also suggested that female songs are potentially less stereotyped than those of males.     

Phylogeny and the evolution of acoustic communication in extant Ensifera (Insecta, Orthoptera)

Ensifera present an appropriate and interesting model for the study of acoustic communication, because of their diverse signal and communication modalities, and due to their accessibility for field and laboratory studies. Several hypotheses have been proposed to explain the acoustic evolution of Ensifera, but they were elaborated without any reference to a falsifiable phylogeny, and were consequently highly speculative. Similarly, phylogenetic relationships between ensiferan clades have not hitherto been studied using modern standard methodology, and the sole cladistic analysis by Gwynne in 1995 was methodologically flawed. No sound hypothesis therefore currently exists for ensiferan phylogeny, which precludes historical analysis of their communication modalities. In the present paper, the phylogeny is established on the basis of morpho‐anatomical characters and used to analyse the evolution of acoustic communication in this clade by mapping the characters related to auditory and stridulatory structures onto the resultant trees. Cladistic analyses resulted in two equi‐parsimonious cladograms (length 154, C 64, CI 58, RI 61) with the following topologies: (1) [(Grylloidea–Gryllotalpidae) (Rhaphidophoridae (Schizodactylidae (Gryllacrididae ((Stenopelmatidae–Cooloola) (Anostostomatidae (Prophalangopsis (Cyphoderris (Tettigoniidae–Lezina))))))))] (2) [(Grylloidea–Gryllotalpidae)(Rhaphidophoridae (Schizodactylidae (Gryllacrididae–Cooloola–(Stenopelmatidae (Anostostomatidae (Prophalangopsis (Cyphoderris (Tettigoniidae–Lezina))))))))]. According to these topologies, Ensifera were ancestrally devoid of acoustic and hearing systems. An acoustic (tegminal or femoro‐abdominal) apparatus appeared a number of times independently with convergent structures. Similarly, tibial tympana developed several times independently. Moreover, four hypotheses (each according to a definite pattern of character transformation) can be proposed to explain the evolution of acoustic communication in the different ensiferan clades and relate it to a definite communicatory context. These hypotheses do not apply equally to ensiferan subclades. Grylloidea and Gryllotalpoidea could have experienced convergently a direct development of an intraspecific acoustic communication. Acoustic communication in Tettigoniidea has evolved more ambiguously, and may either have resulted from a direct evolution analogous to that having occurred in Gryllidea, or have developed in a completely different behavioural context. Future studies of acoustic communication in the different ensiferan clades will have to take into account the fact that the involved structures most often are not homologous and that their evolution may not have taken place in similar conditions. Different hypotheses of acoustic communication evolution may apply to different clades, and there may be no single explanation for acoustic communication in Ensifera.     

Intrinsic bursting enhances the robustness of a neural network model of sequence generation by avian brain area HVC

Avian brain area HVC is known to be important for the production of birdsong. In zebra finches, each RA-projecting neuron in HVC emits a single burst of spikes during a song motif. The population of neurons is activated in a precisely timed, stereotyped sequence. We propose a model of these burst sequences that relies on two hypotheses. First, we hypothesize that the sequential order of bursting is reflected in the excitatory synaptic connections between neurons. Second, we propose that the neurons are intrinsically bursting, so that burst duration is set by cellular properties. Our model generates burst sequences similar to those observed in HVC. If intrinsic bursting is removed from the model, burst sequences can also be produced. However, they require more fine-tuning of synaptic strengths, and are therefore less robust. In our model, intrinsic bursting is caused by dendritic calcium spikes, and strong spike frequency adaptation in the soma contributes to burst termination.     

Evolution and plasticity: Divergence of song discrimination is faster in birds with innate song than in song learners in Neotropical passerine birds

Plasticity is often thought to accelerate trait evolution and speciation. For example, plasticity in birdsong may partially explain why clades of song learners are more diverse than related clades with innate song. This “song learning” hypothesis predicts that (1) differences in song traits evolve faster in song learners, and (2) behavioral discrimination against allopatric song (a proxy for premating reproductive isolation) evolves faster in song learners. We tested these predictions by analyzing acoustic traits and conducting playback experiments in allopatric Central American sister pairs of song learning oscines (N = 42) and nonlearning suboscines (N = 27). We found that nonlearners evolved mean acoustic differences slightly faster than did leaners, and that the mean evolutionary rate of song discrimination was 4.3 times faster in nonlearners than in learners. These unexpected results may be a consequence of significantly greater variability in song traits in song learners (by 54–79%) that requires song‐learning oscines to evolve greater absolute differences in song before achieving the same level of behavioral song discrimination as nonlearning suboscines. This points to “a downside of learning” for the evolution of species discrimination, and represents an important example of plasticity reducing the rate of evolution and diversification by increasing variability.     

Global macroevolution and macroecology of passerine song

Studying the macroevolution of the songs of Passeriformes (perching birds) has proved challenging. The complexity of the task stems not just from the macroevolutionary and macroecological challenge of modeling so many species, but also from the difficulty in collecting and quantifying birdsong itself. Using machine learning techniques, we extracted songs from a large citizen science dataset, and then analyzed the evolution, and biotic and abiotic predictors of variation in birdsong across 578 passerine species. Contrary to expectations, we found few links between life‐history traits (monogamy and sexual dimorphism) and the evolution of song pitch (peak frequency) or song complexity (standard deviation of frequency). However, we found significant support for morphological constraints on birdsong, as reflected in a negative correlation between bird size and song pitch. We also found that broad‐scale biogeographical and climate factors such as net primary productivity, temperature, and regional species richness were significantly associated with both the evolution and present‐day distribution of bird song features. Our analysis integrates comparative and spatial modeling with newly developed data cleaning and curation tools, and suggests that evolutionary history, morphology, and present‐day ecological processes shape the distribution of song diversity in these charismatic and important birds.     

Gene rearrangement and sequence analysis of mitogenomes suggest polyphyly of Archaeobalanid and Balanid barnacles (Cirripedia: Balanomorpha)

The acorn barnacles (Cirripedia, Thoracica, Balanomorpha) are a diverse group of crustaceans found in virtually all marine and estuarine habitats. Barnacles are important model species in various biological researches, including evolution, intertidal ecology, larval biology and antifouling. However, there remains a lack of a thorough understanding of the phylogeny for this group of animals, particularly at higher taxonomic levels. In this study, we attempt to determine the phylogenetic relationships among balanomorphan families based on analysis of complete mitochondrial genome from various barnacle families and investigate the evolution of mitogenome in barnacles. Whole mitogenomes of six barnacles were newly sequenced, including Acasta sulcata (Archaeobalanidae), Armatobalanus allium (Archaeobalanidae), Chelonibia testudinaria (Chelonibiidae), Octomeris sp. (Chthamalidae), Savignium biporata (Pyrgomatidae) and Tetraclitella divisa (Tetraclitidae), which exhibit five different gene arrangements. Phylogenetic analysis on 15 complete mitochondrial genome sequences from major barnacle families supported Chthamalidae, Pyrgomatidae and Tetraclitidae formed monophyletic units, but suggested polyphyly of both Archaeobalanidae and Balanidae. Chthamalidae was the earliest diverged lineage in Balanomorpha. Chelonibiidae + Tetraclitidae formed the sister taxon to the monophyletic superfamily Balanoidea (Archaeobalanidae + Balanidae + Pyrgomatidae). The members of Archaeobalanidae and Balanidae intermingled in the inferred topology with the monophyletic Pyrgomatidae deeply nested within. Two Megabalanus species from the family Balanidae and A. sulcata from the family Archaeobalanidae share the same six‐gene‐cluster inversion as compared to the other ten balanomorphan barnacles, providing further evidence for the non‐monophyly for the two families. We showed here that the informativeness of the complete mitogenome sequence and rare genomic events in resolving various questions concerning Balanomorpha relationships. The non‐monophyletic status of Archaeobalanidae and Balanidae falsified many previous hypotheses concerning the complex evolution of Balanomorpha and call for further investigations and careful revision on the taxonomy of the group. Future study focusing on the enigmatic and tentatively basal lineages, for example, Chionelasmatoidea Pachylasmatoidea and Catophragmidae, would be most helpful in fully resolving the phylogeny and mitogenome evolutionary history of acorn barnacles.     

Evidence for acoustic niche partitioning depends on the temporal scale in two sympatric Bornean hornbill species

Understanding niche partitioning of closely related sympatric species is a fundamental goal in ecology. Acoustic communication space can be considered a resource, and the acoustic niche hypothesis posits that competition between species may lead to partitioning of communication space. Here, we compare the calling behavior of two sympatric Bornean hornbill species—the rhinoceros hornbill (Buceros rhinoceros) and the helmeted hornbill (Rhinoplax vigil)—to test for evidence of acoustic niche partitioning. Both hornbill species emit calls heard over many kilometers and have similar habitat preferences which is predicted to result in interspecific competition. We collected acoustic data on sympatric populations of both hornbill species using 10 autonomous recording units in Danum Valley Conservation Area, Sabah, Malaysia. We found that there was substantial spectral overlap between the calls of the two species, indicating the potential for competition for acoustic space. To test for evidence of acoustic niche partitioning, we investigated spatial and temporal patterns of calling in each species. Both hornbills were strictly diurnal and called throughout the day, and we were equally likely to detect both species at each of our recorders. We did not find evidence of temporal acoustic avoidance at a relatively coarse timescale when we divided our dataset into 1 h bins, but we did find evidence of temporal acoustic avoidance at a finer timescale when we used null models to compare the observed duration of overlapping calls to the expected amount of overlap due to chance.     

Capturing the population structure of microparasites: using ITS‐sequence data and a pooled DNA approach

The internal transcribed spacer (ITS) region of nuclear ribosomal DNA is a common marker not only for the molecular identification of different taxa and strains, but also for the analysis of population structure of wild microparasite communities. Importantly, the multicopy nature of this region allows the amplification of low‐quantity samples of the target DNA, a common problem in studies on unicellular, unculturable microparasites. We analysed ITS sequences from the protozoan parasite Caullerya mesnili (class Ichthyosporea) infecting waterflea (Daphnia) hosts, across several host population samples. We showed that analysing representative ITS‐types [as identified by statistical parsimony network analysis (SPN)] is a suitable method to address relevant polymorphism. The spatial patterns were consistent regardless of whether parasite DNA was extracted from individual hosts or pooled host samples. Remarkably, the efficiency in detecting different sequence types was even higher after sample pooling. As shown by simulations, an easily manageable number of sequences from pooled DNA samples are sufficient to resolve the spatial population structure in this system. In summary, the ITS region analysed from pooled DNA samples can provide valuable insights into the spatial and temporal dynamics of microparasites. Moreover, the application of SPN analysis is a good alternative to the well‐established neighbour‐joining method (NJ) for the identification of representative ITS‐types. SPN can even outperform NJ by joining most of the singleton sequences to representative sequence clusters.