Diversity in olfactory bulb size in birds reflects allometry, ecology, and phylogeny

Diversity and evolution of the vertebrate chemoreceptor gene repertoire

Chemoreception - the ability to smell and taste - is an essential sensory modality of most animals. The number and type of chemical stimuli that animals can perceive depends primarily on the diversity of chemoreceptors they possess and express. In vertebrates, six families of G protein-coupled receptors form the core of their chemosensory system, the olfactory/pheromone receptor gene families OR, TAAR, V1R and V2R, and the taste receptors T1R and T2R. Here, we study the vertebrate chemoreceptor gene repertoire and its evolutionary history. Through the examination of 1,527 vertebrate genomes, we uncover substantial differences in the number and composition of chemoreceptors across vertebrates. We show that the chemoreceptor gene families are co-evolving, highly dynamic, and characterized by lineage-specific expansions (for example, OR in tetrapods; TAAR, T1R in teleosts; V1R in mammals; V2R, T2R in amphibians) and losses. Overall, amphibians, followed by mammals, are the vertebrate clades with the largest chemoreceptor repertoires. While marine tetrapods feature a convergent reduction of chemoreceptor numbers, the number of OR genes correlates with habitat in mammals and birds and with migratory behavior in birds, and the taste receptor repertoire correlates with diet in mammals and with aquatic environment in fish.

Neuroanatomy of the late Cretaceous Thescelosaurus neglectus (Neornithischia: Thescelosauridae) reveals novel ecological specialisations within Dinosauria

Ornithischian dinosaurs exhibited a diversity of ecologies, locomotory modes, and social structures, making them an ideal clade in which to study the evolution of neuroanatomy and behaviour. Here, we present a 3D digital reconstruction of the endocranial spaces of the latest Cretaceous neornithischian Thescelosaurus neglectus, in order to interpret the neuroanatomy and paleobiology of one of the last surviving non-avian dinosaurs. Results demonstrate that the brain of Thescelosaurus was relatively small compared to most other neornithischians, instead suggesting cognitive capabilities within the range of extant reptiles. Other traits include a narrow hearing range, with limited ability to distinguish high frequencies, paired with unusually well-developed olfactory lobes and anterior semicircular canals, indicating acute olfaction and vestibular sensitivity. This character combination, in conjunction with features of the postcranial anatomy, is consistent with specializations for burrowing behaviours in the clade, as evidenced by trace and skeletal fossil evidence in earlier-diverging thescelosaurids, although whether they reflect ecological adaptations or phylogenetic inheritance in T. neglectus itself is unclear. Nonetheless, our results provide the first evidence of neurological specializations to burrowing identified within Ornithischia, and non-avian dinosaurs more generally, expanding the range of ecological adaptations recognized within this major clade.

Phylogeny, Ecology, and Gene Families Covariation Shaped the Olfactory Subgenome of Rodents

Olfactory receptor (OR) genes represent the largest multigenic family in mammalian genomes and encode proteins that bind environmental odorant molecules. The OR repertoire is extremely variable among species and is subject to many gene duplications and losses, which have been linked to ecological adaptations in mammals. Although they have been studied on a broad taxonomic scale (i.e., placental), finer sampling has rarely been explored in order to better capture the mechanisms that drove the evolution of the OR repertoire. Among placental mammals, rodents are well-suited for this task, as they exhibit diverse life history traits, and genomic data are available for most major families and a diverse array of lifestyles. In this study, 53 rodent published genomes were mined for their OR subgenomes. We retrieved more than 85,000 functional and pseudogene OR sequences that were subsequently classified into phylogenetic clusters. Copy number variation among rodents is similar to that of other mammals. Using our OR counts along with comparative phylogenetic approaches, we demonstrated that ecological niches such as diet, period of activity, and a fossorial lifestyle strongly impacted the proportion of OR pseudogenes. Within the OR subgenome, phylogenetic inertia was the main factor explaining the relative variations of the 13 OR gene families. However, a striking exception was a convergent 10-fold expansion of the OR family 14 among the phylogenetically divergent subterranean mole-rat lineages belonging to Bathyergidae and Spalacidae families. This study illustrates how the diversity of the OR repertoire has evolved among rodents, both shaped by selective forces stemming from species life history traits and neutral evolution along the rodent phylogeny.

Disentangling Mechanical and Sensory Modules in the Radiation of Noctilionoid Bats

AbstractWith diverse mechanical and sensory functions, the vertebrate cranium is a complex anatomical structure whose shifts between modularity and integration, especially in mechanical function, have been implicated in adaptive diversification. Yet how mechanical and sensory systems and their functions coevolve, as well as how their interrelationship contributes to phenotypic disparity, remain largely unexplored. To examine the modularity, integration, and evolutionary rates of sensory and mechanical structures within the head, we analyzed hard and soft tissue scans from ecologically diverse bats in the superfamily Noctilionoidea, a clade that ranges from insectivores and carnivores to frugivores and nectarivores. We identified eight regions that evolved in a coordinated fashion, thus recognizable as evolutionary modules: five associated with bite force and three linked to olfactory, visual, and auditory systems. Interrelationships among these modules differ between Neotropical leaf-nosed bats (family Phyllostomidae) and other noctilionoids. Consistent with the hypothesis that dietary transitions begin with changes in the capacity to detect novel food items followed by adaptations to process them, peak rates of sensory module evolution predate those of some mechanical modules. We propose that the coevolution of structures influencing bite force, olfaction, vision, and hearing constituted a structural opportunity that allowed the phyllostomid ancestor to take advantage of existing ecological opportunities and contributed to the clade's remarkable radiation.

Review of the Effects of Enclosure Complexity and Design on the Behaviour and Physiology of Zoo Animals

The complexity of the habitat refers to its physical geometry, which includes abiotic and biotic elements. Habitat complexity is important because it allows more species to coexist and, consequently, more interactions to be established among them. The complexity of the habitat links the physical structure of the enclosure to the biological interactions, which occur within its limits. Enclosure complexity should vary temporally, to be able to influence the animals in different ways, depending on the period of the day and season and throughout the year. In the present paper, we discuss how habitat complexity is important, and how it can positively influence the physical and mental states of zoo animals. We show how habitat complexity can ultimately affect educational projects. Finally, we discuss how we can add complexity to enclosures and, thus, make the lives of animals more interesting and functional.

Cranial osteology and palaeobiology of the Early Cretaceous bird Jeholornis prima (Aves: Jeholornithiformes)

Jeholornis is a representative of the earliest-diverging bird lineages, providing important evidence of anatomical transitions involved in bird origins. Although ~100 specimens have been reported, its cranial morphology remains poorly documented owing to poor two-dimensional preservation, limiting our understanding of the morphology and ecology of the key avian lineage Jeholornithiformes, in addition to cranial evolution during the origin and early evolution of birds. Here, we provide a detailed description of the cranial osteology of Jeholornis prima, based primarily on high-quality, three-dimensional data of a recently reported specimen. New anatomical information confirms the overall plesiomorphic morphology of the skull, with the exception of the more specialized rostrum. Data from a large sample size of specimens reveal the dental formula of J. prima to be 0–2–3 (premaxillary–maxillary–dentary tooth counts), contrary to previous suggestions that the presence of maxillary teeth is diagnostic of a separate species, Jeholornis palmapenis. We also present evidence of sensory adaptation, including relatively large olfactory bulbs in comparison to other known stem birds, suggesting that olfaction was an important aspect of Jeholornis ecology. The digitally reconstructed scleral ring suggests a strongly diurnal habit, supporting the hypothesis that early-diverging birds were predominantly active during the day.

Down a Rabbit Hole: Burrowing Behaviour and Larger Home Ranges are Related to Larger Brains in Leporids

Studies on the evolution of brain size variation usually focus on large clades encompassing broad phylogenetic groups. This risks introducing ‘noise’ in the results, often obscuring effects that might be detected in less inclusive clades. Here, we focus on a sample of endocranial volumes (endocasts) of 18 species of rabbits and hares (Lagomorpha: Leporidae), which are a discrete radiation of mammals with a suitably large range of body sizes. Using 60 individuals, we test five popular hypotheses on brain size and olfactory bulb evolution in mammals. We also address the pervasive issue of missing data, using multiple phylogenetic imputations as to conserve the full sample size for all analyses. Our analyses show that home range and burrowing behaviour are the only predictors of leporid brain size variation. Litter size, which is one of the most widely reported constraints on brain size, was unexpectedly not associated with brain size. However, a constraining effect may be masked by a strong association of litter size with temperature seasonality, warranting further study. Lastly, we show that unreasonable estimations of phylogenetic signal (Pagel’s lamba) warrant additional caution when using small sample sizes, such as ours, in comparative studies.

Anatomy and dietary specialization influence sensory behaviour among sympatric primates

Senses form the interface between animals and environments, and provide a window into the ecology of past and present species. However, research on sensory behaviours by wild frugivores is sparse. Here, we examine fruit assessment by three sympatric primates (Alouatta palliata, Ateles geoffroyi and Cebus imitator) to test the hypothesis that dietary and sensory specialization shape foraging behaviours. Ateles and Cebus groups are comprised of dichromats and trichromats, while all Alouatta are trichomats. We use anatomical proxies to examine smell, taste and manual touch, and opsin genotyping to assess colour vision. We find that the frugivorous spider monkeys (Ateles geoffroyi) sniff fruits most often, omnivorous capuchins (Cebus imitator), the species with the highest manual dexterity, use manual touch most often, and that main olfactory bulb volume is a better predictor of sniffing behaviour than nasal turbinate surface area. We also identify an interaction between colour vision phenotype and use of other senses. Controlling for species, dichromats sniff and bite fruits more often than trichromats, and trichromats use manual touch to evaluate cryptic fruits more often than dichromats. Our findings reveal new relationships among dietary specialization, anatomical variation and foraging behaviour, and promote understanding of sensory system evolution.

Possible link between brain size and flight mode in birds: Does soaring ease the energetic limitation of the brain?

Elucidating determinants of interspecies variation in brain size has been a long-standing challenge in cognitive and evolutionary ecology. As the brain is an energetically expensive organ, energetic tradeoffs among organs are considered to play a key role in brain size evolution. This study examined the tradeoff between the brain and locomotion in birds by testing the relationship between brain size, flight modes with different energetic costs (flapping and soaring), and migratory behavior, using published data on the whole-brain mass of 2242 species. According to comparative analyses considering phylogeny and body mass, soarers, who can gain kinetic energy from wind shear or thermals and consequently save flight costs, have larger brains than flappers among migratory birds. Meanwhile, the brain size difference was not consistent in residents, and the size variation appeared much larger than that in migrants. In addition, the brain size of migratory birds was smaller than that of resident birds among flappers, whereas this property was not significant in soarers. Although further research is needed to draw a definitive conclusion, these findings provide further support for the energetic tradeoff of the brain with flight and migratory movements in birds and advance the idea that a locomotion mode with lower energetic cost could be a driver of encephalization during the evolution of the brain.

Fungal ecology: Truffle-guzzling birds

A new study of truffle fungi in Patagonia reveals the importance of native bird species in spore dispersal. This has wide implications for the study of animal-fungal symbioses in the Southern Hemisphere.

Olfactory receptor subgenome and expression in a highly olfactory procellariiform seabird

Procellariiform seabirds rely on their sense of smell for foraging and homing. Both genomes and transcriptomes yield important clues about how olfactory receptor (OR) subgenomes are shaped by natural and sexual selection, yet no transcriptomes have been made of any olfactory epithelium of any bird species thus far. Here we assembled a high-quality genome and nasal epithelium transcriptome of the Leach's storm-petrel (Oceanodroma leucorhoa) to extensively characterize their OR repertoire. Using a depth-of-coverage-assisted counting method, we estimated over 160 intact OR genes (∼500 including OR fragments). This method reveals the highest number of intact OR genes and the lowest proportion of pseudogenes compared to other waterbirds studied, and suggests that rates of OR gene duplication vary between major clades of birds, with particularly high rates in passerines. OR expression patterns reveal two OR genes (OR6-6 and OR5-11) highly expressed in adults, and four OR genes (OR14-14, OR14-12, OR10-2, and OR14-9) differentially expressed between age classes of storm-petrels. All four genes differentially expressed between age classes were more highly expressed in chicks compared to adults, suggesting that ORs genes may exhibit ontogenetic specializations. Three highly differentially expressed OR genes also had high copy number ratios, suggesting that expression variation may be linked to copy number in the genome. We provide better estimates of OR gene number by using a copy number-assisted counting method, and document ontogenetic changes in OR gene expression that may be linked to olfactory specialization. These results provide valuable insight into the expression, development, and macroevolution of olfaction in seabirds.

Infrasound as a Cue for Seabird Navigation

Seabirds are amongst the most mobile of all animal species and spend large amounts of their lives at sea. They cross vast areas of ocean that appear superficially featureless, and our understanding of the mechanisms that they use for navigation remains incomplete, especially in terms of available cues. In particular, several large-scale navigational tasks, such as homing across thousands of kilometers to breeding sites, are not fully explained by visual, olfactory or magnetic stimuli. Low-frequency inaudible sound, i.e., infrasound, is ubiquitous in the marine environment. The spatio-temporal consistency of some components of the infrasonic wavefield, and the sensitivity of certain bird species to infrasonic stimuli, suggests that infrasound may provide additional cues for seabirds to navigate, but this remains untested. Here, we propose a framework to explore the importance of infrasound for navigation. We present key concepts regarding the physics of infrasound and review the physiological mechanisms through which infrasound may be detected and used. Next, we propose three hypotheses detailing how seabirds could use information provided by different infrasound sources for navigation as an acoustic beacon, landmark, or gradient. Finally, we reflect on strengths and limitations of our proposed hypotheses, and discuss several directions for future work. In particular, we suggest that hypotheses may be best tested by combining conceptual models of navigation with empirical data on seabird movements and in-situ infrasound measurements.

Discovering the role of Patagonian birds in the dispersal of truffles and other mycorrhizal fungi

Dispersal is a key process that impacts population dynamics and structures biotic communities. Dispersal limitation influences the assembly of plant and microbial communities, including mycorrhizal fungi and their plant hosts. Mycorrhizal fungi play key ecological roles in forests by feeding nutrients to plants in exchange for sugars, so the dispersal of mycorrhizal fungi spores actively shapes plant communities. Although many fungi rely on wind for spore dispersal, some fungi have lost the ability to shoot their spores into the air and instead produce enclosed belowground fruiting bodies (truffles) that rely on animals for dispersal. The role of mammals in fungal spore dispersal is well documented, but the relevance of birds as dispersal agents of fungi has been understudied, despite the prominence of birds as seed dispersal vectors. Here, we use metagenomics and epifluorescence microscopy to demonstrate that two common, widespread, and endemic Patagonian birds, chucao tapaculos (Scelorchilus rubecula) and black-throated huet-huets (Pteroptochos tarnii), regularly consume mycorrhizal fungi and disperse viable spores via mycophagy. Our metagenomic analysis indicates that these birds routinely consume diverse mycorrhizal fungi, including many truffles, that are symbiotically associated with Nothofagaceae trees that dominate Patagonian forests. Epifluorescence microscopy of fecal samples confirmed that the birds dispersed copious viable spores from truffles and other mycorrhizal fungi. We show that fungi are a common food for both bird species and that this animal-fungi symbiosis is widespread and ecologically important in Patagonia. Our findings indicate that birds may also act as cryptic but critical fungal dispersal agents in other ecosystems.

Distinct interhemispheric connectivity at the level of the olfactory bulb emerges during Xenopus laevis metamorphosis

During metamorphosis, the olfactory system of anuran tadpoles undergoes substantial restructuring. The main olfactory epithelium in the principal nasal cavity of Xenopus laevis tadpoles is associated with aquatic olfaction and transformed into the adult air-nose, while a new adult water-nose emerges in the middle cavity. Impacts of this metamorphic remodeling on odor processing, behavior, and network structure are still unexplored. Here, we used neuronal tracings, calcium imaging, and behavioral experiments to examine the functional connectivity between the epithelium and the main olfactory bulb during metamorphosis. In tadpoles, olfactory receptor neurons in the principal cavity project axons to glomeruli in the ventral main olfactory bulb. These projections are gradually replaced by receptor neuron axons from the newly forming middle cavity epithelium. Despite this reorganization in the ventral bulb, two spatially segregated odor processing streams remain undisrupted and behavioral responses to waterborne odorants are unchanged. Contemporaneously, new receptor neurons in the remodeling principal cavity innervate the emerging dorsal part of the bulb, which displays distinct wiring features. Glomeruli around its midline are innervated from the left and right nasal epithelia. Additionally, postsynaptic projection neurons in the dorsal bulb predominantly connect to multiple glomeruli, while half of projection neurons in the ventral bulb are uni-glomerular. Our results show that the “water system” remains functional despite metamorphic reconstruction. The network differences between the dorsal and ventral olfactory bulb imply a higher degree of odor integration in the dorsal main olfactory bulb. This is possibly connected with the processing of different odorants, airborne vs. waterborne.

Olfactory receptor gene evolution is unusually rapid across Tetrapoda and outpaces chemosensory phenotypic change

Chemosensation is the most ubiquitous sense in animals, enacted by the products of complex gene families that detect environmental chemical cues and larger-scale sensory structures that process these cues. While there is a general conception that olfactory receptor (OR) genes evolve rapidly, the universality of this phenomenon across vertebrates, and its magnitude, are unclear. The supposed correlation between molecular rates of chemosensory evolution and phenotypic diversity of chemosensory systems is largely untested. We combine comparative genomics and sensory morphology to test whether OR genes and olfactory phenotypic traits evolve at faster rates than other genes or traits. Using published genomes, we identified ORs in 21 tetrapods, including amphibians, reptiles, birds, and mammals and compared their rates of evolution to those of orthologous non-OR protein-coding genes. We found that, for all clades investigated, most OR genes evolve nearly an order of magnitude faster than other protein-coding genes, with many OR genes showing signatures of diversifying selection across nearly all taxa in this study. This rapid rate of evolution suggests that chemoreceptor genes are in "evolutionary overdrive," perhaps evolving in response to the ever-changing chemical space of the environment. To obtain complementary morphological data, we stained whole fixed specimens with iodine, µCT-scanned the specimens, and digitally segmented chemosensory and nonchemosensory brain regions. We then estimated phenotypic variation within traits and among tetrapods. While we found considerable variation in chemosensory structures, they were no more diverse than nonchemosensory regions. We suggest chemoreceptor genes evolve quickly in reflection of an ever-changing chemical space, whereas chemosensory phenotypes and processing regions are more conserved because they use a standardized or constrained architecture to receive and process a range of chemical cues.

A quantitative analysis of cerebellar anatomy in birds

The cerebellum is largely conserved in its circuitry, but varies greatly in size and shape across species. The extent to which differences in cerebellar morphology is driven by changes in neuron numbers, neuron sizes or both, remains largely unknown. To determine how species variation in cerebellum size and shape is reflective of neuron sizes and numbers requires the development of a suitable comparative data set and one that can effectively separate different neuronal populations. Here, we generated the largest comparative dataset to date on neuron numbers, sizes, and volumes of cortical layers and surface area of the cerebellum across 54 bird species. Across different cerebellar sizes, the cortical layers maintained relatively constant proportions to one another and variation in cerebellum size was largely due to neuron numbers rather than neuron sizes. However, the rate at which neuron numbers increased with cerebellum size varied across Purkinje cells, granule cells, and cerebellar nuclei neurons. We also examined the relationship among neuron numbers, cerebellar surface area and cerebellar folding. Our estimate of cerebellar folding, the midsagittal foliation index, was a poor predictor of surface area and number of Purkinje cells, but surface area was the best predictor of Purkinje cell numbers. Overall, this represents the first comprehensive, quantitative analysis of cerebellar anatomy in a comparative context of any vertebrate. The extent to which these relationships occur in other vertebrates requires a similar approach and would determine whether the same scaling principles apply throughout the evolution of the cerebellum.

Find the food first: An omnivorous sensory morphotype predates biomechanical specialization for plant based diets in phyllostomid bats

The role of mechanical morphologies in the exploitation of novel niche space is well characterized; however, the role of sensory structures in unlocking new niches is less clear. Here, we investigate the relationship between the evolution of sensory structures and diet during the radiation of noctilionoid bats. With a broad range of foraging ecologies and a well-supported phylogeny, noctilionoids constitute an ideal group for studying this relationship. We used diffusible iodine-based contrast enhanced computed tomography scans of 44 noctilionoid species to analyze relationships between the relative volumes of three sensory structures (olfactory bulbs, orbits, and cochleae) and diet. We found a positive relationship between frugivory and both olfactory and orbit size. However, we also found a negative relationship between nectarivory and cochlea size. Ancestral state estimates suggest that larger orbits and olfactory bulbs were present in the common ancestor of family Phyllostomidae, but not in other noctilionoid. This constellation of traits indicates a shift toward omnivory at the base of Phyllostomidae, predating their radiation into an exceptionally broad range of dietary niches. This is consistent with a scenario in which changes in sensory systems associated with foraging and feeding set the stage for subsequent morphological modification and diversification.

Endocranial Anatomy of the Giant Extinct Australian Mihirung Birds (Aves, Dromornithidae)

Dromornithids are an extinct group of large flightless birds from the Cenozoic of Australia. Their record extends from the Eocene to the late Pleistocene. Four genera and eight species are currently recognised, with diversity highest in the Miocene. Dromornithids were once considered ratites, but since the discovery of cranial elements, phylogenetic analyses have placed them near the base of the anseriforms or, most recently, resolved them as stem galliforms. In this study, we use morphometric methods to comprehensively describe dromornithid endocranial morphology for the first time, comparing Ilbandornis woodburnei and three species of Dromornis to one another and to four species of extant basal galloanseres. We reveal that major endocranial reconfiguration was associated with cranial foreshortening in a temporal series along the Dromornis lineage. Five key differences are evident between the brain morphology of Ilbandornis and Dromornis, relating to the medial wulst, the ventral eminence of the caudoventral telencephalon, and morphology of the metencephalon (cerebellum + pons). Additionally, dromornithid brains display distinctive dorsal (rostral position of the wulst), and ventral morphology (form of the maxillomandibular [V2+V3], glossopharyngeal [IX], and vagus [X] cranial nerves), supporting hypotheses that dromornithids are more closely related to basal galliforms than anseriforms. Functional interpretations suggest that dromornithids were specialised herbivores that likely possessed well-developed stereoscopic depth perception, were diurnal and targeted a soft browse trophic niche.

Ontogenetic Shifts in Brain Size and Brain Organization of the Atlantic Sharpnose Shark,

Throughout an animal’s life, species may occupy different environments and exhibit distinct life stages, known as ontogenetic shifts. The life histories of most sharks (class: Chondrichthyes) are characterized by these ontogenetic shifts, which can be defined by changes in habitat and diet as well as behavioral changes at the onset of sexual maturity. In addition, fishes experience indeterminate growth, whereby the brain and body grow throughout the organism’s life. Despite a presupposed lifelong neurogenesis in sharks, very little work has been done on ontogenetic changes in the brain, which may be informative about functional shifts in sensory and behavioral specializations. This study quantified changes in brain-body scaling and the scaling of six major brain regions (olfactory bulbs, telencephalon, diencephalon, optic tectum, cerebellum, and medulla oblongata) throughout ontogeny in the Atlantic sharpnose shark, <i>Rhizoprio­nodon terraenovae</i>. As documented in other fishes, brain size increased significantly with body mass throughout ontogeny in this species, with the steepest period of growth in early life. The telencephalon, diencephalon, optic tectum, and medulla oblongata scaled with negative allometry against the rest of the brain throughout ontogeny. However, notably, the olfactory bulbs and cerebellum scaled hyperallometrically to the rest of the brain, whereby these structures enlarged disproportionately as this species matured. Changes in the relative size of the olfactory bulbs throughout ontogeny may reflect an increased reliance on olfaction at later life history stages in <i>R. terraenovae</i>, while changes in the relative size of the cerebellum throughout ontogeny may be indicative of the ability to capture faster prey or an increase in migratory nature as this species moves to offshore habitats, associated with the onset of sexual maturity.

Visual Adaptations in Predatory and Scavenging Diurnal Raptors

Ecological diversity among diurnal birds of prey, or raptors, is highlighted regarding their sensory abilities. While raptors are believed to forage primarily using sight, the sensory demands of scavengers and predators differ, as reflected in their visual systems. Here, I have reviewed the visual specialisations of predatory and scavenging diurnal raptors, focusing on (1) the anatomy of the eye and (2) the use of vision in foraging. Predators have larger eyes than scavengers relative to their body mass, potentially highlighting the higher importance of vision in these species. Scavengers possess one centrally positioned fovea that allows for the detection of carrion at a distance. In addition to the central fovea, predators have a second, temporally positioned fovea that views the frontal visual field, possibly for prey capture. Spatial resolution does not differ between predators and scavengers. In contrast, the organisation of the visual fields reflects important divergences, with enhanced binocularity in predators opposed to an enlarged field of view in scavengers. Predators also have a larger blind spot above the head. The diversity of visual system specializations according to the foraging ecology displayed by these birds suggests a complex interplay between visual anatomy and ecology, often unrelatedly of phylogeny.

Comparative growth in the olfactory system of the developing chick with considerations for evolutionary studies

Despite the long-held assumption that olfaction plays a relatively minor role in the behavioral ecology of birds, crown-group avians exhibit marked phylogenetic variation in the size and form of the olfactory apparatus. As part of a larger effort to better understand the role of olfaction and olfactory tissues in the evolution and development of the avian skull, we present the first quantitative analysis of ontogenetic scaling between olfactory features [olfactory bulbs (OBs) and olfactory turbinates] and neighboring structures (cerebrum, total brain, respiratory turbinates) based on the model organism Gallus gallus. The OB develops under the predictions of a concerted evolutionary model with rapid early growth that is quickly overcome by the longer, sustained growth of the larger cerebrum. A similar pattern is found in the nasal cavity where the morphologically simple (non-scrolled) olfactory turbinates appear and mature early, with extended growth characterizing the larger and scrolled respiratory turbinates. Pairwise regressions largely recover allometric relationships among the examined structures, with a notable exception being the isometric trajectory of the OB and olfactory turbinate. Their parallel growth suggests a unique regulatory pathway that is likely driven by the morphogenesis of the olfactory nerve, which serves as a structural bridge between the two features. Still, isometry was not necessarily expected given that the olfactory epithelium covers more than just the turbinate. These data illuminate a number of evolutionary hypotheses that, moving forward, should inform tradeoffs and constraints between the olfactory and neighboring systems in the avian head.

Allometric Scaling Rules of the Cerebellum in Galliform Birds

Although the internal circuitry of the cerebellum is highly conserved across vertebrate species, the size and shape of the cerebellum varies considerably. Recent comparative studies have examined the allometric rules between cerebellar mass and number of neurons, but data are lacking on the numbers and sizes of Purkinje and granule cells or scaling of cerebellar foliation. Here, we investigate the allometric rules that govern variation in the volumes of the layers of the cerebellum, the numbers and sizes of Purkinje cells and granule cells and the degree of the cerebellar foliation across 7 species of galliform birds. We selected Galliformes because they vary greatly in body and brain sizes. Our results show that the molecular, granule and white matter layers all increase in volume at the same rate relative to total cerebellum volume. Both numbers and sizes of Purkinje cells increased with cerebellar volume, but numbers of Purkinje cells increased at a much faster rate than size. Granule cell numbers increased with cerebellar volume, but size did not. Sizes and numbers of Purkinje cells as well as numbers of granule cells were positively correlated with the degree of cerebellar foliation, but granule cell size decreased with higher degrees of foliation. The concerted changes among the volumes of cerebellar layers likely reflects the conserved neural circuitry of the cerebellum. Also, our data indicate that the scaling of cell sizes can vary markedly across neuronal populations, suggesting that evolutionary changes in cell sizes might be more complex than what is often assumed.

On the Selection and Analysis of Clades in Comparative Evolutionary Studies

Researchers commonly present results of comparative studies of taxonomic groups. In this review, we criticize the focus on named clades, usually, comparably ranked groups such as families or orders, for comparative evolutionary analyses and question the general practice of using clades as units of analysis. The practice of analyzing sets of named groups persists despite widespread appreciation that the groups we have chosen to name are based on subjective human concerns rather than objective properties of nature. We demonstrate an effect of clade selection on results in one study and present some potential alternatives to selecting named clades for analysis that are relatively objective in clade choice. However, we note that these alternatives are only partial solutions for clade-based studies. The practice of analyzing named clades obviously is biased and problematic, but its issues portend broader problems with the general approach of employing clades as units of analysis. Most clade-based studies do not account for the nonindependence of clades, and the biological insight gained from demonstrating some pattern among a particular arbitrary sample of groups is arguable. [Clades; comparative biology; taxonomic groups.].

Quantification of neurons in the olfactory bulb of the catsharks Scyliorhinus canicula (Linnaeus, 1758) and Galeus melastomus (Rafinesque, 1810)

In vertebrates, the olfactory bulb (OB) is the zone of the brain devoted to receiving the olfactory stimuli. The size of the OB relative to the size of the brain has been positively correlated to a good olfactory capability but, recently, this correlation was questioned after new investigation techniques were developed. Among them, the isotropic fractionator allows to estimate the number of neurons and non-neurons in a given portion of nervous tissue. To date, this technique has been applied in a number of species; in particular the OB was separately analyzed in numerous mammals and in a single crocodile species. Thus, a quantitative description of the OB's cells is available for a small portion of vertebrates. Main aim of this work was to apply isotropic fractionator to investigate the olfactory capability of elasmobranch fishes, whose traditional concept of outstanding olfaction has recently been scaled down by anatomical and physiological studies. For this purpose, the OB of two elasmobranch species, Galeus melastomus and Scyliorhinus canicula, was studied leading to the determination of the number of neurons vs non-neurons in the OB of the specimens. In addition, the obtained cell quantification was related to the olfactory epithelium surface area to obtain a new parameter that encapsulates both information on the peripheral olfactory organ and the OB. The analyzed species resulted in an overall similar quantitative organization of the peripheral olfactory system; slight differences were detected possibly reflecting different environment preference and feeding strategy. Moreover, the non-neurons/neurons ratio of these species, compared to those available in the literature, seems to place elasmobranch fishes among the vertebrate species in which olfaction plays an important role.

Maternal Investment, Ecological Lifestyle, and Brain Evolution in Sharks and Rays

Across vertebrates increased maternal investment (via increased pre- and postnatal provisioning) is associated with larger relative brain size, yet it remains unclear how brain organization is shaped by life history and ecology. Here, we tested whether maternal investment and ecological lifestyle are related to variation in brain size and organization across 100 chondrichthyans. We hypothesized that brain size and organization would vary with the level of maternal investment and habitat depth and complexity. We found that chondrichthyan brain organization varies along four main axes according to (1) absolute brain size, (2) relative diencephalon and mesencephalon size, (3) relative telencephalon and medulla size, and (4) relative cerebellum size. Increased maternal investment is associated with larger relative brain size, while ecological lifestyle is informative for variation between relative telencephalon and medulla size and relative cerebellum size after accounting for the independent effects of reproductive mode. Deepwater chondrichthyans generally provide low levels of yolk-only (lecithotrophic) maternal investment and have relatively small brains, predominantly composed of medulla (a major portion of the hindbrain), whereas matrotrophic chondrichthyans-which provide maternal provisioning beyond the initial yolk sac-found in coastal, reef, or shallow oceanic habitats have relatively large brains, predominantly composed of telencephalon (a major portion of the forebrain). We have demonstrated, for the first time, that both ecological lifestyle and maternal investment are independently associated with brain organization in a lineage with diverse life-history strategies and reproductive modes.

Anatomy of avian rictal bristles in Caprimulgiformes reveals reduced tactile function in open-habitat, partially diurnal foraging species

Avian rictal bristles are present in many species of birds, especially in nocturnal species. Rictal bristles occur along the upper beak and are morphologically similar to mammalian whiskers. Mammalian whiskers are important tactile sensors, guiding locomotion, foraging and social interactions, and have a well‐characterised anatomy. However, it is not yet known whether avian rictal bristles have a sensory function, and their morphology, anatomy and function have also not been described in many species. Our study compares bristle morphology, follicle anatomy and their association with foraging traits, across 12 Caprimulgiform species. Rictal bristle morphology and follicle anatomy were diverse across the 12 species. Nine of the 12 species had mechanoreceptors around their bristle follicles; however, there was large variation in their musculature, mechanoreceptor numbers and bristle morphology. Overall, species with short, thin, branching bristles that lacked mechanoreceptors tended to forage pre‐dusk in open habitats, whereas species with mechanoreceptors around their bristle follicle tended to forage at night and in more closed habitats. We suggest that rictal bristles are likely to be tactile in many species and may aid in navigation, foraging and collision avoidance; however, identifying rictal bristle function is challenging and demands further investigation in many species.

Oceans of stimuli: an individual-based model to assess the role of olfactory cues and local enhancement in seabirds' foraging behaviour

Oceans are extremely dynamic environments, which poses challenges for top-predators such as seabirds to find food resources. Yet, seabirds evolved sensorial abilities (olfactory senses) along with complex behaviours (social information transfer through local enhancement) to improve foraging efficiency. Using the Cory's shearwater (Calonectris borealis) as a model species, we developed an individual-based model to explore the complementary role of different searching mechanisms (olfactory foraging and local enhancement) for the optimal foraging behaviour of pelagic seabirds during 1-day foraging trips around breeding colonies. Model outputs were compared with observed patterns of Cory's shearwaters distribution during local foraging trips. Also, the foraging efficiency of virtual individuals was analysed considering hypothetical scenarios of foraging conditions and densities of foraging individuals around breeding colonies. The results support the use of a combination of searching strategies by Cory's shearwaters, which produced representative patterns of space use from tracked individuals, including spatial foraging segregation of neighbouring sub-colonies. Furthermore, while the mechanisms underpinning local enhancement played a key role in mitigating sub-optimal foraging conditions, the use of olfactory senses conferred great adaptive foraging advantages over a wide range of environmental conditions. Our results also indicate a synergistic effect between the two strategies, which suggests that a multimodal foraging strategy is useful to forage in extremely dynamic environments. The developed model provides a basis for further investigation regarding the role of foraging mechanisms in the population dynamics of colonial animals, including the adaptive foraging behaviour of marine top predators to dynamic environmental conditions.

Sensory systems in birds: What we have learned from studying sensory specialists

"Diversity" is an apt descriptor of the research career of Jack Pettigrew as it ranged from the study of trees, to clinical conditions, to sensory neuroscience. Within sensory neuroscience, he was fascinated by the evolution of sensory systems across species. Here, we review some of his work on avian sensory specialists and research that he inspired in others. We begin with an overview of the importance of the Wulst in stereopsis and the need for further study of the Wulst in relation to binocularity across avian species. Next, we summarize recent anatomical, behavioral, and physiological studies on optic flow specializations in hummingbirds. Beyond vision, we discuss the first evidence of a tactile "fovea" in birds and how this led to detailed studies of tactile specializations in waterfowl and sensorimotor systems in parrots. We then describe preliminary studies by Pettigrew of two endemic Australian species, the plains-wanderer (Pedionomus torquatus) and letter-winged kite (Elanus scriptus), that suggest the evolution of some unique auditory and visual specializations in relation to their unique behavior and ecology. Finally, we conclude by emphasizing the importance of a comparative and integrative approach to understanding avian sensory systems and provide an example of one system that has yet to be properly examined: tactile facial bristles in birds. Through reviewing this research and offering future avenues for discovery, we hope that others also embrace the comparative approach to understanding sensory system evolution in birds and other vertebrates.

Olfaction in raptors

Raptors from the orders Accipitriformes and Falconiformes have been considered to rely principally on vision. Historically, this assumption has led scientists to discount any possible sense of smell in these birds, until work on cathartid vultures indicated that these species at least rely on olfaction to find carrion. In this review I provide evidence that raptors in general have functional olfactory systems that they may use in a range of different contexts. Anatomical studies show that raptors have well-developed olfactory bulbs that are within the range of other bird species. Furthermore, all raptors studied have multiple functional olfactory genes, with, for instance, 283 olfactory genes in the Oriental honey buzzard, Pernis orientalis, of which 81.5% are functional. It has also been shown that some raptors species may functionally use olfactory cues to forage and, potentially, for communication. While further research is required, the available evidence suggests that olfaction may be a more important sensory modality in these birds than previously thought.

Comparative Brain Morphology of the Greenland and Pacific Sleeper Sharks and its Functional Implications

In cartilaginous fishes, variability in the size of the brain and its major regions is often associated with primary habitat and/or specific behavior patterns, which may allow for predictions on the relative importance of different sensory modalities. The Greenland (Somniosus microcephalus) and Pacific sleeper (S. pacificus) sharks are the only non-lamnid shark species found in the Arctic and are among the longest living vertebrates ever described. Despite a presumed visual impairment caused by the regular presence of parasitic ocular lesions, coupled with the fact that locomotory muscle power is often depressed at cold temperatures, these sharks remain capable of capturing active prey, including pinnipeds. Using magnetic resonance imaging (MRI), brain organization of S. microcephalus and S. pacificus was assessed in the context of up to 117 other cartilaginous fish species, using phylogenetic comparative techniques. Notably, the region of the brain responsible for motor control (cerebellum) is small and lacking foliation, a characteristic not yet described for any other large-bodied (>3 m) shark. Further, the development of the optic tectum is relatively reduced, while olfactory brain regions are among the largest of any shark species described to date, suggestive of an olfactory-mediated rather than a visually-mediated lifestyle.

Olfactory receptor repertoire size in dinosaurs

The olfactory bulb (OB) ratio is the size of the OB relative to the cerebral hemisphere, and is used to estimate the proportion of the forebrain devoted to smell. In birds, OB ratio correlates with the number of olfactory receptor (OR) genes and therefore has been used as a proxy for olfactory acuity. By coupling OB ratios with known OR gene repertoires in birds, we infer minimum repertoire sizes for extinct taxa, including non-avian dinosaurs, using phylogenetic modelling, ancestral state reconstruction and comparative genomics. We highlight a shift in the scaling of OB ratio to body size along the lineage leading to modern birds, demonstrating variable OR repertoires present in different dinosaur and crown-bird lineages, with varying factors potentially influencing sensory evolution in theropods. We investigate the ancestral sensory space available to extinct taxa, highlighting potential adaptations to ecological niches. Through combining morphological and genomic data, we show that, while genetic information for extinct taxa is forever lost, it is potentially feasible to investigate evolutionary trajectories in extinct genomes.

The navigational nose: a new hypothesis for the function of the human external pyramid

One of the outstanding questions in evolution is why Homo erectus became the first primate species to evolve the external pyramid, i.e. an external nose. The accepted hypothesis for this trait has been its role in respiration, to warm and humidify air as it is inspired. However, new studies testing the key assumptions of the conditioning hypothesis, such as the importance of turbulence to enhance heat and moisture exchange, have called this hypothesis into question. The human nose has two functions, however, respiration and olfaction. It is thus also possible that the external nose evolved in response to selection for olfaction. The genus Homo had many adaptations for long-distance locomotion, which allowed Homo erectus to greatly expand its species range, from Africa to Asia. Long-distance navigation in birds and other species is often accomplished by orientation to environmental odors. Such olfactory navigation, in turn, is enhanced by stereo olfaction, made possible by the separation of the olfactory sensors. By these principles, the human external nose could have evolved to separate olfactory inputs to enhance stereo olfaction. This could also explain why nose shape later became so variable: as humans became more sedentary in the Neolithic, a decreasing need for long-distance movements could have been replaced by selection for other olfactory functions, such as detecting disease, that would have been critical to survival in newly dense human settlements.

No evidence of mirror self-recognition in keas and Goffin’s cockatoos

So far only one bird species, a corvid, passed the mark test for mirror self-recognition (MSR) although the results have been questioned. We examined the capacity for MSR in another large-brained avian taxon, parrots, with keas (Nestor notabilis) and Goffin’s cockatoos (Cacatua goffini). After several weeks of mirror habituation, they were subjected to the mark test using different marks and mark placements while facing horizontal and vertical mirrors simultaneously. The keas had an additional control condition in which their reaction towards a marked or non-marked conspecific behind a transparent partition was compared to their own reflection. No evidence of MSR was found in either species. Keas responded to their reflection comparably to a conspecific behind a clear separation. Goffin’s cockatoos showed fewer social responses towards their horizontal reflection compared to their vertical reflection, suggesting that they may interpret them differently.

The relationship between social rank and spatial learning in pheasants, Phasianus colchicus: cause or consequence?

Individual differences in performances on cognitive tasks have been found to differ according to social rank across multiple species. However, it is not clear whether an individual’s cognitive performance is flexible and the result of their current social rank, modulated by social interactions (social state dependent hypothesis), or if it is determined prior to the formation of the social hierarchy and indeed influences an individual’s rank (prior attributes hypothesis). We separated these two hypotheses by measuring learning performance of male pheasants, Phasianus colchicus, on a spatial discrimination task as chicks and again as adults. We inferred adult male social rank from observing agonistic interactions while housed in captive multi-male multi-female groups. Learning performance of adult males was assayed after social rank had been standardised; by housing single males with two or four females. We predicted that if cognitive abilities determine social rank formation we would observe: consistency between chick and adult performances on the cognitive task and chick performance would predict adult social rank. We found that learning performances were consistent from chicks to adults for task accuracy, but not for speed of learning and chick learning performances were not related to adult social rank. Therefore, we could not support the prior attributes hypothesis of cognitive abilities aiding social rank formation. Instead, we found that individual differences in learning performances of adults were predicted by the number of females a male was housed with; males housed with four females had higher levels of learning performance than males housed with two females; and their most recent recording of captive social rank, even though learning performance was assayed while males were in a standardized, non-competitive environment. This does not support the hypothesis that direct social pressures are causing the inter-individual variation in learning performances that we observe. Instead, our results suggest that there may be carry-over effects of aggressive social interactions on learning performance. Consequently, whether early life spatial learning performances influence social rank is unclear but these performances are modulated by the current social environment and a male’s most recent social rank.

Sight or smell: which senses do scavenging raptors use to find food?

Raptors are usually considered to be mainly visually dependent, and the use of other sensory modalities has rarely been studied in these birds. Here, we investigated experimentally which senses (vision and/or olfaction) Turkey vultures (Cathartes aura) and Southern caracaras (Caracara plancus) use to find hidden food. First, two identical stainless-steel perforated balls, one containing a putrefied piece of meat and the other an odorless control, were presented to birds in binary choice experiments. Both species interacted more with the smelling ball than with the control, suggesting that they were attracted by the odor of the hidden meat. In a second experiment, individuals were accustomed to eat in one specifically colored ball (blue or green). In the test phase, the meat was hidden in the opposite color with respect to the one each bird had become accustomed to. Vultures still interacted more with the smelly ball disregarding the color, while caracaras interacted equally with the two balls. The prevalence of olfaction in Turkey vultures may partly explain why they are the first raptors to find carcasses in tropical forests. In contrast, caracaras forage on the ground opportunistically, a strategy where both olfaction and sight may be involved. Our experiments suggest that both species are able to use olfactory cues for foraging. However, olfaction could be the predominant sense in Turkey vultures while olfaction and sight could play an equivalent role in Southern caracaras.

Olfactory-cued navigation in shearwaters: linking movement patterns to mechanisms

After foraging in the open ocean pelagic birds can pinpoint their breeding colonies, located on remote islands in visually featureless seascapes. This remarkable ability to navigate over vast distances has been attributed to the birds being able to learn an olfactory map on the basis of wind-borne odors. Odor-cued navigation has been linked mechanistically to displacements with exponentially-truncated power-law distributions. Such distributions were previously identified in three species of Atlantic and Mediterranean shearwaters but crucially it has not been demonstrated that these distributions are wind-speed dependent, as expected if navigation was olfactory-cued. Here we show that the distributions are wind-speed dependent, in accordance with theoretical expectations. We thereby link movement patterns to underlying generative mechanisms. Our novel analysis is consistent with the results of more traditional, non-mathematical, invasive methods and thereby provides independent evidence for olfactory-cued navigation in wild birds. Our non-invasive diagnostic tool can be applied across taxa, potentially allowing for the assessment of its pervasiveness.

Anatomical evidence for scent guided foraging in the turkey vulture

The turkey vulture (Cathartes aura) is a widespread, scavenging species in the Western Hemisphere that locates carrion by smell. Scent guided foraging is associated with an expansion of the olfactory bulbs of the brain in vertebrates, but no such neuroanatomical data exists for vultures. We provide the first measurements of turkey vulture brains, including the size of their olfactory bulbs and numbers of mitral cells, which provide the primary output of the olfactory bulbs. Comparative analyses show that the turkey vulture has olfactory bulbs that are 4× larger and contain twice as many mitral cells as those of the sympatric black vulture (Coragyps atratus), despite having brains that are 20% smaller. The turkey vulture has the largest olfactory bulbs in absolute terms and adjusted for brain size among birds, but the number of mitral cells is proportional to the size of their olfactory bulbs. The combination of large olfactory bulbs, high mitral cell counts and a greatly enlarged nasal cavity likely reflects a highly sensitive olfactory system. We suggest that this sensitive sense of smell allowed the turkey vulture to colonize biomes that are suboptimal for scavenging birds and become the most widespread vulture species in the world.

Comparative morphology of snake (Squamata) endocasts: evidence of phylogenetic and ecological signals

Brain endocasts obtained from computed tomography (CT) are now widely used in the field of comparative neuroanatomy. They provide an overview of the morphology of the brain and associated tissues located in the cranial cavity. Through anatomical comparisons between species, insights on the senses, the behavior, and the lifestyle can be gained. Although there are many studies dealing with mammal and bird endocasts, those performed on the brain endocasts of squamates are comparatively rare, thus limiting our understanding of their morphological variability and interpretations. Here, we provide the first comparative study of snake brain endocasts in order to bring new information about the morphology of these structures. Additionally, we test if the snake brain endocast encompasses a phylogenetic and/or an ecological signal. For this purpose, the digital endocasts of 45 snake specimens, including a wide diversity in terms of phylogeny and ecology, were digitized using CT, and compared both qualitatively and quantitatively. Snake endocasts exhibit a great variability. The different methods performed from descriptive characters, linear measurements and the outline curves provided complementary information. All these methods have shown that the shape of the snake brain endocast contains, as in mammals and birds, a phylogenetic signal but also an ecological one. Although phylogenetically related taxa share several similarities between each other, the brain endocast morphology reflects some notable ecological trends: e.g. (i) fossorial species possess both reduced optic tectum and pituitary gland; (ii) both fossorial and marine species have cerebral hemispheres poorly developed laterally; (iii) cerebral hemispheres and optic tectum are more developed in arboreal and terrestrial species.

Quantitative comparative analysis of the nasal chemosensory organs of anurans during larval development and metamorphosis highlights the relative importance of chemosensory subsystems in the group

The anuran peripheral olfactory system is composed of a number of subsystems, represented by distinct neuroepithelia. These include the main olfactory epithelium and vomeronasal organ (found in most tetrapods) and three specialized epithelia of anurans: the buccal-exposed olfactory epithelium of larvae, and the olfactory recess and middle chamber epithelium of postmetamorphic animals. To better characterize the developmental changes in these subsystems across the life cycle, morphometric changes of the nasal chemosensory organs during larval development and metamorphosis were analyzed in three different anuran species (Rhinella arenarum, Hypsiboas pulchellus, and Xenopus laevis). We calculated the volume of the nasal chemosensory organs by measuring the neuroepithelial area from serial histological sections at four different stages. In larvae, the vomeronasal organ was relatively reduced in R. arenarum compared with the other two species; the buccal-exposed olfactory epithelium was absent in X. laevis, and best developed in H. pulchellus. In postmetamorphic animals, the olfactory epithelium (air-sensitive organ) was relatively bigger in terrestrial species (R. arenarum and H. pulchellus), whereas the vomeronasal and the middle chamber epithelia (water-sensitive organs) was best developed in X. laevis. A small olfactory recess (likely homologous with the middle chamber epithelium) was found in R. arenarum juveniles, but not in H. pulchellus. These results support the association of the vomeronasal and middle chamber epithelia with aquatic olfaction, as seen by their enhanced development in the secondarily aquatic juveniles of X. laevis. They also support a role for the larval buccal-exposed olfactory epithelium in assessment of oral contents: it was absent in X. laevis, an obligate suspension feeder, while present in the two grazing species. These initial quantitative results give, for the first time, insight into the functional importance of the peripheral olfactory subsystems across the anuran life cycle.

Mate choice for major histocompatibility complex complementarity in a strictly monogamous bird, the grey partridge (Perdix perdix)

Background

Sexual selection has been hypothesised as favouring mate choice resulting in production of viable offspring with genotypes providing high pathogen resistance. Specific pathogen recognition is mediated by genes of the major histocompatibility complex (MHC) encoding proteins fundamental for adaptive immune response in jawed vertebrates. MHC genes may also play a role in odour-based individual recognition and mate choice, aimed at avoiding inbreeding. MHC genes are known to be involved in mate choice in a number of species, with ‘good genes’ (absolute criteria) and ‘complementary genes’ (self-referential criteria) being used to explain MHC-based mating. Here, we focus on the effect of morphological traits and variation and genetic similarity between individuals in MHC class IIB (MHCIIB) exon 2 on mating in a free-living population of a monogamous bird, the grey partridge.

Results

We found no evidence for absolute mate choice criteria as regards grey partridge MHCIIB genotypes, i.e., number and occurrence of amino acid variants, though red chroma of the spot behind eyes was positively associated with male pairing success. On the other hand, mate choice at MHCIIB was based on relative criteria as females preferentially paired with more dissimilar males having a lower number of shared amino acid variants. This observation supports the ‘inbreeding avoidance’ and ‘complementary genes’ hypotheses.

Conclusions

Our study provides one of the first pieces of evidence for MHC-based mate choice for genetic complementarity in a strictly monogamous bird. The statistical approach employed can be recommended for testing mating preferences in cases where availability of potential mates (recorded with an appropriate method such as radio-tracking) shows considerable temporal variation. Additional genetic analyses using neutral markers may detect whether MHC-based mate choice for complementarity emerges as a by-product of general inbreeding avoidance in grey partridges.

Electronic supplementary material

The online version of this article (doi:10.1186/s12983-017-0194-0) contains supplementary material, which is available to authorized users.

Olfactory Assessment of Competitors to the Nest Site: An Experiment on a Passerine Species

Since most avian species have been considered anosmic or microsmatic, olfaction and associated behavioural patterns have hardly been investigated. Most importantly, empirical data on avian olfaction is not equally distributed among species. Initial investigations focused on species with relatively big olfactory bulbs because they were thought to have better olfactory capabilities. Hence, in this study we tested the ability of house sparrows (Passer domesticus) to use chemical cues as parameters to estimate nest features. House sparrows are a commonly used model species, but their olfactory capabilities have not been studied so far. We offered two different odours to males and females, namely the scent of mouse urine (Mus musculus domesticus), representing a possible competitor and a threat to eggs and hatchlings, and the odour of hay, representing a familiar and innocuous odour. The experiment was performed at the sunset to simulate a first inspection to new possible roosting or nesting sites. Interestingly, males but not females preferred to spend significantly more time in front of the hay odour, than in front of the scent of mouse urine. Our results strengthen the hypothesis that oscines can not only perceive odours but also use olfaction to assess the environment and estimate nest site quality.

Sexual selection predicts brain structure in dragon lizards

Phenotypic traits such as ornaments and armaments are generally shaped by sexual selection, which often favours larger and more elaborate males compared to females. But can sexual selection also influence the brain? Previous studies in vertebrates report contradictory results with no consistent pattern between variation in brain structure and the strength of sexual selection. We hypothesize that sexual selection will act in a consistent way on two vertebrate brain regions that directly regulate sexual behaviour: the medial preoptic nucleus (MPON) and the ventromedial hypothalamic nucleus (VMN). The MPON regulates male reproductive behaviour whereas the VMN regulates female reproductive behaviour and is also involved in male aggression. To test our hypothesis, we used high-resolution magnetic resonance imaging combined with traditional histology of brains in 14 dragon lizard species of the genus Ctenophorus that vary in the strength of precopulatory sexual selection. Males belonging to species that experience greater sexual selection had a larger MPON and a smaller VMN. Conversely, females did not show any patterns of variation in these brain regions. As the volumes of both these regions also correlated with brain volume (BV) in our models, we tested whether they show the same pattern of evolution in response to changes in BV and found that the do. Therefore, we show that the primary brain nuclei underlying reproductive behaviour in vertebrates can evolve in a mosaic fashion, differently between males and females, likely in response to sexual selection, and that these same regions are simultaneously evolving in concert in relation to overall brain size.

Immunohistochemical Localization of Somatostatin in the Brain of Chinese Alligator Alligator sinensis

In this study, the regional distribution and histological localization of somatostatin (SS) immunoreactive (IR) perikarya and fibers was investigated for the first time in the brain of adult Chinese alligator by immunohistochemical method. The results showed SS-IR perikarya and fibers were widely distributed in various parts of the brain except for olfactory bulbs. In the telencephalon, SS-IR perikarya were predominantly located in the cellular layer and deep plexiform layer of dorsomedial and medial cortex, less in the dorsal and lateral cortex, while SS-IR fibers were found in all layers of the cerebral cortex. SS-IR perikarya and fibers were also detected in the dorsal ventricular ridge, hippocampus cortex, accessory olfactory bulb nuclearus, lenticular nucleus, and caudate nucleus. In the diencephalon, SS-IR perikarya and fibers were mainly present in supraoptic nucleus, paraventricular nucleus of hypothalamus, recessus infundibular nucleus, median eminence, the pineal gland and pituitary gland, in which the IR-fibers were abundant, appearing dot-shaped and varicosity-like. In the mesencephalon, they were present in tectum cortex, ependyma of cerebral aqueduct and the periaqueductal grey matter. Additionally, they were also detected in Purkinje's cellular layer of cerebellum, in the reticularis nucleus and raphe nucleus of medulla oblongata. The distribution pattern of SS-IR perikarya and fibers in the brain of Chinese alligator is generally similar to that reported in other reptiles, but also has some specific features. The wide distribution indicated that SS might be a neurotransmitter or neuromodulator which acts on many kinds of target cells with a wide range of physiological functions. Anat Rec, 300:507-519, 2017. © 2016 Wiley Periodicals, Inc.

MOXD2, a Gene Possibly Associated with Olfaction, Is Frequently Inactivated in Birds

Vertebrate MOXD2 encodes a monooxygenase DBH-like 2 protein that could be involved in neurotransmitter metabolism, potentially during olfactory transduction. Loss of MOXD2 in apes and whales has been proposed to be associated with evolution of olfaction in these clades. We analyzed 57 bird genomes to identify MOXD2 sequences and found frequent loss of MOXD2 in 38 birds. Among the 57 birds, 19 species appeared to have an intact MOXD2 that encoded a full-length protein; 32 birds had a gene with open reading frame-disrupting point mutations and/or exon deletions; and the remaining 6 species did not show any MOXD2 sequence, suggesting a whole-gene deletion. Notably, among 10 passerine birds examined, 9 species shared a common genomic deletion that spanned several exons, implying the gene loss occurred in a common ancestor of these birds. However, 2 closely related penguin species, each of which had an inactive MOXD2, did not share any mutation, suggesting an independent loss after their divergence. Distribution of the 38 birds without an intact MOXD2 in the bird phylogenetic tree clearly indicates that MOXD2 loss is widespread and independent in bird lineages. We propose that widespread MOXD2 loss in some bird lineages may be implicated in the evolution of olfactory perception in these birds.