The form and function of avian rictal bristles

Although mechanoreception is present throughout the animal kingdom, it is still relatively under-studied and poorly understood, especially in nocturnal birds. A particular type of facial feather, the rictal bristles, are thought to carry out a similar tactile function to mammalian whiskers, of which they superficially resemble. If they do, such a function could enhance foraging behaviour and facilitate obstacle avoidance, especially in dark, complex habitats. However, as rictal bristles are the least described of any feather, little is known about them. Therefore, this thesis characterises rictal bristle form and function by describing: i) bristle morphology and follicle anatomy, ii) the development of rictal bristles, and iii) the associated mechanosensory brain areas. It will also explore: iv) rictal bristle evolution and v) function. Results in this thesis demonstrated that rictal bristle morphology and the presence of mechanoreceptors around the follicle varied between species. Specifically, diurnal species did not have mechanoreceptors around their bristle follicles and had shorter bristles. Associated mechanosensory brain areas also varied between species, but there was no clear association between the neuroanatomy, rictal bristle morphology or foraging traits. Rictal bristles were absent in two species of altricial hatchlings, and only emerged after their eyes opened. Stimulation of the rictal region in these chicks led to behavioural feeding responses, especially coinciding with when chicks started to feed independently. Rictal bristle evolution underwent multiple events of disappearance and gain during avian evolution, and therefore, the presence and morphology of the rictal bristles also varied between orders, families and genera. Short rictal bristles with barbs at the base were likely to be present in the common ancestor of the phylogeny (108 mya). Rictal bristle presence and length were associated with nocturnality and foraging methods, and diet is also likely to be associated with rictal bristle length. Consequently, this thesis suggests that, in adult birds, rictal bristles are likely to act as facial tactile sensors in species that forage in low-light conditions in complex habitats. Rictal bristles are may, therefore, play a role in collision avoidance, foraging and eye protection. Species foraging in the daytime might have rictal bristles with a reduced tactile function. However, identifying rictal bristle function is challenging and demands further investigation. This thesis provides the first comparative description of avian rictal bristle form and function, and is an important foundation for further investigation of the sense of touch in birds

Anatomy of bristles on the nares and rictus of western barn owls (Tyto alba)

Many nocturnal avian species, such as Strigiformes, Caprimulgiformes and Apterygiformes, have sensitive vibrotactile bristles on their upper bill, especially on their rictus. The anatomy of these bristles can vary, especially in terms of sensitivity (Herbst corpuscle number), bristle length and bristle number. This variation is thought to be associated with foraging – such that diurnal, open foragers have smaller and less-sensitive bristles. Here, we describe bristle morphology and follicle anatomy in the western barn owl (Tyto alba) for the first time, using both live and roadkill wild owls. We show that T. alba have both narial and rictal bristles that are likely to be vibrotactile, since they have Herbst corpuscles around their follicles. We observed more numerous (~8) and longer bristles (~16 mm) on the nares of T. alba, than on the rictal region (~4 and ~13 mm respectively). However, the narial bristle follicles contained fewer Herbst corpuscles in their surroundings (~5) than the rictal bristles (~7); indicating that bristle length is not indicative of sensitivity. As well as bristle length and number varying between different facial regions, they also varied between individuals, although the cause of this variation remains unclear. Despite this variation, the gross anatomy of facial bristle follicles appears to be conserved between nocturnal Strigiformes, Caprimulgiformes and Apterygiformes. Understanding more about how T. alba use their bristles would, therefore, give us greater insights into the function of avian bristles in general

The evolutionary origin of avian facial bristles and the likely role of rictal bristles in feeding ecology

Facial bristles are one of the least described feather types and have not yet been systematically studied across phylogenetically diverse avian species. Consequently, little is known about their form, function and evolutionary history. Here we address this knowledge gap by characterising the evolution of facial bristles for the first time. We especially focus on rictal bristle presence and their associations with foraging behaviour, diet and habitat preferences in 1022 avian species, representing 91 families in 29 orders. Results reveal that upper rictal, lower rictal and interramal bristles were likely to be present in the most recent common ancestor of this avian phylogeny, whereas narial bristles were likely to be absent. Rictal bristle presence, length and shape varied both within and between avian orders, families and genera. Rictal bristles were gained or lost multiple times throughout evolution, which suggest that the different morphologies observed within species might not be homologous. Phylogenetic relatedness is also not likely to be the only driver of rictal bristle presence and morphology. Rictal bristle presence and length were associated with species-specific ecological traits, especially nocturnality. Our findings suggest that species foraging in low-light conditions are likely to have longer rictal bristles, and that rictal bristles are likely to have evolved in early birds

Les mots du LVMT (Laboratoire Ville Mobilité Transport)

77 pagesL’objectif de ce document est d’offrir des regards pluriels sur des termes jugés importants dans les débats actuels, sans prétention d’exhaustivité, en mettant au coeur de la démarche les diversités disciplinaire et de statut des rédacteurs (chercheurs, enseignants-chercheurs, post-doctorants, doctorants). Il s’agit de montrer que loin d’une série de définitions univoques, la recherche sur la ville est empreinte de complexité et que les regards apposés se nourrissent les uns les autres. Le laboratoire Ville, Mobilité, Transport, créé en 2003, a dès le début fait le pari de cette interdisciplinarité – non pas des disciplines qui se juxtaposent, mais qui se parlent. Sociologie, géographie, économie, ingénierie, anthropologie, sciences politiques, sciences de l’aménagement, sciences du transport trouvent ici un forum pour échanger sur des termes regroupés selon quatre grandes catégories, ayant émergé de débats collectifs ayant eu lieu entre Septembre 2015 et Juin 2016, lors de séminaires internes transversaux :•les changements récents dans les transports et la mobilité•les gares et les alentours des gares•les systèmes territoriaux•les instruments de connaissance et d’évaluation utiles pour l’action sur la ville et les transportsAu total, 23 mots, 49 entrées sont proposés par 29 auteurs, illustrant la diversité des approches des chercheurs du LVMT. Ce projet a été coordonné par Florent Le Néchet dans le cadre des séminaires internes de laboratoire de 2015 et 2016. Il n’y a ni exhaustivité des termes mobilisés, ni des regards disciplinaires portés sur chaque mot, ni même pour chaque mot une couverture exhaustive des approches possibles. Il s’agit plutôt dans notre esprit d’illustrer certains travaux de recherche menés au LVMT dans le contexte des enjeux sociétaux dans lesquels ils s’inscrivent