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Insects have evolved very elaborate sensing systems. The airflow sensors of crickets are among the most sensitive sensors in the animal world. The sensor comprises a thin hair, which protrudes from the surface of the cuticle and sits in a specialised socket. Its elliptical base is surrounded by a flexible joint membrane to allow the hair to rotate. The polarity of the base restricts the rotation of the hair to a preferred plane of movement. The results of the morphometric analysis of the airflow sensors presented in this study show that the maximal diameter of the hair is a strong predictor for the other parameters determining the sensors geometry, such as the hair length, its socket geometry, as well as the hair's elliptical base, which is otherwise hidden within the socket and out of view unless the hair and its base are removed.

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No description available.

Barriers to interbreeding limit gene flow between sister taxa, leading to reproductive isolation and the maintenance of distinct species. These barriers come in many forms, and can act at different stages in the reproductive process. Pre-copulatory barriers may be due to individuals discriminating against heterospecifics in mate choice decisions. These decisions may be informed through a range of sensory modalities. If a female is mated and inseminated, then there may be multiple postmating-prezygotic barriers that affect the success of heterospecific sperm in attaining fertilisations. Post-zygotic barriers can be very early acting, resulting in embryonic fatality, or may be later acting, affecting the fitness of hybrid offspring. In this thesis I investigate potential reproductive barriers between the interbreeding field crickets Gryllus bimaculatus and G. campestris. I find that females of both species show only weak preference for conspecific calling song, and may even respond phonotactically to songs typical of heterospecific males. Female G. bimaculatus are repeatable in their preferences and strength of response. G. bimaculatus females presented with synthetic songs prefer those with longer inter-pulse intervals, whereas G. campestris show no discrimination between these songs. Upon meeting, G. campestris females strongly discriminate against heterospecific males, behaving aggressively towards them. This is likely driven by females responding to close range species recognition cues, including chemoreception. The species differ in their cuticular hydrocarbon profiles, and females that are no longer able to use their antennae to receive chemosensory information reduced their aggressive behaviour towards heterospecific males. G. bimaculatus females will mate with heterospecific males, though less readily than to conspecifics. When sequentially mated to both conspecific and heterospecific males, these females will preferentially take up and store sperm from the conspecific male, and sperm from conspecific males is more likely to sire offspring than would be predicted from the proportion of sperm in storage. Eggs from inter-species mating pairs are less likely to begin embryogenesis, and are more likely to suffer developmental arrest during the early stages of embryogenesis. However hybrid embryos that survive to later stages of development have hatching success similar to that of pure-bred embryos. After mating, phonotaxis of G. bimaculatus females towards male songs follows a pattern of suppression and subsequent recovery, likely triggered through detection of seminal proteins transferred in the male ejaculate, or detection of mechanical filling of the spermatheca. This pattern of suppression and recovery of phonotaxis does not differ between females mated to conspecific or heterospecific males. Females that lay few or no eggs do not experience a refractory period.

Plus de 150 espèces de grillons (Ensifères, Orthoptères) sont présentes en Nouvelle-Calédonie avec un taux d’endémisme de 90%. Cette microfaune, abondante dans les milieux forestiers et sensible aux conditions biotiques et abiotiques, peuvent être des bio-indicateurs de premier choix dans le suivi de la biodiversité. L’échantillonnage et l’enregistrement de l’activité acoustique (méta-acoustique) des communautés sous différentes conditions écologiques (invasions biologiques et dynamique forestière) est la base de ce travail de thèse.En bioacoustique : quelle est l’activité acoustique des communautés grillon en Nouvelle-Calédonie ? Cette activité varie-t-elle en fonction de la structure de la végétation (maquis, para-forestier et forêt dense) ? Finalement, est-ce que cette activité acoustique peut se décrire sous forme de « niches acoustiques », avec les paramètres du chant (temporels et spectraux), le nycthémère (l’heure de la journée) et les indices comportementaux (les postes de chants, le bruit ambiant) ?Fourmis invasives : est-ce que les fourmis envahissantes (Wasmannia auropunctata, Anoplolepis gracilipes et Pheidole megacephala) impactent les densités relatives et la diversité spécifique des populations d’Orthoptères ? Si oui, est-ce un phénomène de compétition par prédation directe (sur les œufs, juvéniles ou adultes) ou par compétition indirecte (site de chant et site de repos indisponible, accès à la reproduction réduit) ?Nous avons 3 principaux objectifs : (1) Taxonomie : accumuler des connaissances sur cette microfaune peu connue qui présente un taux d’endémisme supérieur à 90%. Créer et enrichir une collection de base et de référence sur les Orthoptères de Nouvelle-Calédonie ; (2) Ecologie fonctionnelle : déterminer l’impact des changements globaux (fourmis invasives et structure forestière) sur la dynamique et la structure des populations d’Orthoptères ; (3) Gestion du patrimoine : créer un outil de mesure non-invasif de la biodiversité des forêts néo-calédoniennes et de l’état des écosystèmes grâce à la bioacoustique de cette microfaune. / In the context of global biodiversity crisis at world scale, research of efficient environmental proxies are urgently required, especially in tropical island ecosystems, to better assess environment quality and select conservation priorities. In New Caledonia ecosystems, crickets have a dominant contribution to natural communities, according to their richness, diversity and range of colonized habitats. They are highly abundant in ecosystems and also have a high contribution to the soundscape with their ability to produce species-specific airborne signals. In this context of search of efficient environmental proxies, we measured the response of cricket communities in a ecological succession on utlramafic soils and facing the spread of 2 invasive ants (Wasmannia auropunctata and Anoplolepis gracilipes). Through both classical community census and bioacoustic approach through passive acoustic monitoring, we have been able to characterize specific cricket assemblage of species in each succession stage, with a striking sensitivity for biological invasions. Also, a global acoustic analysis of soundscape, greatly dominated by crickets, provides similar results without taxonomic or acoustic identification or knowledge. These preliminary results provide critical insights for the management of ecosystems, Our findings open up promising field of research in order to generalized innovative bio-indication concepts using cricket community in other cricket rich tropical regions