Seasonal changes in the diel surfacing behaviour of the bimodally respiring turtle Rheodytes leukops

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Abstract:

The purpose of this study was to determine whether a relationship existed between the diel surfacing trends of the bimodally respiring freshwater turtle Rheodytes leukops and daily fluctuations in specific biotic and abiotic factors. The diel surfacing behaviour of adult R. leukops was recorded over four consecutive seasons (Austral autumn 2000 – summer 2001) within Marlborough Creek, central Queensland, Australia, using pressure-sensitive time–depth recorders. Additionally, diurnal variations in water temperature and aquatic PO2 level, as well as the turtle's behavioural state (i.e., active versus resting), were monitored. In autumn and summer, surfacing frequency increased significantly during the daylight hours, with peak levels normally occurring around dawn (0500–0700) and dusk (1700–1900). However, no consistent diel surfacing trend was recorded for the turtles in winter or spring, owing to considerable variation among individual R. leukops. Diurnal surfacing trends recorded for R. leukops in autumn and summer are attributed to periods of increased activity (possibly associated with foraging) during the daylight hours and not to daily variations in water temperature or aquatic PO2 level. Turtles generally remained at a depth greater than 1 m throughout the day, where the effect of diel fluctuations in water temperature (<0.5 °C) and aquatic PO2 level (<15 mm Hg (1 mm Hg = 133.322 Pa)) was considered to be negligible.

Notre étude vise à déterminer s'il existe une relation entre les patterns journaliers de remontée en surface de la tortue d'eau douce à respiration mixte Rheodytes leukops et les fluctuations journalières de certains facteurs biotiques et abiotiques. Des chronobathymètres enregistreurs sensibles à la pression nous ont permis d'enregistrer les comportements de remontée en surface de tortues adultes au cours de quatre saisons consécutives (automne austral 2000 – été 2001) à Malborough Creek, Queensland central, Australie. Nous avons aussi suivi les variations journalières de la température et du niveau de PO2 de l'eau et noté le comportement des tortues (i.e. activité ou repos). En automne et en été, la fréquence des remontées augmente significativement durant les heures d'éclairement, avec habituellement des maximums aux environs de l'aube (0500–0700) et du crépuscule (1700–1900). En hiver et au printemps, cependant, il n'y a pas de pattern journalier uniforme de remontée en surface à cause de la variation individuelle importante des déplacements des tortues. Les patterns journaliers observés en automne et en été s'expliquent par des périodes d'activité accrue (peut-être associée à la recherche de nourriture) durant les heures d'éclairement, mais non par des variations de température ou de niveau de PO2 de l'eau au cours de la journée. Les tortues passent généralement la journée à des profondeurs supérieures à 1 m où les effets des fluctuations journalières de température (<0,5 °C) et de PO2 (<15 mm Hg (1 mm Hg = 133.322 Pa)) de l'eau semblent négligeables.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: September 1, 2003

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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