The influence of body size on the diving behaviour and physiology of the bimodally respiring turtle, Elseya albagula

Abstract

In aquatic vertebrates that acquire oxygen aerially dive duration scales positively with body mass, i.e. larger animals can dive for longer periods, however in bimodally respiring animals the relationship between dive duration and body mass is unclear. In this study we investigated the relationships between body size, aquatic respiration, and dive duration in the bimodally respiring turtle, Elseya albagula. Under normoxic conditions, dive duration was found to be independent of body mass. The dive durations of smaller turtles were equivalent to that of larger individuals despite their relatively smaller oxygen stores and higher mass specific metabolic rates. Smaller turtles were able to increase their dive duration through the use of aquatic respiration. Smaller turtles had a relatively higher cloacal bursae surface area than larger turtles, which allowed them to extract a relatively larger amount of oxygen from the water. By removing the ability to respire aquatically (hypoxic conditions), the dive duration of the smaller turtles significantly decreased restoring the normal positive relationship between body size and dive duration that is seen in other air-breathing vertebrates.

Effect of water depth, velocity and temperature on the surfacing frequency of the bimodally respiring turtle Elseya albagula

“…This factor would further lower the threshold at which aquatic respiration becomes the more efficient mode for juvenile E. albagula . The results of a study by Mathie & Franklin (2006) further support the capacity for and importance of respiratory partitioning in juvenile E. albagula . Mathie and Franklin showed that in aquatic normoxia, juvenile E. albagula had a higher percent aquatic oxygen consumption than adults as a result of a larger mass‐specific cloacal bursae surface area.…”

“…This morphology resembles that of R. leukops , a species thought to demonstrate the greatest aquatic respiratory ability among aquatic chelonians (Legler & Georges 1993). Elseya albagula is believed to have a medium to high reliance on aquatic respiration, with aerobic dives of greater than 3 h recorded in the field and aquatic oxygen consumption percent in the laboratory ranging from 20–40% (adults) up to 100% (hatchlings) (Mathie & Franklin 2006; Gordos et al . 2007).…”

Contemporary genetic structure reflects historical drainage isolation in an Australian snapping turtle,Elseya albagula

“…Elseya albagula is considered a habitat specialist and co‐exists with two other locally endemic riverine specialist turtles ( Rheodytes leukops Legler & Cann, 1980, and Elusor macrurus Cann & Legler, 1994). Their requirement for well‐oxygenated, flowing waters seems closely associated with an interesting physiological adaptation allowing them to respire aquatically via highly vascularized cloacal bursae (Legler & Georges, ; Mathie & Franklin, ; Clark, Gordos & Franklin, ). Accordingly, these species are potentially highly sensitive to changes in habitat and flow regimes associated with river regulation and climate change (Thomson et al ., ; Hamann et al ., ).…”

Diving behaviour, aquatic respiration and blood respiratory properties: a comparison of hatchling and juvenile Australian turtles

“…Aquatic respiration and diving behaviour in hatchling and juvenile turtles may be influenced by species morphology, physiology and behaviour. Owing to their small size, the mass‐specific surface area of hatchling and juvenile turtles is high, allowing them to extract a relatively larger amount of oxygen from the water compared with adult turtles (Mathie & Franklin, 2006). Reliance on aquatic respiration is therefore expected to be high in hatchling and juvenile turtles and this is likely to affect dive duration.…”