Lung ventilation during treadmill locomotion in a terrestrial turtle,

Terrapene carolina

Landberg, T., Mailhot, J.D., Brainerd, E.L. “Lung ventilation during treadmill locomotion in a terrestrial turtle, Terrapene carolina.” Journal of Experimental Biology. 206 (2003): 3391-3404.

Background InformationBackground Information Anatomy with regard to breathing Anatomy with regard to breathing

mechanisms mechanisms Limb girdles (pectoral and pelvic) and lungs Limb girdles (pectoral and pelvic) and lungs

both located within bony shellboth located within bony shell Rigid shell contains fixed volumeRigid shell contains fixed volume

Air in lungs displaced when axial/appendicular Air in lungs displaced when axial/appendicular elements move within the shellelements move within the shell

Retraction of pectoral/pelvic limb and girdle Retraction of pectoral/pelvic limb and girdle elements into shell drives air out of lungselements into shell drives air out of lungs

Protraction of limb elements creates subatmospheric Protraction of limb elements creates subatmospheric pressures, producing inhalationpressures, producing inhalation

Mechanical interactions between locomotion and breathing in extant Mechanical interactions between locomotion and breathing in extant tetrapods are of particular interest because lung ventilation is hypothesized tetrapods are of particular interest because lung ventilation is hypothesized to conflict with locomotion in the common ancestor of amniotesto conflict with locomotion in the common ancestor of amniotes

In primitive amniotes, locomotion and ventilation come into mechanical In primitive amniotes, locomotion and ventilation come into mechanical conflict because locomotion requires unilateral activity of axial conflict because locomotion requires unilateral activity of axial musculature while costal ventilation requires bilateral activity of those musculature while costal ventilation requires bilateral activity of those same musclessame muscles

Some vertebrates have independently evolved to cope with this constraint Some vertebrates have independently evolved to cope with this constraint by developing body postures or alternative ventilatory mechanisms that by developing body postures or alternative ventilatory mechanisms that partially decouple breathing from locomotionpartially decouple breathing from locomotion

i.e. mammals, birds, crocodiliansi.e. mammals, birds, crocodilians Lizards – gular pump to supplement lung ventilation while costal musculature Lizards – gular pump to supplement lung ventilation while costal musculature

is used for locomotionis used for locomotion Alternative breathing mechanisms such as gular pump may be employed Alternative breathing mechanisms such as gular pump may be employed

during locomotion for turtles, if limb movements interfere with their breathing; during locomotion for turtles, if limb movements interfere with their breathing; however, previous studies show that gular oscillations do not contribute to lung however, previous studies show that gular oscillations do not contribute to lung ventilation of resting turtlesventilation of resting turtles

Two main breathing mechanismsTwo main breathing mechanisms

1. Action of oblique (OA) and 1. Action of oblique (OA) and transverse abdominis (TA), transverse abdominis (TA), diaphragmaticus, and striatum diaphragmaticus, and striatum pulmonale musclespulmonale muscles

TA and OA alternate bilateral muscle TA and OA alternate bilateral muscle activity to produce exhalation-activity to produce exhalation-inhalation breathing cycles at restinhalation breathing cycles at rest

TA and OA considered primary TA and OA considered primary ventilation mechansim for turtlesventilation mechansim for turtles

present in all extant speciespresent in all extant species active consistently during lung active consistently during lung

ventilationventilation 2. Limb-pump ventilation mechanism2. Limb-pump ventilation mechanism

Limbs and girdles contribute to Limbs and girdles contribute to ventilation and redistribution of air ventilation and redistribution of air into lungsinto lungs

Muscles of pectoral/pelvic limbs and Muscles of pectoral/pelvic limbs and girdles are active during ventilation girdles are active during ventilation at rest as well as during limb at rest as well as during limb movement during locomotionmovement during locomotion

HypothesisHypothesis

If these muscles are used for both If these muscles are used for both breathing and locomotion, then breathing and locomotion, then locomotion may either interfere or locomotion may either interfere or assist breathing.assist breathing. Respiratory and locomotor Respiratory and locomotor

functions of vertebrates often functions of vertebrates often highly integratedhighly integrated

Many vertebrates couple Many vertebrates couple breathing and locomotionbreathing and locomotion

Goals of this study were to Goals of this study were to determine whether determine whether T. carolinaT. carolina breathes during locomotionbreathes during locomotion Does locomotion alter breathing Does locomotion alter breathing

performanceperformance Are ventilation and locomotion Are ventilation and locomotion

temporally coupledtemporally coupled Are airflow rates directly affected Are airflow rates directly affected

by stride cycleby stride cycle Are lung ventilation mechanisms Are lung ventilation mechanisms

the same as in resting animalsthe same as in resting animals

Information about breathing Information about breathing performance during locomotion performance during locomotion may help interpret evolution of may help interpret evolution of lung ventilation mechanisms in lung ventilation mechanisms in relation to turtle’s unique relation to turtle’s unique morphologymorphology

MethodsMethods Three individual Three individual Terrapene carolina triunguisTerrapene carolina triunguis

Controlled temperature of 30 deg C to maximize voluntary locomotionControlled temperature of 30 deg C to maximize voluntary locomotion

Constructed pneumotach masks that did not interfere with vision, hearing, or breathingConstructed pneumotach masks that did not interfere with vision, hearing, or breathing

Holes made for nares and mouthHoles made for nares and mouth Connected to a differential pressure transducerConnected to a differential pressure transducer

Ventilatory airflow recorded simulataneously with lateral view x-ray and light video imagesVentilatory airflow recorded simulataneously with lateral view x-ray and light video images

Four part experiment:Four part experiment: Acclimation to mask, treadmill chamber, and temperatureAcclimation to mask, treadmill chamber, and temperature Pre-exercisePre-exercise LocomotionLocomotion RecoveryRecovery

ResultsResults Airflow recordings show large exhalations accompany head and limb Airflow recordings show large exhalations accompany head and limb

retraction and plastral adduction; lung ventilation still occurs in fully retraction and plastral adduction; lung ventilation still occurs in fully retracted positionretracted position

Front and back halves of plastron connect to each other and the carapace by Front and back halves of plastron connect to each other and the carapace by ligamentous connective tissueligamentous connective tissue

Lungs are located in the dorsal region of the carapace with large neck retractor Lungs are located in the dorsal region of the carapace with large neck retractor muscles situated between themmuscles situated between them

high domed shape of carapace allows for large residual lung volumehigh domed shape of carapace allows for large residual lung volume

Lung ventilation occurs continuously during treadmill locomotionLung ventilation occurs continuously during treadmill locomotion

Evidence that gular pump is not employed because airflow recordings would Evidence that gular pump is not employed because airflow recordings would show small inhalations followed by little or no exhalationshow small inhalations followed by little or no exhalation

Highest breath frequency recorded during period of locomotionHighest breath frequency recorded during period of locomotion An average airflow rate was calculated for inhalations and exahalations to An average airflow rate was calculated for inhalations and exahalations to

determine whether limb movements affect airflow rates during locomotiondetermine whether limb movements affect airflow rates during locomotion Results not consistentResults not consistent Few statistically significant differences between inhalatory and exhalatory peak Few statistically significant differences between inhalatory and exhalatory peak

airflow ratesairflow rates

X-ray recordings tracked X-ray recordings tracked movement of inguinal movement of inguinal flanks during breathingflanks during breathing

Determine whether Determine whether abdominal muscles are abdominal muscles are mechanism for breathing mechanism for breathing during locomotionduring locomotion

At rest and locomotion: At rest and locomotion: exhalation accompanied by exhalation accompanied by dorsal movement of the dorsal movement of the marker; inhalation marker; inhalation accompanied by ventral accompanied by ventral movement of the markermovement of the marker

Inguinal flanks move in Inguinal flanks move in phase with ventilatory phase with ventilatory cycle and indepently cycle and indepently from stride cyclefrom stride cycle

Discussion

Green sea turtles exhibit breathing that ceases during locomotion, whereas box turtles have been found to breathe continuously Findings did not support the hypotheses

1. T. carolina does not couple breathing with locomotionMammals and birds: breathing and locomotion are coupled due to pressurization cycles of stride and breath in thoracic cavity

2. Limb movements do not contribute to lung ventilation during locomotion

Lizards: breathing performance is impeded with increasing locomotive speed because axial muscles are needed at times for breathing and locomotion simultaneously

Timing of breaths relative to stride cycleAt rest and during locomotion:

Little difference between peak inhalatory and exhalatory airflow rates

Indicates that locomotion has no mechanical effect on breathing

Breathing and stride cycle are independent of each other

Lung ventilation mechanism must be separate from locomotor system

TA and OA muscles used to breathe when at rest and most likely are the mechanism for breathing during locomotion

– No evidence for gular pump or limb mechanism– Species lacks diaphragmaticus and striatum pulmonale

muscles

Chelonia mydas vs. Terrapene carolina

Kinematics of locomotionC. mydas: front limbs retract simultaneously to push body forward, a bilateral synchronous motor pattern which is also used during limb-pump lung ventilation

May cease breathing during locomotion because pressurized lungs are used to stabilize limb movements

T. carolina: alternating gait with one diagonal pair of limbs extended while other pair is flexed

A more balanced effect on internal shell volume, in addition to abdominal muscles separate from the locomotor muscles, provides explanation for absence of effect of locomotion on ventilation

ConclusionConclusion Specialized ventilatory functions of abdominal muscles were Specialized ventilatory functions of abdominal muscles were

favored by natural selection since they permit breathing during favored by natural selection since they permit breathing during locomotionlocomotion Shell-less ancestor of turtle most likely relied on mechanism Shell-less ancestor of turtle most likely relied on mechanism

similar to that of extant lizards (axial bending during similar to that of extant lizards (axial bending during locomotion, rotation of ribs during ventilation) and would have locomotion, rotation of ribs during ventilation) and would have experienced a mechanical conflict as do lizardsexperienced a mechanical conflict as do lizards

Hypothetical ancestor gave rise to turtles as ribs abandoned Hypothetical ancestor gave rise to turtles as ribs abandoned ventilatory function and fused into the shellventilatory function and fused into the shell

Thus, extant turtles are not subject to the constraint experienced Thus, extant turtles are not subject to the constraint experienced by shell-less ancestor or extant lizards because their ribs do not by shell-less ancestor or extant lizards because their ribs do not contribute to either locomotion or ventilationcontribute to either locomotion or ventilation