torrente, a. G. | bioRxiv Science

bioRxiv2026

Food reward in Bottlenose Dolphins (Tursiops truncatus) and Belugas Whales (Delphinapterus leucas) reduces heart rate and increase heart rate variability.

1.BackgroundHeart rate (HR) and HR variability (HRV) reflect the autonomic modulation of cardiac activity and are key indicators of physiological state and stress in vertebrates. However, measuring these parameters in cetaceans has been historically challenging due to the difficulty of recording electrocardiograms (ECGs) underwater. MethodsWe developed an all-in-one ECG suction-cup to record HR during apnea, respiration and food rewards in bottlenose dolphins (Tursiops truncatus, N = 8) and belugas (Delphinapterus leucas, N = 2). Moreover, we obtain comparative measurements of ECG waveform and HR oscillation in one killer whale (Orcinus orca). ResultsSpecies-specific ECG patterns were observed, including biphasic T waves in all three species and bifid P waves unique to belugas. All three species exhibited oscillations in resting HR and pronounced bradycardia during short apnea ([~]1 min), reflecting respiratory-linked autonomic modulation. Moreover, HR oscillations persisted throughout apnea, possibly reflecting a mechanism to cyclically improve body oxygenation during diving. Short-term food deprivation had no significant effects on bottlenose dolphins and belugas HR, while subsequent feeding ad libitum reduced HR (by [~]20% in dolphins, [~]40% in belugas) and increased HRV, suggesting the activation of vagal modulation. ConclusionsThis study establishes baseline HR and HRV parameters during breathing, apnea and food reward in three cetacean species, highlighting autonomic modulation across different behaviors and conditions and validate a non-invasive tool for studying marine mammal physiology.

physiology↗

bioRxiv2025

Abnormal autonomic regulation of heart rate underlies age-related and sexdependent cardiac dysfunction in the small primate Microcebus murinus.

Ageing is a major risk factor for cardiovascular disease associated with the decline of maximal heart rate (HR) and HR variability (HRV). Such a decline could reduce cardiac adaptability to physiological needs and increase susceptibility to arrhythmias. The small primate Grey Mouse Lemur (Microcebus murinus), is a valuable model of ageing because it spontaneously develops neurodegenerative diseases. Moreover, in a lifetime it generates about three billion heartbeats as humans. Thus, it could also represent a new effective model to study cardiac ageing. We investigated cardiac responses to handling stress in young (1-5 years) and aged (6-12 years) lemurs of both sexes by using a mini-Holter for electrocardiogram (ECG) recordings. Moreover, we measured urinary catecholamine, the effect of pharmacological blockade of the autonomic modulation and cardiac contractility. Aged lemurs, particularly aged males, displayed slower HR and abnormal HRV under stress, delayed recovery of cardiac rhythm following stress and a dissociation between HR and HRV metrics. They also exhibited reduced adrenaline levels, a blunted response to pharmacological vagal blockade and diastolic dysfunction with preserved ejection fraction. These findings indicate that ageing, especially in male lemurs, impairs cardiac adaptation and recovery from stress through disrupted autonomic balance and sympathetic incompetence.

physiology↗