Bottlenose dolphin calves have multi-year elevations of plasma oxytocin compared to all other age classes

Abstract

Providing for infants nutritionally via lactation is one of the hallmarks of mammalian reproduction, and infants without motivated mothers providing for them are unlikely to survive. Mothers must maintain regular contact with infants both spatially and temporally while utilising their environment to forage, avoid threats and find shelter. However, mothers can only do this and maximise their reproductive success with some degree of cooperation from infants, despite their developing physical and cognitive capabilities. The neuropeptide hormone oxytocin (OT) triggers proximity-seeking behaviour and acts in a positive feedback loop across mother-infant bonds, stimulating appropriate pro-social behaviour across the pair. However, data on infant OT levels is lacking, and it is unclear how important infants are in maintaining mother-infant associations. The bottlenose dolphin (Tursiops truncatus) is a mammalian species that is fully physically mobile at birth and has multi-year, but individually variable, lactation periods. We investigated OT concentrations in mother-infant pairs of wild individuals compared to other age and reproductive classes. An ELISA to detect OT in dolphin plasma was successfully validated with extracted plasma. We highlight a statistical method for testing for parallelism that could be applied to other ELISA validation studies. OT concentrations were consistently elevated in calves up to at least 4 years of age with lactating mothers (12.1 ±0.9 pg/ml), while all mothers (4.5 ±0.4 pg/ml) had OT concentrations comparable to non-lactating individuals (5.9 ±0.5 pg/ml). Concentrations within infants were individually variable, and may reflect the strength of the bond with their mother. The OT system likely provides a physiological mechanism for motivating infants to perform behaviours that prevent long-term separation from their mothers during this crucial time in their life history. Elevated infant OT has also been linked to energetic and developmental advantages which may lead to greater survival rates. 3 Environmental or anthropogenic disturbances to OT release can occur during bond formation or can disrupt the communication methods used to reinforce these bonds via OT elevation. Variation in OT expression in infants, and its behavioural and physiological consequences, may explain differences in reproductive success despite appropriate maternal behaviour expression.

Comparisons of Serum Progesterone and Progestagen Concentrations in Normal and Abnormal Bottlenose Dolphin (Tursiops truncatus) Pregnancies

“…Therefore, it would have been surprising for either P4 or PGs to have any correlation with these events. Because this phenomenon appears to be maternally influenced, hormones associated with maternal care, such as oxytocin, may be able to distinguish between post-natal calf survival and FTT calves (Robinson et al, 2019).…”

Joyful by nature: approaches to investigate the evolution and function of joy in non‐human animals

“…Thus, it is premature to conclude that increased OT or mesotocin is as good an indicator of positive emotion as is often purported (Rault et al ., 2017); indeed, a recent study on horses suggests that lower OT baseline levels might be associated with improved well‐being, but is not a good measure of a discrete positive emotional change like joy (Lansade et al ., 2018). Due to its role in mother–offspring relationships, it is also often permanently elevated in dependent offspring (Robinson et al ., 2020).…”

Social creatures: Model animal systems for studying the neuroendocrine mechanisms of social behaviour

“…There are currently few examples of animal species outside of classic laboratory models that have been used to investigate neuroendocrine impacts on social behaviour in natural environments. However, every year, methods of investigating species novel to the field are validated both in captivity (eg, gorillas and wolves [ Canis lupus ] ) and in the wild (eg, bottlenose dolphin Tursiops truncates ). Wildlife and domestic species can provide unique opportunities to investigate physiological drivers of social behaviour outside of laboratory environments or in completely natural systems and thus future work will broaden the range of species available for such research at the same time as providing insights into neuropeptide functionality that can be applied across more conventional study species and humans.…”