Abstract
The neuropeptide hormone oxytocin modulates numerous social and parental behaviours across a wide range of species, including humans. We conducted manipulation experiments on wild grey seals (Halichoerus grypus) to determine whether oxytocin increases proximity-seeking behaviour, which has previously been correlated with endogenous oxytocin concentrations in wild seal populations. Pairs of seals that had never met previously were given intravenous injections of 0.41 µg kg−1 oxytocin or saline and were observed for 1 h post-manipulation. The dose was designed to mimic endogenous oxytocin concentrations during the observation period, and is one of the lowest doses used to manipulate behaviour to date. Seals given oxytocin spent significantly more time in close proximity to each other, confirming that oxytocin causes conspecifics to seek others out and remain close to one another. Aggressive and investigative behaviours also significantly fell after oxytocin manipulations. Despite using a minimal oxytocin dose, pro-social behavioural changes unexpectedly persisted for 2 days despite rapid dose clearance from circulation post-injection. This study verifies that oxytocin promotes individuals staying together, demonstrating how the hormone can form positive feedback loops of oxytocin release following conspecific stimuli, increased motivation to remain in close proximity and additional oxytocin release from stimuli received while in close proximity.
Highlights
Behaviour is frequently perceived as the most plastic and adaptable aspect of an organism
Plausible predictor variables considered for inclusion in these models were the sex of the focal individual, the time spent in captivity in days, the type of manipulation given to individuals in a trial, the meeting the pair were given the manipulation and an interaction term between manipulation type and meeting
The oxytocin manipulation designed and used in this study confirmed that elevated oxytocin concentrations cause an increase in proximity-seeking behaviour in this species, a relationship that has been previously detected in natural contexts [13]
Summary
Behaviour is frequently perceived as the most plastic and adaptable aspect of an organism. Plausible predictor variables considered for inclusion in these models were the sex of the focal individual, the time spent in captivity in days, the type of manipulation given to individuals in a trial (oxytocin or saline), the meeting the pair were given the manipulation (initial or second) and an interaction term between manipulation type and meeting The identities of both individuals in the trials were fitted as two random effect smooths (focal and response animal) [25] to control for pseudo-replication in the dataset due to use of the same individuals in multiple trials and to control for consistent individual differences in behaviour [23,26].
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