During the first postpartum month two dolphin mothers surfaced with both eyes open on average in 93 and 98% of the time while in their calves both eyes were open in 90 and 60% of the cases. Calves surfaced to breathe more often than their mothers between the postpartum age of 2 and 8 weeks. Dolphin mothers and their calves exhibited a complete disappearance of rest at the surface for a minimum of 2 months postpartum, swimming in echelon formation on average in 97–100% of the observation time. The behavior of three dolphin mother–calf pairs was monitored from birth to 13 months postpartum. The aim of this study was to examine the postpartum sleep behavior of bottlenose dolphin calves and their mothers. Aspects such as sentinel functions and breathing are likely to be proximate evolutionary phenomenon of this form of sleep.Īdult dolphins are capable of sleeping with one eye open and exhibiting slow wave activity in the electroencephalogram (EEG) of one hemisphere at a time. Lastly, the possible selection pressures leading to this form of sleep are examined, leading us to the suggestion that the selection pressure necessitating the evolution of cetacean sleep was most likely the need to offset heat loss to the water from birth and throughout life. Three suggested functions of USWS (facilitation of movement, more efficient sensory processing and control of breathing) are discussed. We then compare the anatomy of the mammalian somnogenic system with what is known in cetaceans, highlighting areas where additional knowledge is needed to understand cetacean sleep. We find that for cetaceans sleep is characterized by USWS, a negligible amount or complete absence of rapid eye movement (REM) sleep, and a varying degree of movement during sleep associated with body size, and an asymmetrical eye state. We trace the discovery of this phenotypically unusual form of mammalian sleep and highlight specific aspects that are different from sleep in terrestrial mammals. Our knowledge of the form of lateralized sleep behavior, known as unihemispheric slow wave sleep (USWS), seen in all members of the order Cetacea examined to date, is described. The results from the current study provide novel insight into the cerebral asymmetry in a species previously ignored within the literature, thus improving our understanding on the extent of laterality in cetaceans and on the evolutionary history of hemispheric laterality for vertebrates in general. No significant differences were reported for flipper use either during the interaction with conspecifics or with objects. Porpoises swam preferentially with their right pectoral fin upward and their left pectoral fin downward with a clockwise swimming direction and also displayed a consistent bias for a counterclockwise barrel-roll direction. Analyses of 360 observations recorded over two months revealed that, at group level, porpoises showed laterality in swimming behaviors. Using event sampling methods, several behaviors such as flipper-body touching, object touching, barrel-rolls, side swimming, and swimming direction were recorded from six captive porpoises (three males and three females). While many studies have been conducted on laterality among several cetacean species, no studies investigating the Yangtze finless porpoise have been conducted. The Yangtze finless porpoise ( Neophocaena asiaeorientalis asiaeorientalis) is a critically endangered species with less than 1000 individuals expected to be left in the wild. Future research into the natural history of vision loss could help elucidate the function of vision and inspire innovations in how to address vision loss in humans. We applied phylogenetic comparative methods to a mammalian tree to explore the evolution of visual acuity using ancestral state estimations. We explore the ancestral emergence of vision in vertebrates, and the loss of vision in blind species with reference to an evolution-based classification scheme. To unravel the similarities between blind individuals and blind species, we review concepts of "blindness" and its behavioral correlates across a range of species. Models that incorporate evolutionary history, natural variation in visual ability, and experimental manipulations can help disentangle visual ability at a superficial level from behaviors linked to vision but not solely reliant upon it, and could assist the translation of ophthalmological research in animal models to human treatments. Research on the origin of vision and vision loss in naturally “blind” animal species can reveal the tasks that vision fulfills and the brain's role in visual experience.
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