Comparison of acoustic structures between heads of a narrow-ridged finless porpoise fetus and its mother

Computed tomography (CT) was used to compare the tissue structures involved in sound production and reception in a fetus and its maternal body of a female finless porpoise ( Neophocaena asiaorientalis sunameri ) found stranded at Huian, Fujian Province, China, in April 2014. Qualitative assessment of the CT images revealed the physical development of main acoustic tissues including melon, blubber, mandibular fat, muscle, and connective tissue in a 10-month old fetus. Compared to the maternal body, the cranium of the fetus was not enclosed, air sacs and nasal meatus were both absent, and the maxilla was much thinner. Furthermore, Hounsfield unit (HU) measurements from CT scanning were used to quantify the difference between the fetus and its maternal body for melon, blubber, mandibular fat, muscle, and connective tissue. Statistical analyses revealed significant differences in HU between all 5 structures melon, blubber, mandibular fat, muscle, and connective tissue ( P < 0.001) both in the fetus and maternal body. The median HU values of melon, blubber, mandibular fat, and muscle in the fetus (−61.0, −74.0, −24.0, and 25.0, respectively) were higher than those recorded in the maternal body (−85.0, −85.0, −69.0, and 12.0, respectively). However, the median HU value of connective tissue (50.0) in the fetus was lower than that recorded in the maternal body (60.0). The results show that the acoustic tissue structures were not fully developed in the fetus and depending on the actual age of the fetus the structures may not be fully formed by the time of birth. Further studies are needed to determine at what age finless porpoise calves have fully developed the tissue structures needed to produce and use ultrasound beams for echolocation

Sensory perception in cetaceans: Part I – Current knowledge about dolphin senses as a representative species

International audienceA large part of the literature on sensory perception and behavior in dolphins is devoted to its well-developed vocal and echolocation abilities. In this review, we aim to augment current knowledge by examining the literature on dolphins’ entire “Merkwelt” (which refers to everything a subject perceives, creating a crucial part of the subject’s Umwelt). We will show that despite extensive knowledge on audition, aspects such as context relatedness, the social function of vocalizations or socio-sexual recognition, remain poorly understood. Therefore, we propose areas for further lines of investigation. Recent studies have shown that the sensory world of dolphins might well be much more diverse than initially thought. Indeed, although underwater and aerial visual systems differ in dolphins, they have both been shown to be important. Much debated electro- and magnetoreception appear to be functional senses according to recent studies. Finally, another neglected area is chemoreception. We will summarize neuroanatomical and physiological data on olfaction and taste, as well as corresponding behavioral evidence. Taken together, we will identify a number of technical and conceptual reasons for why chemosensory data appear contradictory, which is much debated in the literature. In summary, this article aims to provide both an overview of the current knowledge on dolphin perception, but also offer a basis for further discussion and potential new lines of research