Diversity of vibrissal follicle anatomy in cetaceans

Most cetaceans are born with vibrissae but they can be lost or reduced in adulthood, especially in odontocetes. Despite this, some species of odontocetes have been found to have functioning vibrissal follicles (including the follicle itself and any remaining vibrissal hair shaft) that play a role in mechanoreception, proprioception and electroreception. This reveals a greater diversity of vibrissal function in odontocetes than in any other mammalian group. However, we know very little about vibrissal follicle form and function across the Cetacea. Here, we qualitatively describe the gross vibrissal follicle anatomy of fetuses of three species of cetaceans, including two odontocetes: Atlantic white-sided dolphin (Lagenorhynchus acutus), harbour porpoise (Phocoena phocoena), and one mysticete: minke whale (Balaenoptera acutorostrata), and compared our findings to previous anatomical descriptions. All three species had few, short vibrissae contained within a relatively simple, single-part follicle, lacking in muscles. However, we observed differences in vibrissal number, follicle size and shape, and innervation distribution between the species. While all three species had nerve fibers around the follicles, the vibrissal follicles of Balaenoptera acutorostrata were innervated by a deep vibrissal nerve, and the nerve fibers of the odontocetes studied were looser and more branched. For example, in Lagenorhynchus acutus, branches of nerve fibers travelled parallel to the follicle, and innervated more superficial areas, rather than just the base. Our anatomical descriptions lend support to the observation that vibrissal morphology is diverse in cetaceans, and is worth further investigation to fully explore links between form and function

Electrosensing in cetaceans: anatomy and implications

Offshore wind developments are increasing the amount of artificial electromagnetic fields (EMFs) in the ocean, and these are known to have behavioural and physiological impacts on many marine species. A previous investigation on a cetacean (Guiana dolphin, Sotalia guianensis) found that an individual was able to electrosense accredited to their vibrissal follicles. However, it is not known whether this sensory modality is present in other cetaceans, or if they are affected by artificial EMFs. Therefore, the aim of this thesis is to evaluate the potential and impact of electrosensing in cetaceans by i) identifying potential electrosensory organs, ii) identifying cetacean species that may be able to detect electric and magnetic fields from ecological characteristics and phylogeny, and iii) reviewing the data on movement and interactions of cetaceans around windfarms. The vibrissal follicles of three species of foetal cetaceans were characterised here for the first time. Vibrissal follicles in two species, the harbour porpoise (Phoconea phocoena) and minke whale (Balaenoptera acutorostrata), displayed follicles like that of mechanosensory hair follicles observed in mysticetes. In contrast, the Atlantic white-sided dolphin (Lagenorhynchus acutus) had follicles that were closer to the electrosensing Guiana and the bottlenose dolphin (Tursiops truncatus). These delphinid species had follicles that had a characteristic innervation pattern around the base and sides of the follicle. Members of the Delphinidae are therefore of great interest to further study the effects of EMFs. Around the UK, sighting data are available for several species of cetacean. However, these records do not overlap with the dates and positions of windfarm sites, and it is therefore not possible to infer the effects of EMFs on cetacean distribution and behaviour in situ. Future work would need to survey cetacean distribution and behaviour at windfarm sites over the long-term. Anatomical studies and psychophysical studies of captive animals will complement the data in this study and provide a greater understanding of electrosensory form, function and sensitivity in cetaceans. Although the ability of both magneto- and electrosensing in cetaceans is not fully understood, these sensory modalities may be crucial in relation to detecting the increasing levels of EMFs from the increasing developments of offshore windfarms. Therefore, more information is needed to characterise the possible impacts of EMFs on cetacean physiology and behaviour