Fused traditional and geometric morphometrics demonstrate pinniped whisker diversity.

Vibrissae (whiskers) are important components of the mammalian tactile sensory system, and primarily function as detectors of vibrotactile information from the environment. Pinnipeds possess the largest vibrissae among mammals and their vibrissal hair shafts demonstrate a diversity of shapes. The vibrissae of most phocid seals exhibit a beaded morphology with repeating sequences of crests and troughs along their length. However, there are few detailed analyses of pinniped vibrissal morphology, and these are limited to a few species. Therefore, we comparatively characterized differences in vibrissal hair shaft morphologies among phocid species with a beaded profile, phocid species with a smooth profile, and otariids with a smooth profile using traditional and geometric morphometric methods. Traditional morphometric measurements (peak-to-peak distance, crest width, trough width and total length) were collected using digital photographs. Elliptic Fourier analysis (geometric morphometrics) was used to quantify the outlines of whole vibrissae. The traditional and geometric morphometric datasets were subsequently combined by mathematically scaling each to true rank, followed by a single eigendecomposition. Quadratic discriminant function analysis demonstrated that 79.3, 97.8 and 100% of individuals could be correctly classified to their species based on vibrissal shape variables in the traditional, geometric and combined morphometric analyses, respectively. Phocids with beaded vibrissae, phocids with smooth vibrissae, and otariids each occupied distinct morphospace in the geometric morphometric and combined data analyses. Otariids split into two groups in the geometric morphometric analysis and gray seals appeared intermediate between beaded- and smooth-whiskered species in the traditional and combined analyses. Vibrissal hair shafts modulate the transduction of environmental stimuli to the mechanoreceptors in the follicle-sinus complex (F-SC), which results in vibrotactile reception, but it is currently unclear how the diversity of shapes affects environmental signal modulation.

Morphology and microanatomy of harbor porpoise (Phocoena phocoena) dorsal fin tubercles.

The unique pattern of small tubercles on the leading edge of the dorsal fins of harbor porpoises (Phocoena phocoena) has been widely noted in the literature, though their structure or function has never been conclusively identified. We examined external morphology and microanatomy of the tubercles for further understanding of the nature of the tubercles. Measurements were taken of height and peak-to-peak distance of the tubercles using scaled photographs. Mean tubercle height was standardized as a percentage of the dorsal fin height and ranged from 0.63 to 0.87%. Mean peak-to-peak distance ranged from 4.2 ± 2.0 to 5.6 ± 2.0 mm. The microstructure analysis of the dorsal fin leading edge, trailing edge and tubercles revealed an epidermal thickness of 0.7-2.7 mm with the thickest epidermis at the tubercular apex. The epidermis contained three distinct strata (=layers), including the stratum corneum, spinosum, and basale. The stratum corneum was significantly thickened in tubercles, over four times thicker than in the leading or trailing edge of the fin. The stratum spinosum, composed of lipokeratinocytes and lamellar oil bodies, was significantly thinner in the trailing edge than in the other two sites. There was no significant difference in the stratum basale among the three sites. Volume fraction of lipokeratinocytes was significantly higher at the sides of the leading edge and the apex of the tubercles, while volume fraction of lamellar oil bodies was significantly lower at the apex of the tubercles. Though the function of the tubercles is unknown, their position, hardened structure and increased epidermal stratum corneum suggest that they may have hydrodynamic importance.