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How smooth is a dolphin? The ridged skin of odontocetes.

ABSTRACT: Dolphin skin has long been an inspiration for research on drag reduction mechanisms due to the presence of skin ridges that could reduce fluid resistance. We gathered in vivo three-dimensional surface data on the skin from five species of odontocetes to quantitatively examine skin texture, including the presence and size of ridges. We used these data to calculate k+ values, which relate surface geometry to changes in boundary layer flow. Our results showed that while ridge size differs among species, odontocete skin was surprisingly smooth compared to the skin of other swimmers (average roughness = 5.3 µm). In addition, the presence of ridges was variable among individuals of the same species. We predict that odontocete skin ridges do not alter boundary layer flows at cruising swimming speeds. By combining k+ values and morphological data, our work provides evidence that skin ridges are unlikely to be an adaptation for drag reduction and that odontocete skin is exceptionally smooth compared to other pelagic swimmers.

SUBMITTER: Wainwright DK

PROVIDER: S-EPMC6684989 | biostudies-literature | 2019 Jul

REPOSITORIES: biostudies-literature

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How smooth is a dolphin? The ridged skin of odontocetes.

Wainwright Dylan K DK Fish Frank E FE Ingersoll Sam S Williams Terrie M TM St Leger Judy J Smits Alexander J AJ Lauder George V GV

Biology letters 20190717 7

Dolphin skin has long been an inspiration for research on drag reduction mechanisms due to the presence of skin ridges that could reduce fluid resistance. We gathered in vivo three-dimensional surface data on the skin from five species of odontocetes to quantitatively examine skin texture, including the presence and size of ridges. We used these data to calculate k<sup>+</sup> values, which relate surface geometry to changes in boundary layer flow. Our results showed that while ridge size differ ...[more]

PMID: 31311484

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Project description:BackgroundOdontocete cetaceans occupy the top position of the marine food-web and are particularly sensitive to the bioaccumulation of lipophilic contaminants. The effects of environmental pollution on these species are highly debated and various ecotoxicological studies have addressed the impact of xenobiotic compounds on marine mammals, raising conservational concerns. Despite its sensitivity, quantitative real-time PCR (qRT-PCR) has never been used to quantify gene induction caused by exposure of cetaceans to contaminants. A limitation for the application of qRT-PCR is the need for appropriate reference genes which allow the correct quantification of gene expression. A systematic evaluation of potential reference genes in cetacean skin biopsies is presented, in order to validate future qRT-PCR studies aiming at using the expression of selected genes as non-lethal biomarkers.ResultsTen commonly used housekeeping genes (HKGs) were partially sequenced in the striped dolphin (Stenella coeruleoalba) and, for each gene, PCR primer pairs were specifically designed and tested in qRT-PCR assays. The expression of these potential control genes was examined in 30 striped dolphin skin biopsy samples, obtained from specimens sampled in the north-western Mediterranean Sea. The stability of selected control genes was determined using three different specific VBA applets (geNorm, NormFinder and BestKeeper) which produce highly comparable results. Glyceraldehyde-3P-dehydrogenase (GAPDH) and tyrosine 3-monooxygenase (YWHAZ) always rank as the two most stably expressed HKGs according to the analysis with geNorm and Normfinder, and are defined as optimal control genes by BestKepeer. Ribosomal protein L4 (RPL4) and S18 (RPS18) also exhibit a remarkable stability of their expression levels. On the other hand, transferrin receptor (TFRC), phosphoglycerate kinase 1 (PGK1), hypoxanthine ribosyltransferase (HPRT1) and beta-2-microglobin (B2M) show variable expression among the studied samples and appear as less suitable reference genes for data normalization.ConclusionIn this work, we have provided essential background information for the selection of control genes in qRT-PCR studies of cetacean skin biopsies, as a molecular technique to investigate ecotoxicological hazard in marine mammals. Of 10 HKGs tested, those encoding for YWHAZ and GAPDH appear as the most reliable control genes for the normalization of qRT-PCR data in the analysis of striped dolphin skin biopsies. Potentially useful reference genes are also those encoding for ribosomal proteins L4 and S18.

Project description:Hepatic trematodiasis is a common condition in a number of free-ranging cetacean species, which occasionally result in severe hepatic and/or pancreatic lesions. However, even the basic pathological information of this disease is unknown for the majority of affected species. The current study describes and compares the histomorphology and immune reaction induced by hepatic trematodes of the family Brachycladiidae in the liver of the harbor porpoise (Phocoena phocoena, n = 8), Dall's porpoise (Phocoenoides dalli, n = 8), and Hubbs' beaked whale (Mesoplodon carlhubbsi, n = 2). Immunohistochemistry for eight antibodies (CK19, CD3, Foxp3, CD20, Iba1, CD68, CD163, and CD204) was conducted to analyze the pathology of these parasitic infections. In all three odontocete species, the changes observed in the trematode-affected biliary epithelium were comparable with marked hyperplasia and goblet cell metaplasia, as well as lymphoplasmacytic and eosinophilic inflammation. Additionally, regions of the Glisson's sheath were diffusely and severely fibrotic in all examined species, regardless of the physical presence of trematodes. Differences among the three species included the presence of characteristic lymphoid follicles formed in the fibrotic bile duct walls of only the two porpoise species. In the Hubbs' beaked whale, the degree of lymphoplasmacytic cholangitis was more severe, and ductular reaction was generally more prominent. In terms of the overall macrophage population among the three species, CD163- and CD204-positive cells (M2 macrophages) outnumbered Iba1- and CD68-positive cells (M1 macrophages), indicating a chronic infection stage in all analyzed individuals. Species-specific differences among the infiltrating macrophages included numbers of CD68-positive cells being significantly more abundant in the harbor porpoises, whereas CD163-positive cells were significantly more numerous in the Dall's porpoises. The numbers of CD204-positive macrophages were higher in the Hubbs' beaked whales compared to those in the porpoises. Trematode species of the harbor and Dall's porpoises were Campula oblonga, while they were Oschmarinella macrorchis in the Hubbs' beaked whales. This study concludes that interspecies differences in the tissue reactions to hepatic trematode infections are present among odontocete species and that the immune reaction varies depending on the species. This information aids in furthering our understanding of the pathogenesis of hepatic trematodiasis in cetaceans.

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How smooth is a dolphin? The ridged skin of odontocetes.

Publications

How smooth is a dolphin? The ridged skin of odontocetes.

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