Histological structure of baleen plates and its relevance to sampling for stable isotope studies

In this study, stable isotope analysis was combined with optical microscopy examination of fin whale (Balaenoptera physalus) baleen plates to understand the ontogeny of the two histological components. In both of them, the δ15N values followed a sinewave pattern along the growth axis of the baleen plate. However, the δ15N values of the cortex appeared to be advanced compared to those of the medulla. Additionally, the amplitude of the δ15N values in the oscillations was higher in the cortex than in the medulla. The histological examination revealed that these differences are caused by earlier and faster synthesis of the cortex layer compared to that of the medulla. Because the stable isotope ratios of the two layers differ, we propose that in this type of studies only the outer-most part (closest to the surface) of the cortex should be subsampled and analysed. Additionally, to include the most recently formed tissue, this subsampling should start well below the zwischensubstanz, or baleen “gum”.

Source: Mammalian Biology - October 25, 2019 Category: Biology Source Type: research