Validation of Growth Layer Group (GLG) depositional rate using daily incremental growth lines in the dentin of beluga (Delphinapterus leucas (Pallas, 1776)) teeth.

David A Waugh,Joseph D Ortiz,Robert S Suydam,J G M Thewissen,Carlos M Isales

doi:10.1371/journal.pone.0190498

David A Waugh, Joseph D Ortiz + Show 3 more

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https://doi.org/10.1371/journal.pone.0190498

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Abstract

Counts of Growth Layer Groups (GLGs) in the dentin of marine mammal teeth are widely used as indicators of age. In most marine mammals, observations document that GLGs are deposited yearly, but in beluga whales, some studies have supported the view that two GLGs are deposited each year. Our understanding of beluga life-history differs substantially depending on assumptions regarding the timing of GLG deposition; therefore, resolving this issue has important considerations for population assessments. In this study, we used incremental lines that represent daily pulses of dentin mineralization to test the hypothesis that GLGs in beluga dentin are deposited on a yearly basis. Our estimate of the number of daily growth lines within one GLG is remarkably close to 365 days within error, supporting the hypothesis that GLGs are deposited annually in beluga. We show that measurement of daily growth increments can be used to validate the time represented by GLGs in beluga. Furthermore, we believe this methodology may have broader applications to age estimation in other taxa.

Highlights

Counts of growth layers in the dentin of marine mammal teeth are widely used as indicators of age [1,2]
We report the presence of short-period incremental growth lines, which we interpret as daily in beluga dentin, and have used them to estimate the number of days represented by one Growth Layer Groups (GLGs)
Incremental growth lines in dentin have been recognized in a number of taxa [45,46,47,48,49,50,51,52,53], and it is no surprise we observe them in beluga

Summary

Introduction

Counts of growth layers in the dentin of marine mammal teeth are widely used as indicators of age [1,2]. With respect to beluga whales, the periodicity of deposition of these large-scale growth layers has remained the subject of uncertainty. We used short-period incremental lines [6] that are assumed to represent daily pulses of dentin mineralization to test the hypothesis that largescale growth layers in beluga dentin are deposited on a yearly basis. The use of dentin growth layers to assess the age of marine mammals began in the 1950s and was rapidly adopted as a valid age assessment tool in toothed-whale populations [2,7].

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