Baleens read like a whale's history book
Date:
December 8, 2021
Source:
Royal Netherlands Institute for Sea Research
Summary:
Chemically analyzing sequential samples from the baleen of dead
whales makes it possible to read not only the history of the diet,
but also the migration route of the animals. In a new study,
researchers present their results of a novel way of analyzing
nitrogen isotopes in animal tissue.
FULL STORY ==========================================================================
By chemically analyzing sequential samples from the baleen of dead
whales, it is possible to read not only the history of the diet, but
also the migration route of the animals. In the latest issue of the
journal Royal Society Open Science, NIOZ researcher Philip Riekenberg
and colleagues from Utrecht University and Wageningen Marine Research
present their results of a novel way of analyzing nitrogen isotopes in
animal tissue. "In this study, we have shown for the first time that
you can take measurements of individual amino acids across the length
of a baleen, to reconstruct in great detail the history of the animal,"
marine geochemist Marcel van der Meer of NIOZ, and one of the coordinators
of the study says.
========================================================================== Grows like a hair For his research, Riekenberg drilled powdered samples
from individual baleens from beached whales, or animals that were found
dead on the bow of a ship coming into harbor. Those baleens are plate-like structures that sit like a curtain on the upper jaw of whales from the
suborder Mysticeti or baleen whales. After taking a mouthful of seawater, baleen whales squeeze the water back out, leaving food, such as krill
behind 'in the curtains'.
Baleens are made of horn-like material and, like hair or nails, grow at a
fixed rate, in this case 10 to 16 cm per year. The further away from the whale's upper jaw, the further back in time the baleen was formed. And
because 'a whale is what it eats', Riekenberg and colleagues wanted to investigate how exactly to reconstruct information about its diet or
foraging location on Earth.
Isotopes For their study they looked at, among other things, the various isotopes of nitrogen. In addition to the most abundant 'nitrogen-14'
there is also a heavier version, 'nitrogen-15' that has an extra
neutron. When an animal digests plankton, part of the protein from the
plankton is used to create the animal's own proteins. In this process,
the concentration of the heavy nitrogen increases a little at each
step in the food chain. As a result, animals higher up the food chain
contain more and more nitrogen-15. Plankton contains less of the heavy nitrogen-15,than krill, which in turn contains less of the heavy nitrogen
than fish that eat krill, and so on.
==========================================================================
But even in different places on Earth, the concentrations of nitrogen-15
are not equal: the higher north in the Atlantic ocean you go, the heavier nitrogen becomes in the water and thus in plankton.
Individual amino acids To be able to tell the potential effects of
position in the food chain and latitude of the foraging area apart,
Riekenberg applied a new trick: he analyzed the different nitrogen forms
in individual amino acids.
Certain amino acids (the building blocks of protein) cannot be made by the body. As a result, those essential or source amino acids remain mostly
intact throughout the food chain. It does no't become progressively
heavier with each step of eating or being eaten. Other, so-called
trophic amino acids are reworked and do change in each step of the food
chain. Thus, the difference in nitrogen composition between trophic
and source amino acids is a measure of how high up the food chain it is (regardless of changing regional stable nitrogen isotope composition).
The trophic vs source amino acid difference appeared to be constant
across the baleen, meaning that these individuals ate at the same level
in the food chain the whole period their baleen was formed. Thus, the differences in nitrogen isotopes in the baleen had to be a 'geographic
effect', recording the presence of the whales in waters with different
nitrogen composition.
Analyzing the layers from the baleens, Riekenberg indeed observed annual migration patterns between the Arctic and North Atlantic oceans. The concentration of nitrogen-15 in the layers of the baleens varied from relatively high to low and back again during that period.
Proof-of-principle Van der Meer is excited about the results of
this study. "We have shown that it is possible to analyze individual
amino acids and extract very detailed information from them. In the
first instance, this was mainly a proof-of- principle. But in the
future, we may be able to find out not only what a beached whale
has eaten but also where it has been swimming in recent months,
which can help to identify migration pathways for threatened
populations. That information can even still be extracted from
whales in museum collections. This may be useful in identifying
longer term changes in diet and migrations due to human impacts." ========================================================================== Story Source: Materials provided by Royal_Netherlands_Institute_for_Sea_Research. Note: Content may be edited
for style and length.
========================================================================== Journal Reference:
1. Philip M. Riekenberg, Jaime Camalich, Elisabeth Svensson, Lonneke L.
IJsseldijk, Sophie M. J. M. Brasseur, Rob Witbaard, Mardik
F. Leopold, Elisa Bravo Rebolledo, Jack J. Middelburg,
Marcel T. J. van der Meer, Jaap S. Sinninghe Damste',
Stefan Schouten. Reconstructing the diet, trophic level and
migration pattern of mysticete whales based on baleen isotopic
composition. Royal Society Open Science, 2021; 8 (12) DOI:
10.1098/rsos.210949 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2021/12/211208123343.htm
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