January 7, 2019, Max Planck Society
Little more than 50 years after
the German ornithologist Wolfgang Makatsch published his book titled No
Egg Is Like Another (Kein Ei gleicht dem anderen), new research at the Max
Planck Institute for Ornithology in collaboration with the Max Planck Institute
of Biochemistry and the University of Hohenheim reveals exactly how right he
was. The study describes for the first time the egg albumen and yolk
proteomes—that is, all measurable proteins—of a common songbird, the blue tit.
It shows that breeding females can fine tune their eggs' composition to the
needs of their young.
The quality of an egg resides in
its size and its composition. In all egg-laying species, larger eggs produce
larger, more viable and more performant offspring, while specific
egg components (such as antioxidants or antimicrobial proteins) can support
offspring growth, development or immunity. Egg quality varies broadly in wild
animals and can even vary within a clutch and induce differences among
siblings. To understand what drives this variation, researchers have turned to
a population of blue tits (Cyanistes caeruleus) breeding in southern Germany.
They measured the nutrient content of the eggs, as well as the individual
concentrations of six carotenoids (adding three new compounds to the list of
avian egg carotenoids) and almost 300 egg proteins, and explored how the
complex composition of the eggs varies in the population.
Blue tits are small, socially
monogamous songbirds that breed once per year. Females use the nutrients they
acquire from their daily food to produce one egg per day until the clutch has
seven to 15 eggs, and a total weight that often exceeds her own body mass. Such
a reproductive endeavour is difficult to sustain, and larger clutches contain
smaller eggs. Moreover, the capacity to acquire, synthesize and deposit egg
nutrients varies among females, resulting in eggs with very different
composition.
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