EGG: motion, stability, and morphology

(Hauber Lab, Colaborator: Iva Ljubicic)

The relationship of egg form in regard to movement and spatial stability is an incredibly understudied topic, particularly considering the relevance that stability has for successful reproduction for egg-laying taxa.

 
 
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Model system: Auks

The largest body of work has been relegated to the avian family of Alcidea, specifically to the Common Murre (Uria aalge) and Thick-billed Murre (Uria lomvia) as to the adaptive value of the genera’s curiously pyriform egg . These studies attempt to demonstrate how the ‘pear’ or pyriform shape of the shell prevents clutch loss by rolling in a consistent and tight circle, reducing the distance an egg is displaced when these parents lose hold during conflict or predator avoidance. The advantage of the pear-form seems highly intuitive given these species incubate their single egg without a nest along the rock ledges of tall cliffs, which are often flat or uneven and can be as shallow as the egg is long.

Shape and Movement

The pointed end of these eggs have a highly conical quality, with a large proportion of their profile ranging from gently curved to tightly linear, which is thought to provide a stable point of contact to the resting surface. The pointed end, or ‘conical element’, is thought to determine both the angle at which the egg rests and the rolling radius, with the radial axis pointing to a theoretical center-loci of the rolling arch. Comparatively, more rounded eggs of a similar size and width to length proportion would produce a smaller resting angle, a larger radius, and, hence, displacement.

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Larger and Controlled Morphological Range

One aspect of our study is to break down the shape of the egg into different variables, and analyze what variables are responsible for what aspects of egg motion. Previous studies lacked proper quantification of geometric variables, so computer modeling and 3D printing allowed for motion studies with controlled morphometrics. Older studies failed to control for any variation in length, mass and intraspecific variation. 

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Nesting Ecology and Egg Shape

Highly conical, asymmetrical, and elongated shapes are common in rigid/semi-rigid flightless egg-producing organisms (LópezMartínez and Vicens 2012) and could be used elucidate roosting systems within those taxa. Data on non-avian theropod nesting systems, for example, is sparse at best (Zelenitsky and Therrien 2008) with the majority of species having intensely elongated and asymmetrical eggs.