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Modelling eggshell maculation

Posted on 24. November, 2015.

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The great diversity of avian eggshell pigmentation and its possible adaptive significance has fascinated biologists for over a century. Ancestrally, avian eggshells were most likely homogenously white and immaculate although not necessarily devoid of pigment. Since then, however, they have evolved remarkable variation in both the basal ground colour and in the presence and patterns of superficial pigmentation, or maculation, which can include speckles, spots, blotches and streaks.

A number of hypotheses have been proposed to explain the functional significance of eggshell maculation. These include, but are not limited to, crypsis to avoid predation and brood parasitism, egg recognition, thermoregulation, signalling maternal health, increasing eggshell strength, and providing defence against bacterial infection.

However, despite renewed interest in the function of eggshell maculation, we still have a relatively poor understanding of the underlying causal mechanisms, even though this is crucial to understanding the evolution of maculation patterns and the factors constraining their production.

Here, the author presents a simple model of eggshell maculation, which is based on the known biology of pigment deposition, and which can produce a range of realistic maculation patterns. In particular, it provides an explanation for previous observations of maculation heterogeneity and diversity, and allows testable predictions to be made regarding maculation patterns, including a possible signalling role.

Read the full article in Avian Biology Research, Volume 8, Number 4, December 2015, pp. 237-243.

Keywords: random field, pigmentation, protoporphyrin, shell-gland membrane

Author: Thomas W. Pike
School of Life Sciences, University of Lincoln, Lincoln LN6 7DL, UK

Image: Japanese quail (Coturnix japonica) eggs showing examples of different maculation patterns, varying in spot size, distribution and ‘smoothness’.