The evolution of milk secretion and its ancient origins

Jun 29th, 2015
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Lactation has an evolutionary origin and biological context within which its secretory processes and milk constituents evolved.

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animalAnimal (2012), 6:3, pp 355368 & The Animal Consortium 2011doi:10.1017/S1751731111001935The evolution of milk secretion and its ancient originsO. T. OftedalSmithsonian Environmental Research Center, Smithsonian Institution, Edgewater, MD 21037, USA(Received 8 August 2011; Accepted 8 September 2011; First published online 14 October 2011)Lactation represents an important element of the life history strategies of all mammals, whether monotreme, marsupial, oreutherian. Milk originated as a glandular skin secretion in synapsids (the lineage ancestral to mammals), perhaps as early as thePennsylvanian period, that is, approximately 310 million years ago (mya). Early synapsids laid eggs with parchment-like shellsintolerant of desiccation and apparently dependent on glandular skin secretions for moisture. Mammary glands probably evolvedfrom apocrine-like glands that combined multiple modes of secretion and developed in association with hair follicles. Comparativeanalyses of the evolutionary origin of milk constituents support a scenario in which these secretions evolved into a nutrient-richmilk long before mammals arose. A variety of antimicrobial and secretory constituents were co-opted into novel roles related tonutrition of the young. Secretory calcium-binding phosphoproteins may originally have had a role in calcium delivery to eggs;however, by evolving into large, complex casein micelles, they took on an important role in transport of amino acids, calci

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