Male Lactation: Why, Why Not and Is It Care?
Opinion Male lactation: why, why not and is it care? Thomas H. Kunz1 and David J. Hosken2 1 Center for Ecology and Conservation Biology, Department of Biology, Boston University, Boston, MA 02215, USA 2 Centre for Ecology and Conservation, School of Biosciences, University of Exeter, Cornwall Campus, Tremough, Penryn TR10 9 EZ, UK Mammals are characterised by their ability to provision the impact of paternity on care has been the subject of much offspring with milk, but lactation is normally restricted debate [2,7,8], the simplest and most general models suggest to females. Why do most males not share this trait? The that Trivers was correct [7], even though other factors such morphological and physiological modifications necess- as the adult sex ratio and the intensity of sexual selection on ary for male lactation are possible and, although restric- males can also influence male care (Box 1). Additionally, tive, the ecological factors that could select for male because fertilisation in mammals is internal and requires lactation seem common enough. Until quite recently, female investment at least until parturition, males might be there was no evidence for male lactation in wild mam- able to desert before females – assuming there are benefits to mals, but it has now been reported in two species of Old doing so. Therefore, if one parent is likely to evade care, it is World fruit bats. Here we review mechanisms that can more likely to be the male [5]. cause milk production in males and also consider the Nevertheless, there are instances of male care in mam- possibility that male lactation in these bats is a unique mals, humans being a case in point, and some degree of adaptive phenomenon.
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