Empirical and Theoretical Constraints on the Evolution of Lactation

Abstract

For 829 mammalian species, data on age at weaning or age at first solid food were analyzed with respect to body mass, phylogeny, habitat, diet, length of gestation, basal metabolism, and neonatal development. The primary influence on lactation length is female mass, but phylogenetic constraints are important. Thus, lactation can be characterized as short (earless seals and baleen whales), long (marsupials, bats, and primates), or average (remaining eutherians). Among average mammals, lagomorphs have short lactations.Lactation may have different functions, evolutionary constraints, and physiological control depending on whether young first eat solid food near weaning or well before it. First solid food eaten near weaning occurs in polytocous species with altricial young; in this case, lactation has a clear energetic role. In contrast, first solid food well before weaning is common for mammals with single, precocial offspring. For these species, the energetic and nutritional constraints on lactation may be less important than the benefits of maintaining contact between mother and young, such as reduced juvenile mortality and increased opportunities for learning social or foraging patterns. Thus, the age at first solid food relative to the age at weaning may indicate the function of lactation within the reproductive biology of a given mammal.Delayed development and implantation alter the timing of energetic investment during gestation, so too, the age at first solid food may alter or reflect the rate of energetic investment during lactation. Thus, the age at first solid food relative to the age at weaning may indicate the function of lactation within the reproductive biology of a given mammal. Testing these hypotheses will require data from diverse species on the nutritional and energetic value of milk before and after first solid food as well as on the mechanics and consequences of nursing or suckling during the course of lactation. (Key words: evolution of lactation, allometry, reproductive effort, parental investment)Abbreviation key: BMR = basal metabolic rate.

Evolution of mammals: lactation helps mothers to cope with unreliable food supplies

“…Of course the trade-off we explore here is unlikely to be solely responsible for the evident variation in the form and function of lactation across mammalian taxa. Once parental feeding from maternal reserves evolved in the mammalian lineage it is likely that other functional opportunities were created leading to the evolution of a wide range of mammalian traits and strategies (Pond 1977(Pond , 1998Hayssen et al 1985;Blackburn et al 1989;Hayssen 1993). For example, the nutritional quality of milk encourages very rapid postnatal growth, allowing the production of relatively small neonates and early maturation.…”

“…Moreover, the adoption of lactation as a mode of feeding young is thought to be related directly to the evolution of many other mammalian traits (Pond 1977(Pond , 1998Hayssen et al 1985;Blackburn et al 1989;Hayssen 1993). However, since Darwin, the evolution of lactation has troubled evolutionary biologists.…”

“…However, since Darwin, the evolution of lactation has troubled evolutionary biologists. It is a 'complex adaptation' with highly integrated components, including the morphological, physiological and behavioural aspects of milk production, ingestion and digestion (Blackburn et al 1989;Hayssen 1993). Indeed, early critics of Darwin's thesis targeted lactation as a problem for gradualist explanations (Mivart 1871), and the incipient stages in the evolution of milk production remain particularly difficult to explain (Blackburn et al 1989).…”

Nutritional sub-fertility in the dairy cow: towards improved reproductive management through a better biological understanding

“…In this case, the trade-off is between two aspects of reproduction: investment in the viability of the current calf and investment in future offspring ( Figure 1). Although lactation is a key adaptation in mammals (Pond, 1977;Blackburn, 1993;Hayssen, 1993), milk becomes the central aspect of the parent-offspring conflict (Trivers, 1974). The calf gains most by stimulating prolonged milk production and the cow gains most by minimising milk production once the calf has attained an adequate level of viability.…”

Understanding mammary activity in red-rumped agouti and implications for management and conservation of this Neotropical game species

“…Mean (± SE) birth weight (g) of all young, male young and female young in agoutis with different parturition numbers. as well as in marsupials (5-12 nipples) (Hayssen, 1993;Senger, 2013). …”