Energy Costs of Reproduction

Abstract

Listen

Translate article

This article provides a brief overview and a few glimpses of how various factors influence the reproductive energetics of terrestrial reptiles, birds, and mammals. The amount of energy allocated to various phases of reproduction (courtship and mating, incubation, gestation, lactation, parental care, and the pre- and postfledging or postlactational periods) is, in part, influenced by the type of reproduction (oviparity vs. vivaparity), different types of mating system (monogamy, polygyny, and polyandry), rates of posthatching and postnatal growth, competitive interactions with members of the same or different species, and extrinsic factors such as habitat quality, food availability, and climate. In general, costs of courtship and mating are higher for males that typically compete for females by developing elaborate structures or behaviors used in courtship display to show females that they are fit and by defending either mating territories or females. The energy investment that male vertebrates make in the production of gametes is relatively small compared with that made by females, and female reptiles and birds typically invest more in egg production (both size and number) than do female mammals. Apart from the production of a relatively large number of eggs, few reptiles exhibit maternal care once the young hatch. In contrast, birds and mammals often invest extensively in their young once they hatch or are born. Female birds allocate large amounts of energy to brooding and feeding their young until they have reached or exceed adult size. Some bird species invest further in their offspring by tutoring them once they have fledged. In contrast, mammals typically produce a relatively small number of eggs that are fertilized internally, the fetus develops in the uterus that is protected from environmental extremes, young are born alive, and females nurse their young with milk for variable periods of time and in many species may provide extended care to their offspring. Among males, courtship and mating are the most energetically expensive activities in reptiles, birds, and mammals. The production of nutrient- and energy-rich eggs is the most energetically expensive phase of reproduction in female reptiles. Production and incubation of eggs and feeding of nestlings comprise the most energetically expensive phase of reproduction in female birds. Lactation is the most energetically expensive period of reproduction in female mammals. In addition to the physiological costs of reproduction, we describe how some mammals may expend energy to provide behavioral forms of parental care (including paternal and alloparental care); however field data quantifying these activities are severely lacking, so their costs are rarely included in studies on reproductive energetics.