The social formation of fitness: Lifetime consequences of prenatal nutrition and postnatal care in a wild mammal population

Research in medicine and evolutionary biology suggests that the sequencing of parental investment has a crucial impact on offspring life history and health. Here we take advantage of the synchronous birth system of wild banded mongooses to test experimentally the lifetime consequences to offspring of receiving extra investment prenatally versus postnatally. We provided extra food to half of the breeding females in each group during pregnancy, leaving the other half as matched controls. This manipulation resulted in two categories of experimental offspring in synchronously born litters: (1) ‘prenatal boost’ offspring whose mothers had been fed during pregnancy; and (2) ‘postnatal boost’ offspring whose mothers were not fed during pregnancy but who received extra alloparental care in the postnatal period. Prenatal boost offpsring lived substantially longer as adults, but postnatal boost offspring had higher lifetime reproductive success (LRS) and higher glucocorticoid levels across the lifespan. Both types of experimental offspring had higher LRS than offspring from unmanipulated litters. We found no difference between the two experimental categories of offspring in adult weight, age at first reproduction, oxidative stress, or telomere lengths. These findings are rare experimental evidence that prenatal and postnatal investments have distinct effects in moulding individual life history and fitness in wild mammals.

Methods
Here we report a long running field experiment in a wild cooperative mammal, the banded mongoose (Mungos mungo), which we use to test the lifetime physiological and life history consequences of varying investment received by offspring in prenatal versus postnatal periods of development.

Data was collected as part of the long term field study of Banded Mongoose Research Project, at the field site in Mweya, Uganda, from wild banded mongooses in the study area that are observed in the field and regularly trapped for collection of biological samples. We followed two categories of offspring born in an experimental design where half of the pregnant mongoose females were supplementary fed during gestation. We measured offspring weight, longevity and reproductive success as well as physiological measures: oxidative stress, telomere length and fecal glucocorticoids. Data were combined to the long term data consisting of field observations, on individual life span, helping behaviour and breeding success.