No abstract

In mammals, olfactory cues play a major role in individual recognition and urine is one source of potentially individual‐specific olfactory cues. We studied how soon young of the extremely precocial domestic guinea‐pig (Cavia porcellus) establish specific preferences for maternal urine smell by offering 5–30‐d‐old young a simultaneous choice between a urine sample of the mother and urine from an unfamiliar unrelated lactating female. Young showed increasing preference for the smell of maternal urine from day 5 of life onwards. On day 10 of life, they discriminated between maternal urine and that of other lactating females when these were unfamiliar and related, unfamiliar and unrelated or familiar unrelated, but not when the urine of the other female came from a familiar and related lactating animal. The last result is based on fewer litters and, therefore has to be considered as preliminary. As our results are based on spontaneous preferences for just one source of olfactory cues, discrimination of live animals is likely to be even better than demonstrated here. Learning or phenotype matching of individual specific cues enable these precocial young to form a specific bond with their mother soon after birth.

Reproduction is one of the costliest processes in the life of an animal. Life history theory assumes that when resources are limiting allocation to reproduction will reduce allocation to other essential processes thereby inducing costs of reproduction. The immune system is vital for survival. If reproduction reduces investment in immune function, this could increase the risk of disease, morbidity and mortality. We here test in the guinea pig, if even under ad libitum food conditions, pregnancy and lactation reduce the activity of the adaptive and innate immune system compared to the reaction of non-reproducing animals. In response to a challenge with keyhole limpet haemocyanin the antibody-mediated adaptive immunity during (pregnancy and) lactation was reduced. Pregnant and lactating females showed higher levels of bacterial killing activity, an integrated measure of innate immunity, than non-reproducing females. However, two major effectors of the innate immunity, the natural antibody and the complement of pregnant and lactating females showed lower levels than in nonreproducing females. Pregnant and lactating females did not differ significantly in the expressed levels of innate immunity. Our results indicate that changes in the immune response during reproduction are physiological adjustments to predictable allocation problems, because they happen even under ad libitum food availability.