Age-related reproductive effort and senescence in free-ranging moose, Alces alces

A general prediction for aging placental mammals is that they should show a decline in reproductive value, and reproductive effort is therefore predic ted to increase with age. To test this, we monitored known-age radio-collar ed females of a large ungulate, the moose (Alces alces), in a Swedish popul ation. Female moose showed senescence in reproduction (i.e., litter size) f rom about 12 yr of age. Further evidence of senescence was a decrease in pa rental care during summer (expressed as increased offspring mortality) with the mother's age. Moreover, aging females facing a declining reproductive value increased their reproductive effort by giving birth to heavier offspr ing regardless of litter size. A logistic regression model showed that olde r moose have to give birth to heavier offspring to achieve the same offspri ng summer survival as that for offspring of younger mothers. This suggests that females increase their reproductive effort (by increasing offspring ma ss) as they get older. Furthermore, the rather intense harvest in our popul ation may select for an increased reproductive effort in terms of litter si ze, which furthermore may select for an earlier onset of senescence in repr oductive characters and mortality.