Deer with larger harems age faster

I don't know anyone who is happy about getting older. This is because ageing entails a deterioration of the organism which leads to decreased survival and reproductive performance. The process, however, varies between individuals, with some individuals experiencing more of the negative consequences of ageing than others. The disposable soma theory attempts to explain some of this variability by arguing that an animal that allocates more energy to reproduction early in life will have less energy to

allocate to cell and tissue repair during the same time period. In consequence, organisms that devote more energy to early life reproduction will exhibit increased senescence (loss of function due to ageing), which would translate into the deterioration of fitness-related traits later in life. Most of the studies that test the disposable soma theory have been performed in females, perhaps because of the general perception that energy investment in reproduction is higher in females than males. However, in many species, male competition for females and territories is fierce and, therefore, the disposable soma theory should also apply to these males. Red deer are one such animal; males actively compete for mates and a large amount of energy is allocated to the development of antlers. Do male deer with larger harems and bigger antlers during their youth therefore suffer the consequences later in life?

Jean-Francois Lemaître and colleagues from the Université de Lyon, France, the University of Edinburgh, UK, and the University of Cambridge, UK, analysed 40 years' worth of data from 155 male red deer. For each male, they looked at harem size and at the number of points of the deer's antlers throughout the years as indicators of energy allocation to reproduction during different life stages and, therefore, of ageing.

Although the number of points in the deer antlers did not decrease with age, harem size decreased between the ages of 10 and 16 years. Those males with larger harems during their youth also had larger harems later in life; however, the decrease in the number of females in their harem was faster than the decrease for males that had smaller harems in early life. In other words, by using harem size as an indicator of senescence, Lemaître and his team were able to show that the deer that allocated more energy to reproduction earlier in life aged faster.

This is the first study to show that a larger energetic investment in reproduction in early life stages is correlated with a more rapid deterioration of a fitness-related trait in males in a wild population. The authors suggest that a higher degree of tissue and cellular damage in these individuals due to the allocation of fewer resources to repair could lead to faster deterioration of the organism and therefore a more rapid decrease in reproductive performance. However, the faster degree of ageing in these deer might not negatively affect their overall reproductive output, because, even in later life, their harems are still larger than those of males who invest less in reproduction earlier in their lives.