Male reproductive traits of full-sibs of different age classes in three-spined sticklebacks (Gasterosteus aculeatus).

The process of ageing is associated with negative effects of mutations acting late in life, which range from those affecting cells to those affecting the whole organism. In many animal taxa, the deterioration of the phenotype with age also affects traits such as males' primary and secondary sexual characteristics. In three-spined sticklebacks (Gasterosteus aculeatus), males usually reproduce at one or two years of age.