Empirical evidence of a trade-off between reproductive effort and expectation of future reproduction in female three-spined sticklebacks

Optimal life-history models generally predict that the reproductive effort of iteroparous organisms may increase with age, as their expectation of fut ure reproduction decreases. The population of three-spined sticklebacks (Ga sterosteus aculeatus) in the Camargue (Rhone River Delta, France) is annual , all adults dying after their first breeding season. As the three-spined s tickleback is a multiple spawner, we tested the hypothesis that reproductiv e effort ma): increase during the breeding season on field data. From 1987 to 1998, 653 female sticklebacks were collected in the field during the bre eding seasons. The body size, body weight and weights of the liver, gonads and carcass were measured for these individuals. Only gravid females with m ature eggs (176 fish) were included in the analysis. Considering the female three-spined stickleback as a capital breeder, the energetic resources ava ilable for allocation between soma and gonads were estimated by its body we ight. Somatic condition decreased during the breeding season and reproducti ve effort (gonad weight relative to body weight) increased. These patter ns did not vary significantly between years. These observed variations in rep roductive effort during the breeding season can be interpreted as empirical evidence of a trade-off between reproductive effort and expectation of fut ure reproduction.