A HIERARCHICAL RESPONSE TO DIFFERENCES IN RATION SIZE IN THE REPRODUCTIVE-PERFORMANCE OF FEMALE 3-SPINED STICKLEBACKS

The response of female three-spined sticklebacks (Gasterosteus aculeatus) to differences in food ration during the breeding season was quantified for several variables related to reproductive performance. The measured protein and lipid contents (mg g(-1)) of eggs were unaffected by ration. Egg size increased with an increase in both ration and female size, but the proportional increase in egg size was much smaller than the proportional increase in ration. The best predictor of mean batch (clutch) fecundity and weight was female size. There was a small but significant increase in batch fecundity with ration, but the increase was not directly proportional to the increase in ration. The rate of spawning, total breeding season fecundity and total weight of eggs spawned over the breeding season were sensitive to ration with breeding season fecundity and weight increasing in direct proportion to ration. Thus, in female sticklebacks, there is a hierarchy of sensitivity to ration in the response of variables related to reproduction.