SWORDTAIL MATE CHOICE AND REPRODUCTIVE ALLOCATION: EFFECTS OF MALE CONDITION

Abstract

We investigated the mechanisms behind reproductive allocation in sheepshead swordtail fish (Xiphophorus birchmanni). Classic life history theory predicts a trade-off between offspring size and number such that females with more offspring make smaller eggs and females with fewer eggs allocate more resources per egg. However, female swordtails with larger broods have been shown to designate more yolk per egg than those with fewer offspring. One explanation for this pattern is that females allocate differentially depending on the quality of their mate. We manipulated male diet to determine if females had a mate preference based on male chronic condition. Afterward, we dissected the females and measured their allocation using egg size and egg number. We found that females allocated more to fecundity when mated with males that were chronically underfed. This effect was strongest in females mated with low-food males that were exposed to high-food males. These results are unexpected and motivate future research on the relationship between mate quality and allocation to offspring size and number.