Interactions Among Female Guppies (Poecilia reticulata) Affect Growth and Reproduction

Competition among females over resources may have consequences for their resource budgets and thereby the resource allocation between growth and reproduction. In addition, the consequences of femalefemale interactions may differ for dominant and subordinate individuals, with the dominant ones being at an advantage. In this study, we investigated the consequences of femalefemale competition in guppies by manipulating the competitive environment of females. We found that large guppy females dominated smaller females and that interactions between females likely are costly because females exposed to competition grew less. These females compensated by growing at a higher rate when no longer subjected to competition. The higher growth rate might in turn be the cause of the reduced reproductive effort in the more competitive treatments. Furthermore, interactions were more costly for females when they were in the subordinate role than in the dominant role, because the reduction in growth and reproductive effort was highest in females exposed to larger competitors. Whether there was a differential allocation of resources into growth and reproduction depending on dominance status needs further investigation. However, in general, smaller females had a higher growth rate than larger females, independent of competitive level. We also found a negative relationship between reproduction and growth in all treatments, indicating a cost of reproduction.