Size‐independent age effects on reproductive effort in a small, short‐lived fish

Abstract

Summary1. Age‐related changes in reproductive effort have been predicted by theoretical models and observed in a wide range of organisms. However, for indeterminate growers such as fish, an allometric relationship linking gonad weight to body size is commonly observed. There is often a positive linear relationship when these variables are log‐transformed, which by implication reduces the influence of age on reproductive effort.2. Contrasting with this usual pattern, we report a nonlinear relationship between gonad weight and fish size (after log‐transformation) in mosquitofish (Gambusia holbrooki), clearly resulting from age changes. The declining rate of increase of gonad mass as a function of body size revealed a higher reproductive effort for younger individuals relative to size.3. This size‐independent age effect on reproductive effort was predicted based on previous studies of mosquitofish and is certainly related to their particular life‐history strategy, combining an early maturation and short lifespan with the physiological costs of reproduction and over‐wintering. Our findings probably apply to other small, short‐lived species with similar life history.