Population differences in the onset of cranial ossification in pumpkinseed (Lepomis gibbosus), a potential cost of rapid growth

Interspecific comparisons suggest that a trade-off exists between development and somatic growth rate. We provide evidence for a trade-off between cranial ossification and growth rate within a single species, the pumpkinseed sunfish (Lepomis gibbosus). We compare fish derived from two populations known to differ in their somatic growth rates. Fish were hatched from eggs and maintained under common conditions. Juveniles were sampled weekly through the first 8 weeks after hatching, preserved, and stained to determine the onset of ossification of superficial cranial bones. Fish from both populations showed a similar pattern of ossification in the cranial bones, but fish from the fast-growth population showed an average delay of 2 days in the onset of ossification for each bone. As a result, the fast-growth fish were both older and larger at each stage of ossification. We suggest that such a delay in ossification may have fitness effects through feeding ability, swimming ability, and (or) defense against predators.