Patterns of Fitness and Fluctuating Asymmetry Across a Broad Hybrid Zone

We estimated levels of developmental instability in leaves, as indicated by fluctuating asymmetry (i.e., random deviations from perfect bilateral symmetry), across a broad hybrid zone between two taxa in the Piriqueta caroliniana complex. Previous studies have indicated that this hybrid zone was initiated in southern Florida and has expanded northward. We found that plants from the hybrid zone generally had higher levels of leaf developmental instability than plants from allopatric regions, but the increase in asymmetry was not substantial. Although it is usually assumed that developmental instability is associated with lower fitness, these Piriqueta hybrids from central Florida are similar in fitness (estimated by vegetative growth, survival, and reproduction over three growing seasons) to plants from the allopatric regions, and levels of asymmetry were not correlated with fitness for population averages or individuals. We interpret these patterns as evidence that mildly deleterious genetic incompatibilities, which contribute to developmental instability, may have been fixed in hybrid populations as a result of genetic drift