DEVELOPMENTAL INSTABILITY ANALYSIS OF BKD-INFECTED SPRING CHINOOK SALMON, ONCORHYNCHUS-TSHAWYTSCHA, PRIOR TO SEAWATER EXPOSURE

Stress in organisms results in energy dissipation, making developmenta l pathways less stable. Effects of chronic stress, manifested as small random departures from phenotypic symmetry, reflect developmental ins tability, are considered to be epigenetic and an effect produced by co mpromised fitness. instability is detectable and effectively interpret ed among sites or populations if samples are collected randomly, the s tressor is present throughout character development, characters are id entified accurately and excessive mortality does not erase the existen ce of developmental instability. Bacterial kidney disease (BKD) is a c hronic systemic disease in salmonids that, after vertical transmission from parent to egg, persists and spreads throughout ontogeny, potenti ally affecting developmental processes. Because levels of progeny infe ction reflect parental infection levels, groups of offspring from pare nts with high and low levels of BKD infection can be compared to asses s the effects of disease-mediated developmental stress. Analyses of fl uctuating asymmetry in five bilateral characters were inconclusive, bu t significant reductions in the proportion of unusable scales, in the number of circulus errors, and in the directional asymmetry of branchi ostegal rays were observed in fish from the high-BKD group. This group also contained individuals of significantly larger size. These result s are opposite to those expected from traditional developmental instab ility theory in suggesting that surviving high-BKD fish have greater d evelopmental stability. This reversal appears to be produced by select ive mortality having a greater effect than sublethal stress in alterin g developmental instability patterns. These results are discussed with respect to size selectivity, heterosis and the assumptions supporting developmental instability as a tool for detecting chronic sublethal s tress.