Effect of Genetic Restoration on Critical and Repeat Swimming Performance in Aurora Trout

Genetic restoration has been shown to increase the genetic diversity and fitness of inbred species and populations such as the Florida panther. Aurora trout (Salvelinus fontinalis timagamiensis) is a nominal subspecies of brook trout with depauperate genetic diversity that may be experiencing inbreeding depression due to a severe historical bottleneck.  Comparative life history trials have shown that aurora trout have severely reduced fitness in comparison with normal brook trout, and show many symptoms of inbreeding depression.  Experimental breeding crosses of aurora trout with brook trout are assessing the comparative survival and fitness of pure and introgressed aurora trout to test the potential value of facilitating a genetic influx from conspecific brook trout to restore aurora trout fitness.  To test ecological performance of the different crosses, swimming performance was used as an estimate of somatic fitness to determine if increased genetic variability resulted in increased performance of introgressed versus genetically pure aurora trout.  Aurora trout, brook trout,  bidirectional F1 hybrids (50% ancestry of both aurora and brook trout) and four types of backcross categories (75% aurora trout ancestry and 25% brook trout ancestry) were tested for critical and repeat swimming performance under controlled conditions.  Single-pass (unrepeated) critical swimming performance trials showed no difference between treatment types when corrected for body condition factor (Fulton’s K).  In repeated swim trials, however, pure aurora trout had much poorer performance than all other treatment types.  Performance of F1 hybrids and all backcrosses types (75% aurora trout ancestry) were broadly similar and significantly better than that for aurora trout, although less than wild-type brook trout.  Among the different hybrid and backcross treatments, backcross aurora trout with a maternal brook trout grandfather displayed the best combination of  critical and repeat swimming performance.  These results suggest that directionality of hybrid and backcross parentage may have significant effects on the fitness of genetic rescue efforts, and that genetic rehabilitation of aurora trout by controlled, limited introgression with wild-type brook trout merits further investigation.