INBREEDING DEPRESSION IN 4 POPULATIONS OF COLLINSIA-HETEROPHYLLA NUTT(SCROPHULARIACEAE)

The effects of one and two generations of inbreeding were studied in p lants from four natural populations of the annual plant, Collinsia het erophylla, using inbred and outcrossed plants generated by hand pollin ations to create expected inbreeding coefficients ranging from 0-0.75. The selfing rates of the populations were estimated using allozyme ma rkers to range from 0.37-0.69. Inbreeding depression was mild, ranging from 5-40%, but significant effects were detected for characters meas ured at all stages of the life cycle. Fitness components declined sign ificantly with the inbreeding coefficient, and regression of fitness c haracters on inbreeding coefficients gave no evidence of any strongly synergistic effects attributable to the different genetic factors that contribute to decline in fitness under inbreeding. The magnitude of i nbreeding depression did not clearly decrease with the populations' le vels of inbreeding. This is not surprising because the selfing rates a re similar enough that it is unlikely that the populations have been c haracterized for long periods of time by these different inbreeding le vels.