Detecting heterozygosity — growth relationships: How should growth be computed?

Abstract

Individual multilocus heterozygosity (MLH) for eight polymorphic allozyme loci and weekly fresh weight (FW) over four weeks were measured in juvenile earthworrns (Eisenia fetida, n = 85) raised in a moderately stressful environment (25°C, 3 ml H₂O/g peat moss). Initial FW of earthworms was 6.6±0.4 mg. The growth curve of heterozygotes (MLH ≥ 4) diverged from that of homozygotes (MLH ≦ 3) throughout the experiment after which weight of heterozygotes and homozygotes was 106.1±6.0 and 71.1±4.6 mg, respectively. MLH-growth curves were compared for several computations of growth. MLH-FW curves were significantly positive four of the five times weight was measured. MLH-Δ FW/week curves were significantly positive in three of four weekly intervals. MLH-standardized Δ FW/week curves (i.e. adjusted for initial FW) were significantly positive in two of four weekly intervals. MLH-instantaneous growth rate curves were significantly positive in only one of four intervals because of contrasting autocorrelations between FW and MLH (+) vs. FW and instantaneous growth (-). The best computations of growth for detecting relationships with MLH in populations with divergent sizes are size adjusted for differences in age and change in size per unit time.