INBREEDING DEPRESSION AND VARIANCE STRUCTURES FOR HEIGHT AND ADAPTATION IN SELF- AND OUTCROSS THUJA PLICATA FAMILIES IN VARYING ENVIRONMENTS

摘要

Field trials of self- and outcross families from 24 parent trees of western redcedar, a species that has a high rate of natural self-pollination, were established on three sites: a low-elevation nursery site, Cowichan Lake Research Station (CLRS), atclose spacing (24 parents); a fertile low-elevation site, Jordan River Low (JRL), (16 parents); and a nearby high elevation site, Jordan River High (JRH), (12 parents). Heights and survival were recorded to age 9 except at CLRS (to age 7 only) Growth wasfastest at JRL (mean year-9 height 4.6 m) followed by CLRS (2.1 m at age 7), and slowest at JRH (1.2 m at age 9), Mortality remained very low (<3 %) throughout. Inbreeding depression (ID) was almost nil for seed production and growth in the nursery, however it became appreciable with time at both ,JRL and CLRS, reaching about 10 % at mean height ca 25 m, but with little subsequent increase. ID at JRH, however, was very slight (<3 %) Genetic correlations for seed-parent performance between mating typeswere generally high (r_g>0.7, and not declining with time), indicating that self-family performance predicts parental breeding values well, but there was some statistically significant seed-parent X mating-type interactions reflecting r_g<1. There was evidence of appreciable genetic variation in height for recurrent selection with individual narrow-sense heritabilities of ca 0,3 and additive genetic coefficients of variation of over 10%. In general, the results fit the expectation that an inbreeding species will have little if any genetic load resulting from strongly deleterious recessive genes affecting viability and general fitness, but significant genetic load of mildly suboptimal effects and not necessarily strongly recessive The implications are discussed in relation to the putative Quaternary history of the species and the likely evolutionary stability of mating systems.