The effects of age and environment on the expression of inbreeding depression in Eucalyptus globulus

Abstract

Inbreeding adversely affects fitness traits in many plant and animal species, and the magnitude, stability and genetic basis of inbreeding depression (ID) will have short-and longterm evolutionary consequences. The effects of four degrees of inbreeding (selfing, f ¼ 50%; full-and half-sib matings, f ¼ 25 and 12.5%; and unrelated outcrosses, f ¼ 0%) on survival and growth of an island population of Eucalyptus globulus were studied at two sites for over 14 years. For selfs, ID in survival increased over time, reaching a maximum of 49% by age 14 years. However, their inbreeding depression for stem diameter remained relatively stable with age, and ranged from 28 to 36% across years and sites. ID for survival was markedly greater on the more productive site, possibly due to greater and earlier onset of inter-tree competition, but was similar on both sites for the diameter of survivors. The deleterious trait response to increasing inbreeding coefficients was linear for survival and diameter. Nonsignificant quadratic effects suggested that epistasis did not contribute considerably to the observed ID at the population level. Among-and within-family coefficients of variation for diameter increased with inbreeding degree, and the variance among the outcrossed families was significant only on the more productive site. The performance of self-families for diameter was highly stable between sites. This suggests that, for species with mixed mating systems, environmentally stable inbreeding effects in open-pollinated progenies may tend to mask the additive genotype-by-environment interaction for fitness traits and the adaptive response to the environment.

The genome of Eucalyptus grandis

“…Eucalypts are preferentially outcrossing with late-acting post-zygotic selfincompatibility resulting in outcrossing rates that can exceed 90% 1 , high levels of nucleotide variation 23,24 and accumulation of genetic load and expression of inbreeding depression 4 . A microsatellite survey of BRASUZ1 and its inbred siblings indicated putative hotspots of genetic load (Supplementary Information section 4).…”

Clonality, interspecific hybridisation and inbreeding in a rare mallee eucalypt, Eucalyptus absita (Myrtaceae), and implications for conservation

“…E. aggregata, Field et al 2008). Inbreeding in the form of self-fertilisation (selfing) or mating between close relatives (biparental inbreeding), is known to result in inbreeding depression in eucalypts, impairing fitness and compromising genetic quality of seed collections, as it can result in both short-and long-term detriments to growth and survival (Eldridge and Griffin 1983;Potts and Wiltshire 1997;Costa e Silva et al 2011). However, despite a high potential for inbreeding in small and rare populations, outcrossing rates are generally high in eucalypt seed cohorts (Byrne 2008) due to efficient postzygotic selection mechanisms against inbreeding within the seed capsule (James and Kennington 1993), resulting in seed abortion and thus smaller seed crops that maintain high overall outcrossing rates (Kennington and James 1997b;Krauss et al 2007).…”

Progress in Myrtaceae genetics and genomics: Eucalyptus as the pivotal genus

“…Knowledge is particularly lacking on the frequency of QTL alleles and distribution of effects in natural and breeding populations. Finally, long generation times and high rates of inbreeding depression in outbred eucalypt species (Costa e Silva et al 2011;Griffin and Cotterill 1988) have precluded the development of inbred lines with contrasting alleles, which are needed to isolate and characterize (Mendelize) individual allele effects.…”