Survival of the Currently Fittest: Genetics of Rainbow Trout Survival Across Time and Space

Abstract

As a fitness trait, survival is assumed to exhibit low heritability due to strong selection eroding genetic variation and/or spatio-temporal variation in mortality agents reducing genetic and increasing residual variation. The latter phenomenon in particular may contribute to low heritability in multigeneration data, even if certain cohorts exhibit significant genetic variation. Analysis of survival data from 10 year classes of rainbow trout reared at three test stations showed that treating survival as a single trait across all generations resulted in low heritability (h 2 ¼ 0.08-0.17). However, when heritabilities were estimated from homogeneous generation and test station-specific cohorts, a wide range of heritability values was revealed (h 2 ¼ 0.04-0.71). Of 64 genetic correlations between different cohorts, 20 were positive, but 16 were significantly negative, confirming that genetic architecture of survival is not stable across generations and environments. These results reveal the existence of hidden genetic variation for survival and demonstrate that treating survival as one trait over several generations may not reveal its true genetic architecture. Negative genetic correlations between cohorts indicate that overall survival has limited potential to predict general resistance, and care should be taken when using it as selection criterion.

Genetic architecture of rainbow trout survival from egg to adult

“…Resistances to different mortality factors do not necessarily share a common genetic determination (Gjøen et al, 1997;Henryon et al, 2005;Bubliy & Loeschcke, 2005;Ødega˚rd et al, 2007 ;Kjøglum et al, 2008). This is for example highlighted by the fact that moderate genotyperenvironment interaction was also found for rainbow trout survival during the grow-out period, as shown by the non-unity genetic correlations between environments (Vehvila¨inen et al, 2008 ;present study). Similarly, different alleles of a single gene may provide resistance against different diseases or mortality factors (Shook & Johnson, 1999 ;Grimholt et al, 2003).…”

“…89) genetically correlated than in the whole data. This sort of difference between datasets is expected if there is spatio-temporal variability in mortality factors causing variation in genetic parameters (Vehvila¨inen et al, 2008). For instance, in our previous study, we showed that heritability for rainbow trout survival during grow-out stage ranges between 0 .…”

“…98)] between survival in freshwater and different sea environments. This means that to some extent genotypes rank differently for survival in separate environments even within life stage (Vehvila¨inen et al, 2008). In the current study, we found a slightly lower between environment genetic correlation (freshwater versus sea grow-out r G =0 .…”

“…Thus only individuals robust enough to overcome these challenges will become parents of the next generation. Survival is an ultimate robustness trait because it is a measure of an individual's resistance against multiple mortality factors occurring in an environment (Vehvila¨inen et al, 2008).…”

“…In animal breeding, a common goal is that animals would be robust against multiple environmental disturbances, stressors and mortality factors throughout all life stages (Mulder & Bijma, 2005 ;Pertoldi et al, 2007 ;Vehvila¨inen et al, 2008). Genetic analyses of survival, and its underlying component traits, across environments and during different growth or life stages will increase our ability to utilize survival as a selected trait in breeding programmes.…”