Unidirectional response to bidirectional selection on body size II. Quantitative genetics

Abstract

Anticipating the genetic and phenotypic changes induced by natural or artificial selection requires reliable estimates of trait evolvabilities (genetic variances and covariances). However, whether or not multivariate quantitative genetics models are able to predict precisely the evolution of traits of interest, especially fitness‐related, life history traits, remains an open empirical question. Here, we assessed to what extent the response to bivariate artificial selection on both body size and maturity in the medaka Oryzias latipes , a model fish species, fits the theoretical predictions. Three lines (Large, Small, and Control lines) were differentially selected for body length at 75 days of age, conditional on maturity. As maturity and body size were phenotypically correlated, this selection procedure generated a bi‐dimensional selection pattern on two life history traits. After removal of nonheritable trends and noise with a random effect (“animal”) model, the observed selection response did not match the expected bidirectional response. For body size, Large and Control lines responded along selection gradients (larger body size and stasis, respectively), but, surprisingly, the Small did not evolve a smaller body length and remained identical to the Control line throughout the experiment. The magnitude of the empirical response was smaller than the theoretical prediction in both selected directions. For maturity, the response was opposite to the expectation (the Large line evolved late maturity compared to the Control line, while the Small line evolved early maturity, while the opposite pattern was predicted due to the strong positive genetic correlation between both traits). The mismatch between predicted and observed response was substantial and could not be explained by usual sources of uncertainties (including sampling effects, genetic drift, and error in G matrix estimates).

Ecological ramifications of adaptation to size-selective mortality

“…; SL i in small-breeder = 18.9 mm ± 1.4; SL i in large-breeder = 19.4 mm ± 1.4; ANOVA: F 1, 358 = 13.70, p < 0.001) were selected to generate 24 populations composed of individuals from the same line (48 populations in total), but from distinct families to limit inbreeding (mean kinship coefficient = 0.23 ± 0.1 and 0.17 ± 0.1 s.e.m. in LB and SB populations, respectively; further details available in [ 26 ]). Fish were anaesthetized with MS-222 and marked using visible implant elastomer (VIE; Northwest Marine Technology, Shaw Island, WA, USA) to render each fish individually identifiable within each population and to allow the calculation of individual somatic growth rate.…”

“…We used two lines of medaka originating from a size-selection experiment performed over 10 generations. The selection procedure consisted of mimicking either fishing mortality where small-bodied individuals are favoured to reproduce (small-breeder SB line), or a more natural mortality regime that favours large-bodied individuals (large-breeder LB line) [ 25 , 26 ]. Under controlled laboratory conditions, the LB and SB lines evolved different life-history traits and behaviours: small-breeder medaka grew slower, matured earlier and were less willing to forage than the large-breeder medaka [ 23 , 25 , 27 ].…”

Within-species variation in the gut microbiome of medaka (Oryzias latipes) is driven by the interaction of light intensity and genetic background

“…We used two lines of medaka originating from a ten-generation size selection experiment, carried out under controlled laboratory conditions. The selection procedure consisted of mimicking either fishing mortality where only small-bodied individuals were allowed to reproduce (small-breeder SB line), or a more natural mortality regime rather favoring the reproduction of large-bodied individuals (large-breeder LB line) (Reneville et al 2020, Le Rouzic et al 2020). As we have previously reported, the LB and SB lines evolved opposite life-history traits and behaviors: small-breeder medaka grew slower, matured earlier and were less efficient foragers than the large-breeder medaka (Diaz Pauli et al 2019, Evangelista et al 2021).…”

Genomic prediction of growth in a commercially, recreationally, and culturally important marine resource, the Australian snapper (Chrysophrys auratus)

“…It is also expected that selective breeding programs increase the frequency of genetic variants underlying improved growth through the successive selective breeding of only the fastest growing individuals in each cohort. Experiments in the laboratory, where either large or small individuals are removed for several generations, have shown drastic changes in allele frequencies, loss of genetic diversity, and increased linkage disequilibrium in specific parts of the genome ( Le Rouzic et al 2020 ; Valenza‐Troubat et al 2021a). Some genes and genomic regions associated with growth have been identified in a few marine fish species ( Wang et al 2015 ; Robledo et al 2016 ; Wu et al 2019 ; Zhou et al 2019 ; Yang et al 2020 ; Valenza‐Troubat et al 2021c).…”