Correlated genetic effects on reproduction define a domestication syndrome in a forest tree (original) (raw)
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Annals of Botany, 2012
Aims The study of local adaptation in plant reproductive traits has received substantial attention in short-lived species, but studies conducted on forest trees are scarce. This lack of research on long-lived species represents an important gap in our knowledge, because inferences about selection on the reproduction and life history of short-lived species cannot necessarily be extrapolated to trees. This study considers whether the size for first reproduction is locally adapted across a broad geographical range of the Mediterranean conifer species Pinus pinaster. In particular, the study investigates whether this monoecious species varies genetically among populations in terms of whether individuals start to reproduce through their male function, their female function or both sexual functions simultaneously. Whether differences among populations could be attributed to local adaptation across a climatic gradient is then considered. † Methods Male and female reproduction and growth were measured during early stages of sexual maturity of a P. pinaster common garden comprising 23 populations sampled across the species range. Generalized linear mixed models were used to assess genetic variability of early reproductive life-history traits. Environmental correlations with reproductive life-history traits were tested after controlling for neutral genetic structure provided by 12 nuclear simple sequence repeat markers. † Key Results Trees tended to reproduce first through their male function, at a size (height) that varied little among source populations. The transition to female reproduction was slower, showed higher levels of variability and was negatively correlated with vegetative growth traits. Several female reproductive traits were correlated with a gradient of growth conditions, even after accounting for neutral genetic structure, with populations from more unfavourable sites tending to commence female reproduction at a lower individual size. † Conclusions The study represents the first report of genetic variability among populations for differences in the threshold size for first reproduction between male and female sexual functions in a tree species. The relatively uniform size at which individuals begin reproducing through their male function probably represents the fact that pollen dispersal is also relatively invariant among sites. However, the genetic variability in the timing of female reproduction probably reflects environment-dependent costs of cone production. The results also suggest that early sex allocation in this species might evolve under constraints that do not apply to other conifers.
In plant quantitative genetic studies conducted ex situ, the large number of seeds produced per individual has promoted the use of open-pollinated progeny tests. In subsequent analyses, seeds collected on the same mother-plant are assumed to be half-sibs. The consequences of the departure from half-sib assumption in progeny tests have been investigated since the 1960s using simulation approaches and, more recently, using molecular-based experimental approaches. This review aims to synthesize the results and conclusions of these simulation and empirical studies. We focus on tree species, where controlled crosses are difficult to carry out experimentally and departures from half-sib assumptions occur frequently in natural populations. First, the average level of relatedness expected within maternal progeny for many tree populations is higher than that of half-sibs. This is the consequence of non-random mating resulting from the small number of effective pollen donors per female, unequal male reproductive success and/or selfing. As result, estimates of genetic variance and heritability for quantitative traits may be upward biased. Alternatively, inbreeding depression, dominance effects and the heterogeneity of the male gamete pool among females are often neglected, which may lead to underestimation of the heritability of traits. A correction based on the mean genetic relatedness between offspring and the relatedness between parents is often used to compensate those biases. However, such correction cannot accurately adjust the estimates in situations where variable levels of genetic relatedness among families, dominance effects or inbreeding depression exist within the progeny. An alternative and promising approach is the use of the "animal model" approach, which optimizes the use of molecular data and paternal information to estimate heritability more accurately. This study is part of Julie Gauzere PhD thesis, which aims at understanding the role of adaptation and gene flow in the phenotypic variation of traits related to climate response along an altitudinal gradient of a temperate tree species, Fagus sylvatica. Sylvie Oddou-Muratorio is a population geneticist studying the impact of pollen and seed dispersal and climate-driven selection on adaptive dynamics of forest trees natural populations under climate change. François Lefèvre's research is targeted at the issues of sustainable management of forest genetic resources and adaptation of the forests to climate change. Christian Pichot is a population geneticist and quantitative geneticist studying the role of forest tree genetic resources on population dynamics. Etienne Klein research is targeted on dispersal of plant propagules (pollen and seeds), and their impact on the genetic composition of populations.
Forest Systems December 2021 • Volume 30 • Issue 3 • e010, 2021
Aim of study: Forest geneticists developed various methods to predict an early selection age for forest tree species in order to shorten the breeding cycles. This study aims to estimate age-age correlations among diameter growth of trees at different ages and predict early selection age for Pinus brutia Ten. Area of study: P. brutia populations in the study were sampled from the most productive distribution range of the species, which is an important forest tree in the eastern Mediterranean Basin. To understand genetic variation and determine early selection age for the species, a common garden experiment was established in two test sites near Antalya city, Turkey, in 1979. Material and methods: Wood increment cores at breast height were collected at age 30 years, and diameters (dbh) were measured for the ages 13, 15, 19, 21, 23, 25, and 27 years on the cores. Diameters at ground level (dgl) and dbh were also measured on live trees at age 35. Variance components, age-age correlations, heritability and selection efficiency were estimated for the diameters. Main results: Age-age genetic correlations for diameters were high (mostly > 0.90). Genetic correlations between dgl (at age 35) and dbh (at all measurement ages) ranged from 0.84 to 0.99. Regressions of genetic correlation on natural log of age ratio (LAR) of juvenile age to older age were significant (P < 0.0001). Selection efficiencies estimated by employing the prediction equation indicated that for rotation age 40, the optimum selection age would be between 3 to 5 years, and for rotation age 100 it would be between 5 to 9 years. Research highlights: The results of this study provide information that can be used to find early selection ages in P. brutia. On relatively poor test sites most trees may not attain enough height growth to have measurable dbh trait. In such cases, dgl and/or tree height traits (both of which are highly correlated with dbh traits of all ages) can be measured and used instead of dbh trait for evaluations.
Tree Genetics & Genomes, 2017
Genotype by environment interaction (G×E) refers to the comparative performances of genotypes differing among environments, representing differences in genotype rankings or differences in the level of expression of genetic differences among environments. G×E can reduce heritability and overall genetic gain, unless breeding programmes are structured to address different categories of environments. Understanding the impact of G×E, the role of environments in generating G×E and the problems and opportunities is vital to efficient breeding programme design and deployment of genetic material. We review the current main analytical methods for identifying G×E: factor analytic models, biplot analysis and reaction norm. We also review biological and statistical evidence of G×E for growth, form and wood properties in forest species of global economic importance, including some pines, eucalypts, Douglas-fir, spruces and some poplars. Among these species, high levels of G×E tend to be reported for growth traits, with low levels of G×E for form traits and wood properties. Finally, we discuss possible ways of exploiting G×E to maximise genetic gain in forest tree breeding. Characterising the role of environments in generating interactions is seen as the basic platform, allowing efficient testing of candidate genotypes. We discuss the importance of level-of-expression interaction, relative to rankchange interaction, as being greater than in many past reports, especially for deployment decisions. We examine the impacts of G×E on tree breeding, some environmental factors that cause G×E and the strategies for dealing with G×E in tree breeding, and the future role of genomics.
Assortative mating and gene flow generate clinal phenological variation in trees
Background: On-going climate change is shifting the timing of bud burst (TBB) of broad leaf and conifer trees in temperate areas, raising concerns about the abilities of natural populations to respond to these shifts. The level of expected evolutionary change depends on the level and distribution of genetic variation of TBB. While numerous experimental studies have highlighted the role of divergent selection in promoting clinal TBB differentiation, we explored whether the observed patterns of variation could be generated by the joint effects of assortative mating for TBB and gene flow among natural populations. We tested this hypothesis using an in silico approach based on quantitative genetic models. Results: Our simulations showed that genetic clines can develop even without divergent selection. Assortative mating in association with environmental gradients substantially shifted the mean genetic values of populations. Owing to assortative mating, immigrant alleles were screened for proximal or distant populations depending on the strength of the environmental cline. Furthermore, we confirmed that assortative mating increases the additive genetic variance within populations. However, we observed also a rapid decline of the additive genetic variance caused by restricted gene flow between neighboring populations resulting from preferential matings between phenologically-matching phenotypes. Conclusions: We provided evidence that the patterns of genetic variation of phenological traits observed in forest trees can be generated solely by the effects of assortative mating and gene flow. We anticipate that predicted temperature increases due to climate change will further enhance genetic differentiation across the landscape. These trends are likely to be reinforced or counteracted by natural selection if phenological traits are correlated to fitness.
Time trends in genetic parameters for height and optimal age for parental selection in Scots pine
Forest science, 2003
Data used to estimate time trends in genetic parameters and the optimal age for parental selection were obtained from 13 Scots pine (Pinus sylvestris L.) progeny tests in southern Sweden. The final age at measurement was between 24 and 39 yr, corresponding to approximately half the rotation age in southern Sweden. Trees in each test have been measured for height 4-6 times, covering ages from 5 to 39 yr. Individual tree heritability for height averaged 0.16, and increased slightly over time, although there were differences among tests. The average additive coefficient of variation for height (CV A ), which decreased with age, was 6.0% while the average nonadditive coefficient of variation (CV D ) was 3.8% and did not show any significant trend over time. A model based on the natural logarithm of the ratio between the two ages at measurement was used to predict genetic age-age correlations. The efficiency of early selection was also examined, in an analysis considering total height at age 30 as the target trait. The optimal age for parental selection based on gain per unit time peaked at 11 yr, with a time lag for breeding of 10 yr. In the southern tests, the peak came some years earlier than in the northern tests. Selection efficiency based on present value with an interest rate of 5% showed the optimum at 11 yr. FOR. SCI. 49(5):696-705.
Using among-year variation to assess maternal effects in Pinus aristata and Pinus flexilis
Botany, 2014
Maternal effects, the effect of the maternal environment during development on offspring growth, can complicate the interpretation of common garden studies. Growing one or more generations in a common environment can help minimize maternal effects, but is often not practical with long-lived species. In Pinus aristata Engelm. and Pinus flexilis James, we assessed maternal effects by growing offspring sourced over multiple years from the same mother trees, comparing growth traits between source years. Additionally, we explored the effect of maternal environment on seed characteristics by collecting five twig clippings from each mother tree and measuring characteristics indicative of the relative vigor of the tree during each seed source year. The effect of year was significant for twig growth characteristics, seed size, and seedling performance. For both species, there were significant relationships between the relative inter-annual (RIA) variation in seed mass and the RIA variation in numerous seedling traits including cotyledon length, seedling total dry mass, and needle length. Variation in seed mass was not predicted by yearly variation in the maternal plant's phenotypic traits. These results support the hypothesis that maternal effects translate into variation in early seedling growth and suggest possibilities to statistically account for them in common garden studies involving long-lived species.
Journal of Theoretical Biology, 2018
In forest tree breeding, family-based Q uantitative T rait L oci (QTL) studies are valuable as methods to dissect the complexity of a trait and as a source of candidate genes. In the field of conifer research, our study contributes to the evaluation of phenotypic and predicted breeding values for the identification of QTL linked to complex traits in a three-generation pedigree population in Scots pine (Pinus sylvestris L.). A total of 11 470 open pollinated F 2-progeny trees established at three different locations, were measured for growth and adaptive traits. Breeding values were predicted for their 360 mothers, originating from a single cross of two grandparents. A multilevel LASSO association analysis was conducted to detect QTL using genotypes of the mothers with the corresponding phenotypes and Estimated Breeding Values (EBV). Different levels of genotype-by-environment (G × E) effects among sites at different years, were detected for survival and height. Moderate-to-low narrow sense heritabilities and EBV accuracies were found for all traits and all sites. We identified 18 AFLPs and 12 SNPs to be associated with QTL for one or more traits. 62 QTL were significant with percentages of variance explained ranging from 1.7 to 18.9%. In those cases where the same marker was associated to a phenotypic or an ebv QTL, the ebv QTL always explained higher proportion of the variance, maybe due to the more accurate nature of Estimated Breeding Values (EBV). Two SNP-QTL showed pleiotropic effects for traits related with hardiness, seed, cone and flower production. Furthermore, we detected several QTL with significant effects across multiple ages, which could be considered as strong candidate loci for early selection. The lack of reproducibility of some QTL detected across sites may be due to environmental heterogeneity reflected by the genotype-and QTL-byenvironment effects.