Estimating numbers of embryonic lethals in conifers

Savolainen, Outi; Kärkkäinen, Katri; Kuittinen, Helmi

doi:10.1038/hdy.1992.130

Cited by 43 publications

(27 citation statements)

References 13 publications

(7 reference statements)

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“…These studies also generally find substantial, early-stage, inbreeding depression in outcrossing species, in line with theoretical predictions (Charlesworth et al 1990;Husband and Schemske 1996). Interestingly, results from studies in outcrossing plants, particularly conifers (e.g., Savolainen et al 1992;Remington and O'Malley 2000), show substantial embryonic-stage inbreeding depression, while we find evidence for only one or two mutations affecting survival during the embryonic stage of the oyster, from fertilization through the nonfeeding trochophore stage (0-24 hr).…”

Section: Stage-specific Expression Of Genetic Loadsupporting

confidence: 66%

Quantitative Trait Locus Analysis of Stage-Specific Inbreeding Depression in the Pacific OysterCrassostrea gigas

2011

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Inbreeding depression and genetic load have been widely observed, but their genetic basis and effects on fitness during the life cycle remain poorly understood, especially for marine animals with high fecundity and high, early mortality (type-III survivorship). A high load of recessive mutations was previously inferred for the Pacific oyster Crassostrea gigas, from massive distortions of zygotic, marker segregation ratios in F 2 families. However, the number, genomic location, and stage-specific onset of mutations affecting viability have not been thoroughly investigated. Here, we again report massive distortions of microsatellite-marker segregation ratios in two F 2 hybrid families, but we now locate the causative deleterious mutations, using a quantitative trait locus (QTL) interval-mapping model, and we characterize their mode of gene action. We find 14-15 viability QTL (vQTL) in the two families. Genotypic frequencies at vQTL generally suggest selection against recessive or partially recessive alleles, supporting the dominance theory of inbreeding depression. No epistasis was detected among vQTL, so unlinked vQTL presumably have independent effects on survival. For the first time, we track segregation ratios of vQTL-linked markers through the life cycle, to determine their stage-specific expression. Almost all vQTL are absent in the earliest life stages examined, confirming zygotic viability selection; vQTL are predominantly expressed before the juvenile stage (90%), mostly at metamorphosis (50%). We estimate that, altogether, selection on vQTL caused 96% mortality in these families, accounting for nearly all of the actual mortality. Thus, genetic load causes substantial mortality in inbred Pacific oysters, particularly during metamorphosis, a critical developmental transition warranting further investigation.

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Section: Stage-specific Expression Of Genetic Loadsupporting

confidence: 66%

Quantitative Trait Locus Analysis of Stage-Specific Inbreeding Depression in the Pacific OysterCrassostrea gigas

2011

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“…It should be stressed that the reported selfing rates can be underestimated, because our estimates did not account for seed abortion, which is highly correlated with selffertilization (Koski 1971;Savolainen et al 1992;Kärkkäinen et al 1999). The total probability of survival of a seed can be expressed as P(B)=sw s +(1−s)w t , where s is the actual self-fertilization rate, w s and w t is the proportion of progeny survived after selfing and outcrossing, respectively.…”

Section: Discussionmentioning

confidence: 99%

Bayesian approach reveals confounding effects of population size and seasonality on outcrossing rates in a fragmented subalpine conifer

Chybicki

Dzialuk

2014

Tree Genetics & Genomes

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Mating systems have long been recognized as key factors determining genetic structure within and between populations. Outcrossing promotes genetic diversity and gene flow between populations, while inbreeding, on the other hand, decreases recombination rates, facilitating fixation of co-adapted genes. In small populations, selfing moderates pollen limitation because of low mate availability, but at the cost of increased inbreeding depression. These conflicts are of more than theoretical interest; they are critical for the management of endangered species. In order to help designing conservation strategies for the management of the gene pool of fragmented populations of Pinus cembra, a protected species in Poland, we have characterized pollen flow and mating structure using nuclear microsatellite markers. We demonstrated that P. cembra in the studied stands of the Tatra Mts. is characterized by an average outcrossing rate (t) of 0.72. Unlike with the existing approaches, using the newly developed Bayesian method, we found that population size and seasonal variation had confounding effects on outcrossing rates. In concordance with predictions, large populations showed significantly higher outcrossing rates (t=0.89) than smaller ones (t=0.51). Temporal variation revealed in the outcrossing rate might be linked with masting behavior of the species. On the other hand, we showed that outcrossing rates were not associated with a trunk diameter of a mother tree. Our study also demonstrated that biparental inbreeding is a significant component of mating system. However, we further show that pollen dispersal follows a fat-tailed distribution (with the average dispersal distance of 1,267 m) so that at least some long-distance pollen dispersal must be occurring.Overall, we conclude that the high inbreeding (both selfing and mating between relatives) found in P. cembra buffers for pollen limitation. We argue that small, isolated stands can be at risk of gene pool erosion, despite the potential for longdistance pollen and seed dispersal.

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“…The number of embryonic lethal equivalents could be as high as 11 in conifers (Savolainen et al, 1992) and experimental results generally support the assumption of an additive effect of recessive alleles (Remington and O'Malley, 2000a). However, in Pinaceae, a stage-specific death peak occurring during early embryogenesis could be caused by partial dominance or overdominance of deleterious genes (Williams, 2007(Williams, , 2008.…”

Section: Introductionmentioning

confidence: 56%

“…The rate of empty seeds among well-conformed seeds, which generally indicates the presence of embryonic lethals (Savolainen et al, 1992), was low (17%) and its variation was not related to selfing rate. Furthermore, juvenile mortality was also very low in this study.…”

Section: Effects Of Selfing On Germination and First Year Growth In Nmentioning

confidence: 99%

Variation of selfing rate and inbreeding depression among individuals and across generations within an admixed Cedrus population

2010

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We investigated the variation and short-term evolution of the selfing rate and inbreeding depression (ID) across three generations within a cedar forest that was established from admixture ca 1860. The mean selfing rate was 9.5%, ranging from 0 to 48% among 20 seed trees (estimated from paternally inherited chloroplast DNA). We computed the probability of selfing for each seed and we investigated ID by comparing selfed and outcrossed seeds within progenies, thus avoiding maternal effects. In all progenies, the germination rate was high (88-100%) and seedling mortality was low (0-12%). The germination dynamics differed significantly between selfed and outcrossed seeds within progenies in the founder gene pool but not in the following generations. This transient effect of selfing could be attributed to epistatic interactions in the original admixture. Regarding the seedling growth traits, the ID was low but significant: 8 and 6% for height and diameter growth, respectively. These rates did not vary among generations, suggesting minor gene effects. At this early stage, outcrossed seedlings outcompeted their selfed relatives, but not necessarily other selfed seedlings from other progenies. Thus, purging these slightly deleterious genes may only occur through within-family selection. Processes that maintain a high level of genetic diversity for fitness-related traits among progenies also reduce the efficiency of purging this part of the genetic load.

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Estimating numbers of embryonic lethals in conifers

Cited by 43 publications

References 13 publications

Quantitative Trait Locus Analysis of Stage-Specific Inbreeding Depression in the Pacific OysterCrassostrea gigas

Quantitative Trait Locus Analysis of Stage-Specific Inbreeding Depression in the Pacific OysterCrassostrea gigas

Bayesian approach reveals confounding effects of population size and seasonality on outcrossing rates in a fragmented subalpine conifer

Variation of selfing rate and inbreeding depression among individuals and across generations within an admixed Cedrus population

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