DOCSLIB.ORG

Selection on Breeding Date and Body Size in Colonizing Coho Salmon, Oncorhynchus Kisutch

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Selection on Breeding Date and Body Size in Colonizing Coho Salmon, Oncorhynchus Kisutch Molecular Ecology (2010) 19, 2562–2573 doi: 10.1111/j.1365-294X.2010.04652.x Selection on breeding date and body size in colonizing coho salmon, Oncorhynchus kisutch J. H. ANDERSON,* P. L. FAULDS,† W. I. ATLAS,‡ G. R. PESS§ and T. P. QUINN* *School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, WA 98195, USA, †Seattle Public Utilities, 700 5th Avenue, Suite 4900, Seattle, WA, 98124, USA, ‡Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC, Canada V5A 1S6, §National Marine Fisheries Service, Northwest Fisheries Science Center, 2725 Montlake Boulevard East, Seattle, WA 98195, USA Abstract Selection during the colonization of new habitat is critical to the process of local adaptation, but has rarely been studied. We measured the form, direction, and strength of selection on body size and date of arrival to the breeding grounds over the first three cohorts (2003–2005) of a coho salmon (Oncorhynchus kisutch) population colonizing 33 km of habitat made accessible by modification of Landsburg Diversion Dam, on the Cedar River, Washington, USA. Salmon were sampled as they bypassed the dam, parentage was assigned based on genotypes from 10 microsatellite loci, and standardized selection gradients were calculated using the number of returning adult offspring as the fitness metric. Larger fish in both sexes produced more adult offspring, and the magnitude of the effect increased in subsequent years for males, suggesting that low densities attenuated traditional size-biased intrasexual competition. For both sexes, directional selection favoured early breeders in 2003, but stabilizing selection on breeding date was observed in 2004 and 2005. Adults that arrived, and presumably bred, early produced stream-rearing juvenile offspring that were larger at a common date than offspring from later parents, providing a possible mechanism linking breeding date to offspring viability. Comparison to studies employing similar methodology indicated selection during colonization was strong, particularly with respect to reproductive timing. Finally, female mean reproductive success exceeded that needed for replacement in all years so the population expanded in the first generation, demonstrating that salmon can proficiently exploit vacant habitat. Keywords: behaviour, conservation, dams, natural selection, reintroduction, sexual selection Received 4 February 2010; revision received 25 March 2010; accepted 1 April 2010 important traits influencing production and survival of Introduction offspring. Sexual selection tends to favour traits in males that Large individuals of both sexes enjoy reproductive increase their access to receptive mates and traits in advantages. Large males can dominate competitors in females that aid in competition for breeding resources contests for mates or breeding territories, and females required for nest sites or parental care (Andersson 1994; may prefer large males (Andersson 1994). However, Clutton-Brock 2009). However, reproductive success is small males can sometimes be successful, especially if determined not only by the number of offspring that an they gain fertilizations via sneaking or other alternative individual produces but also how many of them sur- behaviours (Taborsky 1994). Large females can produce vive to reproductive maturity (Clutton-Brock 1988). more numerous and larger offspring (Stearns 1992; Ei- Body size and breeding date are among the most num et al. 2004). In addition, large size may provide advantages in competition for nest sites (van den Ber- Correspondence: J. H. Anderson, Fax: +1 206 685 7471; E-mail: ghe & Gross 1989) or other resources necessary for [email protected] parental care provided by females (Andersson 1994). Ó 2010 Blackwell Publishing Ltd SELECTION IN COLONIZING COHO SALMON 2563 Breeding date is also linked to sexual selection and selection on traits such as body size. Thus there are con- offspring survival. Breeders arriving early may have a flicting predictions regarding the strength of selection prior residence advantage in competition for mates or during colonization, but its role in adaptive evolution reproductive territories (Foote 1990; Haley 1994). In has most often been inferred well after population birds, both clutch size and offspring survival often establishment and not directly measured in the very decline over the course of the breeding season (Perrins first generations. 1970; Svensson 1997). Early emergence of young pro- Here we present the results of a study using DNA- vides increased growth opportunities, resulting in based parent–offspring assignments to characterize higher survival rates when mortality is size selective selection on breeding date and body size in a popula- (Landa 1992; Einum & Fleming 2000; Feder et al. 2008). tion of coho salmon expanding above a former migra- However, juveniles hatching too early may face tion barrier. Our primary goal was to quantify the increased predation risk (Bra¨nna¨s 1995; O’Donoghue & form, direction and magnitude of selection on these Boutin 1995) or unfavourable habitat conditions and traits. To identify a potential mechanism for selection food availability (Crecco & Savoy 1985). on breeding date, we measured the body size of age-0 Coho salmon (Oncorhynchus kisutch) are ideal subjects juvenile coho salmon sampled from the stream and pre- for studies of competition in sexual and natural selec- dicted that early breeding parents would produce off- tion. Females compete for, construct, and guard nest spring that were larger at the end of the summer than sites, and the largest individuals were estimated to those produced by later breeding parents. We also com- enjoy a 23-fold advantage over the smallest due to egg pared selection on body size with a simple length-based production, territory quality, and nest defence (van den egg production model to evaluate the importance of Berghe & Gross 1989). Males compete for access to breeding competition amongst females. Finally, to test receptive females and large males typically win (Flem- the hypothesis that selection is strong during coloniza- ing & Gross 1994) but small males maturing at a youn- tion, we compared our selection gradients with others ger age (‘jacks’) can sneak fertilizations and may in a comprehensive review of selection in natural popu- represent a evolutionarily stable strategy (Gross 1985). lations (Kingsolver et al. 2001) and similar salmonid Other than a brief (c. 1–2 weeks) period of nest defence studies (Seamons et al. 2007; Ford et al. 2008). by the female following egg deposition, coho salmon provide no parental care and invariably die after breed- Methods ing (Sandercock 1991). Thus females determine the off- spring’s environment almost exclusively by spawning Sampling site and date, and parents cannot compensate for adverse conditions by feeding or protecting their off- This study was conducted in the Cedar River, Washing- spring from predators. Adults breed in late fall or win- ton, USA, where Landsburg Diversion Dam blocked ter, embryos incubate in streambed gravels for several fish migration from 1901 to 2003. During the past cen- months before emerging in the spring, and juveniles tury, coho salmon persisted in the Cedar River and its commonly grow in freshwater for 1 year before migrat- tributaries below the dam (located at river 35.1 km), ing to sea (Sandercock 1991). although precise abundance estimates were unavailable. Pacific salmon have repeatedly colonized new habi- In fall 2003, the dam was modified with fish passage tats throughout their range, and such episodes provide structures, and management adopted a policy of natural special opportunities for phenotypic evolution and local recolonization rather than transplantation. Salmon adaptation. Much of the native habitat currently occu- accessed the new habitat on their own volition and pied by Pacific salmon was colonized following glacial spawned primarily in the lower reaches of the Cedar recession (c. 10 000–15 000 years, McPhail & Lindsey River immediately above the dam (Anderson & Quinn 1986), and indeed this is an ongoing process (e.g. Gla- 2007). Thus, expansion of an existing population into cier Bay, Alaska, Milner et al. 2000). In general, intro- newly accessible habitat, as opposed to the founding of duced or invading populations often experience rapid a population in an isolated new area, best describes the rates of adaptive evolution due to the opportunity for colonization demographics in this case. population growth (Reznick & Ghalambor 2001), and Adult salmon were sampled as they ascended the fish selection may be primarily responsible for phenotypic ladder, including a measurement of body length (tip of evolution during population expansion (Clegg et al. snout to fork of tail), determination of sex based on 2002; Koskinen et al. 2002; Yeh 2004). Although rapid external examination, and excision of a small piece of evolution would imply strong selection during coloniza- tissue for subsequent DNA analysis. The ladder was tion, low densities typical of colonization might attenu- operated such that all salmon accessing the new habitat ate sexual selection (Kokko & Rankin 2006), reducing were handled from well before the first coho salmon Ó 2010 Blackwell Publishing Ltd 2564 J. H. ANDERSON ET AL. arrived (approximately 1 month) until the run dwin- age-1 fish about to migrate downstream. Juveniles were dled to 1–2 salmon per week (late January in most collected over a range of dates so we adjusted observed
Load more

Recommended publications
  • An Introgression Analysis of Quantitative Trait Loci That Contribute to a Morphological Difference Between Drosophila Simulans and D
    Copyight 0 1997 by the Genetics Societv of America An Introgression Analysis of Quantitative Trait Loci That Contribute to a Morphological Difference Between Drosophila simulans and D. mauritiana Cathy C. Laurie, John R. True, Jianjun Liu and John M. Mercer Department of Zoology, Duke University, Durham, North Carolina 27708 Manuscript received August 12, 1996 Accepted for publication October 29, 1996 ABSTRACT Drosophila simulans and D. maum'tiana differ markedly in morphology of the posterior lobe, a male- specific genitalic structure. Bothsize and shapeof the lobe can be quantifiedby a morphometric variable, PC1, derived from principal components and Fourier analyses. The genetic architectureof the species difference in PC1 was investigated previously by composite interval mapping, which revealed largely additive inheritance, with a minimum of eight quantitative trait loci (QTL) affecting the trait. This analysis was extended by introgression of marked segments of the maun'tiana third chromosome into a simulans background by repeated backcrossing. Thetwo types of experiment are consistentin suggesting that several QTL on the third chromosome may have effects in the range of 10-15% of the parental difference andthat all or nearly all QTL have effects in the same direction. Since the parental difference is large (30.4 environmental standard deviations), effects of this magnitude can produce alternative homozygotes with little overlap in phenotype. However, these estimates may not reflect the effects of individual loci, since each interval or introgressed segment may contain multiple QTL. The consistent direction of allelic effects suggests a history of directional selection on the posterior lobe. HE genetic analysis of a quantitative trait usually ual genes that affect continuously variable traits.
    [Show full text]
  • Microevolution and the Genetics of Populations ​ ​ Microevolution Refers to Varieties Within a Given Type
    Chapter 8: Evolution Lesson 8.3: Microevolution and the Genetics of Populations ​ ​ Microevolution refers to varieties within a given type. Change happens within a group, but the descendant is clearly of the same type as the ancestor. This might better be called variation, or adaptation, but the changes are "horizontal" in effect, not "vertical." Such changes might be accomplished by "natural selection," in which a trait ​ ​ ​ ​ within the present variety is selected as the best for a given set of conditions, or accomplished by "artificial selection," such as when dog breeders produce a new breed of dog. Lesson Objectives ● Distinguish what is microevolution and how it affects changes in populations. ● Define gene pool, and explain how to calculate allele frequencies. ● State the Hardy-Weinberg theorem ● Identify the five forces of evolution. Vocabulary ● adaptive radiation ● gene pool ● migration ● allele frequency ● genetic drift ● mutation ● artificial selection ● Hardy-Weinberg theorem ● natural selection ● directional selection ● macroevolution ● population genetics ● disruptive selection ● microevolution ● stabilizing selection ● gene flow Introduction Darwin knew that heritable variations are needed for evolution to occur. However, he knew nothing about Mendel’s laws of genetics. Mendel’s laws were rediscovered in the early 1900s. Only then could scientists fully understand the process of evolution. Microevolution is how individual traits within a population change over time. In order for a population to change, some things must be assumed to be true. In other words, there must be some sort of process happening that causes microevolution. The five ways alleles within a population change over time are natural selection, migration (gene flow), mating, mutations, or genetic drift.
    [Show full text]
  • Patterns and Power of Phenotypic Selection in Nature
    Articles Patterns and Power of Phenotypic Selection in Nature JOEL G. KINGSOLVER AND DAVID W. PFENNIG Phenotypic selection occurs when individuals with certain characteristics produce more surviving offspring than individuals with other characteristics. Although selection is regarded as the chief engine of evolutionary change, scientists have only recently begun to measure its action in the wild. These studies raise numerous questions: How strong is selection, and do different types of traits experience different patterns of selection? Is selection on traits that affect mating success as strong as selection on traits that affect survival? Does selection tend to favor larger body size, and, if so, what are its consequences? We explore these questions and discuss the pitfalls and future prospects of measuring selection in natural populations. Keywords: adaptive landscape, Cope’s rule, natural selection, rapid evolution, sexual selection henotypic selection occurs when individuals with selection on traits that affect survival stronger than on those Pdifferent characteristics (i.e., different phenotypes) that affect only mating success? In this article, we explore these differ in their survival, fecundity, or mating success. The idea and other questions about the patterns and power of phe- of phenotypic selection traces back to Darwin and Wallace notypic selection in nature. (1858), and selection is widely accepted as the primary cause of adaptive evolution within natural populations.Yet Darwin What is selection, and how does it work? never attempted to measure selection in nature, and in the Selection is the nonrandom differential survival or repro- century following the publication of On the Origin of Species duction of phenotypically different individuals.
    [Show full text]
  • Natural Selection One of the Most Important Contributions Made to The
    Natural Selection One of the most important contributions made to the science of evolution by Charles Darwin is the concept of natural selection. The idea that members of a species compete with each other for resources and that individuals that are better adapted to their lifestyle have a better chance of surviving to reproduce revolutionized the field of evolution, though it was not accepted until several decades after Darwin first proposed it. Today, natural selection forms the foundation for our understanding of how species change over time. Natural selection may act to change a trait in many ways. When environmental pressures favor the average form of the trait, selection is said to be stabilizing. Directional selection occurs when selection pressures favor one extreme of the trait distribution. Selection is disruptive when the average form of the trait is selected against while either extreme is unaffected. In addition to natural selection, there are two other types of selection. Sexual selection, which Darwin believed was distinct from natural selection, involves the selection of traits based on their role in courtship and mating. Artificial selection is the selective breeding of species by humans to increase desirable traits, though the traits do not necessarily have to confer greater fitness. Summary of Types of Natural Selection Natural selection can take many forms. To make talking about this easier, we will consider the distribution of traits across a population in using a graph. To the right is a normal curve. For example, if we were talking about height as a trait, we would see that without any selection pressure on this trait, the heights of individuals in a population would vary, with most individuals being of an average height and fewer being extremely short or extremely tall.
    [Show full text]
  • Supplementary Information for Vyssotski, 2013
    Supplementary Information for Vyssotski, 2013 www.evolocus.com/evolocus/v1/evolocus-01-013-s.pdf Evolocus Supplementary Information for Transgenerational epigenetic compensation and sex u al d imorph ism 1,2,3 Dmitri L. Vyssotski Published 17 May 2013, Evolocus 1, 13-18 (2013): http://www.evolocus.com/evolocus/v1/evolocus-01-013.pdf In natu ral popu lation transgenerational epigenetic compensation is by unknown mechanisms, the mechanisms those were difficult to generated in h omoz y gou s mu tants, mainly in males. It d oes not imagine, and this possibility was abandoned for over 47 years. immed iately affect th e ph enoty pe of h omoz y gou s mu tants, w h ere The higher variability in males can be a result of a not so good it w as generated . Transgenerational epigenetic compensation is canalization of their ontogenesis, and the canalization of localiz ed not in th e same locu s as original mu tation and it is ontogenesis is modulated by sex hormones. Thus, we can d ominant, b ecau se it affects th e ph enoty pe ev en if it is receiv ed imagine that the canalization of ontogenesis in males is from one parent. In fu rth er generations, starting from F 2, it is more artificially decreased in comparison with females by means of ex pressed in females th an in males: it increases fitness of hormonal differences. h omozy gou s mu tant females, d ecreases fitness of w ild ty pe The shift of the female distribution to the right was not females and h as w eak effect on h eterozy gou s females.
    [Show full text]
  • Stabilizing Selection Shapes Variation in Phenotypic Plasticity
    bioRxiv preprint doi: https://doi.org/10.1101/2021.07.29.454146; this version posted July 29, 2021. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. 1 Stabilizing selection shapes variation in phenotypic plasticity 2 3 4 5 Dörthe Becker1,2,*, 6 Karen Barnard-Kubow1,3, 7 Robert Porter1, 8 Austin Edwards1,4, 9 Erin Voss1,5, 10 Andrew P. Beckerman2, 11 Alan O. Bergland1,* 12 13 14 1Department of Biology; University of Virginia, Charlottesville/VA, USA 15 2Department of Animal and Plant Sciences; University of Sheffield, Sheffield, UK 16 3Department of Biology, James Madison University, Harrisonburg/VA, USA 17 4Biological Imaging Development CoLab, University of California San Francisco, 18 San Francisco/CA, USA 19 5Department of Integrative Biology, University of California Berkeley, 20 Berkeley/CA 21 22 * to whom correspondence should be addressed: 23 DB ([email protected]), AOB ([email protected]) 24 25 26 27 Keywords: stabilizing selection; phenotypic plasticity; heritability; Daphnia; 28 defense morphologies 1 bioRxiv preprint doi: https://doi.org/10.1101/2021.07.29.454146; this version posted July 29, 2021. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. 29 Abstract 30 The adaptive nature of phenotypic plasticity is widely documented in natural 31 populations. However, little is known about the evolutionary forces that shape 32 genetic variation in plasticity within populations. Here we empirically address this 33 issue by testing the hypothesis that stabilizing selection shapes genetic variation 34 in the anti-predator developmental plasticity of Daphnia pulex.
    [Show full text]
  • An Evolutionary Perspective on Physical Attractiveness
    Evolutionary Anthropology 97 An Evolutionary Perspective on Physical Attractiveness DOUG JONES Everyday experience suggests that physical attractiveness is important in per- to others, and that mate choices based sonal-and especially sexual-relationships. This impression is confirmed by a on these preferences have evolution- large body of social psychological research.’ z2 Cross-cultural surveys and ethno- ary consequences. However, he did graphic accounts show that concern with the attractiveness of potential mates is not take up the question of where pref- also common in non-Westernsocietiesand in tribal and peasant cultures3 However, erences come from in the first place - social psychologists and anthropologists have often had a hard time explaining why e.g., why peahens prefer peacocks attractiveness should count for so much, or why some features rather than others with large and showy trains. In recent should seem particularly attractive. The theoretical difficulties in accounting for work on sexual selection and mate physical attraction are brought out in a Brazilian saying, “Beleza n2o p6e na mesa” choice,6,7 this question occupies a cen- (“Good looks don’t put anything on the table”), which points to the absence of any tral place. This work asks how natural evident practical advantage to choosing an attractive mate. Faced with these diffi- selection might affect mating prefer- culties, a growing number of researchers in biology, psychology, and anthropology ences and why one set of mating pref- have turned to the modern theory of sexual selection, which has been highly suc- erences might lead to greater cessful in explaining nonhuman animals’ attractions to traits of no direct ecological reproductive success than another.
    [Show full text]
  • Uncovering the Genetic Signature of Quantitative Trait Evolution with Replicated Time Series Data
    Heredity (2017) 118, 42–51 & 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved 0018-067X/17 www.nature.com/hdy ORIGINAL ARTICLE Uncovering the genetic signature of quantitative trait evolution with replicated time series data SU Franssen, R Kofler and C Schlötterer The genetic architecture of adaptation in natural populations has not yet been resolved: it is not clear to what extent the spread of beneficial mutations (selective sweeps) or the response of many quantitative trait loci drive adaptation to environmental changes. Although much attention has been given to the genomic footprint of selective sweeps, the importance of selection on quantitative traits is still not well studied, as the associated genomic signature is extremely difficult to detect. We propose ‘Evolve and Resequence’ as a promising tool, to study polygenic adaptation of quantitative traits in evolving populations. Simulating replicated time series data we show that adaptation to a new intermediate trait optimum has three characteristic phases that are reflected on the genomic level: (1) directional frequency changes towards the new trait optimum, (2) plateauing of allele frequencies when the new trait optimum has been reached and (3) subsequent divergence between replicated trajectories ultimately leading to the loss or fixation of alleles while the trait value does not change. We explore these 3 phase characteristics for relevant population genetic parameters to provide expectations for various experimental evolution designs. Remarkably, over a broad range of parameters the trajectories of selected alleles display a pattern across replicates, which differs both from neutrality and directional selection. We conclude that replicated time series data from experimental evolution studies provide a promising framework to study polygenic adaptation from whole-genome population genetics data.
    [Show full text]
  • Biol2007 - Evolution of Quantitative Characters
    1 BIOL2007 - EVOLUTION OF QUANTITATIVE CHARACTERS How do evolutionary biologists measure variation in a typical quantitative character? Let’s use beak size in birds as a typical example. Phenotypic variation (Vp) in a quantitative character Some of the variation in beak size is caused by environmental factors (VE). Some of the variation is caused by genetic factors (VG). If there was no variation in genotype between birds then individuals would differ in beak size only because of different rearing environments. Quantitative geneticists think in terms of how the value of a character in an individual compares to the mean value of the character in the population. The population mean is taken to be a neutral measure and then particular phenotypes are increases or decreases from that value. AT LEVEL OF INDIVIDUAL Phenotype = genotype + environment P = G + E AT LEVEL OF POPULATION Phenotypic variance = genotypic variance + environmental variance VP = VG + VE Genotypic variance is divided into additive, dominance and interaction components VG = VA + VD + V I VA = Additive variance – due to the additive effects of individual alleles (inherited) VD = Dominance variance - reflect the combinations of alleles at each locus (homo- versus (homozygotes versus hetero-zygotes) in any given generation but are not inherited by offspring. An intra-locus effect. VI = Interaction/epistatic variance - reflect epistatic interactions between alleles at different loci. Again not passed onto offspring; they depend on particular combinations of genes in a given generation and are not inherited by offspring. An inter-locus effect. ___________________________________________________________ The following section (italicised) provides the alebgra to backup my assertion that VD and VI are not heritable.
    [Show full text]
  • Directional Selection Can Drive the Evolution of Modularity in Complex Traits
    Directional selection can drive the evolution of modularity in complex traits Diogo Melo1 and Gabriel Marroig Departamento de Genética e Biologia Evolutiva, Instituto de Biociências, Universidade de São Paulo, Sao Paulo, SP 05508-090, Brazil Edited by Stevan J. Arnold, Oregon State University, Corvallis, OR, and accepted by the Editorial Board December 2, 2014 (received for review December 9, 2013) Modularity is a central concept in modern biology, providing a promotes changes in only one trait of a module, the other traits powerful framework for the study of living organisms on many within this module will suffer an indirect selection pressure and organizational levels. Two central and related questions can be change as well, even if this response leads to lower fitness (8). This posed in regard to modularity: How does modularity appear in the indirect response in other traits is due to their genetic correlation first place, and what forces are responsible for keeping and/or with the selected trait. Understanding how traits become associated, changing modular patterns? We approached these questions using or correlated, is therefore a central question in evolutionary biology. a quantitative genetics simulation framework, building on pre- The question of how modular patterns evolve in each level of vious results obtained with bivariate systems and extending them complexity is still open to intense scrutiny (9–11). In morpho- to multivariate systems. We developed an individual-based model logical systems, one condition for the evolution of variational capable of simulating many traits controlled by many loci with pattern is the existence of genetic variation in the association variable pleiotropic relations between them, expressed in pop- between traits in a population.
    [Show full text]
  • Mutational Pleiotropy and the Strength of Stabilizing Selection Within and Between
    Genetics: Early Online, published on February 1, 2018 as 10.1534/genetics.118.300776 1 2 Mutational pleiotropy and the strength of stabilizing selection within and between 3 functional modules of gene expression 4 5 6 7 Julie M. Collet*1, Katrina McGuigan, Scott L. Allen, Stephen F. Chenoweth, Mark W. Blows 8 School of Biological Sciences, The University of Queensland, 4072, Australia 9 1current affiliation: CBGP, INRA, CIRAD, IRD, Montpellier SupAgro, Univ. Montpellier, 10 Montpellier, France 11 12 Data Archival Location: NCBI Gene Expression Omnibus (N lines: GSE49815; S lines: 13 GSE54777). 14 15 1 Copyright 2018. 16 Variational and functional modularity 17 Keywords: modularity, pleiotropy, genotype-phenotype map, Drosophila serrata, gene 18 expression 19 * corresponding author: [email protected] 20 ABSTRACT 21 Variational modules, sets of pleiotropically covarying traits, affect phenotypic evolution, and 22 therefore are predicted to reflect functional modules, such that traits within a variational 23 module also share a common function. Such an alignment of function and pleiotropy is 24 expected to facilitate adaptation by reducing the deleterious effects of mutations, and 25 allowing coordinated evolution of functionally related sets of traits. Here, we adopt a high- 26 dimensional quantitative genetic approach using a large number of gene expression traits in 27 Drosophila serrata to test whether functional grouping, defined by GO terms, predicts 28 variational modules. Mutational or standing genetic covariance was significantly greater 29 than among randomly grouped sets of genes for 38% of our functional groups, indicating 30 that GO terms can predict variational modularity to some extent. We estimated stabilizing 31 selection acting on mutational covariance to test the prediction that functional pleiotropy 32 would result in reduced deleterious effects of mutations within functional modules.
    [Show full text]
  • Pleiotropy As a Factor Maintaining Genetic Variation in Quantitative Characters Under Stabilizing Selection
    Genet. Res. Camb. (1996), 68, pp. 65-73 With 1 text-figure Copyright © 1996 Cambridge University Press 65 Pleiotropy as a factor maintaining genetic variation in quantitative characters under stabilizing selection A. GIMELFARB Department of Ecology and Evolution, University of Chicago, Chicago, IL 60637, USA (Received 11 July 1995 and in revised form 16 January 1996) Summary A model of pleiotropy with TV diallelic loci contributing additively to N quantitative traits and stabilizing selection acting on each of the traits is considered. Every locus has a major contribution to one trait and a minor contribution to the rest of them, while every trait is controlled by one major locus and N—\ minor loci. It is demonstrated that a stable equilibrium with the allelic frequency equal to 0-5 in all A' loci can be maintained in such a model for a wide range of parameters. Such a ' totally polymorphic' equilibrium is maintained for practically any strength of selection and any recombination, if the relative contribution by a minor locus to a trait is less than 20 % of the contribution by a major locus. The dynamic behaviour of the model is shown to be quite complex with a possibility under sufficiently strong selection of multiple stable equilibria and positive linkage disequilibria between loci. It is also suggested that pleiotropy among loci controlling traits experiencing direct selection can be responsible for apparent selection on neutral traits also controlled by these loci. mutation-selection balance models, it remains un- 1. Introduction certain whether this mechanism can account for the The maintenance of genetic variation under natural amounts of genetic variation in quantitative characters selection in multilocus genetic systems controlling that are observed in natural populations (Barton & quantitative traits is an important and long-standing Turelli, 1989; Keightley & Hill, 1990).
    [Show full text]