The Quantitative and Molecular Genetic Architecture of a Subdivided SpeciesMichael Lynch; Michael Pfrender; Ken Spitze; Niles Lehman; Justin Hicks; Deborah Allen;Leigh Latta; Marcos Ottene; Farris Bogue; John ColbourneEvolution, Vol. 53, No. 1. (Feb., 1999), pp. 100-110.Stable URL:http://links.jstor.org/sici?sici=0014-3820%28199902%2953%3A1%3C100%3ATQAMGA%3E2.0.CO%3B2-7Evolution is currently published by Society for the Study of Evolution.Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available athttp://www.jstor.org/about/terms.html. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtainedprior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content inthe JSTOR archive only for your personal, non-commercial use.Please contact the publisher regarding any further use of this work. 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For more information regarding JSTOR, please contact [email protected]://www.jstor.orgThu Aug 30 13:10:13 2007Elolirrio~i,53(1). 1999. pp. 100-1 10 THE QUANTITATIVE AND MOLECULAR GENETIC ARCHITECTURE OF A SUBDIVIDED SPECIES MICHAELLYUCH,~ MICHAEL KENSPITZE,' DEBORAHPFRENDER,~ NILESLEHMAU,~JUSTIUHICKS,~ ALL EN,^ LEIGHLATTA,~MARCOSOTTEUE,' FARRISBOGLE,~ AND JOHNCOLBOCRUE~ 'Departnzent of Bzologj, Uizzve~s~t) of Oregoiz, Eugene, Oregon 97403 'E-nzazl nzlj izch @oregoiz ~~oregolz edzc 3Departnzent of Bzologj, Unzvers~t) of Mzanzz, Cola1 Gables, Flol~c-la 33124 4Departnzent of Bzologzcal Sc~ences, Unzvers~h at Alban>, State Unzverszn of New York, Albanj, ~Velt Yolk 12222 5Departnzent of Zoolog), Unzverszt[) of G~relph, Guelplz, Oiztar~o hTlG 2W1, Cailada Abstract.-In an effort to elucidate the evolutionary mechanisms that determine the genetic architecture of a species, we have analyzed 17 populations of the microcrustacean Dnphizia pzile.~ for levels of genetic variation at the level of life-history characters and molecular markers in the nuclear and mitochondrial genomes. This species is highly subdivided, with approximately 30% of the variation for nuclear molecular markers and 50% of the variation for mitochondrial markers being distributed among populations. The average level of genetic subdivision for quantitative traits is essentially the same as that for nuclear markers, which superficially suggests that the life-history characters are diverging at the neutral rate. However, the existence of a strong correlation between the levels of population subdivision and broadsense heritabilities of individual traits argues against this interpretation. suggesting instead that the among-population divergence of some quantitative traits (most notably body size) is being driven by local adaptation to different environments. The fact that the mean phenotypes of the individual populations are also strongly correlated with local levels of homozygosity indicates that variation in local inbreeding plays a role in population differentiation. Rather than being a passive consequence of local founder effects, levels of homozygosity may be selected for directly for their effects on the phenotype (adaptive inbreeding depression). There is no relationship between the levels of variation within populations for molecular markers and quantitative characters. and this is explained by the fact that the average standing genetic variation for life-history characters in this species is equivalent to only 33 generations of variation generated by mutation. Key I-vords.-Dnphnia pulex, genetic architecture. life-history evolution, microsatellite loci, mitochondrial DNA. quan-titative genetics. Received March 3, 1998. Accepted October 19, 1998. A comprehensive understanding of phenotypic evolution more demanding than for molecular variation. This is because at the species level requires information on the evolutionary most phenotypic traits are products of genes, environment, forces operating on populations and on the relative conse-and developmental noise, whereas most molecular marker quences of such forces for phenotypic divergence within and profiles are insensitive to variation in the environment. As a among populations. Numerous studies have surveyed the dis- consequence, only a few attempts have been made to com- tribution of molecular genetic variation within and among prehensively investigate patterns of molecular and quanti- natural populations of plants and animals (reviewed in Avise tative-genetic variation at both the within- and among-pop- 1994), but while a few exceptions exist (e.g., Hollocher et ulation levels (Prout and Barker 1993; Spitze 1993; Long and al. 1992; Lai et al. 1994), such assays generally yield very Singh 1995; Podolsky and Holtsford 1995; Bonnin et al. little direct insight into the process of phenotypic evolution. 1996; Yang et al. 1996; Kremer et al. 1997; Kuittinen et al. Molecular markers do, however, provide indirect insight into 1997). Thus, we still have only a crude understanding of the the evolutionary process. Markers such as allozymes, micro- forces that determine the range of phenotypic variation at the satellites, and RFLPs generally have weak enough associa- level of species. tions with the phenotype that, as a first approximation, their The purpose of this study is to investigate the genetic ar- evolutionary dynamics are often essentially immune to nat- chitecture of a highly subdivided species, the cladoceran ural selection on short time scales. This effective neutrality Dnpiznia p~~le,~, which is a common member of the zooplank- is an asset in that the theory of neutral genes can be used to ton community of temporary ponds throughout the Holarctic. estimate various aspects of gene flow,