DOI: 10.1126/science.1079707 , 1738 (2003); 299Science et al.Daniel D. Heath,Rapid Evolution of Egg Size in Captive Salmon www.sciencemag.org (this information is current as of January 12, 2007 ):The following resources related to this article are available online at http://www.sciencemag.org/cgi/content/full/299/5613/1738version of this article at: including high-resolution figures, can be found in the onlineUpdated information and services, http://www.sciencemag.org/cgi/content/full/299/5613/1738/DC1 can be found at: Supporting Online Materialfound at: can berelated to this articleA list of selected additional articles on the Science Web sites http://www.sciencemag.org/cgi/content/full/299/5613/1738#related-content 40 article(s) on the ISI Web of Science. cited byThis article has been http://www.sciencemag.org/cgi/content/full/299/5613/1738#otherarticles 9 articles hosted by HighWire Press; see: cited byThis article has been http://www.sciencemag.org/cgi/collection/evolutionEvolution : subject collectionsThis article appears in the following http://www.sciencemag.org/help/about/permissions.dtl in whole or in part can be found at: this articlepermission to reproduce of this article or about obtaining reprintsInformation about obtaining registered trademark of AAAS. c 2006 by the American Association for the Advancement of Science; all rights reserved. The title SCIENCE is a CopyrightAmerican Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. Science (print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by the on January 12, 2007 www.sciencemag.orgDownloaded fromRapid Evolution of Egg Size inCaptive SalmonDaniel D. Heath,1* John W. Heath,2Colleen A. Bryden,3Rachel M. Johnson,4Charles W. Fox5Captive breeding and release programs, widely used to supplement popu-lations of declining species, minimize juvenile mortality to achieve rapidpopulation growth. However, raising animals in benign environments maypromote traits that are adaptive in captivity but maladaptive in nature. Inchinook salmon, hatchery rearing relaxes natural selection favoring largeeggs, allowing fecundity selection to drive exceptionally rapid evolution ofsmall eggs. Trends toward small eggs are also evident in natural populationsheavily supplemented by hatcheries, but not in minimally supplementedpopulations. Unintentional selection in captivity can lead to rapid changesin critical life-history traits that may reduce the success of supplementationor reintroduction programs.The use of captive breeding programs iswidespread, and increased use of such pro-grams for species preservation has been rec-ommended (1, 2). However, there is consid-erable debate over the wisdom of “ex situ”conservation because of the cost, disease risk,and possible genetic impacts (1–6). One po-tential genetic impact associated with captivebreeding is unintentional selection (3, 4, 7).Although the possibility of unintentional se-lection in the captive environment is oftensuggested (4, 7), there is little empirical ev-idence. Most studies have been based onphenotypic differences between captive- andwild-bred individuals and do not differentiatebetween acclimation or behavioral condition-ing, and true genetic evolutionary responses(8). Because mortality is generally low inwell-managed captive populations, the poten-tial for large selection-driven effects isthought to be low (8, 9). However, this re-duction in mortality may itself drive the evo-lution of traits that increase fecundity at theexpense of offspring survival under nonman-aged conditions.In salmon, ex situ conservation takes theform of “supplemental” breeding (8, 10, 11);returning adult salmon are artificially spawnedand their offspring reared in hatcheries untilthey are released back into the river as fry. Thenumber of released hatchery-reared salmon fryaveraged over 550 million per year from 1987to 1996 in British Columbia, Canada (12).Although the practice of supplemental breed-ing is expected to have less impact thancaptive breeding programs on the genetic ar-chitecture of the population (8, 10), there is1Great Lakes Institute for Environmental Research andDepartment of Biological Sciences, University ofWindsor, 401 Sunset Avenue, Windsor, Ontario N9B3P4, Canada.2Yellow Island Aquaculture Limited,1681 Brook Crescent, Campbell River, British Colum-bia V9W 6K9, Canada.3AXYS Environmental Consult-ing Limited, 2045 Mills Road West, Sidney, BritishColumbia V8L 3S8, Canada.4Biology, College of Sci-ence and Management, University of Northern BritishColumbia, 3333 University Way, Prince George, Brit-ish Columbia V2N 4Z9, Canada.5Department of En-tomology, University of Kentucky, S-225 Ag ScienceCenter North, Lexington, KY 40546– 0091, USA.*To whom correspondence should be addressed. E-mail: [email protected]. 1. Relationships between egg mass and (A)early juvenile survival and (B) relative fecundityin chinook salmon; each point represents afull-sib family from a single dam. (A) Egg masswas measured as the mean mass of 20 to 50unfertilized eggs taken from 3-year-old dams atthe time of spawning. Each family was sepa-rately incubated in vertical stack incubationtrays, and all families were spawned over a7-day period. Early survival was measured bycounting eggs at fertilization and documentingmortality to the onset of exogenous feeding.All relationships were significant at the P ⬍0.01 level or higher (nonlinear regression anal-ysis). (B) Relative fecundity was calculated asthe total number of eggs produced divided bythe total body mass of the dam (aged 3 and 4years); this transformation assumes a linearrelationship between female body mass andegg number, which was the case in all yearsexamined (linear regression coefficient equal toor greater than those for power function, ex-ponential, and log-linear curves). Examinationof residuals showed no bias, and leverage was⬍0.10 for all points in all years. Relationshipsbetween relative fecundity and egg size weresignificant at the P ⬍ 0.0001 level (regressionanalysis). The study population was founded in1985 with fertilized eggs from the RobertsonCreek hatchery and has been maintained with⬍200 parental fish per generation at the YIALfacilities.R EPORTS14 MARCH 2003 VOL 299 SCIENCE www.sciencemag.org1738 on January 12, 2007 www.sciencemag.orgDownloaded fromstill considerable controversy (3, 8, 11), and anumber of studies have