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Quantitative genetics and management of wild populations
Quantitative gciletics and management of wild populations
The traditinnal strltcgw for managcmcnr and prcwrvatlon tit’ UIIJ populatwns ha\c focuv*d on gvnctiv pwpcrtio lhbt may bc rhwactcrircd in tc’r,ris of:rllcl~c v:iri::tion. Stud& on Notxcgian s:raln$ of 4tlanllc sillnion indicnte thal IIlk 0’ .I,~.w~c~~ral t’ramcaarh may bc too restricted to provide z?propriale management stratcglcs. it i5 suggcs;c d that the con~cptsol’quantitati~c‘gcnctrcs should hc cpplied as an additional source of information to Improve the strategies.
.11.1 *-rR::;: -;C‘T;,:N
The &sic concepts oiq!rantitat;ve genetics were developed around the start oi this ct:w~ry h:, rionccrs l&r: F .2&n, K. Pearson, R.;l. Fisher and S. Wright. -The regularities of the inheritance o? meristic traits were d-Abed in mathematical and statistical terms. and the models ..crc exte.,,ed tc explain evoirltion,?ry processes and the gcnctic dynamic? nf populations (see e.g. Mather and !inks, 197 I; Lande, 1988: Falconcr. I989 1. Quantitative genetics assume tb3t most !raits c1 mrc i--” I,,...~.;r~~~by a Inrge number ot’urritientified genes and that the genetic performance of an individua! is the ~.~c::rnul:tcd effxt of all such genes. A certain accumuktcd gcnotypk vatI:;: dc.::s IIOL ~&ct a fixed. urAque s&t of alleles. but t*lay occur a~ a result of a large number I>I different allttie combinations. It :cmrns likely that this assumption is true for tl aits I ihe gent&mlsurviv n! Ind reproductive successin wild populations ( r,‘~ow, 1989). The qlrantitative approach grovidcd :;olutions to several paradoxes in classical Vendt-lian genetics when applied to evolutionary processes. Lcng-tn_rru c! -ectional selection tin sing:? gzncs in closed populations was exprltcd to result tn tixa;ion and loss of G&s. Sti!l. genetic variations sxms 1~1be ,rldint;rir.cd iI1 mnst popuM:zc under c!:rectionA sclcction. tn quan?itativz genetics. substantial I :.~pc-~sc!C 4erticn may be explained witnout assuming large cl:anges in frequencieb of single alleles.
alleles in different populations). Furthermore, quantitative studies of different body size measurements have shown thal the genetic variation between river strains of Norwegian salmon is quite narrow compared to the variation within strains (Gunnes and Gjedrem. 1978: Rehie and Stcine. 1978).
MANAGEMENT
OF QCIANTIT%TIVE
PROPERTIES
The strategies for management and prcseripation of wild populations should be chosen according to the expected level of genetic diversification between populations. Strategies designed to maintain the qualitative :,,enetic properties of a population ;lay be totally inefficient if ttc poput.ltiu,,:: arc characterized by allele frequencies rather than unique attetcs. The qua!itative approach may encourage the popular assumption that any lndlvtdua! in ;I given population is carrying the unique genetic setup of the popuiation. ‘This may lead to stock reinforcement programs or cryopreservation programs based on small numbers of selected breeders. Until now. this has been a common strategy in the management of many Norwegian salmon strains. However, this approach is not expected to maintain the allele frequencies of the population. Equal contributions from a large numter of random breeders are needed if the aim is preservation of quantitative properties. Furthermore. if ti strain or popula tion is threathened by cotfagse because of tow survival rates until breeding, the qualitative approach will tend to emphasize measures IO prevent immigration frcjm other populations. However, the main effects of such gc netic bottlenecks on the quantitative properties of the population *it! bc ret:uccd genetic variability. reduced adaptability tc, crlr;ironmcntat changes, inc;:;lrcd inbreeding and increased risks of extinction. A quantitative managcament strategy wcll!d then bc to reintroduce any lost genetic variability by incrclsing the immigration tales from populations that are not expected to differ qu~tittitively from the nczr ai:cestcrs (If the thrcatcncd po~&arion. Finally. the entire concept of g,;retic preservation of populations :,houtd probably bc reconsidered. if the: genetic Jibcrsilication I;ctwccn popuMc.ns has not reached a quatitatil c tevc!. Continuous changes of altelr* frcqLcncies are a major component of the short-term genetic dynamics ot’porlulatic)ns. In ~IIIAI, uprdri @,upULiiullS i;k: luorwegian salmon StUii;-, allele t’rcquenr lex 3re no! expected to be constant 01 er long pcrious. Thr: all& frequencies of today arp probably not tinique pm.iacts of !g,ng-term cv~!ui;e>n \l~lt)lil, czcb strain, but rather the results of recc;nt events, inc1udir.g human manipulation such as seLTr*tive liarvesting. stoch reinforcement programs within and across; popuhthr ?nrl ,:vir(:;;;;;:L;; ;II disturbances tiffcc:in;; ;hc natural sclcctiorl in the . 5 r3.4er strains.
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ti.tl
BENTSkN
.I \ 1.. IUK~ (&itntllaIlvc gcnr~ks. cr~olog~ and cvolutiqn. In. CIS. Weir. E.J. Eiscn. Inlcrnat~onalC’onMM ( ;q4rll:in 3nd (;. Y:rnrk.clcrng ( 7. i~t~rrs). I’rclccr~dingsoflhcSc~l~nr! Icrcncl. on t,)u;lntlt3tlvc trcnctlcs. Ralctgh. NC’. 31 Ma)-5 June 1987. Smautr. Sundcrland pp. Wh-boo. In; W.G. Hill and T.F.C. Mackay “IOW. J.);.. 19119. Fttnpss v;lri;*‘!nS i* natural populations. . (Editors). Evolution and Animal BrccJ;ng. <‘.X.B. lntctnational. Walhugforl: pp. 91-97. Falkxlncr. D.S., 1989. Quantitative Genetics. Longman Scientific& Technical. Harlow. 47.I pp. Gunncs. K. and Gjedrcm. 1.. 1978. Sclcctioll ?apcriments v:ll ’ ;a salmon. IV. Growth of Atiantic salmon during two years in the sea. Aquaculturc. 15: ;9-33. L;lndc. P lY88. Quantitative pcnctics and evolutionary theory. In: B.S. Weir, E.J. Eisi,i. M.M. Confcr(Goodman and (i Namkoong (Editors ;. Proceedings ni the Second Internarional I’~CI’on Quant Itatt T (;cnrtics. Raleigh, NC’. 3 I May-5 June 1987. Siuaucr. Sundcrland. pp. 7 I-b. H ,,I :.,*I
5 I t K’S, I‘U4 I. I’rcrcxx+dlng\ ol’thc 148 I Stock f‘llncc*nt lnlcrnational Svmpozirlm (STOCS). Al“. ISST-!U23. I~xrm. t )nt.. 29 Scptrmbcr-9 t j
57 1’1’
The traditinnal strltcgw for managcmcnr and prcwrvatlon tit’ UIIJ populatwns ha\c focuv*d on gvnctiv pwpcrtio lhbt may bc rhwactcrircd in tc’r,ris of:rllcl~c v:iri::tion. Stud& on Notxcgian s:raln$ of 4tlanllc sillnion indicnte thal IIlk 0’ .I,~.w~c~~ral t’ramcaarh may bc too restricted to provide z?propriale management stratcglcs. it i5 suggcs;c d that the con~cptsol’quantitati~c‘gcnctrcs should hc cpplied as an additional source of information to Improve the strategies.
.11.1 *-rR::;: -;C‘T;,:N
The &sic concepts oiq!rantitat;ve genetics were developed around the start oi this ct:w~ry h:, rionccrs l&r: F .2&n, K. Pearson, R.;l. Fisher and S. Wright. -The regularities of the inheritance o? meristic traits were d-Abed in mathematical and statistical terms. and the models ..crc exte.,,ed tc explain evoirltion,?ry processes and the gcnctic dynamic? nf populations (see e.g. Mather and !inks, 197 I; Lande, 1988: Falconcr. I989 1. Quantitative genetics assume tb3t most !raits c1 mrc i--” I,,...~.;r~~~by a Inrge number ot’urritientified genes and that the genetic performance of an individua! is the ~.~c::rnul:tcd effxt of all such genes. A certain accumuktcd gcnotypk vatI:;: dc.::s IIOL ~&ct a fixed. urAque s&t of alleles. but t*lay occur a~ a result of a large number I>I different allttie combinations. It :cmrns likely that this assumption is true for tl aits I ihe gent&mlsurviv n! Ind reproductive successin wild populations ( r,‘~ow, 1989). The qlrantitative approach grovidcd :;olutions to several paradoxes in classical Vendt-lian genetics when applied to evolutionary processes. Lcng-tn_rru c! -ectional selection tin sing:? gzncs in closed populations was exprltcd to result tn tixa;ion and loss of G&s. Sti!l. genetic variations sxms 1~1be ,rldint;rir.cd iI1 mnst popuM:zc under c!:rectionA sclcction. tn quan?itativz genetics. substantial I :.~pc-~sc!C 4erticn may be explained witnout assuming large cl:anges in frequencieb of single alleles.
alleles in different populations). Furthermore, quantitative studies of different body size measurements have shown thal the genetic variation between river strains of Norwegian salmon is quite narrow compared to the variation within strains (Gunnes and Gjedrem. 1978: Rehie and Stcine. 1978).
MANAGEMENT
OF QCIANTIT%TIVE
PROPERTIES
The strategies for management and prcseripation of wild populations should be chosen according to the expected level of genetic diversification between populations. Strategies designed to maintain the qualitative :,,enetic properties of a population ;lay be totally inefficient if ttc poput.ltiu,,:: arc characterized by allele frequencies rather than unique attetcs. The qua!itative approach may encourage the popular assumption that any lndlvtdua! in ;I given population is carrying the unique genetic setup of the popuiation. ‘This may lead to stock reinforcement programs or cryopreservation programs based on small numbers of selected breeders. Until now. this has been a common strategy in the management of many Norwegian salmon strains. However, this approach is not expected to maintain the allele frequencies of the population. Equal contributions from a large numter of random breeders are needed if the aim is preservation of quantitative properties. Furthermore. if ti strain or popula tion is threathened by cotfagse because of tow survival rates until breeding, the qualitative approach will tend to emphasize measures IO prevent immigration frcjm other populations. However, the main effects of such gc netic bottlenecks on the quantitative properties of the population *it! bc ret:uccd genetic variability. reduced adaptability tc, crlr;ironmcntat changes, inc;:;lrcd inbreeding and increased risks of extinction. A quantitative managcament strategy wcll!d then bc to reintroduce any lost genetic variability by incrclsing the immigration tales from populations that are not expected to differ qu~tittitively from the nczr ai:cestcrs (If the thrcatcncd po~&arion. Finally. the entire concept of g,;retic preservation of populations :,houtd probably bc reconsidered. if the: genetic Jibcrsilication I;ctwccn popuMc.ns has not reached a quatitatil c tevc!. Continuous changes of altelr* frcqLcncies are a major component of the short-term genetic dynamics ot’porlulatic)ns. In ~IIIAI, uprdri @,upULiiullS i;k: luorwegian salmon StUii;-, allele t’rcquenr lex 3re no! expected to be constant 01 er long pcrious. Thr: all& frequencies of today arp probably not tinique pm.iacts of !g,ng-term cv~!ui;e>n \l~lt)lil, czcb strain, but rather the results of recc;nt events, inc1udir.g human manipulation such as seLTr*tive liarvesting. stoch reinforcement programs within and across; popuhthr ?nrl ,:vir(:;;;;;:L;; ;II disturbances tiffcc:in;; ;hc natural sclcctiorl in the . 5 r3.4er strains.
,‘hh
ti.tl
BENTSkN
.I \ 1.. IUK~ (&itntllaIlvc gcnr~ks. cr~olog~ and cvolutiqn. In. CIS. Weir. E.J. Eiscn. Inlcrnat~onalC’onMM ( ;q4rll:in 3nd (;. Y:rnrk.clcrng ( 7. i~t~rrs). I’rclccr~dingsoflhcSc~l~nr! Icrcncl. on t,)u;lntlt3tlvc trcnctlcs. Ralctgh. NC’. 31 Ma)-5 June 1987. Smautr. Sundcrland pp. Wh-boo. In; W.G. Hill and T.F.C. Mackay “IOW. J.);.. 19119. Fttnpss v;lri;*‘!nS i* natural populations. . (Editors). Evolution and Animal BrccJ;ng. <‘.X.B. lntctnational. Walhugforl: pp. 91-97. Falkxlncr. D.S., 1989. Quantitative Genetics. Longman Scientific& Technical. Harlow. 47.I pp. Gunncs. K. and Gjedrcm. 1.. 1978. Sclcctioll ?apcriments v:ll ’ ;a salmon. IV. Growth of Atiantic salmon during two years in the sea. Aquaculturc. 15: ;9-33. L;lndc. P lY88. Quantitative pcnctics and evolutionary theory. In: B.S. Weir, E.J. Eisi,i. M.M. Confcr(Goodman and (i Namkoong (Editors ;. Proceedings ni the Second Internarional I’~CI’on Quant Itatt T (;cnrtics. Raleigh, NC’. 3 I May-5 June 1987. Siuaucr. Sundcrland. pp. 7 I-b. H ,,I :.,*I
5 I t K’S, I‘U4 I. I’rcrcxx+dlng\ ol’thc 148 I Stock f‘llncc*nt lnlcrnational Svmpozirlm (STOCS). Al“. ISST-!U23. I~xrm. t )nt.. 29 Scptrmbcr-9 t j
57 1’1’