...-...:.. - .... ---.

This paper not to be cited without prior reference to the author

International Council for theExploration of the Sea

C.M.1983/F: 11Mariculture Cttee.

•RECENTLY REPORTED, CURRENTLY FUNDEO OR PROPOSED U.S. STUDIES

IN AQUACULTURE GENETICS, OR ON GENETICS OF NATURAL OR STOCKED POPULATIONSOF SOME RELEVANCE TO CONCEPTS OF STOCK MANAGEMENT *

A. Crosby Longwell

National Marine Fisheries ServiceNortheast Fisheries Center

Milford LaboratoryMilford, Connecticut 06460

* First presented as a background paper at the April 27-29,meeting of the Genetics Working Group, Lowestoft, U.K.

.-~

University Programs Supported by the Oepartment of Agriculture Current andRecentlyCompleted ::",' ", i . ,:: ,';' ,::";:,,., ..

~~.: '.".

Oysters

At high MSX prevalence levels in Oelaware Bay in 1980, laboratory-bred stocks

of resistant oysters experienced mortality rates 20~50% those of native,wild:stocks

which also developed, through natural selection, .some degree.of diseas~:resistance

(H. H. Haskin, Rutgers University, New Brunswick, New Jersey).

. . .

At the University cf Guam, Agana, Guam, .there is 'an ongoing 'attempt to effect

an interspecies hybridization of Macrobrachium (0. E. ·Matlock).

Salmonids

t. '.' Freshwater Prawn ••The genetic basis of electrophoretically variable enzymes in brook, brown,

rainbow and lake trout and their hybrids is the subject of past and continuingre­

search at Pennsylvania State University, Univers~ty Par~ (J. E. Wright), aimed.at

understanding the evolution of trout genomes. Extensive cytogenetic analyses are

performed, including chromosome banding and meiotic studies of.both.spermatocytes

and oocytes, the first such 'in-depth analyses accomplished on an aquacul,tured fish

species. ~

In an ongoing breeding;and g~netic study at the University of California (Oavis)

significant non-genetic sources of variation were found to influence growth rate in

rainbow trout - spawn date, itank, density, stress',' water temperature and rate of

sexual maturation (G. A. E. Gall). However, growthto one year was fOlmdto :be

heritable.' Rainbow trout and golden trout crosses produced viablesecond genera­

tion progeny. Also, standard electrophoretic and histochemical techniques are

being used to identifyprotein and enzyme polymorphisms inwildtrout populations.

Mosaicpolyploids were'produced in brook trout by cold shock (University of,

Rhode Island, Kingston, L. T. Smith). These appeared to grow at a faster rate

than non-polyploids, but no~sterility was noted.

- 2 -

•

Catfish

Quantitative data on the growth rates cf different strains of channel catfish,

and their performance on differentdietary formulations were recently collected at

Kansas State University, 'Manhattan (J. R: Kelley, Jr., C. Deyce, and B. E. Klaassen).

At'A~burn University, Auburn, Alabama, realized heritability for body weight

in a wild strain of channel catfish was found to be sufficient to Yield an 11%

increase in growth through one generation of selection. Generally, intra-specific

crossability did not differ, but only crossbred individuals hybridiied with blue

catfish~Genotype x environment interactions were significant when the environ­

mental variable was stocking density (R. O. Smitherman).

A bi-directional selection program for body weight and size uniformity at the

Georgia Coastal Plan Experiment Station, Tifton, increased body weight in one" .

generation about 22%, and total length ~bout 9% at 40 weeks of age. The rates of

decline in the downward direction were about 19% and 4%, respectively. One genera­

tion of inbreeding in channel catfish resulted in about 7% and 6% growth depression

at 16 and 40 weeks of age, respectively (K. Bondari, T. K. Hill~ and J~ W. Andrews, Jr.).

The genetic variability"inmortality rate at a low level of dissolved oxygen

was .recently examined for somegeographic strains and families of catfish (Louisiana

State University, Baton Rouge, J. W. Avault).

Striped Bass

At North Carolina State University, Raleigh, the potential of striped bass x

white bass, and striped bass x white perch hybrids was evaluated for use in aqua­

culture (J. H. Kerby, M. T. Huish, and K. R. Keller).

~ 3 -

,----------- ---- ------- - - -- --- ---- ------------ -----

..

Projects Recently Completed or Ongoing Under the Sea Grant Program

Clams

An effort was recently completed to develop improved strains.,of.cthe. hard. clam.,.' '.

(Mercenaria mercenaria) for maric~lt~re by determining relationships between allo-~ . ~ . ' '., ,. .

zyme genotypes, production: characters, fertil i.ty andfecundity. (C. Adamkewicz,

George Mason University).

Shrimp and Crawfisn

At the South Carolina.Sea Grant.Consortium, the.mechanics.of~hrimp and craw-

fish ~ertilizati~n are being studied, and reproductive structures and behavio~. are ~,

being described with the intent of developing successful in vitro fertilization.- .

I

penaeid shrimp and stocks are being selected: • I

Hou~t~~ (J. Lester). One ~urpose of this is,

to survey genetic variation within• h • .

and among geographie populations of three Penaeus shrimp in_the Gulf of Mexico.:'.'. . . I ; . .,' .;- " ,",

.Eff~~ts ~re being expended:on development of a method of.obtainingandusing

' .. electrophoretic genotypes of female broodstock.and progeny to estimate herita-.' I.. ~. ". . , " . ~ ~

bilities of commercially important traits. Selection crite~ia based o~m~rphometric~

analysis are being planned.

t ." ..Lobster

,<

. Among other .objectives of a research program at the University of C~lifornia• .' '. i·'... ..... ',\

at Riverside, is the determination of how long lobster sperm can be stored in,vitro. .. . \ ., .,. ..

in spermatophores (P. Talbot).

. i : Salmon

At the University of Alaska the biochemical genetic ,variability of presumed• .• . ~', t .' . ~ _. .' ••

discrete breeding groups,of pink salmon was examined. The.purpose wasto examine. . . ~ .' ". ;.' '- , .',

ultimately the extent tO.which Auke Creek.hatchery.fish.interbreed.with naturally, .' • • J <' , '. _ .'~' • '. " •

- 4

spawned stock in Auke Creek. Genetic tags were developed in a stockt and effects

of these on viability await further study. The genetic differentiation of some

natural stocks was demonstrated (G. Gharrett).

The rate of return of various donor stocks of chum salmon and their crossbreeds

to a newhatchery is the subject of another study at the same university (Wo Smoker).

The long-range goal of a University of Washington project is the development

of a eoho salmon stock with desired traits for marine fish eulture (Wo Hershberger).

Recombinant DNA technology is being used at Oregon State University to develop

~ viral vaccines in fish. The model virus being used is the infectious pancreatic

necrosis virus (J. Fryer).

Yellow Perch(as a representative eoolwater fish)

The feasibility of employing androgens t estrogens t and related anabolie sub­

stances in coolwater fish culture to control sexual differentiation and enhance

•

growth and ,food conversion efficiency is being examined at the University of

Wisconsin (C. Amundson and T. Kayes). There appear to be no direct growth-promoting

effects in 17-30 mm perch t but after treatment was terminated t fish treated with

high doses grew far faster than normal. It appears that the sex of perch and

walleye can be manipulated by incorporating androgens and estrogens in the diet of

the fish at the time of gonadal differentiation.

Cryopreservation

The continuing program on cryopreservation at the University of Minnesota now. .

has as its primary objective the examination of factors affecting the freezing t

storage t and thawing of the egg (both unfertilized and fertilized)t embryo and

fry - freshwater fish (E. Graham).

Sea Grant Aguaculture Plan'1983~1987

The following is an exeerpt from thisplan and two tables that treat the sub-

ject of ge~etics. This plan was prepared by the Aquaculture Committee of the

-"5 -

Council of Sea Grant Directors after soliciting contributions from aquaculture

researchers and the respective industries. The reco~ended targeting of funds,• I

Iaccording to development of'respective culture industries, reflects the current

administrative view in the U.S. that industry should conduct more ofits own re-I • •

search and development programs. It has been officially recommended that the Sea

Grant Program and federal laboratory research in aquaculture be terminated.

Whether this recommendation 'will be followed is still uncertain.

Programs Ongoing in Federal Laboratories

Northeast Fisheries Center, National ~1arine Fisheries Service, Milford(Connecticut) Laboratory e.

Oysters

The 'second generation of American oysters selected for fast and for slow growth

in a bi-directional selection experiment (the third hatchery-bred generation) failed

to provide sufficient gametes in the spring of 182 to produce a subsequent genera­

tion for selection. It is expected though that this will be accomplished this

spring. Performance was measured in 182, and these data provide a basis for de­

termining continued favorable response to selection for faster growth, its degree,

continuity, and limits (E. Losee, S. Stiles, A. Longwell and S. Dudley).

,The effect of high pressure on the segregation and other behavior of the meiotic ~

chromosome groups in spawned and fertilized oyster eggs is being examined with

respect to its likely application in obtaining haploid andjor polyploid oysters for

various purposes (So Stiles and J. Choromanski).

Northwest and Alaska Fisheries Center, Seattle Laboratory

Salmon

Female sex-reversal techniques have been attempted on Atlantic salmon using

DES, progesterone, and estradiol to induce early and/or synchronous maturation'and

ovulation.

I,I

- 6

Level of CommerclalDevelopment Specles

Table 1. Marin9 and Great Lakes orgaT'.ismsgroupedby level ofu.s.commercialllquacuftural d!Jvelopmenl.

EXCERPT FROM SEA GRANT AQUACULTURE PLAN1983-1987Genetics and Selective Breeding

. .Aquaculturc now raiscs l,asic<\IIy "wild" animals. 111

wiltl populations, ~cn<."tic \'ariatioo.is morc extcnsivctll~\Il in tnu]ilional ugricullural populations. This varia­til)li must 1Ic cvalualcd hcf(u"c scleclivc hrceding andgcnetic cilgincl'ring silIdies ('an Lc dOllc. J)Ol\lcsticalioll

" rC(luires l'OnlroI of mal 11 ration ,md rcproduction, und"s)'stcmatie changcs in th(~ gcnctic l11ake-Ull ofthc aquu­('ultural pOI)ubtion. AIIII:l<:ullunlI specics also exhibit 0.1

uumber oflmits that fi\cilitatc gcnclic manipulalion am]domcsti<·at.illil. These <\(.'colllplisllllll·n ts fCC(uirc thor­ough undcrstanding of rcprmluctive IIIcchanisllls und ofthe influence orcllvironmcntal stimuli, lIutrilional .mljllstmcnts amI ph)'siologieallllOl]iIlcations.

Aqllalic specit~s also display uniqllc propertic5. suchus indctcnninate growlh and u grt'atcr susl.·eplihility toenvironmcntal ami dClllogmphie inOuences, whi<.'h ren- .

. " der in:tppropriate many mcthotls ofgcnetic l11aninula-• tiOIl dcvclopcd for terrestrial organism5. l1lCrt'fore, new

experimental protocols and technologies I11I1St !Je devel­opell alollg with ur Lcfore gcnctic/rcprodlldive manipu­lalioll to makc fun use uf thc advantagcous properties.Nccds fur special stu<1ies include comparison ofcllviron­mcntally and gcnctil."ally caused variations in production;<lc\"(~I()plllentufcllcctivc metItods ur tag,~in~ individllals;and de\'clopmcnt uftcclmillllCS fi)r hromlstock manage­mcnt. These stm]ics willrcquirt> a lung-t<:nllcoonli­nated effort.

lähll! 3 gh'cs pCrl.·l·nta~(~sof<wai1.lhlc funding fi)r~Cllcti<:S stmlics that will he tar~ctl·d tn stmlies ofspc­einc prohl(>m5 in g(,llctics nnd selcctivc hrccding. hylen'l oftechnologie;)l dc"c1opmcnt. (Sec also TalJlc 1.)

•

Cornmercial Industry

Infant Industry

Technology Developedto Pilot Scala

Tcchnology PartiallyDevelop.ed

Major lack ofTcchnorogy

troutbailfishpenaeld shrimpprawns (Hawaii)salmon (neVpen rearing and ocean

ranching)yeJlow perch .oyster (hatcherylnursery production)musseIs .abaloneprawns (continenlal United States)scallops (bay and rock)

. seaweeds "clarnscelsbaitleechstriped basschannel bass .scallops (other than bay and rock)lobsterred drumsturgeonsoutharn f10underspeckled Irout

. red snapperpompanomilklishH2S ba,cteria

Tablo 3. nccommended targeting ollunds lor research in genetics .md selective breeding 01 aquacultural organisms. Numbers arc .pcrcentages und ar/} based on iJ 100 percenllavel 01 funding for a speci..~s at each level ollcchnological d<Jvelopmenl. See also Table 1,which classifies aquacultural organisms by level 01 aquaculturallechnol('gical development.

Level of Technological Development

Research Problem

MaturationOvulation/spawningFertilization .Oromhto::.k managementStoct( '~varuation

Sr,lcclion.brccdingO"r.ct:c engineering

Total

Major lack ofTechnology

%555

15303010

100

Technology TechnologyPartlally Developed

Developed to Pilot Scale

% %10 1710 1710 1625 25:30 2015 5

100 100

- Ga -

InfantIndustry .

%403030

100

CommerclalInduslryExists

%50

.3020

100

Proposed National Fisheries Genetics Projects(U.S. Department of the Interior)

Draft plans call for the development of procedures for cryopreservation of

gametes or embryos of endangered species to conserve genetic resources of sport

fish which might otherwise be lost through artificial selection, hybridization in

nature, or through habitat degradation.

The need was noted for developing stocks of key sport fish able to better

withstand acid precipitation and heated effluents. A chronic problem with the

recommended use of the redear sunfish (Lepomis microlophus)with other centrarchids

. 4It for stocking midwestern and southern sport fishing grounds has been overpopulation

and stunting of the Lepomis. Some sunfish hybrids in the presence of largemouth

bass do not overpopulate or stunt at all as grown in midwestern U.S. ponds.

Hybrids though must yet be evaluated for use in ponds in southern U.S. states,

and this is proposed.

The national plan makes a case for application in current U.S. sport fish

culture of molecular and other new genetic techniques. As discussed in the pro­

posals, these include nuclear transplantation,cloning and gene transfer.

For information on the status of the proposals and details contact R. Gasaway,

R. B. Russell Federal Bldg., Atlanta, Georgia.

- 7 -

PART II. GENETICS OF NATURAL OR STOCKED POPULATIONS

Research by Species Group

Salmon

At the Northwest and Alaska Fisheries Center Seattle Laboratoryresearch con­

tinues in the development of genetic methods to identify stocks in domestic and

international mixed fisheries. The objective is to apply biochemicalgenetic

techniques for identification of upper and lower river stocks of chinook salmon

in the fishery at the mouth of the Columbia River. Collection of baseline genetic

information has been extended to include the Pacific coast from the Canadian boundary~.

to the Sacramento River.

The University of Alaska (A. Gharrett) has a grant to procure baseline data

relevant to the genetic structure of Alaskan chinook salmon stocks through electro­

phoretic techniques. Routine stock identification of the chinook there would help

with the current complex allocation problems and have international significance.

At the University of Massachusetts Fishery Cooperative Unit, electrophoretic

variation of successful Atlantic salmonrecruits to the Connecticut River restora-

tion project is being looked to for identification of the source of the successful

transplants. Many sources of salmon were used in restoring the run.

Trout* •At the University of California, Davis, Loudenslager and Gall studied genetic

differentiation and evolutionary relationships among 30 populations representing

5 subspecies of Salmo clarki, assaying 35 genetic loci with starch gel electrophoresis.

Using Nei's formulae, there is low genetic variability within, and great genetic

subdivision among subspecies inhabiting independent basins and drainages. Generally,

results are in agreement with chromosomal analysis of the groups and topographie

changes in western North America.

Busack and Gall compared two populations of Paiute cutthroat trout and Lahontan

cutthroat trout and rainbow trout meristically and electrophoretically. This was to

* Also see page 2 ref. to research of J. E. Wright.- 8 -

elucidate their population structure and verify suspected occurrence of intro-·

gressive hybridization. Evidence supports the introgression of rainbow trout

genes into a population of cutthroat trout in one creek. Electrophoresis seemed

more discriminatory than meristic characters in detecting introgression, but

application of both techniques is best in the view ·of these authors.

An electrophoretic survey of 26 loci in rainbow trout inhabiting a geo­

thermally heated stream in the Yellowstone National Park, Wyoming, revealed no

unique genotypes along a temperature gradient. Average heterozygosites for 2

~ stations along a gradient were not significantly different from one another or

from a hatchery strain from which founding fish were stocked years aga (Fisher

et al., University of California, Davis).

Electrophoretic variation in muscle lactate dehydrogenase in a cutthroat

trout subspecies has been studied at one of the National Fish Hatcheries'in

Virginia (Klar,et al.).

The influence of stocking'of hatchery trout on native stocks was examined

in grants to T. Bjornn, University of Idaho, andto H. Menzel, Iowa State Univer­

sity. Emphasis of these studies, though, was more ecological than genetic.

Marine Fish

~ Populationsof pricklebacks from California were sampled to determine whether

lactate dehydrogenase gene frequencies along an independent transect near the

southern end of the species distribution are consisterit with the interpretation

that geographie patterns reflect the influence of environmental factors. Obser­

vations suggest that this interpretation be reevaluated (Sassaman et al., Univer­

sity of California, Riverside).

In the milkfish, 38 loci were examined in samples from 4 locations across

the Pacific Ocean. The magnitude of interpopulation divergence was extremely

low, even between samples separated by up to 10,000 km. Considerable population

divergence at 4 polymorphie loci was seen between samples taken in Hawaii. Gene

- 9 -

flow there might be redueed by loeal oeeanie gyres: (Winans, Hawaii Institute of .

Marine Biology and University of Hawaii).

In an in'tense study atthe University of Ma ine, Kornfiel d et a1. found

genetic evidenee for discrete fall and spring spawning,populations. 'Ripe Atlantie

herring were sampled from 7 diserete spawning grounds in the Gulf of Maine and

Gulf of St. Lawr~nee over aperiod of 3 years. Five highly polymorphie loei were

used to assess the populatio~ strueture. Within both spring and fall spawning

population~,signi~ieant spatial heterogeneity was noted for partieular years

but was not temporally stable. The low levels of geneticheterogeneity and ab-,

senee of both temporal stability within fall spawning samples and spatial stability~

e·are not eonsistent with the existenee of mor~ than a single genetie population of

fall spawning herring in the northwest Atlantie.The Mendelian heritability of

the polymorphie loei employed was earlier established through breeding:experiments.

Only sexually eompetent fish from known spawning aggregates were sampled beeause.

the aetual extent and duration of population mixing during various life stages

is unknown. The authors stress the importanee of temporal stability in a study.

as this, and.note that they tested this in 2 and/or 3 eonseeutive years. The

possibility remains that small genetie differenees exist between the m~ny diserete

spawning populations of herring but simply have not been deteeted. It was reeom- •I

mended that any further studies of this be done through tagging programs or by

direet analysis of rapidly evolving DNA.

Freshwater Fish

The population or stock strueture of lake whitefish, Coregonus elupeaformis,

in northern Lake Miehigan was reeently deseribed by H. Imhof, R. LeaTY and H. ,F.

Booke of the Wiseonsin Cooperative Fishery Research Unit. Electrophoretic analysis

of 3 polymorphie isozymes·provided evidenee that at least four populations exist

in the northern part of the lake. There was much spatial and temporal overlapI

among population ranges, but.one allele still exhibited elinal variation from

- 10 -

. .

•

Biochemical genetic variability of Macrobacterium on Guam is the subject of

a research grant to D. Matlock at the University of Guam.

Sguid

An eleetrophoretie study of seleet proteins from the market squid, Loligo

opalescens, was conducted by J. Christofferson et ale at California State College.

Results on theesterase loei seem to support the hypothesis that there is a sub­

population off the eoast of Mexieo whieh periodieally migrates northward.

- 11 -

. .

Proposed Projects on Sport Fish (U.S. Departmentof the Interior)

In a draft proposal of aNational Fisheries Genetic Project (Interior Depart­

ment)* it is noted that identification and delineation of sport fish stocks have

been attempted for only'a fewspecies, and thatsome groups'in particular would

benefit from such attention; , . '

The striped'bass, (Morone saxatilis)~ the white bass (Morone chrysops), and

reciprocal hybrids are being cultured and stocked extensively in reservoirs and

impoundments throughout most of the country. Ecologicalimpacts and genetic im-

pacts (as due to the reproductive success of the Fl hybrids in nature and their ~ .

backcrossing with native stocks of white bass) have not been assessed adequately.

There has'further been extensive mixing of Atlantic and Gulf coaststocks of

striped bass. Genetic studies of striped bass have beenlimited to those found

in only parts of the Atlantic coast and have not encompassed fish from their

entire range.

The lake trout (Salvelinus namaycush) has a very broad geographie range

naturally. Management programs have included the expansion of its range into

newly created environments, as well as its introduction into lakes wher~ it had

earlier been eliminated, particularly the Great Lakes. Little information exists

on the identityand natureof its stocks, and a need for such is indicated 'in

the proposal.

Largemouth bass' populations provide some of the most valuable sport fisheries

in the U.S. Genetic variability exists, both in and between these populations,

and it is recognized that some strains grow in selected habitats but do poorly

elsewhere. It is recommended that extensive management of this sport fishery in

several U.S. states make genetic consideration paramount in managers' plans.

* For more information contact R. Gasaway, R. B. Russell Federal Bldg., Atlanta, GA.

- 12'-

•

•

.' .New Procedures in Population Studies

Chromosome Banding in Marine Mammals and Marine Fish

In recent years comparisons of chromosomal characteristics have proven very

fruitful in elucidating relationships between populations of mammals. lJhile the

G-banding p~tterns of chromosomes appear to be quite stable in many groups of

mammals, one of the most active mechanisms giving rise to karyotypic variation is

addition, deletion and other changes involving constitutive heterochromatin.

Such studies were recently extended to marine mammals.

Onesuch study compared ~hromosomes of cultured cells of two Pacific porpoise

species. Major. problems exist in defining the nature of boundaries between stock

,of these species, which are impacted by the tuna fishery. This study was conducted

at the Animal CytogeneticsLaboratory, Utah State University (A. Stock) for the

National Marine Fisheries Service. Conspicuous heteromorphism between the C-band

heterochromatin of several pairs of chromosomes was noted in all individuals

examined. In addition, variation was noted in the amounts of heterochromatin in

individual s' of onespecies •. To fully eval u<ite the procedure,. it is necessary to

examine larger numbers of .individuals within the porpoise populations.

In a U.S.-supported study conducted at the Genetics Institute in Lund,

~ Sweden, the banding patterns of gray and sperm whale karyotypes were examined.

An earlier study ofkiller whales by the same Swedish scientistrevealed conspicuous

C-band polymorphism which rendered every individual unique. The gray and sperm

whales show~d less karyotypic variability leading to the general~ conclusion that

karyological v~riability is conservative in these marine mammals compared to such

groups as rodents and insects, and some speculation'as to why this might be so.

Abrief report was also made recently on the chromosomes.of an otter (Davis

et al., Brookfield Zoo). The karyotype of the bowhead whale was also reported

on by G. Jarrell of the University of Alaska.

The C-banding of chromosomes fromthree estab1ished marine fish ce11 1ines

_. was reported by P. Gregory of the University of Souther~ MississippL It was

- 13 -

~ ..concluded that this procedure is an important practical 'aid in distinguishing

between similar-appearing chromosomes in difficult fish karyotypes. '

Silver staining techniques were applied to the chromosomes of the.killifish,

to locate the nucleolus organizer regions on these fish chromosomes. Several such

major and minor sites were recognized (Howell and Black, Samford University,• . I

Alabama). In ajoint study~between researchers at,the University of Texas andI

in Brazil, the same technique was used to locate the NOR (nucleolus-organizer)

regions on the chromosomes of a Tilapia species (F. Foresti et al.)'. ,"

At Texas A&M University,J. Gold is developing techniques for more,rel iable

chromosome banding of trout'(also bass and catfish). The intent is to analyze',

populations for banding differences. Technical success with 4 speciesiof 3

cyprinid genera reveals that fish have 1imited variability in G-, Q~ and R-bands.

Constitutive heterochromatin (C-) banding, however, appears heterogeneaus, both

within and among species. Variation in the NOR region of a chromosome'ina minnow., .

was noted.

Restriction Endonucleases'- Basis for ~heir Application to Population'Studies:

In ä 1979 paper J.,Avise et al. of the University of Georgia; introduced'to

natural population an~lysis :a molecular techni~ue pr~viously ~pplied a1most ex­

clusively to problems of molecular biology. That was the use of aseries of'I

restriction endonucleases to cleave DNA moleeules isolated from various animals

into fragments which are then sized by gel electrophoresis. The enzymes recognize'

specific nucleotidesequences and, given certain assumptions, the sizes of the'

fragments reflect sequence differences in recognition sites. Mitochondrial DNA'

was chosen for study because of its small size and ease of isolation. 1~1ito­

chondria" DNA is maternally 'inherited.' It was known to have considerable sequence

heterogeneity ..

Using 6 enzymes and 23 samples of several individuals of the field mouse,

heterogeneity within a singl~ locale was found to show less than 0.5% divergence;

that from conspecific populations separated by 50 to 500 mi1es 1.5%, sib1ing species

by 13-17% 'and non-sibling species by more than 20%.- 14 -

•

•

Since,then, a'1981 paper from the University of Ca1ifornia, Berke1ey, has

reported extensive polymorphisms in ,the mitochondria1DNA of apes (S. Ferris et

a1.).,~'The authors makethe casethat this demonstration of 1arge genetic differ­

enceswithin ape species ca11s for renewed attention to the management of breeding

co1onies of captive and wild apes.

There are severa1 other recent studies of a simi1ar nature, as one on the

intraspecific variation in chloroplast ribosoma1 DNA in Eug1ena'(Wurtz, University

of I11inois).

Noting the rapid accumu1ation of data on DNA polymorphisms detected by restric­

tion endonuc1eases, M. Nei and F. Tajima, University of Texas, reported in 1980 on

procedures for analysis of such data quantitative1y~ To do this they used data on

mitochondria1 DNA from 3 Drosophila species. A1though their analysis required

severa1 assumptions, they noted that study of DNA polymorphisms with restriction

enzymes has on1y begun.

A major advantage of this method is that it can be used for any segment of

the genome regard1ess of whether it codes for a soluble protein. It is on1y neces­

sary to be ab1e to identify the particu1ar fragments of interest by prior purifi­

cation of a given c1ass of DNA.

A 1981 paper by Eng1es (University of Wisconsin) also presented statistica1

procedures for estimating genetic divergence and genetic variabi1ity with restric­

tion endonuc1eases. An important defect in the procedure is noted, but its 1ike1y

importance for studying genetic differences in regions of the genome not accessib1e

in other ways was recognized.

A yet more recent paper by Adams and Rothman (1982) is critica1 of the use

of DNA restriction patterns in the estimation of phy10genetic re1ationships. In

this somewhat theoretica1 study they used 54 endonuc1eases to ana1yze human mito­

chondrial DNA along with that of several viruses and bacteria.

- 15 -

In wheat, where.very sophisticatedgenome relationships between groups'are

determined,.combinations of molecular DNA techniques with such cytogenetictech­

niques as those that define the nucleolus-organizer regions of the chromosome:.are

provingparticularly.powerful. There:seems to be no reasonallthese procedures

will not play.some role inthe future in population studies of marineresource

.species.

- 16 -