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Drosophila Subobscura. AN ANALYSIS OF TH:gEE WILD POPULATIONS OF DROSOPHILA S U]3OBSC URA BY CECIL GORDON, ~ IIELEN SPURWAY AND P. A. R. STREET Deyart,;ne~t of Biometry, U~versity Cotlege, London (With Plate II and Five Text-figures) CONTENTS PAGE i. In:groduc~ion 37 2. ~a%er[~l and method 38 3. "i~xperimenM] procedure '÷ 4] No:go on culture oonditions . 42 4. Descr[p%ion of %he 21 and F. segregations 4:2 5. Effects due 4o single ~utosoma.] mu:ga,tions 45 6. 9"alse mutan%s ... , . 80 7. ltfa~formed abdo.msn . 61 8. Vein ubnormalities, the inheritance of which is unprecHctable 63 ~)escriptbn of pheno:gypes 63 The F~ seg,'egations 66 The E2 s~greg~t.ions 66 Iden~i%y tests . 73 9. ]~o.ughs 79 ~0, Estimation of the frequency of muta, ted loci, and the comparison of populations 82 II_ Discussion 84 12. Summary 88 ~eferenees 89 Expla.ua%bn of Plate II . 90 1. INTRODUCTION ~[NDIVIDUALS he~erozygous for recessive l~lutations have been found in wild populations of many species of animals, e.g. DrosopAih~. species (Tschetverikoff, 1928; Timofgeff-~essovsky, 1927a; Balkaschina and Romaschoff, 1935; CJordon, 1936), Dermestes w@i,us (Philip, unpublished commnnieation), Ga.m~narus chevreuxi (Spooner, 1932) and Perov~yseus (Sumner, 193@ Similar heterozygotes also exist among plants, as is shown by the increased variabilRy, but average decrease, of the growth rate and productivity, the segregation of sterility factors and abnormal forms snch as chlorophyll defects, produced by inbreeding plants from 1 Carnegie Teaching Fellow, Department of Na:gm'tfl History, Aberdeen UniversRy, 38 Analysis of Three Wild Popv2ations of D. subobscura species that are normally cross-fertilized, e.g. red clover (Williams,1937 a, b) and S',inc~Tis cdbc~ (Sal-tykovsky & Federov, 1936). The frequencies of flies he£erozygous for various mutations have been used to compare wild popuIations of D~'osophi~c~ mela'r~ogaster (Dabinin et al. 19.34, 1936), D. ~seudoobseurc~ (Sturtevant, 1937; Dobzhansky & Queal, 1938) and this paper reports the analyses of samples of /). s~&- obsc.z~ra from three localities in the south of England. Stocks existed in the two for m.er species which enabled autosomal lethals to be detected and thelr frequencies measured. ~.n D. subobse~,ra, however, we have had to use a method of analysis by which only sex-linked lethals, and mutatious producing a visible effect when homozygous, could be d.egected. The work was designed by Gordon, and the inbreeding, extracting, and testing for identities was done jointly in the season 19.36-7. In August 19;37 Gordon went to Aberdeen, leaving the linkage of the vein characters with Spurway. An analysis of the Slough sample by Street and of the New Forest and Studland samples by Spuzway, were accepted by the University of London as theses for the degrees of ~faster of Science and. Doctor of Philosophy respectively. This paper has been re- written by Spurway from the two theses. Oomplete records of the inbreeding results have been given to the Statistics Archives of the. British Museum (Natural History). ~, ~ATE2%IAL A27D METt~OD The three populations analysed came from Slough in Buckingham- shire, from Eingwood in the New Forest, Hampshire, and from Stndland in Dorset (Fig. 1). As the flies were trapped they may have flown from great distances, so it is not known over what areas the populations ex- amined extend. The Slough sample came from the grounds of the Biological Field St.atiml of the Imperial College of Science and Technology, where Gordon (1936) had caught his flies in 1933 and I934. Traps were put down. in two places in an area of 8 acres, the altitude of which was 180 ft., on the grass- less patches under apple trees in an orchard, and white willows (Se/i;s alb@ on the banks of a stream. The New Forest flies were trapped in. two areas at gingwood.. The first of about 19~- a,ores surroun.ds a private house, and is 138 ft. above sea-level, on the Barton beds. It contains a gravel 5ii1 covered with gorse and. heath descending to a stream which flows through pasture land. with sallows (&diz ci~zerea and, auri~e), marshes, and a small oak and birch wood. The second[ area is a wood of 9 acres, half a mile from the C!EOIL O0ICDON, ~{ELEN SI~T_rRWAy _~ND P. A. R, STREET 39 ©F, o %8 S O i o .q I .4 F ~T ~ -< bJ~. i 40 A'~zcdys'is of Three WiZd Popzdc, t ior~s of D. subobseura first on a clay soil 2741%. above sea-level. The trees are oak, ash, al~d sweet cllesbnut, with a sprinkling of birch and. aspen, and a hazel under- growth. At Studland flies were caught over a much larger area, which was only 10 t'~. above sea-level. The soil consists of Bagshot beds covered with blown sand, and fl~e vegetation is add heath with scattered, marsh and shrub. The sample was caught in two litde woods of birch and sallow shrub 1600 yards apart. One of these was over SO acres ir~ area and the caller only just over 8 acres. The ~rapping was done from June go November 1936. As Naehtsheim (1928) and Dubinin (I928) have shown ~11a$ only the last fertilization is effective, the offspring of eada wild female caugh~ are assumed to be the offspring of a single male. Dominant mutatimls will be revealed in the ~,ild fly, or in the 2g], if they had been present in the mate. The ex- pectations for the segregations of single recessive factors are given in Table I from Gordon (1936). TABLE I Possible ty~Jes de.ri,vedfrom si,~.qlefe.mc~es fert£ized in tt~e ~oild Wild parents F1 F.~ cultures AA? xAa~[ 25 °2/~5all _&A, 50 % (IAA. : IAa), As9 x AAc~j I~A : 1As % (1/kN :2As :laa) Aa9 x Aa~ 1~ : 2Aa :]aa Not requkred SS? × syc? as? Sy~ INS? ; INs?, iSyd : lsyc~ Ss~ :<Syc~ lss9 :ISs?, lSy~ :isyc~ No~ required A and S denote normal autosomal and sex-linked genes respectively, a and s theh" recessive ~llelomorphs. Effects dee to several factors might be detected. Less than a quarter of the flies in a culture segregating for such an abnormality will show it, IPor example, if mutations at two loci were equally essential a ratio of 15 : 1 would be expected in. one out of six~een cultures. Autosomal lethals cannot be looked for in this species as the material for the necessary testing stocks has not yet been collected, but Gordon (19.36, q.v.) has explained some of his abnormal segregations of auto- somal recessi.ves as being due to their linkage to a lethal. He describes the segregations expected from el1 possible distributions of the visible and. l.ethal recessives a~d their normal aibbm.orphs between the four homo- logous chromosomes of the two wild parents. 0ECIL GO1%DON, HELEN SPUIR%¥AY AND 1D. A. R. STREET 41 3. ]~XI~F~RIMENTALPI%OCEDURE The wild females trapped were presumed to have been mated, and were put singly into cultua'e vessels. Thlrty-two males of the E 1 of each family were examined for mutant characters, and the females emerging at the same time were counted. 8ex-Hnked lethal factors would be detected by this method.. If any abnormality was observed among the males, ~he females were examined, to distinguish between sex4inked and aatosoma.I mutations, and com-- plete counts were made of the culture. If no abnormalities were observed the Y z was discarded when the thirty-two males had been examined. From the/~1 flies, sixteen F~ rantings were made up in pairs. Sixty~ four flies were usually examined for all mutants in a series of F~ cultures )~ in number. The number of cultures examined for all mutants was theoretieally eight, but whei1 less than eight cultures in the av2 produced flies, ]~ is less than eight, and when one or more of the first eight cultures failed to yield sixty-four flies, one or more extra ones were examined in detail, and ]c is greater than eight. If an abnormaIi V suspected of being genetic was detected, the culture was not discarded when sixty-four flies had been examined, but counted to the end, solely for the segregation of that mutant. Similarly, cultures ill excess of /c were examined and counted for the segregations of all mutants found in the first ~ cultures. All abnormalities not observed in the first sixty-four flies examined in one at least of the ]~ eult~u.es have been ignored. Any character thought to be due to a mutation was carried to the F3 by mating abnormal flies together, by mating them to their wild- type sibs, and by mass marinas of those wild-type sibs. If the abnormal x abnormal crosses did not produce offspring, and confirmation depended on abnormal x wild-type and mass wild-type rantings, a negative was not assumed to have been proved until an _F4 and sometimes an Fs had been examined. No detailed records were kept of these crosses, and the number of cultures and flies examined depended partly on the tempera- ment of the investigator. When a mutant was confirmed, the information which was gained about its ~dability, fertility and penetranee from the three kinds of cross made up with the ~ies fl'om a segregating F~ culture was considered, and it was decided whether or not a stock of it should be kept.
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