TEMPERATURE AND TME OF DEVELOPMENT THE TWO SEXES N DROSOPHLA BY GERT BONNER. (From the Zootomcal nsttuton, Unversty of Stockholm.) (Receved th May.) (Wth Four Text-fgures.). NTRODUCTON. METHODS. ALL who have worked wth Drosophla know that the females are the frst to hatch n the culture-bottles. Ths fact makes t very probable that the females develop n a shorter tme than do the males. However, t s not a pror necessary that t must be so. t could also possbly depend upon a hghly selectve mortalty among the frst eggs from each female. n order to study ths queston n more detal the followng nvestgaton was undertaken. The fles used belong to the yellow stock. The sex-lnked mutant yellow has a vablty almost as great as that of the wld type fles. The cause why these latter fles were not used, was that possessed a culture of trplods carryng yellow n ther X-chromosomes, and that t was my ntenton to compare the tme of development not only of the two normal sexes but also of the ntersexes. Unfortunately, have untl now not succeeded wth the ntersexes. Before the experments were begun a rather great number of ordnary culture-bottles (about 0) were made up and fve to eght pars of fles were put n each of them. There they were left for about three days n order to make t probable that all the females had been fertlsed. Next, the same number of culture-bottles was made up, but contrary to the ordnary method, to these bottles no paper was added. The fles from the old bottles were then transferred to the new ones where they were left for two hours only. When the two hours had elapsed, the bottles were empted and left n the ncubator untl pupaton began. n bottles wthout paper pupaton takes place ether on the surface of the food or on the walls of the bottle, and snce my bottles are cylndrcal n shape and only contan 00 c.c. each, t s qute mpossble for the pupae to escape observaton. Durng the whole perod of pupaton the bottles were controlled every second hour, and the pupae, whch had pupated durng the last -hour perod were transferred to vals contanng mostened flter-paper. These vals were then labelled wth the pupaton-perod and left n the ncubator untl the begnnng of hatchng. As n the case of pupaton, the vals were controlled every second hour durng the whole tme of hatchng. By ths method t s possble to be nformed for each ndvdual female and each ndvdual male upon how many perods of hours t takes, () from^fe layng of the egg up to the moment of pupaton, and () from ths moment upto the moment of hatchng. There s one possble source of error due to the fact that
Temperature and Tme of Development of the Sexes n Drosophla sometmes develop to some extent before layng. thnk, however, that ^P does not nfluence the averages very much, and snce the am of ths nvestgaton s to compare the tme of development of dfferent groups of anmals, the error may be left out of consderaton by ths comparson. As stated above, the eggs for whch the tme of development have been calculated, have all been lad wthn a perod of only hours. Ths means that t s very much a matter of chance f we get many or few ndvduals upon whch to control the tme. The experments, whch have been carred out n an ncubator, have been made at two dfferent temperatures, vz. C. and 0 0 C. n the frst case got a qute suffcent number of ndvduals, vz. 0. n the second, however, got only ndvduals. Ths low fgure s almost certanly due to the heavy mortalty at the hgh temperature of 0 C. Snce ths last experment nevertheless gave some decsve results and snce the experments are rather laborous (t s necessary to control the cultures for hours or more) they were not repeated.. THE EXPERMENTS. n the calculaton of the tme of development up to the moment of pupaton, we may magne that all the eggs have been lad just at the mddle of the -hour perod. And lkewse, n the calculaton of the pupal tme t s magned that all the pupae have pupated just at the mddle of the dfferent -hour perods. Ths approxmaton s necessary for the statstcal treatment of the problem and does not nvolve any error snce, on an average, the same number of eggs have been lad before as after the md-pont of the perod and the same number of pupae have pupated before as after the md-pont. Experment at 0 C. (a) Tme from egg-layng up to pupaton. The dstrbuton of ths tme for the dfferent ndvduals s shown n Tables and and n Fg.. From the tables we fnd the mean and ts mean error to be For the females - ± 0- hours, For the males......... - ± 0-0 hours. The dfference between these two tmes s 0- hours and ts mean error s 0- hours. And as 0- : 0- = 0- t s obvous that the dfference between the tme of development of the females and of the males s wthout any statstcal sgnfcance. (b) Tme durng the pupal stage. Ths tme s to be found n Tables and and n Fg.. Here we have the mean and ts mean error: For the females - ± 0- hours, For the males - ± 0- hours. 'The dfference of these tmes and ts mean error are respectvely -0 hours ^B hours; and as *0 : 0-0 = 0- t s correct to conclude that the males are sgnfcantly slower n ther development durng the pupal stage than are the females. -
GERT BONNER Table. Showng the number of Females dstrbuted accordng to ther tme of development at 0 C.; () up to the moment of pupaton, and () durng the pupal stage. Tme n hours up to the moment of pupaton Hours - 0 0-0 0-0 0-0 0-0 0- - - " - " - - - - - - - Tme n hours durng the pupal stage 0 0 0-0 0-0 0-0 00 n - - - - 0 0 0 0? 0 H 0 0 n Table. Shovnng the number of Males dstrbuted accordng to ther tme of development at 0 C.; () up to the moment of pupaton, and () durng the pupal stage. Tme n hours up to the moment of pupaton Hours 0- O 0-0 0- "- " S- - - - - - - - c > G w OD. g * s 0-0- - - - - - - - - - 0 A 0 0 0 0 ' O 0 0 Table. Showng the number of Females dstrbuted accordng to ther tme of development at 0 0 C.; () up to the moment of pupaton, and () durng the pupal stage. Tme n hours up to the moment of pupaton Tme n hours durng the pupal stage Hours ^ - - - - - - - - - - -0 0-0 0-0 0-0 0 0
0 GERT BONNER Experment at 0 0 C. (a) Tme from egg-layng up to pupaton. The means are (Tables and Fg. ): For the females... - ± 0* hours, For the males... 0- ± 0- hours. The mean error of the dfference s 0- hours, and snce(o- -) :o- = - t s very probable that the dfference between the tme of development of the two sexes s of a real sgnfcance. Table V. Showng the number of Males dstrbuted accordng to ther tme of development at 0 0 C.; () up to the moment of pupaton, and () durng the pupal stage. m c ft E- Hours - - - - - - - - Number - 0-0 Tme n hours up to the moment of pupaton -0 / N 0-0 va ' ; O-O 0 V 0-0 0-0 > Hours - 0 0 0 0 0 0 U) 0 0 Fg.. Tme of development up to the moment of pupaton at 0 0 C. of females and males. 0 0
Temperature and Tme of Development of the Sexes n Drosophla Tme durng the pupal stage. The means for ths perod are (Tables and Fg. ): For the females - ± 0-0 hours, For the males - ± 0- hours. The dfference and ts mean error beng respectvely -n and o-o, we have - : o-o = 0-, and the dfference must thus be of a real sgnfcance. Number 0 0 / * A -' / V / s f Hours - - - - - - - - - - - Fg.. Tme of development durng the pupal stage at 0 0 C. of f femalesl d and males l. J
GERT BONNER. DSCUSSON. As may be seen from the above statements, there s at 0 as well as at 0 0 a markedly longer tme of development for the males than for the females. At 0 C, however, ths lengthenng s confned to the pupal stage, the tme up to pupaton beng the same for the two sexes. t seems not unlkely that ths may be correlated wth the fact that the essental parts of the secondary sexual characters are developed durng the pupal stage. But f ths correlaton s a true one, then probably we also may suppose that at 0 0 C. these characters develop earler, not only n an absolute sense, but also n a relatve one, snce namely the fgures show that here the tme up to pupaton as well as that durng the pupal stage s longer for the males than for the females. Ths supposton must, however, be confrmed by an embryologc nvestgaton. f we look at the tables, especally Tables and V, t s seen that the fgures to a great extent are dstrbuted along the dagonal endng n the upper rght corner. Ths fact ndcates that there s some knd of correlaton between the tme up to pupaton and the tme durng the pupal stage. From Tables and ( C.) we also fnd the coeffcent of correlaton, r, to be (accordng to Bravas' formula): For the females r = 0- ± 0-00, For the males r = 0-0 ± 0-0. t s therefore probably correct to suppose that at least for the males for those ndvduals whch have had a consderably long tme of development up to the moment of pupaton, ths long tme as a rule s compensated by a shorter tme durng the pupal stage and vce versa. That the tme of development s shorter at the hgher than at the lower temperature s qute conformng wth what we know about the nfluence of temperature on development. But there s a very nterestng fact to note, namely, that the shortenng of the tme at 0 0 C. as compared wth that at 0 C. s much more pronounced for the tme durng the pupal stage than durng the tme up to pupaton. As a coeffcent of the shortenng we may ntroduce the quotent between the tme at 0 C. and that at 0 C. t s obvous, then, that the smaller ths coeffcent s, the greater s the shortenng. n order to make the comparsons more clear, let us ntroduce a notaton. Let the means of the tmes up to pupaton be M^ and M 0 and ther mean errors m^ and nu^. Let, lkewse, the means of the tmes durng the pupal stage be P^ and P 0 and ther mean errorsp^ and p 0. Let, fnally, and /? =?. * We have then to compare a and /? and to make ths comparson for the two sexes separately. From the fgures of the dfferent tables we fnd that for the females a = 0- and ) = 0-0, for the males a = 0- and js = 0-.
Temperature and Tme of Development of the Sexes n Drosophla ^Let now the mean error of a be /x and the mean error of j be v. Snce M 0 ^Bdependent of M& and P 0 s ndependent of P^, /n and v must satsfy to the close-approxmaton formula: and thus and v = lef * - p a Wth the ad of the foregong fgures we therefore fnd that for the females /x = 0-00 an<^ v = ' O, for the males /x = 0-00 anc * v = 0-00. The mean error of the dfference between a and j s, as usual, p = V^ + v*. Hence r ths dfference and ts mean error have the values: For the females O- ± 0-00, For the males 0- ± 0-000. And, fnally, we fnd the values of the quotent - - to be For the females -, For the males -0. We may therefore wthout hestaton conclude that the more pronounced nfluence of the rasng of the temperature upon the pupal stage as compared wth the nfluence upon the pre-pupal stages s of a real and absolute sgnfcance. The method commonly used when studyng the nfluence of temperature on development s to observe the tme from the begnnng of the development up to a certan stage and to compare for a number of dfferent temperatures. The results are often plotted on a scale and t s usually tred to fnd a mathematcal expresson whch fts the curve thus obtaned. But t may tve asked f these studes are of more than of a purely descrptve value, or f they really nform us on the processes of development. As we have seen, an ncrease n the temperature has a dfferent nfluence on dfferent stages of the development. n fact, t shortens n Drosophla the tme durng the pupal stage relatvely more than t shortens the tme up to pupaton. But f we not only consder Drosophla but the organsms n general, there may exst some maxmum temperature above whch the development s not accelerated but retarded. Snce, however, dfferent stages are dfferently susceptble to the nfluence of temperature, ths maxmum temperature may very well be a dfferent Afor dfferent stages. magne, then, that a rasng of the temperature accelerates one part of the development and retards one other part, but n such a way that the total tme of development s unaltered. From a graphcal or mathematcal treatment
GERT BONNER we would then have concluded that temperature s wthout nfluence on the tme of development but n realty t had been an obscured but nevertheless real nflu^k of temperature. As the above data show, the tme up to pupaton n Drosoptma s the same for the two sexes at 0 C. but probably not the same at 0 0 C. As, however, the tme up to pupaton nvolves such dfferent phases of the development as the embryonc phases phases of dfferentaton and the larval stages phases of growth t may possbly only be the total tme up to pupaton n 0 C. whch concde for the two sexes, whereas for nstance one part may be slower for the males and one other part slower for the females. t seems, therefore, to me that when studyng temperature-coeffcents and other fgures of that knd, the methods ofted used are too rough to be of a greater value. f we wsh to be able to conclude anythng about the physcal and physcochemcal nature of the processes of development from the varaton of the tme of ths development n dfferent temperatures, t s necessary to study short ntervals of the development separately, and to choose the ntervals n such a way that we may nfer that there s about the same knd of processes gong on durng the whole of each separate nterval. The dffcultes here are, however, of a practcal knd: t s not easy to fnd sutable objects for such a study. The best objects are probably those wth transparent eggs where t s possble to follow each morphologcal stage. The methods then to be followed are the ordnary ones: for each separate nterval the tme of development s noted for a number of dfferent temperatures and the correspondng curve s traced. Conformng then wth the facts, shown above, to hold good n Drosophla, t s probable that the rule should be that curves, correspondng to dfferent ntervals, would be of a qute dfferent knd, ndcatng dfferent natures of the processes durng the varous ntervals.. SUMMARY.. The tme of development at 0 C. up to the moment of pupaton s found to be for females and males respectvely - ± 0- and - ± 0-0 hours. Durng the pupal stage the two tmes are - ± 0- and - ± 0- hours.. At 0 0 C. the correspondng fgures are (n the same order): - ± 0-, 0- ± 0-, - ± 0-0 and - ± 0- hours.. These fgures show that there s a statstcal sgnfcance n the dfferences of the tmes of development of the two sexes for both the perods at 0 C. but only for the pupal stage at 0 C. t s ponted out that the fact that the longer tme of male development as compared wth female development at C. s confned to the pupal stage, may be correlated wth the other fact that the essental parts of the secondary sexual characters are developed durng ths stage.. t s shown that there s a negatve correlaton between the pre-pupau pupal tmes of development, ndcatng that the longer the frst tme s, the shojtev s, as a rule, the other tme and vce versa.
Temperature and Tme of Development of the Sexes n Drosophla Wth the ad of statstcal methods t s shown that the shortenng of the ^of development at 0 0 C. as compared wth the tme at C. s much more pronounced for the pupal than for the pre-pupal stage.. Ths last fact s dscussed and t s emphassed that the ordnary methods of studyng the nfluence of temperature on development are too rough to be of more than of a descrptve value, the only way of gettng a deeper nsght nto the processes of development by temperature studes beng the separate studes of a number of short ntervals.