Alahiotis, S.N.

Kilias, G.

English

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The Journal of Heredity 7353-58. 1982. f Mating propensities and variations in enzyme activities in long-term cage populations of Drosophila melanogas ter - .. ""'d~th .ire, respectively iissondte professor. 'Â¥f'lfxto~ allow, in the Department of Genetics, vpB1h ni Patras-Greece They th'ink Professor '^nos. Chairman of the Genetics Department, rJicai reading of the miinuscript. CIS well as ' ^ T E Berger. Biology Department, Dartmouth W Hanover. New Hampshire for helpful ':%ions 'Â¥' . h e r i ~ d n  Genetic Association ABSTRACT: Environmentdependent reproductive isolation was established between cage population? (Bs) of Drosophila melanogaster originated from a Greek natural population (summer 1973) and maintained ?. r about five years under different diets (poor-rich). The detected deviation from random mating involved no homogametic or heterogametic pref- erence but rather, a significantly increased activity of males from populations maintained on the rich food medium. This observation indicates that the male parental investment is not negligible and under certain conditions sexual isolation can be a function not only of female behavior but also of male behavior. Differences also were found in various enzyme activities an the inter- and intra-vpulation levels. Given those observations as well a s  the observed different behavioral patterns of Be and Cs-Dc  population^^^, a preliminary attempt was made to associate adaptive evolution with differences in enzyme activities. The dif- ferences in enzyme activities between populations reared on different media are not due to allozymic differences. It also was shown that in some populations environmental effects do not always ellicit differences in enzyme activity. It was concluded, therefore, that the observed variations were the result of environmental effects interacting with modifier genes. ONE OF 'I H E  important questions in evo- lutionary theory. relates to how species are formed and what kind and magnitude of genetic differentiation characterizes species formation Heretofore, several mechanisms l^ , -mrn h.i-.ixrn amrih ~ i c - i v r - ' " l  a <T th'at cnor'iatinn invnlvpc a a p n ~ t i r  r ~ n r w i n i m t i o r  denen- dent on a founder event, followed by one or more cycles of exponential population growth and a sudden contraction or crash9-'2. Moreover, according to P r a k a ~ h ~ ~  founder e ents, inbreeding, and geographic isolation are considered as major factors in the development of reproductive isolation. In contrast, speciation also is considered a by-product of the process of adaptation, characterized by changes in behavioral and structural gene [allozymic) v a r i a t i ~ n ~ - ~ ~ - ~ ~ .  Experimental evidence exists for all the above view~6,30-3~, a fact indicating that the development of reproductive isolation is not unimodal. We recently demonstrated1" tha, stable environment-dependent sexual isolation had been established between cage pop+ lations of Drosophila melanoguster main- tained under different environmental r n i r l i t i n n c  ftrtmnoraturi^ ~ n r l  hiimiirlih~! f n ~  ahoilt five w a r s  w h ~ r ~ a s  the isolation of  populations alone did not lead to ethologi- cal isolation. Since the isolation of popula- tions is considered to be an important factor in the development of reproductive isola- t i ~ n ~ ~ ,  we investigated a set of four addi- tional cage populations (possessing a com- mon gene pool at their origin) maintained [in duplicate] under different food media (poor-rich)l, for about six years, in order to assess: 1) whether or not reproductive iso- lation was established and, if so, whether it was correlated to environmental manip- ulation or to the isolation of populations. 2) Since the environmental factor used in the present study (food medium) differs from those utilized beforeI9 (temperature-rela- tive humidity), a comparison also was made regarding the patterns of ethological isola- tion. The ecological factor food medium (poor-rich] was found to induce dramatic genetic differentiation in Adh and a-Gpdh allozymic and inversion frequencies3 as well as in the frequencies of lethal bearing chromosomes1 during the initial 30 gener- ations. Tak'ng into account the situation already revealed in the populations, we thought it  of interest also to measure the quantitative genetic variation of enzyme activities in our preliminary effort to see whether or not correlcition exists between changes in enzyme activities and in repro- ductive isolation. Since it was suggested21 that in natural populations there may be several polymorphic loci affecting the ex- pression of a given structural gene and therefore contribute to variation in the en- zyme activity, this study may ultimately prove useful to test the adaptive signifi- cance of enzyme qua~..itative variability. At the same time, it also \\ill have a bearing on the suggestion that regulatory variation of enzyme activity is a more important source of adaptive variation than structural vari- ati0n8 1-1.21.34. Materials and Methods Four cage populations designated lBi ,  1B2, 1B3, lBj were studied. Enzyme activi- ties were measured in flies from two addi- 9A X dB and 9 B  X <5A. respectively, and \ tional cage populations [lC, ID). The last = XAA + Xt3t3 + X.\H + XB.X two populations have been studied and SE of I = \'(I - J V N .  described p rev iou~ ly~~ .  The B5 populations originated from a common parental popu- A value of zero for this index indicates lation (1B) by replication, 10 generations random mating; <0, negative assortative after the latter originated. Consequently, we and >0, positive assortative mating, ~h~ may regard the four derived populations as flies of each sex that were mated werp possessing practically the same gene pool tested by chi-square if females and males at their origin. Population 1B was estab- of one population mated more frequent]\ lished in the autumn of 1973 from flies than those from other populations, and if captured during the summer of 1973 from assortative mating occurred. Experiments, the Greek island of -a (for more were carried out 210 weeks after the origin details see Alahiotisl]. All Bs populations of populations. were maintained at 25 Â 0.5" and a mean The enzyme activities were measured relative humidity- of 43 k 4 percent, in 12- in about eight replic.-'es in at least tku, hour daylight cycles. Populations IBi and separate experiments. The flies used wer, 1B2 were kept on the dead-yeast-sugar-agar 3 to 4 days old in all assays. The enzlm,, medium, which is considered a rich food assays have b e ~ n  described elsewhere medium (RFMI1, while populations 1 8 3  and (ACHE and IDH2, ADHl5, aGPDH:' 1B4 were maintained on the cornmeal- NAD-SoDHs 7, 6PGD and G6PD22). Thf sugar-agar medium, which is characterized enzymes assayed in this study are: CY-G]!. as a poor food medium [PFM)]. The size of cerophosphate dehydrogenase (a-glycero the PFM populations was estimated at 1.100 3-phosphate:NAD+ oxidoreductase, EC (average]' flies, and that of the RFM pop- 1.1.1.8.), glucose-6-pb +hate dehydroge. ulations at 2.800 (average] flies1. Sexual nase (G6PD; D-glucose-6-phosphatt isolation index was measured according to NADP+ oxidoreductase, EC 1.1.1.49.1. 6. the method followed in our previous phosphogluconate dehydrogenase (6PGC study 19, i.e., random mating was tested by 6-phospho-D-gluconate: NADP+ oxidore- chi-square and the joint-isolation index of ductase, EC 1.1.1.44.], alcohol dehydroge- Mologolowkin-Cohen et aLZ3: nase (ADH; alcohol: h Â¥^D oxidoreductasi EC 1.1 .I.I.], isocitrate dehydrogenasr = ' + xnn - - NADP[1"H-NADP4 L,-isocitrate NAD? where XM, XBB, X,iR, XHA stand for the oxidoreductase (decarboxylating, E( four types of matings, 9A X 8 A, 9B x 8 B, 1.1.1.42.], acetylcholinesterase (ACHE Table I. Mating preferences in crosses between isolated cage populations of Drosophila melanogastur Cross xW] xWG'f1 Isolation A X  B AQ X A8 A9 X B3 BQ X A3 BQ X B3 xqldf]Q ~9 l(ff)d assort total index i SE Table 11. Mating preferences in crosses between Or-k flies raised on RFM or PFM Cross (A X Bl xTlclf) ~ T l d f l  Isolation Or-knFkl X Or-kpFhg AQ X A8 A 9 X  BS B9 X A3 BQ X Bo8 xTldf] i  x2(ldf]8 assort total index * SE Generations 1 25 26 24 26 0 010 0 089 0.010 0.305 0.010 Â 0 099 3 23 22 21 22 0.045 0.000 0.045 0.023 0.022 Â 0.106 5 23 22 23 22 0.000 0 014 0.000 0.044 0.000 i 0 105 Or-k x Or-k 19 22 20 22 0.012 0.301 0.014 0.326 -0.012 A 0.109 (in common conditions) / 54 The  Journal of Heredity Alahiotis and  Kilias: Variations in e n q m e  activitit" 

Mating propensities and variations in enzyme activities in long-term cage populations of Drosophila melanogaster.

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Mating propensities and variations in enzyme activities in long-term cage populations of Drosophila melanogaster.

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