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Enzymatic heterozygosity and morphological variance in synthetic populations of Drosophila melanogaster

Enzymatic heterozygosity and morphological variance in synthetic populations of Drosophila... and variance Enzymatic heterozygosity morphological in of Drosophila synthetic populations melanogaster Gloria BLANCO LIZANA J.A. SANCHEZ PRADO de Universidad de Gen6tica, Oviedo, Asturias, Spain Departamento Summary Several have shown a correlation between and reports negative allozyme heterozygosity In this carried out on of variance and work, morphological asymmetry. synthetic populations we have tried to find out if a can be established between the Drosophila melanogaster, relationship of 4 characters and for 5 variability (and symmetry level) morphometric homozygosity enzymatic loci. Our results to a correlation between (and point positive morphological variability asymmetry) and loci. In of loci also influenced for the other homozygosis enzymatic addition, heterozygosity developmental stability. words : mela- variance, homeostasis, Key Morphological enzymatic polymorphism, Drosophila nogaster. Résumé et variance dans des Hétérozygotie enzymatique morphologique populations synthétiques de Drosophila melanogaster. Plusieurs montrent taux élevé l’individu ou la de expériences qu’un d’hétérozygotie (de est associé à une faible variance et un faible population) généralement morphologique degré Dans ce réalisé dans des de travail, d’asymétrie. populations synthétiques Drosophila melanogaster, nous avons de voir s’il était d’établir une relation entre la variabilité essayé possible (et de caractères et le taux déterminé sur 5 locus l’asymétrie) morphométriques d’homozygotie Nos résultats une corrélation entre variabilité enzymatiques. indiquent positive (et asymétrie) et taux déterminé sur les locus De le morphologique d’homozygotie enzymatiques analysés. plus, taux du reste du influe aussi sur la stabilité du d’homozygotie génome développement. Mots clés : Variance homéostasie, morphologique, polymorphisme enzymatique, Drosophila melanogaster. I. Introduction a lot of data have been forward that variabi- Recently put showing morphological and decrease with of & lity asymmetry heterozygosity enzyme polymorphisms (M I TT ON For MI TT ON examined 3 of Fundulus GRANT, 1984). example, (1978) populations heteroclitus for 7 characters and 5 and found loci, morphological polymorphic enzyme that tended to have lower variation than E ANES heterozygotes phenotypic homozygotes. came to a similar conclusion after 6 loci and 2 (1978) examining polymorphic morpholo- traits in the monarch Danaus has been gical butterfly, plexippus. Enzyme heterozygosity as associated with either rate or in a wide reported growth developmental stability of birds et shellfish & al. , Z OUROS , 1978 ; range organisms : (F LEISCHER 1983), (S INGH Z OUR os et K OEHN & salamanders & al., 1980 ; S HUNWAY, MI TT ON , 1982), (PIERCE 1982), fish & & MI TT ON et (V RIJENHOECK L ERMAN, MI TT ON , 1980 ; C ll., 1982), plants (K NOWLES and insects 1981 ; EL -K ASSABY, 1981 ; B IEMONT , However, 1982) (G UNAWAN, 1983). there are a few results where these correlations were not found 1980 ; (H ANDFORD, McANDREW et al., 1982). Studies on were carried out on characters with bilateral symmetry morphological distribution L EARY et because 1979 ; K AT , 1982 ; al., B IEMONT , (S OULE , 1983 ; 1983), bilateral is a direct measure of which is the main homeostasis, symmetry developmental cause to which several to the classical work of L ERNER authors, according (1954), attribute this In if homeostasis is defined as the fact, relationship. developmental of an to form an in the face of external capability organism average phenotype a small deviation from bilateral should consti- perturbations (L ERNER , 1954), symmetry tute a reasonable measure of a decrease in homeostasis 1967 and (S OULE , 1979). the authors found it difficult to account for their that Generally, finding enzyme are less variable than In found it homozygotes. particular they heterozygotes surprising that such effects should be observed when 5 or 6 loci were screened out of the only thousands to be In recent different mechanisms expected polymorphic. papers possible are K OBLIANSKY & L IVSHITS in human and L EDING et al. suggested. (1983), populations, in are inclined to attribute the correlation to L EARY et al. (1983), pitch pine, inbreeding. considered that the locus itself influenced (1984) particular enzyme development. MI TT ON & K OEHN that is linked to (1985), propose enzyme heterozygosity energy of individuals and that the reflects the balance. budgets developmental stability energy The of exhibit is that explanation why they greater developmental stability heterozy- on the a and these gotes have, average, higher positive energy balance, genotypes should be less affected environmental variations. during development by stressing These results are also to the the germane controversy concerning adaptive signifi- cance of If the correlation between protein polymorphisms. negative enzyme heterozy- in these correla- and and gosity morphological variability asymmetry is, fact, general, tions cannot be in with a neutral for the and maintenance of agreement theory origin The variation at these loci should be at maintained, enzyme polymorphisms. enzymatic least in a et L EARY et part, by heterozygous advantage (McA ND REW al. , 1982 ; al. , 1984). we In our carried out on of work, melanogaster, synthetic populations Drosophila have between the and of examined the relationship variability symmetry morphometric characters and of for 5 biochemical loci chosen at random. In degree homozygosity our allowed us to measure the influence of addition, heterozygosity experimental design the of background genotype. II. Materials and methods a balanced lethal stock isochromosomal lines for chro- Using (CyL/Pm TM3/Pr), mosomes II and III were established from a natural of melano- population Drosophila in the wild. gaster recently caught Of these 117 were chosen because did not and were inversions, lines, they present for the different allelic variants of the 5 loci homozygous enzymatic analyzed (Adh, and Taken as a whole these lines constitute what we Est-6, Aph-l, a-Gpdh Lap-D). shall call The HHP with the same population (HHP). lines, highly homozygous for the 5 were crossed and maintained mass-culture. The 8 loci, genotype enzymatic by so constitute what we shall term formed, homozy- subpopulations altogether, partially 5 loci were in a In these the gous populations (PHP). PHP, enzymatic homozygous but the of the natural was reconstruc- state, background genotype population partially et because in all cases 10 or more HHP lines were ted, (NEi al. , 1975). Finally, pooled the PHP lines with for the 5 loci were crossed ; complementary genotypes enzymatic the of these 4 crosses were and will be offspring possible immediately analyzed, referred to as heterozygotes (HET). and fifth abdominal sternite The numbers of dorsocentral, scutellar, sternopleural bristles have been studied as characters. All but the last of these are morphometric bilateral characters and exhibit in the because they fluctuating asymmetry populations of individuals is the difference between a character on the left and sides right normally distributed about a mean of zero. In these cases the bristle numbers were determined for the left and sides on individual. The individuals were then classified right every to the absolute values of the difference between bristle number on the right according and left sides. We calculated the variance over all the individuals in morphological (s’) sampled each class PHP and the is the (HHP, HET) ; asymmetry percentage (A) average deviation in each class and the variation shown the individuals symmetry range (D) by the minimum and maximum values of found in each class. represents asymmetry we know that the for the different do not differ Moreover, homozygotes electromorphs from each other with to the values of of these any morphometric respect average characters Runic, (B LANCO 1983). Horizontal starch was carried out with 12 100 starch. Flies gel electrophoresis p. were in 0.01 ml of starch the method of J OHNSON homogenized gel buffer, using (1964). References of buffer and stain utilized are indicated in table 1. systems III. Results and discussion The null tested here is that individuals for the 5 hypothesis heterozygous enzymatic of and variance as the individuals loci have the same level morphological symmetry for the same loci. Table 2 shows the variance of characters homozygous morphometric in the 3 classes of and table 3 shows the results on bilateral populations analyzed, were with a t-test corrected for The values of symmetry. asymmetry (A), compared and the variances a one-tailed F-test & unequal variances, morphological by (S OKAL individuals in each The size is the number of R OHLF , analyzed 1979). sample (n) taken from all the lines of each class. In all cases the HHP individuals population, showed both the variance for the 4 characters greatest morphometric analyzed (tabl. 2) other and a deviation with to the bilateral On the greater respect symmetry (tabl. 3). the HET individuals the least variance and the of hand, displayed greatest degree 11 of the 14 made between both classes of individuals were symmetry ; comparisons 2 and The PHP individuals showed intermediate statistically significant (tabl. 3). variance and values 2 and differ from the HET in symmetry (tabl. 3) ; they significantly 2 of the 6 made and from the HHP in 4 of the 6 2 and comparison comparisons (tabl. The same results were obtained the of In 2 of the 3 3). using magnitude asymmetry. characters the HET showed the least variation 3 and symmetry range (tabl. fig. 1). These results are similar to those obtained in other works where it becomes evident that the individuals show for traits homozygous greater variability morphometric coefficient of of than the variance, variation, (estimated by degree symmetry, etc.) MI TT ON & for a GRANT, 1984, ieterozygous (see review). In our when we the HET with the individuals case, compared homozygous (HHP and the same was observed : the showed variance PHP), tendency homozygous greater and for the characters the diffe- However, greater asymmetry morphometric analyzed. rences between HHP and HET were in 79 100 of the cases, statistically significant p. whereas the differences between PHP and HET were in 33 only statistically significant 100 of the made. p. comparisons The HHP differ from the PHP individuals in 66 100 of the cases. significantly p. These differences were not due to differences in the 5 biochemical loci analyzed (both the level of the of individuals were for but to homozygous them), homozygosity types rest of the HHP individuals are for chromosomes II genotype (the totally homozygous of and which 80 100 of all the D. III, melanogaster, represent approximately p. genome L EWO NTIN , 1974). The made between HET and PHP individuals were similar in to comparisons type those carried out in other works with individuals taken from natural dealing popula- of tions. In both cases the individuals were classified to their level homozygo- according for some biochemical loci. In our case the differences between HET and PHP were sity to the constitution which these individuals showed for the 5 due, genetic fundamentally, biochemical loci For the rest of there was no evidence to analyzed. genotype suggest that there were differences between because to obtain the PHP and the HET them, a minimum of 10 or 20 different lines were Material and populations, pooled (see NEi et al. have demonstrated that a random of 10 chromo- methods). (1975) sample about 100 of the total somes from a natural reconstruction of 90 population permits p. contained in these natural genetic variability populations. The data the null tested here and are consistent with presented reject hypothesis the that the the level the further these individuals hypothesis higher homozygosity away are from the center of the character distribution and from bilateral morphological symmetry. These between and relationship protein heterozygosity developmental stability to be but are not universal McAN- 1980 ; appear general, they certainly (H ANDFORD, DREW et these are not in all al. , relationships expected characters, 1982). Certainly, S OULE that this is more to be found when (1982) predicts relationship likely stabilising selection can be shown to on the character The results operate analysed. negative et al. in the fit this McANDREW reported by (1982) plaice (Pleuronectes platessa) may In the 2 of the characters and prediction. present study morphological (dorsocentral D. scutellar showed a canalization in natural of melanogas- bristles) strong populations whereas in the other two and fifth abdominal sternite no ter, (sternopleural bristles) selection can be demonstrated. in our case the 2 of However, stabilising types characters showed the same with to the tendency respect enzymatic heterozygosity 2 and the HET were less variable and more than (tabl. 3) ; symmetric homozygous individuals. This correlation between and negative allozyme heterozygosity morphological variance and be in different One asymmetry may interpreted ways. interpretation that the biochemical marker loci are to linked the suggests genes determining morpho- the observed is caused linked or chromosome character ; logical relationship by genes and not the loci alone. This does not seem feasible to segments by enzyme hypothesis our results because : explain It is difficult to that from thousands of biochemical loci of a) accept among 5 of chosen at are associated with trait them, random, loci, Drosophila, morphological also chosen at random. Our have no chromosomal inversion. b) synthetic populations is not a common in of Droso- c) Linkage disequilibrium phenomenon populations of natural reveal little or no phila ; surveys populations generally linkage disequili- and studies in reveal that the brium, experimental populations linkage disequilibrium stochastic et C LEGG initially generated by processes decays (H EDRICK al. , 1978 ; quickly et SnrrcHEZ & al., 1980 ; R UBIO ). Another considered LE nxY et al. is that the of possibility, by (1984), heterozygosity due to the the influences In this the effect is case, enzymes causally development. Ldh-3 of rainbow trout indicate that null itself. Their results with the locus enzyme allele and allele are more than for the active heterozygotes asymmetrical homozygotes is This is not our that the locus itself case, asymmetry. they suggest enzyme affecting show that the for the because results & (B LANCO Rusio, 1983) homozygotes preliminary different at individual loci do not differ from each other with to electromorphs respect in this of the characters utilized morphometric study. any forward to correlation between Another the hypothesis put explain heterozygosity and is MrrroN & K OEHN that developmental stability proposed by (1985). They suggest to since an for and face during development organism requires energy biosynthesis stressful environmental the should be less affected changes, heterozygotes during environmental variations since these on the in are, development by genotypes average, a and because of this the exhibit balance, heterozygotes greater higher positive energy In the data there are no consistent indications developmental stability. presented here, to or to this but in our it seems more reasonable to reject accept hypothesis, opinion In the level of the vs our results. fact, genetic background (HHP explain heterozygosity as well as the at 5 loci vs show influence PHP) heterozygosity enzymatic (HET PHP), on the level of characters and we think that this variability morphological phenomenon effect. is an of a expression general heterozygous on of are more studies enzyme required. Certainly, physiology polymorphisms Received 1985. May 23, 18, Accepted April References B IEMONT 1983. and in natural C., Homeostasis, enzymatic inbreeding heterozygosity depression of 179-189. Genetica, 61, populations Drosophila melanogaster. B LANCO Ru B to 1983. Relaciones entre variantes enzimaticas caracteres cuantitativos en G., J., y lineas isocromos6micas de D. XIX Jornadas de melanogaster. Proceeding of Luso-Espanolas 20-24 Instituto Botanico Dr. Julio Genetica, Coimbra, septem6re 1983, p. 157, Henriques, Universidade de Coimbra. Coimbra, C LEGG K IDWELL H ORCH 1980. and correlated V. M.T., J.F., C.R., Dynamics genetic systems. Rates of of in of decay linkage disequilibria experimental populations Drosophila melanogas- ter. 217-234. Genetics, 94, E ANES 1978. variance and in the monarch W.F., Morphological enzyme heterozygosity butterfly. 263-264. Nature, 276, EL -K ASS nsY 1982. Associations between and traits in Y.A., allozyme genotypes quantitative menziesii 103-115. Douglas-fin (Pseudotsuga (miirb) Franco). Genetics, 101, F LEISCHER J OHNSTON KL1 TZ 1983. and R.C., R.F., W.J., Allozymic heterozygosity morphological variation in house 628-629. Nature, 304, sparrows. G RELL 1967. of in E.H., variants Electrophoretic a-glycerophosphate dehydrogenase Drosophila 1319-1320. Science, 158, melanogaster G RELL J ACOBSON MURPHY 1965. Alcohol in melano- E.H., K.B., J.B., dehydrogenase Drosophila Science, 149, gaster. G UNAWAN 1981. The between and variation in D. buzzatii. B., relationship quantitative allozymic In : GtBSON O AKESHO TT J.B., J.G. Genetic Studies 147-157. (ed), of Drosophila Populations, Australian National Canberra. Press, University H ANDFORD 1980. at loci and variation. 261- P., Heterozygosity Nature, 286, enzyme morphological H EDRICK J AIN H OLDEN 1978. Multilocus in evolution. In : H ECHT P., S., L., M.K., systems H OLDEN S TEERE W ALLACE B. vol. L., W.C., 11, (ed.), Evolutionnary Biology, 101-184. Plenum New York. Press, J OHNSON 1964. Genetic variation of ADH in D. 906-907. F.M., melanogaster. Nature, 204, K AT 1982. The between for loci and P.W., relationship heterozygosity enzyme developmental homeostasis in of bivalves Am. 824- Nat., 119, peripheral populations aquatic (Unionidae). 832. in K NOWLES MI TT ON 1980. Genetic and radial Pinus P., J.B., heterozygosity growth variability contorta. Silvae 114-118. Genetica, 29, K OBYLIANSKY L IVSHITS 1983. between biochemical and E., G., morpho- Relationship heterozygosity in Hum. 215-223. human Ann. 47, logical variability populations. Genet., K OEHN S HUNWAY 1982. A for differential rate E., R.K., genetic/physiological explanation growth of Mar. Biol. individuals the American Crassostrea Lett., 3, among oyster virginica (Gmelin). 35-42. L EARY A LLENDORF K NUDSEN 1983. and hetero- R.F., F.W., K.L., Developmental stability enzyme in rainbow trout. 71-72. zygosity Nature, 301, L EARY A LLENDORF K NUDSEN 1984. of R.F., W.F., K.L., heterozy- Superior developmental stability Am. 540-551. at loci in salmonid fishes. gotes enzyme Nat., 124, L EDING G URIEs B ONEFIELD 1983. The relation of to in F.T., R.P., B.A., growth heterozygosity 1227-1238. Evolution, 37, pitch pine. L ERNER 1954. Genetic Homeostasis. 134 Oliver and LM., pp., Boyd, Edinburgh. LE woNTIN 1974. The basis 346 Columbia R.C., genetic of evolutionary change. pp., University New York. Press, between McANDREW WARD B EARDMORE 1982. Lack of B.J., R.D., J.A., relationship morphological variance and in the Pleuronectes 117-125. 48, enzyme heterozygosity plaice platessa. Heredity, MI TT ON 1978. between for loci and variation of J.B., Relationship heterozygosity enzyme morpho- characters in natural 661-662. Nature, 273, logical populations. MI TT ON K NOWLES STURGEON L INHART D AVIS 1981. Associations between J.B., P., K.B., Y.B., M., and rate variables in western forest trees. In : C ONCLE M.T. heterozygosity growth (ed.), Proc. North American Forest Trees and Forest General Insects, USDA, Symp. Isozymes Technical 27-34. D.C. : USGPO. PSW-48, Report Washington MI TT ON GRANT 1984. Associations and J.B., M.C., rate, among protein heterozygosity, growth Rev. 479-499. homeostasis. Ann. Ecol. developmental Syst., 15, MI TT ON K OEHN 1985. Shell variation in the blue mussel edulis and its J.B., R.K., L., shape Mytilus association with J. Mar. Biol. 73-80. enzyme heterozygosity. Exp. Ecol., 90, N EI M ARUYAMA The bottleneck effect and in C HAKRABORTY 1975. M., T., R., genetic variability 1-10. Evolution, 29, populations. PIERCE and in the B.A., MI TT ON 1982. J.B., Allozymic heterozygosity growth tiger salamander, J. 250-253. 73, Ambystoma tigrinum. Heredity, S AKAI TUNG S KANDALIOS 1969. studies of R.K., D.A., J.S., Developmental genetics L-aminopepti- dase in Mol. Gen. Genet., 105, 24-29. Drosophila melanogaster. S ANCHEZ R UBIO J. Evolution du des loci dans des J.A., polymorphisme enzymatiques populations de III. de liaison entre les loci Adh et exp6rimentales Drosophila melanogaster. D6s6quilibre to a-Gpdh (Submitted Genetica). S INGH Z OUROS 1978. Genetic variation associated with rate in the American S.M., E., growth 342-345. oyster (Crassostrea virginica). Evolution, 32, S OKAL R OHLF 1979. Biometria. 483 Edi. Madrid. R.R., F.J., pp., Blume, S OULE 1967. Phenetics of natural II. and evolution in a lizard. Am. M., populations. Asymmetry 140-167. Nat., 101, S OULE 1979. and another look. 396- M., Evolution, 33, Heterozygosity developmental stability : S OULE 1982. Allomeric variation. 1. The and some Am. 751- M., theory consequences. Nat., 120, and Vp uEN HOECK L ERMAN 1982. and under sexual R.C., S., Heterozygosity developmental stability asexual 768-776. Evolution, 36, breeding systems. W ALLIS Fox 1968. Genetic and between two alkaline B.B., A.S., developmental relationship in Biochem. Genet., 141. phosphatases Drosophila melanogaster. 2, WRIGHT 1963. The of an esterase in 787- T.R.F., Genetics, 48, genetics Drosophila melanogaster. Z OUR os S INGH MILES 1980. Growth rate in an overdominant S.M., H.E., E., oyster : phenotype and its 856-867. Evolution, 34, possible explanations. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Genetics Selection Evolution Springer Journals

Enzymatic heterozygosity and morphological variance in synthetic populations of Drosophila melanogaster

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Springer Journals
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Copyright © Inra 1986
Subject
Life Sciences; Animal Genetics and Genomics; Evolutionary Biology; Agriculture
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1297-9686
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10.1186/1297-9686-18-4-417
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Abstract

and variance Enzymatic heterozygosity morphological in of Drosophila synthetic populations melanogaster Gloria BLANCO LIZANA J.A. SANCHEZ PRADO de Universidad de Gen6tica, Oviedo, Asturias, Spain Departamento Summary Several have shown a correlation between and reports negative allozyme heterozygosity In this carried out on of variance and work, morphological asymmetry. synthetic populations we have tried to find out if a can be established between the Drosophila melanogaster, relationship of 4 characters and for 5 variability (and symmetry level) morphometric homozygosity enzymatic loci. Our results to a correlation between (and point positive morphological variability asymmetry) and loci. In of loci also influenced for the other homozygosis enzymatic addition, heterozygosity developmental stability. words : mela- variance, homeostasis, Key Morphological enzymatic polymorphism, Drosophila nogaster. Résumé et variance dans des Hétérozygotie enzymatique morphologique populations synthétiques de Drosophila melanogaster. Plusieurs montrent taux élevé l’individu ou la de expériences qu’un d’hétérozygotie (de est associé à une faible variance et un faible population) généralement morphologique degré Dans ce réalisé dans des de travail, d’asymétrie. populations synthétiques Drosophila melanogaster, nous avons de voir s’il était d’établir une relation entre la variabilité essayé possible (et de caractères et le taux déterminé sur 5 locus l’asymétrie) morphométriques d’homozygotie Nos résultats une corrélation entre variabilité enzymatiques. indiquent positive (et asymétrie) et taux déterminé sur les locus De le morphologique d’homozygotie enzymatiques analysés. plus, taux du reste du influe aussi sur la stabilité du d’homozygotie génome développement. Mots clés : Variance homéostasie, morphologique, polymorphisme enzymatique, Drosophila melanogaster. I. Introduction a lot of data have been forward that variabi- Recently put showing morphological and decrease with of & lity asymmetry heterozygosity enzyme polymorphisms (M I TT ON For MI TT ON examined 3 of Fundulus GRANT, 1984). example, (1978) populations heteroclitus for 7 characters and 5 and found loci, morphological polymorphic enzyme that tended to have lower variation than E ANES heterozygotes phenotypic homozygotes. came to a similar conclusion after 6 loci and 2 (1978) examining polymorphic morpholo- traits in the monarch Danaus has been gical butterfly, plexippus. Enzyme heterozygosity as associated with either rate or in a wide reported growth developmental stability of birds et shellfish & al. , Z OUROS , 1978 ; range organisms : (F LEISCHER 1983), (S INGH Z OUR os et K OEHN & salamanders & al., 1980 ; S HUNWAY, MI TT ON , 1982), (PIERCE 1982), fish & & MI TT ON et (V RIJENHOECK L ERMAN, MI TT ON , 1980 ; C ll., 1982), plants (K NOWLES and insects 1981 ; EL -K ASSABY, 1981 ; B IEMONT , However, 1982) (G UNAWAN, 1983). there are a few results where these correlations were not found 1980 ; (H ANDFORD, McANDREW et al., 1982). Studies on were carried out on characters with bilateral symmetry morphological distribution L EARY et because 1979 ; K AT , 1982 ; al., B IEMONT , (S OULE , 1983 ; 1983), bilateral is a direct measure of which is the main homeostasis, symmetry developmental cause to which several to the classical work of L ERNER authors, according (1954), attribute this In if homeostasis is defined as the fact, relationship. developmental of an to form an in the face of external capability organism average phenotype a small deviation from bilateral should consti- perturbations (L ERNER , 1954), symmetry tute a reasonable measure of a decrease in homeostasis 1967 and (S OULE , 1979). the authors found it difficult to account for their that Generally, finding enzyme are less variable than In found it homozygotes. particular they heterozygotes surprising that such effects should be observed when 5 or 6 loci were screened out of the only thousands to be In recent different mechanisms expected polymorphic. papers possible are K OBLIANSKY & L IVSHITS in human and L EDING et al. suggested. (1983), populations, in are inclined to attribute the correlation to L EARY et al. (1983), pitch pine, inbreeding. considered that the locus itself influenced (1984) particular enzyme development. MI TT ON & K OEHN that is linked to (1985), propose enzyme heterozygosity energy of individuals and that the reflects the balance. budgets developmental stability energy The of exhibit is that explanation why they greater developmental stability heterozy- on the a and these gotes have, average, higher positive energy balance, genotypes should be less affected environmental variations. during development by stressing These results are also to the the germane controversy concerning adaptive signifi- cance of If the correlation between protein polymorphisms. negative enzyme heterozy- in these correla- and and gosity morphological variability asymmetry is, fact, general, tions cannot be in with a neutral for the and maintenance of agreement theory origin The variation at these loci should be at maintained, enzyme polymorphisms. enzymatic least in a et L EARY et part, by heterozygous advantage (McA ND REW al. , 1982 ; al. , 1984). we In our carried out on of work, melanogaster, synthetic populations Drosophila have between the and of examined the relationship variability symmetry morphometric characters and of for 5 biochemical loci chosen at random. In degree homozygosity our allowed us to measure the influence of addition, heterozygosity experimental design the of background genotype. II. Materials and methods a balanced lethal stock isochromosomal lines for chro- Using (CyL/Pm TM3/Pr), mosomes II and III were established from a natural of melano- population Drosophila in the wild. gaster recently caught Of these 117 were chosen because did not and were inversions, lines, they present for the different allelic variants of the 5 loci homozygous enzymatic analyzed (Adh, and Taken as a whole these lines constitute what we Est-6, Aph-l, a-Gpdh Lap-D). shall call The HHP with the same population (HHP). lines, highly homozygous for the 5 were crossed and maintained mass-culture. The 8 loci, genotype enzymatic by so constitute what we shall term formed, homozy- subpopulations altogether, partially 5 loci were in a In these the gous populations (PHP). PHP, enzymatic homozygous but the of the natural was reconstruc- state, background genotype population partially et because in all cases 10 or more HHP lines were ted, (NEi al. , 1975). Finally, pooled the PHP lines with for the 5 loci were crossed ; complementary genotypes enzymatic the of these 4 crosses were and will be offspring possible immediately analyzed, referred to as heterozygotes (HET). and fifth abdominal sternite The numbers of dorsocentral, scutellar, sternopleural bristles have been studied as characters. All but the last of these are morphometric bilateral characters and exhibit in the because they fluctuating asymmetry populations of individuals is the difference between a character on the left and sides right normally distributed about a mean of zero. In these cases the bristle numbers were determined for the left and sides on individual. The individuals were then classified right every to the absolute values of the difference between bristle number on the right according and left sides. We calculated the variance over all the individuals in morphological (s’) sampled each class PHP and the is the (HHP, HET) ; asymmetry percentage (A) average deviation in each class and the variation shown the individuals symmetry range (D) by the minimum and maximum values of found in each class. represents asymmetry we know that the for the different do not differ Moreover, homozygotes electromorphs from each other with to the values of of these any morphometric respect average characters Runic, (B LANCO 1983). Horizontal starch was carried out with 12 100 starch. Flies gel electrophoresis p. were in 0.01 ml of starch the method of J OHNSON homogenized gel buffer, using (1964). References of buffer and stain utilized are indicated in table 1. systems III. Results and discussion The null tested here is that individuals for the 5 hypothesis heterozygous enzymatic of and variance as the individuals loci have the same level morphological symmetry for the same loci. Table 2 shows the variance of characters homozygous morphometric in the 3 classes of and table 3 shows the results on bilateral populations analyzed, were with a t-test corrected for The values of symmetry. asymmetry (A), compared and the variances a one-tailed F-test & unequal variances, morphological by (S OKAL individuals in each The size is the number of R OHLF , analyzed 1979). sample (n) taken from all the lines of each class. In all cases the HHP individuals population, showed both the variance for the 4 characters greatest morphometric analyzed (tabl. 2) other and a deviation with to the bilateral On the greater respect symmetry (tabl. 3). the HET individuals the least variance and the of hand, displayed greatest degree 11 of the 14 made between both classes of individuals were symmetry ; comparisons 2 and The PHP individuals showed intermediate statistically significant (tabl. 3). variance and values 2 and differ from the HET in symmetry (tabl. 3) ; they significantly 2 of the 6 made and from the HHP in 4 of the 6 2 and comparison comparisons (tabl. The same results were obtained the of In 2 of the 3 3). using magnitude asymmetry. characters the HET showed the least variation 3 and symmetry range (tabl. fig. 1). These results are similar to those obtained in other works where it becomes evident that the individuals show for traits homozygous greater variability morphometric coefficient of of than the variance, variation, (estimated by degree symmetry, etc.) MI TT ON & for a GRANT, 1984, ieterozygous (see review). In our when we the HET with the individuals case, compared homozygous (HHP and the same was observed : the showed variance PHP), tendency homozygous greater and for the characters the diffe- However, greater asymmetry morphometric analyzed. rences between HHP and HET were in 79 100 of the cases, statistically significant p. whereas the differences between PHP and HET were in 33 only statistically significant 100 of the made. p. comparisons The HHP differ from the PHP individuals in 66 100 of the cases. significantly p. These differences were not due to differences in the 5 biochemical loci analyzed (both the level of the of individuals were for but to homozygous them), homozygosity types rest of the HHP individuals are for chromosomes II genotype (the totally homozygous of and which 80 100 of all the D. III, melanogaster, represent approximately p. genome L EWO NTIN , 1974). The made between HET and PHP individuals were similar in to comparisons type those carried out in other works with individuals taken from natural dealing popula- of tions. In both cases the individuals were classified to their level homozygo- according for some biochemical loci. In our case the differences between HET and PHP were sity to the constitution which these individuals showed for the 5 due, genetic fundamentally, biochemical loci For the rest of there was no evidence to analyzed. genotype suggest that there were differences between because to obtain the PHP and the HET them, a minimum of 10 or 20 different lines were Material and populations, pooled (see NEi et al. have demonstrated that a random of 10 chromo- methods). (1975) sample about 100 of the total somes from a natural reconstruction of 90 population permits p. contained in these natural genetic variability populations. The data the null tested here and are consistent with presented reject hypothesis the that the the level the further these individuals hypothesis higher homozygosity away are from the center of the character distribution and from bilateral morphological symmetry. These between and relationship protein heterozygosity developmental stability to be but are not universal McAN- 1980 ; appear general, they certainly (H ANDFORD, DREW et these are not in all al. , relationships expected characters, 1982). Certainly, S OULE that this is more to be found when (1982) predicts relationship likely stabilising selection can be shown to on the character The results operate analysed. negative et al. in the fit this McANDREW reported by (1982) plaice (Pleuronectes platessa) may In the 2 of the characters and prediction. present study morphological (dorsocentral D. scutellar showed a canalization in natural of melanogas- bristles) strong populations whereas in the other two and fifth abdominal sternite no ter, (sternopleural bristles) selection can be demonstrated. in our case the 2 of However, stabilising types characters showed the same with to the tendency respect enzymatic heterozygosity 2 and the HET were less variable and more than (tabl. 3) ; symmetric homozygous individuals. This correlation between and negative allozyme heterozygosity morphological variance and be in different One asymmetry may interpreted ways. interpretation that the biochemical marker loci are to linked the suggests genes determining morpho- the observed is caused linked or chromosome character ; logical relationship by genes and not the loci alone. This does not seem feasible to segments by enzyme hypothesis our results because : explain It is difficult to that from thousands of biochemical loci of a) accept among 5 of chosen at are associated with trait them, random, loci, Drosophila, morphological also chosen at random. Our have no chromosomal inversion. b) synthetic populations is not a common in of Droso- c) Linkage disequilibrium phenomenon populations of natural reveal little or no phila ; surveys populations generally linkage disequili- and studies in reveal that the brium, experimental populations linkage disequilibrium stochastic et C LEGG initially generated by processes decays (H EDRICK al. , 1978 ; quickly et SnrrcHEZ & al., 1980 ; R UBIO ). Another considered LE nxY et al. is that the of possibility, by (1984), heterozygosity due to the the influences In this the effect is case, enzymes causally development. Ldh-3 of rainbow trout indicate that null itself. Their results with the locus enzyme allele and allele are more than for the active heterozygotes asymmetrical homozygotes is This is not our that the locus itself case, asymmetry. they suggest enzyme affecting show that the for the because results & (B LANCO Rusio, 1983) homozygotes preliminary different at individual loci do not differ from each other with to electromorphs respect in this of the characters utilized morphometric study. any forward to correlation between Another the hypothesis put explain heterozygosity and is MrrroN & K OEHN that developmental stability proposed by (1985). They suggest to since an for and face during development organism requires energy biosynthesis stressful environmental the should be less affected changes, heterozygotes during environmental variations since these on the in are, development by genotypes average, a and because of this the exhibit balance, heterozygotes greater higher positive energy In the data there are no consistent indications developmental stability. presented here, to or to this but in our it seems more reasonable to reject accept hypothesis, opinion In the level of the vs our results. fact, genetic background (HHP explain heterozygosity as well as the at 5 loci vs show influence PHP) heterozygosity enzymatic (HET PHP), on the level of characters and we think that this variability morphological phenomenon effect. is an of a expression general heterozygous on of are more studies enzyme required. Certainly, physiology polymorphisms Received 1985. 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Journal

Genetics Selection Evolution – Springer Journals

Published: Dec 1, 1986

Keywords: Morphological Variance; Full Article; Synthetic Population; Enzymatic Heterozygosity

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