Natural selection for covariation in growth components in Tribolium castaneum

Mechanisms o f Ageing and Development, 6 (1977) 173-184

173

©Elsevier Sequoia S.A., Lausanne - Printed in the Netherlands

NATURAL SELECTION FOR COVARIATION NENTS IN TRIBOLIUM CASTANEUM

IN GROWTH

COMPO-

M. HANI SOLIMAN Department of Microbiology and Genetics, University o f New England, Armidale, N.S.W. 2351 (,4ustralia)

F. A. LINTS* Laboratoire de G~n~tique, Universit~ de Louvain, Place Croix du Sud 2, B-1348 Louvain-La-Neuve (Belgium)

(Received June 4, 1976;in revised form October 30, 1976)

SUMMARY The relationships between various components of growth were studied, both at the intra- and inter-populational levels, in twelve laboratory populations of Tn'bolium castaneum with widely different geographic backgrounds. The components of growth related to body weight - at the 13th day of larval life, Lw, at the first day of pupal life, Pw, at the first day of adult life, Aw, - and to developmental time - at pupation, Pt, at emergence of the adults, At. The relationships between those traits, presumably brought about by natural selection, were compared with similar relationships as disclosed in a study using lines artificially selected for some growth components. The correlations between Pw and Aw and between Pt and At are positive in both naturally and artificially selected populations. This is due to the fact that the rate of decrease in weight between Pw and Aw depends on Pw and to the fact that the developmental time between Pt and At is constant. The consistent significant correlation between growth rate, Lw, and both Pt and At contrasts with the absence of association between Lw and either Pw or Aw. This indicates that the rate of growth relates to developmental time and not to the final body weight. This is confirmed by the lack of consistent correlations, both at the intra- and inter-populational level, between weight, Pw and Aw, and developmental time, Pt and At. The balance achieved between those components of growth are discussed in terms of natural versus artificial selection and their bearing on various traits related to fitness are analyzed.

*To whom reprint requests should be addressed.

174 INTRODUCTION The relationship between various components of growth has been recently under extensive investigation in the flour beetle, Tribolium castaneum. Bell, his associates and others [1, 2] have demonstrated that such components are under genetic control. The interest of T. castaneum for growth studies stems from the fact that in that species selection for developmental time is generally effective [3-5]. In contrast, selection for developmental time appears to be impossible in Drosophila. In that species selection for a shorter developmental time was shown to be ineffective [6-9] and more recently, in strictly controlled experimental conditions, selection for developmental time was found to be ineffective in either direction when not biased by selection for another trait [10]. The two obvious components of growth in insects are body weight and development time. Number of instars could also be considered as a growth component. In T. castaneum the phenotypic variation of those components, which exist in various "wild" populations [11, 12] is for a part genetically controlled. On the other hand, as in Drosophila [13, 14], environmental agents, e.g. temperature and population density, also influence both traits in different ways: increasing temperature results in shorter developmental time and reduced body weight whereas increasing density prolongs developmental time and reduces body weight. The complex effect of such, and many more agents of natural selection will eventually lead to the establishment of given genotypes with particular genetic relationships between growth traits. This genetic link between body weights and developmental time was recently measured by the degree of variation in one trait when the other is selected for [15]. Previous studies [1, 2, 15] have used synthetic populations - namely the Purdue and Berkeley foundations, which are pools of a large number of laboratory populations - as a base for selection experiments. The present study will show that laboratory populations of T. castaneum, when studied individually under the same experimental conditions, show relationships, at both the intra- and inter-population levels, between the adult and pupal weights and between the pupation and eclosion times similar to those shown by selected lines [15]. However, at the inter-population level, the relationships between larval weight at a fixed age (growth rate) and body weights (lst-day pupa or adult) and between developmental time and body weights are different. Those last relationships are important in terms of strategy of adaptation by various populations under natural conditions. An objective of the present paper is thus to compare the effects of natural and artificial selection on the relationships between growth traits. The relatively large number of populations used allows a meaningful comparison between natural selection which under the influence of a large and undefined set of environmental conditions tends to maintain and/or adapt phenotype and genotype and artificial selection which aims at extracting the available genetic variability present within a given base population. Furthermore, the present study will call attention to the danger of using materials from limited origins to draw general conclusions about the behaviour of growth traits, and to the wide spectrum of population adaptations through development and rate of growth as observed even in a single set of environmental conditions.

175 MATERIALSAND METHODS Twelve populations are used in this study. Their choice was determined by their availability at the time of the study. The history of these populations before the beginning of this experiment is reported by Soliman and Hardin [11]. The populations are identified according to their geographical origin as follows: (1)CS (Capetown, South Africa), (2) CU (Chicago, USA), (3) ES (Edinburgh, Scotland), (4) KJ (Kyoto, Japan), (5) KJM (Kingston, Jamaica), (6) KN (Kano, Nigeria), (7) LE (London, England), (8) LP (Lisbon, Portugal), (9) MK (Makakos, Kenya), (10) MS (Madrid, Spain), (11) VB (Vicosa, Brazil), and (12) VM (Veracruz, Mexico). Eight populations are replicated five times; the other four from one to four times. Each replicate starts with thirty 13-day-old larvae. The experimental conditions are 33 °C, 70% relative humidity and a standard culture medium composed of 95% whole wheat flour and 5% dried brewer's yeast. Further details about the experimental conditions are to be found in Soliman and Hardin [ 11 ]. The tralts, measured on separately reared individuals, are length of developmental periods and body weights at various stages of development. Two traits related to developmental time (pupation time, Pt; and adult emergence time, At) are observed. Pupation time is measured from egg to pupation; adult emergence time from egg to eclosion and thus includes pupation time and duration of the pupal stage. (The adult emergence time so defined is different from the adult emergence time as described by Englert and Bell [15], and which related to the duration of the pupal stage only.) Body weight traits are: 13-day larval (Lw), first-day pupal (Pw), and first-day adult (Aw) weights. Pupal weight and adult weight are weights at a fixed time in the life cycle (pupation, emergence). Larval weight is at fixed calendar time (13th day after egg collection): it~'is a growth rate, Since the two sexes display similar behaviours, the graphic presentation will be restricted to the data for the males.

RESULTS

lntra-population relations Pupal and adult weights In all twelve populations, pupal weight is consistently and highly correlated with adult weight (rr~x Aw in Table I). A regression analysis has shown that the regression coefficients are significantly different from zero at least at the 0.05 level of probability. However, a test of homogeneity (Table II) indicates that in both males and females the r~gression coefficients am'ong the eight populations with five replications are not homogeneoos, although the regression lines appeared to be quite similar. This is due to the small standard deviations of the coefficients of regression. Similar relations between pupal and adult weights were also found by other investigators [2, 15] and were furthermore shown to be affected very little by various environmental or genetical differences [17].

176 TABLE I PHENOTYPIC CORRELATION COEFFICIENTS BETWEEN BODY WEIGHTS (Lw, Pw and Aw)

Population

N

rLw × Pw

N

rLw X Aw

rpw X Aw

72 78 70 65 70 75 61 50 15 32 70 78

-0.38* 0.14 -0.06 0.03 0.23 0.34* -0.15 0.44* 0.63* -0.16 0.00 -0.10

71 77 68 64 70 75 61 49 14 32 67 75

-0.29* 0.10 -0.05 0.10 0.05 0.37* -0.14 0.44* 0.63* -0.16 0.00 -0.10

0.90* 0.88* 0.88* 0.92* 0.88* 0.85* 0.84* 0.82* 0.97* 0.93* 0.97* 0.94*

75 69 79 72 78 67 57 67 11 28 75 71

-0.32* 0.40* 0.08 0.11 0.19 0.05 0.22 0.12 0.33 -0.24 0.16 -0.08

75 66 79 72 78 67 57 66 10 28 74 71

-0.31" 0.32* 0.16 0.18 0.30* 0.18 0.17 0.22 0.32 -0.33 0.17 -0.03

0.89* 0.87* 0.91" 0.93* 0.84* 0.90* 0.89* 0.71" 0.83* 0.87* 0.95* 0.92*

Males CS CU ES KJ KJM KN LE LP MK MS VB VM

Females CS CU ES KJ KJM KN LE LP MK MS VB VM

*Significant from zero at the 0.05 level of probability T A B L E II TEST OF HOMOGENEITY OF REGRESSION LINES FOR THE EIGHT POPULATIONS

Population (y on x) Aw on At on Pt on At on

Pw Pt Lw Lw

F values Males

Females

9.54* 1.82 9.81" 9.39*

2.10" 0.55 11.82" 9.44*

d.f. = 7 and 547 for males and 7 and 451 for females. *Significant at the 0.05 level of probability.

Developmental times The c o r r e l a t i o n s b e t w e e n p u p a t i o n time and adult e m e r g e n c e time are c o n s i s t e n t l y positive and highly significant (rptx At in Table III). This is in a g r e e m e n t w i t h the results

177 TABLE III PHENOTYPIC CORRELATION COEFFICIENTS BETWEEN DEVELOPMENTALTRAITS (Pt AND At) AND BODY WEIGHTS (Lw, Pw AND Aw)

Population N

rLwXPt

rpwxP t N

rLwXAt

rpwxA t

rptXAw rptxAt

rAwXAt

72 78 70 65 70 75 61 50 15 32 70 78

-0.60* -0.71" -0.68* -0.65* -0.79* -0.58* -0.72* -0.72* -0.78* -0.75* -0.77* -0.63*

0.37* -0.24* 0.29* 0.06 -0.17 -0.21 0.34* -0.25 -0.75* 0.59* 0.33* 0.46*

71 77 68 64 70 75 61 49 14 32 67 75

-0.67* -0.74* -0.68* -0.62* -0.79* -0.55* -0.71" -0.'/6" -0.59* -0.77* -0.76* -0.58*

0.43* -0.15 0.39* 0.09 -0.17 -0.23 0.40* -0.18 -0.40 0.53* 0.34* 0.52*

0.38* -0.15 0.32* 0.01 -0.08 -0.19 0.40* -0.30* -0.74* 0.58* 0.33* 0.48*

0.96* 0.91" 0.85* 0.97* 0.95* 0.98* 0.92* 0.93* 0.61" 0.92* 0.96* 0.93*

0.40* -0.13 0.33* 0.04 -0.09 -0.24* 0.35* -0.26 -0.45 0.47* 0.34* 0.48*

75 69 79 72 78 67 57 67 11 28 75 71

-0.59* -0.71" -0.72* -0.57* -0.64* -0.51" -0.51" -0.79* -0.76* -0.52* -0.66* -0.64*

0.23* -0.50* 0.19 0.20 -0.05 0.12 -0.03 -0.04 -0.22 0.11 0.18 0.25*

75 66 79 72 78 67 57 66 10 28 74 71

-0.61" -0.70* -0.73* -0.60* -0.63* -0.55* -0.57* -0.75* -0.86* -0.50* -0.60* -0.67*

0.30* -0.52* 0.27* 0.19 0.02 0.12 -0.14 -0.04 -0.24 0.15 0.23 0.27*

0.27* -0.44* 0.17 0.11 -0.08 0.15 0.02 -0.17 0.09 0.24 0.17 0.26*

0.97* 0.89* 0.89* 0.97* 0.90* 0.96* 0.88* 0.92* 0.74* 0.97* 0.94* 0.94*

0.31" -0.52* 0.20 0.07 -0.07 0.11 -0.10 -0.17 -0.34 0.25 0.19 0.22

Males CS CU

ES KJ KJM KN

LE LP MK MS VB VM

Females CS CU

ES KJ KJM KN

LE LP MK

MS VB VM

*Significant from zero at the 0.05 level of probability. of Dawson [ 18]. A test of homogeneity for the regression lines (Table II) indicates no significant difference among the regression slopes of the different populations for either males or females.

Developmental times and body weights (Pw, Aw) The correlations between pupal weight and pupation time or adult emergence time are not consistent among populations, some being positive and significantly different from zero, some others negative and significantly different from zero (rpwxP t and rpwx At in Table III). The same is true for the relation between adult weight and pupation time or adult emergence time (rAw x m and rAwx At in Table III). These results are somewhat in contrast with Dawson's [18]. When selecting for pupation time he found a negative correlation between pupal weight and pupation time. This correlated response was, however, not the same in both sexes and the correlation was of a higher significance in males.

178

Growth rate {L w) and other growth components Body weight. The correlation between larval weight, which because of the manner in which we measured it is in fact a measurement of growth rate, and pupal weight or adult weight vary considerably among populations (rLwx Pw and rLwX Aw in Table I). Some populations show significantly negative values while some others show significantly positive values. When a coefficient of correlation between Lw and Pw is significant for a given strain and a given sex, the coefficient of correlation between Lw and Aw is accordingly significant (except for KJM). It may therefore be concluded that growth rate, at least as it is measured in the present study, bears no relation to pupal or to the final adult weights. Similar results were reported by Englert and Bell [15] in lines selected for various growth components. However, the coefficient of correlation between two other estimates of growth rate, Le. the ratios Aw/At and Pw/Pt is perfect (r = 1.00) and the coefficient of correlation between Lw and the ratio Pw/Pt is, for the twelve populations, positive and significant (r = 0.72; n = 12;P < 0.01 for males and r = 0.78; n = 12; P < 0.01 for females,Developmental time. In contrast it clearly appears that growth rate (Lw) has a direct influence on both pupation time and adult emergence time - the higher the growth rate the shorter the pupation and adult emergence times. This is shown by the significant negative correlation between larval weight and pupation time or adult emergence time present in all populations (rLwx ~ and rLw x At in Table III). Similar results were also reported by various investigators selecting either for growth rate, i.e. larval weight at a specific age or developmental time and observing the correlated response in either trait

[1,2,151. A regression analysis has shown that the eight regression coefficients of adult emergence time on larval weight (At on Lw) are significantly different from zero. A test of homogeneity (Table II) indicates that the differences in regression coefficients among the eight populations are significant for both pupation time and adult emergence time on larval weight for both males and females.

Inter-population correlation As for the intra-p0pulation relationships, the inter-population correlation coefficients between pupal weight and adult weight (Fig. 1A), pupation time and adult emergence time (Fig. 1B) are highly significant. Also, growth rate Lw is negatively correlated with both pupation time and adult emergence time (Fig. 1C). There seems to be no relationship between weight (pupal or adult) and developmental time (pupation or eclosion). The coefficients of correlation referring to all those relationships are presented in Table IV. All these results agree with those reported by Englert and Bell [15] for nineteen genetically diverse populations. On the other hand, the relationship between larval weight and both adult and pupal weights is not significant as reported by these authors, although it is positive in both studies. Since all populations are reared in the same environment, since the number of individuals within populations is large, since there are wide genetic differences among

179 32

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205 245 285 PUPAL WEIGHT (10 - 5 GRAMS) 32

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PUPATION TIME (DAYS)

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cse "c "C-U%.vM ESK...., oMS

~ ----082 24
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;5 65 105 LARVAL WEIGHT (10 "S GRAMS)

Fig. 1. Relationship between the means of adult weight and pupal weight (A), adult emergence time and pupation time (B) and adult emergence time and growth rate (C) of twelve populations of 7'. castaneum (see text for population identification).

TABLE IV CORRELATION COEFFICIENTS BETWEEN BODY WEIGHT MEANS AND DEVELOPMENTAL TIME MEANS OF TWELVE POPULATIONS OF TR IBOLIUM CASTANEUM

Lw Pw Aw Pt

Pw

Aw

Pt

At

0.31

0.20 0.99**

-0.79** 0.03 0.07

-0.82** -0.05 0.06 1.00"*

**P < 0.01.

populations, and since the relationships in populations selected for various components of growth are similar, it is possible to assume that the observed phenotypic correlations between traits is mainly genetic in origin. DISCUSSION

Components of growth In discussing the relationship between growth traits it is important to keep in mind that the sources of variation at the intra-population level are genetic as well as environ-

180 mental, while those at the inter-population level are mainly genetic. In other words, the relationships disclosed at the intra-population level are representative of the results of an adaptational trend which is not necessarily uniquely related to morphogenesis, while the relationships disclosed at the inter-population level are mainly morphogenetic. Some Of the phenotypic correlation coefficients (Pw × Aw, Pt × At and Lw × Pt or At) are quite consistent among populations (Tables I and III) and the same relationships hold true at the inter-population level (Table IV). This consistency strongly suggests that those relationships are under genetic control, a conclusion which is also justified on the basis of artificial selection studies [15]. Such genetic correlations between characters may be due either to pleiotropy, or to linkage. Our experimental approach does not ihclude selection, Le. a rearrangement of the genetic information and/or a modification of the gene frequencies, nor inbreeding or crossbreeding, i.e. a modification of the genotype frequencies. It therefore does not allow us to discriminate with any certainty between those two possibilities. Furthermore in the present case, which refers to traits directly related to development, a genetic control of growth patterns acting for instance through the ontogenetic regulation of growth hormones could be another cause for an apparent genetic correlation. Several other relationships (Lw × Pw or Aw and Pw or Aw × Pt or At, Tables I and III) are both not consistent among populations and non-significant at the inter-population level (Table IV). These relationships deserve closer attention. Since both body weight and development time are influenced by a large number of genes, natural selection may result in various combinations of genes distributed among different linkage groups and showing various degrees of dominance. The complexity of such an integrated genetic structure controlling quantitative traits may lead to situations where selection for a trait may or may not result in a response for another. Gene-environment interactions also have significant effects on the expression of both body weight and development time [2, 11, 12]. The interaction not only affects the individual traits but also the relationship between them. For example, the phenotypic correlation betweerl 15-day larval weight and adult weight was found to be positive and significant at 40% r.h. and non-significant at 70% r.la. In the same way, the correlation between adult weight and age at pupation was found to be positive and significant at 70% r.h., while negative and non-significant at 40% r.h. [ 17]. Concerning the relation between development time (Pt or At) and weight (Pw or Aw) it is expected, at first glance, that a population that takes a longer time to develop will have heavier adults. However, artificial selection for early pupation time produced strains showing a positive relationship between pupation time and pupal weight, while selection for late pupation time produced two strains, out of three, where pupation time and pupal weight were negatively correlated [4]. This inconsistency was suggested to be due to genetic drifts. The present results do not substantiate this interpretation. Indeed, the population that took the longest time to develop (K J) is not the heaviest (Fig. 2) and the second to it (VB) yielded the smallest individuals. Furthermore, different populations may exhibit correlations between pupation time and pupal weight which are significant and either positive or negative (Table III).

181 290

200

,,o • ---

15

19 TIME

25

• KJ A CU

31

(DAYS)

Fig. 2. Overall growth curves of the eight populations of T. eastaneum used in the analyses of variance (see text for population identification). The larval weight at fixed age and pupal weight have been shown to be positively correlated to a high degree [15, 17]. In the present study this was true only for KN, LP and MK males and CU females and actually in one population, CS, the relationship was significantly negative for both males and females. Larval weight at fixed age is not a simple trait as it combines weight and development time, in fact it is an index of growth rate. The observed highly significant negative correlation between pupation time and 13-day larval weight (Lw × Pt; Table III) was expected, since a delayed pupation, due to a longer development time, will automatically result in smaller larvae at a fixed age. This relationship has a genetic basis [4, 15]. The negative sign of the correlation indicates that there is a balance between the two traits where developmental time acts as a stabilizer to find weights acceptable to the natural limits. In Drosophila, Robertson [16] found that the presence or absence of correlation between body size and duration of larval period is important in stabilizing body weight and in providing an alternative route for a similar size. A different diet may also have a different effect on the relationship [16]. Growth curve

A better understanding of the dynamics of growth may be obtained when the components of growth, i.e. weight and developmental time are brought together in growth curves. Figure 2 shows the means of the 13-day larval, pupal and adult weights [11] plotted against their respective mean developmental times [12] for the eight populations which were studied by means of five replicates. In general these growth curves resemble those of T. confusum [19] and of T. castaneum [1, 17, 20]. During development larval weight gradually increases, reaches a peak prior to pupation, after which weight gradually decreases until adult emergence [1, 17, 19, 20]. In the present study the expected exponential nature of the curve cannot be detected for there is only one measurement of body weight at each stage of development. Most of the populations here studied, although there are still some differences between

182 them, closely resemble each other. The VB and KJ populations are however quite distinct from the others, VB being characterized by light pupal and adult weight, KJ by a long developmental time. These differences between the two lines may be due to differences in number of instars [20. 21]. T. castaneum has usually six instars [20, 21] but some individuals might have eleven or more [2]. However, increasing the number of instars increases the time to pupation and the pupal weight [17, 20, 21]. Furthermore, it was also found that the number of instars is negatively correlated with the 15-day larval weight [17]. It is also apparent from Fig. 2 that a population which develops rapidly may yield individuals with a heavy adult body weight. This shows that it is not only the increase in the number of larval moults which causes an increase in body weight but that another mechanism may also be involved. These mechanisms seem to oppose each other. (Actually, Englert and Bell [17] found that the number of instars is positively correlated with pupation time at 40 and 70% rJa. but with body weight at 70% r.h. only.) The present results fndicate that such a second mechanism may be more common than the first one (number of larval moults) since it is less dependent on environmental variations. LE o

o3 5O ~E

LE CoS.KN • MS VMo • L P

CSeoES oVM

0

I'-"i-

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MS o KJM •

(3c (-3

40

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190

I

2tO

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230 PUPAL

WEIGHT

I

250 (10 - 5

I

270

I

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::'90

GRAMS)

Fig. 3. Relationship between the means of pupal weight and the differences between pupal and adult weights of twelve populations of T. castaneum (see text for population identification). The loss of weight observed between the pupal and adult stages (Fig. 2) depends on the pupal weight both in males and in females (Fig. 3). The same is true in lines selected for various growth components as a calculation of the correlation between pupal weight and rate of loss between the pupal and adult stages performed on the data of Englert and Bell [15] has shown (r = 1.00; n = 19). Both results indicate that in becoming an adult a heavy pupa loses proportionately more weight than a light pupa. This may be due to a proportionately larger water content and/or to a larger surface of the heavy pupae. Furthermore, this loss seems to be independent of the duration of the pupal period which was shown to be similar for all populations [ 12, 15].

Effect of the distribution of development on body weight The inconsistency of the relationship between developmental time and pupal or adult weight (Pt and Aw or Pw; At and Aw or Pw; Table III) is remarkable. It may be

183 argued that such inconsistency is due to the effect of the distribution of developmental time on body weight. Howe [20, 22-24] drew attention to this problem in his studies of both laboratory and field populations of 7'. castaneum. The problem was also emphasized by King and Dawson [2] and Kence [21]. The g~ and g2 statistics, which measure the deviations from a normal distribution by measuring the degree of skewness and kurtosis, have been calculated. The distributions, symmetrical for 10 populations, are leptokurtic for all 12 populations. This indicates that there is more concentration around the means than for a normal distribution. This could be due to the sampling procedure. Indeed Kence [21] found that the handling procedure may affect the distribution of developmental times. Another reason for this concentration could be the relatively small sample size used in the present study. Both Howe and Kence used a larger sample size. Leptokurtosis could also be due to the environmental temperature used in the present experiment which is higher than that used by Howe and Kence. A lower temperature extends developmental time and reveals a bimodality which because of a smaller range of pupation time, may be masked at a higher temperature. Humidity also influences bimodality. Holdaway [26] found that shortening developmental time by increasing humidity obscures the bimodality which is apparent when developmental time is longer because of a lower humidity. Such dimorphism, although influenced by crowding, handling and various environmental factors was claimed to have a genetic basis and to be controlled by the number of instars [20, 21 ]. Both Howe [20] and Kence [21] have shown that the bimodality of the pupation time is associated with some changes in the pupal weight. Considering the whole population, they found a low positive correlation between those two traits, but separating the fast from the slow fraction revealed a high negative correlation within each of the two fractions. Accordingly, it was expected that artificial selection for pupation time would result in a response for that negative relationship. Englert and Bell [4, 15] demonstrated, however, that such a relationship could not be selected for even when the selection intensity was of 20%, i.e. equivalent to the slow fraction observed by Howe and Kence. This observation is supported by the present study where that relationship is not significant either at the inter-population level (Table I V ) o r within the populations (Table III). The relations between development time and body weight with two other quantitative traits, reproductive fitness and longevity, will be discussed in two other papers

(27, 2s). REFERENCES 1 A. E. Bell, The nature of selection responses in Tribolium, Jap. J. Genet., 44 (Suppl. 1) (1969) 299. 2 C. E. King and P. S. Dawson, Population biology and the Tribolium model, Evol. Biol., 5 (1972) 133. 3 P. S. Dawson, Genetic homeostasis and developmental rate in Triboliurn, Genetics, 51 (1965) 873. 4 D. C. Englert and A. E. Bell, Selection for time of pupation in Tribolium castaneum, Genetics, 64 (1970) 541. 5 M. H. Soliman, Variable effects of X-irradiation on Tribolium castaneum and T. confusum due to strain and "age at pupation", Ph.D. Thesis, University of Alberta, (1972).

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