Nikola Tucić

GENETIC CAPACITY FOR ADAPTATION TO COLD RESISTANCE AT DIFFERENT DEVELOPMENTAL STAGES OF DROSOPHILA MELANOGASTER

There are few studies on the genetic control of resistance to cold temperature in Drosophila, despite the fact that this component of fitness may be an important adaptation to extreme fluctuations or constant low temperature. Data suggest that in some species of Drosophila seasonal variation in gene arrangement frequencies are related to temperature adaptation. Dubinin and Tiniakov (1945, 1946) in D. funebris, Dobzhansky (1948, 1956, 1958) in D. pseudoobscura, Levitan (1951) in D. robusta, and Mohn and Spiess (1963) in D. persimilis have provided evidence that particular chromosomal segments (marked by inversions) may be responsible for the control of resistance to low temperature. Marinkovic et al. (1969) have provided evidence in D. pseudoobscura that cold resistance is associated with certain chromosomal inversion types. Astaurov (1963) stressed that every stage of development in poikilotherms must be adapted to the environmental conditions in which they live. Crumpacker and Marinkovic (1967) measured the survival of eggs, larvae, pupae and adults of D. pseudoobscura in a series of different exposures to low temperatures (from 0 C to -10 C), under laboratory conditions. Jefferson et al. (1974) have also provided evidence that different levels of resistance to cold can be demonstrated in different developmental stages of D. pseudoobscura. The studies reported here on D. melanogaster were undertaken for two reasons: (1) to understand the potential of each developmental stage in overwintering under natural conditions; and (2) to learn more about the genetic determination of this complex character during development.

Laboratory evolution of longevity in the bean weevil (Acanthoscelides obtectus)

In this study we examined the effects of long‐term selection on early and late reproduction in the bean weevil. The pure lines and the hybrids between the lines within a selection regime were compared for longevity, early and late female fecundity, male mating ability, pre‐adult developmental time and wet adult weight. Comparison of hybrid with pure lines provided some evidence for inbreeding despression in the lines from both selection regimes. We found that virgin and mated adults of both sexes from the “old” lines lived longer than “young” line beetles. Comparisons of the hybrid “young” with hybrid “old” lines revealed a trade‐off between early and late fecundity of females. For noncompetitive mating ability of males there was no difference between the lines with different rates of senescence when the males were young. But, when the males were older, beetles from the lines selected for delayed senescence expressed superior mating ability. In addition, the “old” line beetles take longer to develop and are heavier than those from “young” line beetles. Although these data suggest that shorter pre‐adult developmental time may imply more rapid senescence, there is the possibility of inadvertent selection for rapid development in the “young” lines and this complicates the interpretation of the observed trade‐off between the pre‐adult and adult performances.

Adaptation of the gypsy moth to an unsuitable host plant

The pattern of adaptation with regard to life history traits and traits thought to be important in feeding habits of caterpillars in two populations of the gypsy moth (Lymantria dispar L.; Lepidoptera: Lymantriidae) originating from the locust tree (Robinia pseudoacacia; Fabaceae) and oak (Quercus petrea; Fagaceae) forests were investigated in the laboratory. The Robinia population has experienced unsuitable locust tree leaves as an exclusive food resource for more than 40 years. Since Quercus species are the principal host plants of the gypsy moth, the specific objectives of this study have been to measure the extent of differentiation between ancestral and derived populations in several life history traits (egg‐to‐adult viability, duration of larval and pupal stages, and pupal weight) and nutritional indices – relative growth rate (RGR), relative consumption rate (RCR), assimilation efficiency (AD), gross growth efficiency (ECI), and net growth efficiency (ECD). Significant differences between the Quercus and Robinia populations were detected in pupal duration, RGR, RCR, and AD. The presence of a significant population × host interaction in traits such as preadult viability, duration of pupal stage, RGR, and ECI suggests that adaptation of the gypsy moth to the unsuitable host might be ongoing. Using a full‐sib design, we screened for genetic variation in life history traits within both populations, and examined the genetic correlations of performance across oak and locust leaves within both populations. The genetic variances for analyzed life history traits were lower under conditions that are commonly encountered in nature. Our data show that positive cross‐host genetic correlations preponderate within both populations.

LABORATORY EVOLUTION OF LIFE-HISTORY TRAITS IN THE BEAN WEEVIL (ACANTHOSCELIDES OBTECTUS): THE EFFECTS OF SELECTION ON DEVELOPMENTAL TIME IN POPULATIONS WITH DIFFERENT PREVIOUS HISTORY

In this study we examined the direct and correlated responses for fast and slow preadult development time in three laboratory populations of the bean weevil (Acanthoscelides obtectus). The first population (“base,” B) has experienced laboratory conditions for more than 10 years; the second (“young,” Y) and the third (“old,” O) populations were selected for early and late reproduction, respectively, before the onset of the present experiments. All three populations are successfully selected for both fast and slow preadult development. The realized heritabilities are very similar in all populations, suggesting a similar level of the additive genetic variance for preadult development. We studied the correlated responses on the following life‐history traits: egg‐to‐adult viability, wet body weight, early fecundity, late fecundity, total realized female fecundity, and adult longevity. All life‐history traits examined here, except for the egg‐to‐adult viability, are affected by selection for preadult development in at least in one of the studied populations. In all three populations, beetles selected for slow preadult development are heavier and live longer than those from the fast‐selected lines. The findings with respect to adult longevity are unexpected, because the control Y and O populations, selected for short‐ and long‐lived beetles, respectively, do not show significant differences in preadult development. Thus, our results indicate that some kind of asymmetrical correlated responses occur for preadult development and adult longevity each time that direct selection has been imposed on one or the other of these two traits. In contrast to studies with Drosophila, it appears that for insect species that are aphagous as adults, selection for preadult development entails selection for alleles that also change the adult longevity, but that age‐specific selection (applied in the Y and O populations) mostly affects the alleles that have no significant influence on the preadult development. Implications of these findings on the developmental and evolutionary theories of aging are also discussed.

LABORATORY EVOLUTION OF LIFE-HISTORY TRAITS IN THE BEAN WEEVIL (ACANTHOSCELIDES OBTECTUS): THE EFFECTS OF DENSITY-DEPENDENT AND AGE-SPECIFIC SELECTION

Four types of laboratory populations of the bean weevil (Acanthoscelides obtectus) have been developed to study the effects of density‐dependent and age‐specific selection. These populations have been selected at high (K) and low larval densities (r) as well as for reproduction early (Y) and late (O) in life. The results presented here suggest that the r‐ and K‐populations (density‐dependent selection regimes) have differentiated from each other with respect to the following life‐history traits: egg‐to‐adult viability at high larval density (K > r), preadult developmental time (r > K), body weight (r > K), late fecundity (K > r), total realized fecundity (r > K), and longevity of males (r > K). It was also found that the following traits responded in statistically significant manner in populations subjected to different age‐specific selection regimes: egg‐to‐adult viability (O > Y), body weight (O > Y), early fecundity (Y > O), late fecundity (O > Y), and longevity of females and males (O > Y). Although several life‐history traits (viability, body weight, late fecundity) responded in similar manner to both density‐dependent and age‐specific selection regimes, it appears that underlying genetic and physiological mechanisms responsible for differentiation of the r/K and Y/O populations are different. We have also tested quantitative genetic basis of the bean weevil life‐history traits in the populations experiencing density‐dependent and age‐specific selection. Among the traits traded‐off within age‐specific selection regimes, only early fecundity showed directional dominance, whereas late fecundity and longevity data indicated additive inheritance. In contrast to age‐specific selecton regimes, three life‐history traits (developmental time, body size, total fecundity) in the density‐sependent regimes exhibited significant dominance effects. Lastly, we have tested the congruence between short‐term and long‐term effects of larval densities. The comparisons of the outcomes of the r/K selection regimes and those obtained from the low‐ and high‐larval densities revealed that there is no congruence between the selection results and phenotypic plasticity for the analyzed life‐history traits in the bean weevil.

Homosexual behaviour and its longevity cost in females and males of the seed beetle Acanthoscelides obtectus

The level of homosexual behaviour is evaluated in one laboratory population of seed beetle and derived lines selected to reproduce early (E) or late in life (L), where inadvertent selection for either low or high heterosexual activity has been detected. The magnitudes of homosexual interaction, measured as chasing and mounting individuals of the same sex, are estimated over different age classes. These magnitudes are correlated with previously observed levels and patterns of age‐specific variation of heterosexual activity of both sexes in the E and L experimental lines. The results obtained support the perception error hypothesis proposing that a low degree of sexual discrimination is genetically correlated with high sexual activity. The fitness costs of the same‐sex interactions are tested by assessing their effects on longevity. In both sexes, the longevities of homosexual pairs are reduced relative to individually‐housed virgin beetles in both the E and L lines, although homosexual interactions have a more pronounced effect on male survival than on female survival. Although the results obtained suggest that the longevity cost of homosexual interactions can be substantial, this cost is much smaller than the cost of heterosexual interactions.

Genetic variation and covariation among life history traits in populations of Acanthoscelides obtectus maintained on different hosts

We explored the extent to which two populations of Acanthoscelides obtectus (Coleoptera: Bruchidae), maintained in the laboratory for about 60 generations on common bean (Phaseolus vulgaris) and chickpea (Cicer arietinum) seeds, differ genetically in life history traits. Using a half‐sib breeding design, we screened for genetic variation in oviposition preference for two hosts within both populations, and examined whether this variation is correlated with weevil pre‐adult (egg‐to‐adult viability and egg‐to‐adult developmental time) and adult (female fecundity and longevity) fitness components on these two hosts. Significant differences between the Phaseolus and Cicer population were detected in viability, developmental time and oviposition preference, but not in female fecundity and longevity. The absence of a significant population × host interaction in all traits, except for developmental time in males, indicates that the Cicer population has not attained the status of ‘host race’. The estimated narrow‐sense heritabilities within population within host plant were in the low‐to‐moderate level (range: 1%–79%), with an overall average of about 24%. Within the population maintained on the chickpeas we detected significant genetic correlations between female developmental time on chickpea seeds and preference for chickpeas. In the population maintained on the primary host of this weevil species (the ‘Phaseolus’ population) we found no significant preference/performance genetic correlations. Data are also presented on the genetic correlations of preference and performance across host seeds within both populations. These correlations are found to be positive for all traits in both populations, indicating the absence of trade‐offs in either performance or behavioural response that might impose selection for host specialization within populations.

ACTIVITY OF SUPEROXIDE DISMUTASE AND CATALASE IN THE BEAN WEEVIL (ACANTHOSCELIDES OBTECTUS) SELECTED FOR POSTPONED SENESCENCE

Relationship of superoxide dismutase and catalase activities and aging were tested using bean weevil lines selected for postponed senescence. The beetles of different age (young and old) and mating status (virgin and mated) from the extended longevity lines were compared with their counterparts derived from the short-lived lines for activities of SOD and catalase. The old beetles from the long-lived lines had statistically significant higher activity of SOD than their controls. Although we did not find a significant effect of catalase on longevity, beetles originating from both types of lines exhibited an increased catalase activity during mating processes. In addition, we did observe an increased activity of catalase in one-day-old beetles of the short-lived lines relative to the same-aged individuals of the long-lived lines.

The effects of selection for early and late reproduction on metabolite pools in Acanthoscelides obtectus Say

Abstract  The present study was aimed at revealing the responses of metabolite pools to selection for alternative reproductive schedules in the seed beetle, Acanthoscelides obtectus Say (Coleoptera: Chrysomelidae: Bruchinae). The levels of metabolites (free sugars, glycogen, lipids, soluble and hydrophobic proteins) that were determined in virgin females and males at three ages from adult eclosion onwards were compared among the base population (B) and two derived lines that were selected for either early (Y) or late (O) reproduction. The results showed differences in the accumulation of metabolites during pre‐adult development, as well as in the pattern of their changes during adult ageing. Generally, in comparison to the B population, the short‐lived beetles from the Y line showed increased protein content and reduced carbohydrate and lipid content, whereas the opposite was true for the long‐lived beetles from the O line. Females from the O line exhibited slower utilization of energy reserves and a slower increase in protein contents than females from the Y line. Females contained higher levels of free sugars, glycogen and hydrophobic proteins and lower levels of lipids and soluble proteins than males, although the sexual dimorphism was not evenly expressed among lines. Age‐specific changes in metabolite contents were slower in females than males. Our findings suggest that trade‐offs among capital resources are a physiological basis of early/late fitness trade‐offs and point to a conservation of resources that can be used for somatic maintenance.

Phenotypic plasticity and character differentiation in a subdivided population ofIris pumila (Iridaceae)

Variation patterns in phenotypic plasticity and broad sense heritability of 26 characters were examined within and among closely adjacent habitats of the bearded iris,Iris pumila. It was found thatI. pumila has considerable differentiation for phenotypic plasticity and genetic variation over short distances. An analysis of relationships between character differentiation and phenotypic plasticity suggests that they could have evolved independently. Possible mechanisms for maintaining local differentiation of the observed plastic and genetic variation are also discussed.