Adult Viability Research Articles

GENETICS OF HOST-CACTUS RESPONSE AND LIFE-HISTORY EVOLUTION AMONG ANCESTRAL AND DERIVED POPULATIONS OF CACTOPHILIC DROSOPHILA MOJAVENSIS.

The extent of host-specific genetic variation for two life-history traits, egg to adult developmental time and viability, and one morphological trait closely tied to fitness, adult thorax size, was exposed by employing a nested half-sib/full-sib breeding design with Baja and mainland populations of Drosophila mojavensis recently extracted from nature. This study was motivated by the presence of substantial variation in life histories among populations of D. mojavensis that use the fermenting tissues of particular species of columnar cacti for feeding and breeding in the Sonoran Desert. Full-sib progeny from all sire-dam crosses were split into cultures of agria cactus, Stenocereus gummosus, and organ pipe cactus, S. thurberi, to examine patterns of genotype-by-environment interaction for these fitness components. Baja flies expressed shorter egg-to-adult developmental times, higher viabilities, and smaller body sizes than mainland flies consistent with previous studies. Significant sire and dam components of variance were exposed for developmental time and thorax size. Genotype-by-environment interactions were significant at the level of dams for developmental time and nearly significant for viability (P = 0.09). Narrow- and broad-sense heritabilities were influenced by host cactus, sex, and population. No strong pattern of genetic correlation emerged among fitness components suggesting that host-range expansion has not been accompanied by formation of coadapted life histories, yet the ability to estimate genetic correlations and their standard errors was compromised by the unbalanced nature of the data set. Genetic correlations in performance across cacti were slightly positive, evidence for ecological generalism among populations explaining the observed pattern of multiple host cactus use within the species range of D. mojavensis.

Genetic and environmental effects on the expression of peptidases and larval viability in Drosophila melanogaster.

The peptidase system in Drosophila melanogaster, consisting of dipeptidase-A, dipeptidase-B, dipeptidase-C and the leucine aminopeptidases, was used as a model to study the adaptive significance of enzyme activity variation. The involvement of the peptidases in osmoregulation has been suggested from the ubiquitous distribution of peptidase activities in nearly all tissues and the high concentration of amino acids and oligopeptides in the hemolymph. Under this hypothesis, larvae counteract increases in environmental osmotic stress by hydrolyzing peptides into amino acids both intra- and extracellularly to increase physiological osmotic concentration. The expression of the peptidases was studied by assaying for peptidase activities in third instar larvae of isogenic lines, which were reared under increasing levels of environmental osmotic stress using either D-mannitol or NaCl. Second and third chromosome substitution isogenic lines were used to assess the relative contribution of regulatory and structural genes in enzyme activity variation. Results indicate that: (1) genetic variation exists for peptidase activities, (2) the effect of osmotic stress is highly variable among peptidases, (3) changes in peptidase activities in response to osmotic stress depend on both genetic background and osmotic effector and (4) peptidase activities are correlated with each other, but these phenotypic correlations depend on genetic background, osmotic effector, and level of osmotic stress. Osmotic concentration in the larval hemolymph is correlated with leucine aminopeptidase activity, but changes in hemolymph osmotic concentration in response to environmental osmotic stress depend on the osmotic effector in the environment. Although these findings suggest that genetic and environmental factors contribute significantly toward the expression of enzymes with similar functions, a relative larval viability study of genotypes that differed significantly in dipeptidase-B (DIP-B) activity revealed that low DIP-B activity did not confer any measurable reduction in larval viability under increasing levels of environmental osmotic stress. These negative results suggest that, either DIP-B does not play a major role in osmoregulation or differential osmoregulation is not related to egg to adult viability in these tests.

Effects of High Temperature Stress on Adults and Eggs of Drosophila robusta and D. tripunctata

-The effects of high temperature stress on adult viability, fertility and egg mortality were studied in 13 strains each of Drosophila robusta and D. tripunctata. Sexes were studied separately. Adult viability of D. robusta was significantly greater than that of D. tripunctata at 27 and 30 C, temperatures approximating their maximum ambient temperatures in nature. At 20 C there were no significant differences between species in adult viability. Viability differences between strains and sexes were generally not significant at any temperature. Fertility decreased with increased treatment temperature. There were no significant differences in fertility between the species or sexes at any temperature except for 27 C, at which female fertility was significantly lower than male fertility for both species. Egg mortality of D. tripunctata was significantly higher at 27 compared to 20 C, while there was no significant difference in the egg mortality of D. robusta between those two temperatures. These results are consistent with the hypothesis that temperature primarily regulates the seasonal abundances of D. robusta and D. tripunctata in nature.

The evolutionary history of Drosophila buzzatii. XVI. Fitness component analysis in an original natural population from Argentina

SummaryThe adaptive significance of the chromosomal polymorphism of Drosophila buzzati has been studied by means of fitness component analysis in an original population from Argentina. The results show evidence of selection acting through pupal viability, longevity (adult viability) and fecundity on the second chromosome polymorphism, and through pupal viability and virility on the fourth chromosome polymorphism.Changes in chromosomal inversion frequencies throughout the life‐cycle suggested an endocyclic pattern of directional selection, which at first seems to be the only detectable mechanism responsible for the maintenance of the polymorphism. However, slow, long‐term frequency changes cannot be ruled out. The way in which endocyclic selection acts on this population is different from that in a colonized population previously studied; that is, different fitness components are involved in the maintenance of chromosomal polymorphism. The possible factors that may explain these differences are discussed.

Ovicidal and Sterilant Effects of Pyriproxyfen on Codling Moth and Oriental Fruit Moth, 1990

Abstract CM (1 to 4 dold, n = 400-1,236 per age) and OFM eggs (1 to 3 d-old, n = 318-963 per age) were exposed to pyriproxyfen, a juvenile hormone mimic, by immersion in aqueous solutions (3 replicates/dose). One-d-old CM eggs (n = 1,440) on nectarines were immersed in a 10 ppm aqueous solution of pyriproxyfen for 5 s. Eggs were incubated for 7-11 d to determine hatch. Two-d-old unsexed CM adults were topically exposed to pyriproxyfen in methanol solutions (3 replicates of 30 adults/dose). Either 15 CM females or males (1-2 d-pld) or 15 OFM females or males (1-d-old) were exposed to residues of 2,700 g (AI)/ha for 2 d and mated to an equal number of unexposed adults of the opposite sex (3 replicates per exposed sex of each species). Adult fecundity and egg viability were evaluated by placing treated adults in ovipositional cages made from cylindrical paper cartons (17 cm tall × 17 cm diam). Waxed paper sheets were used as an ovipositional surface. The waxed paper egg sheets were collected and replaced with new sheets every 2-5 d. Eggs were incubated at 26.8°C for at least 7 d, counted, and examined for hatch. Controls were handled in the same manner as test insects but never exposed to pyriproxyfen.

Fitness and its components in Drosophila melanogaster.

Fitness and its components in Drosophila melanogaster were estimated under the homozygous condition. All of these parameters, except for egg-to-adult viability and female fecundity, were measured under interspecific competition with D. hydei. The following results were obtained: (1) Significant genetic variation was detected in fitness, productivity, adult viability, total egg-to-adult viability and female fecundity. (2) Significant correlation was obtained between fitness and productivity (rp = 0.792 for phenotypic correlation, rg = 0.945 for genotypic correlation), between fitness and total egg-to-adult viability (rp = 0.355, rg = 0.395), and between fitness and female fecundity (rp = 0.451, rg = 0.511). (3) There was no significant correlation between total egg-to-adult viability and fecundity (rp = -0.046). The biological implications of the interrelationship between fitness and its components are discussed.

Effect of larval crowding on adult mating behaviour in Drosophila melanogaster

The effect of larval density on male mating success has been investigated with two strains of Drosophila melanogaster, a wild strain and a mutant strain, under low and high larval competition, and four different genotypic frequencies. The results show a strong sexual selection against mutant males when flies have been raised under low larval competition. Under high larval competition, there is a reduction in mating disadvantage of mutant males. In both instances, a frequency-dependent sexual selection exists. These results explain adequately the evolution of experimental populations where egg to adult viability and male mating success are the most important components of fitness.

Potential germline competition in animals and its evolutionary implications.

Mutation, mitotic crossing over and mitotic gene conversion can create genetic diversity in otherwise uniform diploid cell lineages. In the germline this diversification may result in competition between diploid germline phenotypes, with subsequent biases in the frequency of alleles transmitted to the offspring. Sperm competition is a well documented feature of many higher organisms and a model is developed to quantify this process. Competition, and hence selection, can also occur by differential survival of diploid lineages before meiosis. It is concluded that under certain circumstances germline selection is an efficient means of eliminating unfavorable alleles from the population. This does not require differences in adult fertility or viability which is the usual mechanism cited as causing changes in gene frequency in a population. It is proposed that such competition may play a role in maintaining the efficiency of basic metabolic pathways.

Differential mortality, fecundity and egg viability of Caribbean fruit fly, Anastrepha suspensa adults fed on three diets

Adults of the Caribbean fruit fly, Anastrepha suspenso (Loew) were fed on three diets in order to identify one that was optimal for adult longevity, fecundity and egg viability. The diets were a dry mixture of Brewer’s (hydrolysed) yeast and sugar (Diet A); Brewer’s yeast, sugar, agar, and water (Diet B); and a dry commercial diet (BioServ) with Brewer’s yeast, sugar and casein (Diet C). There were no significant differences in per cent adult mortality among the three diets. However, the longevity of females in Diet C was significantly reduced in comparison to that of females fed the other two diets. Diet C was also suboptimal for fecundity and egg viability. Diets A and B were optimal for and had similar effects on all parameters evaluated in this study. However, Diet A appeared to be the best if preparation time and ingredient costs are considered along with biological effects.

Survival and productivity of the tsetse, Glossina morsitans morsitans Westwood (Diptera: Glossinidae) maintained under different feeding regimens through four successive reproductive cycles in Zambia

Adult survival, puparial production, weight and viability, and the sex ratio of adults emerging from puparia of Glossina morsitans morsitans Westwood maintained through four successive reproductive cycles on daily (SO), every other day (SI) and every third day (S2) feeding regimen, respectively were investigated at Chilanga, Zambia. Only in puparial production (0.8 under SO and SI, 0.7 under S2) and puparial weight (25.1±0.2mg under S0, 24.1±0.3mg under S1, 22.5±0.3mg under S2) were significant differences (P<0.05 and <0.01 respectively) detected between feeding regimens. Nevertheless, a combination of SI and S2 regimens is recommended for further evaluation as a more convenient and economical alternative to the SO regimen for tsetse mass production in Africa.

Studies of Sibling Drosophila Species from Laguna Verde, Veracruz, Mexico: I. Species Frequencies, Viability, Desiccation Resistance, and Vagility

The sibling species Drosophila melanogaster and D. simulans were collected at Laguna Verde, Veracruz, Mexico. D. melanogaster was found in significantly greater frequency than was D. simulans. Ten isofemale lines of each species were tested for egg to adult viability, desiccation resistance, and vagility. D. melanogaster surpassed D. simulans in all three characteristics. The findings are discussed with reference to the climatic conditions at Laguna Verde and the expected effect of such an environment on the relative frequencies of these species. The dichotomous results in regard to desiccation resistance and vagility that were observed between recently collected D. melanogaster and the Oregon-R laboratory stock of that species are also discussed.

Estimation of population fitness of parental races Drosophila nasuta nasuta and Drosophila nasuta albomicana and of the newly evolved Cytoraces I and II

Interracial hybridization between Drosophila nasuta nasuta (2n = 8) and Drosophila nasuta albomicana (2n = 6) has resulted in the emergence of new karyotypic strains called Cytorace I (♀ 2n = 7; ♂ 2n = 6) and Cytorace II (♀ and ♂ 2n = 6). The parental and the newly evolved Cytoraces were assessed for parameters of fitness, i.e., fecundity, egg to adult rate of development, egg to adult viability, and adaptedness. The newly evolved Cytoraces not only differ from each other but also differ from their parental races in their fitness phenotypes. Each one of these four strains represent features of different genetic systems with different adaptive phenotypes.Key words: Drosophila, interracial hybridization, population fitness.

Identification in transgenic animals of the Drosophila decapentaplegic sequences required for embryonic dorsal pattern formation.

Mutant alleles of the Drosophila decapentaplegic (dpp) gene affect embryonic dorsal-ventral pattern formation, larval viability, and adult cuticle formation from the imaginal disks. The dpp DNA required for this array of functions spans almost 50 kb. We report that the embryonic lethal, ventralizing alleles of the dpp gene are rescued in transgenic animals by an 8-kb fragment of the wild-type dpp DNA. Full rescue, from embryonic lethality to adult viability, is obtained in two situations: in animals hemizygous for the haplolethal dpp gene, and in animals hemizygous for either of two recessive embryonic lethal alleles. In embryos null for dpp, the transformation of dorsal cuticle to ventral cuticle is blocked by one copy of the dpp transposon; two copies permit the hatching of the larvae. The portion of dpp sufficient for these embryonic functions encodes a protein with homology to the transforming growth factor-beta (TGF-beta) family of proteins (Padgett et al. 1987). The larval and imaginal disk functions of dpp are not rescued by the 8-kb portion of the gene and must require additional sequences from the 50 kb of DNA.

Sensitivity to larval density in populations of Drosophila mojavensis: Influences of host plant variation on components of fitness.

Chromosomally polymorphic populations of Drosophila mojavensis from Baja California feed and breed on agria cactus, Stenocereus gummosus; whereas, monomorphic Arizona populations are associated exclusively with organ pipe cactus, S. thurberi. The effects of this host plant shift in expanding the kinds of feeding and breeding sites were assessed by manipulating larval density and recording differences in egg to adult development time and viability, and adult thorax size in both populations on artificially rotted substrates of both cactus species. Older agria rots increased development time but had no effect on viability. Organ pipe rots were qualitatively poorer substrates than agria rots for both monomorphic and polymorphic populations of D. mojavensis, especially at higher larval densities causing longer egg to adult development times, lower viabilities, and smaller thorax sizes than agria.The Baja population expressed shorter development times, higher viabilities, and smaller thorax sizes than the Arizona population on both cactus substrates. No evidence for cactus host race formation was found. The Baja population was less sensitive to increasing larval densities for all fitness characters studied on both cactus substrates indicating greater developmental homeostasis than in the monomorphic Arizona population. These data support the hypothesized central-marginal population structure within this species coincident with the distribution of host plants and lend insight into the process of adaptive divergence at different life history stages caused by host plant shifts.

Photodynamic action of erythrosin B as a toxic mechanism for infective larvae of bovine gastrointestinal nematodes

The effect of erythrosin B on adults and 3rd stage larvae of gastrointestinal nematodes of cattle was studied by treating calves per os with 20 mg kg −1, 40 mg kg −1, and 60 mg kg −1 of the dye daily for 21 days and monitoring its effect. Erythrosin B had no detectable effect on adult nematode fecundity or viability. Data collected did indicate, however, that erythrosin B produced a consistent toxic effect on 3rd stage larvae after exposure to fluorescent light. This toxic effect was dependent upon dosage of erythrosin B administered, time of light exposure and, to a much lesser extent, the length of time the larvae were left in culture in the presence of the dye.

Frequency-dependent selection at the diazinon resistance locus of the Australian sheep blowfly, Lucilia cuprina

The egg to adult viability of susceptibles (SS) at the diazinon resistance locus of L. cuprina was facilitated by RS in mixed (1:1) cultures at diazinon concentrations greater than 0·0002 per cent (W/V) in the concentration range 0–0·00053 per cent (W/V). SS survived in mixed culture at concentrations lethal to pure cultures of this genotype. The egg to adult viability of RS was not influenced by the presence of SS.Trials at 0 per cent and 0·0002 per cent (W/V) diazinon showed the viability of both genotypes decreased in the presence of diazinon and with increasing density. Viability of RS was independent of its frequency in mixed culture but SS viability was enhanced at frequencies ≦20 per cent at the 0·0002 per cent (W/V) concentration. There was no indication of density × frequency interaction.

TISSUE-SPECIFIC AND COMPLEX COMPLEMENTATION PATTERNS IN THE PUNCH LOCUS OF DROSOPHILA MELANOGASTER

Mutations in the Punch locus result in loss of GTP cyclohydrolase activity, but all mutations do not affect the enzyme in the same way. There are at least three classes of Punch mutations. One class results in a dominant eye color, recessive lethal phenotype. A second class of mutations also causes a recessive lethal phenotype, but heterozygous mutants have normal eye color. They show loss of GTP cyclohydrolase function in all tissues where activity can be measured. Alleles comprising a third class are recessive eye color mutations that are homozygous viable. Individuals with this third type of mutation show loss of enzyme activity in the eye, but show normal or near-normal activity elsewhere. In order to examine the organization and function of this locus further, we have performed interallelic complementation tests on 25 Punch mutations, monitoring viability and enzyme activity in prepupae and adults. Most allele combinations are lethal. Those that complement do so in ways that are tissue-or stage-specific and unpredictable. Tests of mutants with tissue-specific phenotypes and of individuals mutant for complementing Punch lethal alleles lead us to conclude that Punch is a complex locus, both with respect to its organization and to its products.

Targeted selection experiments and enzyme polymorphism: negative evidence for octanoate selection at the G6PD locus in Drosophila melanogaster.

Published studies have reported significant selection with respect to the G6pd locus for Drosophila melanogaster reared on Na-octanoate food. We have reexamined the selective effects of Na-octanoate on egg to adult viability with respect to the G6pd polymorphism using specially constructed X chromosomes. Four experiments were carried out using different 6Pgd backgrounds in two recombinant sets of chromosomes segregating for the G6pd locus but constructed so as to minimize variation over most of the X chromosome. In addition, two measures of viability were used, and the size of the experiments and their associated degrees of freedom are approximately double those reported in the former studies. Our results find no evidence for differential selection on G6pd genotypes (males and females) by Na-octanoate and, therefore, do not corroborate the positive results of selection reported by other investigators. The reasons for our different results are discussed.

LIFE HISTORY STUDIES OF THE LESSER SNOW GOOSE (ANSER CAERULESCENS CAERULESCENS). IV. THE SELECTIVE VALUE OF PLUMAGE POLYMORPHISM: NET VIABILITY, THE TIMING OF MATURATION, AND BREEDING PROPENSITY.

Cooch (1961, 1963) suggested that changes in the genotypic composition of snow goose colonies comprising the Hudson Bay-Foxe Basin population could be attributed to selection favoring the blue phenotype. In the preceding paper (Cooke et al., 1985), we examined potential differences in net fecundity between the two phenotypes at La Pérouse Bay in northern Manitoba. No substantial differences in any component of fecundity were detected. In the present paper, we examined potential differences in pre-reproductive and adult viability, age of maturation, and breeding propensity. Again, no differences associated with the plumage polymorphism were detected in any of these life history characteristics. Thus, despite a thorough analysis of the complete life cycle, we were unable to uncover any evidence supporting a selection hypothesis for the persistence and dynamics of this conspicuous polymorphism. An alternate hypothesis based primarily on gene flow and assortative mating appears more plausible.

Lecithin-dependent Phytosterol Utilization by Larvae of Culex pipiens (Diptera: Culicidae)

Without sterol in synthetic dietary media Culex pipiens L. could not develop beyond the second instar. With cholesterol as the only dietary lipid, good development to the adult stage occurred, whereas with ergosterol or stigmasterol, development was no better than in the absence of sterol, and with all other phytosterols tested development was variously restricted. When the basic diet incorporated a lipid supplement containing the arachidonic acid needed for newly emerged adults to fly and survive, larval/pupal development and adult viability with ergosterol, stigmasterol, and most phytosterols were as good as with cholesterol. Besides arachidonic acid, the lipid supplement contained an antioxidant, ascorbyl palmitate, and synthetic dipalmitoyl lecithin as a dispersing agent; but with lecithin alone supplementing the basic diet, good development to the adult stage was facilitated with ergosterol, stigmasterol, and other phytosterols, although adults lacking arachidonic acid were not viable. On the basis of diets supplemented with lecithin, we concluded that ergosterol, stigmasterol, sitosterol, 24-methylenecholesterol, fucosterol, desmosterol, and perhaps 7-dehydrocholesterol could support growth and development as well, or almost so, as cholesterol. With cholestanol, development to the fourth instar was good, but nearly all individuals failed to metamorphose. With lathosterol or 22- trans -cholestadienol, development was markedly inferior compared with cholesterol and the well utilized phytosterols, and survival through metamorphosis was severely reduced. These results are discussed in relation to current views on the metabolism of sterols by phytophagous/omnivorous insects.