Epistatic contributions to quantitative traits in Tribolium castaneum

Summary Triple-testcross experiments were used to analyze epistatic contributions to larva weight, pupa weight, pupa width and adult weight in Tribolium castaneum. Seven diverse inbred lines and the F₁. produced by crossing the two tester lines were examined for indications of epistasis. Larva weight was the only trait for which no significant epistasis was detected. There was significant epistasis for pupa weight in three of the inbred lines; for pupa width in four of the inbred lines; for adult weight in five of the inbred lines. Only one inbred line and the F₁ line failed to exhibit significant epistasis for any trait. Each inbred line had a unique pattern of epistasis, suggesting that a number of different loci were contributing to the detected epistasis.This paper (No. 76-5-158) is published with the approval of the Director of the Kentucky Agricultural Experiment Station.     

Epistatic contributions to quantitative traits in Tribolium castaneum

Summary Triple-testcross experiments were used to analyze epistatic contributions to % hatchability of eggs, age of pupation, number of eggs laid in 24-hour period, and survival from hatching to day 35. Seven diverse inbred lines and the F₁ produced by crossing the two tester lines were examined for the presence of epistasis. There was evidence of epistasis for each of the 4 traits in at least one of the 8 lines tested. Epistasis was a major source of variation in survival in all of the lines tested.     

Individual and group selection for productivity in Tribolium castaneum

Summary The usefulness of a non-random group selection method in the improvement of a character influenced by interactions among individuals has been experimentally tested in a population of Tribolium castaneum. The selected trait —number of adults produced in a fixed period of time —showed a clear increase after 11 generations of selection. This increase is related to a reduction in developmental time, and it was specific for the population structure in which selection was applied, vanishing when this structure was altered.     

Mutational variance for pupa weight in Tribolium castaneum

Summary Directional selection for heavier pupa weight in Tribolium castaneum was practiced for 18 generations in two replicates of an inbred line, each separately maintained in small population cages for more than 90 generations. Mutational variance was estimated in two ways, based on Hill's (1982a) prediction equation for response to directional selection where an equilibrium state between effective population size and variation created by new mutation is assumed. Estimates of mutational variance based on response to selection in a selected population and from a sire-offspring regression analysis in an unselected control population were in strong agreement within each replicate population. Significant differences between the two replicates were observed. Estimates of the ratio of mutational variance to environmental variance ranged from 0.0002 to 0.0012, depending upon the assumptions made about effective population sizes maintained in the two replicate lines. Estimates of realized heritability from the 18 generations of selection were 0.23±0.02 and 0.12±0.02 in the two replicates. The results support the hypothesis that mutation may have played a significant role in supplying useful genetic variation for long-continuing response to selection for this trait in experiments reported earlier.     

Experimental comparison of methods for simultaneous selection of two correlated traits in Tribolium

Summary Two lines of Tribolium castaneum were selected in each of three replicates for egg laying between 7 and 11 days after adult emergency and for adult weight at 12 days, using theoretical (IT) and empirical (IP) index selection methods. Index coefficients were given empirically in the IP line and they were adjusted in the successive generations of selection according to the results obtained in the previous ones. Highly repeatable selection responses in all replicates occurred in both lines for the aggregate genotype (egg laying plus adult weight) and for each individual trait. The IP line tended to increase slightly more than the IT line for aggregate genotype and egg laying, while the highest response in adult weight was obtained with the IT method. The two methods gave consistently different responses in each replicate. The expected results were that IT selection should not exceed IP selection for the aggregate genotype and egg laying while theoretically the IT method should have been superior for increase adult weight. Theoretical expectations for adult weight have been fulfilled in practice. The IP method would be preferred in a practical sense because of its simplicity and freedom from need of parameter estimation.     

Artificial selection for 18-day pupa weight and opposing simulated naturel selection in Tribolium castaneum

Summary The effect of simulated opposing natural selection on the response to mass selection for 18-day pupa weight of Tribolium castaneum was studied for 10 generations of selection. Natural selection was simulated in replicated treatment lines by imposing a negative relationship between mid-parent genetic value for pupa weight and fertility. Responses to selection and realized heritabilities were smaller (P < 0.05 and P < 0.10, respectively) for the treatment lines than for control lines under selection for pupa weight only. One treatment, line E3G1, reached an intermediate selection plateau by generation 10, and responded linearly to 4 generations of artificial selection after natural selection had been discontinued. Possible explanations for the different behaviors of the replicate lines E3G1 and E3G2 were also discussed.     

Critical examination of postulated cladistic relationships among species of flour beetles (genus Tribolium,Tenebrionidae, Coleoptera)

Cytological considerations have led to the hypothesis that Tribolium confusum (CF) evolved from an ancestor similar to T. castaneum (CS) by translocation of an autosome to the X chromsome, and that T. destructor (DEST) was derived from CF. T. brevicornis (BREV) is regarded as the most primitive on morphological grounds. Electrophoretic analyses of 19 strains of CS, 7 of CF, and 1 each of DEST and BREV do not support this postulated evolutionary pathway. CF and CS are much more similar to BREV than they are to each other. (Comparisons of morphological mutations in CS and CF also indicate that the two species are not similar genetically.) DEST and CF are very dissimilar electrophoretically. It is likely that the species evolved independently from an ancestral stock which may be represented by BREV. Recognition of gene homology in different species is the keystone for all attempts at constructing genetically meaningful evolutionary pathways. The difficulties involved in doing so are pointed out.     

Experimental comparison of selection methods to improve a non-linear trait in Tribolium

Summary Five lines of Tribolium castaneum (flour beetle) were selected in each of three, replicates for biomass, using quadratic (Q) and linear (L) selection indices, direct selection for biomass (B) and indirect selection for each component trait, i.e. pupal weight (P) and family size (F), respectively, for five generations. The highest response in biomass was obtained in the Q line using an exact quadratic index in which the genetic value for each trait was based on information from both traits. The expected results were that Q selection would not exceed L selection while the L method would be superior with respect to direct selection for biomass (B line); P selection would be better and F selection worse than B selection. Selection was effective for pupal weight in the Q, L, B and P lines, but was not effective for family size, although the Q line increased slightly. The lines had no linear response for family size. Selection for biomass was influenced more by family size than by pupal weight. It is advantageous to include terms such as squares and products in the selection index, even though the response to selection may have been non-linear because of the low heritability of family size and an intermediate optimum for this component trait.     

Sites of Fgf signalling and perception during embryogenesis of the beetle Tribolium castaneum

The development of multicellular embryos depends on coordinated cell-to-cell signalling events. Among the numerous cell-signalling pathways, fibroblast growth factors (FGFs) are involved in important processes during embryogenesis, such as mesoderm formation during gastrulation and growth. In vertebrates, the Fgf superfamily consists of 22 family members, whereas only few FGFs are contained in the less complex genomes of insects and worms. In the recently sequenced genome of the beetle Tribolium, we identified four Fgf family members representing three subfamilies. Tribolium has Fgf1 genes that are absent in Drosophila but known from vertebrates. By phylogenetic analysis and microsynteny to Drosophila, we further classify Tc-fgf 8 as an ancestor of pyramus and thisbe, the fly Fgf8 genes. Tc-fgf8 expression in the growth zone suggests an involvement in mesoderm formation. In the embryonic head, expression of Tc-fgf8 subdivides the brain into a larger anterior and a smaller posterior region. The Fgf Tc-branchless is expressed in the embryonic tracheal placodes and in various gland-like structures. The expression patterns of the only Tribolium Fgf receptor and the adaptor molecule Downstream-of-Fgfr are largely congruent with Tc-Fgf8 and Tc-bnl. Thus, in contrast to Drosophila, only one Fgf receptor canalises Fgf signalling in different tissues in Tribolium. Our findings significantly advance our understanding of the evolution of Fgf signalling in insects.     

Directional and stabilizing selection for developmental time and correlated response in reproductive fitness in Tribolium castaneum

Summary Directional and stabilizing selection for developmental time (DT) were done for seven generations in replicated lines of Tribolium castaneum. There were no significant differences between sexes or among replicates in means or coefficients of variation. For directional selection, there were significant responses in both directions, measured as deviation from control, viz. -0.35±0.15 day per generation for Fast (F) and 0.73±0.15 day for Slow (S). The unselected control (C) and the stabilizing selection (I) lines were similar, with average response per generation not significantly different from zero. — Phenotypic variation, from the first generation, was larger in the S line than in the other three lines. The I line showed a significant decrease in phenotypic variation, due mainly to a decrease in genetic variance. The realized heritability was 0.219±0.045 for F and 0.324±0.036 for S, the difference being highly significant. — Correlated response in reproductive fitness (number of pupae produced) was significant only for S (r_p=-0.88 and r_{G realized}=-0.79). Regression of the correlated response on DT in this line was-19.28±4.77 pupae per day (phenotypic) and -28.77±10.06 pupae per day (genetic).     

Tribolium Wnts: evidence for a larger repertoire in insects with overlapping expression patterns that suggest multiple redundant functions in embryogenesis

Wingless (wg)/Wnt family genes encode secreted glycoproteins that function as signalling molecules in the development of vertebrates as well as invertebrates. In a survey of Wnt family genes in the newly sequenced Tribolium genome, we found a total of nine Wnt genes. In addition to wg or Wnt1, Tribolium contains orthologs of the vertebrate Wnt5-7 and Wnt9-11 genes. As in Drosophila, Wnt1, Wnt6 and Wnt10 are clustered in the genome. Comparative genomics indicates that Wnt9 is also a conserved member of this cluster in several insects for which genome sequence is available. One of the Tribolium Wnt genes appears to be a member of the WntA family, members of which have been identified in Anopheles and other invertebrates but not in Drosophila or vertebrates. Careful phylogenetic examination suggests an Apis Wnt gene, previously identified as a Wnt4 homolog, is also a member of the WntA family. The ninth Tribolium Wnt gene is related to the diverged Drosophila WntD gene, both of which phylogenetically group with Wnt8 genes. Some of the Tribolium Wnt genes display multiple overlapping expression patterns, suggesting that they may be functionally redundant in segmentation, brain, appendage and hindgut development. In contrast, the unique expression patterns of Wnt5, Wnt7 and Wnt11 in developing appendages likely indicate novel functions.     

The <Emphasis Type="Italic">Tribolium spineless</Emphasis> ortholog specifies both larval and adult antennal identity

The morphology of insect antennae varies widely among species, but our understanding of antennal development comes almost solely from studies of one species—the fruit fly, Drosophila melanogaster. Moreover, this knowledge applies mostly to adult structures, since Drosophila lacks external larval appendages. In contrast to Drosophila, the red flour beetle, Tribolium castaneum, has both larval and adult antennae, which are very different from one another in morphology. Thus, Tribolium provides an ideal system to compare modes of antennal development both within and between species. Here, we report that the Tribolium ortholog of spineless (Tc-ss) is required in both the larval and adult antennae. Knockdown of Tc-ss by RNAi during either larval or imaginal development causes transformation of the distal portion of the antennae to legs. Thus, the function of ss is conserved between Drosophila and Tribolium with respect to adult antennal specification and also between Tribolium larval and adult antennal development. The similarity of the Tc-ss RNAi phenotype to that of a classically described Tribolium mutation, antennapedia (ap) (of no relationship to the Drosophila Hox gene of the same name), led us to characterize the original ap mutation and two newly identified ap alleles. Our mapping and phenotypic data suggest that Tc-ss is the best candidate for the ap locus. These results represent a first step in characterizing larval and adult antennal patterning in Tribolium, which should provide important insights into the evolution of insect antennal development.     

Relative efficiency of selection methods to improve a ratio of two traits in Tribolium

Summary Three generations of upward selection for the egg mass/adult weight ratio were carried out in Tribolium castaneum. The experiment involved five lines: E — selected for increased egg mass; W — selected for decreased adult weight; R — selected for egg mass/adult weight directly; L — linear index selected with economic weights of m ₂: -m ₁ egg mass to adult weight (m ₁ and m ₂ are the means for adult weight and egg mass, respectively); NL — nonlinear index selected. Adult weight (7 days after adult emergence) and egg mass (between 7 and 11 days) were measured. The NL, E, and L lines had the greatest observed responses for the ratio; the R and W lines were not effective in improving the egg mass/adult weight ratio. It was expected that the NL line would be superior to the E, L, and R lines, and that the W line would respond the least. Observed response was significant for egg mass in the NL line, and for adult weight in the E, W, and R lines. Strong selection to increase egg mass seems to represent the optimal criterion for the ratio to be improved. The usefulness of nonlinear indices as selection criteria to improve a nonlinear trait, previously found to be optimal for a trait defined as the product of two component traits, appears to hold also for the selective improvement of the ratio of two traits. Serious limitations expected for direct selection of the ratio have been confirmed in this experiment.     

Sequence and phylogenetic analysis of the complete mitochondrial genome of the flour beetle Tribolium castanaeum

We describe the first complete mitochondrial genome sequence from a representative of the insect order Coleoptera, the flour beetle Tribolium castaneum. The 15,881 bp long Tribolium mitochondrial genome encodes 13 putative proteins, two ribosomal RNAs and 22 tRNAs canonical for animal mitochondrial genomes. Their arrangement is identical to that in Drosophila melanogaster, which is considered ancestral for insects and crustaceans (Boore et al., 1998; Hwang, et al., 2001a). Nucleotide composition, amino acid composition, and codon usage fall within the range of values observed in other insect mitochondrial genomes. Most notable features are the use of TCT as tRNA(Ser(AGN)) anticodon instead of GCT, which is used in most other arthropod species, and the relative scarcity of special sequence motifs in the 1431 bp long control region. Phylogenetic analysis confirmed resolving power in the conserved regions of the mitochondrial proteome regarding diversification events, which predate the emergence of pterygote insects, while little resolution was obtained at the level of basal perygote diversification. The partition of faster evolving amino acid sites harbored strong support for joining Lepidoptera with Diptera, which is consistent with a monophyletic Mecopterida.     

Estimation of maternal,sex-linked and additive x additive epistatic gene effects for body size of Tribolium

Summary The genetic structure of two quantitative traits, 13-day larval weight and pupal weight, in two unselected populations of Tribolium castaneum was investigated by the genetic model of Carbonell et al. (1983). The variability among two and three-way crosses was analyzed into components due to: general and specific combining abilities, maternal, sex-linkage, specific reciprocal and additive-by-additive epistasis. Also, indirect evidence of higher order epistasis was studied. It is concluded that the heterotic trait larval weight is highly affected by sex-linked genes and by non-additive gene action with additive-by-additive as well as higher order epistasis playing major roles. Pupal weight, on the other hand, is determined mostly by additive gene action although epistasis is also a significant source for genetic variability. Both traits are significantly influenced by maternal effects.Journal Paper No. 9033 from Purdue University Agricultural Experiment Station. Based in part on PhD Theses submitted by the first two authors at Purdue University     

Identification of the Drosophila and Tribolium receptors for the recently discovered insect RYamide neuropeptides

One year ago, we discovered a new family of insect RYamide neuropeptides, which has the C-terminal consensus sequence FFXXXRYamide, and which is widely occurring in most insects, including the fruitfly Drosophila melanogaster and the red flour beetle Tribolium castaneum (F. Hauser et al., J. Proteome Res. 9 (2010) 5296–5310). Here, we identify a Drosophila G-protein-coupled receptor (GPCR) coded for by gene CG5811 and its Tribolium GPCR ortholog as insect RYamide receptors. The Drosophila RYamide receptor is equally well activated (EC₅₀, 1 × 10⁻⁹ M) by the two Drosophila RYamide neuropeptides: RYamide-1 (PVFFVASRYamide) and RYamide-2 (NEHFFLGSRYamide), both contained in a preprohormone coded for by gene CG40733. The Tribolium receptor shows a somewhat higher affinity to Tribolium RYamide-2 (ADAFFLGPRYamide; EC₅₀, 5 × 10⁻⁹ M) than to Tribolium RYamide-1 (VQNLATFKTMMRYamide; EC₅₀, 7 × 10⁻⁸ M), which might be due to the fact that the last peptide does not completely follow the RYamide consensus sequence rule. There are other neuropeptides in insects that have similar C-terminal sequences (RWamide or RFamide), such as the FMRFamides, sulfakinins, myosuppressins, neuropeptides F, and the various short neuropeptides F. Amazingly, these neuropeptides show no cross-reactivity to the Tribolium RYamide receptor, while the Drosophila RYamide receptor is only very slightly activated by high concentrations (>10⁻⁶ M) of neuropeptide F and short neuropeptide F-1, showing that the two RYamide receptors are quite specific for activation by insect RYamides, and that the sequence FFXXXRYamide is needed for effective insect RYamide receptor activation. Phylogenetic tree analyses and other amino acid sequence comparisons show that the insect RYamide receptors are not closely related to any other known insect or invertebrate/vertebrate receptors, including mammalian neuropeptide Y and insect neuropeptide F and short neuropeptide F receptors. Gene expression data published in Flybase (www.flybase.org) show that the Drosophila CG5811 gene is significantly expressed in the hindgut of adult flies, suggesting a role of insect RYamides in digestion or water reabsorption.