Population differentiation in an annual legume: genetic architecture

Abstract. The presence or absence of epistasis, or gene interaction, is explicitly assumed in many evolutionary models. Although many empirical studies have documented a role of epistasis in population divergence under laboratory conditions, there have been very few attempts at quantifying epistasis in the native environment where natural selection is expected to act. In addition, we have little understanding of the frequency with which epistasis contributes to the evolution of natural populations. In this study we used a quantitative genetic design to quantify the contribution of epistasis to population divergence for fitness components of a native annual legume, Chamaecrista fasciculata . The design incorporated the contrast of performance of F₂ and F₃ segregating progeny of 18 interpopulation crosses with the F₁ and their parents. Crosses were conducted between populations from 100 m to 2000 km apart. All generations were grown for two seasons in the natural environment of one of the parents. The F₁ often outperformed the parents. This F₁ heterosis reveals population structure and suggests that drift is a major contributor to population differentiation. The F₂ generation demonstrated that combining genes from different populations can sometimes have unexpected positive effects. However, the F₃ performance indicated that combining genes from different populations decreased vigor beyond that due to the expected loss of heterozygosity. Combined with previous data, our results suggest that both selection and drift contribute to population differentiation that is based on epistatic genetic divergence. Because only the F₃ consistently expressed hybrid breakdown, we conclude that the epistasis documented in our study reflects interactions among linked loci.     

Evidence for coadaptation in geographic populations of Drosophila bipectinata

In order to test whether there is genetic coadaptation in geographic populations of Drosophila bipectinata with respect to body size, reciprocal crosses were made among five strains derived from ecogeographically different localities in India. Wing length was used as an index of body size, and was measured in all the five strains, and their crosses in F and F₂ generations. The statistical analysis of the data show that there is significant interpopulation variation in body size and in all the crosses, there is an increase in body size in F₁ generation when compared with mid-parent value. Further, there is a decrease in body size in F₂ generation as compared to F₁ in most of the crosses with increased variability. These results provide evidence for genetic coadaptation in geographic populations of D. bipectinata .     

Can Extensive Reticulation and Concerted Evolution Result in a Cladistically Structured Molecular Data Set?

Hierarchy is the main criterion for informativeness in a data set, even if no explicit reference to evolution as a causal process is provided. Sequence data (nuclear ribosomal DNA ITS) from Armeria (Plumbaginaceae) contains a certain amount of hierarchical structure as suggested by data decisiveness and distribution of tree lengths. However, ancillary evidence suggests that extensive gene flow and biased concerted evolution in these multicopy regions have significantly shaped the ITS data set. This argument is discussed using parsimony analysis of four data sets, constructed by combining wild sequences with those from different generations of artificial hybrids (wild + F₁, F₂, and backcrosses; wild + backcrosses; wild + F₁; wild + F₂). Compared to the F₁ hybrids, F₂ show a certain degree of homogenization in polymorphic sites. This effect reduces topological disruption caused by F₁ and is considered to be illustrative of how extensive gene flow and biased concerted evolution may have modeled the wild ITS data. The possibility that hierarchy has arisen as a result of—or despite a significant contribution from—those two such potentially perturbing forces raises the question of what kind of signal are we recovering from this molecular data set.     

Genetic and in vitro molecular hybridization of malate dehydrogenase isozymes in interspecific bass (Micropterus) hybrids

Supernatant malate dehydrogenase (MDH) isozymes (as visualized by starch gel electrophoresis) are encoded by two distinct gene loci in both the largemouth and smallmouth bass. When an interspecific F₁ hybrid is formed between these two fish, a unique MDH isozyme is generated. The results of freeze-thaw molecular hybridization (which is the first application of this technique to MDH) indicate that this unique isozyme in the F₁ hybrid is a heterodimer composed of one subunit of each parental type. The F₁ hybrids produced F₂ hybrids which in turn formed the F₃ hybrid population. The inheritance of alleles at the MDH-B locus is consistent with a single Mendelian autosomal locus. Furthermore, there is no evidence of linkage between the lactate dehydrogenase-E locus and the MDH-B locus.     

Resurrection of Aedes (Halaedes) ashworthi Edwards 1921: Morphological Characterisation and Separation from its Sibling Aedes (Halaedes) australis (Erichson) 1842 (Diptera: Culicidae)

The result of population crosses of members of the Ae. australis complex and the examination of the male genitalia of these populations have shown that Ae. ashworthi Edwards 1921 should be reinstated as a valid species. the parent females laid viable eggs when cross mated to males of different species, but the resulting F₁ females and males were largely sterile. When F₁ females were blood-fed and examined 3–8 d later, usually fewer than 10 ovarioles per ovary developed recognisable follicles and none of these formed eggs. F₁ males in nearly all cases possessed half-size testes, and there was no spermatid development in the reduced testes. A few males had normal-sized testes, but the spermatids were mostly tailless. the male of Ae. ashworthi can be separated from Ae. australis by the shape of the gonocoxite and the length of the gonostylus of the genitalia. the larvae of both species are identical, and the females differ only in the colour of some scale patches and the integument, which may prove to be too variable to be useful when more populations are compared. the morphological similarity of the two mosquitoes as larvae and adults supports the proposal that they should be recognised as sibling species, with Ae. ashworthi as the derived member of the Ae. australis complex. It is clear from morphological evidence, the viability of the F₁ hybrids and the unusual habitat occupied by both species, that they have diverged recently.     

Artificial hybridization within Saxifraga pentadactylis (Saxifragaceae)

Saxifraga pentadactylis subsp. almanzorii , an endemic to the subalpine nucleus of Sierra de Gredos (central Spain), differs from its closest relative, subsp. willkommiana , by its less showy petals. An artificial crossing program was carried out in order to assess the degree of reproductive isolation between the subspecies. To facilitate interpretation of the results, the program was extended to 10 other interspecific hybrid combinations within sect. Saxifraga . All the data gathered are congruent with the occurrence of two evolutionary scenarios. Interspecific crossings, rendering moderate to high seed-set (in obtaining the F₁), and vigorous but relatively sterile F₁ offspring, reveal reproductive barriers at the level of the F₁ fertility, probably originated as a byproduct of divergent evolution. In contrast, intraspecific crossings within S. pentadactylis resulted in seed-set values lower than expected (in obtaining the F₁), in a majority of weak non-viable F₁ offspring but also in a few fertile F₁ hybrid specimens which were able to originate F₂ offspring. This second pattern reveals reproductive barriers at the level of the F₁ vitality, probably arisen in a quite abrupt fashion. The lower P/O for subsp. almanzorii as compared to subsp. willkommiana , together with the rest of the evidence suggest that the reproductive barriers between them might be the product of active selection against hybridization achieved by incrementing the levels of autogamy in the former.     

Mating Types and Mating Type Inheritance in Euplotes minuta Yocom (Ciliata, Hypotrichida)

SYNOPSIS. Thirty-one stocks of a marine ciliate, Euplotes minuta Yocom, collected from different localities, can be grouped in seven mating types. True pairs are formed only in mixtures of stocks belonging to different mating types. No selfing pairs or intraclonal conjugation have ever been observed. Synclonal inheritance of mating types is the rule, although about 10% of pairs show clonal inheritance. The latter can be explained by assuming syncaryon formation through cytogamy or through caryogamy of pronuclei derived from different products of meiosis. Mating type determination is due to 7 alleles at the single locus mt . There is complete dominance among the 7 alleles which can be orderly seriated, as shown in Table 3, according to their dominance relationship. The 5 stocks, and only these 5, of mating type VII have the autogamy trait. The mortality rate in F₁ and F₂ is very low–a maximum of 10%; however, the F₂'S obtained by autogamy from F₁ progenies in which mating type VII is involved have a very high mortality rate. The two facts (high mortality rate in F₂ and strict association of autogamy trait with mating type VII in natural populations) have been considered as evidences of a probable isolation mechanism existing between mating type VII and the other 6 mating types. Thus, the 7 mating types have been assigned to the same syngen only tentatively.     

Environmental influences on epistatic interactions: viabilities of cytochrome c genotypes in interpopulation crosses

Abstract .The genetic incompatibilities that underlie F₂ hybrid breakdown and reproductive isolation between al-lopatric populations may be susceptible to environmental interactions. Here we show that epistatic interactions between cytochrome c ( CYC ) alleles and mitochondrial DNA (mtDNA) variation are dramatically influenced by environmental temperature in interpopulation hybrids of the copepod Tigriopus californicus . CYC is a nuclear-encoded gene that functionally interacts with electron transport system (ETS) complexes composed in part of mtDNA-encoded proteins. Previous studies have provided evidence for functional coadaptation between CYC and ETS complex IV (cytochrome c oxidase) and for cytoplasmic effects on the fitness of CYC genotype in copepod hybrids. In this study, selection on CYC genotype is shown to continue into advanced generation hybrids (F₂-F₈) increasing the likelihood that CYC itself is involved in the interaction (and not a linked factor). Relative viabilities varied markedly between copepods raised in two different temperature/light regimes. These results suggest that both intrinsic coadaptation and extrinsic selection will influence the outcome of natural hybridizations between populations. Furthermore, the results indicate that the fitness of particular hybrid genotypes depends on additional non-mtDNA encoded genes that interact with CYC.     

Accumulation and utilization of triacylglycerol and polysaccharides in Liposcelis bostrychophila (Psocoptera, Liposcelididae) selected for resistance to carbon dioxide

Abstract: Two populations of the psocid, Liposcelis bostrychophila Badonnel, were exposed to two CO₂-enriched atmospheres (35% CO₂ + 21% O₂, and 55% CO₂ + 21% O₂, balance N₂) for 30 generations. Controls were reared in normal atmospheres. The reserves of triacylglycerol and polysaccharides were evaluated in adults of the two experimental and the control populations in generations F₁₅ and F₃₀. The utilization rate of triacylglycerol and polysaccharides in the CO₂-enriched atmospheres were also determined in generation F₃₀. The results indicated that the reserves of triacylglycerol and polysaccharides increased significantly during selection for CO₂ resistance; the higher the resistance level, the greater the reserves. Exposure of these populations to controlled atmosphere was associated with a steady utilization of the reserves. By contrast, the unselected population responded to controlled atmospheres by accelerated utilization of triacylglycerol and polysaccharides. Comparison of the utilization rates during CO₂ exposure showed that triacylglycerol is the main energy source, and polysaccharides contribute to metabolic energy supply only to a small extent.     

The ATP-dependent synthesis of factor 390 by cell-free extracts of Methanobacterium thermoautotrophicum (strain ΔH)

Abstract Cell-free extracts of Methanobacterium thermoautotrophicum (strain ΔH) converted the 8-OH-5-deazaflavin coenzyme F₄₂₀ to factor 390, a 8-adenylyl derivative (F₄₂₀-AMP). Activity was only observed upon exposure of the crude cell-free extract to oxygen. The ability to synthesize F₃₉₀ was lost when crude cell-free extract was subsequently brought to an anaerobic reducing environment. The enzymatic reaction used ATP and oxidized coenzyme F₄₂₀ as substrates and inorganic pyrophosphate was formed next to F₃₉₀. GTP could be used instead of ATP resulting in a guanylylated derivative. The crude cell-free extract showed K _m values of 154 μM for coenzyme F₄₂₀ and 2.4 mM for ATP. A partially purified enzyme preparation exhibited a K _eq of 0.32. In accordance, coenzyme F₄₂₀ and ATP could be synthesized from F₃₉₀ and PPi by the reverse reaction.     

Sex ratio bias in the F1 adult progeny of African rice gall midge, Orseolia oryzivora H. and G. (Dipt., Cecidomyiidae)

Abstract:  Against the background of conflicting reports of variable sex ratio distribution in different populations of the African rice gall midge (AfRGM), Orseolia oryzivora Harris and Gagne, the number and sex ratios of F₁ adult progeny produced per female from wild and screen house populations were investigated in the screen house at 27 ± 3°C, 60–70% relative humidity and 12 : 12 h (light : dark) photoperiod. Results indicated the occurrence of a single sex-biased ratio in all the F₁ adult progeny produced per female of this pest. Regardless of the source, whether from wild or screen house population, each mated female AfRGM produced a full complement of either sex only but never both. The difference between the number of eggs laid and F₁ adult progeny that emerged per female from wild and screen house populations was not significant (P > 0.05), indicating consistency in the occurrence of this phenomenon among AfRGM populations. The reason for this could not be ascertained in this study but AfRGM eggs must be fertilized for development and eclosion to occur. No F₂ adults emerged when a cohort of emergents from the same female were allowed to re-infest susceptible seedlings, indicating absence of parthenogenesis.     

Grey plumage colouration in the duck is genetically determined by the alleles on two different, interacting loci

Based on the observation of a grey phenotype in the F₁ generation from a cross between two white plumage duck varieties, the white Kaiya and the white Liancheng , we hypothesized a possible interaction between two autosomal loci that determine grey plumage. Using the parental and F₁ individuals, seven testing combinations including five different F₁ intercrosses (F₂) and two different backcrosses (BC₁ and BC₂) were designed to test our hypothesis. It was demonstrated by chi-squared analysis that six test matings produced offspring in the expected ratios between the grey and white, with P- values ranging from 0.50 to 0.99. Another mating, where all white offspring were expected, produced 33 white individuals. These results verified that the interaction between two loci produced the grey phenotype. The C locus, which carries the recessive allele ( c ), was previously thought to be the only gene responsible for white plumage in the duck. This is the first report that an allele ( t ), carried by the white Liancheng at a different autosomal locus, also determines white plumage in ducks. Furthermore, the dominant alleles at both loci can interact with each other to produce the grey phenotype, and a new dark phenotype, observed in some F₂ individuals, can be attributed to the dosage effect of the T allele.     

Fertility of roach × bream hybrids, Rutilus rutilus (L.) ×Abramis brama (L.), and their identification

Adult roach, bream and their presumed F₁ hybrid from an Anglian Water reservoir were identified on the basis of morphological and meristic characteristics. The hybrid was clearly intermediate. Four hybrid breeding crosses were induced to spawn by hypophysis. A bream × roach cross (female named first) failed to produce fertile eggs, whereas F₁ hybrid × roach, roach × F₁ hybrid and F₁ hybrid × F₁ hybrid all produced fry. Fertility (defined as survival of eggs to hatching) was high for the F₁ hybrid × roach back-cross (56%) but low for the others (<2%), in comparison to the pure species controls (roach 69%, bream 76%). Progeny from these crosses were reared until anal fin rays could be counted. These counts indicated intermediacy between the parents and back-crossed individuals, and similarity between F₁ hybrids and their F₂ progeny.     

IN VIVO METHYLATION AND TURNOVER OF RAT BRAIN HISTONES

Abstract— The turnover of the different histone components from brain nuclei was studied after the administration of l -[³H]lysine and l -[¹⁴C-methyl]methionine to newborn rats. The radioactivities of the different histone subfractions as well as other proteins were determined over a 280-day period. Biphasic type decay curves (³H and ¹⁴C) were obtained for total brain histones and all the subfractions. From 6 to 40 days of age the half life of total brain histones was 19 days. After reaching brain maturity the half life was 132 days. The lysine rich histone (F₁) was found to turnover the fastest of all the histones, having half lives of 13 and 112 days, respectively. The decay curve for the slightly lysine rich histones (F_2a2, F_2b) gave half lives of 25 days up to 40 days of age and 189 days after reaching brain maturity. The arginine rich histones (F_2a1, F₃) gave a half life of 32 days up to 40 days of age, while no turnover was observed after maturity. The turnover rates of the methyl groups and/or methionyl residues did not vary significantly from the turnover rates of the lysyl residues in the F₂ and F₃ histones. The lysine-rich histones did not contain significant amounts of methionyl residues or methyl groups.
Amino acid analysis of the brain histones revealed that about 3·6 per cent of the lysyl residues in the slightly lysine rich histones were methylated, mainly as ε-N-dimethyllysine. About 13 per cent of the lysyl residues in the arginine rich histones were methylated, mainly as ε-N-monomethyllysine and ε-N-dimethyllysine.     

COMPARISON OF ENERGY RESERVES AND UTILIZATION IN LIPOSCELIS BOSTRYCHOPHILA POPULATIONS SELECTED FOR TOLERANCE TO CONTROLLED ATMOSPHERE

Abstract  One population of Liposcelis bostrychophila Badonnel (CA selected) was exposed to a controlled atmosphere (CA) (35% CO₂+ 1% O₂, balance N₂) for 30 generations. Another population (control) was reared under natural atmospheric conditions. Reserves of triacylglycerol, polysaccharides and free amino acids were evaluated in adults of the CA selected and the control populations in generations F₁₅ and F₃₀. The utilization rate of triacylglycerol and polysaccharides in the CA exposure were also determined in generation F₃₀. The results indicate that the reserves of triacylglycerol and polysaccharides increased significantly during selection for CA tolerance; the higher the tolerance level, the greater the reserves. A total of 15 free amino acids constituents were detected in both populations. The total amino acid content in the CA selected population was obviously higher than that in the control population. Exposure of this population to a controlled atmosphere was associated with a steady utilization of reserves. In contrast, the unselected population responded to the controlled atmosphere by accelerated utilization of triacylglycerol and polysachharides. Comparison of utilization rates during CA exposure showed that triacylglycerol is the main energy source, and polysaccharides contribute only a small extent to the metabolic energy supply.     

Gametophyte-specific transposition of the maize Ds element in transgenic tobacco

To assess the potential advantages of a transposon-tagging system based on gametophyte-specific transposition a fusion between the anther-specific Arabidopsis thaliana apg promoter and the maize Ac transposase gene was constructed and introduced into tobacco. The ability of this transposase source to activate Ds transposition in a developmentally controlled manner was monitored by crossing to plants harbouring the cell autonomous excision marker gene construct, Ds —SPT. A number of fully green, streptomycin-resistant seedlings resulting from germinal transposition events were observed in the progeny of apg -TPase x Ds —SPT F1 plants. Streptomycin-resistant sectors were not observed in either F₁ seedlings or F₂ progeny, indicating a complete lack of somatic excision. Further crosses of apg —TPase sources to plants containing Ds—bar herbicide selection excision marker constructs gave reproducible gametophytic excision frequencies of up to 0.3%. Sequencing of Ds excision sites from F₂ seedlings derived from single F₁ plants revealed various sequence alterations in the original Ds insertion 'footprint' indicative of independent Ds excision events. Independent re-insertion was confirmed by Southern analysis of F₂ siblings. It is concluded that apg -controlled Ac transposase expression activates male gametophyte-specific Ds transposition.     

Biosynthesis of Prostacyclin in Rat Cerebral Microvessels and the Choroid Plexus

Abstract: Microvessels, predominantly capillaries, were isolated from rat cerebrum by a modification of published procedures. The morphology and purity of the preparations were monitored by light and electron microscopy and by enrichment in alkaline phosphatase, γ-glutamyl transpeptidase, and prostacyclin synthetase. A reversed-phase high-pressure liquid chromatographic method was used in the purification of prostaglandins after extraction from aqueous incubation solutions. Prostacyclin synthesis in brain is localized in cerebral blood vessels and capillaries. The endogenous biosynthetic capacity of the isolated cerebral capillary fractions for prostacyclin, measured as its chemically stable breakdown product, 6-keto-prostaglandin F_1α, was 11 ng/mg protein/10 min. Choroid plexus and intact surface vessels synthesized 6-keto-prostaglandin F_1α at 37 and 35 ng/mg protein/10 min, respectively. The prostacyclin-synthesizing enzyme of the cerebral capillaries also converted the exogenously added prostaglandin endoperoxides to 6-keto-prostaglandin F_1α. Comparison of the synthesis of prostaglandins 6-keto-F_1α, E₂, and F_2α showed that 6-keto-prostaglandin F_1α was the major prostaglandin formed in the microvessels, in the larger surface vessels, and in the choroid plexus. Prostaglandin D₂ was not detected. Prostacyclin synthesis by the cerebral vasculature is similar to that in other blood vessels and cultured human endothelial cells. Possible physiological roles of prostacyclin in the cerebral microvasculature are discussed with special regard to the autoregulation of cerebral blood flow.     

A comprehensive analysis of QTL for abdominal fat and breast muscle weights on chicken chromosome 5 using a multivariate approach

Quantitative trait loci (QTL) influencing the weight of abdominal fat (AF) and of breast muscle (BM) were detected on chicken chromosome 5 (GGA5) using two successive F₂ crosses between two divergently selected 'Fat' and 'Lean' INRA broiler lines. Based on these results, the aim of the present study was to identify the number, location and effects of these putative QTL by performing multitrait and multi-QTL analyses of the whole available data set. Data concerned 1186 F₂ offspring produced by 10 F₁ sires and 85 F₁ dams. AF and BM traits were measured on F₂ animals at slaughter, at 8 (first cross) or 9 (second cross) weeks of age. The F₀, F₁ and F₂ birds were genotyped for 11 microsatellite markers evenly spaced along GGA5. Before QTL detection, phenotypes were adjusted for the fixed effects of sex, F₂ design, hatching group within the design, and for body weight as a covariable. Univariate analyses confirmed the QTL segregation for AF and BM on GGA5 in male offspring, but not in female offspring. Analyses of male offspring data using multitrait and linked-QTL models led us to conclude the presence of two QTL on the distal part of GGA5, each controlling one trait. Linked QTL models were applied after correction of phenotypic values for the effects of these distal QTL. Several QTL for AF and BM were then discovered in the central region of GGA5, splitting one large QTL region for AF into several distinct QTL. Neither the 'Fat' nor the 'Lean' line appeared to be fixed for any QTL genotype. These results have important implications for prospective fine mapping studies and for the identification of underlying genes and causal mutations.     

Electron transfer reactions for the reduction of NADP+ in Methanosphaera stadtmanae

Abstract Methanosphaera stadtmanae , a member of the Methanobacteriales reduces methanol, but not CO₂ with H₂ or 2-propanol to produce methane. In cell-free extracts of M. stadtmanae the activities of several enzymes involved in electron transfer were measured. The activities of an F₄₂₀-nonreactive hydrogenase, NADP⁺: F₄₂₀ oxidoreductase, NADP⁺-dependent 2-propanol dehydrogenase, and a methyl viologen dependent F₄₂₀ dehydrogenase were observed. Based on the presence of these particular enzyme activities, their cofactor requirements and the absence of F₄₂₀-dependent hydrogenase activity, a model of the electron transport pathway through the coenzyme F₄₂₀ to provide electrons for biosynthesis, was formulated.     

Calcium taste preferences: genetic analysis and genome screen of C57BL/6J x PWK/PhJ hybrid mice

To characterize the genetic basis of voluntary calcium consumption, we tested C57BL/6J mice (B6; with low avidity for calcium), PWK/PhJ mice (PWK; with high avidity for calcium) and their F₁ and F₂ hybrids. All mice received a series of 96-h two-bottle preference tests with a choice between water and the following: 50 m m CaCl₂, 50 m m calcium lactate, 50 m m MgCl₂, 100 m m KCl, 100 m m NH₄Cl, 100 m m NaCl, 5 m m citric acid, 30 μ m quinine hydrochloride and 2 m m saccharin. Most frequency distributions of the parental and F₁ but not F₂ groups were normally distributed, and there were few sex differences. Reciprocal cross analysis showed that B6 × PWK F₁ mice had a non-specific elevation of fluid intake relative to PWK × B6 F₁ mice. In the F₂ mice, trait correlations were clustered among the divalent salts and the monovalent chlorides. A genome screen involving 116 markers showed 30 quantitative trait loci (QTLs), of which six involved consumption of calcium chloride or lactate. The results show pleiotropic controls of calcium and magnesium consumption that are distinct from those controlling consumption of monovalent chlorides or exemplars of the primary taste qualities.